copolymerization

Free radical copolymerization of AA, MAA and the corresponding N-substituted amides with other monomers gives linear branched and cross-linked copolymers soluble in water or organic solvents. Carbochain polyamide homo- and copolymers are superior to the corresponding ester counterparts in terms of strength properties, have higher glass transition temperatures, and are more difficult to hydrolyze. It was also shown that the initial amide monomers CH 2 =CRCONR"R" differ from esters with similar structure by a higher polymerization rate.

The technology for obtaining acrylamide copolymers is basically the same as for homopolymers. However, the copolymerization of AA or MAA with various monomers proceeds more slowly than the homopolymerization of acrylamides, which may lead to an increase in the content of residual monomers in the copolymers, which are usually toxic. Also undesirable is the formation of polymers with a lower average MW during copolymerization than during AA homopolymerization. This is due to the higher values ​​of the chain transfer constant k M for comonomers than for AA, for which the value of k M is very small.

Main types of copolymers

Based on acrylamides, a wide range of both ionic (cationic and anionic) and nonionic copolymers has been obtained.

The most common water-soluble cationic copolymers are AA copolymers with N-(dialkylaminoalkyl)acrylates and methacrylates (primarily with NN-dimethylaminoethylmethacrylate) in neutralized or quaternized form. Recently, similar copolymers with N-(dialkylaminoalkyl)acrylamides have attracted attention. Copolymers with N-(dimethylaminopropyl)methacrylamide are superior to copolymers with dimethylaminoalkyl methacrylates in terms of resistance to hydrolysis in an alkaline medium.

Anionic copolymers are obtained by copolymerizing AA or MAA, primarily with AA or MAA and their salts. From MAA and MAA, the Metas copolymer is obtained in industry, which is used as a protective agent in drilling equipment and for other purposes. Polymers, the macromolecules of which consist of elementary amide units and an AA salt, or MAA, are also formed as a result of the hydrolysis of PAA and PMAA, I, as well as during the polymerization of AA and MAA in the presence of hydrolyzing agents. However, these polymers differ from AA copolymers obtained by radical copolymerization in the nature of the distribution of elementary units in macromolecules. Anionic copolymers, aqueous solutions of which have increased resistance to phase separation under the action of divalent metals, are synthesized by copolymerization of AA with monomers in which the acid group is not directly bonded to the vinyl group, for example, sodium 3-acrylamido-3-methylbutanoate and 2-acrylamido-2 -sodium methylpropanesulfonate. Copolymers of N-n-alkylacrylamide (alkyl group - C 8 , C 10 , C 12) and sodium 3-acrylamido-3-methylbutanoate form aqueous solutions, the viscosity of which does not decrease under the action of electrolytes.

Copolymerization of 2-acrylamido-2-methylpropanesulfonic acid with styrene and 9-vinylphenanthrene or 1-vinylpyrene in organic solvents yielded polymers containing both hydrophilic and hydrophobic segments, the former (in the form of salts) having a high ability to solubilize the latter. in water. These copolymers serve as a medium for photosensitized electron transfer reactions. Copolymers of AA with n-styrenesulfonic acid and its salts are widely known.

Among ionic acrylamide copolymers, polyampholytes are of increasing interest. Thus, by copolymerization of AA in water with sodium methacrylate, 5-vinyl-1,2-dimethylpyridinium methyl sulfate, and NN-methylene-bis-acrylamide, swelling and collapsing polyampholytic networks were obtained. Polyampholytes are synthesized from mixtures of monomers containing salts ("comonomers"), the cation and anion of which have vinyl groups involved in copolymerization, for example, 3-methacryl-amidopropylmethylammonium, 2-acrylamido-2-methylpropanesulfonate.

Based on acrylamides, various nonionic copolymers are obtained. These include copolymers of AA or MAA with N-substituted acrylamides that do not contain or contain functional groups in the substituent, copolymers, for which only substituted amides are used, copolymers of AA and MAA with b, c-unsaturated nitriles, esters and other monomers.

AA is copolymerized with N-n-alkylacrylamides (alkyl group - C 8 , C 10 , C 12) to obtain "hydrophobically associated" polymers. The presence in copolymers of only 0.25 - 0.5% (wt.) units of the second monomers contributes to the preservation or even increase in the viscosity of aqueous solutions of polymers when electrolytes are added to them.

On the basis of AA and N-(1,1-dimethyl-3-oxobutyl)acrylamide, copolymers are obtained, the limiting viscosity numbers of which at zero shear increase as a result of the addition of mono- and divalent salts. It is assumed that this effect is associated with the presence of cycles in macromolecules due to the formation of hydrogen bonds.

For intermolecular crosslinking of polymers based on AA, substituted acrylamides and other monomers, N,N "-methylene-bis-acrylamide, N,N" -methylene-bis-methacrylamide and other AA-based monomers containing two or more polymerizable groups are widely used. . With an increase in the proportion of cross-linking agents in a mixture of monomers, the degree of conversion at which these agents cause gel formation decreases.

Hydrogels with a high degree of swelling (moisture absorbents) were synthesized based on AA and sodium acrylate using carboxymethylcellulose allyl ether as a polyfunctional crosslinking agent, and the swollen hydrogels had good deformation-strength characteristics.

To prepare thermosetting aryl and other polymers, N-hydroxymethacrylamide or N-hydroxymethylmethacrylamide unit units are often introduced into macromolecules by copolymerization. The structuring of polymers containing N-hydroxymethylamide groups is facilitated by the presence of unsubstituted amide groups in macromolecules. During the copolymerization of acrylonitrile and 0.5 - 0.7% N-hydroxymethyl-methacrylamide in the absence or presence of 1-8% AA, thermally crosslinkable fiber-forming copolymers are formed. By copolymerization of methyl methacrylate, N-hydroxymethylmethacrylamide and N,N "-methylene-bis-methacrylamide, modified organic glass can be obtained.

New directions in the synthesis of AA copolymers include the copolymerization of AA with macromonomers (M n = 1100-4600) of structure

CH 2 \u003d CHCOOSCH 2 CH 2 S (CH 2 CH) n H

SOOS 12 H 25

synthesized by telomerization of dodecyl acrylate in the presence of 2-mer-captoethanol as telogen, followed by acylation of telomeres with acryloyl chloride. In this case, copolymers with a ratio of elementary units in the main chain of 160: (2.5-1) were obtained.

Patterns of copolymerization

The laws of copolymerization are determined, first of all, by the structure of the initial monomers and the medium in which the process is carried out. Both factors are fully manifested during the copolymerization of unsaturated amides. For "classical" variants of copolymerization, the contribution of these factors is estimated by their influence on the rate of copolymerization, the degree of polymerization, and the relative activities of the monomers (copolymerization constants) r 1 and r 2 . In this case, r 1 \u003d k 11 /k 12 and r 2 \u003d k 22 /k 21, where k 11, k 12 are the rate constants of the reactions of the macroradical M 1 with "own" (M 1) and "foreign" (M 2) monomers ; k 22 , k 21 - rate constants of reactions of macroradical M 2 with monomers M 2 and M 1 .

As is well known, indicators of the activity of monomers during copolymerization are also the semi-empirical parameters Q and e proposed by Alfrey and Price and characterizing the resonant (presence of conjugation) and polar effects, respectively. It should be noted that many real polymerization and copolymerization processes involving AA and substituted acrylamides; are complicated (“special”) processes. Therefore, the reported values ​​of r 1 , r 2 , Q 1 , Q 2 , e 1 , e 2 , k 11 , k 12 , k 22 , k 21 are often averaged (effective) values.

Influence of the structure of acrylamides on their reactivity during copolymerization. The reactivity of substituted AAs varies widely depending on the nature of the substituents. The influence of the latter is expressed in the form of polar, resonant and steric effects. Considering the copolymerization in the series of substituted unsaturated amides, it is possible to deduce the regularities of the influence of individual effects even in cases where other effects also have a significant influence.

When studying the radical copolymerization of AA with MAA, it was found that at 25 °C r 1 = 0.74 ± 0.11 and r 2 = 1.1 ± 0.2. The slightly higher reactivity of the second monomer is associated with the fact that the substitution of the a-hydrogen atom in AA by a methyl group leads to an increase in the stability of the transition state due to hyperconjugation. At the same time, when interacting with the same monomer, the methacrylamide radical is much less reactive than the acrylamide radical.

In this case, the steric effect plays a decisive role. When interacting with the MMA radical, N-arylmethacrylamide also turned out to be more active than AA having the same substituent.

During the copolymerization of substituted acrylamides CH 2 \u003d CHCONR "R" with AN in a DMF medium, the value of r 1 decreases in the same series in which the rate of homopolymerization of the same amides changes (R "and R" are given):

N, CH 3 > N, N > N, n-C 4 H 9 > C 6 H 5, C 6 H 5? CH 3 , CH 3 .

The reactivity of para-substituted N-phenylmethacrylamides (1 / r 2) during copolymerization in bulk of these monomers with MMA (M 2) also decreases with a decrease in the electron-donor and an increase in the electron-withdrawal ability of the para-substituent:

CH 3 O > CH 3 > H > Cl.

When studying the copolymerization of N-substituted methacrylamides with AN, linear dependences of the reactivity lg(l/r 2) of 4-substituted N-phenylmethacrylamides on the Hammett o-constants and of N-alkyl-methacrylamides and N-phenylmethacrylamide on the Taft o-constants were established. The constants characterizing the resonant (BR) and steric (Es) effects in the Hammett and Taft equations did not significantly affect the value of 1/r 2 ; the change in the reactivity of the monomers under consideration depends mainly on the polar effect of the substituents. Small absolute values ​​of p (-0.13) and p* (-0.033) in the Hammett and Taft equations are characteristic of hemolytic reactions. The negative values ​​of these constants, as well as the p* constants for the reaction of N-monosubstituted amides with the methyl methacrylate radical, are due to the fact that when passing to an amide with a more electron-withdrawing substituent, its reactivity with respect to acrylonitrile or methyl methacrylate radicals decreases, in which the substituent is also an electron acceptor. It should be noted that in the IR spectra of N-monosubstituted amides, the C=C and C=O absorption bands shift towards longer wavelengths with an increase in the electron-donating properties of the substituents.

When studying the binary copolymerization of 1-acrylamido-1-deoxy-D-glucite and 1-deoxy-1-methacrylamido-D-glucite with various vinyl monomers, it was found that when vinyl acetate is used as a comonomer, the presence of resonance stabilization in the molecule of the first monomer plays a decisive role and its absence in the second (r 1 > r 2); in the case when both monomers are conjugated (M2 - CT, MMA), the ability to copolymerize is determined mainly by the fact that steric hindrances play a much greater role in the first monomer than in the second (r 1<< r 2) .

The copolymerization constants of N-acryloylpyrrolidrone with ST in benzene (60°C) turned out to be 1.5 and 0.35. The values ​​Q = 0.42 and e = 1.60 calculated from these data for N-acryloylpyrrolidone indicate that this monomer is highly polar, but does not show a significant tendency to resonance stabilization (coupling effect is small). The replacement of the acryloyl derivative by the methacryloyl derivative of the same lactam in the indicated pair of monomers changes the relative activities of the monomers (r 1< 1; r 2 >1), which is associated with the appearance of noticeable steric hindrances in the system. During the copolymerization of N-methacryloyl-6-caprolactam with ST, these obstacles are even more significant, and therefore r 1 becomes equal to zero (the substituted amide does not undergo homopolymerization). The value of r 2 = 1 in this pair of monomers indicates that the ratio of the rate constants of the styrene radical with both monomers is largely determined by the opposite polarity of these monomers.

When studying the copolymerization of N-(n-octyl)acrylamide, N-(1,1,3,3-tetramethylbutyl)acrylamide, and N-(n-octadecyl)acrylamide with MMA and ST, it was found that in these systems r 1< 1 и r 2 >1, i.e. these substituted acrylamides are inferior in reactivity to comonomers. The proximity of r 1 and r 2 in these pairs of monomers and pairs of N-(n-octadecyl)acrylamide - MMA (ST) and n-octadecyl acrylate - MMA (ST) suggests that the steric effect (obstacles created by alkyl groups) determines the reactivity acrylamides having long bulky substituents on the nitrogen.

The presence of two substituents at the AA nitrogen does not prevent either homo- or copolymerization of monomers, but the steric hindrance caused by these substituents strongly affects the kinetic parameters of polymer formation. Thus, the copolymerization constants in DMF (60 °C) of N,N-dimethyl- and N,N-dibutylacrylamides with ST are 0.23 and 1.23, respectively; 0.32 and 1.65. In these systems of conjugated monomers, despite the opposite polarity of the compounds, the styrene radical preferentially reacts with ST (r2 > 1), apparently due to steric hindrances in N,N-disubstituted acrylamides. Based on the copolymerization constants of a number of N,N-disubstituted acrylamides and the growth rate constants during the homopolymerization of the corresponding monomers, the rate constants of the interaction of the substituted amide radical with "foreign" monomers (k 12) and "foreign" radicals with amides k 21 were calculated. It turned out that k 12 depends very strongly on the nature of the substituents in the amide. For example, when copolymerized in bulk (30 °C) with MMA for N-acryloyl-substituted dimethylamine, pyrrolidone and piperidine, the k 12 values ​​are 66:14:1. Since the values ​​of k 21 for all three N, N-disubstituted amides upon interaction with the same monomer are of the same order, it can be concluded that the decrease in k 12 is due to an increase in steric hindrances in the amide radical created by substituents at nitrogen.

N,N-Dialkyl- and N-alkyl-N-arylmethacrylamides, which do not undergo radical homopolymerization, copolymerize with some conjugated monomers, for example, with ST, MMA, AN, N,N-methylene-bis-acrylamide. However, the copolymers obtained at low conversions are depleted in amide units compared to their content in monomer mixtures. Thus, during the copolymerization of N,N-dimethylmethacrylamide and MMA in dioxane (80 °C) r 1 = 0.175, r 2 = 8.92. The predominant contribution of the steric factor to the reactivity of N,N-disubstituted methacrylamides is confirmed by the fact that N-methacryloyl-aziridine, in which the mobility of substituents at nitrogen is limited (since they are part of a strained three-membered heterocycle), in contrast to the indicated N,N-disubstituted methacrylamides, undergoes not only co-, but also homopolymerization by the radical mechanism. Copolymers of two disubstituted methacrylamides, N-methacryloylpiperidine and N-methacryloylanabasine, were also obtained, N-substituents of each of which are part of heterocycles.

The assumption that the resistance to homopolymerization of N,N-di-substituted methacrylamides is due to the excess of the experimental temperature above the critical temperature of polymerization is refuted by the fact that N,N-dimethylmethacrylamide did not turn into a polymer under the action of UV radiation and at -78 °C.

Copolymerization with nonionic monomers. The regularities of copolymerization are greatly influenced by the conditions of the process. It is known that the appearance of a phase boundary during copolymerization, even in the absence of interfacial interaction, often leads to a change in the composition of the copolymer and a deviation of the process as a whole from the Mayo-Lewis scheme. In homophase copolymerization, if the monomers do not undergo dissociation, association, or specific solvation by solvent molecules, and subject to a number of other conditions, the process of copolymer formation is described by equations arising from the classical theory of copolymerization. Below, we consider to what extent the copolymerization of b, c-unsaturated amides with nonionic monomers deviates from the Mayo-Lewis scheme, namely, with monomers that, as a rule, do not dissociate under copolymerization conditions and exhibit a weak tendency to autoassociation and interaction with the solvent. In such systems, deviations from this scheme are determined mainly by the structure of the acrylamide component.

The most indicative for the deviation of copolymerization patterns from the Mayo-Lewis scheme is the dependence of r 1 and r 2 on the nature of the solvent. A number of works present data on the dependence of r 1 and r 2 on the nature of the solvent in the copolymerization of AA and CT. As can be seen from Table. 6, the values ​​of r 1 decrease and r 2 increase when going from benzene and 1,2-dichlorobenzene to benzonitrile, ethers, DMSO and alcohols.

Table 6

Relative activities of AA and ST during copolymerization in various solvents at 30 0 C (10% solutions) .

			Absorption, cm-1
1,2-dichlorobenzene
Besonitrile
dimethyl ether diethylene glycol
2-(2-methoxyethoxy)ethanol
Water-tert-butanol

*In 1% solution r 1 = 9.14 ± 0.27; r 2 = 0.67 ± 0.08.

Approximately in the same sequence, the shift of the NH bands of the amide group in the IR spectrum of AA solutions in the listed solvents increases towards longer wavelengths compared to the absorption in carbon tetrachloride, referred to an infinitely dilute solution. At the same time, some shift of the C=0 band is also observed, but in its absolute value it is much inferior to the shift of the NH bands. It follows from these data that the dependence of r 1 and r 2 on the nature of the solvent is associated mainly with the formation of hydrogen bonds between the amide hydrogen atoms and solvent molecules, as well as the dipole–dipole interaction between the same compounds. In contrast to these factors, the dielectric constant and dipole moment do not have a decisive influence on the change in the composition of the formed copolymers. The removal of hydrogen atoms from the amide nitrogen atom leads to an increase in its negativity, which extends to the entire amide molecule and causes the mixing of p-electrons of the CH 2 \u003d CH group to methylene and elongation of the carbon-oxygen bond. Since the directions of polarization of AA and ST molecules are opposite, a decrease in the electron-withdrawing ability of the amide group in AA should lead to some convergence of the polarities of both monomers and to a decrease in the values ​​of the constants k12 and k21. As for k 21 , if the dependence of ST reactivity on the medium is small (k 22 = const), its decrease should lead to an increase in r 2 , which is exactly what takes place. Judging by the fact that with an increase in the binding of AA molecules by the solvent r1 decreases, it can be assumed that a decrease in k12 is accompanied by an even greater decrease in k11, in particular, due to an increase in steric hindrances in the collision of specifically solvated monomer and acrylamide radical.

During the copolymerization of AA and MMA in DMSO and chloroform, the addition of small amounts of water leads to a noticeable increase in r1 and has little effect on r2, which is associated with the acceleration of AA homopolymerization (an increase in k11) and is probably due to the solvation of growing chains by water molecules. On the other hand, during the copolymerization of AA and N-vinylpyrrolidone in water, the partial replacement of the latter by glycerol capable of specifically solvating AA also leads to a significant increase in r 1 and a slight decrease in r 2 . So, with an increase in the content of glycerol in the solvent from 0 to 80% (wt.) at 60 C, r 1 increases from 0.60 to 1.06; r 2 drops from 0.17 to 0.11. The data presented indicate a very strong dependence of r 1 and r 2 on the nature of the solvent and the complex nature of this dependence: the same substances, depending on the nature of the system as a whole, can cause opposite effects.

When studying the emulsion copolymerization of AA and ethyl acrylate, it was found that the composition of the copolymer differs under comparable conditions in solution, and under the action of additions of acetone, ethanol, diacyan and other solvents, it changes.

In the copolymerization of MAA and N-methylacrylamide with CT and MMA, a noticeable effect of the medium on the values ​​of r 1 and r 2 is observed, the character is the same as in the copolymerization of AA with CT.

Table 7

Relative activities of N-(1,1-dimethyl-3-oxobutyl) acrylamide and ST during copolymerization in different solvents at 70 C (with a total monomer concentration of 0.8 mol/l)

The study of the copolymerization of N-(1,1-dimethyl-3-oxobutyl)acrylamide with CT and MMA in different solvents showed (Table 7) that the relative activity of the second monomer is practically independent of the reaction medium, while the first one in benzene and dioxane is slightly higher than in ethanol, i.e. the same regularity is observed as in the copolymerization of AA with ST, but it is less pronounced. This may be due to both the relatively large volume of the nitrogen atom substituent and the fact that the molecule of N-(1,1-dimethyl-3-oxobutyl)acrylamide and the corresponding radical has an intramolecular H-bond, as a result of which scheme 5:

CH 2 \u003d CHCON C-CH 3

(CH3) 2 C - CH 2

and solvation in an alcoholic medium by solvent molecules is suppressed. Recall that such solvation leads to a sharp change in k 11 and r 1 during the copolymerization of unsubstituted nitrogen in AA.

The effect of the nature of the solvent on the rate was studied using the AA-AN system as an example. In solvents capable of forming autoassociates via hydrogen bonds (water; acetic acid, methanol, DMF), the polymerization rate sharply decreases when small amounts of AN are added to AA. In solvents not capable of autoassociation, but capable of solvation (dioxane, acetone, acetonitrile), the rate of copolymer formation gradually decreases in proportion to the proportion of AN in the monomer mixture. In inert solvents (n-hexane, benzene, toluene), the rate practically does not change until the content of AA in the mixture of monomers is 40% (wt.), and with further depletion of the mixture with amide, the process slows down.

For nitrogen disubstituted acrylamides and methacrylamides, in the amide group of which there are no mobile hydrogen atoms actively involved in the formation of various kinds of associates and complexes with the molecules of the medium, a noticeable dependence of the reactivity on the nature of the solvent is uncharacteristic. N,N-disubstituted amides form copolymers of the same composition and the same composition distribution during copolymerization in bulk and in various solvents. An exception may be protic solvents. The nature of the solvent does not affect the values ​​of r 1 and r 2 during the copolymerization of also N-monosubstituted acryl- and methacrylamides, if the substituent sterically prevents the unsubstituted amide hydrogen atom from participating in the formation of complexes with solvent molecules. For example, the values ​​of r 1 and r 2 do not depend on the nature of the solvent in the copolymerization of N-(n-octadecyl) acrylamide with MMA and CT.

The dependence of the copolymerization constants of unsubstituted and many nitrogen monosubstituted amides on the nature of the solvents makes it possible to attribute systems containing these monomers to the category of complicated (“special”) systems that do not obey the classical theory of Mayo-Lewis copolymerization. For such systems, the Alfrey-Price scheme is not applicable, since the values ​​of Q and e become ambiguous. For example, for MAA, the following Q and e values ​​are given in the literature: 1.46 and 1.24 , 0.88 and 0.74 , 0.57 and - 0.06 . It is obvious that the values ​​of Q and e should not be used as constants characterizing a given monomer in the case of compounds with a significant tendency to association and solvation (especially specific). When considering "special" systems, the parameters Q and e can only serve as conditional values ​​reflecting the influence of certain factors on the behavior of a given monomer during copolymerization.

More or less stable values ​​of Q and e can be characteristic of N, N-disubstituted amides, as well as of N-monoaminated amides, in which, due to the large volume of substituents, monomer association and access to amide hydrogen atoms of solvent molecules are suppressed or sharply limited. The constancy of Q and e in different media is observed during the copolymerization of N,N-dimethylacryamide with various monomers, the butyric ester of N-hydroxymethylmethacrylamide with MMA and AN, N-(n-octadecyl)acrylamides with MMA and CT. However, taking into account the significant contribution of steric effects to the reactivity of N,N-disubstituted amides, as well as the fact that the Q, e scheme is not applicable to systems containing sterically strongly hindered monomers, the parameters Q and e of the considered amides are not constants characterizing them. resonant stabilization and polarity.

The question of the dependence of the values ​​of r 1 and r 2 on the conversion of monomers deserves special attention. It was quite natural to expect that during the copolymerization of monomers forming “special” systems, as the polymer content in the reaction medium increases, the nature of the interaction between the components of the mixture will change and, consequently, the values ​​of the relative activities of the monomers will change. The data on homophasic and heterophasic copolymerization of AA and AN in aqueous solutions fully confirmed these expectations. For a number of degrees of conversion, the current ratios of the concentrations of amide and nitrile in the monomer mixture (M 1 /M 2 = F) and the corresponding ratios of the amounts of monomers (m 1 /m 2 = f) that went into the composition of the copolymer at a given point in time (" instantaneous composition of copolymers). Further, using the equation of the composition of the copolymer in the form proposed in the work, the found dependences were depicted graphically. At all ratios of monomers, regardless of whether the copolymer was isolated in the form of a solid phase or not, linear dependences were not obtained (Fig. 3).

At the same time, it was shown that the copolymerization constants found from the initial rates at 20 °C in a homophase medium in the absence and in the presence of a copolymer differ sharply:

Without copolymer additives 0.65 + 0.04 2.34 ±0.35

With addition of copolymer 0.027 ± 0.003 1.45 ± 0.41

Rice. 3. Dependence of the composition of the copolymer AA and AN on the composition of the monomer mixture in the coordinates of the Fineman-Ross equation during copolymerization to high degrees of conversion (water, 20 C, initial concentrations: AA - 0.42, AN - 0.95 mol/l)

It should be noted that the main responsibility for the complicated ("special") character of the AA-AN system lies with the first monomer. This is indicated by the results of studying the homophase copolymerization of AN and ST to high degrees of conversion, according to which the relative activities during the process change (r1 decreases) only with the predominance of nitrile in the mixture of monomers. In addition, during the copolymerization of MMA with N,N-dimethylmethacrylamide, in the amide group of which there are no hydrogen atoms involved in the formation of amide associates of variable composition, the values ​​of r1 and r2 remained constant during the process.

During the copolymerization of AA and MAA with MMA in DMSO solutions, the relative activity of amides decreases, while that of the ester increases. It is assumed that for systems of (meth)acrylamide and a monomer that does not participate or only weakly participates in the formation of autoassociates or complexes, the change in the relative activity of monomers is due to the fact that, as homophase copolymerization proceeds, the proportion of the more active amide, which is part of the autoassociates of this monomer, decreases, and the proportion of the less active monomer, which forms mixed associates with the acrylamide units of the copolymer, increases.

On the example of the MAA - MMA system, a method was proposed for quantifying changes in the relative activities of monomers during copolymerization: using the Kelen and Tudosh method to determine r 1 and r 2 according to the average composition of copolymers at high degrees of conversion made it possible to determine the changing "integral" values ​​of r 1 and r 2 achieved at each degree of conversion of monomers into a copolymer (at close conversions in different series of experiments). For the system under consideration, it was found that at a conversion of up to 32%, r 1 gradually decreases from 0.50 to 0.26, and r 2 increases from 4.2 to 5.0. When evaluating the relative reactivity in the AA-ST system on the basis of data on the composition of the copolymer at high degrees of conversion in various solvents, values ​​were obtained that differ markedly from those found at low conversions. The values ​​found in the work can be attributed to the integral r 1 and r 2 .

Let us pay attention to one more feature of the copolymerization of amide-containing systems, which can be classified as “special”. In ternary systems, the composition of which includes amides that tend to form various kinds of associates, the reactivity of the components differs from their reactivity in the corresponding binary systems, and the direction and degree of deviations depend on the nature of intermolecular interactions. Obviously, the nature of associates formed in solution by two compounds can change when a third compound appears in the system. In this regard, the use of the Alfrey and Goldfinger method for calculating the compositions of ternary copolymers based on the values ​​of r 1 and r 2 of the corresponding three binary systems for amide-containing systems can give results that differ markedly from the experimental ones. This position was experimentally confirmed by the example of ternary mixtures of monomers containing, along with the amide, also an acid or an ammonium salt. For the AA - AN - MAA system, even at low degrees of conversion, the copolymers are more enriched in nitrile and acid than it follows from the calculation (Fig. 4).

Rice. 4. Dependence of the calculated (1) and experimentally found (2) composition of the terpolymer on the composition of the monomer mixture (3) in the system AA (M) 1 - acrylonitrile (M 2) - methacrylic acid (M 3)

In the system MAA - hydrochloride N,N-diethylaminoethyl methacrylate-2-hydroxyethyl methacrylate, the resulting copolymer contained fewer units of the second monomer, and more of the third monomer than calculated.

The radical copolymerization of N-n-hydroxyacrylamide and N,N-di-butylacrylamide with ST in toluene (25°C) in the presence of ethylaluminum sesquichloride as a complexing agent results in alternating copolymers.

Copolymerization with unsaturated acids and their salts. An important feature of the copolymerization of AA with monomers containing a free or neutralized acid group, for example, with p-styrenesulfonic acid, b, c-unsaturated mono- and dibasic carboxylic acids and their salts, is the multicomponent nature of the process in ionizing media. It lies in the fact that in the system there is an equilibrium depending on the nature of the medium between various forms of coexistence of positively and negatively charged particles:

A X A - X + A - IIX + A - + X +

The general scheme of ionization equilibrium does not postulate the simultaneous existence in the system of all four forms of an ionogenic monomer [molecular, ionic (contact and separated pairs) and free ions], there can be three or two such forms (for example, A - IIX + and A - + X + ) depending on the nature of the reaction medium. A consequence of the multicomponent nature of the system is the complicated nature of the copolymerization. Therefore, the activity of monomers in the copolymerization reaction depends on the total monomer concentration and composition; the initial monomer mixture, the ionic strength of the solutions, the polarity of the solvent, and the degree of conversion. During copolymerization with ionogenic monomers, a strong dependence of the conformational state of macromolecules on the nature of the reaction medium is also observed.

With a decrease in the dielectric constant of a mixture of water and DMSO, the initial rate of copolymerization of AA with the sodium and potassium salts of n-styrenesulfonic acid decreases. The decrease in the reactivity of the amide observed with this is associated with a shift in the equilibrium between the association of the amide and its solvation towards the latter, an increase in complex formation between DMSO macroradicals, and a decrease in the size of macromolecular coils, leading to a decrease in the local concentration of amide in the region where there are active centers.

In view of the practical significance of MAA and MAA copolymers, it is advisable to consider their synthesis in more detail. When these copolymers are obtained in 40% aqueous solutions (85 °C), as the degree of acid neutralization with sodium hydroxide increases (pH increases), the relative activity of the amide increases (from 0.28 to 0.64), while the acid decreases (from 2, 6 to 0.4) . With an increase in pH, the proportion of protonated amide molecules and radicals, at the ends of which there are elementary units of the protonated amide, decreases, and the degree of dissociation of the acid and the corresponding macroradical increases, i.e. there is a weakening of the repulsion of the amide radical of the amide molecule, an increase in the repulsion of the acid radical of the acid molecule (anions). Therefore, an increase in r 1 and a decrease in r 2 may be due to an increase in k 11 and a decrease in k 22 .

During the copolymerization of AA and MAA, the picture is qualitatively the same as in the copolymerization of MAA and the same acid: at pH< 3, когда кислота очень слабо ионизирована, а константы скоростей роста и обрыва при ее гомополимеризации не зависят от концентрации ионов водорода, величины r 1 и r 2 практически постоянны при изменении рН. При этом r 2 превышает r 1 в еще большей степени, чем системе МАА - МАК. При рН >3 the value of r 2 drops sharply.

Since in amide-acid systems both components can determine the "special" nature of the systems, it is quite natural that during copolymerization to deep conversions, the values ​​of r 1 and r 2 change continuously. The variability of r 1 and r 2 during the copolymerization of AA and unsaturated acids was first established using sodium maleate, sodium succinate, and other salts as the second monomer.

Based on the kinetic data on the copolymerization of AA and AA up to 80% conversion, an attempt was made to determine the relative activity of the monomers by the Kelen-Tyudosh method, which, however, failed (the values ​​of r 1 and r 2 turned out to be 0.50 ± 0, respectively, 06 and 0.79 + 1.67). Fluctuations in r 2 in such a wide range are obviously due to a change in reactivity during copolymerization, although the authors themselves do not make such a conclusion.

Experimental data on the kinetics of the initial period of copolymerization in 7% (wt.) aqueous solutions of MAA and sodium methacrylate, taken in various ratios, are satisfactorily described by the well-known equation, which was proposed by Melville, Noble and Watson. According to this equation, the termination is controlled by chemical reactions, and diffusion processes are not taken into account. At the same time, precisely because of the effect of diffusion on the regularities of chain termination, this equation very often turns out to be inapplicable to the description of the kinetics of copolymerization. It is assumed that the possibility of using the equation in the copolymerization of MAA and sodium methacrylate is due to the fact that in this system the rate constants of termination reactions (due to the interaction of identical and different radicals) are close to each other. In the MAA-sodium methacrylate system, the curve of the dependence of the initial copolymerization rate on the ratio between the monomers passes through a weakly pronounced maximum, which, with the relative closeness of the termination rate constants, is determined by the preference for cross-growth compared to growth due to any homopolymerization (r 1< 1 и r 2 < 1 ). Для системы АА - АК (вода, рН = 4,6) также наблюдается превышение скоростью сополимеризации скоростей гомополимеризации обоих мономеров .

The copolymerization of MAA and MAA (or its salt) proceeds without self-acceleration. The gel effect is apparently overridden by a decrease in individual growth rate constants with an increase in monomer conversion.

When AA and potassium acrylate are copolymerized in water in the presence of a solid initiator that is insoluble in the reaction mixture, a copolymer is formed containing less AA than the copolymer obtained in the presence of a water-soluble initiator, which is apparently due to the selective adsorption of potassium acrylate on the solid initiator.

Copolymerization with unsaturated amines and their salts. Of practical interest are cationic copolymers of AA with allylamine and substituted allylamines. When they are obtained, AA is much more active in copolymerization than the comonomer. So, during copolymerization with AA of allylamine hydrochloride (water; pH = 3.0, 40 ° C) r 1 = 13.35 ± 0.26 and r 2 = 0.08 ± 0.02, diallyl-dimethylammonium chloride (water; pH \u003d \u003d 6.1; 40 ° C) r 1 \u003d 6.7 and r 2 \u003d 0.58. In contrast to monomers containing allylamine fragments and giving relatively stable radicals during copolymerization, other amine- and ammonium-containing comonomers usually outperform AA in activity. In the copolymerization of AA with 4-dimethyl-aminostyrene (methanol; 60 °C) r 1 = 0.15 and r 2 = 3.35, with 5-vinyl-1-methyl-2-picolinium methyl sulfate (water; 48 °C ) r 1 = 0.19 and r 2 = 2.7.

The copolymerization of AA and MAA with monomers in whose molecules the amino group is separated from the vinyl group by chains of 4 or more atoms has been studied in great detail, primarily with dialkylamino-alkyl(meth)acrylates. With heterophase copolymerization in acetone of MAA with dialkylaminoethyl methacrylates in the form of non-ionized bases, the process is close to ideal, r 1 and r 2 differ little from unity). The same picture is observed in the copolymerization of N,N-dimethylaminoethyl methacrylate (DMAEM) with MMA. The closeness of the relative activities to unity indicates that the chain growth rates in these systems are controlled by the rate of diffusion of monomer molecules into macromolecular coils, and the diffusion rates of comonomers differ little from each other.

The transition from dialkylaminoethyl methacrylates to their salts during copolymerization in water leads to a sharp change in the values ​​of the relative activities of the monomers. So, during copolymerization (water; 70 ° C) of MAA with DMAEM hydrochloride r 1 = 0.26 ± 0.13 and r 2 = 2.6 ± 0.14, with N,N-diethylaminoethyl methacrylate hydrochloride (DEAEM) - r 1 \u003d 0.17 ± 0.04 and r 2 \u003d 0.39 ± 0.01. It is assumed that the positive charges of the salt macromolecule promote chain straightening and release of the end of the macroradical, which makes it more accessible to monomer molecules, due to which the growth rate is controlled by the chemical reaction rate and depends on the structure of the reacting particles, i.e., the rate constant of elementary growth reactions during copolymerization , as a rule, can no longer be equal to each other. The decrease in r 1 and in some cases an increase in r 2 upon passing from free bases to their salts is due to the fact that amides are generally less reactive when interacting with free radicals than sterically hindered salts based on N,N-dialkylaminoethyl methacrylates. This may be due to the formation of closed systems in salt molecules (due to the attraction between the ammonium nitrogen atom and the carbonyl oxygen atom), which contribute to the delocalization of the unpaired electron on the a-carbon atom and, thereby, relatively greater stability; corresponding radicals than amide radicals, resulting in k 11< k 12 и k 22 >k 21 . However, the value of r 2< 1 в системах МАА - соль на основе ДЭАЭМ указывает, что рассматриваемые константы сополимеризации зависят и от других факторов. Одним из них может быть электростатическое отталкивание между одноименно заряженными молекулой и радикалом солеобразного производного ДЭАЭМ .

The values ​​of r 1 and r 2 for b, c-unsaturated amides with DEAEM or its salt-like derivatives turned out to be independent of the degree of conversion of monomers during copolymerization, while during copolymerization with acids or nitriles they change dramatically during the process. This difference is probably due to the fact that dialkylaminoalkyl (meth)acrylate units, due to the presence of dialkylaminoalkyl residues occupying a relatively large volume in them, under copolymerization conditions, sterically prevent the association of the monomeric amide with the amide group in the copolymer.

Copolymerization of amides with salt-like derivatives of dialkyl-aminoalkyl(meth)acrylates proceeds at a much higher rate and leads to higher molecular weight copolymers than in copolymerization with free bases. This can be explained by the lower (due to electrostatic repulsion) rate of termination reactions, in which two macrocation radicals participate, than the termination reaction based on the collision of uncharged particles, as well as by the unfolding of growing macrochains and the release of reaction centers during the transition from free bases to salts, facilitating the growth reaction during copolymerization. At the same time, copolymerization of amides with dialkylaminoalkyl methacrylates in the presence of a twofold excess of HCl with respect to amines does not give a noticeable effect compared to copolymerization in the absence of HCl. Due to the shielding of positive charges by an excess of chlorine counterions, the growing chains are coiled and the approach of monomer molecules to them is sterically hindered just as in the case of copolymerization with free bases. Thus, to obtain copolymers of amides with dialkylaminoalkyl(meth)acrylates at a high rate and sufficient viscosity, the base must first be neutralized or converted into a quaternary ammonium salt. A similar result is achieved by combining the processes of alkylation of dialkylaminoalkyl(meth)acrylate and its copolymerization with amide.

Copolymerization with salts based on dialkylaminoalkyl(meth)-acrylates is carried out in the presence of peroxide initiators, with dialkylaminoalkyl(meth)acrylates in the form of free bases - in the presence of initiators that do not interact with the amino group (azo compounds). The copolymerization of MAA and non-neutralized dialkyl methacrylates in acetone practically stops when 60-70% conversion of monomers is reached, despite the presence of an initiator.

In this work, copolymerization of AA and MAA with DEAEM hydrochloride (molar ratio 4:1) in aqueous solutions to high degrees of conversion resulted in copolymers that are poorly soluble in water. In both systems, due to the course of the process in an acidic medium, cross-linking of macromolecules is possible due to the formation of intermolecular secondary amide (-CONHCO-) ​​bridges. In addition, in the case of the MMA-based system, due to the higher values ​​of r 2 compared to r 1 , fractions that are poorly soluble in water and enriched in amide units are formed at high conversions. This explanation is consistent with the fact that it was possible to improve the solubility of the MAA-hydrochloride copolymer by dosing the more active monomer, DEAEM hydrochloride, during the copolymerization. At the same time, the degree of homogeneity in the composition of the copolymer macromolecules increased simultaneously.

radical sonopolymerization usually initiated in the same way as radical polymerization. It is characterized by the same mechanisms of chain growth, termination and transfer.

Consider the copolymerization of two monomers M, and M 2 . If the activity of growth radicals is determined only by the type end link, then four elementary growth reactions should be taken into account:

The corresponding rates of elementary stages of chain growth can be written as

The kinetics of the chain growth reaction determines the composition of copolymers and the entire complex of their chemical and physicomechanical properties. The model, which takes into account the effect of the end link on the reactivity of the active site with respect to monomer molecules and considers four elementary reactions of a growing chain with a different type of end link (M *) with a monomer (M (), was called "end link model" copolymerization. This model was independently proposed in 1944 by the American chemists F. Mayo and F. Lewis. Kinetic processing of the above scheme in the quasi-stationary approximation makes it possible to establish the relationship between composition of copolymers and the composition of the initial mixture of monomers, those. an equation that describes the composition of the “instantaneous” copolymer, as well as the composition of the copolymer formed at initial conversions, when changes in monomer concentrations can be neglected.

Assumptions Required for Conclusion copolymer composition equations(dependence of the composition of the copolymer on the composition of the monomer mixture), include:

• 2) reactivity M* and M: * does not depend on P p;
• 3) the quasi-stationary condition: the concentrations of M* and M* remain constant if the rates of their mutual transformation are the same, i.e. Vp |2 = K p 21;

4) small conversions.

The rates of conversion of monomers during copolymerization are described by the equations

where from, and t 2 - concentration of monomer units in the copolymer.

The ratio of the rates of these reactions leads to the expression

Taking into account the stationarity condition for the concentrations of radicals, it is easy to obtain the following expression, which characterizes the dependence of the composition of the obtained copolymer on the composition of the monomer mixture at the initial stages of the transformation, when the change in the concentration of monomers [M,] and [M 2] can be neglected:

where k iV k 22 are the rate constants for the addition of its monomer by the radical; k vl , k. n are the rate constants of addition of a foreign monomer by a radical; g, = k n /k l2, r 2 = k 22 /k 2l- copolymerization constants, depending on the chemical nature of the reacting monomers.

Often instead of concentrations, the corresponding mole fractions are used. Let us denote by /, and / 2 mole fractions of comonomers in the mixture, and through F( and F2- mole fractions of units M ( and M 2 in the copolymer:

Then, combining expressions (5.28)-(5.30), we obtain

The dependence of the composition of copolymers on the composition of a mixture of monomers is conveniently characterized by a composition diagram (Fig. 5.1). At r(> 1 and r 2 1 the copolymer is enriched in Mj units (curve 1) at r x 1 and r2 > 1 copolymer is enriched with M. units; (curve 2). If r, \u003d r 2 \u003d 1, then the composition of the copolymer is always equal to the composition of the initial mixture (direct line 3).

Rice. 5.1.

If a r( r ( > 1 and r2 > 1, then there is a tendency to separate polymerization of the monomers in the mixture (curve 5). If the composition curve intersects the diagonal of the composition diagram, then at the intersection point, called azeotropic, the composition of the copolymer is equal to the composition of the comonomer mixture.

The properties of binary copolymers depend on the average composition of the copolymer, its compositional heterogeneity, and the distribution of monomer units in macromolecules. With the same composition, the distribution of links along the chain can be different (block, statistical, alternating or gradient). The composition of an individual macromolecule may differ from the average composition of the entire sample, which leads to compositional inhomogeneity of the copolymer. Distinguish instantaneous and conversion heterogeneity of copolymers. Instantaneous compositional inhomogeneity arises as a result of the statistical nature of the process. Conversion compositional heterogeneity is due to a change in the composition of the monomer mixture during copolymerization (except for azeotropic copolymerization), its contribution to the overall compositional inhomogeneity is much higher than the contribution of instantaneous inhomogeneity.

During copolymerization at deep stages of transformation, the composition of the monomer mixture (except for the case of azeotropic copolymerization) changes continuously during the course of the reaction: the relative content of the more active monomer decreases, and the less active one increases (Fig. 5.2).

Rice. 5.2. Dependence of the composition of the copolymer on the composition of the monomer mixture for cases of unilateral enrichment (curve1: r, > 1; r2 2: r x one; r2 > 1)

For the same composition of the monomer mixture (Fig. 5.2, point BUT) products are formed with different contents of the first component: corresponding in the first case - to the point AT at the second point D". During the reaction, the mole fraction M, will constantly change: in the first case, it will decrease, in the second, it will increase. At the same time, the instantaneous compositions of the resulting copolymers will change: in the first case, the copolymer will be constantly depleted in M ​​p units, in the second case, the copolymer will be enriched in M ​​units. In both cases, products of various “instantaneous” compositions are accumulated, which leads to the appearance of a conversion compositional inhomogeneity of the resulting copolymer. However, the average composition of the final product in both cases will be the same: at 100% conversion, it is equal to the composition of the monomer mixture and corresponds to the point WITH.

In copolymerization with a tendency to alternate (see Fig. 5.1, curve 4) For an arbitrary composition of the initial monomer mixture, there are two composition regions on the composition curve: one lies above the bottom line and the other lies below this diagonal. They are separated by the azeotrope point ( ), which is located at the intersection of the composition curve with the diagonal. With the exception of the azeotrope point, during copolymerization, the instantaneous compositions of the copolymer change along the curve to the right. Thus, in this case as well, copolymerization at deep conversions leads to compositionally inhomogeneous products.

An exception is the azeotropic copolymerization of a monomer mixture, during which the compositions of the copolymer and monomer mixture do not change during the course of the reaction and remain equal to the initial composition of the monomer mixture until the monomers are completely exhausted. The invariance of the composition of the copolymer during azeotropic sonopolymerization leads to the production of homogeneous products, the compositional inhomogeneity of which is minimal and is associated only with its instantaneous component. The condition for the formation of an azeotropic composition has the form

The quantities Г[ and g 2 can be determined experimentally. Knowing them makes it possible to predict the composition of the copolymer and the distribution of monomer units in the chains at any ratio of monomers in the mixture. Values ​​r, and g 2 during radical sonopolymerization and, consequently, the composition of the copolymer usually weakly depends on the nature of the solvent and changes very little with temperature.

The exception is:

• 1) phenomena associated with donor-acceptor interactions of reagents. If one of the monomers is a strong donor and the other is a strong acceptor, alternating copolymers are formed (styrene - maleic anhydride, r = 0 and g 2 = 0);
• 2) co-polymerization of ionic monomers depending on pH (acrylic acid - acrylamide, pH = 2, g, = 0.9 and g 2 = 0.25; pH = 9, g, = 0.3 and g 2 = 0, 95);
• 3) co-polymerization of the pair "polar monomer - non-polar monomer" in polar and non-polar solvents (bootstrap effect, styrene - n-butyl acrylate, g = 0.87 and g 2 = 0.19 in mass and g = 0.73 and g 2 = 0.33 in DMF; 2-hydroxymethyl methacrylate - tert- butyl acrylate, g, = 4.35 and g 2= 0.35 in mass and g, = = 1.79 and g 2 = 0.51 in DMF);
• 4) heterophase co-polymerization. In heterophasic sonopolymerization, selective sorption of one of the monomers by the polymer phase can lead to a deviation from the composition characteristic of homogeneous copolymerization of the same nara (styrene - acrylonitrile: coolimerization in bulk and in emulsion; MM A - N-vinylcarbazole in benzene r = 1 ,80 and g 2 = 0.06, in methanol g = 0.57 and g 2 = 0,75).

Consideration of the quantities r, and g 2 in the framework of the theory of ideal radical reactivity leads to the conclusion that r, r 2 = 1, i.e. the rate constants of addition of one of the monomers to both radicals are the same number of times greater than the rate constants of addition of the other monomer to these radicals. There are a number of systems for which this condition is well realized experimentally. In such cases, monomeric units of both types are arranged randomly in macromolecules. Most often, g g., 1, which is associated with polar and steric effects, which cause a tendency to alternation of monomer units M, and M 2 in macromolecules. In table. 5.12 shows the values ​​of copolymerization constants for some pairs of monomers. Conjugation with a substituent reduces the activity of the radical to a greater extent than it increases the activity of the monomer, so the monomer that is more active in copolymerization is less active in homopolymerization.

To quantitatively characterize the reactivity of monomers in radical copolymerization, the semi-empirical method is used.

Radical copolymerization constants for some monomers

circuit Q-e, proposed in 1947 by American chemists T. Alfrey and K. Price. Within this framework, it is assumed that

where P Q- parameters corresponding to the conjugation energies in the monomer and the radical according to the theory of ideal radical reactivity. Quantities e ( and e 2 take into account the polarization of the reacting monomers. Then

Using this scheme, it was possible to estimate the relative reactivity of monomers and the role of polar factors for a large number of pairs of copolymerizable monomers.

The standard monomer was taken styrene with values Q= 1, e= 0.8. During the copolymerization of styrene with other monomers (M), the latter were characterized by their Q values. and e~, which made it possible to predict the behavior of these monomers in copolymerization reactions with other monomers, for which the values ​​were also established Q and e.

For active radicals, the activity of monomers depends on resonance factors. With the increase Q constant k l2 increases. For inactive radicals (styrene, butadiene), the activity of monomers depends on polarity. In table. 5.13 shows the values ​​of Qn e some monomers.

Table 5.13

ValuesQandesome monomers

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The copolymerization reaction was carried out according to scheme 6:

The study of the copolymerization reaction under these conditions showed that the reaction solutions were homogeneous over the entire range of compositions, and the resulting copolymers were readily soluble in water.

As is known, during the homopolymerization of AG and MAG, microheterogeneity of the reaction solution is observed at conversion degrees of more than 5%. Especially, this phenomenon is expressed for MAG. The authors explain the heterogeneity of the reaction medium found during the polymerization of MAG in H 2 O by conformational transformations of PMAG, manifested in chain folding - similar to the well-known processes of denaturation of a number of proteins, as well as synthetic polymers - protein analogues (for example, polyN-vinylpyrrolidone, PVP), about which has been reported in detail in a number of papers. It is interesting that for PVP, as follows from these works, low molecular weight guanidine salts are effective denaturing agents. The authors believe that it is the presence of two amino groups in the guanidine molecule, which are able to compete with the C=O carbonyl group, blocking its further interaction with solvent molecules (water), that causes a sharp folding of the PVP chain. Thus, in the presence of guanidine hydrochloride, the inherent viscosity of PVP in alcoholic solutions decreases markedly. K2 changes especially sharply; a value that characterizes the interaction between the polymer and solvent molecules, while PVP molecules, almost completely soluble in alcohol, become insoluble in the presence of guanidine hydrochloride, which is a consequence of blocking the oxygen of the pyrrolidone ring by guanidine chloride molecules, leading to an increase in the forces of intermolecular association of PVP rings through hydrophobic interactions. Moravec and other authors, who studied in detail the influence of various factors on protein denaturation, found that various guanidine salts have a strong denaturing effect on protein molecules when they are introduced into a solution even at low concentrations of ~1% (see Fig. 7).

Rice. 7. Change in the shape of the PAG and PMAG coil in the presence of its own monomer or guanidine hydrochloride

Based on the foregoing, it is quite remarkable that during the copolymerization of MAG with AA, it is possible to level the “denaturing” effect of the guanidine-containing MAG monomer, the copolymerization reaction proceeds under homogeneous conditions to high degrees of conversion (60%).

This means that, as in the case of natural protein molecules, the introduction of units of a “foreign” “neutral” monomer into a copolymer (which in our case is AA) leads to a violation of the tacticity (isomer composition) of the polymer chain, and the greater the number of such “ inclusions” into the PMAG chain, the less pronounced is the effect of the guanidine-containing monomer on the heterogeneity of the MAG polymerization process.

Table 8

Copolymerization rates of AA with MAG in aqueous solutions (pH 7) a

	Initial composition copolymer		Initiator, 510 -3 mol -1	mol -1 s -1	Micro heterogeneity

The composition of the AA:AG copolymers was determined from elemental analysis data, since the chemical shifts of -CH 2 -CH= protons in the 1 H NMR spectra of the comonomers are similar and overlap.

Table 9

Elemental Composition Data for AA:AG Copolymers

Ref. compound				in copolymer

To calculate the content of comonomers, we used the ratio of the content of nitrogen and carbon in the copolymer R = %N/%C, based on the consideration that

N SP \u003d N AG x + N AA (1 - x), (1)

C SP = C AG x + C AA (1 - x), (2)

where N AG and C AG - content in AG; N AA and C AA - content in AA; x is the proportion of AG in the copolymer and (1 - x) is the proportion of AA in the copolymer.

From here we have the equation:

Solving this equation and substituting the values ​​for the content of nitrogen and carbon in the corresponding comonomers, we obtain expressions for calculating x, i.e. share of AG in the copolymer.

The composition of the AA–MAG copolymers was calculated from 1H NMR spectroscopy data using the integral intensity of the signal from the methyl group of the MAG comonomer, which manifests itself in the strongest field and is not overlapped by any other signals. One third of its integral intensity will be equal to the value of the conditional proton for the MAG link - "1H (M 2)". The protons related to the signals of the CH 2 groups of the copolymer chain appear for both comonomers together in the region of chemical shifts 1.5-1.8, therefore, to determine the conditional proton of the AA unit "1H (M 1)" from the total integrated intensity of these protons ( I) the contribution of two protons of the MAG unit was subtracted and the remaining value was divided by 2 (equation (4)):

From the results obtained, the molar content of comonomers in the copolymer, expressed in mol.%, was determined (equations 5 and 6):

M PAAm \u003d ["1H (M 1)": ("1H (M 1)" + "1H (M 2)")] 100% (5)

M PMAG \u003d ["1H (M 2)": ("1H (M 1)" + "1H (M 2)")] 100% (6)

As can be seen from the curves in Fig. 8, at all initial molar ratios of comonomers, the copolymer is enriched in acrylate comonomer units, and the MAG-AA system is characterized by a greater enrichment with MAG comonomer, in contrast to the AG-AA system. This indicates a higher reactivity of MAG in the reaction of radical copolymerization and corresponds to the data on the parameters of the reactivity of acrylic (AA) and methacrylic (MAA) acids available in the literature. The higher reactivity of the MAG monomer compared to AG is probably due to the greater delocalization of the charge of the carboxyl group in the monomer molecule, as indicated by the shift of the vinyl proton signals of MAG to a stronger field compared to AG in 1H NMR spectra.

Rice. 8. Dependence of the composition of the formed copolymers in the systems:

AG-AA (curve 1) and MAG-AA (curve 2)

from the composition of the initial reaction solution

The lower reactivity of acrylamide compared to AG and MAG may be due to the specific structure of ionogenic monomers, in which there is an electrostatic attraction between the positively charged ammonium nitrogen atom and the carbonyl oxygen atom of the methacrylic acid residue, whose electron density is increased (Scheme 7).

where R \u003d H, CH 3

Scheme 7. Zwitterion delocalized structure of AG and MAG

This attraction causes delocalization of the negative charge along the bonds of the carboxylate anion of acrylic and methacrylic acids. Due to this delocalization, the relative stability of the corresponding radicals is higher compared to acrylamide. In the case of MAG, there is a higher delocalization of electrons in the C–O– bond in methacrylate anion compared to AG, which is confirmed by the greater enrichment of copolymers with MAG comonomer compared to AG.

To determine the copolymerization constants in a binary system, various methods are used in practice, which are based on the copolymer composition equation (7):

where and are the concentrations of monomers in the initial mixture; r 1 and r 2 are copolymerization constants, r 1 =k 11 /k 12 and r 2 =k 22 /k 21 .

Some methods can only be applied to low monomer conversions (up to 8%), they make the assumption that the values ​​of M 1 and M 2 remain constant at the initial stage of copolymerization. Therefore, the ratio of monomer consumption rates can be replaced by the ratio of molar concentrations of monomer units and in the copolymer:

This is, for example, the Mayo-Lewis "line intersection" method, the analytical method for calculating copolymerization constants, etc.

Methods have been developed for calculating the copolymerization constants, which make it possible to determine the composition of a monomer mixture or copolymer for almost any monomer conversion, since composition equations are solved in integral form. The simplest of these is the Fineman-Ross method.

Since we studied copolymerization at low degrees of conversion, we used the analytical method to calculate the copolymerization constants.

The basic equation of the analytical method proposed by A.I. Ezrielev, E.L. Brokhina and E.S. Roskin has the following form:

where x = /; k = /, and and are the concentrations of the i-th component in the polymer and the initial monomer mixture. Equation (9) is already symmetrical with respect to r 1 and r 2 , so both constants are determined with the same accuracy.

This equation is also convenient for calculating copolymerization constants by the least squares (LSM) method. In the latter case, the corresponding equations have the form:

and n is the number of experiments.

Then the expression for the relative activities of the monomers is written as:

where gives the mean square error of the experiment, i.e.

The values ​​of the constants calculated by this method are presented in Table. ten.

Since we studied copolymerization at low degrees of conversion, we used the analytical method to calculate the copolymerization constants, and the values ​​of the constants calculated by this method are presented in Table 1. ten.

Table 10

AG (MAG) (M 1) -AA (M 2)

Given in table. 10, the values ​​of r 1 1 and r 2 1 indicate the preferential interaction of macroradicals with a “foreign” than with “own” monomer in both copolymerization systems. The values ​​of the product r 1 × r 2 1 indicate a pronounced tendency to alternation in both copolymerization systems. In addition, r 1 r 2 , which confirms that the probability of addition of comonomer radicals to the monomeric MAG and AG molecule is somewhat higher than to the AA molecule. The closeness of the relative activities to unity during MAG-AA copolymerization indicates that the chain growth rate in this system is controlled by the rate of diffusion of monomer molecules into macromolecular coils, and the diffusion rates of comonomers differ little from each other.

Thus, the radical copolymerization of AA with AG and MAG makes it possible to obtain copolymers with a high content of ionogenic groups.

However, despite the fact that the values ​​of relative activities that we obtained indicate a lower reactivity of the AA monomer compared to MAG and AG, the study of the copolymerization of these comonomers in aqueous solutions showed that as the concentration of ionogenic AG and MAG comonomers in the initial reaction viscosities decrease.

To understand the mechanism of copolymerization of AG and MAG with AA, the rate of this process in an aqueous solution was studied by the dilatometric method. Ammonium persulfate (PSA) was used for initiation.

A study of the kinetics under these conditions showed that the copolymerization of AG and MAG with AA proceeds only in the presence of radical initiators and is completely suppressed when an effective radical inhibitor 2,2,6,6-tetramethyl-4-oxylpyridyl-1-oxyl is introduced into the reaction solution. Spontaneous reaction - polymerization in the absence of a radical initiator - is also not observed.

The reaction solutions were homogeneous over the entire range of compositions, and the resulting copolymers were highly soluble in water.

It is shown that in the reaction under study, the dependence of the degree of conversion on the duration of the reaction under the selected conditions (aqueous medium; total concentration of copolymers [M] = 2 mol-1; [PSA] = 510-3 mol-1; 60 C) is characterized by a linear part of the kinetic curve up to conversion 5-8%.

The study of the kinetics of copolymerization showed that with an increase in the content of the ionogenic monomer in the initial monomer mixture, the values ​​of the initial polymerization rate v 0 and decrease symbatically during the copolymerization of AA with AG and MAG, and for the first system (during polymerization with AG), the course of this dependence is more pronounced. The results obtained are in good agreement with the known data obtained in studies of the kinetics of copolymerization of DADMAC with AA and MAA in aqueous solutions. In these systems, it was also found that the rate of copolymerization decreases with an increase in the content of DADMAC in the initial reaction solution, and this increase is more pronounced for AA than for MAA.

Fig.9. Dependence of the initial rate of copolymerization (1.4) and intrinsic viscosity (2.3) of the copolymer MAG with AA (1.2) and AG with AA (3.4) on the content of ionogenic monomer in the initial reaction mixture.

From fig. It also follows from Table 9 that the highest molecular weight samples of copolymers (judgment by the values ​​of ) are obtained in monomeric mixtures enriched in AA.

The most likely reason for the observed decrease in the chain growth rate constant with an increase in the concentration of the ionic comonomer is that the concentration of strongly hydrated acrylate and methacrylate anions in relatively hydrophobic uncharged coils of macroradicals is lower than their average concentration in solution, which is indirectly confirmed by the decrease in the reduced viscosity of the copolymer solution with an increase in the content of AG and MAG units.

It is more logical to associate the decrease with the structuring effect of AG and MAG ions on water molecules, which leads to a decrease in volumetric effects, i.e. the quality of water as a solvent for PAM is deteriorating.

Obviously, the phenomena observed during radical copolymerization with the participation of ionizable AG and MAG monomers cannot be explained only on the basis of classical concepts, and the parameters r1 and r2 can only serve as conditional values ​​reflecting the influence of certain factors on the behavior of a given monomer during copolymerization.

Thus, the observed features and differences in the series of monomers under consideration are explained by the complex nature of the contributions of various physicochemical processes that determine the course of the copolymerization reaction of acrylamide with guanidine-containing monomers of the acrylic series. At the same time, the main contribution to the change in the effective reactivity of polymerizing particles is made by associative interactions between guanidine and carboxyl groups (both intra- and intermolecular) and the structural organization of the corresponding monomers and polymers during copolymerization.

To establish the equation for the overall rate of copolymerization of AA with AG and MAG, experiments were carried out for variable concentrations of AA, AG, MAG, and the components of the initiating system, while maintaining the constancy of the concentrations of the remaining components of the reaction system and reaction conditions.

3.2 Radical copolymerization of guanidine monomaleatewith acrylate and methacrylate guanidine in aqueous media

Ion-exchange sorbents, coagulants and flocculants, biocides, separating membranes, soil structurators, models of biopolymers, polymer carriers of various kinds of functional fragments - this is by no means a complete list of the practical applications of synthetic polyelectrolytes. One of the most common and promising ways to obtain polyelectrolytes is radical polymerization and copolymerization of monomers ionized in aqueous solutions.

In this work, we consider the synthesis of a biocidal copolymer based on guanidine acrylate and methacrylate with guanidine monomaleate. Radical homopolymerization and copolymerization of guanidine-containing compounds is the object of research by many authors, mainly in connection with the possibility of obtaining polymeric materials with a complex of specific properties, including biocidal ones. However, there is little information in the literature regarding the study of the processes of radical copolymerization of ionogenic monomers containing the same functional groups. In this regard, the study of the processes of copolymerization of guanidine-containing ionogenic monomers seems to us to be very relevant. It is known that due to the symmetry of the structure, spatial factors and the high positive polarity of the vinyl group, maleates do not form homopolymers in the presence of radical initiators. The experimental results obtained in this work also showed that the homopolymerization of guanidine monomaleate (MMG) under the studied conditions is difficult. So, for example, the degree of conversion of the MMG monomer into a polymer under conditions ([MMG] = 2 mol-1; 60 C; [PSA] = 510-3 mol-1; H 2 O; polymerization time 72 hours) is about 3% ( [h] = 0.03 dlg-1). All these facts indicate a significant contribution of the above factors to the process of homopolymerization of the system studied by us.

At the same time, it is important to note that when studying the reaction of radical copolymerization of MMG with guanidine methacrylate (MAG), a number of copolymers of various compositions with sufficiently high intrinsic viscosities and, consequently, molecular weights, were obtained.

Radical copolymerization was studied in aqueous (bidistillate), aqueous methanol, and methanol solutions; the radical initiators were ammonium persulfate (APS) and azobisisobutyric acid dinitrile (AAB) ([I] = 10 - 2-10- 3 moll - 1) in the temperature range of 20 - 60 C.

It was previously established that polymerization does not occur in the absence of an initiator.

The prepared reaction mixture was degassed in ampoules in a vacuum unit (10–3 mm Hg), after which the ampoules were sealed off and placed in a thermostat. In the case of the decomposition of the initiator at low temperatures (20 C, UV), the reaction solution was transferred into quartz cuvettes (in a vacuum).

Copolymerization was carried out to various degrees of conversion (the study of polymerization and copolymerization to high degrees of conversion can give results important in practical terms), and the following regularities were revealed. In all cases, the formation of copolymers enriched in AG and MAG units compared to the initial mixture of comonomers is observed (Table 11), which indicates a higher reactivity of MAG in chain propagation reactions.

Table 11

Dependence of the composition of the copolymer on the initial composition of the reaction solution during the copolymerization of AG (MAG) (M 1) and MMG (M 2) M 1 + M 2 ] = 2.00 mol/l; [PSA]= 5 10-3 mol l-1; H 2 O; 60 C.

	Starting comonomers M 1:M 2, mol.%	Copolymers a M 1: M 2, (mol.%) / b, dl / g

Note. a) Determined by NMR 1 H and IR spectroscopy.

b) Determined at 30 C in 1N NaCl aqueous solution.

Based on studies of the radical copolymerization of MAG and MMG, it can be concluded that copolymerization occurs only with an excess of guanidine methacrylate. If there is an excess of guanidine monomaleate, neither copolymerization nor homopolymerization of guanidine methacrylate is observed.

The composition of the synthesized polymer products was confirmed by 1H NMR and IR spectroscopy.

The predominant contribution of the steric factor to the reactivity of guanidine monomaleate in the copolymerization reaction with AG and MAG is confirmed by the values ​​of the copolymerization constants, which are presented in Table.

Table 12

The value of effective copolymerization constants in systems

AG (MAG) (M 1) - MMG (M 2)

([M] sum \u003d 2 mol - 1; [PSA] \u003d 5H10- 3 mol - 1; 60 C, H 2 O)

3.3 Physicochemical properties of synthesized copolymers

1H NMR and IR spectroscopy studies of the polymer compounds synthesized in this work confirmed the proposed structure of the objects of study. The study of the 1H NMR spectra of the synthesized copolymers made it possible to determine the comonomer composition by analyzing the integrated intensities of various signals.

3.3.1 IR spectral studies of synthesized copolymers

The analysis of the IR spectral characteristics was carried out by comparing the spectra of the monomeric guanide-containing salt and acrylamide, taken as models, as well as by comparing the spectra of polymeric compounds, which were supposed to confirm the corresponding changes in the spectra upon passing from monomers to copolymers. IR spectra of all compounds were recorded in solid form in KBr pellets.

IR spectral characteristics of the initial guanidine-containing monomers are given in table. thirteen.

Table 13

IR spectral data of acrylic derivatives of guanidine a

	Guanidine fragment
	n (NH) valence	n (C=N) valence	n (NH2) deformation	n (CNH) corners. defor.
	3100,			520,
	Z091,			529,
	Vinyl fragment
	n(CH) valence	n (C=O) valence	n (RC=) skeleton. def.	n (CH2=C-) nonplanar def.
	2928,		1240, 1384,	938,
	2929,		1275, 1359,	956,

a The positions of the peaks of the corresponding signals are given in cm-1.

In the study of the IR spectra of copolymers AG and MAG and AA, it was found that in the resulting copolymers there are absorption bands characteristic of the bending vibrations of the N-H bond in acrylamide 1665 cm-1 and intense bands of skeletal bending vibrations in the CH 3 -C = site of methacrylate guanidine at 1470 and 1380 cm - 1 . Moreover, depending on the composition of the copolymer, the intensity of these bands varies. Due to the closeness of the structures of AA and AG, the characteristic bands of the comonomers overlap and the IR spectra for this pair are not sufficiently informative. The spectra also contain an absorption band of the carboxylate ion (1560-1520 cm-1). Bands of stretching vibrations of N-H bonds are strongly shifted towards long waves (3130 and 3430 cm-1) and are quite intense. The spectrum of the copolymer contains an intense broad band with a maximum at 1648 cm–1, which, of course, is distorted by the absorption of deformation vibrations of water in this region, but its intensity and the presence of several kinks on the shoulders indicate that the N= bond is also present in this compound. C and NH 2 group.

The torsional vibrations of CH 2 groups, characteristic of hydrocarbon chains with polar end groups, manifest themselves in the region of 1180-1320 cm-1.

To determine the content of CH 3 - groups used the absorption band 1380 cm -1 related to the symmetrical deformation vibrations. Other bands characterizing the methacrylate anion are also well manifested in the spectrum: 2960, 2928 cm -1 (stretching vibrations of CH bonds) (Fig. 10-13).

Rice. 10. IR spectrum of polymethacrylate guanidine

Rice. 11. IR spectrum of AA-MAG copolymer (50:50)

Rice. 12. IR spectrum of AA-MAG(90:10) copolymer

Rice. 13. IR spectrum of AA-MAG copolymer (30:70)

The IR spectra of MMG copolymers with MAG are characterized by the presence of an absorption band at 1170 cm–1 characteristic of maleates and a band at 1630 cm–1 of monosubstituted guanidinium. Two intense bands at 1680 cm-1 and 1656 cm-1 are associated with C=N stretching vibrations and deformations of NH 2 groups mixed with them. Vibrations of the carbonyl group of monosubstituted maleic acid appear in the spectrum in the region of 1730 cm-1, the absorption bands of methyl groups (1380-1460 cm-1) are clearly pronounced, the intensity of which also varies depending on the composition of the copolymer.

3.3.2 NMR spectral characteristics of copolymersacrylamide and guanidine methacrylate

This section presents the NMR spectral characteristics of the synthesized copolymers. When studying the spectra of proton magnetic resonance, methacrylic acid, acrylate and methacrylate of guanidine, and acrylamide were used as model compounds.

The 1H NMR spectra of acrylic acid (AA) and its guanidine salt AG are of the ABC type, the characteristics of the signals are summarized in Table 14.

Let us note a slight shift to a stronger field of signals of methylene protons (3 C) of AG in comparison with AA. Apparently, this is due to the fact that AG in water (Scheme 13) is more characterized by the structure of a single-bonded hydrogen complex and (or) dimer, which only slightly reduces the deshielding effect of the carboxyl group. On the other hand, the proton signals at 2 C in the spectrum of AG are shifted to a downfield compared to AA; This may probably be due to a change in the AG conformation in solution compared to AA, and the proton at 2C will move from the positive region of the anisotropy cone of the C=O group to the negative region.

Table 14

Spectral characteristics of acrylate derivatives a,b.

Compound

Solvent

Notes: a Main abbreviations: d - the value of the chemical shift of the corresponding protons, in ppm; n is the number of lines in a signal of a given type of protons; J ij - constants of the spin-spin interaction of the corresponding protons, in Hz. b The number of protons according to the integral intensities is consistent with the proposed structure: 1H for all protons of the vinyl system and 6H for the guanidine counterion (manifested as a broadened singlet).

The 1H NMR spectra of methacrylic acid and its guanidine salt MAG belong to the ABX type 3, the characteristics of the signals are summarized in Table 1. fifteen; in all cases, no complete signal splitting was observed; there was a degenerate ABX type 3 spectra.

Table 15

Spectral characteristics of methacrylate derivatives a, b.

Compound

Solvent

Notes: a Main abbreviations: d - the value of the chemical shift of the corresponding protons, in ppm; n is the number of lines in a signal of a given type of protons; J ij - constants of the spin-spin interaction of the corresponding protons, in Hz. b The number of protons according to the integral intensities is consistent with the proposed structure: 1 H for methylene protons, 3 H for methyl protons, and 6 H for the guanidine counterion (manifested as a broadened singlet).

Figure 14. 1H NMR spectrum of methacrylate guanidine in D2 O

Figure 15. 1H NMR spectrum of methacrylate guanidine in DMSO-d6

Note that in all cases no complete signal splitting was observed; there was a degenerate ABX type 3 spectra. This may be due to the strong influence of the COOX group (especially in the case of MAH).

The 1H NMR spectra of the new copolymers of AG and MAG with AAm are characterized by broadened, unresolved (usual for polymer structures) signals of CH 2 and CH groups of the chain and side CH 3 groups in the case of MAG. In the case of AG, due to the proximity of the chemical shifts of protons CH 2 -CH \u003d in both comonomers, it is not possible to separate their contribution by comonomers (Fig. 16,17).

Figure 16. 1H NMR spectrum of AG-AAm copolymer (80:20) in D2O

Figure 17. 1H NMR spectrum of AG-AAm copolymer (40:60) in D2O

In copolymers enriched in acrylamide comonomer, the signals of MAG units are shifted to a weaker field. In copolymers enriched in MAG comonomer, the signals of AA units are shifted to a stronger field. This can be explained by the formation of intra- and intermolecular hydrogen bonds between the side groups of the amide and guanidine counterions. This enhances the deshielding for the MAG links and the shielding for the AA links.

Table 16

Spectral characteristics of copolymers AA (M 1) - MAG (M 2) and the corresponding homopolymers (PAAM and PMAG), measured in D 2 O (in ppm).

Compound	Initial composition
		1,58; 1,73; 1,85
		1,57; 1,73; 1,85
		1,57; 1,73; 1,85

The composition of the copolymers was calculated using the integral intensity of the signal of the methyl group of the MAG comonomer (Figs. 18, 19), which manifests itself in the strongest field and is not overlapped by any other signals according to the method indicated above.

Rice. 18. 1H NMR spectrum of MAG-AA copolymer (10:90) in D2O

Rice. 19. 1H NMR spectrum of MAG-AA copolymer (70:30) in D2O

The 1H NMR spectra of the AG and MAG copolymers with guanidine monomaleate (Figs. 20, 21) indicate the enrichment of the AG and MAG copolymers.

Rice. 20. 1H NMR spectrum of the AG-MMG copolymer (70:30) in D2O

Rice. 21. 1H NMR spectrum of MAG-MMG copolymer (70:30) in D2O

3.3.3 Thermal properties of synthesized copolymers

The resistance of compounds, including polymeric compounds, to various temperatures is an important characteristic of substances that are supposed to be used in various compositions.

To study the thermophysical properties of the synthesized products and initial reagents, we used a hardware-software complex with a software package designed for quantitative processing of derivatograms (curves G, TG, DTG, DTA), developed at the Institute of Chemistry of Solutions, Russian Academy of Sciences (Ivanovo) for measuring and recording output signals from the sensors of the 1000D derivatograph (MOM, Hungary).

On fig. 22 shows the TG curves of the copolymer AA with MAG 50:50 in air. The weight loss of the copolymer is observed at a temperature of 150 C; apparently, this is due to the loss of water and the removal of volatile impurities. A decrease in mass by 10% is observed at a temperature of 150 °C. The rate of thermal and thermal-oxidative decomposition of the copolymer noticeably increases at a temperature of 210 C. Above this temperature, two stages of decomposition can be noted: 250-300 C and 300-390 C; endothermic effect at a temperature of 390 C, which at 520 ºC turns into an exothermic effect, reflecting the thermal-oxidative degradation of the polymer. Above 600 ºC, the coke mass is removed and 8% of the solid residue remains. The total weight loss is 80%.

Fig.22. Dependence of weight loss on temperature of copolymer AA-MAG (50:50)

Rice. 23. DTA(a) and DTG (b) curves of the AA-MAG copolymer (50:50)

Consider the thermal stability of a copolymer with a high content of guanidine methacrylate MAG-AA (90:10)

As can be seen from the TG curve, the mass loss associated with the removal of water and volatile impurities from the sample is observed in the temperature range from 150 to 240 °C, while the mass loss is up to 15%. Then there is a rapid decrease in mass to a temperature of 570 ºC. In this area, decomposition of guanidine residues occurs, as a result, further decomposition proceeds with the formation of volatile products, which leads to foaming of the samples under study. At this temperature, an exothermic effect is observed on the DTA curve, indicating complete thermal oxidation of the polymer. After removing the coke mass, 20% of the solid residue remains.

Rice. 24. Dependence of weight loss on temperature of copolymer AA-MAG (90:10)

When analyzing the TG curves, it was revealed that the mass of the solid residue is higher in samples with a high MAG content.

According to DSC data, it turned out that in the samples of homo- and copolymers taken for research, water is about 20%, i.e. such a characteristic of the thermal stability of compounds as a loss of 10% of the mass requires correction of the DTA data for polymeric compounds. It should be noted that water in copolymers is bound more strongly than in PMAG: in a DSC study, heating PMAG samples to a temperature of 150 C followed by cooling and reheating showed that water was completely removed from this compound, which was not achieved for copolymers.

The samples of copolymers containing a larger amount of acrylamide turned out to be the most stable. For example, a 30% weight loss for the AA-MAG copolymer (90:10) is observed at 300 C, and for a 30:70 copolymer - at 280 C. This is probably due to the more complex structure of copolymers with a high content of guanidine methacrylate. According to the work, during the thermal oxidation of urea derivatives, including guanidine, hydrogen, carbon monoxide, carbon dioxide, and methane can be released.

Rice. 25. DTA(a) and DTG(b) curves of the AA-MAG copolymer (10:90)

Taking into account the possible thermolysis of guanidine with the formation of carbamide, the overall reaction of thermal destruction of the guanidine residue can be simplified as follows:

72СО (NH 2) 2 > 45NH 3 + 15CO + 15H 2 O + 5N 2 + 4CO 2 + 17(NH 2) 2 (CO) 2 NH + 19NH 2 CN

Acrylamide copolymers proved to be more thermally stable than polyacrylamide. Polyacrylamide is thermally stable up to 130 C, and a loss of 30% of the mass is already observed at a temperature of 170 C. At higher temperatures, the destruction of the polymer begins, which, as you know, is accompanied by the release of ammonia, the formation of imide groups, and the appearance of intra- and intermolecular bonds of the type:

Thus, when comparing the thermal stability of polymer products, it can be noted that copolymers turned out to be more stable in the entire temperature range in comparison with homopolymers.

The data of thermophysical studies of the synthesized AG and MAG copolymers with MMG are summarized in Table 1. 17 and 18.

Table 17

Thermophysical properties of initial monomers and copolymers MAG-MMG

copolymers	DTA curve, T pl	curve. DTG the interval is expanded.	Mind-e masses	Mind-e masses	Mind-e masses

Table 18

Thermophysical properties of initial monomers and copolymers AG - MMG

	curve DTA T pl	DTG curve the interval is expanded.	Weight reduction	Weight reduction	Weight reduction

Thus, the study of the thermal stability of copolymers showed that their thermal properties depend on the composition and are much higher than the thermal characteristics of the initial comonomers and homopolymers.

3.4. Study of bactericidal and toxicological properties of new copolymers of acrylate- and methacrylate-guanidine

At the moment, it is difficult to find a group of materials on which microorganisms do not have a destructive effect. The vital activity of various pathogenic microbes causes not only undesirable changes in the structural and functional characteristics of materials and products, but they also realize their destructive effect inside the living cells of the body. In this regard, the development of new biocidal preparations is undoubtedly an urgent task.

Considering that the intrinsic physiological activity of polymers is usually understood as an activity that is associated with the polymer state and is not characteristic of low molecular weight analogs or monomers, the mechanisms for the manifestation of intrinsic physiological activity can include, as an important component, physical effects associated with a large mass, osmotic pressure, conformational rearrangements and others, and can also be associated with intermolecular interactions and with biopolymers of the body. Many body biopolymers are polyanions (proteins, nucleic acids, a number of polysaccharides), and biomembranes also have a net negative charge. Interactions between oppositely charged polyelectrolytes proceed cooperatively, and the resulting polycomplexes are sufficiently strong. It is known that the charge density and molecular weight are of the greatest importance in such interactions. If we talk about biocidal properties, then an important role in this case is played by knowledge of the mechanism of action.

The sequence of elementary acts of the lethal action of polyelectrolytes on bacterial cells can be represented as follows:

1) adsorption of a polycation on the surface of a bacterial cell;

2) diffusion through the cell wall;

3) binding to the cytoplasmic membrane;

4) destruction or destabilization of the cytoplasmic membrane;

5) isolation of cytoplasmic components from the cell;

6) cell death.

First of all, this concerns polycations, since biomembranes have a negative total charge, although cell membranes that are negatively charged in general have isolated polycation regions on which polyanions can be sorbed.

All of the above indicates the prospects and the fundamental possibility of using the guanidine-containing polymer substances synthesized by us as biocidal preparations. Note that these polymers meet a number of requirements that apply to modern drugs of this kind: good solubility in water and physiological saline (1% polymer solutions have pH = 6.5-7.0); the solutions are colorless, odorless, do not cause destruction of the treated materials, and the polymeric nature of these compounds contributes to the absence of inhalation toxicity and the formation of a long-lasting polymer film on the treated surfaces, providing a prolonged biocidal effect.

As is known, the radical copolymerization of acrylamide with vinyl monomers is used to obtain copolymers that have better consumer properties compared to polyacrylamide, which is an industrial flocculant and is used in various industries.

It was assumed that AA copolymers containing guanidine groups would have not only flocculating but also biocidal properties.

Biocidal activity was determined by the methods of counting grown colonies after water treatment with flocculants and by the diffusion method in a cup (see experimental part).

As a result of the research, it was found that the obtained copolymers have significant biocidal activity against Escherichia coli, while the biocidal activity increases with an increase in the content of the guanidine fragment.

Table 19

*Note. 1-polyacrylamide, 2-copolymer AA:MAG (70:30),

3-copolymer AA:AG (80:20), copolymer AA:MAG (90:10).

Table 20

As can be seen from the obtained results, the synthesized guanidine-containing copolymers exhibit bactericidal activity against the studied cell structures, and the most pronounced biocidal activity is observed in copolymers with a high content of guanidine groups.

Biocidal activity of copolymers against Staphylococcus aureus and pathogenic fungal microflora Candida albicans was also studied at the bacteriological station of the SSES KBR.

It was revealed that copolymers AA-MAG (70:30), (50:50), (10:90) have the highest biocidal activity against Staphylococcus aureus. It can be seen that the biocidal activity depends on the amount of MAG in the macromolecular chain. In relation to Candida albicans, the samples AA-MAG (10:90) and AA-AG (20:80) turned out to be the most active. AA-MAG (10:90).

One of the important indicators for the use of a reagent as a flocculant is its toxicological characteristics, since polymers that do not affect humans, animals, fauna and flora of water bodies can be used for water purification.

Bioassay methods for cladocerans occupy a leading position in the system of environmental monitoring of natural waters, and the bioassay for daphnia Daphnia magma Strauss is the most standardized of all known. When biotesting natural waters on zooplankton, behavioral reactions, pathological disorders, metabolic (biochemical) indicators, physiological functions, body color, food grazing rate, etc. are recorded, but the test reaction is considered the most sensitive and reliable, in which reproduction processes are recorded - survival and fertility.

To determine the toxicity of a number of homo- and copolymers, a method for determining the toxicity of water using Daphnia magma Strauss was used. Daphnia in the amount of 20 pieces were planted in Petri dishes with the studied samples. The control was carried out visually and using a binocular, controlling the number of surviving daphnia, and changes in the movement and reproduction of crustaceans were taken into account. In parallel, a control experiment was set up with natural water. Observations were carried out for 96 hours; daphnia were not fed during the experiment. At the end of the experiment, surviving daphnia were counted; daphnia are considered to be survivors if they move freely or float up from the bottom.

The toxicity coefficient in % was calculated by the formula:

where, X 1 and X 2 are the arithmetic mean number of surviving daphnia in control and experiment.

A water sample was assessed as having acute toxicity if 50% or more of Daphnia died in it during 96 hours of biotesting compared to the control.

The toxicological characteristics of the copolymers were studied depending on the composition and concentration at a constant temperature. The corresponding homopolymers, polyacrylamide and guanidine polymethacrylate, were taken as model samples.

Solutions of homopolymers and copolymers without dilution have a depressing effect on the entire process of reproduction of Daphnia (Fig. 26), delay growth, the onset of puberty and the appearance of the first litter, reduce the number of litters and fertility, and increase the release of juveniles and eggs. When diluted in a ratio of 1:2, the toxicity of the copolymers is reduced. The least toxic solutions are copolymer solutions with a concentration of 0.1 to 0.01%. The toxicity of the samples also depends on the composition of the copolymers; with an increase in the content of guanidine methacrylate, toxicity decreases.

Analysis of experimental data on the study of the toxicity of copolymers shows that solutions of copolymers MAG:AA (20:80) and MAG:AA (30:70) with a concentration of 0.1% and 0.01% practically do not affect the fertility of Daphnia, but 15 % shorten the life span. It should be noted that the PMAG homopolymer reduces the fecundity and life span of the studied daphnia by only 7%, and polyacrylamide by 30%. It was found that the toxicity of polyacrylamide is higher than that of copolymers; even a small content of guanidine methacrylate in the copolymers already reduces the toxicity of the polyacrylamide flocculant.

Rice. 26. Dependence of the toxicity coefficient of homo- and copolymers on the composition and concentration.

As is known, the results of biotesting depend on the sensitivity of test organisms. Therefore, in addition to D. magna, for the toxicological assessment of aqueous solutions of polymeric flocculants, larvae of mosquitoes - Chironomus dorsalis bells were also used. The results of the analysis showed that the least toxic under the studied conditions are the copolymers AA with MAG compared to PAA, and the least toxic sample for these test cultures was the copolymer AA:MAG (70:30), in the solution of which the transition of larvae to pupae was observed, and then transformation into an imago. A study of the toxicity of AA with AG showed that these copolymers have even lower toxicity compared to MAG, which is in good agreement with the literature data on the lower toxicity of acrylic acid compared to methacrylic acid.

Taking into account the data obtained, it is possible to vary the composition of copolymers to achieve the maximum effect of the biocidal action with minimal manifestations of toxicity. The presence of chemically active guanidine groups in the structure of the synthesized copolymers opens up the possibility of implementing macromolecular design on their basis, which will expand the areas of practical application of the studied copolymers.

Table 21

Data on biocide and toxicity of AG and MAG copolymers with MMG and a number of model polymers a

	Compound	(original composition)				candida albicans

Notes. Escherichia coli - Escherichia coli, a representative of the gram-negative bacterium and Stophil. Aureus 906 - Staphylococcus aureus, a representative of a gram-positive bacterium; (+++) - continuous lysis of the bacterial cell, completely retards the growth of this strain, (--+) - - partial cell lysis, growth inhibition zones are observed after 48 hours (--+) - partial cell lysis, growth inhibition zones are observed after 72 hours, (---) - inactive. e Minimum inhibitory concentration in wt%.

Copolymers of AG and MAG with MMG are not active against the studied microorganisms, but have a high fungicidal activity against the pathogenic fungal microflora Candida albicans, it is noteworthy that the corresponding homopolymers exhibit bactericidal activity, but do not possess fungicidal activity. Thus, the greatest antifungal effect was obtained for samples of copolymers MAG with MMG with the initial composition of comonomers 50:50 and 70:30.

Thus, the combination of high antifungal activity (due to the content of guanidine groups) in the obtained copolymers with an increased ability to bind to bacterial cells due to guanidine units allowed us to synthesize new effective guanidine-containing biocidal polymers.

3.5 Investigation of the flocculating properties of newacrylamide copolymers

One of the most widely used methods for reducing the amount of suspended matter is sedimentation under the influence of particle gravity. Since the particles of suspension, which cause the turbidity of natural waters, are small in size, their sedimentation is extremely slow; in addition, the presence of colloidal impurities further complicates the sedimentation process.

To intensify the sedimentation process and increase its efficiency, water treatment with coagulants is used. Despite the high efficiency, the water purification technology based on the use of coagulants has a number of disadvantages. The most important of them is the low strength of the flakes formed during coagulation, which does not allow working at high water flow rates and leads to the removal of contaminants from the filter media. When using high-molecular flocculants, the main disadvantages of coagulation are eliminated, the strength of flakes increases and the process of their formation is accelerated. This makes it possible to increase the efficiency of water clarification: to reduce settling time, to increase the productivity of clarifiers with suspended sediment, to increase the dirt capacity of filters and contact clarifiers.

Currently, acrylamide copolymers are the most common flocculants. In this regard, the synthesis and study of the flocculating properties of new acrylamide copolymers is undoubtedly an urgent task.

Typically, determining the effectiveness of flocculants in relation to a particular type of water pollutants consists in determining the concentration of these substances in water before and after treatment with flocculants.

To assess the flocculating activity of polyelectrolytes, it is necessary to use model systems. Water suspensions of kaolin, ocher and bentonite are most often used as models. Moreover, it is on suspensions of kaolin that the regularities of the flocculating action of a large number of cationic polyelectrolytes are described. It is also noted in the literature that at a kaolin concentration of ~ 0.8% and below, suspension particles are able to settle in a free mode, and under these conditions, the experimental results can be used to study the patterns of flocculation.

Since the flocculating ability is affected by the magnitude of the charge of the macromolecule, copolymers with different degrees of content of guanidine methacrylate units in the macromolecular chain were chosen for the study. Polyacrylamide was used as an object of comparison. The flocculating activity was investigated both in the presence and absence of coagulants. Organo-modified clay from the Gerpegezh deposit was used as a coagulant.

On fig. 27. shows the effect of the concentration of flocculants of different composition on the flocculating effect (F), which was calculated by the formula (11)

F \u003d (n 0 - n) / n, (11)

where n 0 and n are, respectively, the optical density of water (determined by the turbidimetric method) in the absence and presence of a flocculant (and a coagulant).

Fig.27. Dependence of the flocculating effect F on the concentration and composition of 1-PAA copolymers; 2-AG-AA (20:80); 3-AG-AA (40:60); 4- MAG-AA (20:80); 5- MAG-AA (40:60); 6- MAG-AA (30:70)

Experiments carried out on one batch of natural water (turbidity 4.2 mg l-1, color 48.5 degrees) showed an increase in the flocculating effect with an increase in the concentration of the copolymer for all flocculants. This is a consequence of an increase in the concentration of macromolecular bridges formed during the adsorption of macromolecules on the surface of particles of the dispersed phase, which formed large aggregates of particles of the dispersed phase and macromolecules and reduced the stability of the system.

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Dependence of changes in thermodynamic quantities on temperature. Method of Sato, Chermen Van Crevelen, Andren-Bair-Watson. Radical copolymerization reaction. Determination of the half-life temperature of polyisoprene. Thermodynamic analysis of the main reaction.

term paper, added 05/28/2012


Characterization, steps and necessary conditions for network formation in three-dimensional homo- or copolymerization of bifunctional monomers. The chemical structure of the soluble copolymer and the content of microgel in it. The essence of the Lange method and its application.

article, added 02/22/2010


Pulsed electromagnetic radiation arising from the loading of composites. Infrared spectroscopy study of polymerization and copolymerization processes in polymer compositions for organic glasses. Dependence of the content of the gel fraction.

summary, added 04/05/2009


Study of the main reactions that determine the formation of the molecular chain of polyisoprene, and their quantitative assessment. Participation of monomer molecules and unsaturated fragments of polyisoprene in determining the concentration of active sites during polymerization.

abstract, added 03/18/2010


Main types of copolymers. Reactions in the polymer-monomer system. Radical polymerization (one-stage, two-stage method). Ionic polymerization, mechanochemical synthesis. Reactions in the polymer-polymer system. Introduction of functional groups into macromolecules.

abstract, added 06/06/2011


Lewis's electronic theory of acids and bases. Arrhenius' theory of electrolytic dissociation. Proton theory, or Bronsted's theory of acids and bases. Basicity and amphotericity of organic compounds. Classification of reagents for organic reactions.

presentation, added 12/10/2012


Dissociation of acids into a hydrogen cation (proton) and an anion of an acid residue in aqueous solutions. Classification of acids according to various criteria. Characterization of the basic chemical properties of acids. Distribution of organic and inorganic acids.

Abstract - Connection of details. Couplings (Abstract)

Grandberg I.I. Organic Chemistry (Document)

Oxygenated Halogen Compounds (Document)

Test in chemistry option 1 (Document)

n1.docx

6.2. Radical copolymerization
6.2.1. Copolymerization rate
Changing the composition of the monomer mixture, as a rule, leads to a noticeable and sometimes dramatic change in the rate and degree of polymerization. This is due to a change in the effective values ​​of the constants of all elementary reactions, and sometimes with the measurement technique.

Measurement of copolymerization rate by dilatometry. As a rule, the rate of copolymerization at the initial stage is measured by dilatometry. The contraction coefficient K in this case is usually calculated based on a linear relationship:

Where K 11 and K 22 - contraction coefficients corresponding to the homopolymerization of monomers M 1 and M 2 ; F 1 and F 2 - mole fractions of monomer units in the copolymer.

However, in many cases the linear relationship is not true. Therefore, to calculate the contraction coefficient, an equation was proposed that takes into account the reaction of cross-growth:

where K 12 is the contraction coefficient corresponding to the formation of an alternating copolymer; b 11 , b 22 and b 12 - the relative amounts of different chemical bonds of the main chain.

Initiation rate. In copolymerization, in contrast to polymerization, the rate of initiation is determined not only by the nature and concentration of the initiator, but often also by the composition of the monomer mixture. In the case of azo compounds, such as azobisisobutyronitrile, it is usually assumed that the rate of initiation is either constant or linearly dependent on the composition of the monomer mixture. It is known that the rate constant of the decomposition of azobisisobutyronitrile depends on the nature of the solvent. In the case of mixed solvents, which include a mixture of monomers, the rate constant for the decomposition of azobisisobutyronitrile can be calculated from the formula:

where? i is the volume fraction of the solvent, k dist, i is the rate constant of the decomposition of azobisisobutyronitrile in this solvent. Deviations of the dependence of the initiation rate on the composition of the monomer mixture from linear are rare and, as a rule, insignificant. Significant deviations were found during the copolymerization of acrylonitrile with methyl methacrylate in a solution of dimethylformamide.

In contrast to azo compounds, the linear dependence of the rate of copolymerization initiation on the composition of the monomer mixture in the case of peroxides is rather an exception. Possible reasons for such deviations are associated with the donor-acceptor interaction of the components of the reaction mixture. It has been shown that during the copolymerization of styrene with methyl methacrylate and acrylonitrile initiated by benzoyl peroxide, monomers have a significant effect on the rate of decomposition of the latter as a result of the formation of donor-acceptor complexes:
PB... AN (MMA), PB... AN (MMA)... St
(PB - benzoyl peroxide, AN - acrylonitrile, MMA - methyl methacrylate, St - styrene).
Table 6.3 Values ​​of the initiation rate constants for the styrene-acrylonitrile system, [PB], [AIBN] = 0.001 mol/mol of the mixture, - AN - mole fraction of acrylonitrilein a monomer mixture

ѓ AN mol. shares	k in 10 -5, s -1 at T, ° С
	60	75	75 (AIBN)	85
0,0	1,23	5,29	2,02	18,80
0,1	1,27	5,34	1,92	22,18
0,2	1,27	5,40	1,94	22,92
0,4	1,45	6,50	2,09	25,81
0,5	1,66	6,67	2,11	27,92
0,7	1,94	8,90	2,28	38,31
0,8	2,08	11,60	2,45	40,32
0,9	2,20	-	3,00	63,85

The presence of these complexes was proved by UV, IR, NMR spectroscopy. The effects of complex formation are most pronounced in the styrene-acrylonitrile system. In table. Table 6.3 shows the data reflecting the influence of the composition of the monomer mixture on the values ​​of the rate constants of initiation of this reaction during the copolymerization of styrene with acrylonitrile initiated by benzoyl peroxide (PB) and 2,2"-azobis(isobutyronitrile) (AIBN).

Formal-kinetic description of copolymerization. Chemical model of chain termination. The non-empirical radical copolymerization rate equation was first proposed by Melville and Walling, who proceeded from the Mayo-Lewis copolymerization model. This model considers four growth reactions (equations (6.1)) and three chain termination reactions:

The copolymerization rate equation has the form:

where [M 1 ] and [M 2 ] are the molar concentrations of the monomers M 1 and M 2 in the monomer mixture;

Options? 1 and? 2 can easily be found from experiments on homopolymerization, the value of the parameter? cannot be established in independent experiments. Usually? are found by comparing the experimental dependence of the copolymerization rate on the composition of the monomer mixture with the theoretical one. So, in the case of copolymerization of styrene with methyl methacrylate, the experimental curve coincides with the theoretical one at? = 13 (Fig. 6.4).


Equation (6.77) has found wide application, as a result of which extensive factual material has been accumulated on the value of ?. Analysis of these data showed that almost always? > 1, moreover, for a number of systems there is a correlation? ~ 1/r 1 r 2 (Table 6.4).

This correlation has been explained in terms of a chemical model of the chain termination reaction in copolymerization, taking into account the polar reactivity factor.

In the above method for finding the value of ?, which can be characterized as a fitted curve method, it is assumed that? = const, i.e. does not depend on the composition of the monomer mixture.
Table 6.4Correlation between? andr 1 · r 2 with radical copolymerization

Monomers	r1	r2	r 1 r 2	?
?-Chlorostyrene - methyl acrylate	1,21	0,14	0,16	147
Styrene - 3,3,3-trichloropropene	7,80	0,017	0,13	63
Styrene - butyl acrylate	0,75	0,15	0,114	35
Styrene - isobutyl methacrylate	0,55	0,40	0,22	21
Methyl Methacrylate - Acrylonitrile	1,20	0,15	0,18	14
Styrene - methyl methacrylate	0,52	0,46	0,23	13
Styrene - methacrylonitrile	0,30	0,16	0,048	6,7
Acrylonitrile - methyl acrylate	0,67	1,26	0,84	2,3
Methyl methacrylate - butyl methacrylate	0,79	1,27	1,0	1,1

Actually it is not. If you calculate the value? separately for each monomer mixture according to the copolymerization rates (equation (6.77)), then, as a rule, a significant dependence is found? from composition. Until now, this dependence has not received an exhaustive explanation, however, the very fact of its existence indicates that the parameter? does not have a complete physical justification and should be considered as corrective. For this reason, the Melville and Walling equation, based on the chemical chain termination model, is rarely used today.

Diffusion model of chain termination. In the 60s. 20th century North proposed a diffusion model of chain termination in radical polymerization. According to this model, the termination reaction rate is limited by chain segmental mobility, which is inversely proportional to the viscosity of the solvent. This dependence was used to experimentally test the diffusion theory of chain termination. Indeed, it turned out that in many cases (but not always) the initial polymerization rate decreases with increasing solvent viscosity. During the polymerization of methyl methacrylate and vinyl acetate, as well as during their copolymerization, the initial rate depends on the viscosity of the reaction mixtures. Data of this kind indicate that the model of diffusion chain termination is applicable to both radical polymerization and copolymerization.

The copolymerization rate equation, taking into account the diffusion mechanism, was first derived by Atherton and North:

This equation includes an effective chain termination rate constant, k o , which is believed to be the same for all three chain termination reactions. Since the mobility of the chain is determined by its composition, it is initially assumed that the value of kо depends on the composition of the copolymer, the simplest form of such a dependence is:

Equations (6.78) and (6.79) made it possible to qualitatively correctly describe the dependence of the rate of copolymerization of methyl methacrylate with vinyl acetate on the composition of the monomer mixture, however, complete quantitative agreement between the theoretical and experimental curves was not achieved. Later, other equations were proposed relating the termination rate constants in copolymerization and homopolymerization. Direct determination of kо in ​​copolymerization and comparison of the experimental and theoretical dependences of the chain termination rate constant on the composition of the monomer mixture showed that the best agreement is observed when using the equations:


where q 1 and q 2 are the proportions of growth radicals ending in m 1 and m 2 units.

The next stage in the development of the theory of the rate of copolymerization is associated with the spread of the technique of pulsed laser polymerization. If this method or another (for example, the rotating sector method) determines the rate constant of chain growth during copolymerization, then the rate of the latter can be expressed by a simple equation of the law of mass action:

where is the “average” chain growth rate constant; - total concentration of growth radicals; [M] - total concentration of monomers. The value is naturally related to the composition of the monomer mixture, the relative activities of the monomers, and the constants of the elementary chain propagation reactions. This relationship can be established based on different models of copolymerization. Based on the end link model, i.e. Mayo-Lewis model, obtained:


However, experimental verification of this equation by the method of pulsed laser polymerization showed its inconsistency in many cases, in particular, in the copolymerization of styrene with methyl methacrylate (Fig. 6.5).

As a result, a hypothesis was put forward about the influence of the nature of the near-terminal link on the rate of radical copolymerization. To quantitatively characterize this effect, in addition to the four copolymerization constants - the relative activities of monomers in the model of the near-terminal link - two new ones were introduced - the relative activities of radicals:

where k 211 , k 111 , k 122 , k 222 are the rate constants of elementary reactions (6.55).

The relative activities of the s 1 and s 2 radicals show how many times the rates of growth reactions of radicals with different near-terminal units differ. Taking into account the effect of the pre-terminal link leads to a more complex expression for the average rate constant of the chain propagation reaction during copolymerization:




where


From the given values ​​of s 1 and s 2 in the caption to Fig. It follows from Table 6.5 that the nature of the pre-terminal link can change the macroradical growth rate constant by several times. The effect of the pre-terminal link, which affects only the growth reaction rate, but not the composition of the copolymer, is called implicit. Both effects - implicit and explicit (influencing the composition of the copolymer) - have a common nature, which will be discussed in the next section.

The radical copolymerization of active monomers with inactive ones is very specific. The former include monomers with?-?-conjugation between the double bond and the substituent, and the latter include all the rest. During the copolymerization of such monomers, the copolymer is excessively enriched in the active monomer, small additions of the latter inhibit the copolymerization. As an example, in fig. 6.6 shows the form of the speed dependence


Table 6.5Relative activities of monomers in the copolymerization of styrene (1)with acrylonitrile (2), defined within the end-of-line modelsand pre-terminal link, 60°С

Wednesday	r1	r2	r 1 1	r 2 1	r 1 2	r 2 2
in mass	0,394	0,063	0,232	0,566	0,087	0,036
in toluene	0,423	0,118	0,242	0,566	0,109	0,105
In acetonitrile	0,485	0,081	0,322	0,621	0,105	0,052

copolymerization of styrene with vinyl acetate from the composition of the monomer mixture. Small additions of the active monomer - styrene (about 0.1%) - reduce the rate of polymerization of vinyl acetate by two orders of magnitude. The reason is the low reactivity of the styrene radical stabilized by conjugation of the sp 2 terminal carbon atom with the aromatic ring. This mechanism will be discussed in more detail below.
6.2.2. The nature of the preterminal link effect
The pre-terminal link model was proposed by Merz, Alfrey, and Goldfinger in 1946, and Equation (6.50) was first obtained by them. For a long time, this model was used in the copolymerization of monomers, one of which is not capable of homopolymerization. As a result, a simplified composition equation containing only two constants (6.51) could be used to calculate the relative activities. This equation was first applied to the copolymerization of styrene (1) with fumaronitrile (2). Since the latter is not capable of homopolymerization, then r 2 = r 12 = 0. It was found r 1 = 0.072 and r 21 = 1.0, which indicates a very strong effect of the pre-terminal link. Equation (6.51) with the above values ​​of the relative activities satisfactorily described the experimental data on the composition of the copolymer.

At present, there is an opinion that the limits of application of the pre-terminal model of copolymerization in that part of it that describes the composition of the copolymer is much wider than previously thought. It is believed, in particular, that the model is widely applicable to the copolymerization of vinyl monomers. In table. 6.5 presents well-known data on the copolymerization constants of styrene with acrylonitrile, determined in accordance with the models of the terminal and pre-terminal link. These data almost unambiguously indicate that the copolymerization proceeds in accordance with the latter model. First, the experimental data on the triadic composition of the copolymer (NMR) coincide with the theoretically calculated data only based on the model of the near-terminal unit. Second, the data characterizing the effect of the near-terminal unit are in quantitative agreement with the data of experiments on the addition of monomers to low-molecular-weight radicals, which model the last two units of the propagating radical.

At present, the nature of the explicit and implicit effects of the pre-terminal link is associated with two components - steric and electronic. Below are schemes of the transition state of the growth reaction during radical (co)polymerization, where only one substituent of the pre-terminal unit X is isolated:


Theoretical calculations show that the values ​​of the pre-exponential factor depend mainly on the freedom of rotation around the formed bond vi, the terminal bond V 2 and vibrations of the transition complex as a whole v 3 (a). It turned out that during rotation around the terminal bond, a significant deceleration potential arises at the ecliptic (against each other) position of the X substituent of the pre-terminal unit and the CH 2 group of the adding monomer. As a result, the value of the pre-exponential factor is halved even at X = CH 3 .

The electronic component of the pre-terminal unit is explained by its effect on the polarity and resonant stabilization of the terminal radical. However, both effects should be rather weak, since they are transmitted through several ?-bonds.
6.2.3. Effect of Temperature and Pressure on Radical Copolymerization
The effect of temperature on the rate and degree of copolymerization is similar to that of homopolymerization (Section 5.1.4). Exceptions may be associated with copolymerization complicated by depolymerization. The influence of temperature on the composition of the copolymer can be established based on the Arrhenius equation, the application of which to relative activities leads to the following dependencies:


For monomers of similar structure, for example, vinyl, the frequency factors differ little: in the first approximation, we can assume that = A 11 / A 12 = A 22 / A 21 = 1. Then


Table 6.6 Relative activities of monomers at different temperatures and ratios of frequency factors

Monomers	r1, r2		A 11 / A 12 , A 22 / A 21
	60°C	131°C
Styrene Methyl methacrylate	0,520	0,590	1,06
Styrene methyl acrylate	0,747	0,825	1,31
Styrene diethylmaleate	6,52	5,48	2,55
Styrene diethyl fumarate	0,301 0,0697	0,400 0,0905	1,50
Styrene N-chlorostyrene	0,742	0,816	1,27
Styrene Trans-stilbene	5.17 (70°C)	7.23 (140°C)	34,34

whence it follows that with increasing temperature r 1 ? 1,r2? 1 regardless of the initial values ​​of the relative activities. In other words, as the temperature increases, the selectivity of the addition of monomers to radicals decreases. However, this effect is small, since the difference in the activation energies of chain growth (E 11 - E 12) and (E 22 - E 21) is small. In table. 6.6 shows the values ​​of the relative activities of the monomers at different temperatures, from which it can be seen that the theoretical ideas for monomers of the same type are justified.

Deviations are observed during the copolymerization of monomers with a different structure, for example, during the copolymerization of styrene with diethyl maleate (1,2-disubstituted monomer) and trans-stilbene (bifunctional monomer CH 2 =CH-C 6 H 4 -CH=CH 2).

The effect of pressure on the rate and degree of copolymerization is qualitatively similar to that described above for homopolymerization. The effect of pressure on relative activities can be predicted from Equation (5.51). Applying it to the product of relative activities, we get:

under the assumption that = , where and is the change in volume during the formation of a transition complex from the initial monomer and radical in cross-growth reactions, i.e. activation volumes of these reactions. From sec. 5.1.4 it follows that
An increase in pressure always leads to an increase in the product r 1 ·r 2 as a result of an increase in the values ​​of both copolymerization constants r 1 and r 2 .
Table 6.7The effect of pressure on the copolymerization of some monomers

M 1	M 2	p 10 -5, Pa	r1	r2	r 1 r 2
Styrene	methyl acrylate	1,0 3039,8	0,704	0,159	0,112
Styrene	Acrylonitrile	1,0 1013,2	0,07	0,37	0,03
Acrylonitrile	Methyl methacrylate	1,0 1013,2	1,34	0,12	0,16
Styrene	diethyl fumarate	1,0 1013,2	0,26	0,06	0,02
Styrene	cis-1,2-dichloroethylene	1,0 1013,2	195	0,00	0,00

Thus, pressure leads to a decrease in the selectivity of the addition of monomers to radicals. It is necessary to pay attention to the fact that the values ​​of the copolymerization constants of sterically hindered monomers, which include 1,2-di- and more substituted ethylene, equal to or close to zero at atmospheric pressure, become different from zero and (or) increase at high pressure (see Table 6.7).
6.2.4. Alternating copolymerization
During the copolymerization of electron-withdrawing (A) and electron-donating (D) monomers, copolymers with regular or close to regular alternation of monomer units are quite often formed.

The electron-donating monomers include monomers with a developed system of ?-?-conjugation, monomers with substituents that increase the electron density on the double bond, as well as olefins. They are divided into the following groups:

1. Ethylene and monomers with?-?-conjugation -?-olefins, cycloalkenes, vinylcycloalkanes, allyl monomers.

2. Monomers with?-p-conjugation - vinyl ethers, vinyl sulfides, N-vinylamines, N-vinylamides, vinyl halides.

3. Monomers with?-?-conjugation - vinylaromatic monomers, trans-stilbene, phenanthrene, acenaphthylene, indene, vinylpyridines, phenylacetylene, etc.

4. Monomers with?-p-?-conjugation - vinyl ethers, N-vinylcarbazole, N-vinylpyrrolidone, N-vinylsuccinimide, N-vinylphthalimide.

Electron-withdrawing monomers have substituents that draw electron density from the double bond:

1. Anhydrides and imides of unsaturated dicarboxylic acids (maleic, itaconic, etc.) and their derivatives.

2. Mono- and dicarboxylic unsaturated acids, their esters, amides, nitriles.

3. Tetrahalogen substituted ethylene.

4. SO 2 belongs to the strongest electron acceptors of radical copolymerization.

The alternating copolymerization of monomers belonging to different classes is a consequence of the formation of charge transfer complexes (CTCs), also called donor-acceptor (DA) complexes, between them or between a monomer of one class and a propagating radical of another. According to Mulliken's theory, the CTC wave function can be represented by a superposition of the wave functions of two limiting structures - without transfer and with full transfer of an electron, the latter being insignificant. It follows from this that the Coulomb interaction does not play a significant role in the formation of bonds between the components of the complex. A characteristic sign of the formation of a CTC is the appearance of a new absorption band in the visible or UV part of the spectrum. Typically, CPC is more reactive than monomers. The reason for this is related to the lighter CTC polarizability compared to monomers due to the more extensive α-electronic structure and the ability to transition to an excited ionized state. In addition to double, ternary DA-complexes of monomers are known. The former are formed between relatively strong electron donors and acceptors, for example, between maleic anhydride and styrene. The latter are formed between weak electron acceptors, such as acrylates, and strong electron donors in the presence of Lewis acids. The role of the latter is to shift the electron density towards itself in the coordination double complexes:

which leads to an increase in the electron-withdrawing properties of the acrylic monomer. In general, the process of formation of triple DA complexes is described by the following equilibria:

where M is an acrylic monomer, D is a donor monomer, X is a Lewis acid. The equilibrium constants for the formation of ternary and double DA complexes of monomers are close. So, for complexes acrylonitrile - ZnCl 2 - styrene, (methyl methacrylate) 2 - SnCl 4 - styrene, the equilibrium constants at room temperature are 0.062 and 0.21 l / mol, respectively. For double DA-complexes, values ​​in the range of 0.1-0.2 l/mol are characteristic.

The hypothesis about the formation of CTC monomers and their ability to polymerize as a single kinetic particle was first put forward by Bartlett and Nozaki more than 50 years ago. Particularly actively alternating copolymerization was studied in the 70-80s. 20th century It has been found that the ability for alternating copolymerization is often related to the thermodynamic equilibrium constant for the formation of CTC by monomers, which in the case of binary complexes has the following form:


where , [M A ], are the equilibrium concentrations of the monomers and the complex; K is the equilibrium constant. With an increase in the equilibrium constant of complex formation, the ability for alternating copolymerization changes as follows:

To
0,01
0,1 (0,1-0,15)
K> 5 - the formation of a stable complex, not capable of polymerization, which can be isolated as an individual substance.

There are two models of copolymerization involving monomer complexes. The first of them - the Seiner and Lit model - provides for the entry of both molecules of the monomeric complex into the chain, the second - the dissociation model - provides for the entry of only one of the monomers of the complex into the chain. According to the first model, it is necessary to take into account in the elementary reaction four reactions of the growth (6.1) of the model of the end link with the participation of free monomers and four reactions with the participation of the complex considered earlier:


as well as the equilibrium reaction of complex formation of monomers (6.93).

According to the "dissociation model" of the complex, it is also necessary to consider eight growth reactions: four involving free monomers and four involving the complex, as well as the reaction of monomer complexation (6.93). This model can be applied to copolymerization in a solvent that forms complexes with a monomer. In this case, two complexation reactions are considered, i.e. each of the monomers with a solvent. The following are the growth reactions involving monomer complexes:


Comparison of (6.94) and (6.95) shows that they differ in the nature of the terminal units of the resulting growth radicals. This is because, according to the “complex dissociation” model, only one of the complex monomers is added in the chain propagation reaction, while the second one plays the role of an activator.

The mechanism of alternating copolymerization is determined by which of the elementary reactions of the considered models is predominant. The mechanism was studied by three methods: based on the composition of the copolymer, the rate of copolymerization (kinetic method) and the EPR method. In the latter case, the "direct" observation of growth radicals at low temperatures was used, as well as the use of a spin trap.

By the "direct" EPR method, as well as by the kinetic method, it was proved that during the copolymerization of SO 2 with dimethylbutadiene, a "complex" mechanism is realized, providing for the entry of both monomers of the complex into the chain. There are two types of independently growing chains in the reaction mixture, which differ in the nature of the terminal link:


It was shown by the spin trap method that the "complex" mechanism is also realized in the alternating copolymerization of cis-butene-2 ​​with SO 2 . In this case, one growth reaction dominates - the addition of a monomeric complex to a growth radical ending in an SO 2 unit:

Kinetic methods of analysis are associated with the phenomenon of the destruction of monomer complexes when reaction mixtures are diluted with a solvent. When a maximum is clearly expressed on the graph of the dependence of the copolymerization rate on the composition of the monomer mixture, its shift is recorded when the reaction mixtures are diluted with a solvent. To calculate the parameters characterizing the process, at least three series of experiments with monomeric mixtures of three different compositions and knowledge of the dissociation constant of the complex (K -1) are required. Using the maximum shift method (Fig. 6.7), it was found that during the copolymerization of maleic anhydride (M 2) with vinyl phenyl ether (M 1)
k 12 /k 21 \u003d 17.6; /k 12 = 7.51; /k21 = 0.355.
The first means that the reactivity of the vinylphenyl ether radical is significantly higher in cross-growth reactions than that of the maleic anhydride radical. This fact corresponds to the prevailing ideas about the "ideal" reactivity of monomers and radicals, according to which, ?-?-conjugation in the latter reduces their reactivity. It follows from the second ratio that complexes of monomers are predominantly added to the maleic anhydride growth radical, and free maleic anhydride is added to the vinylphenyl ether growth radical. Thus, in this case, all types of cross-growth reactions (i.e., leading to the formation of an alternating copolymer) are represented - with the participation of free radicals and complexes of monomers. This mechanism of alternating copolymerization is called mixed. It is also characteristic of the alternating copolymerization of maleic anhydride with allyl monomers. With alternating copolymerization of some monomers, there is no “peak shift” effect. This indicates that the contribution of growth reactions involving monomer complexes to the formation of an alternating copolymer chain is extremely insignificant.




However, this result does not mean that there is no donor-acceptor interaction in the cross-growth reaction. Almost simultaneously with the hypothesis about the role of donor-acceptor comonomer complexes in alternating copolymerization, a hypothesis was put forward about the donor-acceptor interaction in the reaction of electron-donor propagating radicals with electron-withdrawing monomers (and vice versa). According to Walling's hypothesis, the cross-growth reaction involving the styrene radical and the maleic anhydride monomer occurs via an electron transfer step, which lowers its activation energy:


Alternating copolymerization has pronounced features in comparison with the statistical one. These include:

spontaneous initiation,

Insensitivity to the action of most inhibitors and chain transmitters,

High chain growth rate.

These features are clearly manifested in copolymerization with the participation of ternary donor-acceptor complexes of monomers, since in this case it is possible to compare alternating and random copolymerization of the same monomers. Consider, as an example, the copolymerization of butyl methacrylate with dimethyl butadiene. In the absence of a complexing agent, the copolymer composition curve has a weakly pronounced S-shape, which indicates a slight alternation effect (Fig. 6.8). In the presence of (C 2 H 5) 2 AlCl, the rate and degree of copolymerization sharply increase (Fig. 6.9), and the copolymer composition curve takes the form characteristic of the formation of a regularly alternating copolymer (the equimolar composition of the copolymer, regardless of the composition of the monomer mixture). The role of (C 2 H 5) 3 AlCl is to enhance the electron-withdrawing properties of butyl methacrylate:

Using the EPR method, it was found that in this case there is a "sequential" mechanism of alternating copolymerization, when the nature of the radical at the end of growing chains changes sequentially. In this case, the donor-acceptor interaction occurs between the propagating radical and the monomer.
6.2.5. Influence of the reaction medium
Contrary to the opinion that existed for quite a long time after the completion of the quantitative theory of copolymerization, the reaction medium can have a significant effect on the composition and structure of the copolymer. There are two fundamentally different mechanisms of such influence:

1. Through the formation of various kinds of complexes between monomers and radicals, on the one hand, and components of the reaction medium, on the other. The latter may include a solvent or specially introduced substances, most often Lewis acids or bases * (* V. A. Kabanov, V. P. Zubov, Yu. D. Semchikov. Complex radical polymerization. M: Chemistry, 1987.).

2. Through the selective solvation of growing chains by monomers - in the case when the latter have different thermodynamic affinities for the copolymer as solvents** (** Semchikov Yu. B. 1999. V. 41, No. 4. S. 634-748.).

In the first case, effects of two levels are observed. In the absence of a pronounced specific interaction between the reagents and the solvent, an insignificant effect of the latter on the relative activities of the monomers is observed. A well-known example is the copolymerization of styrene with methyl methacrylate in aromatic solvents of different polarity.

A strong effect on the composition and structure of the copolymer is observed when sufficiently strong hydrogen and coordination bonds are formed between the monomers and (or) growth radicals and the solvent or Lewis acid, which can be specially introduced into the reaction mixture as a copolymer composition modifier or polymerization activator. In this case, there are significant changes in the composition of the copolymer, the relative activities of the monomers during the copolymerization of unsaturated carboxylic acids, their amides, amines, nitriles and esters with other monomers. In this case, the rates and degrees of copolymerization often change significantly.

The reaction mixture in bulk copolymerization is a typical solution of a polymer in a mixed solvent. The properties of such solutions depend, among other things, on the thermodynamic characteristics of the mixture used as a solvent. Thus, for solutions with a positive deviation of the mixed solvent from ideality, such phenomena as selective solvation of macromolecules by one of the solvent components and cosolubility, i.e. the dissolution of a polymer in a mixture of solvents, each of which does not dissolve the polymer individually. Signs of a positive deviation of the liquid mixture from ideality are the positive values ​​of the excess Gibbs function of mixing components, i.e. > 0 and a convex dependence of the saturation vapor pressure over the mixture on its composition.

In the copolymerization of monomer mixtures with a positive deviation from ideality, the effect of selective solvation of macroradicals and macromolecules by monomers on the composition of the copolymer and the relative activities of the monomers is often observed. Particularly significant effects were found in the copolymerization of N-vinylpyrrolidone with vinyl acetate, styrene with methacrylic acid, styrene with acrylonitrile, 2-methyl-5-vinylpyridine with vinyl acetate, less significant effects for a number of other systems* (* Semchikov Yu. D. Preferential sorption of monomers and molecular weight effect in radical copolymerization // Macromol Symp., 1996. V. 111. P. 317.). In all cases, there was a dependence of the copolymer composition on the molecular weight, atypical for the “classical” radical copolymerization, which is explained by the dependence of the coefficients of selective solvation of macroradicals on their degree of polymerization.

Thus, the influence of the medium on radical copolymerization is associated with two groups of effects. Electronic effects are associated with the redistribution of electron density in monomers and (or) radicals as a result of their formation of weak complexes with solvents, complexing agents such as Lewis acids. Concentration effects are associated with the selective solvation of propagating radicals by monomers. In all cases, the quantitative copolymerization theory outlined above remains applicable, however, the relative activities of the monomers are effective quantities.
6.2.6. Relation between the structure of the monomer and the radical and the reactivity. SchemeQ- e
In parallel with the development of the quantitative theory of copolymerization, the Alfrey-Price quantitative scheme was developed half a century ago, relating copolymerization constants to empirical parameters of reactivity. According to this scheme, the growth rate constant in radical polymerization and copolymerization is expressed by the empirical equation:

where P i and Q j - parameters that take into account the resonant; e i and e j are polar reactivity factors. Based on (6.96), expressions for the relative activities of monomers can be easily obtained:

Further, multiplying the relative activities of the monomers in (6.97) and taking the logarithm of the resulting product, we obtain:

whence it follows that the tendency to alternation during copolymerization is determined only by the difference in the values ​​of the polar parameters of the monomers.

The Q-e scheme is widely used in copolymerization because it allows one to calculate the relative activities of the monomers, and hence the composition and structure of the copolymer, without copolymerization, from the known Q and e values ​​of the monomers. These values, in turn, were determined by copolymerization of monomers with known and unknown values ​​of Q and e. Styrene was chosen as the initial monomer, to which e - -0.8, Q = 1 was assigned. The significance of the Q-e scheme is also that that it made it possible to assign monomers to certain groups based on the values ​​of the parameters Q and e: active (Q > 0.5) and inactive (Q 0) and, thereby, to predict the type of polymerization process in which it is advisable to use this monomer. Quantum-chemical calculations have shown that the parameters Q and e have a clear physical meaning; this follows from the correlations given in the next section.

An analysis of systematic data in the field of radical (co)polymerization leads to the conclusion that the reactivity of monomers and radicals in the growth reaction is determined by resonance stabilization (conjugation), double bond polarity, and the degree of its shielding by substituents.

Steric factor. The significance of the steric factor is especially pronounced in the reactions of radical addition of disubstituted ethylene. It is known that 1,1-disubstituted compounds are easily polymerized and copolymerized by the radical mechanism, while 1,2-disubstituted compounds, for example, maleic anhydride, are practically incapable of homopolymerization, and during copolymerization their content in the copolymer does not exceed 50%. The reasons for such different behavior of these close classes of unsaturated compounds can be understood by considering the stereochemistry of the chain propagation reaction.

The spatial structure of organic compounds is largely determined by the type of hybridization of carbon atoms. The unsaturated atoms of the growth radical and the monomer have cp 2 hybridization. This means that the axes of the p-orbitals of unsaturated atoms are perpendicular to the plane in which the β-bonds are located. The carbon atoms of the main chain of the radical form a flat zigzag, all of them, with the exception of the terminal unsaturated carbon atom, have cp 3 hybridization. It can be seen from the scheme below that when the conditional tetrasubstituted monomer (AB)C = C(XY) approaches its “own” growth radical, a contact interaction is likely; repulsion of the substituents A and B of the monomer and the carbon atom of the radical until the axes of the p-orbitals coincide. As a result, the growth reaction cannot take place:

A similar situation is observed when tri- and 1,2-disubstituted ethylene come close to their “own” propagating radical. Thus, the polymerization of tetra-, tri-, and 1,2-substituted ethylene is impossible for purely steric reasons. An exception is fluorine-substituted ethylene, during the polymerization of which, due to the small radius of the substituent, steric difficulties do not arise. Unlike polymerization, copolymerization of tetra-, tri- and 1,2-disubstituted ethylene with mono- or 1,1-disubstituted ethylene is possible. In this case, substituents and hydrogen atoms oppose in the "dangerous zone", which, as a rule, does not prevent the approach of the monomer and the radical and the progress of the growth reaction. However, since elementary acts of homopolymerization of a disubstituted monomer are impossible, the content of this monomer in the copolymer does not exceed 50%.
Table 6.1Copolymerization of vinyl acetate (1) with chlorosubstituted ethylene (2)

Monomer	r1	r2
Tetrachloroethylsn	6,8	0
Trichlorethylene	0,66	0,01
cis-dichloroethylene	6,3	0,018
Trans-dichloroethylene	0,99	0,086
Vinylidene chloride	0	3,6
Vinyl chloride	0,23	1,68

In table. 6.8 shows data illustrating the influence of the steric factor in copolymerization. Vinyl chloride and 1,2-disubstituted vinylidene chloride monomer are more active than vinyl acetate (r 1 > r 2). However, tri- and tetrasubstituted chloroethylenes are less active, with r 1 =0, due to their inability to homopolymerize. Trans-1,2-disubstituted are less reactive than cis-1,2-disubstituted, which is a general rule in copolymerization.

resonance factor. The significance of the resonance factor of reactivity or the effect of conjugation on the reactivity of monomers is most pronounced in radical copolymerization and polymerization. Depending on the presence or absence of conjugation of the double bond of the monomer with the unsaturated group of the substituent, all monomers are divided into active and inactive. Typical representatives of each group are presented below:




It can be seen from a comparison of the given structures that only direct α-β-conjugation in the monomer makes it active in copolymerization, other types of conjugation are ineffective.

As a rule, copolymerization is expedient between monomers of the same group, because only in this case it is possible to avoid an excessive difference in the composition of the copolymer from the composition of the monomer mixture. Thus, at the initial stage of copolymerization of equimolar mixtures of inactive vinyl chloride and vinyl acetate monomers and active styrene and acrylonitrile monomers, copolymers are formed containing in the first case 69 mol.% vinyl chloride. in the second - 60 mol.% styrene. During the copolymerization of equimolar mixtures of an inactive monomer with an active one - vinyl acetate with styrene - a copolymer is formed containing 98 mol.% styrene, i.e., practically a homopolymer.

Let us consider the data on the rate constants of elementary chain growth reactions (l/(mol s)) of joint and separate polymerization of vinyl acetate (1) and styrene (2) at 25°С:

k 11	k 22	r1	r2	k 12	k 11
637	40	0,04	55	15900	0,73

It can be seen that the active styrene monomer adds to the vinyl acetate growth radical at a rate four orders of magnitude higher than that of the inactive vinyl acetate monomer (k 12 and k 11). When comparing the resonant ability of radicals, the situation is reversed. The rate of addition of the vinyl acetate radical to its “own” monomer is three orders of magnitude higher than the rate of addition of the styrene growth radical to vinyl acetate (k 11 /k 21 = 873). A similar picture emerges when comparing the rates of addition of styrene and vinyl acetate growth radicals to styrene monomer (k 12 /k 22 =400). Thus, the conjugation or resonance effect affects the reactivity of monomers and radicals in the opposite way - it increases the activity of the former and reduces the activity of the latter. It follows from this that the series of reactivity of the monomers and their corresponding radicals are opposite. This position is known as antibatity rule.
Table 6.9Influence of the resonance factor on the value of the growth rate constant, 20-30°С

Monomer	Q	k Р, l/(mol s)
Vinyl acetate	0,026	1000
Vinyl chloride	0,044	6000
N-Vinylpyrrolidone	0,14	710
Methyl methacrylate	0,74	280
Styrene	1	40
Butadiene-1,3	2,39	8,4
Isoprene	3,33	2,8

The influence of the resonant factor of reactivity is also very significant with respect to the rate of radical polymerization and copolymerization. From Table. 6.9 it can be seen that the rate constants of the growth reaction of a number of monomers decrease with an increase in the resonance parameter Q, i.e. with an increase in the efficiency of conjugation of the double bond of the monomer with the substituent. In particular, the growth rate constant of the inactive vinyl acetate monomer is two orders of magnitude higher than that of the active styrene monomer. At first glance, this result seems surprising, since, due to the antibatity rule, the high activity of the monomer is compensated by the low activity of the corresponding radical, and vice versa. The point is that the effect of conjugation on the reactivity of the monomers and their corresponding propagating radicals is not the same in efficiency - the activity of the monomer increases to a lesser extent compared to stabilization, i.e., a decrease in the reactivity of the radical.

The third important effect due to the resonant reactivity factor is associated with the structure of the polymer chain. Previously, the possibility of chemical isomerism of repeating chain segments consisting of several links due to their different orientation along the chain was considered (Sec. 1.1.5). Below is a diagram showing two possible directions of the growth reaction in the copolymerization of styrene:


In the first case, the aromatic substituent is conjugated with the resulting radical and the transition complex, and therefore the monomer behaves as an active one. In the second case, there is no conjugation, since the unsaturated carbon atom of the radical is separated from the aromatic substituent by two α-bonds, and in this case the monomer is inactive. As a result, the first reaction turns out to be more preferable (k р >> k "р) and the addition of the radical to the monomer occurs with a probability greater than 90% according to the "head" to "tail" type.

The mechanism of action of the resonant reactivity factor is based on the effect of stabilization, a decrease in the α-electron energy of the transition state and the propagating radical due to conjugation with a substituent. Quantitatively, the resonant stabilization factor is taken into account by the parameters P, Q of the Alfrey-Price Q-e scheme and a number of quantum-chemical parameters, among which the bond order P and the localization energy are most often used. Of particular importance for characterizing the reactivity of unsaturated molecules is the localization energy L, the concept of which was first introduced by Ueland. As applied to the growth reaction, its physical meaning is as follows. The carbon atom of the monomer attacked by the radical changes the sp 2 hybridization to sp 3 and thus leaves the conjugation system. The energy required for this is called the monomer localization energy L ? . A similar reasoning can be carried out with respect to the conjugated radical, however, the localization energy of the radical L a does not significantly affect the relative activities of the monomers. L value? can be calculated as the energy of the transition of the monomer to the biradical triplet state:

Let us denote the energy of the ?-electrons of the monomer EM of the radical as Ер and the radical - ? (Coulomb integral). Then the monomer localization energy L ? turns out to be:

In table. 6.10 shows the values ​​of various resonance parameters of monomers calculated by the quantum chemical method. All of them correlate with lnQ and among themselves. On fig. 6.10 shows the correlation between L ? - the most well-known quantum-chemical parameter characterizing the resonance factor of reactivity, and InQ.

From the data in Fig. 6.10 and tab. 6.10 it follows that with an increase in the parameter Q, the absolute value of the monomer localization energy decreases. This means that as the conjugation energy in the monomer increases, the energy required to activate the breaking of its double bond decreases.
Table 6.10Empirical and calculated quantum-chemical resonance parameters of the structuremonomers and radicals

Monomer	InQ	L?	R	L?
CH 2 \u003d C (CN) 2	3,0	1,598	0,835	1,414
CH 2 \u003d CH-CH \u003d CH 2	0,871	1,644	0,894	0,828
CH 2 \u003d C (CH 3) CHO	0,372	-	-	-
CH 2 \u003d CH-CONH 2	0,174	-	-
CH 2 \u003d C (CH 3) CN	0,113	1,639	-	0,897
CH 2 \u003d SNS 6 H 5	0,00	1,704	0,911	0,721
CH 2 \u003d CNSHO	-0,163	-	0,910
CH 2 \u003d C (CH 3) COOSH 3	-0,301	1,737	-	0,691
CH 2 \u003d CH-CN	-0,511	1,696	0,913	0,839
CH 2 \u003d CH-COOCH 3	-0,868	1,783	0,914	0,645
CH 2 \u003d CCl 2	-1,514	1,832	-	0,867
CH 2 \u003d CHCH 2 OH	-3,04	-	-	-
CH 2 \u003d CHCl	-3,12	1,877	0,989	0,474
CH 2 \u003d C (CH 3) 2	-3,41	-	-	-
CH 2 \u003d CH-OC 2 H 5	-3,44	1,841	0,966	1,647
CH 2 \u003d CH-OCOCH 3	-3,65	1,885	0,965	0,445
CH2=CHF	-3,69	-	-	-
CH 2 \u003d CH 2	-4,20	2,000	1,000	0,000
CH 2 \u003d CHCH 3	-6,21	-	-	-

P is the bond order in the monomer, L ? and L? are the localization energies of the monomer and growth radical in units of Р (resonance integral).
Let us consider the change in the potential energy of the approaching monomer and radical, taking into account the localization energy of the monomer L ? . The approach of non-activated particles should lead to the emergence of repulsive forces and, consequently, an increase in potential energy (Fig. 6.11, curve 2). The approach of the radical to the activated monomer, i.e. being in a biradical state, leads to a decrease in potential energy (curve 1), which in this case changes in accordance with the Morse function. The latter describes the change in potential energy when two atoms are separated by a chemical bond. From fig. 6.11 it can be seen that a decrease in the localization energy leads to a decrease in the activation energy of the growth reaction, since the position of the “repulsion” curve (curve 2) is practically independent of the structure of the monomer and the value of L ? .

The approach outlined above, developed by Evans and Schwartz, does not take into account the role of polar and steric factors. The reactivity of monomers and radicals, determined only by the resonance factor, is called the ideal reactivity.


polar factor. The double bond of monomers subject to radical copolymerization is, as a rule, polarized due to the donor-acceptor action of substituents, as is the unsaturated carbon atom of the propagating radical:


The donor-acceptor effect of substituents leads to the appearance of partial charges on the α-carbon atom of the double bond and the α-carbon atom of the terminal unit of the propagating radical (unsaturated).

The effect of the polar reactivity factor is most pronounced in radical copolymerization, where it is responsible for the occurrence of the effect of alternating monomer units. For the first time, Price drew attention to the importance of the polar factor in copolymerization, who concluded that “copolymerization proceeds most easily in such binary systems in which one monomer has an excess, the other has a lack of electrons.” For a long time, the nature of the polar effect was explained from the standpoint of electrostatic interactions, which was subsequently recognized as unsatisfactory. Another hypothesis, which has become widespread to date, explained the propensity for unit alternation during copolymerization by electron transfer between the components of the transition complex, i.e. is a development of Walling's conjecture:


In the above scheme, the monomer CH 2 =CHX, for example methyl methacrylate, and the corresponding growth radical are electron acceptors, and the monomer CH 2 =CHY, for example styrene, is an electron donor. It is believed that the contribution of the ionic structure to the transition state reduces the activation energy of cross-growth, as a result, the copolymerization tends to alternating monomer units, however, the resulting copolymer remains random. The described mechanism is consistent with the data of quantum chemical calculations, according to which, with an increase in the difference between the values ​​of the polar parameters of the monomers |e 1 - e 2 | the charge transfer between the components of the transition complex increases.


Table 6.11Valuesgrowth reaction rate constantsandparameterepair-substituted styrene, 60°С

UDC 541.64:547.32:547.371

Radical Copolymerization of Styrene and Unsaturated Glycidyl Ethers

M.A. Chernigovskaya, T.V. Raskulova

Angarsk State Technical Academy,

665835, Irkutsk region, Angarsk, st. Tchaikovsky, 60, [email protected]

Abstract—The binary radical copolymerization of unsaturated glycidyl ethers (allyl glycidyl ether, ethylene glycol vinyl glycidyl ether) with styrene in toluene has been studied. The copolymerization constants and the microstructure of the resulting copolymers were calculated. It has been established that the composition of the copolymers depends on the structure of the unsaturated glycidyl ether. Copolymers of allylglycidyl ether with any composition of the initial monomer mixture are close in their structure to alternating ones. When styrene is copolymerized with ethylene glycol vinylglycidyl ether, the latter is less reactive. Il. 2. Tab. 3. Bibliography. 14 titles

Keywords: radical copolymerization; styrene; allyl glycidyl ether; vinylglycidyl ether of ethylene glycol.

RADICAL COPOLYMERIZATION OF STYRENE AND UNSATURATED GLYCIDYL ETHERS

M.A. Chernigovskaya, T.V. Raskulova

Angarsk State Technical Academy,

60, Chaikovskogo St., 665835, Angarsk, Irkutsk Region, 665835 Russia, [email protected]

The radical copolymerization of styrene and unsaturated glycidyl ethers (allyl glycidyl ether, ethylene glycol vinyl glycidyl ether) was examined in toluene solution. The reactivity ratios and parameters of copolymer microstructure were calculated. It was found that copolymer composition depends on unsaturated glycidyl ethers structure. Copolymers of styrene and allyl-glycidyl ether have an alternative structure. Ethylene glycol vinyl glycidyl ether has less reactivity than styrene in copolymerization. 2 figures. 3 tables. 14 sources.

Key words: radical copolymerization; styrene; allylglycidyl ether; ethylene glycol vinyl glycodyl ether. INTRODUCTION

One of the promising directions is the synthesis of copolymers with active functional chemistry of macromolecular compounds being onal groups. As monomers

for such syntheses, epoxy compounds and, in particular, unsaturated glycidyl ethers (UGEs) are of increasing interest. Copolymers containing EHE units in their composition are of interest for theoretical studies, since the simultaneous presence of the oxirane ring and oxygen atoms in the side chain in the EHE composition makes complexation effects possible.

On the other hand, such polymers provide the widest opportunity for targeted modification by carrying out polymer-analogous reactions on oxirane cycles and, therefore, open the way to obtaining materials, including composite ones, with a predetermined valuable set of properties.

The range of NGEs used in radical copolymerization reactions is quite wide, however, the most studied at present are methacrylic acid derivatives (for example, glycidyl methacrylate), allylglycidyl ether (AGE), as well as vinylglycidyl ethers of glycols (for example, vinylglycidyl ether ethylene glycol (EGE)). The most interesting as modifiers for industrial polymers are AGE and WGE, since due to their low reactivity they should be included in the composition of polymers in limited quantities, without changing the general complex of properties of the base polymer.

The traditional areas of use of these compounds in copolymerization processes are discussed in detail in the works. Recently, epoxy-containing copolymers are increasingly used for the manufacture of various nanomaterials and nanocomposites [for example, 5,6], as well as functional polymer composite materials. Therefore, the study of the processes of copolymerization of NGE, including AGE and WGE, with basic industrial monomers is of undoubted scientific interest.

The aim of this work was to study the binary radical copolymerization of styrene (St) with AGE and WGE.

EXPERIMENTAL PART

For the synthesis of copolymers, we used commercial St produced by OAO AZP (purity

99.8 %) with constants: p = 0.906 g/mL, 1bp = 145°C, AGE (product of ASHI company) with constants: p = 0.962 g/mL, nip = 154°C, n20 = 1, 4330, and WGE obtained at the Institute of Chemical Chemistry of the Siberian Branch of the Russian Academy of Sciences, purified to chromatographic purity

99.9% with the following constants: p = 1.038

g/ml, ^un = 204 °C, = 1.4310.

The copolymerization was carried out in a toluene solution at a temperature of 60°C and a tenfold excess of the solvent. Azo-bis-isobutyric acid dinitrile was used as an initiator in an amount of 1% wt. The resulting copolymers were isolated by precipitation with isobutanol, purified by reprecipitation with isobutanol from acetone, and dried to constant weight.

The composition of the products obtained was determined from the data of elemental analysis (C, H), functional analysis (content of epoxy groups), and IR spectroscopy. Determination of the content of epoxy groups in the composition of copolymers was carried out by back titration with hydrochloric acid according to . The relative viscosity was determined for 1% solutions in cyclohexanone at 25°C.

THE DISCUSSION OF THE RESULTS

Depending on the composition of the initial mixture, the copolymers obtained are white solid powder or amorphous substances, readily soluble in polar solvents.

The fact that copolymerization proceeded in the studied systems was confirmed using turbidimetric titration data. For example, the turbidimetric titration curves for St–WGE copolymers (Fig. 1) exhibit one inflection, which indicates the formation of copolymers rather than a mixture of two homopolymers. A similar picture is observed for St-AGE copolymers.

In the IR spectra of the EGE, an absorption band is observed in the region of 1620–1650 cm–1, which is characteristic of a double bond. The presence of the oxirane cycle is confirmed by the presence of absorption bands in the spectrum in the following regions: 765 and 915 cm-1, related to asymmetric stretching vibrations of the epoxy ring; 1230 cm-1 related to the symmetrical stretching vibrations of the epoxy ring; 3060 cm-1, corresponding to vibrations of the methylene group in the epoxy ring.

In the IR spectra of the copolymer, there are no absorption bands characteristic of a double bond, which confirms the occurrence of the copolymerization process at the vinyl or allyl groups. In the absorption regions characteristic of the oxirane ring and alkyl groups, the spectra of the copolymers are identical to the spectra of the initial EHEs.

Experimental data obtained as a result of the study of copolymerization processes in the St - VGE and St - AGE systems are presented in Table. one.

It was assumed that the investigated EGE

О 0.2 0.4 0.6 0.8 1.0

Precipitator volume, ml

Rice. Fig. 1. Dependence of the optical density of solutions of St-VGE copolymers on the volume of the added precipitant (methanol). The content of VGE in the original mixture (% mol.): 1 - 10; 2 - 25; 3 - 50

Table 1

General patterns of copolymerization St - NHE in a solution of toluene _ (DAK1% wt., 60 ° C, 2 h) __

No. Composition of the initial mixture, mol %. The composition of the copolymer, mol%. Output, %

St OGE St OGE

St - AGE system

1 95 5 36,36 63,64 3,7

2 90 10 55,14 44,86 12,6

3 70 30 47,16 52,84 32,4

4 50 50 92,32 7,68 20,2

5 30 70 46,73 53,27 19,8

6 10 90 60,13 39,87 19,3

St - VGE system

1 90 10 91,98 8,02 68,5

2 75 25 79,93 20,07 56,7

3 50 50 67,95 32,05 46,2

4 25 75 55,08 44,92 38,1

5 10 90 46,45 53,55 32,5

have a lower reactivity in radical copolymerization than St. Such a picture is indeed observed for St-VGE copolymers. They are enriched in St units in the entire studied range of initial mixtures, while the content of HGE units in the composition of copolymers increases symbately with its amount in the monomer mixture (Table 1).

For copolymers St - AGE observed

a different picture. At any composition of the initial monomer mixture, the content of St and AHE units in the copolymers is practically the same and ranges from 40 to 64 mol %, which indicates the formation of products close to alternating (Table 1).

As an analysis of the literature data shows, AGE is characterized by the occurrence of processes of alternating copolymerization with sufficiently

table 2

General patterns of copolymerization of VC - NHE in a solution of toluene

(DAK 1 wt %, 60 °С, 2 h)

The composition of the initial mixture, mol%. The composition of the copolymer, mol%. Yield, % Viscosity [G|], dl/g

VK OGE VK OGE

VH system - AGE

95,0 5,0 96,79 3,21 3,19 0,20

90,0 10,0 93,92 6,08 2,88 0,15

85,0 15,0 87,92 10,58 2,56 0,08

73,7 26,3 76,19 23,81 2,69 0,04

30,1 69,9 44,69 55,31 2,48 0,04

VH - VGE system

95,0 5,0 95,55 4,45 3,78 0,29

90,0 10,0 92,44 7,56 3,45 0,26

80,0 20,0 88,44 11,56 3,01 0,22

75,0 25,0 78,79 21,21 2,91 0,17

25,0 75,0 36,62 63,38 2,23 0,13

a wide range of monomers [eg 11, 12]. This is explained by the formation of charge-transfer complexes between AGE and the second comonomer, in which AGE plays the role of a donor. However, the study of the binary radical copolymerization of AHE with VC carried out by the authors did not reveal the formation of alternating copolymers (Table 2).

The formation of alternating copolymers during the copolymerization of AGE with St can be associated with the formation of charge-transfer complexes between the epoxy group of AGE and the aromatic ring of styrene. The resulting complex then plays the role of "individual monomer" in the copolymerization, which leads to the production of products of alternating structure.

Product yields generally decrease

with an increase in the content of units of low-active monomers in the composition of copolymers (Table 1), which is due to an increase in the concentration of EHE in the initial mixture of comonomers. An increase in the concentration of an inactive monomer increases its content in the copolymer, but reduces the total chain growth rate and, consequently, reduces the yield of the product and its molecular weight. This reasoning confirms the values ​​of the relative viscosity of solutions of copolymers (for example, St-AGE) and their dependence on the content of esters in the initial mixture (Fig. 2).

The calculation of the relative activity constants of the monomers (copolymerization constants) for the studied systems was carried out by different methods. Copolymerization constants of the system

Rice. 2 Dependence of the relative viscosity of copolymers St - AGE on the content of AGE in the initial mixture

Table 3

Copolymerization constants and average block lengths St ^^ _and NGE ^2) in copolymers_

System M1 m1 r Li L2

St-AGE system 0.70 0.47 r1 = 0.09 1 1

0.50 0.92 r2 = 0.05 21 1

0.75 0.20 n1 = 1.13 ± 0.09 n2 = 0.22 ± 0.02 10 1

System St - VGE 0.50 0.32 9 1

St-AGE was calculated on the basis of functional analysis data using the non-linear least squares method in the MathCAD 11 Enterprise Edition package, which makes it possible to carry out calculations using any sets of experimental data. The copolymerization constants for the St-WGE system were calculated by the standard Feynman-Ross and Kaelen-Tyudosh methods using the Mortimer and Tidwell experimental design method. The values ​​of the constants of copolymerization are presented in table. 3. Based on the values ​​of the copolymerization constants, the parameters of the microstructure of the copolymers were determined, which are also given in table. 3.

The obtained values ​​of the copolymerization constants confirm the earlier conclusion about the different reactivity of NGE in the copolymerization processes with St. For the St-AGE system, the values ​​of the calculated copolymerization constants are close to zero, which is typical for alternating copolymers. The calculation of the microstructure of these copolymers showed that almost strictly alternating products are obtained regardless of the composition of the initial mixture (Table 3).

The values ​​of the relative activity constants for the copolymers St - VGE indicate a lower reactivity of WGE in radical copolymerization compared to St. VGE is present in the data structure of the co-

polymers only in the form of single units, and the length of the blocks of St units in copolymers naturally decreases with a decrease in the share of St in the initial mixture.

Thus, the structure of St and NGE copolymers can apparently be reflected by the following formula:

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