Russian Journal of Applied Chemistry, Vol. 76, No. 2, 2003, pp. 280!283. Translated from Zhurnal Prikladnoi Khimii, Vol. 76, No. 2, 2003, pp. 289!292. Original Russian Text Copyright C 2003 by Kurenkov, Antonovich.

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MACROMOLECULAR CHEMISTRY ÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ AND POLYMERIC MATERIALS

Radical Polymerization of Acrylamide in Aqueous!Dimethyl Sulfoxide Solutions in the Presence of Sodium Acetate V. F. Kurenkov and O. A. Antonovich Kazan State Technological University, Kazan, Tatarstan, Russia Received April 9, 2002

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Abstract The kinetic features of nonisothermal polymerization of acrylamide in aqueous, mixed aqueous dimethyl sulfoxide, and DMSO solutions in the presence of potassium persulfate as initiator and sodium acetate as complexing agent were studied by differential thermal analysis.

Radical polymerization of acrylamide (AA) in concentrated solutions under nonisothermal conditions is a promising procedure for production of water-soluble high-molecular-weight polyacrylamide (PAA) [1]. In this case, polymerization can proceed at a high rate and to a high degree of conversion [23 6]. In addition, as the reaction temperature grows owing to the heat released in polymerization, the viscosity of the reaction mixture decreases and the flexibility of macroradicals increases, so that they more efficiently suppress intermolecular imidization yielding the waterinsoluble polymer. Synthesis of PAA under nonisothermal conditions has not been studied adequately, and data on the influence of the complexing power of CH3COONa (SA) on polymerization of AA are scarce [7310]. Here, we report on the main features of nonisothermal radical polymerization of AA in concentrated solutions in water, mixtures of water with dimethyl sulfoxide (DMSO), and straight DMSO in the presence of SA. EXPERIMENTAL The substances and experimental procedure are similar to those described previously [9, 10]. The polymerization kinetics were studied by differential thermal analysis. Polymerization was carried out in 15-cm3 cylindrical glass ampules. A solution of AA and SA was charged into an ampule and the ampule blown with helium for 30 min and hermetically sealed with a rubber stopper. A solution of the initiator, K2S2O8 (PPS), was introduced into the ampule by a syringe through the rubber stopper, and the ampule was placed in a heating furnace. All the experiments were carried out at the initial temperature of 25oC,

and then the temperature in the furnace was raised at a constant rate of 1.8 deg min31 with a heater used in differential thermal analysis. In the course of polymerization, we recorded the variation of the temperature difference between the reaction mixture and ethanol (reference) with time. After the polymerization was complete, the solution was diluted with water and the polymer was precipitated into acetone. Then, the polymer was filtered, washed with acetone, and dried under reduced pressure at room temperature to constant weight. The intrinsic viscosity of PAA [h] was measured with an Ubbelohde viscometer (d = 0.56 mm) in 0.5 M NaCl at 25 -oC. The viscosity-average molecular weight of PAA M h was evaluated by the formula [11]

h

[ ] = 7.19

0 103 M-h 3

0.77.

The experimental data on nonisothermal polymerization were processed under the following assumptions: the total polymerization heat is expended for heating of the reaction mixture, the heat capacities of the monomer and polymer are the same, and evaporation of the solvent is neglected. In this case, the relation between the rate of variation of the reaction mixture temperature, dT/dt, in the course of polymerization and the rate of monomer consumption, 3d[AA]/dt, is described by the simplified equation [3, 12] dT/dt = (

3DH/C )(3d[AA]/dt ),

where DH is the polymerization heat and C is the heat capacity of the reaction mixture.

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RADICAL POLYMERIZATION OF ACRYLAMIDE IN AQUEOUS DIMETHYL SULFOXIDE SOLUTIONS 281 Parameters of AA polymerization in various media

ÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÂÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄ ³ ³ ³ ³ Reaction order ³Water : DMSO, Molar ratio v, 1/2 ³ /k ³ M h 1036 ³ ³ ³ k ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´ p t vol % : vol % ([SA]/[AA]) 102 deg s31 ³ ³ ³ ³ with respect to AA ³ with respect to PPS ³ ÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄ 1.25 ³ 0.50 ³ 100 : 0 ³ 0 ³ 0.42* ³ 3.30 ³ 1.38 ³ 0.78 ³ 100 : 0 ³ 0.40 ³ 3.50* ³ 4.52 ³ 80 : 20 ³ 0 ³ 0.62 ³ ³ ³ ³ 80 : 20 ³ 1.34 ³ 1.51 ³ ³ ³ ³ 2.65 60 : 40 ³ 0 ³ 0.46 ³ ³ ³ ³ 60 : 40 ³ 1.34 ³ 1.25 ³ ³ ³ ³ 1.90 50 : 50 ³ 0 ³ 0.40 ³ 1.25 ³ 1.25 ³ ³ 50 : 50 ³ 1.34 ³ 1.20 ³ 1.35 ³ 1.35 ³ ³ 40 : 60 ³ 1.34 ³ 1.14 ³ ³ ³ ³ 1.25 20 : 80 ³ 1.34 ³ 1.04 ³ ³ ³ ³ 0.70 0 : 100 ³ 0 ³ ³ 0.79 ³ 0.94 ³ 0.47 ³ 0 : 100 ³ 1.34 ³ 1.00 ³ 1.36 ³ 1.02 ³ ³ 0.25 0 : 100 ³ 2.01 ³ ³ ³ 1.37 ³ 0.60 ³ ÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄ * Values for v 0 104, mol l31 s31.

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Deviation of the reaction orders with respect to the monomer and initiator from 1.0 and 0.5, respectively, did not allow determination of the individual rate constants of chain propagation, kp, and termination, kt. Therefore, we found the kp /k1/2 t values determined from RUSSIAN JOURNAL OF APPLIED CHEMISTRY

3 3 3 3 3 3 3 3 3

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The initial polymerization rate v = dT/dt was determined from variation of the temperature of the reaction mixture with time. The results are listed in the table. Based on the experimental linear dependences log v = f (log [AA]) and log v = f (log [PPS]), we determined the reaction orders with respect to the monomer and initiator in the absence and in the presence of SA (see table). The positive values of the reaction orders in polymerization in aqueous solutions, in a 1 : 1 water3DMSO mixture, and in DMSO show that v grows with increasing initial concentrations of the monomer and initiator. In all the systems studied, with increasing - concentration of AA in the initial mixture, the M h values for PAA vary in parallel with v (Fig. 1), in good agreement with the general pattern of radical polymerization. The increased reaction orders with respect to AA and PPS, found in polymerization in the presence of SA, suggest a complicated mechanism of polymerization of AA in the presence of the complexing agent. The increase in the reaction order with respect to the monomer, observed on adding SA, is caused by participation of AA in the complexation with SA. The increase in the reaction order with respect to the initiator suggests an increase in the contribution of monomolecular termination to the total balance of chain termination reactions.

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the dependence of 1/P on v/[AA]2, where P is the average degree of polymerization. The resulting kp /k1/2 t values are listed in the table. It is seen that v grows upon addition of SA as a result of an increase in the kp /k1/2 ratio, which can be assigned to increased kp . t According to IR, 1H NMR [13], and NMR [14] data, the effect of SA on polymerization of AA is caused by complexation of SA with amide groups of the propagating radical. As a result of the com-

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Fig. 1. M h of PAA vs. AA concentration in polymerization in (1) aqueous solutions, (2, 3) mixture water : DMSO = 1 : 1, and (4, 5) DMSO (1, 2, 4) in the absence and (3, 5) in the presence of 0.034 M SA. [PPS] = 0.82 0 1033 M. No. 2

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KURENKOV, ANTONOVICH

plexing agent and a salt additive affecting the conformation of macroradicals in solution. Addition of small amounts of SA leads to higher v and, evidently, when the concentration of macroradicals that form complexes reaches a maximum, the highest v values are observed. The subsequent decrease of the v values in the presence of SA can be assigned to a decrease of root-meansquare sizes of molecular globules ( r 2 )1/2 as a result of deterioration of the solvent quality owing to addition of large amounts of SA. A similar decrease of (r 2 )1/2 in solutions of lithium bromate was accompanied by a decrease in the rate of AA polymerization [15].

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Fig. 2. Relative rate of AA polymerization, v / v0 , in (1) aqueous solution, (2) 1 : 1 water3DMSO mixture, and (3) DMSO solution vs. the molar ratio [SA]/[AA]. [AA] = 1.41 and [PPS] = 0.82 0 1033 M. v0: (1) 0.42 0 1034 mol l31 s31; (2) 0.4 and (3) 1.17 deg s31.

Fig. 3. Reduced viscosity of the solutions, hsp /c, vs. concentration c of PAA (M h = 2.1 0 106) in (1) aqueous solution and in the water3DMSO mixtures: (2) 4 : 1, (3) 3 : 2, and (4) 1 : 1.

plexation, changes in the conjugation energy and polarity of the macroradical enhanced its reactivity in the events of chain propagation and promoted the increase in the kp /k1/2 t ratio observed in the experiments. The influence of SA concentration on the relative rate of AA polymerization, v/v0 in aqueous solutions, in the 1 : 1 water3DMSO mixture, and in DMSO solutions is shown in Fig. 2. It is evident that, in all the media, the v/v0 values grow with increasing concentration of SA and, after passing through a maximum, decrease. The observed v/v0 = f [SA] dependence with a maximum is due to the dual function of SA as a com-

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Data presented in the table and Fig. 1 suggest that, in polymerization of AA in the presence of SA, v and M h grow in parallel with increasing water content in the mixed water3DMSO solvent. The v values in aqueous3DMSO media in the absence of SA vary in a similar manner (see table), in good agreement with the results of isothermal polymerization of AA [16, 17]. The observed decrease in v in the series water > water : DMSO = 1 : 1 > DMSO is caused by ratio and in the reaction the increase in the kp /k1/2 t order with respect to the monomer. According to published data for isothermal polymerization of AA in aqueous3DMSO media [17], the variation of kp /k1/2 t is caused by rise in kp owing to an increase in the activation energy of reaction. The above kinetic effects are mainly due to variation of the reactivity of the reacting species as a result of complexation (H-bonding) of propagating radicals and monomer with the solvent [18]. According to NMR data [19], an increase in the polarity of the medium on adding water (e = 80) to less polar DMSO (e = 46.6) enhances the capability of the solvent to form intermolecular H-bonds. Formation of H-complexes between the C=O group of AA and water decreases the electron density at the CH2= group and increases v. In addition, complexation between the C=O group of AA and S=O group of DMSO may also exert a certain effect on v [20]. This effect becomes more pronounced with increasing content of DMSO in the solvent; it affects the activity of AA during polymerization. One more reason for the above rise in v is an increase in ( r 2 )1/2 values with growing content of water in the mixed solvent water3DMSO. In this study, the rise in ( r 2 )1/2 was judged from the increased reduced viscosity of PAA solutions hsp /c at c = const (Fig. 3, passing from curve 4 to curve 1), since, as a first approximation, we can assume that (hsp /c) ~ (r 2 )1/2 [21]. It is evident that a rise in ( r 2 )1/2 with increasing water content in the solvent leads to higher local concentration of the monomer

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in the area of active centers and to higher rate of AA polymerization.

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The increase in M h on adding water to DMSO can be caused by decreased contribution of chain transfer involving mobile hydrogen atoms of the methyl groups of DMSO. CONCLUSIONS (1) With increasing concentration of the monomer and initiator, v grows and the dependence of v on the concentration of CH3 COONa passes through an ratio, and the reextremum. The v values, the kp /k1/2 t action order with respect to the monomer increase on adding CH3COONa and in the order DMSO < water : DMSO = 1 : 1 < water.

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(2) The M h grows with increasing concentration of acrylamide and water content in the binary solvent water3DMSO. (3) The influence of CH3COONa on v is due to complexation of CH3COONa with the propagating radical, and the influence of the composition of the water3DMSO mixture on v is due to complexation of the propagating radicals with the solvent owing to formation of H-bonds and also to variation of the conformational state of macroradicals. REFERENCES

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1. Kurenkov, V.F. and Abramova, L.I., Polym.-Plast. Technol. Eng., 1992, vol. 31, nos. 7 8, pp. 659 704. 2. Thomson, R.A.M., Ong, Ch.K., Rosser, C.M., and Holt, J.M., Makromol. Chem., 1983, vol. 184, no. 9, pp. 1885 1892. 3. Kay, T.A. and Rodriguez, F.J., J. Appl. Polym. Sci., 1983, vol. 28, no. 2, pp. 663 666. 4. Kurenkov, V.F., Baiburdov, T.A., and Stupen’kova, L.L., Vysokomol. Soedin., Ser. A, 1987, vol. 29, no. 2, pp. 348 351. 5. Kurenkov, V.F., Baiburdov, T.A., and Stupen’kova, L.L., Zh. Prikl. Khim., 1987, vol. 60, no. 10, pp. 2311 2316. 6. Kurenkov, V.F., Baiburdov, T.A., and Stupenkova, L.L., Eur. Polym. J., 1990, vol. 26, no. 8, pp. 915 918.

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7. Boghina, C.M., Marinescu, N.N., Marinescu, M.M., et al., Abstracts of Papers, Int. Symp. on Macromolecular Chemistry, Bucharest, 1983, Sect. 1, pp. 113 117. 8. Kurenkov, V.F., Verizhnikova, A.S., and Myagchenkov, V.A., Fiziko-khimicheskie osnovy sinteza i pererabotki polimerov (Physicochemical Foundations of Synthesis and Recovery of Polymers), Gorky: Gork. Gos. Univ., 1988, pp. 35 40. 9. Kurenkov, V.F., Aleeva, Yu.V., Verizhnikova, A.S., and Myagchenkov, V.A., Izv. Vyssh. Uchebn. Zaved., Khim. Khim. Tekhnol., 1989, vol. 32, no. 2, pp. 69 73. 10. Kurenkov, V.F., Aleeva, Yu.V., Kuleshov, V.P., and Myagchenkov, V.A., Zh. Prikl. Khim., 1991, vol. 64, no. 1, pp. 150 154. 11. Klein, J. and Conrad, K.-D., Makromol. Chem., 1980, vol. 181, no. 6, pp. 227 240. 12. Tonoyan, O.A., Leikin, A.D., Davtyan, S.P., et al., Vysokomol. Soedin., Ser. A, 1973, vol. 15, no. 8, pp. 1847 1851. 13. Osmanov, T.O., Gromov, V.F., Khomikovskii, P.M., and Abkin, A.D., Vysokomol. Soedin., Ser. A, 1979, vol. 21, no. 8, pp. 1766 1772. 14. Kurenkov, V.F., Nurullina, E.V., Minkin, V.S., and Myagchenkov, V.A., Vysokomol. Soedin., Ser. A, 1994, vol. 36, no. 7, pp. 1076 1080. 15. Osmanov, T.O., Gromov, V.F., Khomikovskii, P.M., and Abkin, A.D., Dokl. Akad. Nauk SSSR, 1978, vol. 240, no. 4, pp. 910 913. 16. Kurenkov, V.F., Akhmed’yanova, R.A., Severinov, A.V., and Myagchenkov, V.A., Khim. Tekhnol. Elementoorg. Soedin. Polim. (Kazan), 1977, vol. 16, no. 6, pp. 20 23. 17. Gromov, V.E., Galperina, N.J., Osmanov, T.O., et al., Eur. Polym. J., 1980, vol. 16, no. 6, pp. 529 535. 18. Kabanov, V.A., Zubov, V.P., and Semchikov, Yu.D., Kompleksno-radikal’naya polimerizatsiya (Radical Complex Polymerization), Moscow: Khimiya, 1987. 19. Zhuravleva, I.L., Zav’yalova, E.N., Bogachev, Yu.S., and Gromov, V.F., Vysokomol. Soedin., Ser. A, 1986, vol. 28, no. 4, pp. 873 877. 20. Bondarenko, S.G., Nikolaev, A.F., lavrov, N.A., and Stepanov, E.M., Zh. Prikl. Khim., 1982, vol. 55, no. 12, pp. 2728 2732. 21. Tanford, Ch., Physical Chemistry of Macromolecules, New York: Wiley, 1963.

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