Journal of Applied Polymer Science, Vol.79, No.9, 1640-1652, 2001
Effect of reaction medium on radical copolymerization of acrylonitrile with vinyl acids
Radical polymerization of acrylonitrile (AN) with methacrylic acid (MAA) and itaconic acid (IA) was carried out in a mixture of dimethylformamide (DMF) and water at 70 degreesC using alpha, alpha'-azobisisobutyronitrile (AIBN) as an initiator. Monomer feed in the polymerization vessel was 98:2 (AN:MAA/IA) in the molar ratio, and the DMF: H2O ratio was varied between 20:80 and 80:20 (w/w). Copolymers were characterized by FTIR, carbon, hydrogen, nitrogen elemental CHN analysis, H-1- and C-13-NMR, and viscometry. The rate of polymerization (R-p) was found to decrease with an increase in DMF concentration in the reaction medium, that is, in 20% DMF for AN-MAA system, the R-p is 1.23% min(-1) in 1 h of polymerization, while in 80% DMF, R-p is reduced to 0.37% min(-1). The nature of the vinyl acid also affects the R-p. It has been shown that the rate of polymerization is higher for an AN-MAA system as compared to an AN-IA system (R-p = 1.0% min(-1)) and the methacrylic or itaconic acid content in the copolymer increases with an increase in the DMF concentration. The MAA content in the poly(AN-MAA) polymer produced in 20% DMF is 3.2 mol %, which increases to 6.1 mol % (calculated through FTIR spectra) when DMF is increased to 80% in the reaction medium. The intrinsic viscosity [eta] of the poly(AN-IA) and poly(AN-MAA) copolymers in DMF was found to be in the range of 0.67-2.90 dLg(-1) depending on the reaction medium. In determining the intrinsic viscosity, a definite deviation from rectilinearity of the concentration dependence in the high-dilution region is observed, thereby demonstrating the polyelectrolyte behavior of these polymers. Through FTIR and NMR spectral studies, PAN homopolymer and other copolymers have shown the formation of a small quantity of acrylamide units. In addition copolymer P-10, which contains 10.1 mol % IA, has shown anhydride formation.