Studies in copolymerization The evaluation of the kinetic coefficients for the system styrene-butyl acrylate

Abstract

The mechanism of the copolymerization of styrene and butyl acrylate has been investigated in mixtures of these monomers using benzoyl peroxide as initiator. The peroxide was decomposed both thermally and photochemically. Experiments on the composition of the polymer as a function of the monomer composition have given the reactivity ratios styrene radical-styrene molecule to styrene radical-butyl acrylate molecule as 0·48 and butyl acrylate radical butyl acrylate molecule to butyl acrylate radical to styrene molecule as 0·15. The kinetics of the copolymerization have been determined, and using the theory already elaborated for the treatment of such reactions, it has been shown by rate and molecular weight measurements that the styrene radicals react with the butyl acrylate radicals more quickly than the mean rate of reaction of styrene to styrene and butyl acrylate to butyl acrylate radicals. The coefficient Ø defining this increased activity is not in this case constant and rises with increasing styrene content to a value of as much as 150. The initiation mechanism is also complicated in that there is no linear relation between the rate of initiation and monomer composition; instead, the rate drops rapidly when styrene is added to the butyl acrylate.