A comparative study of the activation of acetic acid and its chloro-derivatives by dimethylaniline in inducing vinyl photopolymerization

Abstract

Acetic, monochloroacetic, dichloroacetic and trichloroacetic acids readily initiate photopolymerization of methyl methacrylate at 40° with visible light when used in the presence of dimethylaniline (DMA) at catalytic concentrations (10 −2−10 −3 mol l −1). The rate of polymerization ( R p) increases and the inhibition period (I.P.) decreases with increase in the degree of substitution with chlorine in the acid, using comparable concentrations of the acid (5 × 10 −3 mol l −1) and DMA (5 × 10 −3 mol l −1). When benzophenone (BP) is used as a photosensitizer in each of the above acid-amine photoinitiator systems, a similar trend of results is obtained; however, the BP-sensitized photopolymerization produces much lower I.P. and significantly higher R p in each case. Spectrophotometric studies indicate that each acid forms a complex with DMA and that the complex is the actual initiating species. End-group analyses of polymers prepared using the acid-amine initiator systems clearly indicates that initiation of polymerization takes place by radicals derived from the acid and DMA and generated by photodecomposition of the complex.