Mechanistic aspects of sonochemical copolymerization of butyl acrylate and methyl methacrylate

This paper attempts to get a physical insight into the sonochemical emulsion copolymerization using butyl acrylate (BA) and methyl methacrylate (MMA) as model monomers at low to moderate ultrasound intensity. The principal physical mechanism underlying beneficial effects of ultrasound on emulsion polymerization system is cavitation, which affects the system in both chemical (i.e. generation of radicals that can initiate/propagate polymerization process) as well as physical (i.e. emulsification of reaction mixture) way. By taking dual approach of coupling experiments with simulations of cavitation bubble dynamics, we have tried to justify the trends in experiments results. The role of cavitation in the present study is found to be only physical. Quite interestingly, the chemical effect of cavitation is found to have no role to play. Reactivity ratios of both monomers for applied experimental conditions have been found to be less than 1, which hints at moderately alternating behavior of copolymerization. Theoretically calculated copolymer composition using the reactivity ratios of copolymers matched well with experimental values. The copolymer composition for all monomer feed ratios is rich in MMA, due to higher reactivity of MMA than BA. The molecular weight of the copolymer reduced with greater fraction of MMA in the reaction mixture. This effect is attributed to nature of termination of the BA (i.e., combination) and MMA (i.e., disproportionation) monomer radicals.