The kinetics of polymerization of methacrylates in the presence of chain transfer agents

Abstract

A study has been made of the effect of mercaptoesters of the general formula RCOOCH 2CH 2SH (where R is a hydrocarbon radical containing four to fourteen carbon atoms) on the rate of polymerization of methyl methacrylate and methacrylic acid. It was found that addition of small quantities of mercaptoesters to the original monomer composition results in increase in the steady state polymerization rate in homogeneous and heterogeneous systems. It is suggested that the reason for this increase in rate is a “formal” increase in the efficiency of initiation, resulting from the fact that in the presence of a mercaptoester reaction of the primary radicals from the initiator with the chain-transfer agent competes with recombination of these radicals. A greater increase in the rate of polymerization of methacrylic acid is evidently related to the heterogeneity of the system. A reduction in the rate of both homogeneous and heterogeneous polymerization when the quantity of regulator is increased is evidently explained by increase in the part played by reaction of the growing radical with a radical of the transfer agent and by dimerization of the transfer-agent radicals. A shift of the gel effect to higher degrees of conversion in polymerization of methyl methacrylate in the presence of mercaptoesters is evidently because the viscosity of the system necessary to cause the gel effect is reached at higher degrees of conversion as a result of the reduction in molecular weight in the presence of the regulator.