The thiol/dimethyl sulfoxide system as initiator of polymerization in benzene medium, 2. Kinetic studies

The kinetics of butanethiol/dimethylsulfoxide (DMSO) initiated polymerization of methyl methacrylate in benzene medium was studied gravimetrically. The thiol acts as the reducing component of the initiator system and also as a transfer agent. The order with respect to [Butanethiol] is 0,48. In the lower concentration region between 4,69.10−4 and 9,38.10−2mol 1−1, DMSO behaves simply as the oxidant of the initiator system, and the rate of polymerization has the usual square root dependence on [DMSO]. But above the concentration of 9,38.10−2mol 1−1 and up to 1,40mol 1−1, DMSO acts both as an oxidizing agent and as a retarder, forming an adduct with the growing radicals, which propagates the reaction with a retarded rate. The order with respect to monomer concentration is 1,04, when DMSO is used in the lower concentration range and it increases to 1,25 when [DMSO] is higher than 9,38.10−2mol 1−1. Thiols of different structures affect the rate significantly. The rate of polymerization is also dependent on the polarity and viscosity of the solvent being a maximum in benzene and a minimum in ethyl acetate. The efficiency of initiation of the initiator system is 60–80% and the overall activation energy is 72,45 kJ mol−1. An appropriate kinetic expression was derived to explain the results.