Dependence of cross-termination rate on RAFT agent concentration in RAFT polymerization

Abstract

Rate retardation is an intrinsic property of reversible addition-fragmentation chain transfer (RAFT) radical polymerization. One of reasons for this phenomenon is cross-termination reaction between intermediate radicals and other active radicals. With the help of Stationary State Model and experimentally controlling on k t,cross , the kinetics of styrene RAFT polymerization were performed at different concentrations of RAFT agent. Results show that there is a difference in two effects of cross-termination rate coefficient and concentration of intermediate radicals on cross-termination at different RAFT agent concentrations: at the low concentration range, the cross-termination reaction is mainly affected by its rate coefficient, and at the high concentration range, the cross-termination reaction is mainly affected by the concentration of the intermediate radicals. It shows that there is an optimal concentrations of RAFT agent for a RAFT polymerization with the least rate retardation by considering the balance between these two effects.