Effect of Reversible Addition−Fragmentation Transfer (RAFT) Reactions on (Mini)emulsion Polymerization Kinetics and Estimate of RAFT Equilibrium Constant

Abstract

The Smith−Ewart equation has been modified to describe the kinetics of reversible addition−fragmentation transfer (RAFT) (mini)emulsion polymerization. Two types of radicals (propagating and intermediate) are taken into account. The influence of RAFT reactions on the (mini)emulsion polymerization kinetics is investigated using the modified Smith−Ewart theory. In a simplified zero−one case, the average number of propagating radicals per particle can be described by n̄RAFT-1 = n̄blank-1 + 2K[RAFT]0, where K is the RAFT equilibrium coefficient. It is found that the rate retardation is an intrinsic kinetic property of RAFT (mini)emulsion polymerization. The miniemulsion polymerization of styrene is also carried out with styrene oligomers of 1-phenylethylphenyl dithioacetate (PS−PEPDTA) and 2-cyranoprop-2-yl dithiobenzoate (PS−CPDB) as the RAFT agents. The experimental n̄ data are well described by the theory. The K values are estimated to be 314 L/mol for PS−CPDB and 22 L/mol for PS−PEPDTA. The fragmentation rate coefficients appear to be on the order of magnitude of 104−105 s-1.