Easy Access to the RAFT Equilibrium Constant

Abstract

A method is presented for determination of reliable values of the equilibrium constant Keq between propagating radicals (P•) and intermediate radicals (INT•) in reversible addition−fragmentation chain transfer (RAFT) polymerization. The technique is based on EPR measurement of the ratio of concentrations of the two radical species under quasi-equilibrium conditions at low RAFT agent contents. The method requires no calibration of the EPR setup for absolute radical concentration measurement. Data for butyl acrylate polymerization mediated by benzyl propyl trithiocarbonate are presented. The value of Keq at −40 °C was determined to be (1.0 ± 0.1) × 104 L mol−1