Assessing the RAFT Equilibrium Constant via Model Systems: An EPR Study

Reversible addition‐fragmentation chain transfer (RAFT) equilibrium constants, K_eq, for the model system cyano‐iso‐propyl dithiobenzoate (CPDB) – cyano‐iso‐propyl radical (CIP) have been deduced via electron paramagnetic reso1494nce (EPR) spectroscopy. The CIP species is produced by thermal decomposition of azobis‐iso‐butyronitrile (AIBN). In solution of toluene at 70 °C, K_eq has been determined to be (9 ± 1) L · mol⁻¹. Measurement of K_eq = k_ad/k_β between 60 and 100 °C yields ΔE_a = (–28 ± 4) kJ · mol⁻¹ as the difference in the activation energies of k_ad and k_β. The data measured on the model system are indicative of fast fragmentation of the intermediate radical produced by addition of CIP to CPDB.