A 1H NMR Investigation of Reversible Addition−Fragmentation Chain Transfer Polymerization Kinetics and Mechanisms. Initialization with Different Initiating and Leaving Groups

Abstract

In situ 1H nuclear magnetic resonance spectroscopy was used to directly investigate the processes that occur during the early stages (the first few monomer addition steps) of azobis(isobutyronitrile)-initiated reversible addition−fragmentation chain transfer (RAFT) polymerizations of styrene in the presence of cumyl dithiobenzoate at 70 and 84 °C. The change in concentration of important dithiobenzoate species and monomer as a function of time was investigated. The predominant type of growing chain under the reaction conditions carries a cumyl end group. The initialization period (the period during which the initial RAFT agent is consumed) in the presence of cumyl dithiobenzoate in homogeneous media was significantly longer than for equivalent reactions using cyanoisopropyl dithiobenzoate as RAFT agent, and the rate of monomer conversion was correspondingly slower. Very strong fragmentation selectivity of the formed intermediate radicals (to form the tertiary propagating radical) was observed during the i...