Determination and correlation of regioselectivity and dead dormant species from head addition in acrylate RAFT polymerization

Abstract

Regioselectivity, a fundamental feature of radical addition reactions, has not received enough attention in reversible deactivation radical polymerization, especially for acrylates. However, in RAFT polymerization, the primary alkyl radicals, derived from “abnormal” head addition, will react with RAFT agents and produce non-active macro-RAFT agents, i.e. dead dormant species (DDS). Herein, a formula was proposed to correlate the content of DDS (α) with the incidence of head addition (ρ₁) according to a detailed RAFT process involving head addition. And then, by combining a well-designed chain-extension reaction with gradient polymer elution chromatography (GPEC), the DDS in benzyl N-carbazolecarbodithioate-mediated RAFT polymerization of benzyl acrylate (BzA) were readily separated and quantitatively determined using the characteristic UV absorption of the N-carbazolecarbodithioate terminal. Based on these results, typically, the ρ₁ of BzA at 60 °C was estimated to be 0.14%, demonstrating the utility of the method described to determine the incidence of head addition in radical polymerization. This study should be beneficial for a better understanding of RAFT processes, and meanwhile provides a powerful tool to determine regioselectivity of monomers in radical polymerization.