Exploring the Removal of Thiocarbonylthio Chain Ends from Poly(styrene-alt-maleic anhydride) Copolymers

Poly-(styrene-alt-maleic anhydride) (SMAnh), an alternating copolymer composed of electron-rich styrene (STY) and electron-deficient maleic anhydride (MAnh) comonomers, was synthesized via reversible addition-fragmentation chain transfer (RAFT)-mediated polymerization, using either a trithiocarbonate, dithiobenzoate, or dithiocarbamate chain transfer agent (CTA). SMAnh copolymers with different terminal repeat units (MAnh vs STY) were subjected to either radical-induced reduction or thermolysis to facilitate the transformation of the thiocarbonylthio functional chain end. The chemical composition of the ω-chain end and the solvency conditions employed during each end-group removal process were found to significantly influence the rate and extent of removal/transformation of the thiocarbonylthio functional group. MAnh-functional ω-chain ends enhanced the lability of the thiocarbonylthio group for all end-group removal strategies assessed, suggesting that electron-deficient chain ends facilitate higher efficiency removal of thiocarbonylthio functional groups. Additionally, 3,5-dimethyl pyrazole dithiocarbamate chain ends were reduced or thermolyzed faster and to a higher degree than trithiocarbonate- or dithiobenzoate-functional chain ends.