Ring size-reactivity relationship in radical ring-opening copolymerisation of thionolactones with vinyl pivalate

Abstract

The radical ring-opening copolymerisation (rROcoP) of unsubstituted thionolactones of different ring sizes, namely γ-thionobutyrolactone (TBL), δ-thionovalerolactone (TVL), ε-thionocaprolactone (TCL) and ω-thionopentadecalactone (TPDL), with vinyl pivalate has been mechanistically investigated. The crucial effect of the ring-size on the ability of thionolactone to copolymerise and ring-open is depicted, with the fraction of ring-opened thionolactone units following the order 7 > 16 > 5 > 6 membered thionolactone. DFT calculations in combination with experimental results show the importance of the stabilization of the intermediate ring-retained radical for the thionolactone reactivity. A chain-terminating effect was revealed for TBL, TVL and TPDL. The incorporation of thionolactone units in the copolymers was evidenced by substantial decrease in M_w after chemical degradation.