A systematic investigation of poly(MAM)--poly(LAM) synthesis switchable RAFT polymerization employing both blocks as macro-chain transfer agents

Abstract

Reversible addition–fragmentation chain transfer (RAFT) polymerization of structurally diverse monomers remains challenging with a single type of conventional chain transfer agent (CTA). This is due to limited compatibility with monomers having contrasting activation characteristics. In this work, we synthesized an ethyl piperazine-bearing dithiocarbamate-based RAFT agent that exhibits reversible protonation. The catalytic behaviour of both neutral (CTA-1) and protonated (CTA-2) forms of the CTA was systematically investigated towards less activated monomers (LAMs) and more activated monomers (MAMs) under identical reaction conditions. CTA-1 showed very good control over vinyl acetate (VAc) polymerization, affording poly(VAc) with low dispersity (Đ = 1.11), whereas poor control was observed for methyl methacrylate (MMA) polymerization (Đ = 1.86). In contrast, CTA-2 showed good control over MMA polymerization (Đ = 1.19) but showed poor control over VAc polymerization (Đ = 1.74). These results were further supported by the chain transfer coefficient (Ctr). The switchable CTA strategy was subsequently employed to synthesize block copolymers from both MAMs and LAMs as macro-CTAs. Deprotonation of CTA-2-derived poly(MMA) enabled successful chain extension with VAc, producing poly(MMA)-b-poly(VAc) with a molar mass that increased from 16 430 to 43 080 g mol−1 (Đ = 1.27). Conversely, protonation of CTA-1-derived poly(VAc) allowed chain extension with MMA, yielding poly(VAc)-b-poly(MMA) with a molar mass of 32 080 g mol−1 (Đ = 1.65). Furthermore, the selective hydrolysis of poly(t-BA)-b-poly(VAc) afforded a biocompatible amphiphilic poly(AA)-b-poly(VAc) block copolymer with potential biomedical applications.