Biobased triblock thermoplastic elastomer with betulin- or carvacryl-methacrylate end-blocks by RAFT polymerization

Abstract

In this work, fully biobased acrylic ABA triblock copolymers were synthesized via reversible addition-fragmentation chain-transfer (RAFT) polymerization using VISIOMER® Terra C13 (ET13) as the “soft” midblock and two terpenoid-derived methacrylates, betulin methacrylate (BetuMA) and carvacryl methacrylate (CaMA), as the glassy blocks. An “R-linked” bifunctional chain transfer agent (bis-CTA) enabled the formation of ET13 macro-CTAs with controlled molecular weights and narrow dispersity (M_n = 84–229 kg mol⁻¹, Đ ≈ 1.1). RAFT homo-polymerizations of BetuMA and CaMA yielded well-defined homopolymers (M_n = 20–33 kg mol⁻¹, Đ < 1.4) with selective methacrylate reactivity. Chain extension of ET13 macro-CTAs produced a series of ABA triblocks featuring 8–39 mol% glassy content. GPC confirmed molecular weights in the range M_n = 97–415 kg mol⁻¹ (Đ < 1.7), while DSC and TGA analyses showed distinct glass transitions for soft block, close to −50 °C, and good thermal stability. AFM evidenced clear microphase separation. Mechanical testing revealed that BetuMA-based copolymers (BEB series) achieved tensile strengths up to 3.9 MPa and elongations up to 760%, outperforming CaMA-based analogs (CEC series: σ ≤ 1.2 MPa, ε ≤ 710%). These results demonstrate the efficacy of RAFT polymerization of terpenoid methacrylates in producing high-performance, sustainable thermoplastic elastomers, offering a viable alternative to petroleum-derived thermoplastic elastomers (TPEs).