Synthesis of a thermoplastic elastomer from α-methylene-γ-butyrolactone for high temperature applications

Abstract

Thermoplastic elastomers, such as polystyrene-b-polybutadiene-b-polystyrene (SBS), are essential components in a wide array of industries, from seals and gaskets in building construction to binders in Li-ion batteries. However, SBS rubbers are still produced from 100% oil-based materials and their use is limited by relatively low thermal stability. When used in applications where temperatures exceed 100 °C, their mechanical properties become poor and at temperatures above 140 °C a cross-linking reaction is typically triggered. This factually cures (i.e. crosslinks) the system, hardening the rubber and hindering recycling, which is a prominent limitation of SBS rubbers. α-Methylene-γ-butyrolactone (MBL) is a monomer that has recently been under the spotlight, thanks to its bio-renewable nature and the high thermal stability of its corresponding polymer. While a promising candidate for the next generation of thermoplastic elastomers, its successful implementation in functional products has yet to be demonstrated. Herein, we report a simple methodology to produce high quantities of SBS-like elastomers based on BAB terblock copolymers featuring a MBL segment and hexyl methacrylate (HMA) segment, poly(MBL)-block-poly(HMA)-block-poly(MBL). A two-step reversible addition–fragmentation chain-transfer polymerisation using a bis-functional chain-transfer agent ensured controlled and symmetrical growth of the blocks. Tailoring the monomer ratio in the chain-extension step enables the production of copolymers with varying hard/soft block ratios, allowing for tuning of the mechanical properties of the elastomers. Their high thermal stability and the absence of temperature-induced cross-links further enable the remoulding of the rubber without any losses of mechanical properties.