Modular Epoxy-Thiol Oligosiloxane Vitrimers

An emergent class of next-generation materials, vitrimers, combines the structural integrity and bulk properties of cross-linked thermosets with the reprocessability of thermoplastics. In this work, a robust vitrimer network was designed to enable fine-tuning of mechanical properties while maintaining ease of synthesis to achieve tough, lightweight, transparent, and compliant materials. Oligosiloxane-based epoxy-thiol networks were synthesized with varying substituents incorporated into the polymer side chains (-methyl, -ethyl, -isopropyl, and/or -phenyl) to elucidate key structure–property relationships that correlate to different thermomechanical properties. Thiol-epoxy reactions are a form of “click” chemistry with minimal side reactions and enable precise control over cross-link density, resulting in networks with easily tunable material properties. Through oligosiloxane side chain modification and thiol network composition, a material set with a diverse range of properties from near-supersoft networks (elastic modulus <250 kPa) to highly stretchable elastomers (>180% strain) was achieved. Additionally, we demonstrated that extended reprocessing can be accomplished at 150 °C with excellent retention of mechanical properties. The vitrimer toolbox and structure–property relationships identified herein provide key insights that will inform further design and optimization of tunable vitrimer networks with utility in composites, soft optoelectronics, and robotics.