Complete relaxation of thiol-ene vitrimeric elastomers with drastically reduced dynamic content

Abstract

Establishing a balance between polymer flow for reprocessing and mechanical robustness at service temperatures presents a challenge in designing covalent adaptable networks (CANs). In this study, we present a series of thiol-ene vitrimeric materials whose dynamicity is based on disulfide and beta-hydroxyester bonds. Firstly, through a facile epoxy-acid reaction, either a disulfide-containing or disulfide-free allyl precursor was synthesized. Subsequently, the two allyls were mixed in varying proportions and cured by a trithiol crosslinker. A dithiol chain extender was also added into the formulation at varying proportions in order to modify the network architecture and thus regulate dynamicity. The resulting viscoelastic and vitrimeric behavior as influenced by the choice of monomer type and proportion was studied in depth. Results show that disulfide content of as low as 17 % is sufficient to impart full recyclability to these versatile materials. Our tests also revealed that the most significant factor for creep suppression is not the disulfide content but the network connectivity dictated by the average thiol functionality. The cured materials are easily recyclable by heating under pressure, yielding comparable mechanical and thermomechanical properties across several cycles.