Exploring the Cure State Dependence of Relaxation and the Vitrimer Transition Phenomena of a Disulfide-Based Epoxy Vitrimer

Abstract

Vitrimers are a class of polymer networks featuring dynamic covalent crosslinks that can undergo associative bond exchange. These dynamic polymer networks hold a notable promise as recyclable thermosets with self-healing capabilities, provided by network rearrangements at the molecular level, allowing for macroscopic flow. When the relaxation time is sufficiently short, vitrimer material behaves like a thermoplastic even though it is covalently crosslinked. However, temperature-induced malleability remains limited by the high-viscous nature of vitrimers. Therefore, the present article explores the cure dependence of structural relaxation and vitrimer transition phenomena of a dynamic disulfide-containing epoxy vitrimer. Stress relaxation measurements reveal that intermediate cure states—accompanied by lower crosslinking density—exhibit bond exchange and segmental relaxation rates exceeding those of fully cured networks over an order of magnitude. This enhanced dynamics facilitates lower viscosities and residual times during high-temperature malleability processing. Advanced methods combining rheology, cure kinetics, and thermomechanical analysis are utilized to assess the cure dependence of the vitrimer transition temperature (Formula presented.). We outline a distinct cure dependence of (Formula presented.), which may be approximated by a linear correlation, suggesting that viscoelastic flow can be initiated at significantly lower temperatures in undercured networks. These findings provide valuable guidance for enhancing material and processes, contributing to opening doors to the “melt processing” of this family of materials.