Mechanical Insights into Hybrid Vitrimer Network Behavior

Vitrimers fall under the purview of associative covalent adaptive networks, enabling them to undergo topology-altering bond exchange reactions as a response to external stimuli such as temperature. This ability allows these networks to exhibit desirable properties like reprocessability, extreme stretchability, and self-healing while maintaining their solvent resistance and crosslinking density. Vitrimers have also been observed to undergo bond exchanges on applying stress below the glass transition which significantly reduces their operational capabilities. One method to improve their mechanical response at low temperatures is by creating hybrid vitrimer networks consisting of dynamic and permanent covalent linkages. The primary objective is to determine a critical concentration of the dynamic bonds that would suppress the low-temperature creep while retaining the self-healing and reprocessability of vitrimer networks. In this study, we use a hybrid Molecular Dynamics – Monte Carlo model to study the dynamics of glassy hybrid vitrimer networks with different reactive sites while subjecting them to triaxial stretching experiments and comparing their behavior to permanently crosslinked networks. Our results show that vitrimer networks under triaxial stress successfully relax stress through bond exchange reaction even in the glassy regime. The networks exhibit crazing through the bulk before undergoing ultimate failure. Also, for these hybrid vitrimers, the strain at fracture is a direct function of the number of available reactive sites in the network.