Network Topology and Associative Bond Exchange Control the Viscoelastic Response of Elastomeric and Glassy Vitrimer

Vitrimers are covalently cross-linked polymer networks capable of topological rearrangement through associative dynamic bond exchange while preserving network connectivity. This poster examines how network structure and dynamic exchange influence (I) polybutadiene (PB) and (II) polystyrene (PS) vitrimers. PB vitrimers with dioxaborolane linkages (glass transition temperature T_g < 0 °C) were synthesized via thiol–ene photochemistry. Cross-link density was quantified through a network disassembly procedure followed by ¹H nuclear magnetic resonance spectroscopy. Increasing cross-link density elevated glass transition temperature and plateau modulus, consistent with reduced structural defects relative to permanent networks. PS vitrimers with imine linkages (T_g > 100 °C) were synthesized with varying amine-to-aldehyde ratios to tune bond exchange dynamics. The kinetics of PS chain cross-linking in solution were evaluated as a function of the solvent polarity and amine-to-aldehyde ratio. Dynamic light scattering was used to investigate how the imine linkages affected the diffusion and microscopic relaxations of the PS chains. Bulk linear rheology measurements revealed distinct high- and low-frequency relaxation modes associated with fast segmental relaxation and dynamic cross-link exchange, respectively, with the latter accelerating at higher amine content.