Microdynamics in Vitrimers During Curing

While permanent crosslinks provide materials with impressive mechanical, chemical, and thermal properties, they prevent the network from being reprocessed. In a vitrimer, crosslinks undergo externally triggered dynamic bond exchange reactions (BERs) when heated sufficiently above the topology freezing transition temperature (T_v). Once above T_v the BERs become fast enough to enable the network to relieve stress and flow, making it reprocessable. Presumably, when vitrimer networks are formed by curing, the fact that BERs become important at temperatures above T_v result in important differences between the microdynamics during isothermal curing at T >T_v as compared to curing at T<T_v. We characterize the curing microdynamics using in situ X-ray Photon Correlation Spectroscopy with samples containing dilute nanoparticles as reporters of the dynamics for a poly (cyclohexene carbonate) vitrimer. Indeed, the curing microdynamics for T > T_v differ qualitatively from those for T < T_v. In particular, the dependence of relaxation time on scattering vector changes with curing time differently for the two cases.