Unveiling the Multiscale Dynamics of Polymer Vitrimers Via Molecular Dynamics Simulations

The multiscale dynamical behaviors of reversible cross-linked networks (vitrimers) are investigated using coarse-grained molecular dynamics simulations, revealing that these behaviors have different dependencies on temperature and bond swap energy barriers. The simulation model displays significantly slower bond exchange rates compared with segmental relaxations. Short-time segmental scale mobility and relaxation are relatively unaffected by bond exchange, while whole-chain scale relaxation or long-time mobility is more constrained. Specifically, increasing the temperature reduces the dynamical heterogeneity and accelerates segmental relaxations, rendering the time-temperature superposition principles (TTSP) ineffective. The universal correlations between different dynamical behaviors of vitrimers, such as chain segmental relaxations, short-time vibration, and dynamical heterogeneity, are deduced. The comparable rates of chain length scale relaxation and bond exchange influence each other, leading to the breakdown of the TTSP and time-energy barrier superposition principles (TESP). By rational design, the bond exchange scale and whole chain relaxation scale can be tailored to become separated, which provides guidelines for the design of dynamic covalent or noncovalent polymer materials combining fast self-healing and good stability.