Tuning Bond Exchange Rate to Control Long-Time Mobility and Creep in Vitrimer-like Networks.

Vitrimers relax stress through a combination of polymer mobility and associative bond exchange, but connecting exchange kinetics to microscopic dynamics and macroscopic rheology remains challenging. Many simulation schemes do not allow independent control of the exchange rate. Here we utilize a molecular dynamics-Monte Carlo simulation technique for associative networks in which the exchange attempt interval is an explicit, independently tunable control parameter, enabling systematic scans of exchange kinetics at fixed network architecture and interactions. Using mean-squared displacement and creep compliance as indicators of the microscopic dynamics and macroscopic rheology, we show that slowing the bond exchange rate delays the onset of long-time mobility and terminal creep without significantly altering short-time local dynamics, indicating a separation between segmental mobility and topology-change relaxation. Time-temperature superposition is obeyed only partially: no single set of shift factors collapses the full microscopic and rheological responses of the associative networks. Direct analysis of the bond-memory relaxation time reveals an approximately Arrhenius temperature dependence, whereas the permanent-network shift factors follow WLF behavior. The resulting mismatch between the polymer-controlled and exchange-controlled clocks causes their relative positions to change with temperature, thereby controlling the crossover from elastic or plateau response to long-time mobility and terminal creep.