Non-Arrhenius Upturn in precise imine vitrimers synthesized from multifunctional small molecules

A series of imine vitrimers with precise linker length were synthesized from a trialdehyde and diamines with ethylene oxide (EO) or ethylene to understand how the glass transition temperature (T_g) and segmental dynamics affect bond exchange. Vitrimers with EO chains result in lower T_g compared to those with ethylene, and demonstrate faster terminal relaxation at a fixed temperature. The temperature dependence of terminal relaxation in all vitrimers exhibits a non-Arrhenius upturn close to T_g. Segmental dynamics overlap when normalized by T_g for all systems. The terminal relaxation times overlap for ethylene vitrimers, but not for EO when normalized by T_g. A theoretical model describing the bond exchange dynamics of vitrimers was applied and discrepancies are observed with the experimental data, especially in the temperature range where non-Arrhenius upturns occur. A decoupling parameter is needed to capture the relationship between the terminal relaxation time to the segmental process, and the model can provide reasonable values of bond exchange activation energy, Arrhenius prefactor, and strand diffusion.