How segmental dynamics to affects bond exchange processes in acrylate imine vitrimers

Many studies of dynamic covalent networks have probed stress relaxation far above the glass transition temperature (T_g) where the influence of segmental dynamics is negligible. When approaching T_g, segmental motion slows down significantly and there is a knowledge gap to describe how this impacts the bond exchange process. In this work, imine vitrimers with four different Tg backbones were investigated to understand the effect of segmental motion on bond exchange. Three dynamic crosslinkers were used that varied in terms of length and flexibility to understand how the chemistry of the crosslinkers affects the segmental and bond exchange dynamics. The terminal relaxation at fixed temperature varies only by a factor of ~10 even as the segmental dynamics change by six orders of magnitude with different backbones. Higher T_g polymer backbones lead to a larger apparent activation energy of terminal relaxation with the same crosslinker. A theoretical model for associative bond exchange is applied and agrees well with experimental results, and provides insights on the role of bond exchange activation energy, strand diffusion, and segmental dynamics on terminal relaxation.