Influence of Segmental Dynamics on Bond Exchange in Imine Vitrimers with Different Polymer Backbones and Cross-Linkers

Compared with permanent covalent bonds, dynamic bonds allow for the rearrangement and processability of polymer networks through the bond exchange. In recent years, the study of vitrimers has received much attention including self-healing, adhesion, and recyclability of polymeric materials. However, the understanding of how the underlying polymer segmental dynamics impact the bond exchange process both near and far from the glass transition remains a knowledge gap. Acrylic imine vitrimers with different glass-transition temperatures but the same dynamic cross-linker were investigated to understand the effect of segmental motion on dynamic bond exchange. The dynamic cross-linker was then varied in terms of length and flexibility to understand how the chemistry of the cross-linkers affects the segmental and bond exchange dynamics, characterized by oscillatory shear rheology and dielectric spectroscopy. Two theoretical models originally describing the dynamics of associative bond exchange in polymers with the same mathematical expression were applied to the present vitrimers. The theoretical frameworks agree well with experimental results and provide a method to quantify the role of bond exchange activation energy, kinetics, as well as an overall contribution of both cross-linker diffusion and the local unbinding on bulk relaxation. This work provides insights into how different aspects of vitrimer design will lead to their macroscopic dynamic properties.