Experimental Test of Associative Bond Exchange Models in Imine Vitrimers: The Importance of Decoupling of Segmental and Bond Exchange Dynamics

Vitrimers, polymer networks with dynamic covalent bonds, have received much attention in the past decade due to potential applications in recycling, self-healing, and the circularity of materials. However, understanding how bond exchange is influenced by segmental dynamics is still a knowledge gap for the diverse chemistries and architectures being investigated. Recently, a theoretical model was developed to describe the associative bond exchange mechanism for vitrimers, which considers the additive contribution of a local chemistry-specific exchange event and a local unbinding process. To experimentally test the model, a series of precise imine vitrimers was synthesized from trialdehydes and diamines with ethylene or ethylene glycol repeating units between dynamic cross-links. Shear rheology and dielectric spectroscopy were employed to characterize the bulk relaxation time scale and segmental dynamics, respectively, over a wide temperature range above the vitrimer glass transition temperature ( T g ). Non-Arrhenius upturns of the bulk relaxation are exhibited when the temperature approaches T g, agreeing with a 2-step model for associative bond exchange. However, the model demonstrates some discrepancies with the experimental data near T g . The incorporation of a relaxation–diffusion decoupling coefficient into the theoretical framework provides better agreement with experimental data, highlighting the importance of decoupling in the segmental dynamics contribution to the bond exchange process.