Epoxy Vitrimers: The Effect of Transesterification Reactions on the Network Structure

Abstract

Vitrimers are covalently crosslinked polymers that behave as conventional thermosets below the glass transition temperature (T g ) but can flow above a particular temperature, T v > T g , by bond exchange reactions. In epoxy vitrimers, transesterification reactions are responsible for their behavior at T > T v that enables flow, thermoforming, recycling, self-healing and stress relaxation. A statistical analysis based on the fragment approach was performed to analyze the evolution of the network structure of epoxy vitrimers during transesterification reactions. An analytical solution was obtained for a formulation based on a diepoxide and a dicarboxylic acid. A numerical solution was derived for the reaction of a diepoxide with a tricarboxylic acid, as an example of the way to apply the model to polyfunctional monomers. As transesterification acts as a disproportionation reaction that converts two linear fragments (monoesters) into a terminal fragment (glycol) and a branching fragment (diester), its effect on network structure is to increase the concentration of crosslinks and pendant chains while leaving a sol fraction. Changes in the network structure of the epoxy vitrimer can take place after their synthesis, during their use at high temperatures, a fact that has to be considered in their technological applications.

Dynamic Covalent Bonds in Polymeric Materials

“…Since this ground‐breaking discovery, TE has been applied to generate different vitrimeric materials . A few theoretical and mechanistic studies on TE vitrimers have been reported …”

Dynamic Covalent Bonds in Polymeric Materials

“…Since this ground‐breaking discovery, TE has been applied to generate different vitrimeric materials . A few theoretical and mechanistic studies on TE vitrimers have been reported …”

Vitrimers: directing chemical reactivity to control material properties

“…This inuence has been very-well exemplied by Dušek and co-workers 61 in an old study dealing with epoxy thermosets, lately resituated in the context of vitrimers by Williams and co-workers. 62 These two studies are highly relevant for the understanding of epoxy ester vitrimers since they take into account many known side reactions that could potentially occur in the case of (off)-stoichiometric formulations. These in-depth studies especially highlight the impact that the complete reactivity prole can have on material properties, with a special focus on the network formation itself (under off-stoichiometry conditions), and how this inuences reprocessing at high temperature over longer reaction times.…”