Enriching an Exchangeable Network with One of Its Components: The Key to High-Tg Epoxy Vitrimers with Accelerated Relaxation

The curing of epoxy-anhydride vitrimers involves anionic copolymerization of epoxide and anhydride along with anionic homopolymerization of excess epoxide, giving rise to a poly(ester-co-ether) network. By monitoring curing using infrared spectroscopy in different conditions and mapping the presence of OH groups, we demonstrate that generation of hydroxide groups, necessary for transesterification, exclusively relies on side reactions induced by protic impurities and water. To increase the yield in esters and hydroxides, without depressing the thermal properties, we enrich the network with one of its components, DHEBA (bisphenol A bis(2,3-dihydroxypropyl) ether), potentially available from hydroxylation of the starting epoxy monomer as well as from chemical recycling of the final vitrimer network. In the DHEBA-enriched network, the modulus drop associated with the alpha transition occurs at higher temperatures and more steeply than in the pristine network, demonstrating better homogeneity together with improved heat resistance and 3-fold shortened relaxation time throughout the 140–180 °C range.