Dynamic transfer auto-catalysis of epoxy vitrimers enabled by the carboxylic acid/epoxy ratio based on facilely synthesized trifunctional monoesterified cyclic anhydrides

Abstract

Vitrimers based on transesterification exhibit reprocessable and amendable features, but highly rely on external catalyst to accelerate the stress relaxation and network rearrangement. Here we prepared reprocessable auto-catalyzed epoxy vitrimers via introducing dynamic transferrable monoesterified cyclic anhydrides into cross-linked networks. Two trifunctional monoesterified cyclic anhydrides MT and ST were facilely synthesized by catalyst-free melting reaction of maleic anhydride and succinic anhydride with trimethylolpropane, respectively, and were utilized to cure the bisphenol A epoxy DER 331. The excess monoesterified anhydrides (containing catalytic carboxyl groups) grafted in the cross-linked networks could undergo dynamic reversible reactions to transfer from one site to another, as a result, the transesterification at different sites of the networks could be effectively catalyzed. The dynamic transfer of catalytic group followed two mechanisms:i) removal-monoesterification of cyclic anhydrides and ii) transesterification of monoesterified cyclic anhydrides with hydroxyl group. In addition to the excellent reprocessability and rapid stress relaxation, the auto-catalyzed epoxy vitrimers presented high glass transition temperatures of ~110 °C, Young’s modulus of ~3103 MPa and tensile strength of ~70.6 MPa. This dynamic transfer catalysis will provide a new idea to accelerate the stress relaxation and network rearrangement of vitrimers.