Dynamic Transfer Auto-catalysis of Epoxy Vitrimers Enabled by the Carboxylic Acid/epoxy Ratio based on Facilely Synthesized Trifunctional Monoesterified Cyclic Anhydrides

Yanlin Liu, Songqi Ma*, Qiong Li, Sheng Wang, Kaifeng Huang, Xiwei Xu, Binbo Wang, Jin Zhu

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.