Taking advantages of intramolecular hydrogen bonding to prepare mechanically robust and catalyst-free vitrimer

Fabrication of mechanically robust and catalyst-free vitrimers is of great importance, but often challenging. Herein, a facile strategy to achieve this goal by incorporation of intramolecular hydrogen bonds into the dynamic covalent network is demonstrated. Specifically, glycidyl methacrylate (GMA) is reacted with bio-renewable malic acid (MA) to generate a UV-curable resin containing ester linkages. On account of the proximity between the alpha-carbonyl and beta-hydroxyl groups in MA, six-membered-ring intramolecular hydrogen bonds (O-H center dot center dot center dot O=C) are formed in the cross-linked network. This formation of intramolecular hydrogen bonds endows the network with enhanced and outstanding mechanical properties, showing tensile strength and Young's modulus of 117.7 MPa and 3.66 GPa, respectively. Meanwhile, the network is able to efficiently alter its topology without external catalyst through transesterifications reactions at high temperatures. We attributed this phenomenon to the presence of intramolecular hydrogen bonds which make the alpha-carbonyl carbon more positive and be more reactive towards nucleophilic attack, and thus facilitate the transesterification reaction. This work suggests a promising route to achieve catalyst-free thermosets with superior mechanical performances, good self-healing ability and reprocessability.