Synthesis and characterization of bio-based transesterification catalysts for green 3D-printable dynamic photopolymers

To strive towards high-performance polymers with better sustainability, classical thermosets have to be replaced by materials that are recyclable, repairable or reusable whilst still retaining their excellent mechanical properties. The use of dynamic covalent polymers is one strategy to meet this ambitious aim. Herein, we synthesized organic phosphates derived from bio-based precursors, which efficiently promoted bond exchange reactions between hydroxyl ester links at elevated temperature. The new catalysts were obtained at high yields and were readily soluble in various commercially available photoreactive resins. However, in aiming at the preparation of fully bio-based dynamic photopolymers, the new catalysts were introduced in acrylated linseed oil (AELO). To reduce the viscosity and improve the printability of the AELO resin, acrylated eugenol (AEUG) was synthesized and added to the formulation as a bio-derived reactive diluent. The high cure rate and low viscosity of the resins enabled the fabrication of complex 3D objects via vat photopolymerization 3D printing. Once photocured, the 3D-printed photopolymers comprised ample –OH and ester moieties, which underwent thermo-activated transesterification in the presence of the new catalysts. In particular, photocured networks containing AELO and AEUG in a 1 : 1 weight ratio and 5 wt% of a eugenol-based phosphate exhibited high thermal stability (>200 °C) and were able to relax 63% of the original stress within 65 min at 180 °C. The related elastic material recovery was then exploited to thermally heal and re-shape 3D-printed objects, giving rise to the efficiency and versatility of the newly developed dynamic photopolymers.