Recyclable and Fluorescent Epoxy Polymer Networks from Cardanol Via Solvent-Free Epoxy-Thiol Chemistry

The development of multifunctional polymeric materials from renewable resources is of foremost significance from a sustainable development perspective. In this work, a biobased epoxy monomer (EHCPP) with hard core structures and multi-arms was prepared from cardanol with hexachlorocyclotriphosphazene, followed by epoxidation with m-chloroperoxybenzoic acid (m-CPBA). Then, the epoxy polymer networks were prepared via the curing process of EHCPP with four thiol monomers of different thiol groups. The mechanical and thermomechanical properties, thermal stability, solvent resistance, recyclability characteristics, and optical behavior of the cardanol-based epoxy resins were systematically investigated. The results showed that four epoxy resins (EHCPP-2SH, EHCPP-3SH, EHCPP-4SH, and EHCPP-BDB) not only exhibited excellent solvent resistance in 10 wt % aqueous solutions of NaOH, HCl, and NaCl but also showed intrinsic fluorescence, while only the EHCPP-BDB epoxy resin showed phosphorescence behavior. Recyclability was observed in the EHCPP-BDB polymer network due to the presence of dynamic reversible boron ester bonds. These cardanol-based epoxy-thiol polymer networks open a pathway to explore potential biomass resources for high-performance multifunctional materials as a replacement for petroleum-based thermosets in various industrial applications.