Chrysin-Based Bio-Benzoxazine: A Copolymerizable Green Additive for Lowering Curing Temperatures and Improving Thermal Properties of Various Thermosetting Resins
Boran Hao, Jiaqi Wang, Yuan Zhang, Weichen Sheng, Kan Zhang
Abstract
Adding copolymerizable components into thermosetting resins is a common strategy to improve the thermal and mechanical properties of thermosets. However, it remains quite challenging to discover a universal copolymerizable additive that is applicable for various thermosetting systems. Here, the flexible molecular design of benzoxazine allows us to design a biobased benzoxazine monomer (CHR-ac) with several smart functionalities, which can copolymerize with various traditional thermosetting systems, including benzoxazine, epoxy, and bismaleimide resins. CHR-ac has been synthesized using paraformaldehyde, 3-aminophenylacetylene, and natural renewable chrysin as raw materials via the Mannich condensation. Specifically, the built-in intramolecular hydrogen bonding in CHR-ac results in a low polymerization temperature while it still maintains the advantage of long shelf life. In addition, the phenolic hydroxyl and acetylene groups in CHR-ac enable it to cross-link with well-commercialized thermosetting resins and significantly enhance their performance through the formation of highly cross-linked networks. Potentially, the rationally designed biobased benzoxazine in the current work can be used as a generic additive in thermosetting resins for applications spanning from the microelectronic to the aerospace industries.