Design of a Low-Temperature Ring-Opening Benzoxazine System Using a Supramolecular Hydrogen-Bond Structure
Phenolic derivatives capable of reducing the ring-opening temperature of benzoxazine resin have gradually emerged as valuable modules for benzoxazine chemistry, not to mention their good compatibility, coreactivity, and network modifiability. However, the previously reported unsatisfactory promotion effects, unclear reaction mechanisms, and unstable structure have severely limited the development of benzoxazine/phenol systems. Herein, a supramolecular hydrogen-bonded system consisting of resorcinol and 2-aminopyridine benzoxazine (PH-2a) was developed. The PH-2a/resorcinol mixture system with an equivalence ratio of 1:1 exhibited a dramatic reduction in ring-opening peak temperature (Tp) from 283 to 110 °C. Experimental combined with computational investigations supported its supramolecular H-bond behavior. Based on the cross-comparison of PH-2a analogues and other diphenols, the critical roles of H-bonding interactions both in activating reactants and inducing a directional reaction were revealed. These H-bonds with appropriate strengths can self-assembly form and close the distance between potential reaction sites, facilitating the direct production of an adduct. In addition, the application potential of the PH-2a/resorcinol system was also prospected, which can promise network tailoring and low-temperature cross-linking by the design flexibility of PH-2a and resorcinol derivatives, opening up possibilities for the preparation of advanced polybenzoxazine resins at low temperature.
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