Synergistic improvements in the processability and mechanical properties of cyanate esters via aminobenzonitrile-induced chemical tailoring

Abstract

The high curing temperature and long curing cycle severely reduce the processability of cyanate ester (CE) resins and increase production costs. To lower the curing temperature and save costs, prevalent catalysts are normally used, but they frequently result in detrimental effects on the mechanical, dielectric, and thermal properties of the resin. In this study, aminobenzonitrile homologues (ABN_x) were developed to facilitate the curing of bisphenol E cyanate ester (BECE). The amino group within ABN_x functioned as a catalyst to accelerate the curing reaction, while the cyano group within ABN_x engaged in copolymerization with BECE. Therefore, the curing temperature of BECE could be tailored by varying the type and quantity of introduced ABN_x. Among the homologues, meta-aminobenzonitrile (ABN₃) demonstrated the highest reactivity based on the quantum chemical calculation. As a result, the largest reduction of curing temperature of BECE is 100 °C (from 250 °C to 150 °C). Meanwhile, the excellent mechanical properties of BECE were maintained and even improved. The addition of ABN_x up to 15 wt% did not compromise the viscosity of BECE (≤203 mPa s at 30 °C), maintaining it at an optimal level for liquid moulding. Furthermore, the short-beam shear strength and the flexural strength of the quartz fiber reinforced BECE composites were improved by 71% and 37% after incorporating 7 wt% ABN_x, respectively. The current study offers a promising strategy for synergistically enhancing both the processability and mechanical properties of CE resins and their composites in a cost-effective manner.