Synergistic Toughening of Solvent-Free Modified Cyanate Ester Resins for Adhesives and Composites with Enhanced Thermal Stability

Abstract

Novolac cyanate ester (NCE) has the highest thermal stability among commercial cyanate esters but is brittle, and conventional toughening methods often compromise heat resistance. This work developed a solvent-free, multiscale synergistic strategy to modify a hybrid matrix of NCE, bisphenol A cyanate ester, and epoxy (AFG-90H) with poly(ether sulfone), epoxy-terminated nitrile rubber, and core–shell rubber nanoparticles. The optimized formulation, CE2, achieved a 105.7% increase in impact strength while maintaining a glass transition temperature of 267 °C. As a structural adhesive, CE2 reached a shear strength of 21.2 MPa at 25 °C and retained 13.5 MPa at 250 °C. Molecular dynamics simulations identified bulk matrix cohesive yielding, rather than interfacial debonding, as the primary high-temperature failure mechanism. The corresponding glass fiber-reinforced composites achieved a flexural strength of 458.7 MPa and an interlaminar shear strength of 62.4 MPa. This strategy provides a practical route to high-temperature cyanate ester adhesives and composites.