Molecularly designed bio-based phthalonitrile for simultaneous mechanical and thermal reinforcement of bismaleimide resin

A bio-based eugenol-derived phthalonitrile (PN) monomer with allyl groups was synthesized, characterized, and subsequently utilized to modify the bismaleimide (BMI) resins. BMI/PN copolymer were fabricated via melt blending. BMI/PN system reveals a multi-stage curing mechanism involving: (i) an ene reaction between BMI and PN, (ii) homopolymerization of BMI, and (iii) cyclization of PN. This multiple curing mechanism eliminates phase separation and ensures good compatibility between BMI and PN. It also increases cross-linking density, improves toughness, and restricts the thermal motion of polymer chains when heated. The optimized BMI/PN copolymer (BMI: PN = 10:2) exhibited substantial improvements over neat BMI resin, with flexural strength, flexural toughness, tensile strength, and tensile toughness increasing by 194.3 %, 700.7 %, 232.1 %, and 446.9 %, respectively. Moreover, the glass transition temperature ( T g ) and char yield ( Y c ) were elevated by 140 °C and 11.3 %, respectively. This work offers new insights into BMI modification strategies and broadens the application potential of both BMI and PN resins.