Bio-based thermosetting bismaleimide resins using eugenol, bieugenol and eugenol novolac

Abstract

5,5′-Bieugenol (BEG) and eugenol novolac (EGN) were synthesized by the oxidative coupling reaction of eugenol (EG) and the addition–condensation reaction of EG with formaldehyde, respectively. The EG, BEG and EGN were prepolymerized with 4,4′-bismaleimidediphenylmethane (BMI) at 180°C and then compression-molded at finally 250°C for 6h to produce cured EG/BMI (EB), BEG/BMI (BB) and EGN/BMI (NB) resins with eugenol/maleimide unit ratios of 1/1, 1/2 and 1/3. The FT-IR analysis of EBs and 13C NMR analysis of the model reaction product of EG/N-phenylmaleimide (PMI) 1/3 at 200°C for 12h suggested that the ene reaction and subsequent Diels-Alder/ene reactions mainly occurred for EBs. The FT-IR analyses of BBs and NBs supported the occurrence of ene reaction and subsequent thermal addition copolymerization in a similar manner to the well-known curing reaction of 2,2′-diallylbisphenol A and BMI. The glass transition temperature (Tg) and 5% weight loss temperature (T5) of the cured resin increased with increasing BMI content, and EB 1/3 showed the highest Tg 377°C and T5 475°C. The flexural strengths and moduli of EBs and NBs were higher than those of BBs, and EB 1/2 showed the most balanced flexural strength and modulus (84.5MPa and 2.75GPa). The FE-SEM analysis revealed that there is no phase separation for all the cured resins.