Bio-based thermosetting resins composed of cardanol novolac and bismaleimide

Cardanol novolac (CDN) was synthesized by the reaction of cardanol (CD) and paraformaldehyde in the presence of oxalic acid. The prepolymerized compounds of CD/4,4'-bismaleimidediphenylmethane (BMI) and CDN/BMI with CD/maleimide unit ratios 1/2, 1/4 and 1/6 at 200 degrees C were finally compression-molded at 250 degrees C for 5 h to produce cured CD/BMI (cCD/BMI) and cured CDN/BMI (cCDN/BMI) resins. Although the proton nuclear magnetic resonance (H-1-NMR) and Fourier transform infrared spectroscopy (FTIR) analyses of the model reaction product of CD and N-phenylmaleimide (PMI) at 200 degrees C for 8 h suggested the occurrence of the ene reaction and subsequent Diels-Alder reaction, the FTIR analysis of cCD/BMI and cCDN/BMI suggested the occurrence of the ene reaction and addition copolymerization. The cCD/BMI and cCDN/BMI with CD/maleimide ratio lower than 1/2 did not show glass transition until 300 degrees C and had a 5% weight loss temperature higher than 450 degrees C. The cCD/BMI and cCDN/BMI with CD/maleimide ratio 1/4 showed the most balanced flexural properties (flexural strength 60-80 MPa, flexural modulus 2.0-2.5 GPa).