Bio-based thermosetting bismaleimide resins using cardany linolenate and allyl cardanyl ether

Abstract

Cardanyl linolenate (CDLN) and allyl cardanyl ether (ACDE) were synthesized from cardanol (CD) which is one of the inexpensive natural resources. Prepolymerized compounds of CDLN/4,4′-bismaleimidodiphenylmethane (BMI) and ACDE/BMI with the molar ratios of 1/2, 1/2.5 and 1/3 at 200°C were compression-molded at 250°C to produce cured CDLN/BMI and ACDE/BMI resins (cCDLN/BMI and cACDE/BMI), respectively. The thermal and mechanical properties of cCDLN/BMI and cACDE/BMI were investigated in relation to the difference of reactivity between the linolenate group of CDLN and the allyl group of ACDE. The 1H NMR and mass spectral analyses of the reaction product of methyl linolenate and N-phenylmaleimide (PMI) revealed that PMI-rich oligomer was produced by the addition copolymerization. FT-IR analyses of cCDLN/BMI and cACDE/BMI revealed that the terminal olefins have a higher reactivity toward the addition copolymerization or ene reaction with maleimide groups than the internal olefins. Although some components which were not incorporated into the polymer networks for cCDLN/BMIs caused a little reduction of storage modulus (E′) before the glass transition starts, E′s of cACDE/BMIs did not decrease until the glass transition starts at ~300°C. The 5% weight loss temperatures (444–453°C) of cACDE/BMIs were higher than those (327–426°C) of cCDLN/BMIs. Also, cACDE/BMIs displayed much better flexural properties than cCDLN/BMIs. The fact that cACDE/BMIs showed better thermal and mechanical properties was attributed to a higher functionality (1.41) of terminal olefins for ACDE than that (0.41) for CDLN.