Synthesis and properties of chain-extended bismaleimide resins containing phthalide cardo structure

Three novel bismaleimide (BMI) monomers containing phthalide groups in their structures, i.e. 3,3-bis[4-(4-maleimidophenoxy) phenyl] phthalide, 3,3-bis[4-(4-maleimidophenoxy)-3-methylphenyl] phthalide and 3,3-bis[5-isopropyl-4(4-maleimidophenoxy)-2-methylphenyl] phthalide, based on phenolphthalein, o-cresolphthalein and thymolphthalein, respectively, were designed and synthesized. The chemical structures of the monomers were confirmed from H-1 NMR and C-13 NMR spectroscopy and Fourier transform infrared spectroscopy. These monomers exhibit good solubility in common organic solvents, enabling easy solution processing. The thermal curing behavior of the monomers was investigated using differential scanning calorimetry, displaying broad exothermic peaks and large thermal processing windows. Thermogravimetric analysis and dynamic mechanical analysis were used to characterize the thermal stability and thermal mechanical properties of the resulting BMI resins. The results, in contrast to bisphenol A-based BMI resin, indicate that the incorporation of the phthalide structure into the polybismaleimide network can effectively improve the thermal properties. Water absorption tests of the cured products demonstrate the chemical structure has an effect on moisture resistance. (C) 2010 Society of Chemical Industry