Synthesis and properties of novel polybismaleimide oligomers

Two kinds of novel polybismaleimide oligomers containing urethane linkages in the backbone (BMU-H and BMU-T) have been prepared via Diels–Alder reaction of 4,4′-(bismaleimidodiphenyl) methane (BMI) with different bisfuranylmethylcarbamate. The Diels–Alder reaction was carried out in the mixture of 1,4-dioxane and toluene, the DA products were aromatized in the presence of acetic anhydride to form polybismaleimide oligomers BMU-H and BMU-T. All the DA products and polybismaleimide oligomers were characterized by element analysis, FTIR and 1H-NMR spectral studies. The curing behavior of these polybismaleimide oligomers was investigated by using DSC, their curing temperature is in the range of 187–266°C with a ΔH=178 J/g for BMU-H and 206.9 J/g for BMU-T, the apparent activation energy is 101.2 kJ/mol for BMU-H and 105.1 kJ/mol for BMU-T. By using these polybismaleimide oligomers as toughness modification agent, BMU-H or BMU-T was mixed with BMI in different ratios to prepare a series of modified bismaleimide resins. The gel time at 180°C and storage stability of these modified bismaleimide resins as well as the thermal properties of these cured modified bismaleimide resins were investigated in detail. Glass fiber reinforced composites without voids have been prepared by using these modified bismaleimides as matrix resin; the flexural strength is in the range of 400–460 MPa.