Preparation and properties of modified bismaleimide resins by novel bismaleimide containing 1,3,4-oxadiazole

Bismaleimide (BMI) resin is a high-performance thermosetting polymer, but its inherent brittleness hinder a broader range of application. Therefore, it has aroused wide concern to improve the toughness of BMI resins without scarification of their thermal stability. This paper reported some studies on modified BMI resins based on diallyl bisphenol A, novel BMI monomers, e.g. 2-[3-(4-maleimidophenoxy)phenyl]-5-(4-maleimidophenyl)-1,3,4-oxadiazole (m-Mioxd) or 2-[4-(4-maleimidophenoxy)phenyl]-5-(4-maleimidophenyl)-1,3,4- oxadiazole (p-Mioxd) in different proportions (0.87:1, 1:1, 1.2:1; mol/mol). The curing mechanism and kinetics of the copolymerized systems were investigated by differential scanning calorimetry and Fourier transform infrared spectroscopy. Thermogravimetric analysis was applied to study the thermal properties of the cured resins, and the results indicated that the modified resins had excellent thermal stability with high residual weight percentage at 700 degrees C (>50%), temperatures for 5% weight loss around 400 degrees C. Besides, N,N-4,4-bismaleimidodiphenylmethylene and O,O-diallyl bisphenol A resin blends were modified by m-Mioxd and p-Mioxd, respectively. We investigated the effects of mole concentration of m-Mioxd or p-Mioxd on the curing process, mechanical properties, fracture toughness, and heat resistance of the modified resins. The results revealed that the introduction of m-Mioxd and p-Mioxd could improve the impact property of the modified BMI resins. When their proportion was 0.07, the impact strength increased 123.8% and 108.3%, respectively. The novel chain-extended BMIs could reduce the crosslink density of cured resins and improve the brittleness effectively. Copyright (c) 2015 John Wiley & Sons, Ltd.