New chain-extended bismaleimides with aryl-ether-imide and phthalide cardo skeleton (I): Synthesis, characterization and properties

Abstract

New aryl-ether-imide/phthalide-containing bismaleimide oligomers (MPEIBMI) with different molecular weight were designed and synthesized by adjusting the addition amount of diamine compound derived from o-cresolphthaleine, and dianhydride 4,4′-(4,4′-isopropylidene diphenoxy)-bis(phthalicanhydride) (mole ratio: 1.25/1.5/2.0). The chemical structures of the oligomers and their intermediate compounds were confirmed by Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (1H and 13C NMR) spectroscopy and elementary analysis. X-ray diffraction (XRD) results showed a blunt diffraction peak, suggesting an amorphous structure. The oligomers exhibited good solubility in a variety of common organic solvents. The heat flow curves of the oligomers measured by differential scanning calorimeter (DSC) displayed a broad curing exothermic peak. The thermal stability and thermal mechanical properties of the cured resins were investigated by thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). The results indicated that the introduction of phthalide cardo structure and imide rings into the polybismaleimide network could effectively improve the thermal properties. The glass transition temperature and initial thermal decomposition temperature were above 260°C and 423°C, respectively, and the residual weight percentages at 700°C were all >58%. The mechanical tests revealed that the cured MPEIBMI films had excellent tensile strength and good retention at the temperatures above 200°C.