Journal of Applied Polymer Science, Vol.74, No.14, 3365-3375, 1999
Blends of bisphenol A-based cyanate ester and bismaleimide: Cure and thermal characteristics
A dicyanate ester, namely, 2,2-bis-(4-cyanatophenyl)propane, and a bismaleimide, namely, 2,2-bis[4-(4-maleimido phenoxy)phenyl]propane, possessing closely resembling backbone structures, were cured together to derive bismaleimide-triazine network polymers of varying compositions. The blend manifested a eutectic melting behavior at a 1 : 1 composition with a eutectic melting point of 15 degrees C. The cure characterization of the blends was done by DSC and dynamic mechanical analyses (DMA). The near simultaneous cure of the blend could be transformed to a clear sequential one by catalyzing the dicyanate cure to lower temperature using dibutyl tin dilaurate. The two-stage, independent cure of the components of the blend evidenced in DSC was confirmed by DMA. The cure profile of the bismaleimide component predicted from the kinetic data derived from nonisothermal DSC was found to be in league with the isothermal DMA behavior. Both techniques led to optimization of the cure schedule of the blends. The cured polymers were characterized by FTIR and TGA. The cured blends underwent decomposition in two stages, each corresponding to the polycyanurate and polybismaleimide. Enhancing the bismaleimide component did not alter the initial decomposition temperature, but led to reduced rate of thermal degradation at higher temperature. Interlinking of the two networks and enhancing crosslink density through coreaction of the blend with 4-cyantophenylmaleimide unaffected the initial decomposition properties but was conducive for increasing the char residue significantly. Computation of activation parameters for the thermal decomposition of the polymers confirmed that the first step in the degradation of the blends is caused by the polycyanurate component.