Novel ternary molecular composites prepared by a sol-gel process and their conversion into microcellular foams

A carboxylated polysulfone (C-PSF) was reacted with 3-(glycidoxypropyl)trimethoxysilane (GPS) in a sot-gel reaction to form hybrid networks. Specifically, GPS was grafted to the C-PSF chains at their epoxy ends by ring-opening reactions and then the methoxy silane groups at their other ends were crosslinked through the usual hydrolysis and condensation reactions. These C-PSF/GPS cross-linked binary networks are of interest in their own right, but this type of network was also used in the incorporation of polybenzimidazole (PBI) rigid-rod polymer to form a C-PSF/PBI/ GPS ternary composite. In this case, the network structures obtained by carrying out the same reaction in the presence of PBI chains successfully suppressed their undesirable segregation within the composite. The transparencies of the preparative solutions and the dried films indicated that the dispersion of PBI was maintained in these environments, presumably at the nano- or molecular level. The ternary composites were characterized using Fourier-transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), thermal mechanical analysis (TMA), and thermogravimetric analysis (TGA). Some of these composites were converted to closed-cell microcellular foams, which were then characterized in a preliminary way with regard to their morphologies.