Molecular composites by incorporation of a rod-like polymer into a functionalized high-performance polymer, and their conversion into microcellular foams

Molecular composites were prepared from sulfonated modifications of polysulfone and polyphenylsulfone by incorporating relatively stiff polybenzimidazole (PBI) chains into them. The composites were characterized by Fourier-transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC), thermal mechanical analysis (TMA), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The FT-IR results demonstrated strong specific interactions between the sulfonated polymers and the PBI, which was presumed to be the reason for the enhanced miscibility observed. Miscibility was also indicated in the DSC and TMA results, by the presence of a single glass transition temperature (which was composition dependent), although there did appear to be a small degree of phase separation. TGA results showed improvements in the thermal stability of the polymer matrix because of the incorporation of PBI. Results from SEM were also consistent with considerable miscibility. Microcellular foams processed from these molecular composites had partial open-cell cell structures, with average cell sizes ranging from 0.2 to 5 μm, in unusual bimodal cell-size distributions.