High-temperature composites were successfully prepared from aminated polysulfone, polyphenylsulfone, and a rod-like polymer polybenzimidazole (PBI). The single glass transition temperature T-g and the absence of evidence for phase separation in scanning electron microscopy suggested that these systems formed so-called 'molecular composites'. The enhanced miscibility between the polymer pairs was probably due to hydrogen bonding interactions. Compared with the matrix polymers themselves, these composites have improved values of T-g and thermal stability due to a synergistic effect upon incorporation of polybenzimidazole into the polymer matrices. Microcellular foams were successfully prepared from these composites. The foaming behavior and morphologies of the resulting composite foams were much more complicated than those of the pure polymers. In particular, they had unusual bimodal cell size distributions, and some open or partially open-cell structures. (c) 2005 Elsevier Ltd. All rights reserved.