A new family of hyperbranched polymers with chemical bonds between the hyperbranched polyimide and polysilsesquioxane network was synthesized by the reaction of an amine-terminated aromatic hyperbranched polyimide with 3-glycidoxypropyl trimethoxysilane, followed by hydrolysis and polycondensation in the presence of an acid catalyst. The hyperbranched poly(imide silsesquioxane) membranes were fabricated by the casting the aforementioned polymer solution onto a NaCl optical flat, which was followed by heating at 80 degreesC for 24 h. The membranes were characterized by Fourier transform infrared, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, N-2 adsorption and desorption, and CO2 adsorption and desorption. The presence of covalent bonds between the hyperbranched polyimide and polysilsesquioxane segments had a significant effect on the properties of the membranes. N-2 adsorption-desorption isotherms for these membranes showed surface areas of 6-16 m(2)/g, whereas CO2 adsorption-desorption isotherms showed much higher surface areas in the range of 106-127 m(2)/g. (C) 2003 Wiley Periodicals, Inc.