This research was focused on the design and execution of new synthetic routes to low-temperature-curable poly(silarylene-siloxane)polyimides. The synthesis of individual oligoimide and silarylene-siloxane blocks was followed by hydrosilylation polymerization to produce crosslinked copolymers. The silarylene-siloxane and polyimide blocks were structurally characterized by IR and H-1 NMR spectroscopy and size exclusion chromatography. The high-temperature resistance of the copolymers was evaluated through the measurement of heat distortion temperatures (T-HD'S) via thermomechanical analysis and by the determination of the weight loss at elevated temperatures via thermogravimetric analysis. Glass-transition temperatures (T-g's) of the silarylene-siloxane segments were measured by differential scanning calorimetry. Hydrosilylation curing was conducted at 60 degrees C in the presence of chloroplatinic acid (H2PtCl6). The copolymers displayed both high-temperature resistance and low-temperature flexibility. We observed T-g of the silarylene-siloxane segment as low as -77 degrees C and THD of the polyimide segment as high as 323 degrees C. The influence of various oligoimide molecular weights on the properties of copolymers containing the same silarylene-siloxane was examined. The effect of various silarylene-siloxane molecular weights on the properties of copolymers containing the same oligoimide was also examined. (c) 2005 Wiley Periodicals, Inc.