Silicon hydride compounds consisting of silicon and hydrogen constitute a fascinating class of silicon-based polymers because of their ability to form high-quality silicon film by solution-based process. In this study, we synthesize polydihydrosilane by photo-induced ring-opening polymerization of cyclopentasilane, and determine the molar mass, radius of gyration, and intrinsic viscosity of it in cyclohexene by size-exclusion chromatography combined with multi-angle laser light scattering and viscometry. It was found that the molar mass of polydihydrosilane ranges broadly from 10(2) to 10(6) g/mol. Both the intrinsic viscosity and radius of gyration exhibited a scaling behavior with respect to the molar mass with the intrinsic viscosity exponent alpha = 0.206 and radius of gyration exponent v = 0.410. Classification of the polymer structure based on the alpha value suggests that the polydihydrosilane forms a branched-chain structure with a particle-like compact shape rather than a straight chain. (C) 2012 Elsevier Ltd. All rights reserved.