The catalytic dehydrocondensation reaction of alpha,omega-bis(trimethylsiloxy)methylhydridesiloxane and of alpha,omega-bis(trimethylsiloxy)methylhydridesiloxane-dimethylsiloxane with alpha-hydroxy-omega-trimethylsiloxydiorganosilylenes, in the presence of anhydrous caustic potassium, at 1:35 and 1:33 ratio of initial compounds has been investigated and polyorganosiloxanes with rigid polydiorganosilylenes fragment in the side chain, completely soluble in organic solvents, have been obtained. The catalytic dehydrocondensation reaction order, activation energies, and rate constants have been determined. The synthesized copolymers were characterized by thermogravimetric, gel permeation chromatographic, differential scanning calorimetric, and wide-angle X-ray analyses. It was shown that during modification of alpha,omega-bis(trimethylsiloxy)methylhydridesitoxane-dimethylsiloxane with alpha-hydroxy-omega-trimethylsiloxydiorganosilylenes in synthesized block-copolymers, microdomain structure (phase incompatibility) was observed. (c) 2007 Wiley Periodicals, Inc.