The reaction of heterofunctional condensation of organodichlorosiloxycyclotri(tetra, penta) siloxanes and organodichlorosililcarbocyclotrisiloxane with dihydroxydimethylsiloxanes in the presence of pyridine was investigated. It was shown that at small lengths of the linear dimethylsiloxane link (n less than or equal to 4) the reaction of heterofunctional condensation runs both intermoleculary with formation of polymers and intramoleculary with formation of bicyclo-organosiloxanes. It was established that insertion of cyclic fragments in the side chain hinders the chain transfer reactions that proceed with release of the D-type cycles during thermal depolymerization. The conformational and hydrodinamic properties of some polymethylsiloxane copolymers with cyclosiloxane fragments in the side chain have been studied.