Liquid-crystalline compounds having carbon—carbon double bonds were synthesized and subjected to hydrosilylation using poly(hydrosiloxane)s as silylating agents and hexachloroplatinic acid as a catalyst. Even though the silylating agents were polymeric and the mesogenic compounds carried bulky groups as their side chains, the presence of a spacer (polymethylene chain) diminished the steric hindrance and the reaction was possible. Among the mesogens 1-(4′-allyloxybenzoyloxy)-4-(4″-methoxybenzoyloxy)phenylene is a new compound, and its synthesis is described in detail. The final products were side-chain-type liquid-crystalline polymers, that is, mesogenic group-grafted poly(siloxane)s, and a few of their liquid-crystalline properties are also elucidated.