The synthesis of a series of side-chain liquid crystalline siloxane copolymers is reported, and comparative studies of physical properties of members of the series with different side-chain length have been attempted. All the five members show smectic C* and smectic A phases. Measurements of ferroelectricity, relaxation times and electroclinic properties have been carried out, aiming at finding structure-property relationships for the longer side-chain members. A relationship between electroclinic coefficient and side-chain length was also found.