The polysiloxane of formula (I) may be prepared by effecting a co-condensation reaction between a poly(organo-vinyl)siloxanediol and either a polydiorganosiloxanediol (when R1 and/or R2 are an organic group, e.g., methyl) or a poly(organo-fluoroalkyl)siloxanediol (when R1 and/or R2 are fluoroalkyl groups.