The preparation and hydrosilylation crosslinking of well-defined vinyl and allyl polydiethylsiloxane (PDES) telechelics are described. End functionalization has been achieved by using divinyltetramethyldisiloxane as a chain stopper during the cationic polymerization of hexaethylcyclotrisiloxane or by anionic polymerization of hexaethylcyclotrisiloxane with allyllithium followed by end capping with allyldimethylchlorosilane. Hydrosilylation crosslinking yielded model PDES networks which have been characterized by equilibrium swelling, determination of the sol fraction, differential scanning calorimetry and wide angle X-ray diffraction.