The question is unclear. Polymerizations give a distribution for which the molecular weight can be determined by size exclusion chromatography. Dividing the number average by the monomer molecular weight will give you an average degree of polymerization, i.e. the number of monomers making up the polymer (on average). PDMS is usually made by ring opening polymerization using the cyclic tetramer or the condensation reaction of dimethyldichlorosilane. So the answer depends on which monomer was used.