a vinyl chloride homopolymer or copolymer composition contains a silane , a compound capable of generating free radicals and a stabilizer comprising a lead compound or an organotin compound which is effective to prevent discoloration and degradation of the homopolymer or copolymer and does not inhibit the grafting of the vinyl silane on the homopolymer or copolymer . the graft homopolymer or copolymer is exposed to moisture to cross - link it , suitably after molding or otherwise fabricating the graft polymer to form an article . there is also provided a method of moisture cross - linking poly and vinyl chloride copolymers .