Graft copolymers are made by submitting a backbone polymer in a dry or swollen state, or in the presence of a liquid which has no physical or chemical action thereon, to the action of ozone and decomposing the ozonized polymer in the presence of one or more monomers in a polymerization system completely free of any additional polymerization catalyst for polymerizing the monomer or monomers to be grafted, or in a polymerization system containing a reducing agent for decomposing the ozonized polymer. The ozonization of the polymer is preferably effected with the latter in a very finely divided state, e.g. of particle size less than 10 microns.  In certain cases, i.e. in the treatment of objects, the monomers may only be grafted on to parts of the surfaces of the article.  The Specification contains an extensive list of backbone polymers selected from natural rubber, synthetic rubbers, homo-polymers and copolymers of monomers containing a vinylidene group, polyamides, polyesters, polyurethanes, cellulose ethers and esters, silicone polymers, phenoplasts, and aminoplasts.  The monomer or monomers. grafted on to the ozonized backbone polymer are selected from compounds containing one or more ethylenic bonds.  These compounds may also contain an acetylenic bond.  The Specification contains an extensive list of suitable monomers.  The polymerization may be effected in bulk, aqueous media, or organic diluents.  Exemplified backbone polymers are butyl rubber, natural rubber, polyvinylisobutyl rubber, a mixture of polyvinyl chloride and a copolymer of butadiene with acrylonitrile, polyethylene, a copolymer of butadiene and styrene, polystyrene, polymethylmethacrylate, a copolymer of styrene and acrylonitrile, polyacrylic acid, polyvinyl carbazole, polytetrafluorethylene, polyvinyl chloride, cellulose acetate, nylon, polyvinyl alcohol, a graft polystyrene-acrylonitrile polymer.  The backbone polymer is also exemplified in the form of films of polystyrene, polyethylene, polyvinyl chloride, and cellulose acetate, threads of polyacrylonitrile, isotactic polypropylene, and regenerated cellulose, a woven cotton fabric, a polyvinyl chloride tube, a woven nylon fabric, or a sponge of cellular polyvinyl chloride or a polyurethane.  Exemplified monomers are acrylic acid, isoprene, acrylonitrile styrene, butadiene, vinyl-carbazole, vinyl acetate, methyl and ethyl and butyl acrylate, trifluorochloroethylene, vinylidene chloride, vinyl chloride, and acrylamide.  The reducing agent for decomposing the ozonized backbone polymer is of the conventional type employed in redox systems.  Specifications 883,792 and 883,793 also are referred to.  Reference has been directed by the Comptroller to Specification 825,680.ALSO:The hygroscopity of synthetic sponges made of cellular polymeric substances e.g. polyvinyl chloride, or a polyurethane is increased by subjecting the sponge to the action of ozone and then grafting on to the ozonized polymeric substance, under polymerizing conditions a monomer or monomers, (see Group IV(a)). In Example 61, a sponge of a polyurethane made by reacting a polyester with a polyisocyanate, is treated with ozone and subsequently reacted with vinyl acetate; in Example 62 a sponge of a polyurethane made by reacting a polyether with a polyisocyanate, is ozonised and reacted with acrylic acid, whilst in Example 63 a sponge of the same type of polyurethane as in Example 62 is reacted with acrylamide.  Reference has been directed by the Comptroller to Specification 825,680.