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United States Patent Office Patented Jan 3,019,208 United States Patent Office Patented Jan. 30, 1962 2 3,019,208 has of itself properties which were obtained by copoly METHOD OF MAKING GRAFT COPOLYMERS OF merizing comonomers with vinyl chloride. Certain spe WNYEL CHORDE AND POLYACRYLATE cial properties are obtained by using various copoly Robert J. Reid, Canal Fulton, and Chris E. Best, Franklin merizable monoethylenically unsaturated comonomers Township, Summit County, Ohio, assignors to The with the vinyl chloride, and in producing the graft co Firestone Tire & Rubber Company, Akron, Ohio, a polymer up to 10 or 15 percent of such comonomers corporation of Ohio may be used, such as for example vinyl acetate, vinylidene No Drawing. Filled Jan. 18, 1954, Ser. No. 404,806 chloride, trichlorethylene, etc. The term “vinyl chlo 6 Claims. (C. 260-45.5) ride resin' will be used herein generally to include poly 0. vinylchloride and copolymers of vinyl chloride with This invention relates to the production of graft co small amounts of comonomers which are often employed polymers by grafting a vinyl resin (composed of either in making copolymers with vinyl chloride. vinyl chloride or a mixture of vinyl chloride and a The graft copolymerization process is carried out in comonomer) onto an acrylate polymer. The polyacryl latex. Vinyl chloride with or without a small amount of ate is first polymerized in an emulsion, and then without 5 other suitable monomer is added to a previously pre Separation of the polyacrylate from the emulsion the pared latex of polyacrylate. Additional catalyst and vinyl resin is polymerized onto it. emulsifying agent, such as soap, etc., may be added but Acrylate polymer and vinyl polymer or copolymer are are not required. This mixture is then subjected to poly normally incompatible. The graft copolymer is a com merizing conditions; for example, by stirring at a suita patible composition in which the acrylate acts as a plas 20 ble temperature which may be as low as 20° C. or even ticizer for the polyvinyl chloride or copolymer. lower although rates of reaction are slow at such tem Monomeric plasticizers have been used with vinyl peratures and ordinarily temperatures of 30 to 60 or polymers and copolymers, but their usefulness is limited even up to 70° C. or higher will be used. Higher tem because of the ease with which they are separated from peratures may be employed more successfully with vinyl the vinyl composition. They are quite volatile, bleed, 25 chloride than with mixtures of vinyl chloride and a and to some extent are removed by solvents such as comonomer. The higher temperatures are preferred be soapy water, etc. They have become known as fugitive cause they not only speed up the reaction, but also give plasticizers. The need for a non-fugitive plasticizer for a vinyl resin of lower molecular weight. Higher tem vinyl resins has long been recognized. Polymeric plas peratures also increase the efficiency of the grafting ticizers have been employed which in general have lower 30 vapor pressure than the monomeric materials and are process. The resulting latex may be used as such, or the less apt to migrate. However, no polymeric material graft copolymer may be isolated by conventional meth has been found to be entirely satisfactory. Butadiene ods. acrylonitrile copolymers which have been used as plas Molded compositions obtained from the graft copoly ticizers are subject to oxidative attack at the double bond. 35 mer are clear and tough, whereas a mixture of a poly Soft, saturated polymers such as polyacrylates and poly acrylate and vinyl resin, separately prepared, will not be vinyl methyl ketone are not sufficiently compatible with compatible and will not give transparent products. They the vinyl compositions to be entirely satisfactory. Fur will be relatively cheesy. thermore, in general, vinyl compositions containing poly The graft copolymers are suitable for fabrication by meric plasticizers have rather poor low-temperature prop extrusion, calendering, and molding. The latexes them erties. 40 selves and solutions of the graft copolymer may likewise According to this invention vinyl compositions are be used. The graft copolymers do not have the strength plasticized by utilizing them in the form of graft co generally required for filaments. polymers in which vinyl chloride with or without a The invention is illustrated by the following exam comonomer is polymerized onto an acrylate polymer 45 pies in which the polymerization of the acrylate is desig base. The graft copolymer must contain a substantial nated Step A, and the polymerization of the vinyl resin amount of the polyacrylate in order to have a beneficial thereon is designated Step B. effect on the vinyl composition, and normally will com Example I prise substantially 10 to 50 percent by weight of the Step A-A latex of ethyl polyacrylate was prepared graft copolymer. The polyacrylate imparts flexibility 50 by charging the following materials into a crown-capped and softness to the vinyl composition, making it desira bottle: ble for such products as shower curtains, shower caps, table covers, rainwear, etc. Thus the vinyl composition 100 g. ethyl acrylate is internally plasticized eliminating the need of added 425 g. water plasticizer or significantly reducing the amount of such 55 0.6 g. potassium persulfate plasticizer required. The products may be made by cast 1.75 g. sodium lauryl sulfate ing or extruding, or calendering the graft copolymer. 0.2 g. sodium hydroxide The graft copolymer may be used in the form of a solu The system was purged with nitrogen and the bottle was tion or latex. tumbled 2.5 hrs. at 67° C. The polyacrylates which may be used in carrying out 60 Step B.-A quantity of the latex resulting from the the invention are alkyl esters in which the alkyl group above polymerization containing 40 g. of ethyl polyacryl contains up to 10 carbon atoms. Ordinarily the butyl ate was added to a mixture of 57 g. of vinyl chloride ester will be employed. The esters of the lower alcohols and 3 g. of vinylidene chloride. An additional 0.1 g. do not impart as much flexibility to the vinyl composi potassium persulfate was also added. The system was tion as the butyl ester, for example. Where the higher 65 purged of air. Polymerization was essentially complete esters are used the graft polymerization does not appear after 26 hours at 40° C. The polymer was isolated by to be as efficient, the amount being bound to the acrylate coagulation with calcium chloride Solution and dried being the measure of the efficiency. at 40 C. Ordinarily the graft copolymer will be formed with A plaque pressed from this graft copolymer at 170 vinyl chloride without admixture with a comonomer. 70 C. was clear and tough whereas a mixture of ethyl poly The graft copolymer has a lower softening point than acrylate and a vinyl/vinylidene chloride copolymer of polyvinyl chloride, and in this respect and other respects similar over-all composition gave a cloudy plaque which 3,019, 208 4. 3 resin and an alkyl polyacrylate which comprises emulsi was weak and cheesy and had poor tear strength. Fur fying 50 to 90 parts of monomer from the class consist thermore, the graft copolymer gave a clear, homogene ing of (a) vinyl chloride and (b) a mixture of vinyl ous solution in tetrahydrofuran while the mixture of chloride and up to 15 percent of a copolymerizable polymers gave a two-phase solution in this solvent. This monoethylenically unsaturated monomer, in an aque was proof that the product referred to as a “graft co ous emulsion of 50 to 10 parts of an already formed polymer' was not a mere mixture of the separate poly homopolymer of an alkyl ester of acrylic acid, the alkyl merS. group of which contains 1 to 10 carbon atoms, and heat Example II ing the resulting emulsion to 30 to 70° C. in the presence A graft copolymer was prepared using the foregoing of potassium persulfate, as catalyst, and producing the procedure, except that vinyl chloride was used in Step 10 graft copolymer. B instead of the mixture of vinyl chloride and vinylidene 2. The method of forming a graft copolymer which chloride. comprises emulsifying 50 to 90 parts of vinyl chloride The product was essentially the same as that obtained in an aqueous emulsion of 50 to 10 parts of an already in Example I except that the fusion point was higher. formed homopolymer of an alkyl ester of acrylic acid, 15 the alkyl group of which contains 1 to 10 carbon atoms, Example III and heating the resulting emulsion to 30 to 70° C. with A graft copolymer of vinyl-vinylidene chloride on potassium persulfate, as catalyst, and producing the graft butyl polyacrylate was prepared in the same fashion as copolymer. in Example I except that butyl acrylate was substituted 3. The method of forming a graft copolymer which for ethyl acrylate in Step A. The product obtained gave 20 comprises emulsifying 50 to 90 parts of a mixture of a softer, more flexible plaque than did the product of vinyl chloride and up to 15 percent of copolymerizable Example I. The product differed markedly from a mix monoethylenically unsaturated monomer, in an aqueous ture of butyl polyacrylate with a vinyl/vinylidene chlo emulsion of 50 to 10 parts of an already formed homo ride copolymer in being clearer and tougher. polymer of an alkyl ester of acrylic acid, the alkyl group Similar experiments in which the amounts of poly 25 of which contains 1 to 10 carbon atoms, and heating the acrylate and vinyl monomers were varied so as to give resulting emulsion to 30 to 70° C.
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