United States Patent Office Patented July 15, 1958
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2,843,561 United States Patent Office Patented July 15, 1958 1. 2 ployed in preparing the interpolymerized compositions 2,843,561 are unvulcanized copolymers, i. e. they contain ethylenic COMPOSITIONS OF INTERPOLYMERIZED WINYL unsaturation and are soluble in the monomers as pre AROMATIC HYDROCARBONS, ACRYLIC ACID viously mentioned. ESTERS AND RUBBERY BUTADIENE-STYRENE The copolymers of butadiene and styrene to be em COPOLYMERS AND METHOD OF MAKING ployed in preparing the compositions can be copolymers SAME containing in chemically combined form from 40 to 80 Francis L. Ingley, Midland, and Daniel Moldovan, percent by weight of butadiene and from 60 to 20 per Rhodes, Mich, assignors to The Dow Chemical Com cent of styrene. Copolymers prepared from mixtures of pany, Midland, Mich., a corporation of Delaware O from about 60 to 80 percent by weight of butadiene, and from 40 to 20 percent of styrene are usually employed. No Drawing. Application March 29, 1955 Mixtures of any two or more of the butadiene copoly Serial No. 497,802 mers, e. g. a mixture of a soluble copolymer of 40 per 8 Claims. (Cl. 260-45.5) cent by weight of butadiene and 60 percent of styrene 15 and a soluble copolymer of about 75 percent of buta This invention concerns new compositions of matter diene and 25 percent of styrene which mixture of buta which are interpolymerized mixtures of monovinyl aro diene copolymers forms clear or substantially clear gel matic hydrocarbons, acrylic acid esters and copolymers free solutions with the monomers, can also be used. of butadiene and styrene. Methods of making the butadiene copolymers are well The new compositions are transparent polymeric ma 20 known. The copolymers are usually prepared by dis terials possessing good tensile and flexural strength, to persing a mixture of the monomers in an aqueous solu gether with high elongation and impact strength. They tion of an emulsifying agent, then agitating, heating and can be calendered on rolls to form film or sheet, or copolymerizing the monomers. molded by usual compression or injection molding opera The polymerization is accelerated by the addition of tions, or by extrusion methods, to form plastic articles 25 catalysts which provide oxygen such as hydrogen per suitable for a variety of applications. The composi oxide, benzoyl peroxide, tert.-butyl hydroperoxide, tions are soluble in usual organic solvents, e. g. benzene, cumene peroxide, potassium persulfate, etc. The catalyst toluene, xylene, methyl ethyl ketone, or mineral spirits. is usually employed in amount corresponding to from Solutions of the polymeric materials in a solvent can be 0.1 to 2 percent by weight of the materials to be poly cast as layers on glass plates and dried to form film, or 30 merized. applied to wood, metal, or other surfaces and dried to The soluble butadiene copolymers are usually obtained form tough transparent protective films or surface coat by stopping the copolymerization short of completion, 1ngs. e.g. when from 70 to 90 percent of the monomers are It has been discovered that the interpolymerization of polymerized, then separating the unreacted monomers mixtures or solutions of one or more monovinyl aromatic 35 and recovering the copolymer from the aqueous colloidal hydrocarbons of the benzene series, one or more lower solution or latex in usual ways, such as by coagulation of alkyl esters of acrylic acid and one or more copolymers the latex, washing and drying the copolymer, or by dry of butadiene and styrene, which copolymers are soluble ing of the latex on heated rolls, or spray drying the latex. in the monomers and contain ethylenic unsaturation, in Mixtures of the butadiene copolymers, when employed, proportions as hereinafter defined, results in the forma 40 are preferably obtained by mixing together latexes of the tion of transparent or substantially transparent polymeric respective copolymers and thereafter recovering the poly products having good mechanical properties such as ten mer from the mixture of latexes, e.g. by drying the mix sile strength, impact strength, elongation and hardness. ture and recovering the dried latex solids. According to the invention the compositions are pre The soluble butadiene copolymer, or a mixture of two pared by dissolving or dispersing a soluble copolymer of 45 or more of such copolymers of butadiene and styrene, is butadiene and styrene, which copolymer contains ethylenic employed in amount sufficient to form with the mono unsaturation, in a mixture of monomers consisting of at mers, i. e. the monovinyl aromatic hydrocarbon and the least one monovinyl aromatic hydrocarbon, and at least acrylic acid ester starting materials, a clear or substan one ester of acrylic acid and a lower aliphatic alcohol, tially clear solution or colloidal dispersion containing e.g. ethyl acrylate or butyl acrylate, in proportions as 50 from 5 to 10, preferably from 6 to 9, percent by weight hereinafter defined and heating the solution in mass to of the butadiene-styrene copolymer. The employment of polymerize the monomers. The monomers copolymerize the butadiene-styrene copolymer in amount less than 5 with one another and appear to copolymerize at least in percent by weight of the final composition results in a part with the dissolved copolymer of styrene and buta polymeric product having low impact strength. The em diene which contains ethylenic unsaturation to produce 55 ployment of the copolymer in amount greater than 10 a final composition containing the components in chemi percent of the compositions results in formation of final cally combined or interpolymerized form. polymeric products which are soft and have poor tensile It is important that the copolymer of butadiene and strength. styrene be soluble, or infinitely swellable, in the mono Suitable monovinyl aromatic hydrocarbons are styrene, mers, i. e. the monovinyl aromatic hydrocarbon and the 60 ortho-, meta- and para-vinyltoluene, vinylxylene, ethyl acrylic acid ester, to form a solution or colloidal dis-- vinylbenzene, isopropylvinylbenzene, ethylvinyltoluene, persion of the copolymer that is free or substantially free or mixtures of any two or more of such monovinyl aro from gels which are visible to the naked eye. The pres-- matic hydrocarbons. Styrene is preferred. ence or absence of such gels in the solution or dispersion The alkyl ester of acrylic acid to be employed in pre can conveniently be determined by passing the solution, or 65.paring . the compositions is an ester of acrylicd acid and a a portion thereof, through a No. 1 grade Whatman filter saturated monohydricaliphatic alcohol containing from paper. The visible gel particles, if present, are retained one to four carbon atoms in the molecule. Examples of on the filter paper. ." . '. suitable acrylic acid-esters are methyl acrylate, ethyl ... The soluble butadiene-styrene copolymers to be em 70 acrylate, propyl acrylate or butyl acrylate, or mixtures of 2,848,561 3 4. any two or more of such acrylates. Said acrylates have heat-plastified interpolymerized product tends to break the general formula: down and destroy or solubilize any insoluble gel particles such as are sometimes formed during the polymerization reaction, and, thus, frequently improves the appearance of the product. The heat-plastified interpolymer product wherein R represents an alkyl radical containing from may be subjected to subatmospheric pressure while being one to four carbon atoms. milled, e.g. on compounding rolls, so as to facilitate The monovinyl aromatic hydrocarbon and the acrylate vaporization of any volatile ingredients therefrom during starting materials are employed in proportions corre the operation. The devolatilization and hot-milling op 0 erations just mentioned are desirable, but are not re sponding to from 50 to 60 percent by weight of the mono quired. vinyl aromatic hydrocarbon and from 50 to 40 percent Small amounts of additives such as dyes, pigments, of the acrylate. plasticizers, stabilizing agents, antioxidants, or fillers, can The compositions are prepared by forming a solution be incorporated with the resinous composition in usual of the monomers, e.g. a mixture of equal parts by Weight 5 ways, e. g. by heat-plastifying the polymeric product on of styrene and ethyl acrylate, containing from 5 to 10, compounding rolls, and milling the same with the addi preferably from 6 to 9, percent by weight of the butadiene tive, but the presence or absence of such additives is not copolymer and heating the solution to polymerize the required. The additives when used are usually employed OOS. '. The solution or colloidal dispersion of the copolymer in amounts corresponding to from 0.5 to 10 percent by of butadiene and styrene in the monomeric materials can 20 weight of the composition. be prepared by first dissolving the butadiene copolymer The resinous interpolymer product, either as obtained in the monovinyl aromatic hydrocarbon, then adding the from the interpolymerization reaction, or after being acrylate in the desired proportion, or by dissolving the subjected to one or more of the devolatilization, milling, copolymer in a mixture of the acrylate and the mono or compounding operations just mentioned may be cut or vinyl aromatic hydrocarbon starting materials. 25 ground to form particles or granules thereof, suitable for The starting solution of the butadiene copolymer in use in molding operations. The granular product can the monomers is usually prepared at ordinary tempera be compression-molded, or injection-molded, or extruded tures or thereabout, by agitating a mixture of the ingre to obtain shaped articles of the same. dients at atmospheric or substantially atmospheric pres The following examples illustrate ways in which the sure, preferably in the absence or substantial absence of 30 principle of the invention has been applied, but are not air or oxygen. to be construed as limiting its scope. The solution is usually filtered to remove undissolved EXAMPLE 1. gel particles of the butadiene copolymer, together with In each of a series of experiments, a copolymer of any inert solids or impurities, e.g.