3,213,159 United States Patent Office Patented Oct. 19, 1965 1. 2 percent, higher styrene contents leading to greatly re 3,213,159 duced impact strength of the final composition. Such METHOD OF BLENDING AND homopolymers or of butadiene and styrene GRAFT OF STYRENE WITH are commercially available, or may be prepared by BUTADENE polymerization in emulsion in a manner known to the Domas Adomaitis, Chicago, Ill., assignor to Standard Oil art, employing peroxide catalysts or "redox” catalyst Company, Chicago, Ill., a corporation of Indiana Systems. No Drawing. Filed Apr. 26, 1962, Ser. No. 190,211 The graft copolymer component of the compositions 4. Claims. (C. 260-876) produced by the process of the present invention is pre This invention relates to the preparation of polystyrene 10 pared by effecting free of styrene molding compositions. More particularly, it concerns a in the presence of a previously prepared pre-coagulated process for preparing such compositions to afford homo latex of butadiene homopolymer or copolymer with geneous blends of polymeric styrene and rubbery styrene. The amount of styrene which is grafted upon having improved impact properties and which are easy the butadiene containing backbone can be varied from to mold and/or extrude to smooth, glossy uniform 5 about 10 to about 80% by weight based upon the weight articles. The invention is especially concerned with of graft copolymer, desirably 30-50%. In general, processes for the preparation of useful high impact poly polymerization techniques known to the art, employing styrene compositions by compounding certain rubbery free radical generating catalysts can be employed, to graft copolymers with hydrocarbon solutions of polysty gether with such known polymerization ingredients as rene, and to the compositions prepared thereby. 20 emulsifying agents, chain transfer agents and the like for It has hitherto been known to prepare ternary com effecting complete and rapid graft polymerization of the positions comprising mixtures of (1) styrene-type resins, monomeric styrene. In the graft polymerization reac (2) graft copolymers of styrene on a rubbery butadiene tion, it appears that a substantial portion of the poly polymer or copolymer backbone, and (3) rubbery buta styrene becomes attached to the backbone chain, and that diene polymers or copolymers, as for example in U.S. 25 a relatively minor amount of free polystyrene is formed. Patent 2,755,270 of Robert A. Hayes. Such composi As previously discussed, the graft polymerization of tions, especially those containing from 80-95% of poly styrene is effected in the presence of the pre-coagulated styrene based on the weight of polymeric ingredients in polybutadiene or rubbery copolymer of butadiene and the resinous composition are particularly useful for in styrene. The latex of the butadiene homopolymer or jection molding applications in that they combine the 30 copolymer, which comprises a finely divided emulsion of excellent strength and hardness of polystyrene with a polymer, is pre-coagulated by the addition of mineral high degree of resistance to impact. acids, such as sulfuric acid, hydrochloric acid, etc., or by It has now been found that thermoplastic compositions the addition of salts which have a coagulating effect on having good molding characteristics and high impact the latex, e.g., aqueous solutions of sodium chloride, strength can readily be prepared from polystyrene and a 35 calcium chloride and the like. graft polymer of styrene on a rubbery butadiene polymer In grafting styrene onto the rubbery polymer of buta or copolymer by employing a graft copolymer of the diene, the pre-coagulated latex is charged to a polymeriza aforesaid type which has been prepared in a particular tion reactor. Mechanical mixing may be employed for way. The process of the present invention, and the this purpose, and it is obvious that while the pre-coagulum binary compositions produced thereby, are much simpler 40 will be distributed into smaller particles, it does not revert to prepare than those of the prior art which require the to the extremely finely divided, emulsified form, in which presence of three separate and distinct polymeric com it is originally prepared. Styrene to be used in the graft ponents in the final resin composition. polymerization step may be added to the reactor contain The first step in the preparation of the plastic com ing the pre-coagulate just prior to polymerization or it positions of this invention is to provide an aqueous emul 45 may be contacted with the pre-coagulate for a period of sion of polymerized butadiene or of a rubbery copolymer time prior to polymerization to permit swelling of the of butadiene and styrene containing at least 50% buta pre-coagulate with the monomer and thus more intimate diene in the molecule. The next step in the preparation contact of the monomer with all parts of the pre-coagul of the composition is to polymerize styrene monomer lated rubber. in the presence of the aforesaid butadiene resin. This 50 Graft polymerization is effected at temperatures be step is essentially a graft polymerization, in which styrene tween 0° and about 100° C., preferably 20° C. to 80 C., becomes chemically combined as side chains on the poly in the presence of well-known peroxide catalysts, and butadiene base or "backbone' polymer. An essential under autogeneous pressure. feature of the present invention is the step of first pre The graft polymer prepared as described above is then coagulating the polybutadiene or rubbery copolymer of 55 separated from the watery phase and homogeneously dis polybutadiene, and subsequently effecting the graft po persed in a hydrocarbon solution of polystyrene, in which lymerization of styrene on the precoagulum. Finally, the case water accompanying the coagulum can be separated graft copolymer, prepared by reaction of styrene with by azeotropic distillation. The separation of graft copol pre-coagulated rubbery butadiene polymer, is dispersed ymer may be accomplished by addition of coagulating in a hydrocarbon solution of polystyrene to effect homo 60 agents of the type described for coagulation of the poly geneous distribution of the graft polymer in polystyrene, butadiene latex, and the coagulum washed free of adherent and the resultant solution treated for recovery of the catalyst and salts. Polystyrene ordinarily useful for binary graft copolymer-polystyrene composition. molding or for incorporation into molding compositions The rubbery polymer employed to prepare the com can be used as one component of the compositions pro positions described herein comprises a conventional “hot” 65 duced by our process. Such polystyrene resins may be or “cold" rubbery homopolymer of butadiene or a co obtained by bulk or emulsion polymerization of styrene polymer of butadiene and styrene containing at least 50% using peroxidic or other known catalysts. Since the butadiene together with up to 50% styrene. It has present process requires the use of a hydrocarbon solution been found that the proportion of styrene in the 70 of polystyrene, it is preferred to employ a resin solution copolymer is critically maintained below 50 weight prepared by polymerization of styrene in an aromatic sol percent, preferably from about 10 to about 30 weight vent, for example hydrocarbon solutions of polystyrene 3,213,159 3 4. which are obtained in accordance with the processes de polybutadiene was effected by employing the same por scribed in U.S. Patents 2,813,089 and 2,920,065. It is portions of ingredients used in the formula above, the to be understood, however, that solutions of polystyrene monomeric butadiene being substituted by polybutadiene obtained by dissolving polystyrene, prepared in accord and styrene. Styrene in an amount equal to the weight ance with methods well known to the art, in an aromatic of polybutadiene employed (dry basis) was added during hydrocarbon solvent are equally applicable to the present a period of one hour while maintaining the reactor con process. tents with stirring at 60° C. Reaction at 60° C. was Preferred polystyrene resins have an intrinsic viscosity effected over a period of about four hours to practical (measured in benzene at 30° C.) of from about 0.8 to completion. about 1.5 dil./g. and are characterized by impact strength O Upon completion of the polymerization, the reactor in the range of from about 0.25 to 0.40 ft. lbs./in. notch contents were cooled and 1% (based on weight of graft (ASTM D256-56). The polystyrene solution comprises copolymer) of Ionol (butylated-hydroxy-toluene) anti from about 10 to about 50% by weight polystyrene, pref oxidant added to the prepared latex. erably 15-25% polystyrene dissolved in an aromatic hy Example 2 drocarbon such as benzene, toluene, ethylbenzene, xylenes, 15 and the like. The particular solvent employed is not A second portion of the polybutadiene latex prepared critical. The graft copolymer is added in an amonut which as hereinbefore described was employed for preparation will provide, upon removal of water and solvents, a com of a graft polymer without prior pre-coagulation of the position comprising from 5 to 30 parts, preferably 15 to latex. In this example, polybutadiene latex containing 20 parts graft polymer per 100 parts of resin. 20 50 parts (dry basis) polybutadiene was charged together Addition of the graft polymer to the polystyrene solu with 50 parts monomeric styrene and 1.0 part potassium tion yields a suspension which may contain some dis persulfate as catalyst to a closeable polymerization reac solved polymer. This suspension of graft polymer is pref tor. The reactor was purged of air by means of nitrogen, erably homogenized to obtain a more uniform distribu the reactor sealed and the contents heated to 50° C. with tion of the added resin, and to disperse large particles of 25 stirring. Polymerization was effected at 50-58° C. over gel by passage through a homogenizer at a pressure be 4-6 hours to substantial completion. tween about 500 and 5000 p.s.i.g., preferably below 3000 Upon completion of the polymerization, the reactor p.si. Any type of homogenizing equipment may be em contents were cooled and 1% (based on weight of graft ployed for this purpose. Prior to, or after homogeniza copolymer) of Ionol antioxidant added to the prepared tion, other materials including internal lubricants such 30 latex. as mineral oil, butylstearate and the like, color stabilizers, antioxidants, etc., in desired amounts may be blended PREPARATION OF POLYSTYRENE COMPOSITIONS with the polystyrene solution. The graft copolymer latex prepared in each of Ex The homogenized polystyrene solution is then treated amples 1 and 2 was worked up in identical manner. In for removal of solvent and any residual water. For this 35 each case, sufficient 10% aqueous sodium chloride solu purpose, the solution can be passed through a continuous tion was added to the latex to precipitate the graft co vacuum extruder at a temperature between about 100° C. polymer. The copolymer was then filtered, washed with and about 250° C. wherein the solvent is removed under Water to remove inorganic Salts, and the wet crumb dis vacuum and the polystyrene composition recovered as an persed by mechanical stirring in a solution of polystyrene extrudate of uniform composition essentially free of vola 40 in Xylene containing 25% by weight polystyrene (intrinsic tile material. visocsity of about 1.0 dll/g. measured in benzene 30° C.). The blends in each case contained 20 parts of graft PREPARATION OF RUBBER LATEX polymer (dry basis) and 80 parts polystyrene. The blends Polybutadiene latex was prepared using the following Were then homogenized by passing through a homogenizer conventional recipe for “redox' polymerization systems, at 3000 p.S.i.g. pressure. The homogenized dispersion in which the amount of all ingredients employed is based 45 in each case was then passed through a devolatilizing on 100 parts by weight of rubber expected. vacuum extruder for removal of water and xylene. The resultant resinous polystyrene was employed to prepare Butadiene ------100.0 injection molded test specimens which had the following Cumene hydroperoxide ------0.75 properties: Sodium oleate ------3.0 50 Tetrasodium pyrophosphate (.10 H2O) ------0.5 Sodium hydroxide ------0.15 Example 1 Example 2 Dextrose, anhydrous ------1.0 Impact strength: Izod ft.-lbs. S.l.. notch of Ferrous sulfate heptahydrate ------0.0125 unaged Sample ------Versene Fe-3 ------0.1 Elongation, percent: At fail of annealed 2.19 0.40 55 sample ------Water ------200.0 Hardness: Of unaged sample Rockwell 32.4 7.0 The polymerization was carried out in a reactor pro "M" scale.------42.4 46.4 vided with heating and cooling means and with a stirrer. 1 ASTM Test 256-56. All components other than the butadiene were charged, 2ASTMTest D638-56T. stirred to effect solution, and the butadiene then added. 60 3ASTM Test D785-5. The reactor vent was closed, the contents heated to 50 It will be seen from the above data that substantial im C. and the mixture stirred and heated between 50° C. and provement in the physical properties of the polystyrene 65° C. for about 5 hours. Traces of unreacted butadiene composition was achieved by preparation of the graft co were then vented. The latex remaining in the reactor polymer component from a precoagulated rubber back contained about 30% of polybutadiene. 65 bone, as described in Example 1 of the specification. Example 1 Examples 3-10 A portion of the polybutadiene latex prepared as above was pre-coagulated by addition with stirring of 2% sodium The procedure of Examples 1 and 2 were repeated in oleate (based on weight of rubber), and sufficient 10% 70 order to compare the effect of agglomeration prior to sodium chloride solution to convert the latex to a creamy graft copolymer formation on the properties of polystyrene and pasty mixture. The pre-coagulated latex was per compositions of varied composition, as follows. mitted to age overnight. Example 3: Example 1 repeated except that the graft The pre-coagulate thus obtained was charged to a copolymer was employed in an amount of 15% by polymerization reactor. The grafting of styrene onto the 75 weight of the final composition. 3,213,159 5 6 Example 4: Example 2 repeated except that the graft erizing a monomer selected from the group consisting of copolymer was employed in an amount of 15% by butadiene and mixtures of butadiene and styrene contain weight of the final composition. ing at least 50% butadiene in water in the presence of a Example 5: Example 1 repeated except that the graft free radical polymerization catalyst, and an emulsifying copolymer was prepared from 70 parts polybutadiene agent to produce an aqueous emulsion of a butadiene and 30 parts monomeric styrene. polymer, precoagulating said emulsion by addition there Example 6: Example 2 repeated except that the graft to of a coagulating agent, adding monomeric styrene to copolymer was prepared from 70 parts polybutadiene the pre-coagulated polymer, polymerizing styrene in con and 30 parts monomeric styrene. tact with said pre-coagulated polymer to form a graft Example 7: Example 1 repeated except that backbone 10 copolymer containing from about 10 to about 80 parts elastomer was a butadiene-styrene copolymer con grafted styrene per 100 parts graft copolymer, separating taining 70 parts butadiene and 30 parts styrene and graft copolymer was prepared from 70 parts buta said graft copolymer from the water phase, admixing said diene-styrene copolymer and 30 parts monomeric separated graft polymer with a solution of polystyrene in styrene. 15 an inert hydrocarbon solvent to form a resin composi Example 8: Example 2 repeated using polymer of Exam tion containing from about 5 to about 30 parts of said ple 7. graft copolymer per 100 parts of resin and separating Example 9: Example 1 repeated except that backbone from said solvent the resin composition so prepared. elastomer was a butadiene-styrene copolymer contain 2. The process of claim 1 wherein butadiene polymer ing 86 parts butadiene and 14 parts styrene and graft 20 contains from about 10 to about 30 weight percent sty copolymer was prepared from 70 parts butadiene Tene. styrene copolymer and 30 parts monomeric styrene. 3. The process of claim 1 wherein the graft copolymer Example 10: Example 2 repeated using polymer of Ex contains from about 30 to about 50 parts grafted styrene ample 9. per 100 parts graft copolymer. In each of Examples 5 through 10, the final polysty- 25 4. The process of claim 1 wherein sufficient coagulat rene composition comprised 20 parts graft copolymer and ing agent is added to convert said emulsion to a creamy, 80 parts polystyrene. pasty mixture. TABLE I

Graft Blendratio Example Composition of polymer graft/poly- Impact Elongation Hardness backbone ratio back- styrene strength bone?sytrene

8------Polybutadiene.--- 50/50 15/85 1.30 34.6 52.4 4------do------50/50 15785 0.43 16.9 54.2 70/30 20/80 2.46 14.0 34.9 70/30 20.80 1.35 24.8 33.2 7------70 butadiene, 30 70/30 20/80 2.02 22.8 37.7 styrene

------do------70/30 20/80 1.33 23.0 38.6 9------86 butadiene, 14 70/30 20/80 2.60 35.8 33.2 Styrene. 10------do------7030 20/80 2,09 27.9 37.3 It will be apparent from the data reported in Table I References Cited by the Examiner that significantly improved physical properties, especially 45 UNITED STATES PATENTS increased impact resistance, was obtained in each instance by pre-coagulation of the backbone polymer prior to 3,041,310 6/62 Luftglass et al. ------260-876 formation of graft polymer therefrom. 3,062,777 11/62 Allen et al. ------260-876 I claim: 1. A process for the preparation of polystyrene resin 50 MURRAYTILLMAN, Primary Examiner. composition which process comprises the steps of polym LEONJ. BERCOVITZ, Examiner.