MXPA06007126A - Interpolymer resin particles - Google Patents

Abstract

Interpolymer resin particles comprised of 20%to 60%by weight of uncross-linked polyolefin e.g. polyethylene, polypropylene, and from 40%to 80%by weight based on the weight of the particles of a vinyl aromatic monomer, e.g. styrene, that is polymerized in a suspension process or form an interpenetrating network of polyolefin with polymerized vinyl aromatic monomer particles and having a gel content of 0 to 1.5%by weight based on the weight of the particles for improved processability in end-use applications and improved ESCR properties. The interpolymer resin particles have a VICAT softening temperature from about 90°C to about 115°C, and a melt index from 0.2 to 35.0g/10 minutes (Condition ). The particles can be mixed with a blowing agent to form extruded foam articles, such as foam board, and can be used in extrusion, injection molding, rotomolding, and thermoforming processes to form a layer, e.g. sheet, film, and as a tie layer in multi-layer structures to bind adjacent layers consisting of incompatible polymers, i.e. polystyrene and polyethylene for improved rigidity in multi-layer structures.

Description

INTERPOLI ERO RESIN PARTICLES FIELD OF THE INVENTION The present invention relates to polyolefin resin particles containing a vinyl aromatic monomer polymerized in the polyolefin matrix to form an interpenetration network of vinyl aromatic monomer polymerized with polyolefin, for example polystyrene. More particularly, the present invention relates to interpolymer resin particles having little or no gel content; to a process for producing the interpolymer resin particles; to a polymer composition comprising the interpolymer resin particles and a second polymer; and to articles made of the interpolymer resin particles and / or the aforesaid polymer composition. These articles can be formed via processing techniques, for example sheet extrusion, rotomolding, thermoforming, compression molding, injection molding, blown film extrusion, and extrusion of direct injection foamed sheet.

BACKGROUND OF THE INVENTION It is known to polymerize vinyl aromatic monomers, such as styrene, in polyethylene. For example, U.S. Patent No. 3,959,189 issued by Kitamori and Ref. 173945, assigned to Sekisui Kaseihin Kabushiki Kaisha, describes a process for producing polyethylene resin particles. Polyethylene resin particles have a melt index (MI) value of 0.3 to 10 (Condition I, 190 ° C, 2.16 kg), a density of less than 0.93 g / cm3 and a VICAT softening point below 85 ° C. After the polyethylene resin particles are added to an aqueous suspension, 30% to 100% by weight based on the weight of the particles of a styrene monomer and a catalyst for polymerizing the monomer are added to the suspension, and the Styrene monomer polymerizes in this. The embodiments include adding a crosslinking agent to the polyethylene prior to the polymerization and crosslinking of the polyethylene prior to impregnating a blowing agent into the polyethylene resin particles to form foamable polyethylene resin particles. In view of the crosslinking agent, the polyethylene-polystyrene resin particles generally have a high gel content, ie from about 10% to 45% by weight. The gel content of the final foamed shaped article can be as high as 60% to 80% by weight. Even though these cross-linked polyethylene-polystyrene resin foams may have superior hardness and thermal stability, these same characteristics make these resin particles unsuitable for use in processes such as mixing, extrusion processing, and injection molding since the effect crosslinker tends to reduce the melt flow of these particles which affects the processability of these particles because the amperage needed to operate the processing machinery, for example extruder, is increased. The melt fracture therefore increases resulting in surface irregularities, such as holes and ridges. A further example of polystyrene resin polymerized into polyethylene resin particles is described in Japanese Patent No. 32623/70. The crosslinking of the polyethylene resin, polymerization of styrene, and impregnation of the blowing agent are carried out at the same time. Since the polyethylene resin particles are crosslinked, the polyethylene resin particles generally contain a high gel content, ie, at least about 24% by weight, rendering these polyethylene resin particles generally unsuitable for polymer processing, such as extrusion, injection molding, blown film, and extrusion of foamed sheet by direct injection. If the gel content is too high, hard spots are formed on the surface resulting in poor surface quality. Polymer processing proves to be difficult due to the high amperage needed for the machinery used to process the polymer, for example, extruders or injection molding machines. U.S. Patent No. 4,782,098 assigned to General Electric Co. discloses expandable interpolymer beads comprising polyphenylene ether resin and a polymerized vinyl aromatic monomer such as styrene. The vinyl aromatic monomer is polymerized in the presence of a polymerization catalyst to polymerize the vinyl aromatic monomer with the polyphenylene ether to form the interpolymer beads. Optionally, a crosslinking agent is added. A blowing agent is introduced under pressure into the thermoplastic resin beads. The crosslinking agent can be di-t-butyl peroxide, t-butyl cumyl peroxide, dicumyl peroxide, alpha, alpha-bis (t-butyl peroxy) p -di-isopropylbenzene, 2,5-dimethyl-2, 5 -di (t-butyl peroxy) hexin-3, 2, 5-dimethyl-2, 5-di (benzoyl peroxy) exano, and t-butyl peroxy isopropyl carbonate. At this point again, when a crosslinking agent is used, the polyphenylene ether resin has a gel content of at least about 24% by weight. Since the morphology of the polyphenylene ether resin is amorphous, the resin can generally have poor environmental stress cracking resistance (ESCR) properties. U.S. Patent Nos. 4,303,756 and 4,303,757 to Kajimura, et al. and transferred to Sekisui Kaseihin Kogyo Kabushiki Kaisha describes a process for producing • expandable thermoplastic resin beads. The process comprises suspending in an aqueous medium 20% to 70% by weight of a random copolymer of propylene and ethylene (U.S. Patent No. 4,303,756) or polypropylene resin particles (U.S. Patent No. 4,303,757), and 30% to 80% by weight of a vinyl aromatic monomer such as styrene; polymerizing the vinyl aromatic monomer in the presence of a polymerization catalyst to graft the vinyl aromatic monomer onto the structure of the polypropylene; and optionally, adding a crosslinking agent to form the graft copolymerized thermoplastic resin beads; and introducing a blowing agent into the thermoplastic resin beads. In general, the interpolymer resin particles of the prior art are generally expandable thermoplastic resin particles having a high gel content of about 10% to 45% by weight in at least one case and in the other cases about 24% by weight which limits the processability of the beads or particles when they are converted into articles such as solid sheet, film, etc. through processing techniques such as sheet extrusion, rotomolding, thermoforming, compression molding, injection molding, blown film extrusion, and extrusion of foamed sheet by direct injection. In addition, in general, the interpolymer resin particles of the prior art are impregnated with a blowing agent in a further suspension process to form foamable or expandable particles which are used for foam mounds. Expandable interpolymers of polyvinyl aromatic and polypropylene monomers are also disclosed in Kent D. Fudge, U.S. Patent Nos. 4,622,347; 4,677,134 and 4,692,471; and in Bartosiak et al, U.S. Patent No. 4,647,593, all of which are assigned to the Atlantic Richfield Company. These interpolymers can be prepared in accordance with the teachings of the aforementioned U.S. Patent No. 4,303,756. The interpolymers are made expandable by impregnating them with a blowing agent. The particles are expanded under normal conditions for polystyrene particles to foam of low density fine cellular structure by reducing the viscosity of the interpolymers to a melt flow (Condition L) of at least twice its original value and adding a lubricant and agent of cellular control while maintaining the orientation tension in the final product to a minimum. Since the interpolymer particles of these aforementioned patents can be prepared in accordance with U.S. Patent No. 4,303,756, the interpolymer particles have the same limitations summarized in the above discussion of the patent. '756 because the interpolymer particles generally have a high gel content, ie approximately 24% by weight. These interpolymer particles of reduced viscosity are impregnated with a blowing agent in an additional slurry process to produce foamable or expandable particles for foam mounds.

BRIEF DESCRIPTION OF THE INVENTION The invention overcomes the disadvantages described above of the prior art. The present invention provides non-expandable interpolymer resin particles with a crystalline morphology and having little or no gel content, whereby the processing characteristics of the particles in the manufacturing equipment to form articles, such as sheet or film or foam, they get better. The gel content ranges from about 0 to about 1.5% by weight, preferably from about 0 to about 0.8% by weight, and more preferably, from about 0 to about 0.5% by weight based on the weight of the interpolymer particles. The VICAT softening temperature of the interpolymer resin particles ranges from about 90 ° C to about 115 ° C, and the melt index values vary from about 0.2 to about 35.0 g / 10 minutes (Condition G). The invention provides a process for producing interpolymer resin particles comprising: a) suspending in an aqueous medium from about 20% to 60% by weight of polyolefin resin particles having a VICAT softening temperature greater than 85 ° C and a melt flow of approximately 2.1 g / 10 minutes (Condition I, 190 ° C, 2.16 kg); b) minimize or eliminate the crosslinking of the polyolefin resin particles; c) adding to the aqueous suspension from about 40 to 80% by weight of a vinyl aromatic monomer and a polymerization initiator to polymerize the vinyl aromatic monomer within the polyolefin resin particles; and d) polymerizing the vinyl aromatic monomer in the polyolefin resin particles having a gel content ranging from about 0 to about 1.5% by weight, based on the weight of the interpolymer resin particles. The invention provides a process for producing articles with improved ESCR characteristics and / or processability by using the process in the preceding paragraph to produce interpolymer particles and using these particles in polymeric processing techniques such as those described herein.

According to a further aspect of the invention, interpolymer resin particles are provided comprising from about 20% to 60% by weight of polyolefin particles and from about 40 to 80% by weight of polymerized vinyl aromatic monomer and the particles have a gel content ranging from about 0 to about 1.5% by weight, based on the weight of the interpolymer resin particles. In the invention, the degree of crosslinking of the polyolefin in the interpolymer resin particles is minimal or eliminated. This can be done by eliminating the use of high temperature crosslinking agent, for example dicumyl peroxide for the polyolefin, for example polyethylene. The result is an interpolymer resin having a gel content ranging from 0 to 15% by weight based on the weight of the interpolymer resin particles. This feature of the invention in conjunction with the interpolymer particles having a VICAT softening temperature ranging from about 90 ° C to about 115 ° C and a resulting melt index ranging from about 0.2 to about 35.0 g / 10 minutes ( Condition G) improves the processing characteristics or the processability of the interpolymer resins. The interpolymer resin particles preferably do not contain a blowing agent that is impregnated into the resin particles through an additional suspension process. Therefore, the resulting interpolymer resin particles are not expandable or foamable particles such as those of the prior prior art for use in foam mounds. Interpolymer resin particles are generally proposed to be used to produce articles through polymer processing techniques, such as sheet extrusion, injection molding, thermoforming, compression molding, rotomolding of blown film extrusion, and extrusion of direct injection foamed sheet at low energy consumption and without melting fracture. A sheet or layer formed of the interpolymer particles of the invention can be used as a tie layer in multi-layer structures. Different from the interpolymer particles of the prior art, the interpolymer particles of the invention are easily extruded into solid sheets, films, etc. and injection molded articles with improved solvent resistance (ESCR) compared to articles made only of polystyrene or polyethylene. The tensile and flexural properties of the articles formed of the interpolymer resin particles of the invention have values that vary between those values for articles made only of polystyrene and those values for articles made only of low density polyethylene, while the properties Thermal and impact levels are close to those of pure polystyrene. The interpolymer resin particles of the invention are particularly advantageous in end-use applications such as solid sheets, foamed sheets, foamed boards, injection molded articles, barrier films, and as a tie layer in multi-layer structures. In a multi-layered structure, the adjacent layer or layers are generally polyethylene, polystyrene or high impact polystyrene. These formed articles have improved properties such as those discussed in the preceding paragraph. The interpolymer particles can be easily adapted to foam applications where a blowing agent is mixed into the molten interpolymer resin particles in conventional extrusion blowing equipment to produce foamed sheet or foamed cardboard with improved ESCR properties and improved comparative damping with the applications of foamed cardboard or foamed polystyrene sheet. U.S. Patent No. 6,166,099 issued by Steven M. Krupinski (NOVA Chemicals Inc., assignee) on December 26, 2000 teaches in columns 7 and 8, a conventional extrusion process and related equipment, which can be Use for foam applications of interpolymer resin particles, the teachings of which are incorporated herein by reference. The interpolymer resin particles are generally pellets formed through a suspension process, the pellets then become film, sheet, etc. through an extrusion process, or injection molding or thermoforming. The pellets formed in the suspension process generally weigh between about 8 milligrams to about 20 milligrams. According to a further aspect of the invention, the resin particles via blow molding (extrusion or injection), injection molding, rotomolding, profile extrusion, solid sheet extrusion, thermoforming and extrusion of foamed sheet by direct injection. A still further aspect of the invention is to provide a polymer composition comprising the interpolymer particles and a second polymer such as polyethylene and polystyrene. Therefore, an object of the present invention is to provide interpolymer resin particles or a polymeric composition comprising interpolymer particles that result in improved processability to form articles with improved ESCR characteristics, improved vapor barrier characteristics, and / or improved physical properties. A further object of the present invention is to provide interpolymer resin particles having little or no gel content, ie ranging from about 0 to about 1.5% by weight based on the weight of the interpolymer resin particles. These and other objects of the present invention will be better appreciated and understood by those skilled in the art from the single figure and the following description and appended claims.

BRIEF DESCRIPTION OF THE FIGURE Figure 1 is a graph showing the results when Composition A and Composition B are plotted against Total Energy (ft. Pounds) (DYNATUP) against the percentages by weight of polystyrene, which is a component of the Composition A and Composition B.

DETAILED DESCRIPTION OF THE INVENTION The term "polyolefin" as used herein may be resins of polyethylene, polypropylene, thermoplastic olefins (TPO's), or thermoplastic elastomers (TPE's). Preferably, in the invention the polyolefin is a polyethylene resin or polypropylene resin. The term "polyethylene resin" as used in the present specification and the appended claims, is meant to include not only an ethylene homopolymer, but also an ethylene copolymer composed of at least 50 mol%, preferably at least 70 mol% , of an ethylene unit and a minor proportion of a monomer copolymerizable with ethylene, and a mixture of at least 50% by weight, preferably at least 60% by weight, of the copolymer or homopolymer of ethylene with another polymer. Examples of monomers copolymerizable with ethylene are vinyl acetate, vinyl chloride, propylene, butene, hexene, acrylic acid and their esters, methacrylic acid and their esters. The other polymer that can be mixed with the ethylene copolymer or homopolymer can be any polymer compatible with it. Examples are polypropylene, polybutadiene, polyisoprene, polychloroprene, chlorinated polyethylene, polyvinyl chloride, a styrene / butadiene copolymer, a vinyl acetate / ethylene copolymer, an acrylonitrile / butadiene copolymer, a vinyl chloride / acetate copolymer. vinyl, etc. Especially preferred species are polypropylene, polybutadiene and styrene / butadiene copolymer. Examples of polyethylene that can be used advantageously in the present invention are low, medium and high density polyethylene, an ethylene / vinyl acetate copolymer, an ethylene / propylene copolymer, a polyethylene-polypropylene blend, a polyethylene blend and an ethylene / vinyl acetate copolymer, and a mixture of polyethylene and an ethylene / propylene copolymer. The polyethylene resin particles used to form the interpolymer resin particles of the invention have a melt index (MI) of about 2.1 g / 10 minutes under Condition I, 190 ° C, 2.16 kg (equivalent to 11.9 g / 10 minutes under Condition G, 230 ° C, 5.0 kg); an average molecular weight number of 20,000 to 60,000; an intrinsic viscosity, at 75 ° C in xylene, from 0.8 to 1.1; a density of 0.910 to 0.940 g / cm3, and a VICAT softening temperature greater than 85 ° C. In the embodiments herein, the polyethylene resin particles have a VICAT softening temperature of about 94 ° C., a melt index (MI) of 2.1 g / 10 minutes (Condition I, 190 ° C, 2.16 kg which is equivalent to 11.9 g / 10 minutes under Condition G, 230 ° C, 5.0 kg), a density of 0.919 g / cm3, and a weight of approximately 20 milligrams. A suitable low density polyethylene (LDPE) is that obtained from NOVA Chemicals Inc. under the trademark LA-0218-AF. The term "polypropylene resin" as used herein is meant to denote not only a propylene homopolymer, but also a block copolymer containing polypropylene in an amount of at least 50% by weight and another polyolefin, and a mixture of at least 50% by weight of polypropylene and another polyolefin. In the present invention, the other polyolefin includes, for example, polyethylene, an ethylene / vinyl acetate copolymer, an ethylene / vinyl chloride copolymer, an ethylene / propylene rubber, polyisobutylene, butyl rubber, styrene rubber / butadiene, polybutene, and polybutadiene. Similar to the teachings of Kajimura, et al., U.S. Patent No. 4,303,757, the polypropylene resin can be used in particulate form, preferably in the form of spheres, flattened particles or pellets having a diameter of about 0.5 to 10. mm to cause rapid absorption of vinyl aromatic monomer. The amount of polyolefin used in the invention ranges from about 20% to about 60% by weight based on the weight of the interpolymer resin particles. A vinyl aromatic monomer is used in the invention.

Examples of vinyl aromatic monomers are styrene, alpha-methylstyrene, ethylstyrene, chlorostyrene, bromostyrene, vinyltoluene, vinylbenzene, and isopropylxylene. These monomers can be used either alone or as a mixture. A mixture of at least 0.1% of the vinyl aromatic monomer and a monomer copolymerizable therewith, such as acrylonitrile, methyl methacrylate, butyl acrylate, or methyl acrylate can also be used. As used herein, the term "vinyl aromatic monomer" means a vinyl aromatic monomer used alone or as a mixture. In one embodiment, the vinyl aromatic monomer is preferably styrene polymerized within the polyolefin resin particles. The amount of vinyl aromatic monomer ranges from about 40% to about 80% by weight based on the weight of the interpolymer resin particles. In general, the interpolymer resin particles are formed as follows: in a reactor, the polyolefin resin particles are dispersed in an aqueous medium prepared by adding 0.01 to 5%, preferably 2 to 3%, by weight based on the weight of the water of a suspending or dispersing agent such as high water-soluble molecular materials, for example, polyvinyl alcohol, methyl cellulose, and inorganic materials slightly soluble in water, for example, calcium phosphate or magnesium pyrophosphate, and then the vinyl monomers Aromatics are added to the suspension and polymerized within the polyolefin resin particles to form an interpenetration network of polyolefin and vinyl aromatic monomers. Basically any of the commonly used and conventionally known suspension agents for polymerization can be employed. These agents are well known in the art and can be freely selected by one skilled in the art. Water is used in an amount generally from 0.7 to 5, preferably 3 to 5 times. that of the starting polyolefin particles added to the aqueous suspension, on a basis by weight. When the polymerization of the vinyl aromatic monomer is complete, the polymerized vinyl aromatic resin is dispersed uniformly within the polyolefin particles. The resulting interpolymer resin particles can be used as raw materials in the production of articles such as sheets, rods, pipes, and film using an extruder, or in the production of articles via injection molding, or thermoforming processes. A blowing agent can be introduced into the interpolymer resin particles to form the foamed sheet via an extruder. It has been found by the inventor that unexpected results are derived when the interpolymer particles of the invention are produced without a crosslinking agent. That is, in the suspension process no crosslinking agent such as a high temperature initiator, for example dicumyl peroxide, is added to the polyolefin, for example polyethylene or polypropylene. Since the polyolefin particles are not crosslinked, the interpolymer particles have very little or no gel content, i.e., a gel content ranging from about 0 to about 1.5%, preferably from about 0 to about 0.8% by weight , and more preferably from about 0 to about 0.5% by weight, based on the weight of the particles. The VICAT softening temperature for the interpolymer resin particles ranges from about 90 ° C to about 115 ° C, and preferably from about 90 ° C to about 105 ° C. The viscosity of the interpolymer particles of the invention is reduced compared to the interpolymer particles of the prior art having relatively high gel content. The reduced viscosity results in improved processability or processing characteristics of the particles so that better quality shaped articles can be manufactured by extrusion and / or injection processes as discussed hereinabove. In a direct injection foaming process, a blowing agent can be introduced into a melt of the interpolymer particles of the invention to produce a foamed article, such as foam sheet, foam board, etc. Suitable blowing agents include aliphatic hydrocarbons such as n-propane, n-butane, iso-butane, n-pentane, iso-pentane, n-hexane, and neopentane, cycloaliphatic hydrocarbons such as cyclobutane and cyclopentane, and halogenated hydrocarbons such as trichlorofluoromethane, dichlorofluorornetane, dichlorodifluoromethane, chlorodifluoromethane and dichlorotetrafluoroethane, etc. HFC's such as tetrafluoroethane, difluoroethane or HCFC's such as chlorodifluoroethane can be used. These blowing agents can be used alone or as mixtures. A preferred amount of the blowing agent is in a range of about 2 to about 15 by weight based on the weight of the interpolymer particles. Specific types of blowing agents are taught in U.S. Patent No. 3,959,189, the teachings of which are incorporated by reference. Preferably, the interpolymer resin particles are not impregnated with the blowing agent in a suspension process; instead the blowing agent is added during the formation of foam products in a conventional manner and in a conventional extrusion process, more roughly which is discussed hereinafter. A process for producing the interpolymer particles of the invention is conveniently carried out as follows. The polyolefin particles are suspended in an aqueous medium containing a dispersing agent. The dispersing agent can be, for example, polyvinyl alcohol, methyl cellulose, calcium phosphate, magnesium pyrophosphate, calcium carbonate, tricalcium phosphate, etc. The amount of dispersing agent employed is 0.01 to 5% by weight based on the amount of water. A surfactant can be added to the aqueous medium. Generally, the surfactant is used to lower the surface tension of the suspension and to help emulsify the water / vinyl aromatic monomer mixture in the initiates and wax mixtures, if used. The aqueous medium is generally heated to a temperature at which the vinyl aromatic monomer can be polymerized, ie from about 60 ° C to about 120 ° C for a period of time, for example, 12 to 20 hours. During this period of 12 to 20 hours, the vinyl aromatic monomer and the low temperature initiators for polymerizing the vinyl aromatic monomer are added to the resulting suspension containing the polyolefin particles dispersed therein. These materials can be added all at once, or gradually in small portions. The suspension is cooled to room temperature. The interpolymer particles are acidified to remove the surface suspension agent, drained, sieved and dried in a fluidized bed dryer. Polymerization of the vinyl aromatic monomer occurs in the polyolefin particles. Examples of suitable initiators include organic peroxy compounds, such as peroxides, peroxy carbonates and peresters. Typical examples of these peroxy compounds are C6-2o acyl peroxides, such as decanoyl peroxide, benzoyl peroxide, lauroyl peroxide, octanoyl peroxide, stearyl peroxide, peresters, such as t-butyl perbenzoate, peracetate t-butyl, t-butyl perisobutyrate, t-butylperoxy-2-ethylhexyl carbonate, or combinations thereof. Other initiators, other than peroxy compounds, are also possible, such as a, a'-azobisisobutyronitrile and azobis-dimethivaleronitrile. The initiators are generally used in an amount of about 0.05 to 2 weight percent, preferably 0.1 to 1 weight percent, based on the weight of the vinyl aromatic monomer. These initiators can be used alone or in combination of two or more initiators. These initiators can be dissolved in the vinyl aromatic monomers, which will be absorbed in the polyolefin particles. These teachings appear in the aforementioned United States Patent No. 3,959,189. The initiators can be dissolved in a solvent. Such solvents include toluene, benzene and 1,2-dichloropropane, etc. The suspension polymerization is carried out in the presence of suspension stabilizers. Suitable suspension stabilizers are well known in the art and comprise organic stabilizers, such as poly (vinyl alcohol), gelatin, agar, polyvinyl pyrrolidine, polyacrylamide; inorganic stabilizers, such as alumina, bentonite, magnesium silicate; surfactants, such as sodium dodecyl benzene sulfonate; or phosphates, similar to tricalcium phosphate, disodium acid phosphate, optionally in combination with any of the stabilization compounds mentioned above. The amount of stabilizer can suitably vary from about 0.01% to about 5.0% by weight, based on the weight of the aqueous phase. The polyolefin particles, and / or the interpolymer resin particles of the invention may contain an anti-static additive.; a flame retardant; a dye or dye; a filler material; stabilizers; and plasticizers, such as white oil. The interpolymer resin particles of the invention can suitably be coated with compositions comprising silicones, metal or glycerol carboxylates, suitable carboxylates are glycerol mon-, di- and tri-stearate, zinc stearate, calcium stearate, and magnesium stearate; and mixtures thereof. Examples of such compositions may be those described in GB Patent No. 1,409,285 and in Stickley, U.S. Patent No. 4,781,983. The coating composition can be applied to the interpolymer resin particles via dry coating or via a slurry or solution in a readily vaporizing liquid in various types of continuous mixing and batching devices. The coating aids in the transfer of the interpolymer resin particles easily through the processing equipment. The interpolymer resin particles may contain other additives such as chain transfer agents, suitable examples include C2_i5 alkyl mercaptans, such as n-dodecyl mercaptan, t-dodecyl mercaptan, t-butyl mercaptan and mercaptan. n-butyl, and other agents such as pentaphenyl ethane and the dimer of -methyl styrene, as well as nucleating agents, such as polyolefin waxes. Polyolefin waxes, ie, polyethylene waxes, have a weight average molecular weight of 250 to 5,000, which are typically finely divided through the polymer matrix in an amount of 0.01 to 2.0% by weight, based on the amount of resin composition. The interpolymer resin particles may also contain from 0.1 to 0.5% by weight, talc, compounds containing organic bromide, and polar agents as described for example in WO 98/01489 which comprises isalkylsulfosuccinates, C8-C20-carboxylate sorbital , and C8-C2o alkylxylene sulfonates. The interpolymer resin particles can be used in extrusion processing. For example, the particles can be fed into an extruder, and then extruded as a single layer or co-extruded into multiple layer structures, for example sheet or film. Optionally, a blowing agent can be forced into the particles passing through the extruder and a foil, cardboard, or foamed rod can be formed. In additional embodiments, the interpolymer resin particles can be used in injection molding or can be thermoformed into desired forms in a manner well known to those skilled in the art. Alternatively, an extruded film or sheet produced from the interpolymer resin particles can be used as a tie layer in a multilayer structure. A co-extrusion process can be employed wherein the interpolymer resin particles are extruded between incompatible polymer sheets, for example a sheet made of polystyrene or polystyrene and rubber, for example. example high impact polystyrene (HIPS), and a sheet made of polyethylene, thereby producing improved adhesion to the multi-layer structure. It is assumed that the polyethylene resin in the interpolymer resin particles creates a chemical bond with the polyethylene in the polyethylene layer and that the polystyrene in the interpolymer resin particles creates a chemical bond with the polystyrene in the polystyrene layer. This improved adhesion becomes important when a polyethylene cap layer is extruded onto the polystyrene sheet to improve the ESCR, ie, crack resistance due to environmental stress. A further example may belong to the food industry where in view of FDA requirements the food can not come into contact with the substrate layer of the food container. When polypropylene is used as the polyolefin base resin in the interpolymer particles of the invention, it may be preferable to reduce the viscosity of the polypropylene prior to, during or after the formation of the interpolymer. Viscosity reduction is the intentional chain splitting of polypropylene to produce lower molecular weight, a narrower molecular weight distribution, a slow crystallization rate, and faster molecular relaxation time in the molten state. Viscosity reduction can be performed by extrusion under high shear to mechanically degrade the higher molecular weight chains as taught in Fudge, USPatents Nos. 4,622,347 and 4,677,134 above or can be done by the use of peroxides as taught in Fudge, U.S. Patent No. 4,692,471 above during the formation of the interpolymer resin particles. The peroxide mixed with the polymers can be any of the compounds having a half-life temperature of 10 hours of between 100 ° C and 130 ° C such as dicumyl peroxide (117 ° C) or 1,3-bis (a-tert. -butylperoxyisopropyl) benzene (116 ° C). Examples 7 and 8 use dicumyl peroxide to reduce the viscosity of the polypropylene of the interpolymer resin particles of the invention. The interpolymer resin particles of the invention can be combined with a second polymer to form a polymeric composition which can then be used to form articles via processing, eg, sheet extrusion, rotomolding, thermoforming, compression molding, molding. injection, and blown film extrusion. The second polymer can be selected from the group consisting of polyethylene and polystyrene. In this composition, the interpolymer resin particles may be present in an amount ranging from about 0.1 wt% to about 99.9 wt% and the second polymer may be present in an amount ranging from about 99.9 wt% to about 0.1% by weight. In one embodiment of the invention, the interpolymer resin particles are present in an amount ranging from about 10% by weight to about 90% by weight and the second polymer is present in an amount ranging from about 90% to about 10% by weight. % by weight based on the weight of the interpolymer resin. The following examples are intended to assist in the understanding of the present invention, however, in no way, these examples should be construed as limiting the scope thereof.

EXAMPLES Example 1 This example 1 relates to styrene-polyethylene interpolymer resin particles comprised of 60% by weight of polystyrene and 40% by weight of low density polyethylene, based on the weight of the interpolymer resin particles. No dicumyl peroxide cross-linking agent was added to the formulation. A mixture of 520 pounds (236.08 kg) of deionized water, 9.6 pounds (4.35 kg) of tri-calcium phosphate as a suspending agent, and 27 grams of a strong anionic surfactant was charged to a polymerization reactor with the agitator running at 88 rpm to prepare an aqueous medium. The surfactant was Nacconol® 90 (Stephan Chemical Co.), which is sodium n-dodecyl benzene sulfonate. The aqueous medium was heated to about 91 ° C and maintained for about 10 minutes. Then 112 pounds (50.84 kg) of low density polyethylene pellets (LDPE) (LA-0218-AF from NOVA Chemicals Inc.), each weighing approximately 20 milligrams, having a melt index at condition I (190 ° C, 2.16 kg) of 2.1 g / 10 minutes, and a VICAT softening point of about 93 ° C were added to the aqueous medium. This suspension of beads and water continued to be stirred at 88 rpm. The low temperature polystyrene initiators, ie 373 grams of benzyl peroxide (BPO) (75% active) and 70 grams of tertiary butyl perbenzoate (TBP) were dissolved in 84 pounds (38.13 kg) of styrene monomer to prepare a monomer solution, and this mixture was pumped into the reactor for 200 minutes .. A second batch of 84 pounds (38.13 kg) of pure styrene was then added to the reactor for 100 minutes at a temperature of 91 ° C. The contents of the reactor were maintained at 91 ° C for an additional 90 minutes to allow the styrene to soak and react within the polyethylene. Then the contents of the reactor were heated to 140 ° C for 2 hours and maintained for an additional 4 hours to polymerize the remaining styrene in polystyrene within the polyethylene matrix. After polymerization, the reaction mixture was cooled and hydrochloric acid was added to dissolve the suspending agents. The resin particles were then washed and dried. The average gel content for two samples of the resin particles was 0.65% by weight based on the weight of the interpolymer resin particles formed. The melt index was 1046 g / 10 minutes at condition G (230 ° C and 5.0 kg).

Example 2 This example 2 relates to interpolymer polystyrene interpolymer resin particles comprised of 70% by weight of polystyrene and 30% by weight of low density polyethylene, based on the weight of the interpolymer resin particles. No dicumyl peroxide cross-linking agent was added to the formulation. A mixture of 520 pounds (236.08 kg) of deionized water, 9.6 pounds (4.35 kg) of tri-calcium phosphate as a suspending agent, and 27 grams of a strong anionic surfactant (Nacconol® 90) was charged to a reactor. polymerization with the agitator running at 88 rpm to prepare an aqueous medium. The aqueous medium was heated to about 91 ° C and maintained for about 10 minutes. Then 84 pounds (38.13 kg) of low density polyethylene pellets (LA-0218-AF) were suspended in the aqueous medium. The suspension continued to be stirred at 88 rpm. The low temperature polystyrene initiators, ie 356 grams of benzyl peroxide (BPO) and 66.8 grams of tertiary butyl perbenzoate (TBP) were dissolved in 98 pounds (44.49 kg) of styrene monomer to prepare a monomer solution, and this mixture was pumped into the reactor for 200 minutes. A second batch of 98 pounds (44.49 kg) of pure styrene was then added to the reactor for 100 minutes at a temperature of 91 ° C. The contents of the reactor were maintained at 91 ° C for an additional 90 minutes to allow the styrene to soak and react within the polyethylene. Then the contents of the reactor were heated to 140 ° C for 2 hours and kept at this temperature for an additional 4 hours to polymerize the remaining styrene in polystyrene within the polyethylene matrix. After the polymerization, the reaction mixture was cooled and hydrochloric acid was added to dissolve the suspending agents. The resin particles were then washed and dried. The average gel content for two samples of the resin particles was 0.45% by weight based on the weight of the particles. The melt index was .501 g / 10 minutes at condition G (230 ° C and 5.0 kg). Example 3 This example 3 relates to styrene-polyethylene interpolymer resin particles comprised of 50% by weight of polystyrene and 50% by weight of low density polyethylene, based on the weight of the interpolymer resin particles. No dicumyl peroxide cross-linking agent was added to the formulation. A mixture of 520 pounds (236.08 kg) of deionized water, 9.6 pounds (4.35 kg) of tri-calcium phosphate as a suspending agent, and 27 grams of a strong anionic surfactant (Nacconol® 90) was charged to a reactor. polymerization with the agitator running at 88 rpm to prepare an aqueous medium. The aqueous medium was heated to about 91 ° C and maintained for about 10 minutes. Then 140 pounds (63.56 kg) of low density polyethylene pellets (LA-0218-AF) were suspended in the aqueous medium. The suspension continued to be stirred at 88 rpm. The low temperature polystyrene initiators, ie 350 grams of benzyl peroxide (BPO) and 65.63 grams of tertiary butyl perbenzoate (TBP) were dissolved in 70 pounds (31.78 kg) of styrene monomer to prepare a monomer solution, and this mixture was pumped into the reactor for 200 minutes. A second batch of 70 pounds (31.78 kg) of pure styrene was then added to the reactor for 100 minutes at a temperature of 91 ° C. The contents of the reactor were maintained at 91 ° C for an additional 90 minutes to allow the styrene to soak and react within the polyethylene. Then the contents of the reactor were heated to 140 ° C for 2 hours and maintained for an additional 4 hours to polymerize the remaining styrene in polystyrene within the polyethylene matrix. After polymerization, the reaction mixture was cooled and hydrochloric acid was added to dissolve the suspending agents. The resin particles were then washed and dried. The average gel content for two samples of the resin particles was 0.69% by weight based on the weight of the interpolymer resin particles formed. The melt index was 1022 g / 10 minutes at condition G (230 ° C and 5.0 kg).

EXAMPLE 4 This Example 4 is similar to Example 1 in that a polystyrene-styrene-polyethylene interpolymer was produced with 60% by weight of polystyrene and 40% by weight of low density polyethylene based on the weight of the interpolymer particles. In this example 4, however, a chain transfer agent was used in an attempt to increase the melt flow rate of the interpolymer resin. The alpha methyl styrene dimer (a chain transfer agent) in an amount of 163 grams, ie about 0.20 parts percent styrene was added to the suspension with benzyl peroxide (BPO) and tertiary butyl perbenzoate ( TBP). The average gel content for two samples of the resin particles was 1.01% by weight based on the weight of the interpolymer resin particles formed. The melt index was 2,688 g / 10 minutes (Condition G). These results demonstrate that when using a chain transfer agent without a crosslinking agent the melt index was increased compared to Example 1.

Example 5 In this example 5, interpolymer resin particles were produced comprising 60% by weight of polystyrene and 40% by weight of ethylene / vinyl acetate copolymer (EVA), based on the weight of the resin particles. No high temperature crosslinking agent was added, ie dicumyl peroxide initiator. A mixture of 380 pounds (172.52 kg) of deionized water, 13 pounds (5.90 kg) of tri-calcium phosphate as a suspending agent, and 8.6 grams of anionic surfactant Nacconol 90 were charged to a polymerization reactor with the agitator that it works at approximately 102 rpm to prepare an aqueous medium. The aqueous medium was heated to about 60 ° C and maintained for approximately 30 minutes. Then 125 pounds (56.75 kg) of low density polyethylene vinyl acetate (EVA) pellets containing 4.5% by weight of vinyl acetate and 95.5% by weight of ethylene (NA 480 from Equistar Chemicals, LP, Houston, Texas) and which have a density of approximately 0.923 g / cc and a melt index of 0.25 g / 10 minutes (Condition I, 190 ° C, 2.16 kg) were suspended in the aqueous medium. The temperature of the reactor was increased to 85 ° C. The low temperature polystyrene initiators, ie, 246 grams of benzoyl peroxide (BPO) and 30 grams of tertiary butyl perbenzoate (TBP), were dissolved in 22.6 pounds (10.26 kg) of styrene monomer to prepare a solution of monomer, and this mixture was pumped into the reactor for 96 minutes. A second batch of 146 pounds (66.28 kg) of pure styrene and 5.0 Ibs (2.27 kg) of butyl acrylate were then added to the reactor for 215 minutes. Then the contents of the reactor were heated and maintained at 140 ° C for 8 hours to finish the polymerization of styrene inside the polyethylene matrix. After the polymerization was completed, the reaction mixture was cooled and changed to a wash vessel where the muriatic acid (HCl) was added to dissolve the suspending agents from the pellet surfaces. The pellets were then washed and dried. The average gel content for two samples of the resin pellets was 0.46% by weight based on the weight of the interpolymer resin particles formed.

The melt index of the pellets was 0.21 g / 10 minutes (Condition G).

Example 6 This Example 6 relates to interpolymer resin particles comprising 70% by weight of polystyrene based on the weight of the interpolymer resin particles, and 30% by weight of ethylene vinyl acetate copolymer (EVA). No high temperature crosslinking agent was added, that is, no dicumyl peroxide initiator was added. The process for making the particles was similar to that for Example 5. The low density polyethylene vinyl acetate (EVA) used in Example 5 was the same as that used in Example 6. A mixture of 411 pounds (186.59 kg. ) of deionized water, 9.8 pounds (4.44 kg) of tricalcium phosphate as a suspending agent, and 6.5 grams of anionic surfactant (Nacconol 90) were charged to a polymerization reactor with the stirrer operating at approximately 102 rpm to prepare an aqueous medium. The aqueous medium was heated to about 60 ° C and maintained for approximately 30 minutes. Then 87 pounds (39.49 kg) of low density ethyl vinyl acetate pellets were suspended in the aqueous medium. The temperature of the reactor was increased to 85 ° C. The low temperature polystyrene initiators, ie, 246 grams of benzoyl peroxide (BPO) and 30 grams of tertiary butyl perbenzoate (TBP), were dissolved in 22.6 pounds (10.26 kg) of styrene monomer to prepare a solution of monomer, and this mixture was pumped into the reactor for 96 minutes. A second batch of 146 pounds (66.28 kg) of pure styrene and 5.0 lbs (2.27 kg) of butyl acrylate were then added to the reactor for a period of 215 minutes. Then the contents of the reactor were heated and maintained at 140 ° C for 8 hours to finish the polymerization of styrene inside the polyethylene matrix. After the polymerization was completed, the reaction mixture was cooled and changed to a wash vessel where the muriatic acid (HCl) was added to dissolve the suspending agents from the pellet surfaces. The pellets were then washed and dried. The average gel content for two samples of the resin pellets was 0.32% by weight based on the weight of the interpolymer resin particles formed. The melt index of the pellets was 0.25 g / 10 minutes (Condition G). Examples 7 and 8 below show that the use of dicumyl peroxide for viscosity reduction purposes increases the melt index of the resin.

Example 7 This Example 7 relates to interpolymer resin particles comprising 60% by weight of polystyrene based on the weight of the interpolymer resin particles, and 40% by weight of polypropylene. Dicumyl peroxide was added to reduce the viscosity of the polypropylene. A mixture of 520 pounds (236.08 kg) of deionized water, 9.6 pounds (4.35 kg) of tricalcium phosphate as a suspending agent, and 27 grams of Nacconol 90 were charged to a polymerization reactor with the agitator running at approximately 88 ° C. rpm to prepare an aqueous medium. The aqueous medium was heated to about 91 ° C and maintained for about 10 minutes. Then 112 pounds (50.84 kg) of polypropylene pellets (Huntsman P5M4K-046), each weighing approximately 20 milligrams and having an MI of 25.5 g / 10 minutes (Condition G) were suspended in the aqueous medium. The suspension was continued until shaken at 88 rpm. The low temperature polystyrene initiators, ie 473 grams of benzyl peroxide (BPO) and 145 grams of tertiary butyl perbenzoate (TBP), - and 173 grams of dicumyl peroxide (to reduce the viscosity of the polypropylene) were dissolved in 84 pounds (38.13 kg) of styrene monomer to prepare a monomer solution, and this mixture was pumped into the reactor for 200 minutes. A second batch of 84 pounds (38.13 kg) of pure styrene was then added to the reactor for 100 minutes at a temperature of 91 ° C. The reactor contents were maintained at 91 ° C for an additional 90 minutes to allow the -styrene penetrate and react with polypropylene. Then the contents of the reactor were heated to 140 ° C for 2 hours and maintained for an additional 4 hours to polymerize the styrene in polystyrene within the polyethylene matrix. After polymerization, the reaction mixture was cooled and stirred, and an acid was added to dissolve the suspending agents. The average gel content for two samples of the resin particles was 0.47% by weight based on the weight of the interpolymer resin particles formed. The melt index was 32.61 g / 10 minutes (Condition G).

Example 8 This Example 8 relates to interpolymer resin particles comprising 70% by weight of polystyrene based on the weight of the interpolymer resin particles, and 30% by weight of polypropylene. Dicumyl peroxide was added to the formulation to reduce the viscosity of the polypropylene. The process for producing the interpolymer resins is similar to Example 7. A mixture of 520 pounds (236.08 kg) of deionized water, 9.6 pounds (4.35 kg) of tricalcium phosphate as a suspending agent, and 27 grams of an anionic surfactant (Nacconol 90) were charged to a polymerization reactor with the agitator running at about 88 rpm to prepare an aqueous medium. The aqueous medium was heated to about 91 ° C and maintained for about 10 minutes. Then 112 pounds (50.84 kg) of polypropylene pellets (Huntsman P5M4K-046) each weighing approximately 20 milligrams and having an MI of 25.5 g / 10 minutes (Condition G) were suspended in the aqueous medium. The suspension continued to be stirred at 88 rpm. The low temperature polystyrene initiators, ie, 475 grams (215.65 kg) of benzyl peroxide (BPO) (for improved insertion) and 145 grams of tertiary butyl perbenzoate (TBP) (to reduce styrene waste), and 173 grams of dicumyl peroxide to reduce the viscosity of the polypropylene were dissolved in 98 pounds (44.49 'kg) of styrene monomer to prepare a monomer solution, and this mixture was pumped into the reactor for 200 minutes. A second batch of 98 pounds (44.49 kg) of pure styrene was then added to the reactor for 100 minutes at a temperature of 91 ° C. The contents of the reactor were maintained at 91 ° C for an additional 90 minutes to allow the styrene to penetrate and react within the polypropylene. Then the contents of the reactor were heated to 140 ° C for 2 hours and kept for an additional 4 hours to polymerize the styrene in polystyrene within the matrix of the polypropylene. After the polymerization was completed, the reaction mixture was cooled and stirred, and an acid was added to dissolve the suspending agents. The average gel content for two samples was 0.41% by weight based on the weight of the interpolymer resin particles formed. The melting index was 21.92 g / 10 minutes (Condition G). The particles produced in Examples 1-8 were oven dried at 120 ° F (48.4 ° C) and then cast into plates using an Engel Model 80 injection molding machine. Mechanical and physical properties were measured and tested for according to the standards described by ASTM. These properties appear in Table 1 below. As stated hereinbefore, the flexural and tensile properties of the articles formed from the interpolymer resin particles of the invention have values that vary between those values for articles made solely of polystyrene and those values for articles made solely of low density polyethylene, while the thermal and impact properties of the articles made of the interpolymer resin particles approximate those of pure polystyrene.

Table 1 Example 9 Two and three layer sheet structures using the compositions and type of extruders shown in Table 2 were formed in a WELEX® sheet coextrusion line. Each stream at temperatures between 430 ° F (218.9 ° C) and 450 ° F (229.9 ° C) was passed in an extrusion die head (standard 54"backing edge (137.16 cm) WELEX®) to form a continuous multi-layered sheet structure, which in turn was passed through a stack of rollers at roller pressures of approximately 70 psig and roll temperatures ranging from 180 ° to 190 °. ° F (81.4 ° to 86.9 ° C) for a curing process The multi-layer sheet structures were then visually inspected and qualitatively evaluated by adhesion, the results of which appear in Table 2. "Good" indicates no detachment of the layers. "Poor" indicates detachment of the layers.

HIPS 5410 (Product of NOVA Chemicals Inc. - high impact polystyrene i or comprised of styrene and polybutadiene SCLAIR 31E (Polyethylene Fusion Index 11.5) SCLAIR 61C (Polyethylene Fusion Index 5.3).

This Example 9 shows that "good" adhesion occurs when one of the layers of multilayer sheet structures consists of 100% of the particles of interpolymer resin of the invention, ie, Examples 4, 5, and 6.

Example 10 This Example 10 refers to the only Figure that illustrates the instrumented impact test values (DYNATUP-Total Energy in feet Lbs. (J) for Composition A and Composition B. Composition A is the composition of the invention comprising the interpolymer particles of the Example 1 (60% PS / 40% PE) containing polystyrene (NOVA 5 1210-crystal) in the percentages by weight shown in the single Figure. Composition B is a mixture of low density polyethylene (pellets of NOVA-LA-0218-AF) and polystyrene in the percentages by weight shown in the Figure. Composition A and Composition B were produced by dry mixing, mixed in a single screw extruder, and the cut pellets were injection molded into circular 3 inch (7.62 cm) diameter plates for impact testing. The DYNATUP values for Composition A of the invention remained relatively constant as the percentage by weight of increased polystyrene, while those for Composition B fell as the percentage by weight of increased polystyrene. This indicates improved compatibility between polyethylene and polystyrene for the interpolymer particles of the invention compared to pure physical blends of polyethylene and polystyrene.

EXAMPLE 11 This Example 11 illustrates the properties of environmental stress crack (ESCR) resistance of 70% PS / 30% EVA resin (Example 6) against 100% Polystyrene (PS) glass (NOVA grade 1510). Ten specimens were used as control samples. The chemical resistance test results for molded samples are shown in Table 3.

Table 3 Notes: all specimens were conditioned at 23 ° C and 50% relative humidity before the chemical resistance test or exposure. The food substance used was a 50% solution of cottonseed oil and 50% oleic acid (by weight). The entire tensile test was performed using a 0.2 inch (0.50 cm) / minute piston inner protrusion speed using a 2"(5.08 cm) extensiometer.

For a period of 7 days, the "Strain Traction Tension" will decay by 80% for PS glass specimens exposed to 0.5% deformation and a mixture of oils, that is, 6.25 kpsi was reduced to 1.34 kpsi, while the "Fissure Pull Tension" for the interpolymer of Example 6 remained relatively the same, ie 5.07 kpsi versus 5.10 kpsi. Although the present invention has been described particularly in terms of specific embodiments thereof, it will be understood in view of the present disclosure that numerous variations in the invention are now still possible within the scope of the invention. Accordingly, the invention is to be broadly constructed and only limited by the scope and spirit of the claims now appended thereto. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (32)

CLAIMS Having described the invention as above, the contents of the following claims are claimed as property:

1. Process for forming interpolymer resin particles with improved processability characteristics for manufacturing equipment for forming articles, characterized in that it comprises the steps of: a) suspending in an aqueous medium from about 20% to 60% by weight of resin particles of polyolefin having a VICAT softening temperature greater than 85 ° C and a melt index of about 2.1 g / 10 minutes (Condition I, 190 ° C, 2.16 kg); b) minimizing the degree of crosslinking of the polyolefin resin particles; c) adding to the aqueous suspension from about 40 to 80% by weight of a vinyl aromatic monomer and a polymerization initiator to polymerize the vinyl aromatic monomer within the polyolefin resin particles; and d) polymerizing the vinyl aromatic monomer in the polyolefin resin particles to form the interpolymer resin particles with a gel content ranging from about 0 to about 1.5% by weight, based on the weight of the interpolymer resin particle , the interpolymer resin particles have a VICAT softening temperature ranging from about 90 ° C to about 115 ° C and a melt index ranging from about 0.2 to about 35 g / 10 minutes (Condition G).

Process according to claim 1, characterized in that the interpolymer resin particles have a VICAT softening temperature from about 90 ° C to about 105 ° C, and a gel content ranging from about 0 to about 0.8% in weight, based on the weight of the interpolymer resin particles.

Process according to claim 1, characterized in that the steps additionally comprise: e) using the interpolymer resin particles in an extrusion process, and introducing a blowing agent into the interpolymer resin particles to form a foamed article .

Process according to claim 1, characterized in that the weight of the polyolefin particles is about 30% by weight based on the weight of the interpolymer particles, and the weight of the vinyl aromatic monomer is about 70% by weight based on the weight of the interpolymer particles.

5. Process according to claim 1, characterized in that the weight of the polyolefin resin particles is about 40% by weight based on the weight of the interpolymer particles, and the weight of the vinyl aromatic monomer is about 60% by weight based on the weight of the interpolymer particles.

Process according to claim 1, characterized in that the weight of the polyolefin resin particles is about 50% by weight based on the weight of the interpolymer particles, and the weight of the vinyl aromatic monomer is about 50% by weight based on the weight of the interpolymer particles.

Process according to claim 1, characterized in that the vinyl aromatic monomer is selected from the group consisting of styrene, alpha-methylstyrene, ethylstyrene, chlorostyrene, bromostyrene, vinyltoluene, vinylbenzene, isopropylxylene, and mixtures thereof.

Process according to claim 7, characterized in that the polyolefin resin of the polyolefin resin particles is selected from the group consisting of polyethylene, polypropylene, thermoplastic olefins, and thermoplastic elastomer resins.

Process according to claim 8, characterized in that the vinyl aromatic monomer is styrene and wherein the polyolefin resin of the polyolefin resin particles is selected from the group consisting of polyethylene and polypropylene resins.

10. Process according to claim 8, characterized in that the polyethylene resin is selected from the group consisting of low density polyethylene and ethylene / vinyl acetate copolymer.

11. Process according to claim 1, characterized in that the interpolymer resin particles are pellets and each pellet weighs from about 8 milligrams to 20 milligrams.

12. Interpolymer resin particles, characterized in that they are comprised from about 20% to about 60% by weight based on the weight of the particles of uncrosslinked polyolefin resin particles having a VICAT softening temperature greater than 85 ° C and a melt index of approximately 2.1 g / 10 minutes (Condition I, 190 ° C, 2.16 kg); and from about 40% to about 80% by weight based on the weight of the particles (interpolymer of polystyrene particles that have been polymerized in the non-crosslinked polyolefin resin particles to form an interpenetration network of polyolefin resin particles. and polystyrene particles, and the interpolymer resin particles have a gel content ranging from about 0 to about 1.5% by weight based on the weight of the interpolymer resin particles, a VICAT softening temperature ranging from about 90. ° C at about 115 ° C, and a melt index value ranging from about 0.2 to about 35.0 g / 10 minutes (Condition G) 13.

Interpolymer resin particles according to claim 12, characterized in that the particles of interpolymer resin have a VICAT temperature that varies from approximately 90 ° C to aa about 105 ° C and a gel content ranging from about 0 to about 0.8% by weight based on the weight of the interpolymer resin particles.

Interpolymer resin particles according to claim 12, characterized in that the weight of the polyolefin resin particles is approximately 30% by weight and the weight of the polystyrene is approximately 70% based on the weight of the resin particles of interpolymer

15. Interpolymer resin particles according to claim 12, characterized in that the weight of the polyolefin resin particles is approximately 40% and the weight of the polystyrene is approximately 60%, based on the weight of the interpolymer resin particles. .

16. Interpolymer resin particles according to claim 12, characterized in that the weight of the polyolefin resin particles is approximately 50% and the weight of the polystyrene is approximately 50%, based on the weight of the interpolymer resin particles.

Interpolymer resin particles according to claim 12, characterized in that the vinyl aromatic monomer is selected from the group consisting of styrene, alpha-methylstyrene, ethylstyrene, chlorostyrene, bromostyrene, vinyltoluene, vinylbenzene, isopropylxylene, and mixtures thereof. same.

18. Interpolymer resin particles according to claim 17, characterized in that the polyolefin resin of the polyolefin resin particles is selected from the group consisting of resins of polyethylene, polypropylene, thermoplastic olefins (TPO'S), and thermoplastic elastomers ( TPE'S).

19. Interpolymer resin particles according to claim 18, characterized in that the vinyl aromatic monomer is styrene and wherein the polyolefin resin of the polyolefin resin particles is selected from the group consisting of polyethylene resin and polypropylene resin. .

20. Interpolymer resin particles according to claim 19, characterized in that the polyethylene resin is selected from the group consisting of low density polyethylene and ethylene / vinyl acetate.

21. Interpolymer resin particles according to claim 12, characterized in that the resin particles are pellets and each pellet weighs from about 8 milligrams to about 20 milligrams.

22. Extruded article, characterized in that it is made of the interpolymer resin particles according to claim 12.

23. Article according to the claim 22, characterized in that the article is an extruded solid sheet.

24. Article according to claim 22, characterized in that the article is an extruded solid film.

25. Article according to claim 22, characterized in that the article is an extruded foamed sheet.

26. Injection molded article, characterized in that it is made of the interpolymer resin particles according to claim 12.

27. Thermoformed article, characterized in that it is made of the interpolymer resin particles according to claim 12.

28. Multilayer structure, characterized in that it comprises a first layer formed of the interpolymer resin particles according to claim 12 and placed adjacent to at least a second layer wherein the first layer adheres to the second layer to form the structure of multiple layers.

29. Polymer composition, characterized in that it comprises the interpolymer resin particles according to claim 12 and at least one second polymer.

30. Polymer composition according to claim 29, characterized in that the second polymer is selected from the group consisting of polyethylene and polystyrene.

31. Polymer composition according to claim 30, characterized in that the amount of the second polymer ranges from about 0.1% to about 99.9% by weight and the amount of the interpolymer resin particles ranges from about 99.9% to about 0.1% by weight based on the weight of the polymer composition.

32. Process for producing articles with improved ESCR properties, characterized in that it uses the interpolymer resin particles according to claim 12.