MXPA98010498A - Control of morphology in polypropil grafting - Google Patents

Abstract

A graft copolymer comprising a structure of a propylene polymer material having a graft of vinyl monomer polymerized thereto is produced by: (1) treating a propylene polymer material with a free radical polymerization initiator; ) treating the propylene polymer material with at least one graft monomer capable of being polymerized by free radicals, in the presence of a polymerization rate modifier, and (3) removing any unreacted graft monomer from the polymer material of propylene copolymerized in graft, decompose any unreacted initiator, and deactivate any residual free radicals in the material. The use of the polymerization rate modifier increases the polymerization induction time on the polymer surface, thereby facilitating the diffusion of monomer into the polymer particles so as to inhibit the polymerization of the monomer surface.

Description

MORPHOLOGY CONTROL IN POLYPROPYLENE GRAFT COPOLYMERS This invention relates to a process for the graft copolymerization of propylene polymer materials. The morphology of grafted polyolefin particles depends on the polymerization conditions and the porosity of the material used as the structure of the graft copolymer. When the porosity of the starting material is too low, a typical polypropylene graft copolymer with 875 parts of monomer added for many polypropylene parts has a tendency to form a surface layer with a high polymerized monomer content ("peeling"). When the level of monomer addition is high, this flaking often produces a sticky surface in the particles, resulting in low fluidity of the polymer particles, which in turn can cause fouling of the reactor. A variety of polymerization inhibitors have been used during "graft polymerization reactions." For example, US 3,839,172 discloses a process for radiation grafting of acrylic monomers to perhalogenated olefin polymer substrates in which a polymerization inhibitor such as Ferrous ammonium sulfate or copper chloride is present in the grafting medium to prevent the homopolymerization of the acrylic monomer US 4,196,095 describes the use of a polymerization inhibitor such as a combination of copper and copper acetate in a process for grafting by radiation of a hydrophilic compound towards a hydrophobic substrate in the presence of a crosslinking agent and a solvent soluble in polar solvent US 4,377,010 describes the use of homopolymerization inhibitors such as ferrous sulfate or potassium ferricyanide during the graft polymerization initiated by radiation acrylic monomers s toward a base polymer to make a biocompatible surgical device. E.U.A. US 5,283,287 describes the use of polymerization inhibitors such as catechol, hydroquinones, organic sulfides and dithiocarbamates to control the sequence of acrylonitrile units in a process for preparing thermoplastic resin compositions having excellent resistance to HCFC. However, there is still a need for polymerization rate modifiers that will inhibit surface polymerization during graft polymerization of propylene polymer materials and, therefore, improve the processability of the resulting polymer particles. The process of this invention for making a graft copolymer comprises, in a substantially non-oxidizing environment, (a) treating particles of a propylene polymer material with an organic compound that is a free radical polymerization initiator; (b) treating the propylene polymer material for a period of time coinciding with or following (a), with or without overlap, with from about 5 to about 240 parts of at least one graft monomer capable of being polymerized by radial free, per hundred parts of the propylene polymer material, in the presence of a polymerization rate modifier capable of operating in a substantially non-oxidizing environment; and (c) removing any unreacted graft monomer from the resulting grafted propylene polymer material, decomposing any unreacted initiator, and deactivating any residual free radicals in the material. The use of the polymerization rate modifier increases the induction time of polymerization on the surface and consequently facilitates the diffusion of the monomer towards the particles of the propylene polymer material used as the starting material. The surface polymerization is inhibited and therefore, the resulting particles exhibit a lower content of polymerized monomer on the surface of the particles than in the interior of the particles. The polymerization rate modifier has no significant impact on the number average molecular weight and weight average, molecular weight distribution, xylene solubles at room temperature, grafting efficiency, or the mechanical properties of the graft copolymer product. Figure 1 is an infrared Fourier transform (FTIR) scan along the radius of a microtomograph particle of a graft copolymer comprising a polypropylene structure, to which polystyrene was grafted. In (A), no sulfur was added to the monomer feed or polymerization rate modifier (PRM). In (B), 200 parts of sulfur per million parts by weight of styrene were added. In (C), 400 ppm of sulfur was added.

Figure 2 is an FTIR scan along the radius of a microtome particle of a graft copolymer comprising a polypropylene structure, to which polystyrene was grafted. In (A), no sulfur was added to the monomer feed as a PRM. In (B), 400 ppm of sulfur was added. Figure 3 is an FTIR scan along the radius of a graft copolymer comprising a polypropylene structure, to which polystyrene was grafted. Three traces are shown: without the addition of a PRM, with the addition of 50 parts of 1, -benzoquinone per one million parts of styrene, and with the addition of 800 pp "m of 1,4-benzoquinone. is an FTIR scan along the radius of a microtome particle of a graft copolymer comprising a polypropylene structure, to which poly (methyl methacrylate-co-methylacrylate) is grafted Two traces are shown: without the addition of a PRM and with the addition of 1350 parts of 1,4-benzoquinone per million parts by weight of monomer Figure 5 is an FTIR scan along the radius of a microtome particle of a graft copolymer comprising a polypropylene structure. To which polystyrene was grafted, two traces are shown: without the addition of a PRM and with the addition of 750 parts of N, N-diethylhydroxylamine per million parts per mole of styrene, the propylene polymer material used as the structure d the graft copolymer can be: (a) a crystalline propylene homopolymer having an isotactic index greater than 80, preferably from about 85 to about 99; (b) a random crystalline copolymer of propylene and an olefin selected from the group consisting of ethylene and alpha-olefins of C.-C10, as long as the olefin is ethylene, the maximum polymerized ethylene content is 10% by weight. weight, preferably about 4%, and when the olefin is an alpha-olefin of C. ~ C_0, the maximum polymerized content thereof is 20% by weight, preferably about 16% the copolymer having an isotactic index greater than 85; (c) a random crystalline terpolymer of propylene and two olefins selected from the group consisting of ethylene and alpha-olefins of C.-C8, provided that the maximum content of alpha-olefin of C4-Ca polymerized is 20% by weight, preferably about 16%, and, when ethylene is one of the olefins, the maximum polymerized ethylene content is 5% by weight, preferably about 4%, the terpolymer having an isotactic index greater than 85; (d) an olefin polymer composition comprising: (i) about 10 parts to about 60 parts by weight, preferably about 15 parts to about 55 parts, of a homopolymer of Crystalline propylene having an isotactic index greater than 80, preferably from about 85 to about 98, or a crystalline copolymer selected from the group consisting of (a) propylene and ethylene, (b) propylene, ethylene and an alpha-olefin of C.-C ?, and (c) propylene and an alpha-olefin of C4 ~ Cg, the copolymer having a propylene content of more than 85% in weight, of preferably about 90% to about 99%, and an isotactic index greater than 85; (ii) from about 3 parts to about 25 parts by weight, preferably from about 5 parts to about 20 parts, of an ethylene-propylene copolymer or an alpha-olefin of C ^ -Cβ which is insoluble in xylene at temperature ambient; and 10 (iii) from about 30 parts to about 25 parts by weight, preferably from about 20 parts to about 65 parts, of a selected elastomeric copolymer to from the group consisting of (a) ethylene and propylene, (b) ethylene, propylene, and a C4-C8 alpha-olefin, and (c) ethylene and a C4-C8 alpha-olefin, the copolymer optionally containing from about 0.5% to about 10% by weight of a diene, and containing less than 70% by weight, preferably from about 10% to about 60%, more preferably about 12% by weight about 55%, of ethylene and being soluble in xylene at room temperature and having an intrinsic viscosity of about 1.5 to about 4.0 dl / g; the total of (ii) and (iii), based on the total olefin polymer composition that is from about 50% to about 90%, and the weight ratio of (ii) / (iii) being less than 0.4, preferably 0.1 to 0.3, in Wherein the composition is prepared by polymerization in at least two steps and has a flexural modulus of less than 150 MPa; And (e) a thermoplastic olefin comprising: (i) from about 10% to about 60%, preferably from about 20% to about 50%, of a propylene homopolymer having an isotactic index greater than 80, or a crystalline copolymer selected from the group consisting of (a) ethylene and propylene, (b) ethylene, propylene and an alpha-olefin of C.-Cß, and (c) ethylene and an alpha-olefin of C-β, the copolymer having a content of propylene greater than 85% and an isotactic index greater than 85; (ii) from about 20% to about 60%, preferably from about 30% to about 50%, of an amorphous copolymer selected from the group consisting of (a) ethylene and propylene, (b) ethylene, propylene and an alpha-olefin of C.-C8, and (c) ethylene and an alpha-olefin of C.-CB, the copolymer 10 optionally containing from about 0.5% to about 10% d? a diene, and containing less than 70% ethylene and being soluble in xylene at room temperature; and (iii) from about 3% to about 40%, preferably from about 10% to about 20%, of an ethylene-propylene copolymer or a C4-C8 alpha-olefin that is insoluble in xylene at 20%. room temperature, wherein the composition has a higher flexural modulus of 150 but less than 1200 MPa, preferably from about 200 to about 1100 MPa, more preferably, from about 200 to about 1000 MPa. The room temperature is 259C. The C4-a alpha olefins useful in the preparation of (d) and (e) include, for example, butene-1; pentene-1; hexene-1; 4-methyl-l-pentene, and octene-1. The diene, when present, is typically a butadiene; 1,4-hexadiene; 1, 5-hexadiene, or ethylidenebornene. Propylene homopolymer is the preferred propylene polymer material. The preparation of material d? propylene polymer (d) is described in greater detail in the patents of E.U.A. 5,212,246 and 5,409,992, the preparation of which is incorporated herein by reference. The preparation of propylene polymer material (e) is described in greater detail in the patents of E.U.A. 5,302,454 and 5,409,992, whose preparation is incorporated herein by reference. The process of this invention is more effective when the particles of propylene polymer material have a particle size greater than 150 μm. When the particle size is less than 150 μm, the diffusion of the polymerizable monomer to the particle is usually fast enough without using a polymerization rate modifier (PRM).

The monomers that can be polymerized by grafting into the propylene polymer material structure can be "any monomeric vinyl compound capable of polymerizing by free radicals wherein the vinyl radical, H2C = CR-, wherein R is H or methyl, it is linked to a straight or branched aliphatic chain or a heterocyclic, or alicyclic, aromatic, substituted or unsubstituted ring in a mono- or polycyclic compound The typical substituent groups may be alkyl, hydroxyalkyl, aryl and halo Usually the vinyl monomer will be a member of one of the following classes: (1) vinyl-substituted, heterocyclic or alicyclic aromatic compounds, including styrene, vinylnafine, vinylpyridine, vinylpyrrolidone, vinylcarbazole, and homologues thereof, e.g. and para-methylstyrene, methylchlorostyrene, p-tert-butylstyrene, methylvinylpyridine, and ethylvinylpyridine; (2) vinyl esters of saturated and aromatic aliphatic carboxylic acids, including vinyl formate, vinyl acetate, vinyl chloroacetate, vinyl cyanoacetate, vinyl propionate, and vinyl benzoate; and (3) unsaturated aliphatic nitriles and carboxylic acids and their derivatives, including acrylonitrile, methacrylonitrile, acrylamide, methacrylamide: acrylic acid and acrylate esters, such as the methyl, ethyl, hydroxyethyl, 2-ethylhexyl and butyl acrylate esters; methacrylic acid, ethacrylic acid and methacrylate esters, such as methyl, ethyl, butyl, benzyl, phenylethyl, phenoxyethyl, epoxypropyl and hydroxypropylmethacrylate esters; maleic anhydride and N-phenyl maleimide. Polymerizable free radical dienes, such as butadiene, isoprene and their derivatives, can also be used. Multiple monomers of the same or different kinds can be used. Styrene, methyl methacrylate, methylacrylate, methacrylic acid, maleic anhydride and acrylonitrile are preferred graft monomers. The monomers are added in an amount of about 5 parts to about 240 parts per hundred parts of the propylene polymer material, preferably from about 20 to about 100 pph.The graft copolymer is made by forming active grafting sites in the propylene polymer material by treatment with a peroxide or other chemical compound which is a free radical polymerization initiator.The free radicals produced in the polymer as a result of the chemical treatment initiate the polymerization of the monomers at these sites. of graft, the monomers are also polymerized to form a certain amount of ungrafted or free polymer or copolymer The morphology of the graft copolymer is such that the propylene polymer material is the continuous or matrix phase, and the polymerized monomers, both grafted and non-grafted, they are a dispersed phase. The initiator and the grafting monomer are carried out in a substantially non-oxidizing atmosphere, as are the subsequent steps of the process. The term "substantially non-oxidizing", when used to describe the environment or atmosphere to which the propylene polymer material is exposed, means an environment in which the concentration of active oxygen, i.e., the concentration of oxygen in a form that will react with the free radicals in the polymer material, it is less than 15%, preferably less than 5%, and more preferably less than 1% by volume. The most preferred concentration of active oxygen is 0.004% or less in volume. Within these limits, the non-oxidizing atmosphere can be any gas, or mixture of gases, is oxidatively inert towards free radicals in the olefin polymer material, e.g., inert gases such as nitrogen, argon, helium and dioxide. of carbon.

The preparation of graft copolymers by contacting a propylene polymer material with an initiator d? Free radical polymerization such as an organic peroxide and a vinyl monomer is described in greater detail in the U.S. Patent. 5,140,074, the preparation of which is incorporated herein by reference. In the process of this invention, the treatment of the propylene polymer material with the vinyl monomer ST is carried out in the presence of a PRM. The monomer and PRM are continuously fed to the reactor during the course of the polymerization. The PRM can be any free radical polymerization inhibitor that can function in a substantially non-oxidizing environment. Appropriate PRMs include, for example, elemental sulfur, picric acid; benzoquinone and its derivatives; hydroxylamine and its derivatives; p-nitroso-N, N-dimethylaniline; N, N-nitrosomethylaniline; dinitrobenzenes; 1, 3, 5-trinitrobenzene; ferric chloride, and 1, 3, 5-trinitrotoluene. Sulfur, benzoquinone compounds and hydroxylamine compounds are preferred. Suitable benzoquinone compounds include, for example, 1,4-benzoquinone; 2-chloro-l, 4-benzoquinone; 2,5-dimethyl-1,4-benzoquinone; 2,6-dichlorobenzoquinone; 2,5-dichlorobenzoquinone; 2, 3-dimethyl-1,4-benzoquinone, and di-, tri- and tetrachloro-1, -benzoquinones. Suitable hydroxylamine compounds include, for example, N, N-diethylhydroxylamine; N, N-dimethylhydroxylamine; N, N-dipropylhydroxylamine, and N-nitrosophenylhydroxylamine. The amount of PRM used depends on the type of compound selected, but is generally within the range of about 5 parts to about 5000 parts per mole per million parts of monomer. For example, the sulfur is used in an amount of from about 50 to about 2000 parts per million parts of the polymerizable monomer, preferably from about 100 parts to about 1000 parts. A benzoquinone compound or a hydroxylamine compound is used in an amount of from about 50 parts to about 3000 parts per million parts of the polymerizable monomer, preferably from about 100 parts to about 1500 parts. As shown in Figures 1-5, the polymer particles without a PRM form a surface layer rich in polymerized monomer, since the polymerization rate is faster than the rate of diffusion of the monomer towards the polymer particles.

When a PRM is added to the monomer feed, the surface of the particles contains monomer whose polymerization is retarded by the presence of the PRM. The monomer, along with the PRM, diffuses into the polymer particles. As the monomer diffuses into the polymer particle, it has no contact with the fresh feed of monomer containing the PRM, and therefore, begins to polymerize . A radial distribution of PRM occurs due to the reaction between PRM and free radicals. The polymerization starts when the PRM concentration is not high enough to stop the polymerization. This produces a low content of polymerized monomer in the surface layer. The polymer particles with a low surface content of the polymerized monomer have a less sticky surface during the polymerization and thus, better processing capacity. No significant changes in the number average and weight average molecular weight, molecular weight distribution, xylene solubles at room temperature, grafting efficiency, or% conversion of monomer to polymer were found when a PRM was present during the polymerization of graft. It was also found that the use of N, N-dihydroxylamine as the PRM provided the additional benefit of suppressing the gas phase polymerization and, therefore, reducing reactor fouling. The higher the reaction temperature, the reduction in the fouling of the reactor is greater, since the effective concentration of the PRM in the vapor phase increases with the reaction temperature. N, N-diethylhydroxylamine is effective in reducing reactor fouling due to its low boiling point (125s - 130aC) compared to other PRMs and, therefore, a higher concentration in the gas phase under the conditions of reaction. Even when the use of a PRM in a graft polymerization reaction has been described in terms of polymerizable graft monomers towards solid particles 3 of the structure polymer, a PRM can also be used during a suspension or emulsion graft polymerization process or in reactive extrusion, processes that are well known to those skilled in the art. The porosity of the propylene homopolymer as the polymer structure in the manufacture of the graft copolymers in the examples is measured as described in Winslow, N.M. and Shapiro, J.J., "An Instrument for the Measurement of Pore-Size Distribution by Mercury Penetration, "ASTM Bull.", TP 49, 39-44 (February 1959), and Rootare, HM, "A Review of Mercury Porosimetry," 225-252 (In Hirshhom, JS, and Roll, KH, Eds. , Advanced Experimental Techniques- in Powder Metallurqy, Plenum Press, New York, 1970.) The percent of xylene solubles at 25 ° C was determined by dissolving 2 g of polymer in 200 ml of xylene at 135 ° C, cooling in a constant temperature bath to 25SC and filtering through fast filter paper An aliquot of the filtrate was evaporated to dryness, the residue was weighed and the percentage by weight of soluble fraction was calculated.The test methods used to evaluate the molded samples were: Izod Impact ASTM D-256A Tensile Strength ASTM D-638-89 Flex Module ASTM D-790-86 Flexural Strength ASTM D-790-86 Elongation to Break ASTM D-638-89 Melt Flow Regime 230aC, 3.8 kg ASTM 1238 Resistance to welding line ASTM D-638-89 In this specification n all parts and percentages are by weight, unless otherwise noted otherwise.

Example 1 This example demonstrates the effect of using sulfur as a PRM during a graft polymerization reaction using a propylene homopolymer (PP) as the polymer structure, to which ST grafted polystyrene (PS). The propylene homopolymer used as the polymer structure was spherical in shape, had an MFR of 15.5 g / 10 min and a porosity of 0.17 cmVg, and is commercially available from Montell USA Inc. The monomers were grafted onto the polypropylene structure at a grafting temperature of 120eC using the peroxide-initiated graft polymerization process described above. Eighty-five parts by weight of styrene were added per 100 parts of polypropylene. Lupersol PMS 50% t-butyl peroxy-2-yl hexanoate in mineral spirits, commercially available from Elf Atochem, was used as the peroxide initiator. The monomer was fed at 1 pph / min. A molar ratio of monomer to initiator of 105 was used. The reaction conditions were maintained at 120 ° C for 30 minutes after the "monomer" addition was completed and the temperature was then raised to 140 ° C for 60 minutes under a nitrogen purge. The polymerization reactor was a 7.57 liter autoclave equipped with a helical blade agitator and a monomer feed pump, as well as a temperature control system.The graft copolymer is characterized in Table 1. In Table 1, the sulfur content is given as parts per million parts by weight of styrene, the feed rate is given as parts of styrene monomer per hundred parts of propylene homopolymer / min.The total polystyrene was determined with a BioRad FSS analyzer 7 Fourier Infrared Transformation (FTIR) and is expressed as polystyrene parts per one hundred parts of polypropylene. r were made by gel permeation chromatography.

Table 1 Sample Control 1 2 Sulfur (ppm) 0 200 400 Feed rate (pph / min) 1 1 1 Total PS (pph) 77.8 91.6 88.9 Mn (x 10'3) 74 68 72 MW (x 10-3) 291 267 315 Mw /? N 3.9 3.9 4, 4 PS Free (% by weight) 32.5 35.0 33.1 Graft efficiency (% by weight) 25.7 26.8 29.7 Agitator speed Dropped to 0 120 comple- 120 (rpm) when 85 to complepph of motorcycle number were added For the control sample, in which no sulfur was present during the graft copolymerization, there was difficulty with agitation after the addition of about 70 parts of styrene per one hundred parts of polypropylene. After all the monomer was added, the agitator was completely stopped, which resulted in agglomerates and lumps. The data shows that there is no significant difference in molecular weight, molecular weight distribution, or grafting efficiency between the polymer made with sulfur as the PRM and without sulfur. Figure 1 is a plot of the PS / PP ratio along the radius of the polymer particles versus the distance from the surface of the polymer particles in micrometers (A) when no sulfur is added, (B) when 200 parts of sulfur per million parts by weight of styrene were added, and (C) when 400 ppm of sulfur was added. The traces were made by infrared Fourier transform mapping (FTIR). A very pronounced polystyrene surface layer was found in the sulfur-free polymer. When 200 ppm sulfur was added during the graft polymerization, the surface polystyrene concentration was greatly decreased, and the polystyrene concentration increased inside the particles. The concentration of surface polystyrene was further decreased with the addition of 400 ppm of sulfur. At this level of addition, the surface layer had less polystyrene than the interior of the polymer particles.

Example 2 This example demonstrates the effect of using sulfur as a PRM during a graft polymerization reaction using a propylene homopolymer as the polymer structure, to which polystyrene was grafted. The propylene homopolymer used as the polymer structure was spherical in shape, had an MFR of 20 g / 10 min and a porosity of 0.36 cm 3 / g, and is commercially available from Montell USA Inc. The graft copolymer was prepared as is described in Example 1. The graft copolymer is characterized in Table 2.

Table 2 Sample Control 1 2 Sulfur (ppm) 0 400 1200 Feed rate (pph / min) 1 1 1 PS Total (pph) 85.1 85.0 80.3 Mn (x 10"3) 71 71 52 Mw (x 103) 263 288 245 Mw / Mn 3.7 4.1 4.7 PS Free (% by weight) 32.5 34.7 33.0 Graft efficiency (% by weight) 29.4 24.5 25.9 Agitator speed drops to 0 when 120 com- 120 com (rpm) was added pleto pleto 85 pph of monomer The data shows that there is no significant difference in molecular weight, molecular weight distribution, or grafting efficiency between the polymer made with sulfur as the PRM and without sulfur. Figure 2 is a plot of the PS / PP ratio along the radius of the polymer particles versus the distance from the surface of the polymer particles in micrometers (A) when no sulfur was added, and (B) when 400 parts of sulfur per million parts by weight of styrene were added. The strokes were made by FTIR mapping. A surface layer of pronounced polystyrene was found in the sulfur-free polymer. The concentration of surface polystyrene decreased with the addition of 400 ppm of sulfur. At this level of addition, the surface layer had less polystyrene than the portion of the polymer particles below 1-a surface.

Example 3 This example illustrates the effect of the morphology of the polymer particles, the monomer content, and the test conditions on the flowability of the graft copolymer particles in the presence of various amounts of sulfur such as PRM. The graft copolymer was made from a propylene homopolymer structure, to which polystyrene was grafted. The propylene homopolymer used as the structure polymer was the same as in Example 1. The graft copolymer was prepared as described in Example 1. The polymer particles were subjected to a flow test as described below. The amount of sulfur present, the temperature of the test and the concentration of styrene for proper fluidity are shown in Table 3. The flow test was conducted at two temperatures, ie, room temperature (22-25ßC) and 100SC. The samples were placed in a round bottom glass flask which was immersed in an oil bath to control the temperature of the sample. Styrene with 5000 ppm of t-butyl catechol inhibitor was added to prevent thermal polymerization during testing of the polymer at the required dosage and was stirred in the flask for 30 minutes before conducting the flow test. The amounts of monomer added to the samples were 0, 1, 2, 3, 5, 10 and 35% by weight. ASTM D-1895-89, "Aparent Density, Bulk Factor and Pourability of Plastic Materials" was used to evaluate the fluidity of samples prepared under various conditions. The results are given in Table 3.

Table 3 Sulfur Temperature Concentration Comments ppm. (eC) Styrene Maximum (% by weight) 0 Environment < 1 Funnel bifurcated at 0% styrene 0 100 < 1 200 Environment < 3 200 100 < 3 Funnel bifurcated at 2% styrene 400 Environment _Sin limit Up to 30% styrene 400 100 < 30 The fluidity of the samples corresponded very well to their morphology. The prepared samples had a thick layer of polystyrene on the surface of the particles. The flow through the funnel was stopped at a styrene monomer concentration of < 1% due to surface stickiness. The samples prepared with 200 ppm of sulfur had good fluidity until the concentration of styrene monomer reached 3% by weight. The best fluidity was obtained from the samples with 400 ppm of sulfur addition during the polymerization. These samples flowed through the funnel even at a concentration of styrene monomer of 10% by weight at 100 ° C and 30% by weight at room temperature.

Example 4 This example describes the effect of sulfur addition on the mechanical properties of impact modified formulations containing graft copolymers comprising a propylene homopolymer structure, to which polystyrene was grafted. The graft copolymers were made from a propylene homopolymer structure, to which 85 parts of polystyrene per hundred parts of polypropylene were grafted as described in Example 1. The propylene homopolymer used with the polymer structure for copolymer of graft 1 had an MFR of 9 g / 10 min, a porosity of 0.51 cm3 / g and a bulk density of 0.35 g / cm3, and is commercially available from Montell USA Inc. The propylene homopolymer used as the polymer structure for the graft copolymer 2 it had a porosity of 0.17 cm 3 / g. The propylene homopolymer used as the structure polymer for the graft copolymer 3 had a porosity of 0.36 cm 3 / g. The graft copolymers were mixed with 34.9% by weight of a broad molecular weight distribution propylene (BNWD PP) having a polydispersity index of 7.4, an MFR of 1 g / 10 min, and xylene solubles at room temperature. 1.5%, commercially available from Montell USA Inc. The samples were composed of a Leistritz LSM double intermeshing screw extruder, 34 mm co-rotator. Each sample was extruded as granules at barrel temperature of 230SC, a screw speed of 375 rpm, and a production rate of 16.33 kg / hour for Control Sample and Sample 1, and 19.50 kg / hour for Sample 2 The stabilizer package used was 0.1% calcium stearate and 0.2% Irganox B-225 antioxidant, a mixture of 1 part Irganoz 1010 tetrakis stabilizer (methylene (3, 5-di-tert-butyl-4-hydroxyhydrocinna- to) jraethane and 1 part of Irgafos 168 tris (2,, -d-tert-butyl phenyl) phosphite stabilizer, commercially available from CIBA Specialty Chemicals Corporation In Table 4, impact modifiers were Kraton RP6912 triblock copolymer styrene / ethylene-isoprene / styrene, commercially available from Shell Chemical Company, and EPM 306P random ethylene / propylene copolymer having an ethylene content of 57%, commercially available from the Polysar Rubber Division of Miles, Incorporated.

Table 4 Sample Control Sulfur content (ppm) 0 200 400 Graft copolymer 1 (% by weight) 34.9 Graft copolymer 2 (% by weight) 34.9 Graft copolymer 3 (% by weight) 34. 9 BMWD PP (% by weight) 34. 9 3 4. 9 34. 9 Kraton RP 6912 (% by weight) 15. 0 15. 0 15. 0 EPM 306P (% by weight) 15. 0 15. 0 15. 0 Irganox B225 (% by weight) 0. twenty . twenty . 2 Calcium stearate (% by weight) 0.1 0.1 0.1 The composite samples were dried at 80 ° C for at least 4 hours before molding to remove moisture, 2.54 cm x 3.18 mm test bars were used for all physical property measurements. Battenfeld injection molding of 155.50 gr at a barrel temperature of 232SC and a mold temperature of 54 [deg.] C. The results of the property evaluations for each formulation are given in Table 5. In the table, NB = no breakage.

Table 5 Sample Control 1 2 Sulfur content (ppm) 0 200 400 MFR (dg / min), 6.4 4.0 4.5 (230aC, 3.8kg) Bending module (kg / cm2) 75.92 84.36 85.06 (1% secant, 1.27 mm / min) Resistance to bending (kg / cm2) 204.08 227.14 230.09 Izod impact resistance (July / 2.54cm to 23BC) NB19.79 NB19.79 NB19.39 Izod impact strength (July / 2.54cm at -30eC) 5.69 12.07 5.56 Resistance to tension (kg / cm2) 5.08 cm / min) 229.04 244.29 229.81 Elongation at break (%) > 892 820 709 The data show that the physical properties of the samples with addition of sulfur during the polymerization are similar to those of the control made without the addition of sulfur.

Example 5 This example demonstrates the effect of using 1-benzoquinone as a PRM during a graft polymerization reaction using a propylene homopolymer as the polymer structure, to which polystyrene was grafted. The propylene homopolymer used as the structure polymer had a porosity of 0.17 cm 3 / g. The graft copolymer was prepared as described in Example 1. Without benzoquinone, the conversion of monomer to polymer was 91.7%. With the addition of 50 parts by weight of benzoquinone per million parts of styrene, the conversion was 87.1%. With the addition of 800 ppm benzoquinone, the conversion was 96.2%. Without the addition of a benzoquinone PRM, the agitator speed dropped to 0 when 85 parts of styrene were added per one hundred parts of polypropylene. With the addition of 50 ppm benzoquinone, the agitation decreased to 80 rpm. With the addition of 800 ppm benzoquinone, the agitator speed remained at 120 rpm throughout the reaction. Figure 3 is a plot of the PS / PP ratio along the radius of the polymer particles against the distance from the surface of the polymer particles in microns when benzoquinone was not added, when 50 parts of benzoquinone were added. per million parts by weight of styrene and when 800 ppm of benzoquinone was added. The strokes were made by FTI mapping. A very pronounced polystyrene surface layer was found on the polymer particles without benzoquinone. When 50 ppm of benzoquinone was added during the graft polymerization, the surface polystyrene concentration was greatly decreased, and the concentration of polystyrene increased inside the particles. The surface polystyrene concentration was further decreased with the addition of 800 ppm benzoquinone. At this level of addition, the surface layer had less polystyrene than the interior of the polymer particles.

Example 6 This example shows the effect on polymer properties when 1,4-benzoquinone is used as the PRM during a graft polymerization reaction using two different propylene homopolymers such as the structure polymer, to which polystyrene was grafted. The graft copolymers were prepared as described in Example 1. The propylene homopolymer used as the structure polymer for the graft copolymer 4 had a porosity of 0.11 cm 3 / g and a bulk density of 0.48 g / cm 3, and is commercially available from Montell USA Inc.

The propylene homopolymer used as the structure polymer for the graft copolymer 1 had a porosity of 0.51 cm 3 / g. Graft copolymers are characterized in Table 6.

Table 6 Inhibitor Copolymer Mw Mn PS (pph) XSRT Ef.Gr Graft (ppm, weight) (x 103) (x 103) by FTIR (% in (weight%) weight) 4 1350 219 51 73.4 29.0 31.6 4 0 246 67 81.5 36.3 19.3 1 0 216 61 81.9 33.2 26.4 1 1350 245 59 76.9 33.5 23.0 The data shows that there is no significant difference in soluble molecular weight of xylene at room temperature (XSRT), and grafting efficiency between the polymer made with benzoquinone and without benzoquinone, except for a slightly lower grafting efficiency for the graft copolymer 4 without a PRM due to "peeling" during the polymerization, that is, a high content of pomerized monomer in the surface layer.

Example 7 This example describes the effect of the addition of 1,4-benzoquinone on the mechanical properties of graft copolymers containing impact modified formulations comprising a propylene homopolymer structure, to which polystyrene was grafted. The graft copolymers were made from a propylene homopolymer structure, to which 85 parts of. polystyrene per one hundred parts of propylene as described in Example 1. The Propylene homopolymer used as the polymer structure for the graft copolymer 1 had a porosity of 0.51 cm3 / g. The propylene homopolymer used as the structure polymer for the graft copolymer 2 had a porosity of 0.17 cm 3 / g. The propylene homopolymer used as the structure polymer for the graft copolymer 4 had a porosity of 0.11 cm 3 / g. The graft copolymers were mixed with 34.9% of the broad molecular weight distribution polypropylene described in Example 4. samples were composed as described in Example 4, except that the production rate for the Control Sample and Samples 2 and 3 was 16.33 kg / hour, and for Sample 1 it was 18.14 kg / hour. The stabilizer package used was 0.1 wt.% Calcium stearate and 0.2 wt.% Irganox B-225 antioxidant, commercially available from CIBA Specialty Chemicals Corporation. The impact modifiers in Table 7 are described in Example 4.

Table 7 Sample Control 1, 4-Benzoquinone (ppm, weight) 0 1350 1350 1350 Graft Copolymer 1 (% by weight) .34.9 Graft Copolymer 2 (% by weight) 34.9 Graft Copolymer 3 (% by weight) 34.9 Graft Copolymer 4 (5 by weight) 3 4. 9 BMWD PP (% by weight) 34.9 34. 9 34. 9 34. 9 Kraton RP6912 (% by weight) 15.0 15. 0 15. 0 15. 0 EPM 306P (% by weight) 15.0 1 5. 0 15. 0 15. , 0 Irganox B225 (% by weight) - 0.2 0.2 0.2 0.2 Calcium stearate (% by weight) 0.1 0.1 0.1 0.1 The samples were composed and test bars were produced as described in Example 4. The results of the property evaluations for each formulation are given in Table 8. In the table, NO = no breakage.

Table 8 Sample Control 1, 4-Benzoquinone (ppm, weight) 0 1350 1350 1350 MFR (kg / min) (230SC, 3.8kg) 6.4 6.6 6.5 5.8 Bending module (kg / cm2) (1% secant, 1.27 mm / min) 75.92 77.3 76.63 76.63 Resistance to bending (kg / cm2) 204.08 210.28 209.63 208.30 Izod impact strength (July / 2.54 cm at NB NB NB NB 23SC 19.79 20.47 20.34 20.34 Izod impact resistance (July / 2.54 cm at -30SC 5.69 7.73 7.73 11.12 Resistance to tension (kg / cm2) (5.08 cm / min) 229.04 223.13 231.92 236.70 Elongation at break (%) > 892 808 ¡73 892 The data show that the physical properties of the samples with addition of benzoquinone during the polymerization have similar physical properties compared to the control done without addition of benzoquinone. - 3f Example 8 This example illustrates the effect on the polymer characteristics and on the physical properties of the polymer when 1,4-benzoquinone is used as a PRM during a graft polymerization reaction using two different propylene homopolymers such as the polymer structure, to which poly (methyl methacrylate-co-methylacrylate) (PMMA) was grafted. The graft copolymer was prepared as described in Example 1, except that 95 parts of monomer per hundred parts of polypropylene were added, the reaction temperature was 115aC, the ratio of monomer to initiator was 120, and the molar ratio of methylmethacrylate The methylene acrylate was 95 to 5. The propylene homopolymer used as the structure polymer for the graft copolymer 1 had a porosity of 0.51 cm 3 / g. The propylene homopolymer used as the structure polymer for the graft copolymer 4 had a porosity of 0.11 cm 3 / g. The graft copolymers are characterized in Table 9.

Table 9 Copolymer Initiator Mw Mn PMMA XSR Ef. Gr. Graft (ppm, (x 10"3) (x 10" 3) (pph) (% in% by weight) per FTIR weight weight 4 0 280 73 50.8 42.3 - 4 1350 149 60 88.0 38.6 17.6 1 0 109 49 88.0 41.7 11.0 1 800 120 56 83.4 37.2 18.3 1 1350"143 60 81.4 38.1 15.1 The data shows that there is no significant difference in molecular weight, soluble xylene at room temperature, and grafting efficiency between the polymer made with benzoquinone such as PRM and without benzoquinone, except for the graft copolymer 4 without the PRM. The molecular weight is abnormally high due to severe "peeling" that occurred during the polymerization. The samples were composed of a Leistritz LSM double coil screw extruder, 34 mm co-rotator, at a barrel temperature of 210 ° C, a screw speed of 250 rpm, and a production rate of 9.07 kg / hour. The test bars for physical property measurements were prepared as described in Example 4. The results of the property evaluations for each sample are given in Table 10.

Table 10 Sample Control Control Control 1 2 3 Graft copolymer 1, -Benzoqui-none (ppm, weight) 800 1350 1350 Izod Slotted a23aC (July / 2.54 cm) 1.15 1.20 1.14 1.21 0.46 1.35 Izod Slotted at 0aC (July / 2.54 cm) 0.24 0.23 0.23 0.26 0.24 Stress Resistance (kg / cm2) 410.13 409.15 399.37 405.49 355.16 398.67 Resistance to welding line (kg / cm2) 358.39 305.59 367.28 378.07 334.77 313.68 Elongation at break (%) 20 20 16 19 12 19 Bending module (12.7 mm / min) (kg / cm2) 237.61 238.21 230.58 229.88 217.23 222.85 Resistance to bending (12.77 mm / min) (kg / cm2) 713.55 718.47 701.59 703.00 634.11 693.16 MRF (dg / min) (3.8kg, 230aC) 9.3 11.0 12.0 11.0 9.5 The data shows that the physical properties of the benzoquinone samples added during the polymerization have similar physical properties compared to the control done without addition of benzoquinone, except for Control 3 due to the reasons given in the previous example. Figure 4 is a plot of the ratio of PMMA / PP along the radius of the polymer particles (graft copolymer 4) against the distance from the surface of the polymer particles in microns when benzoquinone was not added, and when 1350 parts of benzoquinone per million parts by weight of monomer were added.The traces were made by FTIR mapping A very pronounced surface layer of PMMA was found in the polymer particles without benzoquinone When 1350 ppm of benzoquinone during graft polymerization, the concentration of surface PMMA was greatly decreased.

Example 9 This example shows the effect of using picric acid to a 90% suspension in water as a PRM during a graft polymerization reaction using a propylene homopolymer as the polymer structure, to which polystyrene was grafted. The propylene homopolymer used as the structure polymer had a porosity of 0.17 cmVg. The graft copolymer was prepared as described in Example 1. Without picric acid, the conversion of monomer to polymer was 91.7%. With the addition of 400 parts by weight of picric acid per million parts of styrene, the conversion was 95.8%. Without the addition of a PRM, the agitator speed dropped to 0 when 85 parts of monomer were added per one hundred parts of polypropylene. With the addition of 400 ppm of picric acid, the velocid. jd of the agitator remained at 120 rpm through the reaction.

EXAMPLE 10 This example demonstrates the effect of using N, N-diethylhydroxylamine (DEHA) as a PRM during a graft polymerization reaction using a propylene homopolymer as the polymer structure, to which polystyrene was grafted. The propylene homopolymer used as the structure polymer had a porosity of 0.17 cm 3 / g. The graft copolymer was prepared as described in Example 1. The graft copolymer is characterized in Table 11.

Table 11 DEHA Mw Mn PS (pph) XSRT Ef .Gr (ppm. (X 10"3) (X lO'3) per FTIR (% in {% mol) weight) weight) 0 291 74 77.8 32.5 25.7 830 213 60 78.0 34.2 22.0 1660 204 60 80.3 34.8 21.9 The data shows that there is no significant difference in molecular weight, total polystyrene, xylene solubles at room temperature, or grafting efficiency between the polymer with DEHA as the PRM and without DEHA. Without DEHA, the conversion ratio of monomer to polymer was 91.7. With the addition of 830 parts of DEHA per million parts of styrene (per mole), the conversion was 97.7%, and with 1660 ppm of DEHA (per mole) the conversion was 98.2%. Without the addition of a PRM, the agitator speed dropped to 0 when 85 parts of styrene were added per one hundred parts of polypropylene. With the addition of 830 and 1660 ppm DEHA, the agitator speed remained at 120 rpm through the reaction.

Example 11 This example describes the effect of the addition of DEHA as a PRM on polymer properties during a graft polymerization reaction using a propylene homopolymer as the polymer structure, to which poly (methyl methacrylate-co-methylacrylate) was grafted ). The propylene homopolymer used as the structure polymer had a porosity of 0.11 cm 3 / g. The graft copolymer was prepared as described in Example 1, except that 95 parts of monomer were added per one hundred parts of polypropylene, the molar ratio of monomer to initiator was 120, the reaction temperature was 115aC and the ratio of methyl methacrylate to methylacrylate was 95 to 5. The graft copolymer is characterized in Table 12.

Table 12 DEHA Mw Mn XSRT Ef. Gr. (ppm, mol) (x 10"3) (x 10'3) (% by weight) (% by weight; 1000 127 49 36.3 16.3 1500 135 - 45 37.0 10.0 1750 143 48 36.6 15.4 The data show that there is no significant difference in molecular weight, soluble in xylene at room temperature, and grafting efficiency between the polymer made with various amounts of DEHA such as PRM. With the addition of 1000 parts of DEHA per million parts of "methyl methacrylate (per mole), the conversion of monomer to polymer was 91.2% by weight With the addition of 1500 ppm DEHA (per mole), the conversion was 92.5% With the addition of 1750 ppm DEHA (per mole), the conversion was 88.0% When a PRM was present, the agitator speed remained at 120 rpm throughout the reaction.

Example 12 This example illustrates the effect of the morphology of the polymer particles on the percentage of monomer to polymer conversion and the fluidity of the polymer particles. The graft copolymer was made from two different propylene homopolymers such as the polymer structure, to which polystyrene was grafted. The PRM was DEHA. The graft copolymers were prepared as described in Example 1, except that the polymerization reactor is a 130 liter Littleford reactor having a horizontal mechanical stirrer and is commercially available from Littleford Day, Inc. The propylene homopolymer used as the The polymer structure for the graft copolymer 1 had a porosity of 0.51 cm 3 / g. The propylene homopolymer used as the structure polymer for the graft copolymer 4 had a porosity of 0.11 cprVg. The fluidity of the polymer particles was indicated by the maximum current requirement for the agitator in amperes. The higher the amperage, the lower the fluidity. The results are given in Table 13.

Table 13 DEHA Copolymer Conversion Graft Current Requirement (ppm, mol) (% by weight) Maximum for Agitator (Amps) 1 0 99. 6 6.5 1 1000 - 97., 3 6.4 4 0 95. .6 11.7 750 97. 5 8.2 4 1000 95., 3 7.5 4 1250 98 .2 7.2 The data shows that the fluidity improved when DEHA was present during the polymerization. Figure 5 is a plot of the PS / PP ratio along the radius of the polymer particles (graft copolymer 4) against the distance from the surface of the polymer particles in microns when DEHA is not added and when 750 parts of DEHA per million parts of styrene (per mole) were added. The strokes were made by FTIR mapping. A very pronounced polystyrene surface layer was found on the polymer particles without the addition of DEHA. When 750 ppm DEHA was added during the graft polymerization, the surface polystyrene concentration was greatly reduced, and the concentration of polystyrene increased inside the particles.

Example 13 This example describes the effect on fouling of the reactor of adding DEHA to the monomer feed as a PRM during a graft polymerization reaction. The graft copolymer was made from a propylene homopolymer as the structure polymer, to which polystyrene was grafted. The propylene homopolymer used as the structure of the graft copolymer had a porosity of 0.51 crrvVg. The graft copolymer was prepared as described in Example 1 except that the reaction temperature was 110aC for the Control Sample and Samples 1 and 2, and the molar ratio of monomer to peroxide was 49.0 to 110aC. Forty-five parts of styrene were added per one hundred parts of polypropylene. In order to quantify the degree of fouling of the reactor, a "test coupon", an in-line filter basket containing 40 g of the propylene homopolymer, was placed in the gas recirculation stream. The percentage increase in weight of the test coupon during the reaction was an indication to the degree of fouling of the reactor. The greater the increase in weight, the more reactor fouling occurs. The amount of DEHA introduced, the percentage of calculated yield of the mass balance, the PS content of the product measured by FTIR, the reaction temperature and the percent increase in coupon weight are given in Table 14.

Table 14 Sample PRM Rendi- Content T Teemmpp. Weight increase of PS (% in Product ReacCupon weight) (pph) tion (% by weight) (SC) Control None 95.2 41.1 110 30.0 DEHA, 1000 97.3 42.1 110 17.0 ppm (mol) DEHA, 1000 97.3 38.9 110 23.2 ppm (mol) DEHA, 1000 94.7 37.2 120 6.75 ppm (mol) The data shows that the use of DEHA in the monomer feed resulted in a reduction in the fouling of the gas circuit, especially at the higher reaction temperature.

Example 14 This example describes the effect on reactor fouling by adding DEHA to the monomer feed as a PRM during a graft polymerization reaction. The graft copolymer was made from a propylene homopolymer as the structure polymer, to which was grafted poly (methyl methacrylate-co-methyl methacrylate) (PMMA) The propylene homopolymer used as the structure of the graft copolymer had a porosity of 0.51 cmVg. The graft copolymer was prepared as described in Example 1, except that the reaction temperature was 1152C, the molar ratio of monomer to peroxide was 120, the molar ratio of methyl methacrylate to methylacrylate was 95 to 5, and 45 parts of monomer were added per hundred parts of polypropylene. The degree of reactor fouling was quantified as described in Example 13. The amount of DEHA introduced, the percent yield calculated from the mass balance, the PMMA content of the product measured by FTIR, and the percentage increase in coupons are provided in Table 15.

Table 15 Rendi-Contained Inhibitor Sample Increase in PMMA Weight (% in Coupon Product Weight) (pph) (% by weight) Control None 100.0 33.8 45.5 1 DEHA 100.0 39.6 22.0 500 ppm (mol) DEHA 96.6 39.9 20.0 500 ppm (mol) The data shows that the use of DEHA in the monomer feed resulted in a reduction of fouling of the gas circuit. Other features, advantages and embodiments of the invention described herein will be readily apparent to those who exercise ordinary experience after reading the foregoing exposures. To this respect, even when specific modalities have been described in considerable detail, variations and modifications of these modalities can be effected without abandoning the spirit and scope of the invention as described and claimed.

Claims (6)

1. - A process for making a graft copolymer comprising, in a substantially non-oxidizing environment, (a) treating particles of a propylene polymer material with an organic compound that is an initiator d? free radical polymerization; (b) treating the propylene polymer material for a period of time that coincides with or follows (a), with or without overlap, with about 5 to about 240 parts of at least one graft monomer capable of free radical polymerization , per one hundred parts of the propylene polymer material, in the presence of a polymerization rate modifier capable of operating in a substantially non-oxidizing environment; and (c) removing any unreacted graft monomer from the resulting grafted propylene polymer material, decomposing any unreacted initiator, and deactivating any residual free radicals in the material.

2. The process of claim 1, wherein the propylene polymer material is selected from the group consisting of: (a) a crystalline propylene homopolymer having an istactic index greater than 80; (b) a crystalline random copolymer of propylene and an olefin selected from the group consisting of ethylene and C4-C alpha olefins, as long as the olefin is ethylene, e.g. maximum polymerized ethylene content is 10% by weight, and when the olefin is an alpha-olefin of d-C? _, the maximum polymerized content thereof is 20% by weight, the copolymer having an isotactic index greater than 85; (c) a random crystalline terpolymer of propylene and two olefins selected from the group consisting of ethylene and C4-Cβ alpha-olefins, as long as the maximum content of alpha-olefin of polymerized C ^ -C is 20% by weight, and when ethylene is one of the olefins, the maximum content of polymerized ethylene is 5% by weight, the terpolymer having an isotactic index greater than 85; (d) an olefin polymer composition comprising: (i) about 10 parts to about 60 parts by weight of a crystalline propylene homopolymer having a higher isotactic index d? 80, or a crystalline copolymer selected from the group consisting of (a) propylene and ethylene, (b) propylene, ethylene and a C4-C3 alpha-olefin. and (c) propylene and an alpha-olefin of Ci-CB, the copolymer having a propylene content of more than 85% by weight and an isotactic index greater than 85; 15 (ii) about 3 parts to about 25 parts by weight of an ethylene propylene copolymer or a Ci-Cß alpha olefin which is insoluble in xylene at room temperature; and (iii) about 30 parts to about 70 parts by weight of an organic elasto copolymer selected from the group consisting of (a) ethylene and propylene, (b) ethylene, propylene and an alpha-olefin of C4 -C, and (c) ethylene and an alpha-olefin of C 1 -Cβ, the copolymer optionally containing from about 0.5% to about 10% by weight of a diene, and containing less than 70% by weight of ethylene and being soluble in xylene at room temperature and having an intrinsic viscosity of about 1.5 to about .0 dl / g; 10 the total of (ii) and (iii), based on the total olefin polymer composition that is from about 50% to about 90%, and the weight ratio of (ii) / (iii) being less than 0.4 , wherein the composition is prepared by polymerization in at least two steps and has a flexural modulus of less than 150 MPa; and (e) a thermoplastic olefin comprising: (i) about 10% to about 20 60% of a propylene homopolymer having an isotactic index greater than 80, or a crystalline copolymer selected from the group consisting of (a) ethylene and propylene, (b) ethylene, propylene. and an alpha-olefin of C4-CB, and (c) ethylene and an alpha-olefin of CA-CB, the copolymer having a propylene content greater than 85% and an isotactic index greater than 85; (ii) about 20% to about 60% of an amorphous copolymer selected from the group consisting of (a) ethylene and propylene, (b) ethylene, propylene and a C4-C8 alpha-olefin, and (c) ethylene and a C4-C8 alpha-olefin, the copolymer optionally containing from about 0.5% to about 10% of a diene, and containing less than 70% ethylene and being soluble in xylene at room temperature; and (iii) about 3% to about 40% of an ethylene-propylene copolymer or a C-β-alpha olefin which is insoluble in xylene at room temperature, wherein the composition has a flexural modulus greater than 150 but less than 1200 MPa.

3. The process of claim 2, wherein the propylene polymer material is a propylene homopolymer.

4. - The process of claim 1, wherein the graft monomer is selected from the group consisting of styrene, methyl methacrylate, methylacrylate, methacrylic acid, maleic anhydride and acrylonitrile.

5. The process of claim 1, wherein the polymerization modifier is selected from the group consisting of (a) sulfur, (b) benzoquinone and its derivatives, and (c) hydroxylamine and its derivatives.

6. The process of claim 5, wherein the polymerization modifier is N, -diethylhydroxylamin.