EP1753795A1 - Process for making flame retardant grafted olefin polymers - Google Patents

Abstract

A process for making a radiation initiated flame retardant grafted olefin polymer comprises: a) irradiating an olefin polymer material (A) at a temperature from about 10 °C to about 85 °C with high-energy ionizing radiation to produce free radical initiating site on the backbone of the polymer material; b) treating the irradiated olefin polymer material at a first temperature up to about 100 °C with about 5 to 50 percent by weight of at least one polymerizable flame retardant in the presence of a controlled amount of oxygen, and then maintaining the polymer material at a second temperature from 25°C to a temperature below the softening point of the polymer material, thereby forming a polymer mixture; c) heating the polymer mixture obtained in step b) at a temperature above the melting point of the polymer mixture, thereby producing a graft polymer melt.

Description

PROCESS FOR MAKING FLAME RETARDANT GRAFTED OLEFIN POLYMERS This invention relates to a method for making flame retardant grafted olefin polymer materials with polymerizable flame retardants under various conditions, and their applications. Grafted olefin polymers can be made by various methods known in the state of the art, such as by grafting reactions which may be condμcted in polymer solutions, in the presence of solid polymer or with a polymer in molten state. The active sites on the polyolefin can be formed either in the presence of grafting monomers, or by contacting with the monomers at a later stage. The grafting sites can be produced by treatment with a peroxide or any other chemical compound which is a free radical polymerization initiator capable of extracting a hydrogen free radical from the polymer backbone, or by irradiation with high energy ionizing radiation. The free radicals produced in the reaction as a result of the degradation of peroxides or irradiation treatment act as initiators for polymerization of the monomers, as well as active sites for grafting when the free radicals are formed on the olefin polymers. For example, U.S. Patent No. 5,652,281 discloses a method for making grafted olefin polymers by irradiating olefin polymer particles and treating with a vinyl monomer in liquid form under a non-oxidizing environment which is maintained throughout the process. The unreacted vinyl monomer is subsequently removed from the grafted olefin polymers while maintaining a substantially non-oxidizing environment. Graft copolymers have also been made in an extruder, as disclosed in U.S. Patent No. 3,862,265, in which an organic peroxide initiator was injected into the extruder to initiate the grafting reaction of polyolefins in molten state with vinyl monomers. The reactive extrusion, carried out on the polymer in molten state, offers many advantages such as a fast reaction rate and a simple reaction system. Nevertheless, such graft polymerization requires the use of organic peroxides during extrusion. Since peroxides are unstable and explosive chemicals, they require special safe handling procedures to minimize the risk. Moreover, the degradation products from the organic peroxide, such as t-butyl alcohol, undesirably remain in the final product and render the product unsuitable for certain applications. In addition, since the free radical initiator used in such a process does not only initiate the graft copolymerization but also homopolymerization of the vinyl monomers, relatively low grafting efficiency often occurs and results in low degree of graft monomer content, thus reducing the value of the final products. Flame retardant polymer materials have been prepared by blending flame retardants into the polymer matrix. The useful flame retardants include halogenated, non-halogenated, and phosphorus flame retardants. For examples, U.S. Patent No. 5,605,962 discloses a flame retarding resin composition by adding a phosphate containing flame retardant into the grafted copolymer material. U.S. Patent No. 5,543,447 discloses a novel plastic composition and method for making the same comprising uniformly distributing a red amorphous phosphorus into a host polymer to prepare a flame retarding polymer material. However, it is known in the art that such dispersed flame retardants can often migrate to the surface of the plastic articles causing flame retarding efficiency decrease and surface contamination. Therefore, there is a need for a method of making a flame retarding polymer material in which the flame retardant will not migrate to the surface of the polymer in order to obtain high flame retardancy and high surface purity polymer materials. Accordingly, it is an object of this invention to produce a phosphorus containing flame retarding olefin polymer material in which the flame retardant is chemically bounded with the olefin polymer in order to eliminate the above-mentioned difficulties associated with the use of physical blending of the flame retardant into the olefin polymers. In accordance with the present invention, a flame retardant grafted olefin polymer is prepared by grafting a phosphorus containing polymerizable flame retardant onto an olefin polymer backbone by using radiation initiation generated by a high-energy ionizing radiation source or using peroxide initiation in the presence of a reactive, peroxide-containing olefin polymer as an initiator. In one embodiment, the present invention relates to a process for making a radiation initiated flame retardant grafted olefin polymer comprising: a) irradiating an olefin polymer material (A) at a temperature from about 10 °C to about 85 °C with high-energy ionizing radiation to produce free radical initiating site on the backbone of the polymer material in an atmosphere having an oxygen concentration of at most 0.004% by volume; b) treating the irradiated olefin polymer material at a first temperature up to about 100 °C with about 5 to 50 percent by weight, based on the total weight of the olefin polymer material and polymerizable flame retardants used, of at least one said polymerizable flame retardant in the presence of a controlled amount of oxygen, and then maintaining the polymer material at a second temperature from 25°C to a temperature below the softening point of the polymer material, thereby forming a polymer mixture; c) heating the polymer mixture obtained in step b) at a temperature above the melting point of the polymer mixture, thereby producing a graft polymer melt; and optionally d) pelletizing the graft polymer melt after it is cooled, thereby producing a pelletized graft copolymer. In another embodiment, the present invention relates to a process for making a peroxide initiated flame retardant grafted olefin polymer by using a reactive, peroxide- containing olefin polymer comprising: a) preparing a polymer blend comprising: I. about 50.0 to about 95.0 wt% of a reactive, peroxide-containing olefin polymer (B); and II. about 5 to about 50.0 wt% of at least one polymerizable flame retardant; wherein the sum of components I + II is equal to 100 wt%; b) heating the polymer blend to a temperature from 25°C to a temperature below the softening point of the polymer blend in the presence of a controlled amount of oxygen, thereby forming a polymer mixture; c) heating the polymer mixture at a temperature above the melting point of the polymer mixture, thereby producing a graft polymer melt; and optionally d) pelletizing the graft polymer melt after it is cooled, thereby producing a pelletized graft copolymer. In another embodiment, the present invention relates to a process for making a flame retardant grafted olefin polymer composite comprising: a) preparing a polymer blend comprising: I. about 50.0 to about 90.0 wt% of an olefin polymer material (A); and II. about 10 to about 50.0 wt% of a pelletized graft copolymer; wherein the sum of components I + II is equal to 100 wt% and the pelletized graft copolymer is prepared by the process for making a radiation initiated flame retardant grafted olefin polymer or the process for making a polymeric peroxide initiated flame retardant grafted olefin polymer as defined above; b) heating the polymer blend at a temperature above the melting point of the polymer blend, thereby producing a grafted olefin polymer composite melt; and optionally c) pelletizing the grafted olefin polymer composite melt after it is cooled, thereby producing a pelletized olefin polymer composite. In another embodiment, the present invention relates to an olefin polymer having radiation initiated flame retardant grafts produced by a process comprising: a) irradiating an olefin polymer material (A) at a temperature from about 10 °C to about 85 °C with high-energy ionizing radiation to produce free radical initiating site on the backbone of the polymer material in an atmosphere having an oxygen concentration of at most 0.004% by volume; b) treating the irradiated olefin polymer material at a first temperature up to about 100 °C with about 5 to 50 percent by weight, based on the total weight of the olefin polymer material and polymerizable flame retardants used, of at least one said polymerizable flame retardant in the presence of a controlled amount of oxygen, and then maintaining the polymer material at a second temperature from 25°C to a temperature below the softening point of the polymer material, thereby forming a polymer mixture; c) heating the polymer mixture obtained in step b) at a temperature above the melting point of the polymer mixture, thereby producing a graft polymer melt; and optionally d) pelletizing the graft polymer melt after it is cooled, thereby producing a pelletized graft copolymer. In another embodiment, the present invention relates to an olefin polymer having peroxide initiated flame retardant grafts produced by a process comprising: a) preparing a polymer blend comprising: I. about 50.0 to about 95.0 wt% of a reactive, peroxide-containing olefin polymer (B); and II. about 5 to about 50.0 wt% of at least one polymerizable flame retardant; wherein the sum of components 1 + II is equal to 100 wt%; b) heating the polymer blend to a temperature from 25°C to a temperature below the softening point of the polymer blend in the presence of a controlled amount of oxygen, thereby forming a polymer mixture; c) heating the polymer mixture at a temperature above the melting point of the polymer mixture, thereby producing a graft polymer melt; and optionally d) pelletizing the graft polymer melt after it is cooled, thereby producing a pelletized graft copolymer. In another embodiment, the present invention relates to an olefin polymer composite having flame retardant grafts produced by a process comprising: a) preparing a polymer blend comprising: I. about 50.0 to about 90.0 wt% of an olefin polymer material (A); and II. about 10 to about 50.0 wt% of a pelletized graft copolymer; wherein the sum of components I + II is equal to 100 wt% and the pelletized graft copolymer is prepared by the process for making a radiation initiated flame retardant grafted olefin polymer or the process for making a polymeric peroxide initiated flame retardant grafted olefin polymer as defined above; b) heating the polymer blend at a temperature above the melting point of the polymer blend, thereby producing a grafted olefin polymer composite melt; and optionally c) pelletizing the grafted olefin polymer composite melt after it is cooled, thereby producing a pelletized olefin polymer composite. Olefin polymers suitable for the olefin polymer material (A) and a starting material for the reactive, peroxide-containing olefin polymer material (B) is a propylene polymer material, an ethylene polymer material, a butene-1 polymer material, or mixtures thereof The olefin polymer used in the present invention can be selected from: (a) a crystalline homopolymer of propylene having an isotactic index greater than about 80%, preferably about 90% to about 99.5%; (b) a crystalline, random copolymer of propylene with an olefin selected from ethylene and C₄-C₁0 α-olefins wherein the polymerized olefin content is about 1-10% by weight, preferably about 2% to about 8%, when ethylene is used, and about 1 % to about 20% by weight, preferably about 2% to about 16%, when the C₄-C₁₀ α-olefin is used, the copolymer having an isotactic index greater than about 60%, preferably at least about 70%; (c) a crystalline, random terpolymer of propylene and two olefins selected from ethylene and Gt-Cs α-olefins wherein the polymerized olefin content is about 1% to about 5% by weight, preferably about 1% to about 4%, when ethylene is used, and about 1% to about 20% by weight, preferably about 1% to about 16%, when the C -C₁₀ α-olefins are used, the terpolymer having an isotactic index greater than about 85%; and

(d) an olefin polymer composition comprising: (i) about 10% to about 60% by weight, preferably about 15% to about 55%, of a crystalline propylene homopolymer having an isotactic index at least about 80%, preferably about 90 to about 99.5%, or a crystalline copolymer of monomers selected from (a) propylene and ethylene, (b) propylene, ethylene and a G_t-Cg α-olefin, and (c) propylene and a C - C₈ α-olefin, the copolymer having a polymerized propylene content of more than about 85% by weight, preferably about 90% to about 99%, and an isotactic index greater than about 60%; (ii) about 3% to about 25% by weight, preferably about 5% to about 20%, of a copolymer of ethylene and propylene or a Gi-Cs α-olefin that is insoluble in xylene at ambient temperature; and (iii) about 10% to about 80% by weight, preferably about 15% to about 65%, of an elastomeric copolymer of monomers selected from (a) ethylene and propylene, (b) ethylene, propylene, and a C4-C8 α-olefin, and (c) ethylene and a CVCs α-olefin, the copolymer optionally containing about 0.5% to about 10% by weight of a polymerized diene and containing less than about 70% by weight, preferably about 10% to about 60%, most preferably about 12% to about 55%, of polymerized ethylene, and being soluble in xylene at ambient temperature and having an intrinsic viscosity of about 1.5 to about 6.0 dl/g; wherein the total of (ii) and (iii), based on the total olefin polymer composition is about 50% to about 90% by weight, and the weight ratio of (ii)/(iii) is less than about 0.4, preferably 0.1 to 0.3, and preferably the composition is prepared by polymerization in at least two stages;

(e) homopolymers of ethylene; (f) random copolymers of ethylene and an α-olefin selected from C₃-C₁₀ α-olefins having a polymerized α-olefin content of about 1 to about 20% by weight, preferably about 2% to about 16%; (g) random terpolymers of ethylene and two C3-C1₀ α-olefins having a polymerized α-olefin content of about 1% to about 20% by weight, preferably about 2% to about 16%; (h) homopolymers of butene- 1 ; (i) copolymers or terpolymers of butene-1 with ethylene, propylene or C₅-C₁₀ alpha-olefm, the comonomer content ranging from about 1 mole % to about 15 mole %; and (j) mixtures thereof. Preferably, the olefin polymer is selected from: (a) a crystalline homopolymer of propylene having an isotactic index greater than about 80%, preferably about 90% to about 99.5%; and (b) a crystalline, random copolymer of propylene with an olefin selected from ethylene and C4-C10 α-olefins wherein the polymerized olefin content is about 1-10% by weight, preferably about 2% to about 8%, when ethylene is used, and about 1% to about 20% by weight, preferably about 2% to about 16%, when the C₄-C₁₀ α-olefin is used, the copolymer having an isotactic index greater than about 60%, preferably at least about 70%; Most preferably, the olefin polymer is a propylene homopolymer having an isotactic index greater than about 90%. The useful polybutene-1 homo or copolymers can be isotactic or syndiotactic and have a melt flow rate (MFR) from about 0.1 to 150 dg/min, preferably from about 0.3 to 100, and most preferably from about 0.5 to 75. These butene-1 polymer materials, their methods of preparation and their properties are known in the art. Suitable polybutene-1 polymers can be obtained, for example, by using Ziegler-Natta catalysts with butene-1 , as described in WO 99/45043, or by metallocene polymerization of butene-1 as described in WO 02/10281 1, the disclosures of which are incorporated herein by reference. Preferably, the butene-1 polymer materials contain up to about 15 mole % of copolymerized ethylene or propylene. More preferably, the butene-1 polymer material is a homopolymer having a crystallinity of at least about 30% by weight measured with wide- angle X-ray diffraction after 7 days, more preferably about 45% to about 70%, most preferably about 55% to about 60%. The olefin polymer material (A) and the starting material for the reactive, peroxide- containing olefin polymer (B) can be the same or different from each other. In a process for making a radiation initiated flame retardant grafted olefin polymer, an olefin polymer material (A) is exposed to high-energy ionizing radiation in a substantially non-oxidizing environment wherein the amount of oxygen is at most 0.004% by volume, typically under a blanket of inert gas, preferably nitrogen. The ionizing radiation should have sufficient energy to penetrate the mass of polymer material being irradiated to the extent desired. The ionizing radiation can be of any kind, but preferably includes electrons and gamma rays. More preferred are electrons beamed from an electron generator having an accelerating potential of 500-4,000 kilovolts. Satisfactory results are obtained at a dose of ionizing radiation of about 0.1 to about 15 megarads ("Mrad"), preferably about 0.5 to about 9.0 Mrad. The term "rad" is usually defined as that quantity of ionizing radiation that results in the absorption of 100 ergs of energy per gram of irradiated material regardless of the source of the radiation using the process described in U.S. Patent No. 5,047,446. Energy absoφtion from ionizing radiation is measured by the well-known convention dosimeter, a measuring device in which a strip of polymer film containing a radiation-sensitive dye is the energy absoφtion sensing means. Therefore, as used in this specification, the term "rad" means that quantity of ionizing radiation resulting in the absorption of the equivalent of 100 ergs of energy per gram of the polymer film of a dosimeter placed at the surface of the olefin material being irradiated, whether in the form of a bed or layer of particles, or a film, or a sheet. In a reaction step, the irradiated olefin polymer material is treated with at least one polymerizable flame retardant in an environment with a controlled amount of oxygen less than 15% by volume, preferably less than 5.0%, more preferably less than 1.0% and most preferably greater than 0.004% but less than 0.5%. The reaction step is carried out at a first temperature up to about 100 °C, preferably about 25°C to 85°C, most preferably about 35°C to 65°C and then maintained at a second temperature of at least 25°C but below the softening point of the polymer, preferably about 25°C to 140°C, most preferably about 100^DC to 120°C, thereby forming a polymer mixture. The polymer mixture is then extruded or compounded in the molten state in any conventional manner well known in the art, in batch or continuous mode; for example, by using a Banbury mixer, a kneading machine, a single screw extruder, a twin screw extruder or an autoclave equipped with adequate agitation. The resulting polymer melt can be optionally pelletized to make a pelletized graft copolymer. The polymerizable flame retardant used in the process making a radiation initiated flame retarding graft olefin polymer can be present in an amount from about 5.0 to about 50.0 % by weight, preferably about 8.0 to about 40.0 %, and most preferably about 10.0 to about 20.0 %. In a process for making a peroxide initiated flame retardant grafted olefin polymer by using a reactive, peroxide-containing olefin polymer, the reactive, peroxide-containing olefin polymer (B) may be prepared by an irradiation and oxidation process. A starting olefin polymer is exposed to high energy ionizing radiation in a substantially non-oxidizing environment, i.e., an environment in which the active oxygen concentration is established and maintained at 0.004% by volume or less. The ionizing radiation should have sufficient energy to penetrate the mass of polymer material being irradiated to the extent desired. The ionizing radiation can be of any kind, but preferably includes electrons and gamma rays. More preferred are electrons beamed from an electron generator having an accelerating potential of 500-4,000 kilovolts. Satisfactory results are obtained at a dose of ionizing radiation of about 0.1 to about 15 megarads ("Mrad"), preferably about 0.5 to about 9.0 Mrad. The irradiated olefin polymer material is then oxidized in a series of steps. According to a preferred preparation method, the first treatment step consists of heating the irradiated polymer in the presence of a first controlled amount of active oxygen greater than 0.004% by volume but less than 21% by volume, preferably less than 15% by volume, more preferably less than 8% by volume, and most preferably from 0.5% to 5.0% by volume, to a first temperature of at least 25°C but below the softening point of the polymer, preferably about 25°C to 140°C, more preferably about 40°C to 100°C, and most preferably about 50°C to 90°C. Heating to the desired temperature is accomplished as quickly as possible, preferably in less than 10 minutes. The polymer is then held at the selected temperature, typically for about 5 to 90 minutes, to increase the extent of reaction of the oxygen with the free radicals in the polymer. The holding time, which can be determined by one skilled in the art, depends upon the properties of the starting material, the oxygen concentration used, the irradiation dose, and the temperature. The maximum time is determined by the physical constraints of the fluid bed used to treat the polymer. In the second treatment step, the irradiated polymer is heated in the presence of a second controlled amount of active oxygen greater than 0.004% by volume but less than 21% by volume, preferably less than 15% by volume, more preferably less than 8% by volume, and most preferably from 0.5% to 5.0% by volume to a second temperature of at least 25°C but below the softening point of the polymer. Preferably, the second temperature is from 80°C to less than the softening point of the polymer, and greater than the temperature of the first treatment step. The polymer is then held at the selected temperature and oxygen concentration conditions for about 10 to 300 minutes, preferably about 20 to 180 minutes, most preferably about 30 to 60 minutes, to minimize the recombination of chain fragments, i.e., to minimize the formation of long chain branches. The holding time is determined by the same factors discussed in relation to the first treatment step. In the optional third step, the oxidized olefin polymer material is heated under a blanket of inert gas, preferably nitrogen, to a third temperature of at least 80°C but below the softening point of the polymer, and held at that temperature for about 10 to about 120 minutes, preferably about 60 minutes. A more stable product is produced if this step is carried out. It is preferred to use this step if the reactive, peroxide-containing olefin polymer material is going to be stored rather than used immediately, or if the radiation dose that is used is on the high end of the range described above. The polymer is then cooled to a fourth temperature of about below 50°C under a blanket of inert gas, preferably nitrogen, before being discharged from the bed. In this manner, stable intermediates are formed that can be stored at room temperature for long periods of time without further degradation. As used in this specification, the expression "room temperature" or "ambient" temperature means approximately 25°C. The expression "active oxygen" means oxygen in a form that will react with the irradiated olefin polymer material. It includes molecular oxygen, which is the form of oxygen normally found in air. The active oxygen content requirement of this invention can be achieved by replacing part or all of the air in the environment by an inert gas such as, for example, nitrogen. It is preferred to carry out the treatment by passing the irradiated polymer through a fluid bed assembly operating at a first temperature in the presence of a first controlled amount oxygen, passing the polymer through a second fluid bed assembly operating at a second temperature in the presence of a second controlled amount of oxygen, and then maintaining the polymer at a third temperature under a blanket of nitrogen, in a third fluid bed assembly. In commercial operation, a continuous process using separate fluid beds for the first two steps, and a purged, mixed bed for the third step is preferred. However, the process can also be carried out in a batch mode in one fluid bed, using a fluidizing gas stream heated to the desired temperature for each treatment step. Unlike some techniques, such as melt extrusion methods, the fluidized bed method does not require the conversion of the irradiated polymer into the molten state and subsequent re-solidification and comminution into the desired form. The fluidizing medium can be, for example, nitrogen or any other gas that is inert with respect to the free radicals present, e.g., argon, krypton, and helium. The concentration of peroxide groups formed on the polymer can be controlled easily by varying the radiation dose during the preparation of the reactive, peroxide-containing olefin polymer and the amount of oxygen to which such polymer is exposed after irradiation. The oxygen level in the fluid bed gas stream is controlled by the addition of dried, filtered air at the inlet to the fluid bed. Air must be constantly added to compensate for the oxygen consumed by the formation of peroxides in the polymer. The reactive, peroxide-containing olefin polymer has a peroxide concentration preferably ranging from about 1 to about 200 milli-equivalent per kilogram of the polymer (meq/kg), more preferably from about 5 to about 150 and most preferably from about 10 to 100. In a reaction step, the reactive, peroxide-containing olefin polymer is treated with at least one polymerizable flame retardant in an environment with a controlled amount of oxygen less than 15% by volume, preferably less than 5.0%, more preferably less than 1.0% and most preferably greater than 0.004% but less than 0.5%. The reaction step is carried out at a temperature from 25°C to a temperature below the softening point of the polymer, preferably about 80°C to 130°C, most preferably about 100°C to 120°C, thereby forming a polymer mixture. The polymer mixture is then extruded or compounded in the molten state in any conventional manner well known in the art, in batch or continuous mode; for example, by using a Banbury mixer, a kneading machine, a single screw extruder, a twin screw extruder or an autoclave equipped with adequate agitation. The resulting polymer melt can be optionally pelletized to make a pelletized graft copolymer. The polymerizable flame retardant used in the process making a flame retarding graft olefin polymer by using a reactive, peroxide-containing olefin polymer can be present in an amount from about 5.0 to about 50.0 % by weight, preferably about 8.0 to about 40.0 %, and most preferably about 10.0 to about 20.0 %. In a process for making a flame retardant grafted olefin polymer composite, a polymer blend is prepared by blending the pelletized graft copolymer prepared above and an olefin polymer material (A). The polymer blend is then extruded or compounded in the molten state in any conventional manner well known in the art, in batch or continuous mode; for example, by using a Banbury mixer, a kneading machine, a single screw extruder, a twin screw extruder or an autoclave equipped with adequate agitation. The resulting polymer composite melt can be optionally pelletized to make a pelletized polymer composite. The pelletized graft copolymer used in the process making the flame retardant grafted olefin polymer composite can be present in an amount from about 10.0 to about 50.0 % by weight, preferably about 15.0 to about 40.0 %, and most preferably about 20.0 to about 30.0 %. The polymerizable flame retardant used in this invention is a phosphorus containing monomer, preferably phosphorus containing vinyl monomers, such as vinyl phosphonic acid, most preferably monoacryloxyethyl phosphate (monophosphate ester of hydroxy ethyl methacrylate), Bis(2-methacryloxyethyl) phosphate (diphosphate ester of hydroxy ethyl methacrylate) and mixtures thereof. Unless otherwise specified, the properties of the olefin polymer materials, compositions and other characteristics that are set forth in the following examples have been determined according to the test methods reported below: Melt Flow Rate ("MFR"): ASTM D1238, units of dg/min; 230° C; 2.16 kg; Polymer material with a MFR below 100, using full die; Polymer material with a MFR equal or above 100, using V_ die; unless otherwise specified. Isotactic Index ("I.I."): Defined as the percent of olefin polymer insoluble in xylene. The weight percent of olefin polymer soluble in xylene at room temperature is determined by dissolving 2.5 g of polymer in 250 ml of xylene at room temperature in a vessel equipped with a stirrer, and heating at 135°C with agitation for 20 minutes. The solution is cooled to 25°C while continuing the agitation, and then left to stand without agitation for 30 minutes so that the solids can settle. The solids are filtered with filter paper, the remaining solution is evaporated by treating it with a nitrogen stream, and the solid residue is vacuum dried at 80°C until a constant weight is reached. These values correspond substantially to the isotactic index determined by extracting with boiling n-heptane, which by definition constitutes the isotactic index of polypropylene. Peroxide Concentration: Quantitative Organic Analysis via Functional Groups, by S. Siggia et al., 4th Ed., NY, Wiley 1979, pp. 334-42. Phosphorus Content 5 g of grafted polymer is dissolved in 100 g xylene at 135 °C and then the solution is cooled to ambient temperature. The solution is poured into 500 g of acetone in a container under agitation to precipitate the polymer. The solution with precipitated polymer is then filtered to recover the polymer solid. After vacuum drying, the solid polymer sample is collected and analyzed by using Elemental Analysis to determine the grafted phosphorus content. In this specification, all parts, percentages and ratios are by weight unless otherwise specified. Example 1 A radiation initiated flame retardant grafted olefin polymer was prepared according to the following procedures. 700 g of a polypropylene homopolymer having a MFR of 9.4 dg/min, and I.I. of 96.5%, commercially available from Basell USA Inc. was irradiated at 4.0 Mrad at room temperature under a blanket of nitrogen. The irradiated polymer was then transferred to a jacketed three-liter glass reactor and treated with a monomer, vinyl phosphonic acid at 35°C. The monomer was fed into the reactor by a pump at a feed rate of 7 g/minute. The total weight of the monomer added was 210 g. The monomer was purchased from Aldrich Chemical Company, Inc. and used without further purification. After holding the reaction temperature at 35°C for 90 minutes, the temperature was raised to 140°C and maintained at that temperature for 60 minutes. The polymer was then extruded in a Haake Rheocord extruder, commercially available from Thermo Electron Coφoration, with extrusion temperature of 230°C for all zones. The polymerized monomer content and MFR of the resultant polymer material are summarized in Table I.

The polymerized monomer content by weight increase is calculated by subtracting the weight of the propylene homopolymer from the weight of the resulting polymer material, dividing the difference by the weight of the resulting polymer material and then multiplying the result by 100. Example 2 A radiation initiated flame retarding graft olefin polymer was prepared by irradiating 700 g of a polypropylene homopolymer having a MFR of 9.4 dg/min, and I.I. of 96.5%, commercially available from Basell USA Inc., at 4.0 Mrad at room temperature under a blanket of nitrogen. The irradiated polymer was then transferred to a jacketed three-liter glass reactor and treated with a monomer, Empicryl 6835 (mixture of monophosphate and diphosphate ester of hydroxy ethyl methacrylate), commercially available from Rhodia Inc. at 35°C. The monomer was fed into the reactor by a pump at a feed rate of 7 g/minute. The total weight of the monomer added was 210 g. After holding the reaction temperature at 35°C for 90 minutes, the temperature was raised to 140°C and maintained at that temperature for 60 minutes. The polymer was then extruded in a Haake Rheocord extruder, commercially available from Thermo Electron Coφoration, with extrusion temperature of 230°C for all zones. The MFR of the resultant polymer material was 7.8 dg/min. The polylmerized monomer content and phosphorus content are summarized in Table II. The definition of the polymerized monomer content is the same as in Example 1. Example 3 A flame retarding graft olefin polymer prepared in Example 2 was further compression molded into flex bars with dimensions of 127 mm + 5 mm, by 13 mm + 0.5 mm, by 3.13 mm ± 0.05 mm. Flammability tests were conducted on the compression-molded material using Underwriters Laboratories Inc. UL-94 procedure for vertical burning test, the results of which are reported in Table III. Comparative Example A polypropylene homopolymer having a MFR of 9.4 dg/min, and I.I. of 96.5%, commercially available from Basell USA Inc., which was the same as the starting material for preparation of Example 2 was extruded and compression molded under the conditions reported in Example 3. Flammability tests were conducted on the compression-molded material using Underwriters Laboratories Inc. UL-94 procedure for vertical burning test, the results of which are reported in Table III.

The burn time set forth in Table III shows that the burn time of the flame retarding olefin polymer made according to this invention is much lower than those of the comparative sample. Other features, advantages and embodiments of the invention disclosed herein will be readily apparent to those exercising ordinary skill after reading the foregoing disclosures. In this regard, while specific embodiments of the invention have been described in considerable detail, variations and modifications of these embodiments can be effected without departing from the spirit and scope of the invention as described and claimed.

Claims

1. A process for making a radiation initiated flame retardant grafted olefin polymer comprising: a) irradiating an olefin polymer material (A) at a temperature from about 10 °C to about 85 °C with high-energy ionizing radiation to produce free radical initiating site on the polymer backbone in an atmosphere having an oxygen concentration of at most 0.004% by volume; b) treating the irradiated olefin polymer material of step a) at a first temperature up to about 100 °C with about 5 to 50 percent by weight, based on the total weight of the olefin polymer material and polymerizable flame retardants used, of at least one said polymerizable flame retardant in the presence of a controlled amount of oxygen, and then maintaining the polymer material at a second temperature from 25°C to a temperature below the softening point of the polymer material, thereby forming a polymer mixture; c) heating the polymer mixture obtained in step b) at a temperature above the melting point of the polymer mixture, thereby producing a graft polymer melt; and optionally d) pelletizing the graft polymer melt after it is cooled, thereby producing a pelletized graft copolymer.

2. The process of claim 1 wherein the olefin polymer material (A) is selected from: (a) a crystalline homopolymer of propylene having an isotactic index greater than about 80%; (b) a crystalline, random copolymer of propylene with an olefin selected from ethylene and C₄-C₁₀ α-olefins wherein the polymerized olefin content is about 1-10% by weight when ethylene is used, and about 1% to about 20% by weight when the C₄-C₁₀ α-olefin is used, the copolymer having an isotactic index greater than about 60%; (c) a crystalline, random teφolymer of propylene and two olefins selected from ethylene and Gt-Cg α-olefins wherein the polymerized olefin content is about 1 % to about 5% by weight when ethylene is used, and about 1 % to about 20% by weight when the C₄-C₁₀ α-olefins are used, the teφolymer having an isotactic index greater than about 85%; (d) an olefin polymer composition comprising: (i) about 10% to about 60% by weight of a crystalline propylene homopolymer having an isotactic index at least about 80% or a crystalline copolymer of monomers selected from (a) propylene and ethylene, (b) propylene, ethylene and a C -C₈ α-olefin, and (c) propylene and a C₄-C₈ α-olefin, the copolymer having a polymerized propylene content of more than about 85% by weight, and an isotactic index greater than about 60%; (ii) about 3% to about 25% by weight of a copolymer of ethylene and propylene or a G_t-Cs α-olefin that is insoluble in xylene at ambient temperature; and (iii) about 10% to about 80% by weight of an elastomeric copolymer of monomers selected from (a) ethylene and propylene, (b) ethylene, propylene, and a C4-C₈ α-olefin, and (c) ethylene and a C4-C₈ α-olefin, the copolymer optionally containing about 0.5% to about 10% by weight of a polymerized diene and containing less than about 70% by weight of polymerized ethylene, and being soluble in xylene at ambient temperature and having an intrinsic viscosity of about 1.5 to about 6.0 dl/g; wherein the total of (ii) and (iii), based on the total olefin polymer composition is about 50% to about 90% by weight, and the weight ratio of (ii)/(iii) is less than about 0.4;

(e) homopolymers of ethylene;

(f) random copolymers of ethylene and an α-olefin selected from C₃-C₁₀ α-olefins having a polymerized α-olefin content of about 1 to about 20% by weight;

(g) random teφolymers of ethylene and C₃-C1₀ α-olefins having a polymerized α- olefin content of 1 to 20% by weight;

(h) homopolymers of butene- 1 ;

(i) copolymers or teφolymers of butene-1 with ethylene, propylene or C₅-C₁₀ alpha-olefin, the comonomer content from about 1 mole % to about 15 mole %; and (j) mixtures thereof.

3. The process of claim 2 wherein the olefin polymer material is a crystalline homopolymer of propylene having an isotactic index greater than 80%.

4. A process for making a flame retardant grafted olefin polymer by using a reactive, peroxide-containing olefin polymer comprising: a) preparing a polymer blend comprising: I. about 50.0 to about 95.0 wt% of a reactive, peroxide-containing olefin polymer (B); and II. about 5 to about 50.0 wt% of at least one polymerizable flame retardant; wherein the sum of components I + II is equal to 100 wt%; b) heating the polymer blend to a temperature from 25°C to a temperature below the softening point of the polymer blend in the presence of a controlled amount of oxygen, thereby forming a polymer mixture; c) heating the polymer mixture at a temperature above the melting point of the polymer mixture, thereby producing a graft polymer melt; and optionally d) pelletizing the graft polymer melt after it is cooled, thereby producing a pelletized graft copolymer.

5. The process of claim 4 wherein a starting material for the reactive, peroxide-containing olefin polymer is selected from: (a) a crystalline homopolymer of propylene having an isotactic index greater than about 80%; (b) a crystalline, random copolymer of propylene with an olefin selected from ethylene and C4-C₁0 α-olefins wherein the polymerized olefin content is about 1-10% by weight when ethylene is used, and about 1% to about 20% by weight when the C4-C10 α-olefin is used, the copolymer having an isotactic index greater than about 60%; (c) a crystalline, random teφolymer of propylene and two olefins selected from ethylene and Gt-Cs α-olefins wherein the polymerized olefin content is about 1% to about 5% by weight when ethylene is used, and about 1% to about 20% by weight when the C4-C₁₀ α-olefins are used, the teφolymer having an isotactic index greater than about 85%;

(d) an olefin polymer composition comprising: (i) about 10% to about 60% by weight of a crystalline propylene homopolymer having an isotactic index at least about 80% or a crystalline copolymer of monomers selected from (a) propylene and ethylene, (b) propylene, ethylene and a C₄-C₈ α-olefin, and (c) propylene and a C₄-C₈ α-olefin, the copolymer having a polymerized propylene content of more than about 85% by weight, and an isotactic index greater than about 60%; (ii) about 3% to about 25% by weight of a copolymer of ethylene and propylene or a C -Cs α-olefin that is insoluble in xylene at ambient temperature; and (iii) about 10% to about 80% by weight of an elastomeric copolymer of monomers selected from (a) ethylene and propylene, (b) ethylene, propylene, and a Gt-Cs α-olefin, and (c) ethylene and a C₄-C₈ α-olefin, the copolymer optionally containing about 0.5% to about 10% by weight of a polymerized diene and containing less than about 70% by weight of polymerized ethylene, and being soluble in xylene at ambient temperature and having an intrinsic viscosity of about 1.5 to about 6.0 dl/g; wherein the total of (ii) and (iii), based on the total olefin polymer composition is about 50% to about 90% by weight, and the weight ratio of (ii)/(iii) is less than about 0.4;

(e) homopolymers of ethylene;

(f) random copolymers of ethylene and an α-olefin selected from C₃-C1₀ α-olefins having a polymerized α-olefin content of about 1 to about 20% by weight;

(g) random teφolymers of ethylene and C₃-C₁₀ α-olefins having a polymerized α- olefin content of 1 to 20% by weight;

(h) homopolymers of butene- 1 ; (i) copolymers or teφolymers of butene-1 with ethylene, propylene or C₅-C₁₀ alpha-olefin, the comonomer content from about 1 mole % to about 15 mole %; and (j) mixtures thereof.

6. The process of claim 5 wherein the starting material is a crystalline homopolymer of propylene having an isotactic index greater than 80%.

7. The process of claims 1 or 4 wherein the polymerizable flame retardant is a phosphorus containing vinyl monomer.

8. The process of claim 7 wherein the polymerizable flame retardant is selected from the group consisting of monophosphate ester of hydroxy ethyl methacrylate, diphosphate ester of hydroxy ethyl methacrylate and a mixture thereof.

9. A process for making a flame retardant grafted olefin polymer composite comprising: a) preparing a polymer blend comprising: I. about 50.0 to about 90.0 wt% of an olefin polymer material (A); and II. about 10 to about 50.0 wt% of the pelletized graft copolymer prepared according to claims 1 or 4; wherein the sum of components I + II is equal to 100 wt%; b) heating the polymer blend at a temperature above the melting point of the polymer blend, thereby producing a grafted olefin polymer composite melt; and optionally c) pelletizing the grafted olefin polymer composite after it is cooled, thereby producing a pelletized olefin polymer composite.

10. The process of claim 9 wherein the olefin polymer material (A) is selected from: (a) a crystalline homopolymer of propylene having an isotactic index greater than about 80%; (b) a crystalline, random copolymer of propylene with an olefin selected from ethylene and C4-C10 α-olefins wherein the polymerized olefin content is about 1-10% by weight when ethylene is used, and about 1% to about 20% by weight when the C₄-C₁₀ α-olefin is used, the copolymer having an isotactic index greater than about 60%; (c) a crystalline, random teφolymer of propylene and two olefins selected from ethylene and C4-C8 α-olefins wherein the polymerized olefin content is about 1% to about 5% by weight when ethylene is used, and about 1% to about 20% by weight when the C₄-C₁₀ α-olefins are used, the teφolymer having an isotactic index greater than about 85%;

(d) an olefin polymer composition comprising: (i) about 10% to about 60% by weight of a crystalline propylene homopolymer having an isotactic index at least about 80% or a crystalline copolymer of monomers selected from (a) propylene and ethylene, (b) propylene, ethylene and a C₄-C₈ α-olefin, and (c) propylene and a C₄-C_& α-olefin, the copolymer having a polymerized propylene content of more than about 85% by weight, and an isotactic index greater than about 60%; (ii) about 3% to about 25% by weight of a copolymer of ethylene and propylene or a C₄-Cg α-olefin that is insoluble in xylene at ambient temperature; and (iii) about 10% to about 80% by weight of an elastomeric copolymer of monomers selected from (a) ethylene and propylene, (b) ethylene, propylene, and a C₄-C_& α-olefin, and (c) ethylene and a C₄-C₈ α-olefin, the copolymer optionally containing about 0.5% to about 10% by weight of a polymerized diene and containing less than about 70% by weight of polymerized ethylene, and being soluble in xylene at ambient temperature and having an intrinsic viscosity of about 1.5 to about 6.0 dl/g; wherein the total of (ii) and (iii), based on the total olefin polymer composition is about 50% to about 90% by weight, and the weight ratio of (ii)/(iii) is less than about 0.4;

(e) homopolymers of ethylene;

(f) random copolymers of ethylene and an α-olefin selected from C3-C₁0 α-olefins having a polymerized α-olefin content of about 1 % to about 20% by weight;

(g) random teφolymers of ethylene and two C3-C₁0 α-olefins having a polymerized α-olefin content of about 1% to about 20% by weight;

(h) homopolymers of butene- 1 ; (i) copolymers or teφolymers of butene-1 with ethylene, propylene or C5-C₁0 alpha-olefin, the comonomer content from about 1 mole % to about 15 mole %; and (j) mixtures thereof.

11. The process of claim 10 wherein the olefin polymer material (A) is a crystalline homopolymer of propylene having an isotactic index greater than 80%.

12. An olefin polymer having radiation initiated flame retardant grafts produced by a process comprising: a) irradiating an olefin polymer material (A) at a temperature from about 10 °C to about 85 °C with high-energy ionizing radiation to produce free radical initiating site on the polymer backbone in an atmosphere having an oxygen concentration of at most 0.004% by volume; b) treating the irradiated olefin polymer material at a first temperature up to about 100 °C with about 5 to 50 percent by weight, based on the total weight of the olefin polymer material and polymerizable flame retardants used, of at least one polymerizable flame retardant in the presence of a controlled amount of oxygen, and then maintaining the polymer material at a second temperature from 25°C to a temperature below the softening point of the polymer material, thereby forming a polymer mixture; c) heating the polymer mixture obtained in step b) at a temperature above the melting point of the polymer mixture, thereby producing a graft polymer melt; and optionally d) pelletizing the graft polymer melt after it is cooled, thereby producing a pelletized graft copolymer.

13. An olefin polymer having peroxide initiated flame retardant grafts produced by a process comprising: a) preparing a polymer blend comprising: I. about 50.0 to about 95.0 wt% of a reactive, peroxide-containing olefin polymer (B); and II. about 5 to about 50.0 wt% of at least one polymerizable flame retardant; wherein the sum of components I + II is equal to 100 wt%; b) heating the polymer blend to a temperature from 25°C to a temperature below the softening point of the polymer blend in the presence of a controlled amount of oxygen, thereby forming a polymer mixture; c) heating the polymer mixture at a temperature above the melting point of the polymer mixture, thereby producing a graft polymer melt; and optionally d) pelletizing the graft polymer melt after it is cooled, thereby producing a pelletized graft copolymer.

14. An olefin polymer composite having flame retardant grafts produced by a process comprising: a) preparing a polymer blend comprising: I. about 50.0 to about 90.0 wt% of an olefin polymer material (A); and II. about 10 to about 50.0 wt% of the pelletized graft copolymer prepared according to claims 1 or 4; wherein the sum of components I + II is equal to 100 wt%; b) heating the polymer blend at a temperature above the melting point of the polymer blend, thereby producing a grafted olefin polymer composite melt; and optionally c) pelletizing the grafted olefin polymer composite after it is cooled, thereby producing a pelletized olefin polymer composite.