Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
  • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
  • C08L23/10—Homopolymers or copolymers of propene
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
  • C08L23/26—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers modified by chemical after-treatment
  • C08L23/30—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers modified by chemical after-treatment by oxidation
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
  • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment

Definitions

• This invention relates to a process for enriching the peroxide content of polyolef ⁇ ns with peroxide functionality, in the presence of a controlled amount of oxygen.
• Polyolefins with peroxide functionality can be prepared by using an electron beam irradiation and oxidation process. The process normally includes irradiating a particulate polypropylene material in a substantially inert atmosphere, exposing the irradiated propylene polymer material to a controlled amount of oxygen, and heating the polymer material to a specified temperature for a specified time.
• U.S. Pat. No. 5,817,707 discloses a process of grafting polymerization using peroxide-containing polyolefins prepared by an electron beam irradiation and oxidation process.
• the peroxide-containing polyolefins made by the irradiation and oxidation processes were dispersed in water in the presence of a surfactant to form a solid/water suspension.
• Grafted polyolefins were then produced via a free radical initiation mechanism by adding reducing agents and vinyl monomers added into the suspension under agitation.
• the irradiation and oxidation process is also useful in preparing visbroken polypropylene and fibers as disclosed in U.S. Pat. No. 5,820,981.
• Polypropylene homopolymers with a melt flow rate of 300 dg/min or more were prepared by treating low melt flow rate homopolymers with electron beam irradiation in the substantial absence of oxygen, followed by a multistage treatment in the presence of a controlled amount of oxygen.
• a liquid peroxide process can also be used to prepare peroxide-containing polyolefins, in which a liquid peroxide is mixed with polyolefin materials, followed by oxidation steps, as disclosed in US Patent Application 10/305,816.
• the irradiation process requires the use of an electron beam generator, which typically limits its use to large scale applications, and requires that the oxidation reactor be adjacent to the electron beam generator, due to the short half-life of free radicals generated by the irradiation.
• the liquid peroxide process uses liquid peroxides as free radical initiators, such as diacyl peroxides, ketone peroxides, peroxyesters, dialkyl peroxides, and peroxyketals, etc.
• the liquid peroxides require special storage and handling due to their thermal unstability. Therefore, both processes have inherent drawbacks and are difficult to use, especially for the users without sophisticated reaction equipment and well designed facility.
• the present invention provides a novel approach for preparing peroxide-containing polyolefins with desirable melt flow rates and peroxide contents, by reactivating the peroxide groups at an elevated temperature and forming free radicals on the peroxide- containing olefin polymers without the help of irradiation or liquid peroxide.
• a master batch of an olefin polymer having low peroxide contents, prepared by using either the irradiation or liquid peroxide process, can be used as a starting material for enriched peroxide-containing polyolefin materials with various melt flow rate and peroxide contents.
• a process for enriching the peroxide content of a peroxide-containing olefin polymer comprises: a) contacting the peroxide-containing olefin polymer (A) with a first gas mixture having a first oxygen concentration, from about 0.1 to about 6% by volume of oxygen, preferably about 0.2 to about 4% by volume of oxygen, in a reactor; b) heating the olefin polymer to a first temperature at least equal to a preparative temperature but below a softening point of the polymer, preferably at about 100°C to about 145°C in the presence of a second gas mixture having a second oxygen concentration, preferably about 0.1 to about 6% by volume of oxygen, most preferably about 0.2 to about 4% by volume of oxygen, wherein the preparative temperature is a last heat treatment temperature when making the peroxide-containing olefin polymer (A); and c) maintaining the temperature of the olefin polymer at a second temperature from at least 80°C but below the softening
• a process for making an enriched peroxide-containing polyolefin mixture comprises: a) preparing an olefin polymer mixture (D) in a reactor comprising: I. adding about 10.0 to about 95.0 wt%, preferably about 20.0 to about 90.0 wt%, most preferably about 30.0 to about 70.0 wt% of a peroxide- containing olefin polymer (A) into the reactor in the presence of a first gas mixture having a first oxygen concentration, preferably about 0.1 to about 6% by volume of oxygen, most preferably about 0.2 to about 4% by volume of oxygen, and II.
• an olefin polymer having an enriched peroxide content by a process comprises: a) contacting a peroxide-containing olefin polymer (A) with a first gas mixture having a first oxygen concentration, from about 0.1 to about 6% by volume of oxygen, preferably about 0.2 to about 4% by volume of oxygen, in a reactor; b) heating the olefin polymer to a first temperature at least equal to a preparative temperature but below a softening point of the polymer, preferably at about 100°C to about 145°C in the presence of a second gas mixture having a second oxygen concentration, preferably about 0.1 to about 6% by volume of oxygen, most preferably about 0.2 to about 4% by volume of oxygen, wherein the preparative temperature is a last heat treatment temperature when making the peroxide-containing olefin polymer (A); and c) maintaining the temperature of the olefin polymer at a second temperature from at least 80°C but below the
• an olefin polymer mixture having an enriched peroxide content by a process comprises: a) preparing an olefin polymer mixture (D) in a reactor comprising: I. adding about 10.0 to about 95.0 wt%, preferably about 20.0 to about 90.0 wt%, most preferably about 30.0 to about 70.0 wt% of a peroxide- containing olefin polymer (A) into the reactor in the presence of a first gas mixture having a first oxygen concentration, preferably about 0.1 to about 6% by volume of oxygen, most preferably about 0.2 to about 4% by volume of oxygen, and II.
• Suitable non-oxidized olefin polymers and starting materials for the peroxide- containing olefin polymers can be selected from propylene, ethylene, and butene-1 polymer materials.
• the propylene polymer can be: (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 C 4 -C ⁇ o ⁇ -olefins wherein the polymerized olefin content is about 1-10% 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 -C ⁇ o ⁇
• the ethylene polymer material is preferably selected from: (a) homopolymers of ethylene; (b) random copolymers of ethylene and an ⁇ -olefin selected from C3-C10 ⁇ -olefins having a polymerized ⁇ -olefin content of about 1 to about 20% by weight, preferably about 1% to about 16%; and (c) random terpolymers of ethylene and two C3-C10 ⁇ -olefins having a polymerized ⁇ -olefin content of about 1% to about 20% by weight, preferably about 1% to about 16%; and (d) mixtures thereof; wherein the C3-C10 ⁇ -olefins include the linear and branched alpha-olefins such as, for example, prop
• ethylene polymer When the ethylene polymer is an ethylene homopolymer, it typically has a density of 0.89 g/cm 3 or greater, and when the ethylene polymer is an ethylene copolymer with a C3-C 10 ⁇ -olefins, it typically has a density of 0.91 g/cm 3 or greater but less than 0.94 g/cm 3 .
• Suitable ethylene copolymers include ethylene/butene-1, ethylene/hexene-1, ethylene/octene-1 and ethylene/4-methyl- 1-pentene.
• the ethylene copolymer can be a high density ethylene copolymer or a short chain branched linear low density ethylene copolymer (LLDPE), and the ethylene homopolymer can be a high density polyethylene (HDPE) or a low density polyethylene (LDPE).
• LLDPE and LDPE have densities of 0.910 g/cm 3 or greater to less than 0.94 g/cm 3
• the HDPE and high density ethylene copolymers have densities greater than 0.940 g/cm 3 , usually 0.95 g/cm 3 or greater.
• ethylene polymer materials having a density from 0.89 to 0.97 g/cm 3 are suitable for use in the practice of this invention.
• the ethylene polymers are LLDPE and HDPE.
• the butene-1 polymer material is preferably selected from: (a) homopolymers of butene- 1 ; (b) copolymers or terpolymers of butene-1 with ethylene, propylene or C5-C 1 0 alpha-olefm, the comonomer content ranging from about 1 mole % to about 15 mole %; and (c) mixtures thereof.
• Suitable 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.
• MFR melt flow rate
• 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 02/102811, the disclosures of which are incorporated herein by reference.
• 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%.
• Peroxide-containing olefin polymers can be prepared by either an irradiation process or a liquid peroxide process. In a typical irradiation process, an olefin polymer is irradiated under an electron beam at a dose rate of 0.1-15 megarads (Mrad) in an inert atmosphere.
• the irradiated polymer is then immediately treated with oxygen at a concentration of greater than 0.004% but less than 21% by volume, preferably less than 8%, more preferably less than 5% by volume, and most preferably 1.3% to 3% by volume, at a temperature of at least 25°C but below the softening point of the polymer, preferably about 25°C to about 140°C, more preferably about 25° to about 100°C, and most preferably about 40° to about 80°C.
• the polymer is then heated to a temperature of at least 25°C up to the softening point of the polymer, preferably from 100°C to less than the softening point of the polymer, at an oxygen concentration that is within the same range as in the first treatment step.
• the total reaction time is typically up to three hours.
• the polymer is optionally treated at a stabilization temperature of at least 80°C but below the softening point of the polymer, typically for one hour, in an inert atmosphere such as nitrogen to deactive any active free radicals.
• a stabilization temperature of at least 80°C but below the softening point of the polymer, typically for one hour, in an inert atmosphere such as nitrogen to deactive any active free radicals.
• an olefin polymer is treated with 0.1 to 4% of an organic peroxide initiator while adding a controlled amount of oxygen so that the olefin polymer material is exposed to greater than 0.004% but less than 15% by volume, preferably less than 8%>, more preferably less than 5%> by volume, and most preferably 1.3% to 3% by volume, at a temperature of at least 25°C but below the softening point of the polymer, preferably about 25°C to about 140°C.
• the polymer is then heated to a temperature of at least 25°C up to the softening point of the polymer, preferably from 100°C to less than the softening point of the polymer, at an oxygen concentration that is within the same range as in the first treatment step.
• the total reaction time is typically up to three hours.
• the polymer is optionally treated at a stabilization temperature of at least 80°C but below the softening point of the polymer, typically for one hour, in an inert atmosphere such as nitrogen to deactive any .active free radicals.
• This liquid peroxide process has been disclosed in US Patent Application No. 10/305,816, the disclosure of which is incorporated herein by reference.
• Suitable organic peroxides include acyl peroxides, such as benzoyl and dibenzoyl peroxides; dialkyl and aralkyl peroxides, such as di-tert-buryl peroxide, dicumyl peroxide; cumyl butyl peroxide; l,l,-di-tert-butylperoxy-3,5,5-trimethylcyclohexane; 2,5-dimethyl- l,2,5-tri-tert-butylperoxyhexane,and bis(alpha-tert-butylperoxy isopropylbenzene), and peroxy esters such as bis(alpha-tert-butylperoxy pivalate; tert-butylperbenzoate; 2,5- dimethylhexyl-2,5-di(perbenzoate); tert-butyl-di(perphthalate); tert-butylperoxy-2- ethylhexanoate,
• the peroxides can be used neat or in diluent medium, having an active concentration of from 0.1 to 6.0 pph, preferably from 0.2 to 3.0 pph. Particularly preferred is tert-butyl peroctoate as a 50 weight % dispersion in mineral oil, sold commercially under the brand name Lupersol PMS.
• the peroxide-containing olefin polymers used to prepare the enriched peroxide- containing polyolefin material or mixture have a melt flow rate of about 10 to about 10000 dg/min, preferably, about 50 to 5000 and most preferably, about 100 to 1000.
• a peroxide-containing olefin polymer (A) is contacted with a first gas mixture having a first oxygen concentration in a reactor.
• the oxygen concentration in the gas mixture is typically greater than 0.004% but less than 15% by volume, preferably less than 8%, more preferably from about 0.1 to about 6% by volume, and most preferably from about 0.2% to 4% by volume of oxygen, with respect to the total volume of the gas mixture, wherein the gas mixture typically contains oxygen in nitrogen, which is preferred for the gas mixture employed in the process of the present invention.
• the peroxide-containing olefin polymer is then heated to a first temperature at least equal to a preparative temperature, but below the softening point of the polymer, preferably about 100°C to about 145°C in the presence of a second gas mixture having a second oxygen concentration, from greater than 0.004% but less than 15% by volume, preferably less than 8%, more preferably from about 0.1 to about 6% by volume, and most preferably from about 0.2% to 4% by volume of oxygen, with respect to the total volume of the gas mixture, wherein the gas mixture typically contains oxygen in nitrogen, which is preferred for the gas mixture employed in the process of the present invention.
• the preparative temperature is a last heat treatment temperature used in the preparation of the peroxide-containing olefin polymer (A) by either the irradiation process or liquid peroxide process described above.
• the total reaction time is typically up to three hours.
• the olefin polymer is treated at a second temperature of at least 80°C but below the softening point of the polymer, typically for one hour, in an atmosphere having an oxygen concentration of at most 0.004% by volume to deactivate any active free radicals before it is cooled, discharged and collected, thereby forming an enriched peroxide- containing polyolefin material (B).
• the second temperature can be equal to or different from the first temperature.
• the oxygen concentration of the second gas mixture can be equal to or different from that of the first gas mixture.
• the peroxide content of the enriched peroxide-containing polyolefin material (B) preferably ranges from about 2 to about 200 mmole of peroxide in one kilogram of the peroxide-containing olefin polymer (mmol/kg), more preferably from about 5 to about 150 mmol/kg, and most preferably from about 10 to 100 mmol/kg.
• the ratio of the peroxide content of the enriched peroxide-containing polyolefin material (B) to that of the peroxide- containing olefin polymer (A) is about 1.05 to about 100.
• the polymer mixture in the reactor is heated to a first temperature at least equal to a preparative temperature but below the softening point of the polymer, preferably at about 100°C to 145°C, in the presence of a second gas mixture having a second oxygen concentration, preferably about 0.1 to about 6% by volume of oxygen in nitrogen, most preferably about 0.2 to about 4% by volume of oxygen, with respect to the total volume of the gas mixture, wherein the gas mixture typically contains oxygen in nitrogen, which is preferred for the gas mixture employed in the process of the present invention; wherein the preparative temperature is the same as defined above.
• the total reaction time is typically up to three hours.
• the olefin polymer is treated at a second temperature of at least 80°C but below the softening point of the polymer, typically for one hour, in an atmosphere having an oxygen concentration of at most 0.004% by volume to deactivate any active free radicals before it is cooled, discharged and collected, thereby forming an enriched peroxide-containing polyolefin mixture (C).
• the second temperature can be equal to or different from the first temperature.
• the oxygen concentration of the second gas mixture can be equal to or different from that of the first gas mixture.
• the peroxide content of the enriched peroxide-containing polyolefin mixture (C), preferably ranges from about 0.2 to about 190 mmole of peroxide in one kilogram of the peroxide-containing olefin polymer (mmol kg), more preferably from about 0.5 to about 142.5 mmol/kg, and most preferably from about 1 to 95 mmol/kg.
• the ratio of the peroxide content of the enriched peroxide-containing polyolefin mixture (C) to that of the olefin polymer mixture (D) is about 1.05 to about 100 by mole.
• the number average molecular weight (M n ) of the enriched peroxide-containing polyolefin material or mixture is preferably greater than 10,000, although it may be lower in some cases.
• the enriched peroxide-containing polyolefin materials or mixtures can be used to prepare a grafted copolymer by treating the enriched peroxide-containing polyolefin materials or mixtures with a vinyl monomer compound at an elevated temperature.
• the grafting process comprises treating 100 parts of the enriched peroxide-containing polyolefin materials or mixtures with about from 5 to 240 parts (pph) of at least one polymerizable monomer under free radical polymerization conditions, preferably about 10 to 80 pph, most preferably 20 to 40 pph at a temperature from at least about 50°C to below the softening point of the polymer.
• the vinyl monomer has one or more unsaturated bonds with and the monomer can contain a C 2 -C 2 0, straight or branched aliphatic chain or a substituted or un-substituted aromatic, heterocyclic, or alicyclic ring in a mono- or polycyclic compound.
• the vinyl monomer is a C 2 -C 20 vinyl monomer.
• the vinyl monomers are: styrene, vinylnaphthalene, vinylpyridine, vinylpyrrolidone, vinylcarbazole, methylstyrenes, methylchlorostyrene, p-tert-bulylstyrene, methylvinylpyridine, ethylvinylpyridine, acrylonitrile, methacrylonitrile, acrylic acid esters, methacrylic acid esters, unsaturated acid anhydride, metal salts of unsaturated acids and mixtures thereof, particularly styrene, acrylonitrile, butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, methyl acrylate, butyl methacrylate, and mixtures thereof.
• MFR Melt Flow Rate
• MI Isotactic Index
• 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.
• the samples are prepared at a concentration of 70 mg/50 ml of stabilized 1, 2, 4 trichlorobenzene (250 ⁇ g/ml BHT). The samples are then heated to 170 °C for 2.5 hours to solubilize. The samples are then run on a Waters GPCV2000 at 145°C at a flow rate of 1.0 ml/min. using the same stabilized solvent. Three Polymer Lab columns were used in series (Plgel, 20 ⁇ m mixed ALS, 300 X 7.5 mm).
• Step 1 Preparation of a peroxide-containing olefin polymer A.
• Step 2 Preparation of enriched peroxide-containing polyolefin materials.
• Sample 1 The peroxide-containing olefin polymer A was added into a one-gallon autoclave equipped with a mechanical stirrer. A gas mixture with an oxygen concentration of 0.8%) by volume in nitrogen was introduced into the reactor. The polymer was heated to 145°C and held for 60 minutes.
• Samples 1 and 2 demonstrate that the reaction condition is correlated with the characteristics of the resultant polymer materials as demonstrated by the melt flow rate and the peroxide content changes before and after the reaction.
• the melt flow rate and the peroxide content of the polymers increase with the increase of the oxygen concentration in the enrichment reaction. Therefore, it is possible to make an enriched peroxide-containing polyolefin material with a predetermined peroxide content or melt flow rate under a controlled oxygen concentration.
• Example 2 Step 1 Preparation of a peroxide-containing olefin polymer B.
• the peroxide-containing olefin polymer B was prepared from a crystalline homopolymer of propylene, having a melt flow rate (MFR) of 9.4 dg/min, and LI. of 96.5%, commercially available from Basell USA Inc.
• MFR melt flow rate
• LI. LI. of 96.5%
• the homopolymer of propylene (2000g) was added into a 7 liter two zone reactor as described in General Procedures in U.S. Patent No. 5,696,203.
• a total gas flow rate in the reactor was kept at 28.3 standard liter per hour (SLH).
• Step 2 Preparation of enriched peroxide-containing polyolefin material.
• Sample 1 The peroxide-containing olefin polymer B was added into a one-gallon autoclave equipped with a mechanical stirrer. A gas mixture with an oxygen concentration of 0.8% by volume in nitrogen was introduced into the reactor. The polymer was heated to 145°C and held for 60 minutes. The gas mixture was then purged by nitrogen and the polymer was held for an additional 60 minutes at 145°C before it was cooled, discharged and collected.
• Table II The characteristics of the samples are summarized in Table II. As shown in Table II, the melt flow rate of the sample increased after the enrichment reaction, indicating that the peroxide-containing olefin polymer made by using liquid peroxide process can also been enriched by the process disclosed in this invention.
• Example 3 Step 1 Preparation of a peroxide-containing olefin polymer C.
• a polypropylene homopolymer, having a MFR of 12.0 dg/min and I.I. of 95.0%, commercially available from Basell USA Inc. was irradiated at 4.0 Mrad under a blanket of nitrogen. The irradiated polymer was then exposed to the atmosphere at ambient temperature for 60 minutes and collected in an air-proof bag after the oxygen was removed by nitrogen purge.
• the MFR of the resultant peroxide-containing olefin polymer C was 259 dg/min determined at 190°C. The peroxide concentration was 50.9 meq/kg of polymer.
• Step 2 Preparation of enriched peroxide-containing polyolefin materials.
• Sample 1 The peroxide-containing olefin polymer C was added into a one-gallon autoclave equipped with a mechanical stirrer. A gas mixture with an oxygen concentration of 2.0% by volume in nitrogen was introduced into the reactor. The polymer was heated to 140°C and held for 60 minutes. The gas mixture was then removed by nitrogen purge and the polymer was held for an additional 60 minutes at 140°C before it was cooled, discharged and collected.
• the characteristics of the sample are summarized in Table III. The melt flow rates in this example were determined at 190°C. As shown in Table III, the enriched peroxide- containing polyolefin material had an increased melt flow rate after the reaction.
• Example 4 Step 1 Preparation of a peroxide-containing olefin polymer D.
• a propylene copolymer, having a melt flow rate (MFR) of 3.8 dg/min, and LI. of 88.6% and ethylene content of 9.4%>, commercially available from Basell USA Inc. was irradiated at 2.0 Mrad under a blanket of nitrogen. The ii ⁇ adiated polymer was then exposed to the atmosphere at ambient temperature for 60 minutes and collected in an air-proof bag after the oxygen was removed by nitrogen purge.
• the MFR of the resultant peroxide- containing olefin polymer C was 44 dg/min determined at 190°C.
• the peroxide concentration was 22.2 meq/kg of polymer.
• Step 2 Preparation of enriched peroxide-containing polyolefin materials.
• Sample 1 The peroxide-containing olefin polymer C was added into a one-gallon autoclave equipped with a mechanical stirrer. A gas mixture with an oxygen concentration of
• the melt flow rates in this example are determined at 190°C.
• the enriched peroxide-containing polyolefin material had an increase melt flow rate after the reaction.
• Example 5 Step 1 Preparation of a peroxide-containing olefin polymer E.
• a polypropylene homopolymer, having a MFR of 9.0 dg/min and I.I. of 96.5%, commercially available from Basell USA Inc. was irradiated at 4.0 Mrad under a blanket of nitrogen. The irradiated polymer was then exposed to the atmosphere at ambient temperature for 60 minutes and collected in an air-proof bag after the oxygen was removed by nitrogen purge.
• the MFR of the resultant peroxide-containing olefin polymer C was 703 dg/min determined at 190°C.
• the peroxide concentration was 63.3 meq/kg of polymer.
• Step 2 Preparation of enriched peroxide-containing polyolefin materials.
• Sample 1 The peroxide-containing olefin polymer E was added into a one-gallon autoclave equipped with a mechanical stirrer. A gas mixture with an oxygen concentration of 2.0% by volume in nitrogen was introduced into the reactor. The polymer was heated to 140°C and held for 60 minutes. The gas mixture was then removed by nitrogen purge and the polymer was held for an additional 60 minutes at 140°C before it was cooled, discharged and collected.
• the characteristics of the sample are summarized in Table V.
• the melt flow rates in this example were determined at 190°C.
• the enriched peroxide-containing polyolefin material had an increase melt flow rate after the reaction.

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