Long-chain branched high-density polyethylene and preparation method thereof

Abstract

The present invention relates to a long-chain branched high-density polyethylene, which is obtained by melt-mixing high-density polyethylene and an azo initiator, wherein the high-density polyethylene comprises 88.0-99.999 parts by weight and the azo initiator comprises 0.001-2 parts by weight. The high-density polyethylene is an ethylene homopolymer or copolymer, has a double bond content of 0.01-0.5% by mole, a melt index of 0.001-10 g / 10 min, and a density of 0.940-0.970 g / cm 3 The present invention also relates to a method for preparing long-chain branched high-density polyethylene.

Description

Technical Field

[0001] The present invention relates to a method for preparing high-density polyethylene, in particular to a method for preparing high-density polyethylene containing long-chain branches. Background Art

[0002] High-density polyethylene (HDPE) is a versatile general-purpose resin material used today. Compared to LLDPE and LDPE, it offers superior mechanical properties, such as tensile and flexural properties. HDPE also possesses excellent chemical resistance and electrical insulation properties, making it widely used in a variety of blow-molded products, injection-molded products, films, wires and cables, and pipes. However, because its molecular chains lack long-chain branches, the degree of molecular chain entanglement in the molten state is low, resulting in low melt strength. During extensional flow, the melt exhibits no strain hardening, making HDPE susceptible to edge curling and shrinkage during extrusion coating, fluid flow instability during multi-layer co-extrusion, and cell collapse during extrusion foaming. This limits HDPE's application in molding processes such as thermoforming, large-scale molding, and foaming.

[0003] Long-chain branched high-density polyethylene (HDPE) is a type of polyethylene with high melt strength and pronounced strain hardening properties. Melt strength refers to the maximum stress a polymer melt can withstand before breaking during stretching. Strain hardening, on the other hand, refers to the phenomenon in which the tensile stress increases dramatically with increasing strain during stretching. Polymers exhibiting strain hardening exhibit increased elasticity and self-recovery in the molten state, a wider range of uniform melt deformation, and high melt strength. The presence of long-chain branches increases the processing temperature range of HDPE, overcoming defects such as edge curling and shrinkage during high-speed extrusion coating and cell collapse during extrusion foaming. Due to its excellent rheological properties and high melt strength, products produced from long-chain branched HDPE exhibit excellent dimensional stability, a high heat distortion temperature, and favorable environmental performance. Therefore, long-chain branched HDPE has become a research hotspot in the polyolefin field in recent years.

[0004] Generally, the preparation methods of long-chain branched polyethylene (LCBPE) mainly include direct synthesis, high-energy radiation, and melt branching. The direct synthesis method uses a suitable ethylene polymerization catalyst to introduce long chain branches into the polyethylene main chain during the polymerization process; the high-energy radiation method uses high-energy electron beams or rays to generate macromolecular free radicals in polyethylene, and these macromolecular free radicals can form long-chain branches through coupling reactions; the melt branching method uses polyethylene in a molten state under the action of an initiator to generate macromolecular chain free radicals, and these free radicals can form long-chain branches through coupling reactions. The present invention belongs to the field of preparing long-chain branched polyethylene by melt branching. Summary of the Invention

[0005] The present invention aims to provide long-chain branched high-density polyethylene and a method for preparing the same. The invention utilizes an azo initiator, which reacts only with double bonds within the molecular chain to form macromolecular free radicals. These macromolecular free radicals then couple to form crosslinks in the polyethylene. This crosslinking process does not cause polyethylene chain degradation and maximizes the degree of branching in the polyethylene.

[0006] To this end, the present invention provides a long-chain branched high-density polyethylene, which is obtained by melt-mixing high-density polyethylene and an azo initiator, wherein:

[0007] (1) high-density polyethylene: 88.0-99.999 parts by weight;

[0008] (2) the azo initiator: 0.001-2 parts by weight;

[0009] The high-density polyethylene is an ethylene homopolymer or copolymer, with a double bond content of 0.01-0.5% by mole, a melt index of 0.001-10g / 10min, and a density of 0.940-0.970g / cm 3 between.

[0010] The high-density polyethylene used in the present invention is a specific polyethylene that must contain double bonds. The purpose is to introduce a certain amount of double bonds into the polyethylene chain segments.

[0011] The long-chain branched high-density polyethylene of the present invention is preferably obtained by homopolymerizing or copolymerizing ethylene using an olefin polymerization catalyst at 65-85°C (more preferably 75-85°C), wherein the olefin polymerization catalyst comprises a main catalyst and a co-catalyst, and the molar ratio of aluminum in the co-catalyst to titanium in the main catalyst is controlled at 1 to 500:1;

[0012] The main catalyst is prepared by reacting a magnesium compound, a liquid titanium compound and an organic silane compound.

[0013] The magnesium compound is as follows: 1 ) n Cl 2-n As shown, where R is C2~C 20 The hydrocarbon group is a saturated or unsaturated straight chain, branched chain or cyclic chain, 0≤n≤2;

[0014] The titanium compound is as follows: 2 ) n Cl 4-n As shown, where R 2 It is C2~C 20The hydrocarbyl group is a saturated or unsaturated straight-chain, branched-chain or cyclic chain, where 0 ≤ n ≤ 4;

[0015] The general formula of the organosilane compound is R 3 m SiX n (OR 4 ) k , where R 3 is a hydrocarbyl group of C2 - C 20 and R 3 contains a double bond, X is a halogen, R 4 is a straight-chain or branched-chain alkyl group of C1 - C 20 , m is an integer of 2 - 3, n is an integer of 1 - 2, k is an integer of 0 - 2, and m + n + k = 4;

[0016] Among them, the cocatalyst is an organoaluminum compound with the general formula as shown in AlR' n X 3-n . In the formula, R' is hydrogen or an alkyl group with 1 to 20 carbon atoms, X is a halogen, and n is a number where 1 < n ≤ 3;

[0017] Further preferably, the cocatalyst is AlEt3, Al(iso - Bu)3, Al(n - C6H 13 )3, Al(n - C8H 17 )3 or AlEt2Cl.

[0018] For the long-chain branched high-density polyethylene of the present invention, preferably, in the preparation of the main catalyst, the magnesium compound can specifically be Mg(OEt)Cl, Mg(OEt)2 and long-chain alkoxymagnesium compounds. The organomagnesium compound used in the reaction is further preferably diethoxymagnesium, dipropoxymagnesium, dibutoxymagnesium, dioctoxymagnesium. More preferably, it is a spherical or quasi-spherical particulate solid, and its average particle size range is from 10 to 100 microns.

[0019] For the long-chain branched high-density polyethylene of the present invention, preferably, in the preparation of the main catalyst, the titanium compound is preferably a tetravalent titanium compound because they are usually liquid at room temperature and have good compatibility with some solvents in general cases. Specifically, the further preferred titanium compounds are titanium tetrachloride, triethoxytitanium chloride, dibutoxytitanium chloride, trimethoxytitanium chloride, dimethoxytitanium chloride, trihexoxytitanium chloride or diethoxytitanium chloride. Among them, titanium tetrachloride is more preferably used.

[0020] The long-chain branched high-density polyethylene described in the present invention is preferably selected from the group consisting of 7-octenylallyldichlorosilane, 7-octenylvinyldichlorosilane, 5-hexenylallyldichlorosilane, 7-octenyldi(allyl)chlorosilane, di(7-octenyl)allylchlorosilane, di(7-octenyl)dichlorosilane, tri(allyl)chlorosilane, di(allyl)dichlorosilane, di[2-(5-ethylidene-2-norbornene)ethyl]dichlorosilane, 2-(5-ethylidene-2-norbornene)ethylallyldichlorosilane, and di[2-(3-cyclopentadienyl)ethyl]dichlorosilane in the preparation of the main catalyst.

[0021] The present invention also recommends a method for preparing the main catalyst, and the preparation process preferably includes the following steps:

[0022] (1) contacting a solid magnesium compound with a liquid titanium compound for reaction;

[0023] (2) contacting the reaction product obtained in step (1) with an organosilane for reaction;

[0024] (3) The reaction product obtained in step (2) is further reacted with a liquid titanium compound, and finally washed and dried with an inert solvent to obtain a powdered main catalyst.

[0025] A more preferred solution is:

[0026] (1) contacting a solid magnesium compound and a liquid titanium compound at a temperature within the range of -20-10°C;

[0027] (2) contacting the reaction product obtained in step (1) with an organosilane at 30-80° C. for reaction;

[0028] (3) The reaction product obtained in step (2) is further reacted with a liquid titanium compound at 80-130° C., and finally washed and dried with an inert solvent to obtain a powdered main catalyst.

[0029] Calculated per mole of magnesium compound, the amount of liquid titanium compound used for the first time is controlled within 0.01-50 moles, preferably 0.05-20 moles, the amount of organosilane compound used for the second time is controlled within 0.01-50 moles, preferably 0.02-0.8 moles.

[0030] In the first step of preparing the above-mentioned primary catalyst, in order to ensure the smooth progress of the reaction, it is preferred that the magnesium compound is first dispersed in an inert diluent. The inert diluent is usually selected from aliphatic or aromatic hydrocarbons, such as benzene, toluene, xylene, isobutane, pentane, hexane, heptane or cyclohexane and mixtures thereof. Generally, toluene or xylene is a more suitable inert solvent. The temperature at which the magnesium compound and the liquid titanium compound contact each other depends on the properties of the reactants. Generally, the contact reaction is first carried out at a relatively low temperature, usually at -10 to 20°C, generally at -5 to 10°C. The liquid titanium compound is generally added dropwise. After the addition is completed, the reaction is carried out at a low temperature for 10 to 120 minutes, and then the temperature is gradually increased to 80 to 150°C and the reaction is continued for 20 to 180 minutes.

[0031] The second step in preparing the primary catalyst is primarily to introduce an organosilane compound containing a double bond, which can participate in the polymerization reaction of ethylene and insert into the polyethylene chain. If both double bonds in the organosilane compound participate in the polymerization reaction, a cross-linking reaction will occur in the polyethylene chain segments. If only one double bond in the organosilane compound participates in the polymerization reaction, the remaining double bond can serve as an active site for subsequent reaction with an azo initiator. Under the initiation of the azo compound, the polyethylene chain containing the double bond forms macromolecular free radicals, which can couple to form crosslinks, ultimately forming long-chain branched polyethylene.

[0032] In the second step of preparing the primary catalyst, a liquid titanium compound is added again. This addition removes excess organosilane, improving catalyst activity, enhancing particle strength, and adjusting the final catalyst particle morphology. The reaction temperature for this step is controlled between 80°C and 150°C, and the reaction time is controlled between 20 and 180 minutes.

[0033] After the third step, washing is typically performed to remove excess reactants and byproducts formed during the preparation process. Any inert solvent can be used for this washing step, such as isobutane, pentane, hexane, heptane, or cyclohexane, and mixtures thereof. In experiments, hexane was typically used as the inert washing solvent. After washing, the catalyst suspension can be dried by purging with nitrogen while heating to obtain a primary catalyst powder.

[0034] In the long-chain branched high-density polyethylene of the present invention, it is preferred that the azo initiator includes azobisisobutyronitrile, azobisisoheptanenitrile, azobisisovaleronitrile, and 1,1'-azo-cyanocyclohexane.

[0035] Typically, chemical crosslinking methods for polyethylene use peroxides as initiators to initiate crosslinking. The free radicals formed by the decomposition of the peroxides capture hydrogen atoms from the polyethylene chains, forming polyethylene free radicals. These free radicals then crosslink the polyethylene through coupling. However, polyethylene free radicals are unstable and can undergo dehydrogenation reactions, causing polyethylene degradation. Several auxiliary crosslinking agents have been developed in the prior art to reduce polyethylene degradation, thereby achieving the goal of polyethylene crosslinking. It is generally believed that the free radicals formed by the decomposition of azo initiators cannot capture hydrogen atoms from polyethylene chains and thus cannot initiate crosslinking. However, the present invention has discovered that using azo initiators, as long as the polyethylene chains contain a certain amount of double bonds, can initiate crosslinking of polyethylene chains, and this crosslinking reaction is not accompanied by degradation side reactions.

[0036] The present invention also provides a method for preparing long-chain branched high-density polyethylene, which comprises melt-mixing high-density polyethylene containing double bonds and an azo initiator at 160-230° C. to obtain the long-chain branched high-density polyethylene.

[0037] The melt reaction method of high-density polyethylene and azo initiators can be adopted in the following two ways:

[0038] The first method is to add 88.0-99.999 parts by weight of high-density polyethylene into an internal mixer, control the mixer temperature at 170-210° C., stir for 1-5 minutes, then add 0.001-2 parts by weight of an azo initiator, and stir for 1-10 minutes to obtain long-chain branched high-density polyethylene.

[0039] The second method involves adding 88.0-99.999 parts by weight of high-density polyethylene and 0.001-2 parts by weight of an azo initiator to a screw extruder and reacting for 10-7 minutes to produce long-chain branched high-density polyethylene. The temperature of each section of the extruder is controlled at 160-230°C, and the screw speed is controlled at 50-200 rpm.

[0040] The present invention differs from previous similar technologies, which primarily utilize peroxide initiators. The free radicals generated by the decomposition of the initiator will capture hydrogen atoms on the polyethylene chain to form polyethylene macromolecular free radicals. These free radicals are unstable and prone to chain segment degradation. To reduce the degradation reaction of the polyethylene macromolecular free radicals, other components must be added to stabilize the polyethylene macromolecular free radicals, increasing the complexity of the technology. The present invention utilizes an azo initiator, which reacts only with double bonds in the molecular chain to form macromolecular free radicals. Through coupling between the macromolecular free radicals, polyethylene crosslinks are formed. This crosslinking method does not cause polyethylene chain degradation and can maximize the degree of branching of the polyethylene. DETAILED DESCRIPTION

[0041] The following is a detailed description of the embodiments of the present invention: This embodiment is implemented based on the technical solution of the present invention, and provides detailed implementation methods and processes. However, the protection scope of the present invention is not limited to the following embodiments. The experimental methods in the following embodiments where specific conditions are not specified are generally based on conventional conditions.

[0042] Melt strength test

[0043] The melt strength test experimental apparatus consists of a single-screw extruder equipped with a capillary tube and a melt strength tester. A high-density polyethylene resin melt is first extruded from the extruder die. The resulting melt strand is then pulled by two rollers mounted on a balance beam, moving in opposite directions. The rollers are uniformly accelerated until the strand breaks. The force exerted at the moment of breakage is defined as the melt strength. The melt temperature during testing is controlled at 190°C.

[0044] Example 1

[0045] Preparation of main catalyst:

[0046] (1) In a 200 ml dry reactor containing anhydrous and oxygen-free air, 10 g of magnesium ethoxide (average particle size of 25 μm) and 80 ml of toluene were added and stirred at 0°C for 15 minutes to form a suspension.

[0047] (2) While maintaining the system temperature at 0°C, 15 ml of titanium tetrachloride was added dropwise. After the addition was completed, the system temperature was raised to 90°C and stirred for reaction for 3 hours. Finally, the temperature was lowered to 50°C, 1.2 g of diallyldichlorosilane was added, and the reaction was stirred at 50°C for 2 hours.

[0048] (3) Stop stirring for 30 minutes, allow the particles to settle to the bottom of the reactor, press out the supernatant, add 100 ml of toluene, and stir at 90°C for 15 minutes. Repeat the above steps once to wash the particles.

[0049] (4) After washing, a mixture of 80 ml of toluene and 20 ml of titanium tetrachloride was added, stirred and reacted at 115° C. for 2 hours, and then washed with hexane for more than four times, vacuum-dried, and a main catalyst sample was obtained.

[0050] Ethylene polymerization

[0051] In a 2L polymerization reactor, after sufficient gaseous ethylene replacement, 5mL of a hexane solution of triethylaluminum (AlEt3) (AlEt3 concentration of 0.5mmol / mL), 1L of anhydrous hexane, and 10mg of the primary catalyst component were added at room temperature. Hydrogen was introduced at 0.15MPa. The polymerization pressure was stabilized at 1.0MPa with ethylene. The temperature was raised to 80°C and the polymerization timer was started. Ethylene was continuously added during the polymerization to maintain the polymerization pressure at 1.0MPa. After 2 hours of polymerization, the product was discharged to produce high-density polyethylene. The polyethylene powder was dried and weighed, and the catalyst activity was calculated. The melt strength of the polyethylene resin was tested. The results are listed in Table 1.

[0052] Preparation of long-chain branched high-density polyethylene

[0053] 1000 g of the prepared high-density polyethylene was added with 800 ppm of azobisisobutyronitrile, 1000 ppm of antioxidant 1010, and 1000 ppm of antioxidant 168. After high-speed stirring and mixing, the mixture was melt-extruded using a twin-screw extruder. The feed section and die temperature of the extruder were set at 190°C, the other sections were set at 210°C, and the screw speed was set at 80 rpm. After melt extrusion, the melt index and melt strength of the polyethylene were tested. The results are listed in Table 1.

[0054] Example 2

[0055] Preparation of main catalyst:

[0056] (1) In a 200 ml dry reactor containing anhydrous and oxygen-free air, 10 g of magnesium ethoxide (average particle size of 25 μm) and 80 ml of toluene were added and stirred at -10°C for 15 minutes to form a suspension;

[0057] (2) While maintaining the system temperature at -10°C, 10 ml of titanium tetrachloride was added dropwise. After the addition was completed, the system temperature was raised to 80°C and stirred for reaction for 3 hours. Finally, the temperature was lowered to 50°C, 1.5 g of tri(allyl)chlorosilane was added, and the reaction was stirred at 80°C for 2 hours.

[0058] (3) Stop stirring for 30 minutes, allow the particles to settle to the bottom of the reactor, press out the supernatant, add 100 ml of toluene, and stir at 90°C for 15 minutes. Repeat the above steps once to wash the particles.

[0059] (4) After washing, a mixture of 80 ml of toluene and 20 ml of titanium tetrachloride was added, stirred and reacted at 130° C. for 2 hours, and then washed with hexane for more than four times, vacuum-dried, and a main catalyst sample was obtained.

[0060] Ethylene polymerization

[0061] In a 2L polymerization reactor, after sufficient gaseous ethylene replacement, 5mL of a hexane solution of triethylaluminum (AlEt3) (AlEt3 concentration of 0.5mmol / mL), 1L of anhydrous hexane, and 11mg of the primary catalyst component were added at room temperature. Hydrogen was introduced at 0.15MPa. The polymerization pressure was stabilized at 1.0MPa with ethylene. The temperature was raised to 80°C and the polymerization timer was started. Ethylene was continuously added during the polymerization to maintain the polymerization pressure at 1.0MPa. After 2 hours of polymerization, the product was discharged to produce high-density polyethylene. The polyethylene powder was dried and weighed, and the catalyst activity was calculated. The melt strength of the polyethylene resin was tested. The results are listed in Table 1.

[0062] Preparation of long-chain branched high-density polyethylene

[0063] 1000 g of the prepared high-density polyethylene was added with 800 ppm of azobisisobutyronitrile, 1000 ppm of antioxidant 1010, and 1000 ppm of antioxidant 168. After high-speed stirring and mixing, the mixture was melt-extruded using a twin-screw extruder. The feed section and die temperature of the extruder were set at 190°C, the other sections were set at 210°C, and the screw speed was set at 80 rpm. After melt extrusion, the melt index and melt strength of the polyethylene were tested. The results are listed in Table 1.

[0064] Example 3

[0065] Preparation of main catalyst:

[0066] (1) In a 200 ml dry reactor containing anhydrous and oxygen-free air, 10 g of magnesium ethoxide (average particle size of 25 μm) and 80 ml of toluene were added and stirred at -20°C for 15 minutes to form a suspension;

[0067] (2) While maintaining the system temperature at -20°C, 20 ml of titanium tetrachloride was added dropwise. After the addition was completed, the system temperature was raised to 100°C and stirred for reaction for 3 hours. Finally, the temperature was lowered to 50°C, 1.6 g of di(7-octenyl)dichlorosilane was added, and the reaction was stirred at 30°C for 2 hours.

[0068] (3) Stop stirring for 30 minutes, allow the particles to settle to the bottom of the reactor, press out the supernatant, add 100 ml of toluene, and stir at 90°C for 15 minutes. Repeat the above steps once to wash the particles.

[0069] (4) After washing, a mixture of 80 ml of toluene and 20 ml of titanium tetrachloride was added, stirred and reacted at 80° C. for 2 hours, and then washed with hexane for more than four times, vacuum-dried, and a main catalyst sample was obtained.

[0070] Ethylene polymerization

[0071] In a 2L polymerization reactor, after sufficient gaseous ethylene replacement, 5mL of a hexane solution of triethylaluminum (AlEt3) (AlEt3 concentration of 0.5mmol / mL), 1L of anhydrous hexane, and 12mg of the primary catalyst component were added at room temperature. Hydrogen was introduced at 0.15MPa. The polymerization pressure was stabilized at 1.0MPa with ethylene. The temperature was raised to 80°C and the polymerization timer was started. Ethylene was continuously added during the polymerization to maintain the polymerization pressure at 1.0MPa. After 2 hours of polymerization, the product was discharged to produce high-density polyethylene. The polyethylene powder was dried and weighed, and the catalyst activity was calculated. The melt strength of the polyethylene resin was tested. The results are listed in Table 1.

[0072] Preparation of long-chain branched high-density polyethylene

[0073] 1000 g of the prepared high-density polyethylene was added with 900 ppm of azobisisovaleronitrile, 1000 ppm of antioxidant 1010, and 1000 ppm of antioxidant 168. After high-speed stirring and mixing, the mixture was melt-extruded using a twin-screw extruder. The feed section and die temperature of the extruder were set at 160°C, the other sections were set at 200°C, and the screw speed was set at 60 rpm. After melt extrusion, the polyethylene's melt index and melt strength were tested. The results are listed in Table 1.

[0074] Example 4

[0075] Preparation of main catalyst:

[0076] (1) In a 200 ml dry reactor containing anhydrous and oxygen-free air, 10 g of magnesium ethoxide (average particle size of 25 μm) and 80 ml of toluene were added and stirred at 10° C. for 15 minutes to form a suspension.

[0077] (2) While maintaining the system temperature at 10°C, 15 ml of titanium tetrachloride was added dropwise. After the addition was completed, the system temperature was raised to 50°C and the reaction was stirred for 3 hours. 1.6 g of tri(7-octenyl)chlorosilane was added and the reaction was stirred at 70°C for 2 hours.

[0078] (3) Stop stirring for 30 minutes, allow the particles to settle to the bottom of the reactor, press out the supernatant, add 100 ml of toluene, and stir at 90°C for 15 minutes. Repeat the above steps once to wash the particles.

[0079] (4) After washing, a mixture of 80 ml of toluene and 20 ml of titanium tetrachloride was added, stirred and reacted at 120° C. for 2 hours, and then washed with hexane for more than four times, vacuum-dried, and a main catalyst sample was obtained.

[0080] Ethylene polymerization

[0081] In a 2L polymerization reactor, after sufficient gaseous ethylene replacement, 5mL of a hexane solution of triethylaluminum (AlEt3) (AlEt3 concentration of 0.5mmol / mL), 1L of anhydrous hexane, and 11.5mg of the primary catalyst component were added at room temperature. Hydrogen was introduced at 0.20MPa. The polymerization pressure was stabilized at 1.0MPa with ethylene. The temperature was raised to 80°C and the polymerization timer was started. Ethylene was continuously added during the polymerization to maintain the polymerization pressure at 1.0MPa. After 2 hours of polymerization, the product was discharged to produce high-density polyethylene. The polyethylene powder was dried and weighed, and the catalyst activity was calculated. The melt strength of the polyethylene resin was tested. The results are listed in Table 1.

[0082] Preparation of long-chain branched high-density polyethylene

[0083] 1000 g of the prepared high-density polyethylene was added with 1000 ppm of azobisisoheptanonitrile, 1000 ppm of antioxidant 1010, and 1000 ppm of antioxidant 168. After high-speed stirring and mixing, the mixture was melt-extruded using a twin-screw extruder. The feed section and die temperature of the extruder were set at 160°C, the other sections were set at 200°C, and the screw speed was set at 60 rpm. After melt extrusion, the polyethylene's melt index and melt strength were tested. The results are listed in Table 1.

[0084] Example 5

[0085] Preparation of main catalyst:

[0086] (1) In a 200 ml dry reactor containing anhydrous and oxygen-free air, 10 g of magnesium ethoxide (average particle size of 25 μm) and 80 ml of toluene were added and stirred at -5°C for 15 minutes to form a suspension.

[0087] (2) While maintaining the system temperature at -5°C, 30 ml of titanium tetrachloride was added dropwise. After the addition was completed, the system temperature was raised to 100°C and stirred for reaction for 3 hours. Finally, the temperature was lowered to 50°C, 1.6 g of tri(7-octenyl)chlorosilane was added, and the reaction was stirred at 60°C for 2 hours.

[0088] (3) Stop stirring for 30 minutes, allow the particles to settle to the bottom of the reactor, press out the supernatant, add 100 ml of toluene, and stir at 90°C for 15 minutes. Repeat the above steps once to wash the particles.

[0089] (4) After washing, a mixture of 80 ml of toluene and 20 ml of titanium tetrachloride was added, stirred and reacted at 100° C. for 2 hours, and then washed with hexane for more than four times, vacuum-dried, and a main catalyst sample was obtained.

[0090] Ethylene polymerization

[0091] In a 2L polymerization reactor, after sufficient gaseous ethylene replacement, 5mL of a hexane solution of triethylaluminum (AlEt3) (AlEt3 concentration of 0.5mmol / mL), 1L of anhydrous hexane, and 9.5mg of the primary catalyst component were added at room temperature. Hydrogen was introduced at 0.10MPa. The polymerization pressure was stabilized at 1.0MPa with ethylene. The temperature was raised to 80°C and the polymerization timer was started. Ethylene was continuously added during the polymerization to maintain the polymerization pressure at 1.0MPa. After 2 hours of polymerization, the product was discharged to produce high-density polyethylene. The polyethylene powder was dried and weighed, and the catalyst activity was calculated. The melt strength of the polyethylene resin was tested. The results are listed in Table 1.

[0092] Preparation of long-chain branched high-density polyethylene

[0093] To 1000 g of the prepared polyethylene, 1200 ppm of 1,1'-azo-cyanocyclohexane, 1000 ppm of antioxidant 1010, and 1000 ppm of antioxidant 168 were added. After high-speed stirring and mixing, the polyethylene was melt-extruded using a twin-screw extruder. The feed zone and die temperature of the extruder were set at 180°C, the other zones were set at 210°C, and the screw speed was set at 90 rpm. After melt extrusion, the polyethylene's melt index and melt strength were tested. The results are listed in Table 1.

[0094] Comparative Example 1

[0095] Preparation of main catalyst

[0096] (1) In a 200 ml dry reactor containing anhydrous and oxygen-free air, 10 g of magnesium ethoxide (average particle size of 25 μm) and 80 ml of toluene were added and stirred at 0°C for 15 minutes to form a suspension.

[0097] (2) While maintaining the system temperature at 0°C, 15 ml of titanium tetrachloride was added dropwise. After the addition was completed, the system temperature was raised to 90°C and the reaction was stirred for 3 hours.

[0098] (3) Stop stirring for 30 minutes, allow the particles to settle to the bottom of the reactor, press out the supernatant, add 100 ml of toluene, and stir at 90°C for 15 minutes. Repeat the above steps once to wash the particles.

[0099] (4) After washing, a mixture of 80 ml of toluene and 20 ml of titanium tetrachloride was added, stirred and reacted at 115° C. for 2 hours, and then washed with hexane for more than four times, vacuum-dried, and a main catalyst sample was obtained.

[0100] Ethylene polymerization

[0101] In a 2L polymerization reactor, after sufficient gaseous ethylene replacement, 5mL of a hexane solution of triethylaluminum (AlEt3) (AlEt3 concentration of 0.5mmol / mL), 1L of anhydrous hexane, and 10mg of the primary catalyst component were added at room temperature. Hydrogen was introduced at 0.15MPa. The polymerization pressure was stabilized at 1.0MPa with ethylene. The temperature was raised to 80°C and the polymerization timer was started. Ethylene was continuously added during the polymerization to maintain the polymerization pressure at 1.0MPa. After 2 hours of polymerization, the product was discharged to produce high-density polyethylene. The polyethylene powder was dried and weighed, and the catalyst activity was calculated. The melt strength of the polyethylene resin was tested. The results are listed in Table 1.

[0102] Preparation of long-chain branched high-density polyethylene

[0103] 1000 g of the prepared high-density polyethylene was added with 800 ppm of azobisisobutyronitrile, 1000 ppm of antioxidant 1010, and 1000 ppm of antioxidant 168. After high-speed stirring and mixing, the mixture was melt-extruded using a twin-screw extruder. The feed section and die temperature of the extruder were set at 190°C, the other sections were set at 210°C, and the screw speed was set at 80 rpm. After melt extrusion, the melt index and melt strength of the polyethylene were tested. The results are listed in Table 1.

[0104] Comparative Example 2

[0105] Preparation of main catalyst

[0106] (1) In a 200 ml dry reactor containing anhydrous and oxygen-free air, 10 g of magnesium ethoxide (average particle size of 25 μm) and 80 ml of toluene were added and stirred at 0°C for 15 minutes to form a suspension.

[0107] (2) While maintaining the system temperature at 0°C, 15 ml of titanium tetrachloride was added dropwise. After the addition was completed, the system temperature was raised to 90°C and stirred for reaction for 3 hours. Finally, the temperature was lowered to 50°C, 1.2 g of diallyldichlorosilane was added, and the reaction was stirred at 50°C for 2 hours.

[0108] (3) Stop stirring for 30 minutes, allow the particles to settle to the bottom of the reactor, press out the supernatant, add 100 ml of toluene, and stir at 90°C for 15 minutes. Repeat the above steps once to wash the particles.

[0109] (4) After washing, a mixture of 80 ml of toluene and 20 ml of titanium tetrachloride was added, stirred and reacted at 115° C. for 2 hours, and then washed with hexane for more than four times, vacuum-dried, and a main catalyst sample was obtained.

[0110] Ethylene polymerization

[0111] In a 2L polymerization reactor, after sufficient replacement with gaseous ethylene, 5mL of a hexane solution of triethylaluminum (AlEt3) (AlEt3 concentration of 0.5mmol / mL), 1L of anhydrous hexane, and 10mg of the primary catalyst component were added at room temperature. Hydrogen was introduced at 0.15MPa. The polymerization pressure was stabilized at 1.0MPa with ethylene. The temperature was raised to 80°C, and the polymerization timer was started. Ethylene was continuously added during the polymerization to maintain the polymerization pressure at 1.0MPa. The polymerization was discharged after 2 hours. The polyethylene powder was dried and weighed, and the catalyst activity was calculated. The melt strength of the polyethylene resin was tested. The results are listed in Table 1.

[0112] Preparation of long-chain branched high-density polyethylene

[0113] To 1000 g of the prepared polyethylene were added 800 ppm of 2,5-dimethyl-2,5-di-tert-butyl peroxide, 1000 ppm of antioxidant 1010, and 1000 ppm of antioxidant 168. After high-speed stirring and mixing, the polyethylene was melt-extruded using a twin-screw extruder. The feed section and die temperature of the extruder were set to 190°C, the other sections were set to 210°C, and the screw speed was set to 80 rpm. After melt extrusion, the polyethylene melt index and melt strength were tested. The results are listed in Table 1.

[0114] Table 1

[0115]

[0116] It can be seen from the examples that since an organosilane compound containing two or more double bonds is introduced during the catalyst preparation process, the catalyst can cause partial crosslinking of polyethylene when catalyzing ethylene polymerization. After the extrusion reaction, the crosslinking degree of the polyethylene increases and the melt strength further increases.

[0117] In the comparative examples, in the preparation process of the main catalyst in Comparative Example 1, no organosilane compound with two or more double bonds is used, and the catalyst does not have the cross-linking property. In the subsequent extrusion reaction, the use of an azo initiator cannot induce the cross-linking of polyethylene; in the preparation process of the main catalyst in Comparative Example 2, an organosilane compound with two or more double bonds is used, but a peroxide initiator is used in the extrusion reaction, which will cause the degradation of polyethylene, increase the melt index, and reduce the melt strength.

[0118] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art may make various corresponding changes and modifications based on the present invention, but these corresponding changes and modifications should all fall within the scope of protection of the present invention.

Claims

1. A long-chain branched high-density polyethylene, characterized in that The polyethylene is obtained by melt mixing high-density polyethylene and an azo initiator, wherein High-density polyethylene: 88.0-99.999 parts by weight; The azo initiator: 0.001-2 parts by weight; The high-density polyethylene is an ethylene homopolymer or copolymer, with a double bond content of 0.01-0.5% by mole, a melt index of 0.001-10g / 10min, and a density of 0.940-0.970g / cm 3 between; The high-density polyethylene is obtained by catalyzing ethylene homopolymerization or copolymerization at 75-85° C. with an olefin polymerization catalyst, wherein the olefin polymerization catalyst comprises a main catalyst and a co-catalyst, and the molar ratio of aluminum in the co-catalyst to titanium in the main catalyst is controlled at 1 to 500:1; The main catalyst is prepared by reacting a magnesium compound, a liquid titanium compound and an organic silane compound. The magnesium compound is as follows: 1 ) n Cl 2-n As shown, where R 1 It is C2~C 20 The hydrocarbon group is a saturated or unsaturated straight chain, branched chain or cyclic chain, 0≤n≤2; The titanium compound is as follows: 2 ) n Cl 4-n As shown, where R 2 It is C2~C 20 The hydrocarbon group is a saturated or unsaturated straight chain, branched chain or cyclic chain, 0≤n≤4; The general formula of the organosilane compound is R 3 m SiX n (OR 4 ) k , where R 3 C2-C 20 The hydrocarbon group and R 3 Contains a double bond, X is a halogen, R 4 C1-C 20 A linear or branched alkyl group, m is an integer of 2-3, n is an integer of 1-2, k is an integer of 0-2, and m+n+k=4; Wherein, the co-catalyst is a general formula such as AlR' n X 3-n The organoaluminum compound shown in the formula, wherein R' is hydrogen or an alkyl group having 1 to 20 carbon atoms, X is a halogen, and n is a number of 1 < n ≤ 3; The main catalyst is prepared by the following method: (1) contacting a solid magnesium compound with a liquid titanium compound; (2) contacting the reaction product obtained in step (1) with an organosilane for reaction; (3) The reaction product obtained in step (2) is further reacted with a liquid titanium compound, and finally washed and dried with an inert solvent to obtain a powdered main catalyst.

2. The long-chain branched high-density polyethylene according to claim 1, characterized in that The co-catalyst is AlEt3, Al(iso-Bu)3, Al(n-C6H 13 )3、Al(n-C8H 17 )3 or AlEt2Cl.

3. The long-chain branched high-density polyethylene according to claim 2, characterized in that The organosilane compound is at least one of 7-octenylallyldichlorosilane, 7-octenylvinyldichlorosilane, 5-hexenylallyldichlorosilane, 7-octenyldi(allyl)chlorosilane, di(7-octenyl)allylchlorosilane, di(7-octenyl)dichlorosilane, tri(allyl)chlorosilane, di(allyl)dichlorosilane, bis[2-(5-ethylidene-2-norbornene)ethyl]dichlorosilane, 2-(5-ethylidene-2-norbornene)ethylallyldichlorosilane, and bis[2-(3-cyclopentadienyl)ethyl]dichlorosilane.

4. The long-chain branched high-density polyethylene according to claim 2, characterized in that The titanium compound is titanium tetrachloride, triethoxytitanium chloride, dibutoxytitanium chloride, trimethoxytitanium chloride, dimethoxytitanium chloride, trihexyltitanium chloride or diethoxytitanium chloride.

5. The long-chain branched high-density polyethylene according to claim 2, characterized in that The magnesium compound is Mg(OEt)Cl, diethoxymagnesium, dipropoxymagnesium, dibutoxymagnesium or dioctyloxymagnesium, and is a spherical or quasi-spherical granular solid with an average particle size ranging from 10 to 100 microns.

6. The long-chain branched high-density polyethylene according to claim 1, characterized in that During the preparation of the main catalyst, the amount of the liquid titanium compound used for the first time is controlled at 0.01-50 moles, the amount of the organosilane compound is controlled at 0.01-3 moles, and the amount of the titanium compound used for the second time is controlled at 0.01-50 moles per mole of the magnesium compound.

7. The long-chain branched high-density polyethylene according to claim 6, characterized in that The amount of the liquid titanium compound used for the first time is controlled to be 0.05 to 20 moles, and the amount of the organosilane compound is controlled to be 0.02 to 0.8 moles.

8. The long-chain branched high-density polyethylene according to claim 1, characterized in that The main catalyst is prepared by the following method: (1) reacting a solid magnesium compound and a liquid titanium compound at a temperature within the range of -20-10°C; (2) contacting the reaction product obtained in step (1) with an organosilane at 30-80° C.; (3) The reaction product obtained in step (2) is further reacted with a titanium compound at 80-130°C, and finally washed and dried with an inert solvent to obtain a powdered main catalyst.

9. The long-chain branched high-density polyethylene according to claim 1, characterized in that The azo initiator is azobisisobutyronitrile, azobisisoheptanenitrile, azobisisovaleronitrile or 1,1'-azo-cyanocyclohexane.

10. The method for preparing the long-chain branched high-density polyethylene according to any one of claims 1 to 9, characterized in that: The method comprises the following steps: melting and mixing high-density polyethylene and an azo initiator at 160-230 DEG C to obtain long-chain branched polyethylene.

11. The method for preparing long-chain branched high-density polyethylene according to claim 10, characterized in that: The melt mixing uses an internal mixer or a screw extruder.

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