阅读说明：本技术 超高分子量聚烯烃和低分子量聚烯烃共混物的制备方法 (Process for preparing blends of ultrahigh molecular weight polyolefins and low molecular weight polyolefins ) 是由 历伟 吴雁捷 曹禺 唐鑫 赵彬清 于 2019-09-30 设计创作，主要内容包括：一种超高分子量聚烯烃和低分子量聚烯烃共混物的制备方法,其特征在于包括如下步骤：一、非均相催化剂的制备：①将多孔载体、苯乙烯、选择性使用的共聚单体和引发剂加入反应装置中,浸渍1～24h；②引发孔道内的苯乙烯和共聚单体聚合,得到苯乙烯基共聚物填充的多孔载体；③向苯乙烯基共聚物填充的多孔载体中依次加入苯乙烯基共聚物的良溶剂、第一催化剂后,搅拌10～60min,干燥得到固体颗粒；④向固体颗粒中依次加入苯乙烯基共聚物的不良溶剂、第二催化剂后,搅拌2～24h,干燥后得到非均相催化剂；二、乙烯聚合反应。本申请能在单反应器内实现两者的均匀共混,且能进一步提升超高分子量聚烯烃的分子量。(A preparation method of a blend of ultrahigh molecular weight polyolefin and low molecular weight polyolefin is characterized by comprising the following steps of preparing a heterogeneous catalyst, ① adding a porous carrier, styrene, a comonomer used selectively and an initiator into a reaction device, dipping for 1-24 hours, ② initiating polymerization of the styrene and the comonomer in a pore channel to obtain a porous carrier filled with a styrene-based copolymer, ③ adding a good solvent of the styrene-based copolymer and a first catalyst into the porous carrier filled with the styrene-based copolymer in sequence, stirring for 10-60 minutes, drying to obtain solid particles, ④ adding a poor solvent of the styrene-based copolymer and a second catalyst into the solid particles in sequence, stirring for 2-24 hours, drying to obtain the heterogeneous catalyst, and performing ethylene polymerization reaction.)

1. A method for preparing a blend of ultrahigh molecular weight polyolefin and low molecular weight polyolefin, characterized by comprising the steps of:

firstly, preparing a heterogeneous catalyst:

①, adding a porous carrier with the pore volume of 0.01-10 g/mL, styrene, a comonomer which is optionally used and an initiator into a reaction device, and soaking for 1-24 h, wherein the comonomer only contains one C-C bond and also contains-OH, -COOH and-NH₂-or a halogen unit; the ratio of the total volume of the styrene, the comonomer and the initiator to the pore volume of the porous carrier is 0.1-50; the molar ratio of the comonomer to the styrene is 0-10; the molar ratio of the initiator to the styrene is 0.001-0.1;

②, washing to remove the styrene, the comonomer and the initiator which are free outside the porous carrier, and initiating the polymerization of the styrene and the comonomer in the pore channel to obtain the porous carrier filled with the styrene-based copolymer;

③, sequentially adding a good solvent of the styrene-based copolymer and a first catalyst into the porous carrier filled with the styrene-based copolymer obtained in the step ②, stirring for 10-120 min, loading the first catalyst on the styrene-based copolymer to obtain solid particles, washing the solid particles with the good solvent, and drying to obtain dried solid particles, wherein the first catalyst comprises at least one of a Zeigelr-Natta catalyst, a metallocene catalyst, a late transition metal catalyst, an FI catalyst and a chromium-based catalyst, and the mass ratio of the added amount of the first catalyst to the porous carrier filled with the styrene-based copolymer is 0.1-15 wt%;

④, sequentially adding a poor solvent of a styrene-based copolymer and a second catalyst into the dried solid particles obtained in the step ③, stirring for 2-24 h, loading the second catalyst on the pore walls of a porous carrier to obtain solid powder, washing the solid powder with the poor solvent, and drying to obtain a heterogeneous catalyst, wherein the second catalyst comprises at least one of a Zeigelr-Natta catalyst, a metallocene catalyst, a late transition metal catalyst, an FI catalyst and a chromium-based catalyst, and the mass ratio of the addition amount of the second catalyst to the mass ratio of the styrene-based copolymer-filled porous carrier is 0.1-15 wt%;

secondly, ethylene polymerization reaction:

adding a polymerization solvent, a cocatalyst, ethylene, alpha-olefin with no less than three carbons and the heterogeneous catalyst prepared in the first step into a polymerization reactor, adjusting the polymerization temperature to 0-100 ℃, adjusting the polymerization pressure to 1-30 bar, and carrying out polymerization reaction for 0.1-8 h to obtain the ultrahigh molecular weight polyolefin and low molecular weight polyolefin blend; wherein the cocatalyst comprises at least one of an alkyl aluminum compound, an alkyl lithium compound, an alkyl zinc compound and an alkyl boron compound; the ratio of the molar weight of the cocatalyst to the molar weight of the metal in the heterogeneous catalyst is 1-3000; the molar ratio of the alpha-olefin to the ethylene is 0.01-1; the weight average molecular weight of the ultrahigh molecular weight polyolefin in the mixture is 500000-10000000 g/mol; the weight average molecular weight of the low molecular weight polyolefin is 1000-500000 g/mol.

2. The method of claim 1, wherein: the porous carrier comprises at least one of magnesium dihalide, silicon dioxide, aluminum oxide, zirconium oxide, titanium dioxide, silicon dioxide-aluminum oxide, silicon dioxide-magnesium oxide and montmorillonite.

3. The method of claim 1, wherein: the comonomer comprises 4-chloromethyl styrene, 4-bromomethylstyrene, 3-fluoromethylstyrene, 3-ammonio styrene, 4-carboxystyrene, 1-propylene-3 alcohol or methyl methacrylate.

4. The method of claim 1, wherein: the initiator comprises at least one of azobisisobutyronitrile, azobisisoheptonitrile, dimethyl azobisisobutyrate, nitrogen diisobutyl amidine hydrochloride, ammonium persulfate, potassium persulfate, benzoyl peroxide tert-butyl ester and methyl ethyl ketone peroxide.

5. The method of claim 1, wherein the step ② of initiating polymerization of styrene and comonomer in the channels comprises:

firstly heating for 1-8 h at 40-60 ℃, then heating for 1-4 h at 60-120 ℃, and finally heating for 2-8 h at 120-180 ℃.

6. The method of claim 1, wherein: the good solvent comprises at least one of benzene, toluene, xylene, tetrahydrofuran, dichloromethane and chloroform.

7. The method of claim 1, wherein: the poor solvent comprises at least one of n-hexane, cyclohexane, n-heptane, isopentane and n-octane.

8. The method of claim 1, wherein: the alpha-olefin comprises at least one of propylene, 1-butene, isoprene and 1-hexene.

9. The method of claim 1, wherein: the polymerization solvent comprises at least one of toluene, isobutane, pentane, isopentane, hexane, cyclohexane and heptane.

Technical Field

The invention belongs to the technical field of olefin polymerization reaction, and particularly relates to a preparation method of a blend of ultrahigh molecular weight polyolefin and low molecular weight polyolefin.

Background

After the ultrahigh molecular weight polyolefin and the common polyolefin are blended, the mechanical property of the material can be greatly improved, and the method is widely applied to development of high-performance polyolefin base resin. However, due to the ultra-long molecular chain and a large number of chain winding structures of the ultra-high molecular weight polyolefin, the mobility of the chain segment of the molecular chain is poor, the diffusion speed is slow, and the miscibility of the high polymer and the common polyolefin is greatly restricted. Taking the ultra-high molecular weight polyethylene reinforced high density polyethylene as an example, although the molecular structures of the ultra-high molecular weight polyethylene reinforced high density polyethylene and the ultra-high molecular weight polyethylene are very similar, the highest blending amount of the ultra-high molecular weight polyethylene in the high density polyethylene cannot exceed 10 wt% by a mechanical blending method due to the great difference of the melt viscosities of the ultra-high molecular weight polyethylene and the high density polyethylene, otherwise, a great amount of phase separation structures occur, and the mechanical properties of the blend are rapidly reduced.

The in-line blending method in the reactor is to combine the catalyst technology and the production technology to complete the in-situ blending of two polyethylenes in the ethylene polymerization process. The method utilizes the carrier morphology replication criterion in the polyethylene particle growth process, can realize the blending of two macromolecules in a single polyethylene particle, and compared with a mechanical blending method, the blending effect is obviously improved.

For example, Process for preparing a blend of ultra high molecular weight polyethylene and low molecular weight polyethylene is disclosed in patent publication No. US5684097A issued to Borealis corporation. The method sequentially produces low molecular weight polyethylene, medium molecular weight polyethylene and ultrahigh molecular weight polyethylene by a three-kettle series technology and the same catalyst. The technology improves the blending amount of the ultra-high molecular weight polyethylene to 20 percent, and effectively enhances the mechanical property of the polyolefin. However, although the method realizes the mixing of three polyolefins in the single polyethylene particle, the different types of polyolefins in the particle still have multizone distribution due to the series reaction process of the catalyst, and the blending property is to be improved. In addition, the multi-kettle series process is complex to operate, the energy consumption of the process flow is high, and the process economy is limited.

Also, for example, patent application No. CN201811266072.5, entitled "method for preparing polyolefin blends" (application publication No. CN109486040A), discloses a method for preparing blends of low-entanglement ultrahigh molecular weight polyethylene and high density polyethylene. The method uses a heterogeneous catalyst with polysilsesquioxane isolation to prepare low entanglement ultra-high molecular weight polyethylene in a first reactor and low molecular weight high density polyethylene in a second reactor. The greatly reduced entanglement degree of the ultra-high molecular weight polyethylene chains is beneficial to improving the interface compatibility of the ultra-high molecular weight polyethylene and the high density polyethylene, so that the blending amount of the ultra-high molecular weight polyethylene is increased to 30 percent, and the mechanical property of the blend is improved. However, the method still adopts a two-kettle series process, the blend still has a multi-zone distribution in the single particle, and the operation and control process is still complicated.

Therefore, how to realize the uniform blending of the low-entanglement ultrahigh molecular weight polyolefin and the low molecular weight polyolefin in a single reactor has important significance.

For this reason, patent No. ZL200980127879.3, inventive patent "method for preparing polyethylene" (granted publication No. CN102099386B), simultaneously supported two catalytic components inside a porous carrier, and achieved blending of ultra-high molecular weight polyethylene and low molecular weight polyolefin in a reactor. However, the random distribution of the two catalytic components on the surface of the porous carrier makes the interaction between catalytic molecules strong, easily induces bimolecular deactivation, reduces the molecular weight of the high molecular weight part, and obviously reduces the catalytic activity of each component.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a preparation method of a blend of ultrahigh molecular weight polyolefin and low molecular weight polyolefin aiming at the current situation of the prior art, so that the uniform blending of the ultrahigh molecular weight polyolefin and the low molecular weight polyolefin can be realized in a single reactor, and the molecular weight of the ultrahigh molecular weight polyolefin can be further improved.

The technical scheme adopted by the invention for solving the technical problems is as follows: a method for preparing a blend of ultrahigh molecular weight polyolefin and low molecular weight polyolefin, characterized by comprising the steps of:

firstly, preparing a heterogeneous catalyst:

①, adding a porous carrier with the pore volume of 0.01-10 g/mL, styrene, a comonomer which is optionally used and an initiator into a reaction device, and soaking for 1-24 h, wherein the comonomer only contains one C-C bond and also contains-OH, -COOH and-NH₂-or a halogen unit; the ratio of the total volume of the styrene, the comonomer and the initiator to the pore volume of the porous carrier is 0.1-50; the molar ratio of the comonomer to the styrene is 0-10; the molar ratio of the initiator to the styrene is 0.001-0.1; the above-mentioned comonomer selectively used means that the comonomer may be added or not added, and when the comonomer is not added, that is, when the molar ratio of the above-mentioned comonomer to styrene is 0;

②, washing to remove the styrene, the comonomer and the initiator which are free outside the porous carrier, and initiating the polymerization of the styrene and the comonomer in the pore channel to obtain the porous carrier filled with the styrene-based copolymer;

③, sequentially adding a good solvent of the styrene-based copolymer and a first catalyst into the porous carrier filled with the styrene-based copolymer obtained in the step ②, stirring for 10-120 min, loading the first catalyst on the styrene-based copolymer to obtain solid particles, washing the solid particles with the good solvent, and drying to obtain dried solid particles, wherein the first catalyst comprises at least one of a Zeigelr-Natta catalyst, a metallocene catalyst, a late transition metal catalyst, an FI catalyst and a chromium-based catalyst, and the mass ratio of the added amount of the first catalyst to the porous carrier filled with the styrene-based copolymer is 0.1-15 wt%;

④, sequentially adding a poor solvent of a styrene-based copolymer and a second catalyst into the dried solid particles obtained in the step ③, stirring for 2-24 h, loading the second catalyst on the pore walls of a porous carrier to obtain solid powder, washing the solid powder with the poor solvent, and drying to obtain a heterogeneous catalyst, wherein the second catalyst comprises at least one of a Zeigelr-Natta catalyst, a metallocene catalyst, a late transition metal catalyst, an FI catalyst and a chromium-based catalyst, and the mass ratio of the addition amount of the second catalyst to the mass ratio of the styrene-based copolymer-filled porous carrier is 0.1-15 wt%;

secondly, ethylene polymerization reaction:

adding a polymerization solvent, a cocatalyst, ethylene, alpha-olefin with no less than three carbons and the heterogeneous catalyst prepared in the first step into a polymerization reactor, adjusting the polymerization temperature to 0-100 ℃, adjusting the polymerization pressure to 1-30 bar, and carrying out polymerization reaction for 0.1-8 h to obtain the ultrahigh molecular weight polyolefin and low molecular weight polyolefin blend; wherein the cocatalyst comprises at least one of an alkyl aluminum compound, an alkyl lithium compound, an alkyl zinc compound and an alkyl boron compound; the ratio of the molar weight of the cocatalyst to the molar weight of the metal in the heterogeneous catalyst is 1-3000; the molar ratio of the alpha-olefin to the ethylene is 0.01-1; the weight average molecular weight of the ultrahigh molecular weight polyolefin in the mixture is 500000-10000000 g/mol; the weight average molecular weight of the low molecular weight polyolefin is 1000-500000 g/mol.

In the application, the specific addition amount of the heterogeneous catalyst has no special requirement, and can be designed according to the actual situation, and is generally 10-200 mg.

As an improvement, the porous carrier comprises at least one of magnesium dihalide, silica, alumina, zirconia, titania, silica-alumina, silica-magnesia and montmorillonite.

In the improvement, the comonomer comprises 4-chloromethyl styrene, 4-bromomethyl styrene, 3-fluoromethyl styrene, 3-ammonium styrene, 4-carboxyl styrene, 1-propylene-3 alcohol or methyl methacrylate.

The initiator comprises at least one of azobisisobutyronitrile, azobisisoheptonitrile, dimethyl azobisisobutyrate, nitrogen diisobutyl amidine hydrochloride, ammonium persulfate, potassium persulfate, benzoyl peroxide tert-butyl ester and methyl ethyl ketone peroxide.

The method for initiating polymerization of styrene and comonomers in the channels in step ② is preferably:

firstly heating for 1-8 h at 40-60 ℃, then heating for 1-4 h at 60-120 ℃, and finally heating for 2-8 h at 120-180 ℃.

In the above scheme, the good solvent comprises at least one of benzene, toluene, xylene, tetrahydrofuran, dichloromethane and chloroform.

The poor solvent comprises at least one of n-hexane, cyclohexane, n-heptane, isopentane and n-octane.

Preferably, the alpha-olefin comprises at least one of propylene, 1-butene, isoprene and 1-hexene.

Finally, the polymerization solvent comprises at least one of toluene, isobutane, pentane, isopentane, hexane, cyclohexane, heptane.

Compared with the prior art, the invention has the advantages that: the styrene-based copolymer is implanted into the pore channels of the porous carrier, the solubility of the styrene-based copolymer in the pore channels is utilized to respond to the solvent, the conformation of the styrene-based copolymer chain segment in the good solvent is extended, a first catalyst for preparing the ultra-high molecular weight polyethylene is loaded on the styrene-based copolymer chain segment (because the comonomer in the invention has functional groups such as-OH, -COOH, -NH 2-or halogen, the functional groups can react with the catalyst to load the catalyst in the styrene-based copolymer in the pore channels), the loading position in the copolymer is occupied, then the styrene-based copolymer chain segment in the anti-solvent moves to be in a frozen state, and the other second catalyst for preparing the low molecular weight polyolefin is loaded on the loading position on the pore walls of the porous carrier. Therefore, the partitioned load of the two catalysts is realized in the single carrier, and the bimetallic inactivation effect of the two metal catalytic components is avoided.

The molecular weight of the ultrahigh molecular weight polyolefin is further improved due to the strong mass transfer resistance environment created by the styrene-based copolymer.

In addition, because the polymerization temperature of the styrene-based copolymer is below 100 ℃ and is lower than the glass transition temperature (about 120 ℃) of the styrene-based copolymer, the styrene-based copolymer is in a glass state in the polymerization temperature range during polymerization, and the styrene-based copolymer is incompatible with the thermodynamics of polyolefin chain segments, so that the styrene-based copolymer becomes a grid among active points, the active centers are separated, and a micro-zone reaction unit for chain segment growth is formed, the overlapping probability among molecular chains is greatly reduced, the grown molecular chains are promoted to be preferentially crystallized in the micro-zone reaction unit, and the chain entanglement degree of high molecular weight polyolefin is reduced.

According to the method, the uniform blending of the low-entanglement ultrahigh molecular weight polyolefin and the low molecular weight polyolefin can be realized in a single reactor, so that the rigidity and the toughness of the blend are synchronously improved.

Detailed Description

The present invention will be described in further detail with reference to examples.

When the processing performance and the mechanical property of the product are tested, the following conditions are met:

all air sensitive substances are operated by adopting a standard vacuum double-line anhydrous oxygen-free operation method; all reagents are used after refining treatment.

The high molecular weight fraction and the low molecular weight fraction of the blend are obtained by elution fractionation. The blend was wrapped in quantitative filter paper and placed in a soxhlet extractor and extracted with n-heptane at 110 ℃ under nitrogen for 7 days. Wherein the low molecular weight fraction is dissolved in n-heptane and precipitated by cooling. After drying, the product was used to determine molecular weight and its distribution; the high molecular weight fraction was retained in filter paper and the molecular weight and its distribution were determined after drying.

The molecular weight and the distribution of the polymer are characterized by a gel permeation chromatograph (PL-GPC-220), 1,2, 4-trichlorobenzene is used as a solvent, a sample is prepared by filtration at 160 ℃, polystyrene with narrow molecular weight distribution is used as a standard sample, and the measurement is carried out at 160 ℃.

The tensile strength of the polymer is measured according to the national standard GB/T1040.

The low entanglement characteristics of the polymers are determined by rheology. The low entanglement behavior of the polymers was investigated by rheological tests using rheological analysis of the segment melt dynamics. In rheological analysis, the average molecular weight between segment entanglements (Me) is inversely proportional to the chain entanglement density, and Me and the elastic modulus of the rubber plateau (G') can be quantitatively described by the following relationship:

G'＝g_NρR T/M_e

wherein, g_NIs a quantitative factor; rho is density; r is a gas constant; t is the absolute temperature.

An increase in elastic modulus in the melt at a given temperature represents an increase in the chain entanglement density. Therefore, the mechanism of chain entanglement formation during polymerization can be quantitatively described by rotational rheological analysis. The rheological measurements were determined by a shaft strain rheometer (HAAKE III instrument). The polyethylene powder was tabletted at 120 ℃ for 30min at 20tons to produce a sample with a diameter of 8mm for rheology studies. The bottom plate between the parallel plates of the rheometer was heated to 160 c under nitrogen. The rheology experiment started with 5min stabilization. The dynamic frequency sweep was tested at a fixed frequency of 1 Hz. Dynamic time scanning was tested at a fixed 1 rad/s. According to the established curve of the storage modulus with time measured at 160 ℃ by rotational rheology, the ratio G of the initial storage modulus to the maximum storage modulus (the storage modulus no longer changes with time, the system reaches a thermodynamically stable state)_N ⁰The degree of entanglement in the initial state of the sample can be characterized. Commercially available UHMWPE having a molecular weight of 2300000G/mol, G_N ⁰The surface samples had a very high degree of chain entanglement, 0.95.