Olefin polymer and preparation method thereof

Abstract

The invention provides an olefin polymer. The olefin polymer has the following characteristics: A) the olefin polymer is obtained by copolymerization of ethylene and alpha olefin; b) the weight-average molecular weight of the olefin polymer is 20,000-200,000; and C) the proportion of the low-molecular-weight polymer in the olefin polymer is less than 0.3 wt%, wherein the low-molecular-weight polymer is defined as a part of which the molecular weight is less than 2% of the weight-average molecular weight of the polymer. The olefin polymer has the advantages that the proportion of the low-molecular-weight part is low, the viscosity of the polymer can be obviously reduced, and the olefin polymer has very important significance on transportation and processing of the polymer.

Description

Technical Field

[0001] The present invention relates to an olefin polymer, and in particular to a method for preparing an olefin polymer. Background Art

[0002] Polyolefin elastomer (POE) is a type of polyolefin material formed by copolymerization of ethylene and α-olefins such as 1-butene, 1-hexene, 1-octene, etc. Compared with traditional polyolefin plastics, polyolefin elastomers have a higher content of comonomers in the molecular chain and a lower density. They have the characteristics of both plastics and rubber and are widely used in automotive plastic modification, shoe foaming, photovoltaic films, wires and cables, and artificial turf.

[0003] However, in actual applications, we found that when the ambient temperature is high, due to the presence of oily low molecular weight polymers in the polymer, the particle surface will become sticky, and even clumps will appear in the packaging bag and cannot be poured out smoothly, which seriously reduces the transportation convenience and processing efficiency of the material. Therefore, starting from the microstructure of POE, by optimizing POE catalysts and co-catalysts, reducing the proportion of low molecular weight in the polymer, and avoiding the stickiness of the polymer from the root has become an urgent problem to be solved. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides an olefin polymer and a preparation method thereof. The present invention reduces the content of free trimethylaluminum in POE co-catalyst modified methylaluminoxane (MMAO) to avoid premature transfer of polymer chains to trimethylaluminum during chain growth, resulting in chain termination and formation of low molecular weight polymers.

[0005] In one aspect, the present invention provides an olefin polymer having the following characteristics:

[0006] A) the olefin polymer is obtained by copolymerization of ethylene and α-olefin;

[0007] B) the weight average molecular weight of the olefin polymer is 20,000-200,000;

[0008] C) The proportion of low molecular weight polymer in the olefin polymer is less than 0.3 wt %, wherein the low molecular weight polymer is defined as the part with a molecular weight less than 2% of the weight average molecular weight of the polymer.

[0009] As a preferred embodiment of the present invention, the alpha olefin is selected from 1-butene, 1-hexene or 1-octene;

[0010] As a preferred embodiment of the present invention, the weight average molecular weight of the polymer is 50,000-150,000, more preferably 70,000-130,000;

[0011] As a preferred embodiment of the present invention, the mass proportion of the low molecular weight part is less than 0.25%, more preferably, less than 0.2%;

[0012] A method for preparing the polymer is as follows: in a hydrocarbon solvent, ethylene and alpha olefin are catalyzed by a main catalyst and a co-catalyst to obtain a polymer.

[0013] As a preferred embodiment of the present invention, the hydrocarbon solvent is selected from C5-C20 alkanes, more preferably n-hexane and methylcyclohexane.

[0014] As a preferred embodiment of the present invention, the alpha olefin is selected from 1-butene, 1-hexene or 1-octene;

[0015] As a preferred embodiment of the present invention, the cocatalyst is an alkylaluminoxane or a modified alkylaluminoxane, preferably one or more selected from methylaluminoxane, isobutyl-modified methylaluminoxane or octyl-modified methylaluminoxane, more preferably octyl-modified methylaluminoxane;

[0016] As a preferred embodiment of the present invention, the mass fraction of free trimethylaluminum in the above alkylaluminoxane or modified alkylaluminoxane is less than 1%, more preferably, less than 0.5%;

[0017] As a preferred embodiment of the present invention, the main catalyst is selected from at least one of the following compounds:

[0018]

[0019] As a preferred embodiment of the present invention, the molar ratio of the metal aluminum in the aluminum-containing co-catalyst to the metal M in the main catalyst is (1-10000):1, preferably (200-5000):1;

[0020] As a preferred embodiment of the present invention, the polymerization reaction temperature is 100-200°C, preferably 120-190°C, more preferably 140-180°C, and the polymerization reaction pressure is 1-5MPa, preferably 2-4Mpa, more preferably 2-3Mpa.

[0021] As a preferred embodiment of the present invention, the polymerization reaction is carried out in an organic solvent, and the organic solvent is selected from one or more of IsoparE, toluene, n-hexane, and cyclohexane.

[0022] The beneficial effects of the present invention are:

[0023] The POE with low low molecular weight polymer content disclosed in the present invention has a more anti-sticking property than traditional POE, which is of great significance for the manufacture, processing, transportation and use of POE. The olefin polymer disclosed in the present invention has the characteristics of low low molecular weight polymer content. Compared with traditional POE, the tensile strength and elongation at break of the material are increased, and more importantly, the particle stickiness problem caused by high low molecular weight polymer content in POE is improved. The above characteristics are of great significance for the manufacture, processing, transportation and application of POE. DETAILED DESCRIPTION

[0024] The present invention is further described below by means of specific examples. The examples described in the present invention are only used to illustrate the present invention and do not limit the scope of the present invention.

[0025] Unless otherwise specified, the materials and reagents used in the following examples were obtained from commercial sources. The specific information is as follows:

[0026] 1-Octene: AR, S i gma Al dr i ch

[0027] I sopar E: AR, Exxon Mobile

[0028] MMAO-7 (octyl modified methylaluminoxane) Isopar E solution: AR, Nouryon

[0029] The main catalyst is prepared by the synthesis method in patents (US20120108770, US20040005984);

[0030] The content of trimethylaluminum in the alkylaluminoxane in the following examples was measured using a nuclear magnetic resonance spectrometer (Brucker ARX-400);

[0031] The molecular weight and molecular weight distribution of the polymer obtained in the following ethylene polymerization examples were measured by PL-GPC220 at 150°C, using three PLgel 10μm MIXED-B separation columns connected in series and 1,2,4-trichlorobenzene as the solvent;

[0032] The following polymer stickiness index test method is as follows: set the temperature of the blast oven to 45°C, turn on the oven, keep the temperature constant for 30 minutes after the temperature rises to 45°C, and preheat the weights and plastic bucket related tools in the oven for 30 minutes. Put 150±1g POE particles at the bottom of a 2L plastic bucket, use cardboard to make the surface of the particles flat, then use tweezers to put the round cardboard on the top of the particles in the bucket, and press a 5Kg round weight on the cardboard. Place the plastic bucket and the particle weights as a whole on a tray and place them in a 45°C oven for 2h. After 2h, take out the tray and place it on the laboratory bench, take out the weights, and use tweezers to clip the cardboard out. Hold both sides of the plastic bucket with both hands, slowly lift it to a height of 10cm from the tray, and rotate the plastic bucket toward the inside of the body. During the process, the particles will fall into the tray. When the mouth of the plastic bucket rotates to a horizontal downward position, stop, and keep your hands still without shaking. Time for 10s. After 10s, quickly place the mouth of the plastic bucket horizontally upward on the laboratory bench and weigh the mass of the residual particles in the plastic bucket. The stickiness grade of residual particles below 35g is A, the stickiness grade of residual particles between 35g and 70g is B, the stickiness grade of residual particles between 70g and 105g is C, and the stickiness grade of residual particles greater than 105g is D.

[0033] The following polyolefins are prepared by the following method: 0.5 μmol of the main catalyst is encapsulated into an ampoule bottle and loaded into a 1L high-pressure polymerization reactor in advance. After drying at 120°C for 1h, the temperature is lowered to 100°C and 260ml of n-hexane and 140ml of 1-octene are added. Then, modified methylaluminoxane is added according to Al / Zr=2000:1. The temperature of the reaction system is raised to 140°C, ethylene is introduced and the pressure is set to 3Mpa. The ampoule bottle is broken, and the polymerization reaction begins. The reaction pressure and temperature are kept constant during the entire reaction process. The reaction is stopped after 5 minutes, and the ethylene in the reactor is replaced with nitrogen and then cooled to 100°C. The reaction solution is connected to a beaker containing 500ml of ethanol through the lower discharge port. After the discharge is completed, the solid polymer is filtered and dried.

[0034] The modified methylaluminoxanes with different alkylaluminum contents were prepared as follows: 100 ml of MMAO-7 (3.5% trimethylaluminum content) solution was measured and placed in a 250 ml vacuum distillation flask, the vacuum was set to 10 mbar, all the solvent and part of the trimethylaluminum were evaporated after heating to 80 degrees Celsius, the residual trimethylaluminum was adjusted by controlling the vacuum distillation time, and the residual trimethylaluminum was quantified by nuclear magnetic resonance. MMAO with a specific trimethylaluminum content was added to IsoparE again to prepare a solution for subsequent polymerization verification.

[0035] Table 1. Preparation conditions and product indicators of co-catalysts

[0036]

[0037] Comparative Example: Catalyst 1 and co-catalyst MMAO-7 were selected for polymerization.

[0038] Table 2. Reaction conditions and corresponding performance tests for different application examples

[0039]

[0040]

[0041] The above is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this field can make several improvements and supplements without departing from the method of the present invention. These improvements and supplements should also be regarded as the scope of protection of the present invention.

Claims

1. An olefin polymer, wherein the olefin polymer has the following characteristics: A) the olefin polymer is obtained by copolymerization of ethylene and α-olefin; B) the weight average molecular weight of the olefin polymer is 20,000-200,000; C) The proportion of low molecular weight polymer in the olefin polymer is less than 0.3 wt %, wherein the low molecular weight polymer is defined as the part with a molecular weight less than 2% of the weight average molecular weight of the polymer.

2. The olefin polymer according to claim 1, characterized in that The alpha olefin is selected from 1-butene, 1-hexene or 1-octene.

3. The olefin polymer according to claim 1 or 2, characterized in that The weight average molecular weight of the polymer is 50,000-150,000, more preferably 70,000-130,000; and / or the mass proportion of the low molecular weight part is less than 0.25%, more preferably less than 0.2%.

4. The method for preparing an olefin polymer according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: in a hydrocarbon solvent, ethylene and alpha olefin are subjected to the catalysis of a main catalyst and a co-catalyst to obtain a polymer.

5. The method for preparing an olefin polymer according to claim 4, wherein: The cocatalyst is an alkylaluminoxane or a modified alkylaluminoxane, preferably one or more selected from methylaluminoxane, isobutyl-modified methylaluminoxane or octyl-modified methylaluminoxane, more preferably octyl-modified methylaluminoxane.

6. The method for preparing an olefin polymer according to claim 5, wherein: The mass fraction of free trimethylaluminum in the alkylaluminoxane or modified alkylaluminoxane is less than 1%, more preferably, less than 0.5%.

7. The method for preparing an olefin polymer according to any one of claims 4 to 6, characterized in that: The main catalyst is selected from at least one of the following compounds:

8. The preparation method according to any one of claims 5 to 7, characterized in that: The molar ratio Al / M of the metal aluminum in the aluminum-containing co-catalyst to the metal M in the main catalyst is (1-10000):1, preferably (200-5000):

1.

9. The preparation method according to any one of claims 5 to 8, characterized in that: The polymerization reaction temperature is 100-200° C., preferably 120-190° C., more preferably 140-180° C., and the polymerization reaction pressure is 1-5 MPa, preferably 2-4 MPa, more preferably 2-3 MPa.

10. The preparation method according to any one of claims 5 to 9, characterized in that: The polymerization reaction is carried out in an organic solvent, and the organic solvent is selected from one or more of Isopar E, toluene, n-hexane, and cyclohexane.

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