Method for preparing multi-block segmented copolymer with comonomer content in cascade distribution based on multi-reactor process

Abstract

The invention discloses a method for preparing a multi-block segmented copolymer with comonomer content in cascade distribution based on multiple reactors, which comprises the following steps of: adjusting the comonomer content, the comonomer type, the retention time and the catalyst type of each reactor by adopting a mode of connecting multiple reactors in series; the segmented copolymer with the comonomer content in cascade distribution is adjustable in strength and toughness range and good in product compatibility. The process method provided by the invention is especially suitable for a catalyst system of which the copolymerization capability is sensitive to the content of a comonomer. The block olefin copolymer has the characteristics of high mechanical strength, enhanced toughness, enhanced peel strength with glass or a back plate, increased crosslinking degree and improved light transmittance. The prepared polyolefin product can be widely applied to strength and hardness modification of vinyl polymers or allyl polymers.

Description

Technical Field

[0001] The invention belongs to the field of high molecular polymer preparation, and particularly relates to a method and product for preparing multi-block block copolymers with a stepwise distribution of comonomer content through a multi-reactor process. Background Art

[0002] Block copolymers can be regarded as polymer alloys, which can combine the excellent properties of different polymers and have excellent characteristics. The molecular structure, copolymer composition and relative molecular weight of block copolymers are all designable, and it is one of the hot spots with great research value in the current field of polymer research.

[0003] Polyolefin elastomer (POE) has the characteristics of high comonomer content and long molecular chain branches, which endow the material with extremely complex comprehensive properties. This material can be used as rubber, thermoplastic elastomer, impact modifier and toughening agent for plastics. POE material has excellent cold resistance and aging resistance. Its excellent mechanical properties and processing properties have received in-depth attention in the field of polymer materials and processing, and is widely used in automotive parts, toughening agents and transparent films.

[0004] In 2006, Dow Chemical Company of the United States proposed the concept of chain shuttling polymerization. The chain shuttling polymerization system contains two monomers (ethylene and 1-octene), two single-active site catalysts (MCAT-1 and MCAT-2) with different catalytic properties and a chain shuttling agent (CSA). In the presence of two monomers, ethylene and 1-octene, the catalyst MCAT-1 catalyzes the copolymerization of ethylene and 1-octene to obtain a polymer with extremely low 1-octene content (hard segment), and the catalyst MCAT-2 catalyzes the copolymerization of ethylene and 1-octene to obtain a polymer with high 1-octene content (soft segment). Both active centers can quickly undergo transmetallation reaction with CSA, so that the hard segment and the soft segment are exchanged at the two active centers, and finally a polyolefin multi-block copolymer is obtained.

[0005] The double kettle series technology of Dow's Dowlex process requires adding appropriate catalysts, comonomers, ethylene and solvents to the second reactor during the polymerization process to increase the comonomer content in the copolymer. The double kettle series promotes the copolymerization effect of the catalyst, so that the comonomer is evenly distributed on the product molecular chain, thereby improving product performance. However, the above process also has significant problems. The types of comonomers in the two kettles remain unchanged, and the soft and hard segment distribution of the product is not obvious.

[0006] The traditional method of preparing polyolefin copolymers through a single reactor produces a single type of polymer due to the limitation of reaction conditions. The inflexibility of changing conditions during the process makes it difficult to obtain a multi-block copolymer product with suitable strength and toughness as required. The use of multiple reactors for adjustment can make the copolymerization process more flexible. At the same time, different reactors can use different types of catalysts and comonomers and control the content of materials in each reactor, which greatly increases the diversity of products and can produce reaction products with better performance and more balanced and stable physical properties.

[0007] In consideration of the above problems, the inventors of the present invention have conducted research, hoping to adjust the method and product for preparing multi-block block copolymers with a graded distribution of comonomer content by using multiple reactors and gradient limiting the comonomer concentration of each reactor. Summary of the invention

[0008] In view of the shortcomings of the prior art, the present invention provides a method for preparing multi-block block copolymers with a step-by-step distribution of comonomer content based on a multi-reactor process. The method prepares multi-block multi-block copolymers with a step-by-step distribution of comonomer content by adjusting the type and concentration of comonomers in different reactors, and produces diversified product types with balanced strength and toughness.

[0009] The present invention first provides the following steps:

[0010] The polyolefin catalyst and the co-catalyst are pre-mixed, dissolved and activated in a first solvent to obtain a pre-mixed solution A; the co-monomer is pre-mixed and dissolved with a second solvent to obtain a pre-mixed solution B; the pre-mixed solutions A, B and solvent C are stored in respective feed tanks;

[0011] A dual / multi-reactor series process is adopted, and each reactor is provided with a catalyst, a comonomer and an ethylene compensation port; solution A, solution B, solvent C and main monomer enter the first-stage reactor, wherein after solution B enters the first-stage reactor, the initial comonomer concentration is ω1, and the residence time of the first-stage reactor is t1; then the materials enter the next-stage reactor, the initial comonomer concentration of the i-stage reactor is ωi, and the residence time of the i-stage reactor is ti; i≥2; the comonomer concentration ω1 of the first-stage reactor is in the range of 30-60 mol%; the comonomer concentration ωi of the subsequent reactors is 30-80% of the comonomer concentration ω(i-1) of the previous reactor; the residence time ti of the i-stage reactor is in the range of 1-30min;

[0012] The final product is obtained by discharging the material from the last reactor, removing the solvent and granulating the material.

[0013] The comonomer concentration in the present invention refers to the molar percentage of the comonomer in all monomers in the reactor. According to some embodiments of the present invention, the comonomer concentration ω1 of the first-stage reactor is preferably in the range of 35-55 mol%; the comonomer concentration ωi of the subsequent stages of reactors is preferably in the range of 35-75% of the comonomer concentration ω(i-1) of the previous stage reactor. The residence time ti of the i-th stage reactor is preferably in the range of 3-25 min.

[0014] The present invention utilizes the different reactivity ratios of the catalyst for comonomers of different concentrations to obtain random copolymer segments with a reduced comonomer content gradient. By connecting multiple reactors in series, adjusting the residence time and the type and concentration of comonomers, the combination of different random copolymer segments can be achieved, and finally a multi-block random copolymer with a comonomer content gradient distribution is obtained. The present invention can produce diversified products with adjustable strength and toughness ranges and good product compatibility, and the prepared olefin copolymer can be applied to the strength and hardness modification of vinyl polymers or propylene polymers.

[0015] According to some embodiments of the present invention, the polyolefin catalyst is at least one of a Ziegler-Natta catalyst, a metallocene catalyst, a late transition metal catalyst, a FI catalyst, and a chromium-based catalyst. Preferably, a catalytic system such as a Ziegler-Natta catalyst or a metallocene catalyst is more sensitive to the comonomer content. The catalyst activity time is defined as the time taken for the catalyst activity to decrease to 60% during the polymerization process, which matches the characteristics of this process. The cocatalyst is at least one of an alkyl aluminum compound, an alkyl lithium compound, an alkyl zinc compound, an alkyl boron compound, and a modified alkyl aluminum compound. Wherein, the molar ratio of the cocatalyst to the main catalyst ranges from 1 to 3000, preferably from 2 to 2000, and more preferably from 2 to 1200.

[0016] According to some embodiments of the present invention, the solvents (the first solvent, the second solvent, and the solvent C) are all selected from one or more of toluene, xylene, ethylbenzene, diethylbenzene, hexane, heptane, pentane, cyclohexane, octane, nonane, decane, and Isopar E. The solvents can be blended and adjusted in different proportions according to the characteristics of the copolymer, and the purpose of the adjustment is to increase the solubility of the copolymer in the solvent, so that the reaction is more uniform and efficient.

[0017] According to some embodiments of the present invention, the comonomer is selected from one or more of propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, vinyl acetate, vinyl alcohol, ethyl acrylate, 1,4-butadiene, and pentadiene, and the comonomer types of each reactor may be the same or different. More preferably, it is one or more of 1-butene, 1-hexene, and 1-octene. Thus, an olefin copolymer with a long branched side chain can be prepared, and the olefin polymer has better elasticity and toughness. In addition to the comonomer, the main monomer involved in the polymerization can be at least one of ethylene or propylene.

[0018] According to some embodiments of the present invention, the preset temperature T of each reactor is in the range of 90-200°C, preferably 110-170°C, and the temperature control of the polymerization reaction is controlled by circulating water or circulating oil outside the reactor. The preset pressure P is in the range of 1.0-5.0MPa, preferably 1.5-4.0MPa.

[0019] According to some embodiments of the present invention, the number of reactors connected in series is selected to be more than two reactors, and the tank reactors and the loop reactors can be freely arranged, which can greatly increase the degree of freedom of the process.

[0020] According to some embodiments of the present invention, each reactor is provided with a catalyst, a comonomer and an ethylene compensation port, and the replenishment ratio of the catalyst and the comonomer material in each reactor can be set according to the process requirements to obtain a multi-block polyolefin product.

[0021] The present invention also provides a multi-block polyolefin product obtained by the method. According to some embodiments of the present invention, it presents diversified product performance, wherein the polyolefin elastomer (POE) has the characteristics of step distribution of comonomer content, and presents the characteristics of comonomer block distribution as the molecular chain grows. By adjusting the content gradient of the comonomer in each reactor and the type of catalyst, a diversified product with adjustable strength and toughness range and good product compatibility can be obtained. The prepared polyethylene can be applied to the strength and hardness modification of vinyl polymers or propylene polymers.

[0022] According to some embodiments of the present invention, the multi-block polyolefin product has a weight average molecular weight Mw=5-30×10 4 g / mol; molecular weight distribution index MWD = 2.0-6.0; density range is 0.860-0.950g / cm 3 , preferably 0.863-0.935 g / cm 3 .

[0023] According to some embodiments of the present invention, in the multi-block polyolefin product, as the molecular chain grows, the decay rate of the comonomer content between adjacent blocks is 5mol% / 1000 main chain C-25mol% / 1000 main chain C. That is, as the molecular chain grows, the comonomer content in the next block decreases by 5mol% / 1000 main chain C-25mol% / 1000 main chain C, preferably 8mol% / 1000 main chain C-20mol% / 1000 main chain C, compared with the previous block.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] On the one hand, the molecular chain structure of olefin copolymers determines the mechanical strength, toughness, light transmittance and peel strength of the product. This multi-block olefin copolymer is prepared by connecting multiple reactors in series. The part of the reactor with low comonomer content can promote the crystallization of ethylene segments, thereby improving the mechanical strength and the peel strength between the copolymer and the glass or backplane. In addition, the part of the reactor with high comonomer content can inhibit the crystallization behavior of the segments and promote the cross-linking effect of the cross-linking agent, thereby obtaining an olefin copolymer film material with high cross-linkability, increased amorphous content and improved light transmittance. By setting the polymerization environment in multiple reactors, the product can present an aggregated structure in which crystalline and amorphous regions coexist alternately. The diversification of the reactor polymerization environment will make the product segment structure and aggregated structure also present diversified characteristics, adapting to different application scenarios.

[0026] On the other hand, the preparation method of the multi-block olefin copolymer with a step-by-step distribution of comonomer content based on multi-reactor mediation described in the present invention can obtain a multi-block olefin copolymer with elastic properties, processing properties, mechanical properties and high and low temperature stability close to Dow OBC products. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments.

[0028] Attached Figure 1 : Schematic diagram of double kettle series mode;

[0029] Attached Figure 2 : Schematic diagram of three-kettle series mode;

[0030] Attached Figure 3 : Tank type + loop type + tank type reactor mode;

[0031] Attached Figure 4 : Tank + loop reactor mode;

[0032] Attached Figure 5: Loop tube type + kettle type + loop tube type reactor mode;

[0033] Attached Figure 6 : Schematic diagram of multi-block polyolefin products. DETAILED DESCRIPTION

[0034] The embodiments of the present invention will be described in detail below with reference to examples.

[0035] Methods for characterizing polymer structure and properties:

[0036] (1) Melt index: The melt flow rate is measured according to the conditions of GB / T-3682-2000 (190°C, 2.16 kg load), usually recorded as MI2.16.

[0037] (2) Density: measured according to GB / 1033-1986 method.

[0038] (3) Tensile strength, Young's modulus and elongation at break: measured in accordance with GB / T 1040-2006.

[0039] (4) Weight average molecular weight and molecular weight distribution: measured by high temperature gel permeation chromatography (HT-GPC).

[0040] (5) Comonomer insertion rate: 13 C-NMR measurement and calculation.

[0041] (6) Melting point and crystallinity: measured by differential scanning calorimetry (DSC).

[0042] (7) Light transmittance: measured using a light transmittance tester.

[0043] (8) Glass strength: measured using a tape peel strength tester.

[0044] Embodiment 1:

[0045] This embodiment adopts Figure 1 The dual reactors are regulated in series to prepare multi-block ethylene or propylene-based copolymers with a graded distribution of comonomer content.

[0046] The catalyst used in this embodiment is Ziegler-Natta catalyst, the solvent is Isopar E isoparaffin, and the reactor mode selects double reactors in series. Both reactors are 2L high-pressure reactors, the temperature of the first reactor is 150°C, the pressure is 2.5MPa, the residence time is 12min, the amount of solvent added is 450mL, and the amount of 1-octene added is 200mL; the temperature of the second reactor is 155°C, the pressure is 2.8MPa, the residence time is 6min, the amount of solvent added is 400mL, and the amount of 1-octene added is 80mL.

[0047] This example is based on a two-kettle series polymerization process, and the specific process is as follows:

[0048] 1) The catalyst and the co-catalyst are pre-mixed, dissolved and activated in Isopar E isoparaffin solvent to obtain a pre-mixed solution A; the co-monomer 1-octene is pre-mixed and pre-dissolved in Isopar E isoparaffin solvent to obtain a pre-mixed solution B; the pre-mixed solutions A and B and the Isopar E isoparaffin solvent are stored in respective feed tanks.

[0049] 2) Preheat the autoclave reactor and pipelines required for the copolymerization reaction to the reaction temperature, and start the gas compressor to pressurize ethylene to the reaction pressure.

[0050] 3) Open the feed valves of the two autoclave reactors, add liquid materials, start stirring, and when the pressure and temperature in the reactor are stable, open the ethylene feed valve of autoclave reactor 1. When the ethylene flow rate stabilizes at the desired set value, start counting the reaction time.

[0051] 4) After reaching the preset reaction time, the discharge valve of the autoclave reactor 1 is opened to deliver the material to the autoclave reactor 2, and the ethylene feed valve of the reactor 2 is opened. When the ethylene flow rate stabilizes at the desired set value, the reaction time is started.

[0052] 5) After reaching the preset reaction time, the material is discharged, the solvent is removed, and granulation is performed to obtain the final product.

[0053] 6) After the reaction is completed, the reactor is post-cleaned.

[0054] The properties of the polyethylene elastomer product prepared in this example are shown in Table 1.

[0055] Embodiment 2:

[0056] This embodiment adopts Figure 2 The three-reactor series process is used to prepare multi-block ethylene or propylene-based copolymers with a graded distribution of comonomer content.

[0057] The catalyst used in this embodiment is FI catalyst, the co-catalyst is borane, the solvent is heptane, and the reactor mode selects three reactors in series. All three reactors are 3L high-pressure reactors. The temperature of the first reactor is 155°C, the pressure is 2.3MPa, the residence time is 16min, the amount of solvent added is 500mL, and the amount of 1-octene added is 400mL; the temperature of the second reactor is 150°C, the pressure is 2.8MPa, the residence time is 5min, the amount of solvent added is 400mL, and the amount of 1-octene added is 230mL. The temperature of the third reactor is 160°C, the pressure is 3.2MPa, the residence time is 16min, the amount of solvent added is 300mL, and the amount of 1-octene added is 60mL;

[0058] This example is based on a three-reactor series polymerization process, and the specific process is as follows:

[0059] 1) The catalyst and the co-catalyst are pre-mixed, dissolved and activated in a heptane solvent to obtain a pre-mixed solution A; the co-monomer 1-octene is pre-mixed and pre-dissolved in a heptane solvent to obtain a pre-mixed solution B; the pre-mixed solutions A and B and the heptane solvent are stored in respective feed tanks.

[0060] 2) Preheat the autoclave reactor and pipelines required for the copolymerization reaction to the reaction temperature, and start the gas compressor to pressurize ethylene to the reaction pressure.

[0061] 3) Open the feed valves of the three autoclave reactors, add liquid materials, start stirring, and when the pressure and temperature in the reactor are stable, open the ethylene feed valve of autoclave reactor 1. When the ethylene flow rate stabilizes at the desired set value, start counting the reaction time.

[0062] 4) After reaching the preset reaction time, the discharge valve of the autoclave reactor 1 is opened to deliver the material to the autoclave reactor 2, and the ethylene feed valve of the reactor 2 is opened. When the ethylene flow rate stabilizes at the desired set value, the reaction time is started.

[0063] 5) After reaching the preset reaction time, the discharge valve of the autoclave reactor 2 is opened to deliver the material to the autoclave reactor 3, and the ethylene feed valve of the reactor 3 is opened. When the ethylene flow rate stabilizes at the desired set value, the reaction time is started.

[0064] 6) After reaching the preset reaction time, the material is discharged, the solvent is removed, and granulation is performed to obtain the final product.

[0065] 7) After the reaction is completed, the reactor is post-cleaned. The properties of the polyethylene elastomer product prepared in this example are shown in Table 1.

[0066] Example 3

[0067] This embodiment adopts Figure 3 The tank reactor + loop reactor + tank reactor series polymerization process is adjusted to prepare multi-block ethylene or propylene-based copolymers with a graded distribution of comonomer content.

[0068] The catalyst used in this embodiment is chromium trioxide, the co-catalyst is vinyl trimethylsiloxane, the solvent is toluene, and the reactor mode selects a reactor reactor + a loop reactor + a reactor reactor in series. The reactor reactor uses a 3L high-pressure reactor, and the total volume of the loop reactor is 2L. The temperature of the first reactor is 150°C, the pressure is 2.2MPa, the residence time is 20min, the amount of solvent added is 500mL, and the amount of 1-octene added is 300mL; the temperature of the second loop reactor is 155°C, the pressure is 1.8MPa, the residence time is 7min, the amount of solvent added is 600mL, and the amount of 1-hexene added is 120mL. The temperature of the third reactor is 145°C, the pressure is 1.5MPa, the residence time is 20min, the amount of solvent added is 450mL, and the amount of 1-octene added is 30mL;

[0069] This example is based on a series polymerization process of a tank reactor + a loop reactor + a tank reactor. The specific process is as follows:

[0070] 1) The catalyst and the co-catalyst are pre-mixed, dissolved and activated in a toluene solvent to obtain a pre-mixed solution A; the co-monomer 1-octene is pre-mixed and pre-dissolved in a toluene solvent to obtain a pre-mixed solution B; the pre-mixed solutions A and B and the toluene solvent are stored in respective feed tanks.

[0071] 2) Preheat the autoclave and loop reactors and pipelines required for the copolymerization reaction to the reaction temperature, and start the gas compressor to pressurize ethylene to the reaction pressure.

[0072] 3) Open the feed valves of the three reactors, add liquid materials, start stirring, and when the pressure and temperature in the reactor are stable, open the ethylene feed valve of the autoclave reactor 1. When the ethylene flow rate stabilizes at the desired set value, start counting the reaction time.

[0073] 4) After reaching the preset reaction time, the discharge valve of the autoclave reactor 1 is opened to deliver the material to the loop reactor 2, and the ethylene feed valve of the reactor 2 is opened. When the ethylene flow rate stabilizes at the desired set value, the reaction time is started.

[0074] 5) After reaching the preset reaction time, the discharge valve of the loop reactor 2 is opened to deliver the material to the kettle reactor 3, and the ethylene feed valve of the reactor 3 is opened. When the ethylene flow rate stabilizes at the desired set value, the reaction time is started.

[0075] 6) After reaching the preset reaction time, the material is discharged, the solvent is removed, and granulation is performed to obtain the final product.

[0076] 7) After the reaction is completed, the reactor is post-cleaned. The properties of the polyethylene elastomer product prepared in this example are shown in Table 1.

[0077] Embodiment 4:

[0078] This embodiment adopts Figure 4 The tank reactor and the loop reactor are connected in series to prepare multi-block ethylene-based or propylene-based copolymers with a graded distribution of comonomer content.

[0079] The catalyst used in this embodiment is a Ziegler-Natta catalyst, the solvent is xylene, and the reactor mode selects a reactor reactor and a loop reactor in series. The reactor reactor is a 2L high-pressure reactor, the total volume of the loop reactor is 3L, the temperature of the first reactor is 160°C, the pressure is 2.1MPa, the residence time is 24min, the solvent addition amount is 420mL, and the 1-octene addition amount is 320mL; the loop reactor temperature is 165°C, the pressure is 1.8MPa, the residence time is 9min, the solvent addition amount is 400mL, and the 1-hexene addition amount is 125mL.

[0080] This example is based on a series polymerization process of a tank reactor and a loop reactor. The specific process is as follows:

[0081] 1) The catalyst and the co-catalyst are pre-mixed, dissolved and activated in a xylene solvent to obtain a pre-mixed solution A; the co-monomer 1-octene is pre-mixed and pre-dissolved in a xylene solvent to obtain a pre-mixed solution B; the pre-mixed solutions A and B and the xylene solvent are stored in respective feed tanks.

[0082] 2) Preheating the autoclave reactor, loop reactor and pipeline required for the copolymerization reaction to the reaction temperature, and starting the gas compressor to pressurize ethylene to the reaction pressure.

[0083] 3) Open the feed valves of the two reactors, add liquid materials, start stirring, and when the pressure and temperature in the reactor are stable, open the ethylene feed valve of the autoclave reactor 1. When the ethylene flow rate stabilizes at the desired set value, start counting the reaction time.

[0084] 4) After reaching the preset reaction time, the discharge valve of the autoclave reactor 1 is opened to deliver the material to the loop reactor 2, and the ethylene feed valve of the reactor 2 is opened. When the ethylene flow rate stabilizes at the desired set value, the reaction time is started.

[0085] 5) After reaching the preset reaction time, the material is discharged, the solvent is removed, and granulation is performed to obtain the final product.

[0086] 6) After the reaction is completed, the reactor is post-cleaned.

[0087] The properties of the polyethylene elastomer product prepared in this example are shown in Table 1.

[0088] Embodiment 5:

[0089] This embodiment adopts Figure 5The loop reactor + tank reactor + loop reactor series polymerization process is adjusted to prepare multi-block ethylene or propylene-based copolymers with a graded distribution of comonomer content.

[0090] The catalyst used in this embodiment is zirconocene dichloride, the co-catalyst is trimethylaluminoxane, the solvent is toluene, and the reactor mode selects the loop reactor + kettle reactor + loop reactor series mode. The kettle reactor uses a 2L high-pressure reactor, and the total volume of the loop reactor is also 2L. The temperature of the first loop reactor is 120°C, the pressure is 2.0MPa, the residence time is 28min, the amount of solvent added is 550mL, and the amount of 1-octene added is 385mL; the temperature of the second kettle reactor is 155°C, the pressure is 1.8MPa, the residence time is 11min, the amount of solvent added is 450mL, and the amount of 1-octene added is 100mL. The third loop reactor is 140°C, the pressure is 1.6MPa, the residence time is 28min, the amount of solvent added is 460mL, and the amount of 1-octene added is 50mL;

[0091] This example is based on a loop reactor + kettle reactor + loop reactor series polymerization process, and the specific process is as follows:

[0092] 1) The catalyst and the co-catalyst are pre-mixed, dissolved and activated in a toluene solvent to obtain a pre-mixed solution A; the co-monomer 1-octene is pre-mixed and pre-dissolved in a toluene solvent to obtain a pre-mixed solution B; the pre-mixed solutions A and B and the toluene solvent are stored in respective feed tanks.

[0093] 2) Preheat the autoclave and loop reactors and pipelines required for the copolymerization reaction to the reaction temperature, and start the gas compressor to pressurize ethylene to the reaction pressure.

[0094] 3) Open the feed valves of the three reactors, add liquid materials, start stirring, and when the pressure and temperature in the reactor are stable, open the ethylene feed valve of the loop reactor 1. When the ethylene flow rate stabilizes at the desired set value, start counting the reaction time.

[0095] 4) After reaching the preset reaction time, the discharge valve of the loop reactor 1 is opened to deliver the material to the kettle reactor 2, and the ethylene feed valve of the reactor 2 is opened. When the ethylene flow rate stabilizes at the desired set value, the reaction time is started.

[0096] 5) After reaching the preset reaction time, the discharge valve of the autoclave reactor 2 is opened to deliver the material to the loop reactor 3, and the ethylene feed valve of the reactor 3 is opened. When the ethylene flow rate stabilizes at the desired set value, the reaction time is started.

[0097] 6) After reaching the preset reaction time, the material is discharged, the solvent is removed, and granulation is performed to obtain the final product.

[0098] 7) After the reaction is completed, the reactor is post-cleaned. The properties of the polyethylene elastomer product prepared in this example are shown in Table 1.

[0099] Comparative Example 1:

[0100] The polyolefin is prepared in a single reactor.

[0101] The catalyst used in this comparative example is Ziegler-Natta catalyst, and the solvent is Isopar E isoparaffin. The reactor is a 1L high-pressure reactor, with a reactor temperature of 150°C, a pressure of 2.5 MPa, a residence time of 60 min, a solvent addition amount of 500 mL, and a 1-octene addition amount of 200 mL.

[0102] The specific process is as follows:

[0103] 1) The catalyst and the co-catalyst are pre-mixed, dissolved and activated in Isopar E isoparaffin solvent to obtain a pre-mixed solution A; the co-monomer 1-octene is pre-mixed and pre-dissolved in Isopar E isoparaffin solvent to obtain a pre-mixed solution B; the pre-mixed solutions A and B and the Isopar E isoparaffin solvent are stored in respective feed tanks.

[0104] 2) Preheat the autoclave and pipelines required for the copolymerization reaction to the reaction temperature, and start the gas compressor to pressurize ethylene to the reaction pressure.

[0105] 3) Open the feed valve and discharge valve of the reactor, start stirring, and input liquid materials.

[0106] 4) When the material index reaches the desired value and the pressure and temperature in the reactor are stable, open the ethylene feed valve. When the ethylene flow rate stabilizes at the desired set value, start counting the reaction time.

[0107] 5) After 1 hour of reaction, the material is discharged, the solvent is removed and granulated to obtain the final product.

[0108] 6) After the reaction is completed, the reactor is post-cleaned.

[0109] The properties of the polyethylene elastomer product prepared in this example are shown in Table 1.

[0110] Comparative Example 2:

[0111] This embodiment adopts Figure 1 The two reactors shown in the figure are connected in series to prepare polyolefin elastomer without any gradient restriction on the comonomer concentration.

[0112] The catalyst used in this embodiment is Ziegler-Natta catalyst, the solvent is Isopar E isoparaffin, and the reactor mode selects double reactors in series. Both reactors are 2L high-pressure reactors, the temperature of the first reactor is 150°C, the pressure is 2.5MPa, the residence time is 12min, the amount of solvent added is 500mL, and the amount of 1-octene added is 80mL; the temperature of the second reactor is 155°C, the pressure is 2.8MPa, the residence time is 6min, the amount of solvent added is 400mL, and the amount of 1-octene added is 300mL.

[0113] This example is based on a two-kettle series polymerization process, and the specific process is as follows:

[0114] 1) The catalyst and the co-catalyst are pre-mixed, dissolved and activated in Isopar E isoparaffin solvent to obtain a pre-mixed solution A; the co-monomer 1-octene is pre-mixed and pre-dissolved in Isopar E isoparaffin solvent to obtain a pre-mixed solution B; the pre-mixed solutions A and B and the Isopar E isoparaffin solvent are stored in respective feed tanks.

[0115] 2) Preheat the autoclave reactor and pipelines required for the copolymerization reaction to the reaction temperature, and start the gas compressor to pressurize ethylene to the reaction pressure.

[0116] 3) Open the feed valves of the two autoclave reactors, add liquid materials, start stirring, and when the pressure and temperature in the reactor are stable, open the ethylene feed valve of autoclave reactor 1. When the ethylene flow rate stabilizes at the desired set value, start counting the reaction time.

[0117] 4) After reaching the preset reaction time, the discharge valve of the autoclave reactor 1 is opened to deliver the material to the autoclave reactor 2, and the ethylene feed valve of the reactor 2 is opened. When the ethylene flow rate stabilizes at the desired set value, the reaction time is started.

[0118] 5) After reaching the preset reaction time, the material is discharged, the solvent is removed, and granulation is performed to obtain the final product.

[0119] 6) After the reaction is completed, the reactor is post-cleaned.

[0120] The properties of the polyethylene elastomer product prepared in this example are shown in Table 1.

[0121] Table 1 Product properties in Examples 1-5 and Comparative Examples

[0122]

[0123] As can be seen from the table, when multiple reactors are used to adjust the production of polyolefin products, they have the characteristics of high catalytic activity, low melting point, low crystallinity, and high comonomer insertion rate. Due to the adjustment of the comonomer content, the elongation at break and toughness of the product have been greatly improved, and the product transmittance and peel strength are significantly better than the olefin copolymer in the comparative example. In the products produced by using multiple reactors to adjust the production, due to the increase in the number of reactors, the change in the comonomer content is more flexible, and the reaction conditions can be configured more closely to the product requirements to obtain efficient and stable polyolefin products. On the other hand, based on the setting of the comonomer concentration gradient of each reactor, the product segment presents a high, medium and low gradient distribution of the comonomer content, which can be easier to process on the basis of ensuring the mechanical and optical properties of the product, and is suitable for more diversified application scenarios. At the same time, it is widely used in the toughening of ethylene and propylene polymers.

[0124] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein, on the contrary, the present invention can be extended to all other methods and applications with the same functions.

Claims

1. A method for preparing a block copolymer with a stepwise distribution of comonomer content, characterized in that: The following steps are involved: The polyolefin catalyst and the co-catalyst are pre-mixed, dissolved and activated in a first solvent to obtain a pre-mixed solution A; the co-monomer is pre-mixed and dissolved with a second solvent to obtain a pre-mixed solution B; the pre-mixed solutions A, B and solvent C are stored in respective feed tanks; A dual / multi-reactor series process is adopted, and each reactor is provided with a catalyst, a comonomer and an ethylene compensation port; solution A, solution B, solvent C and main monomer enter the first-stage reactor, wherein after solution B enters the first-stage reactor, the initial comonomer concentration is ω1, and the residence time of the first-stage reactor is t1; then the materials enter the next-stage reactor, the initial comonomer concentration of the i-stage reactor is ωi, and the residence time of the i-stage reactor is ti; i≥2; the comonomer concentration ω1 of the first-stage reactor is in the range of 30-60 mol%; the comonomer concentration ωi of the subsequent reactors is 30-80% of the comonomer concentration ω(i-1) of the previous reactor; the residence time ti of the i-stage reactor is in the range of 1-30min; The final product is obtained by discharging the material from the last reactor, removing the solvent and granulating the material.

2. The method according to claim 1, characterized in that: The polyolefin catalyst is at least one of a Ziegler-Natta catalyst, a metallocene catalyst, a late transition metal catalyst, a FI catalyst, and a chromium-based catalyst; preferably a Ziegler-Natta catalyst or a metallocene catalyst.

3. The method according to claim 1, characterized in that: The co-catalyst is at least one of an alkyl aluminum compound, an alkyl lithium compound, an alkyl zinc compound, an alkyl boron compound, and a modified alkyl aluminum compound.

4. The method according to claim 1, characterized in that The first solvent, the second solvent, and solvent C are each independently selected from one or more of toluene, xylene, ethylbenzene, diethylbenzene, hexane, heptane, pentane, cyclohexane, octane, nonane, decane, and Isopar E.

5. The method according to claim 1, characterized in that The comonomer is selected from one or more of propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, vinyl acetate, vinyl alcohol, ethyl acrylate, 1,4-butadiene, and pentadiene.

6. The method according to claim 1, characterized in that The range of comonomer concentration ω1 is 35-55 mol%; the range of comonomer concentration ωi of subsequent reactors is 35-75% of the comonomer concentration ω(i-1) of the previous reactor; the range of residence time ti of the i-th reactor is 3-25 min.

7. The method according to claim 1, characterized in that The number of reactors connected in series is selected to be more than two reactors, and the reactors are tank reactors or loop reactors. The tank reactors and loop reactors can be arranged freely.

8. The method according to claim 1, characterized in that Each reactor is provided with catalyst, comonomer and ethylene compensation port, and the replenishment ratio of catalyst and comonomer materials in each reactor is set according to the process requirements to obtain multi-block polyolefin products.

9. A multi-block polyolefin product prepared according to the method of any one of claims 1 to 7, wherein the polyolefin elastomer (POE) has the characteristics of step distribution of comonomer content and exhibits the characteristics of comonomer block distribution as the molecular chain grows.

10. The multi-block polyolefin product according to claim 9, characterized in that In the multi-block polyolefin product, as the molecular chain grows, the decay rate of the comonomer content between adjacent blocks is 5 mol% / 1000 main chain C-25 mol% / 1000 main chain C.

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