A process for the preparation of a block copolymer having a gradient distribution of comonomer content

Abstract

The application discloses a preparation method of a block copolymer with a gradient distribution of a comonomer content, the method being characterized by adjusting the comonomer content, the comonomer type and the polymerization time in three different polymerization stages in a single reactor to prepare a triblock olefin copolymer with a gradient reduction of the comonomer content along the molecular chain. The method is particularly suitable for a catalyst system which is sensitive to the comonomer content. The triblock olefin copolymer has the characteristics of high mechanical strength, enhanced toughness, enhanced peeling strength from glass or back plate, increased crosslinking degree and improved light transmittance, and can be applied not only to photovoltaic film materials but also to the modification and enhancement of ethylene-based polymers or propylene-based polymers.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of high molecular polymer preparation, and particularly relates to a preparation method of a block copolymer with a gradient distribution of comonomer content. The block olefin copolymer product in the present application has high mechanical strength, enhanced toughness, enhanced peeling strength from glass or backboard, increased crosslinking degree, and improved light transmittance. BACKGROUND

[0002] The block copolymer refers to a special polymer prepared by connecting two or more polymer segments with different properties together, which can combine the excellent properties of various polymers together to obtain a functional polymer material with superior performance. The molecular structure of the polymer is designable, the composition is variable, and the molecular weight is controllable, which is one of the research hotspots in the field of high polymers. The assembly prepared by the block copolymer can greatly enhance the physical, chemical, biological and other properties of the material. The block copolymer prepared can be used as a drug carrier, a thermoplastic elastomer, a blending compatibilizer, an interfacial modifier, a porous separation membrane, a biomimetic template, an optoelectronic material, etc., and has a wide application in the fields of medicine, construction and chemical industry.

[0003] In 2006, Dow Chemical Company of the United States proposed the concept of chain shuttling polymerization (Science, 2006, 312(5774): 714-9). The chain shuttling polymerization system contains two monomers (ethylene and 1-octene), two catalysts with different catalytic properties (MCAT-1 and MCAT-2) and a chain shuttling agent (CSA). In the presence of ethylene and 1-octene, the catalyst MCAT-1 catalyzes the copolymerization of ethylene and 1-octene to obtain a polymer with a very low content of 1-octene (hard segment), and the catalyst MCAT-2 catalyzes the copolymerization of ethylene and 1-octene to obtain a polymer with a high content of 1-octene (soft segment). The two active centers can quickly undergo a transmetalation reaction with the 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. This polyolefin multi-block copolymer has the properties of both hard segment and soft segment, and has excellent high and low temperature stability, superior processing performance, excellent resilience, outstanding compression set performance and good fatigue resistance.

[0004] The two-kettle series technology of Dowlex process (US Patent 5064802) needs to add appropriate catalyst, comonomer, ethylene and solvent in the second reaction kettle during polymerization to increase the comonomer content in the copolymer, and the two-kettle series promotes the copolymerization effect of the catalyst, so that the comonomer is uniformly distributed on the molecular chain of the product, thereby improving the product performance. However, the above process also has significant problems, such as high requirement for catalyst, unchanged type of comonomer in the two kettles, and non-obvious distribution of soft and hard segments of the product. At the same time, since the reactant needs to pass through two series polymerization kettles to produce polyethylene elastomer, the process has significant problems such as large equipment size, high engineering investment, high operation cost and complex operation process. SUMMARY

[0005] In view of the above problems, the present application provides a preparation method of block copolymer with gradient distribution of comonomer content. The present application uses a single reactor to produce a polyolefin product with multiple blocks and gradient distribution of comonomer content. Specifically, the present application uses the control of comonomer content and corresponding polymerization time in the single reactor to shorten the polymerization process, optimize the polymerization effect and improve the product compatibility, while producing olefin copolymer products with adjustable strength, toughness, crosslinking degree and light transmittance. The process has significant advantages such as simple process, low equipment investment cost, wide application range of catalyst and wide adjustable range of product properties.

[0006] One of the purposes of the present application is to provide a preparation method of block copolymer with gradient distribution of comonomer content, and another purpose is to produce olefin copolymer products with adjustable strength, toughness, peel strength, crosslinking degree and light transmittance by adjusting the comonomer content and corresponding polymerization time, and the prepared olefin copolymer can be widely used in the modification and reinforcement field of ethylene-based polymers or propylene-based polymers.

[0007] The present application can obtain random copolymer segments with gradient reduction of comonomer content in a single reactor by using the different reactivity of catalysts to different concentrations of comonomer, and by adjusting the polymerization time, comonomer type and concentration, a combination of multiple different random copolymer segments can be realized, and finally a multi-block random copolymer with gradient distribution of comonomer content is obtained.

[0008] The block copolymer described in the present application has a density range of 0.860-0.950 g / cm 3 , preferably 0.863-0.935 g / cm 3 .

[0009] The preparation method of block copolymer with gradient distribution of comonomer content provided by the present application comprises the following steps:

[0010] In a single reactor, at preset temperature T and pressure P, solvent, first comonomer and co-catalyst component are added, then main catalyst and olefin monomer are introduced, first stage polymerization is carried out, the initial content of first comonomer in the reactor is ω1, after reaction time t1, second comonomer is added to the reactor again, second stage polymerization is carried out, the initial content of second comonomer in the reactor is ω2, after reaction time t2, third comonomer is added to the reactor for the third time, third stage polymerization is carried out, the initial content of third comonomer in the reactor is ω3; after the polymerization time reaches t1+t2+t3, the polymerization in the reactor is completed, the product is discharged, and after desolventizing and granulating, a multi-block olefin copolymer with a gradient distribution of comonomer content is obtained.

[0011] Preferably, the first stage polymerization time t1 accounts for 20%-58% of the total polymerization time; the second stage polymerization time t2 accounts for 12%-50% of the total polymerization time; and the third stage polymerization time t3 accounts for 8%-30% of the total polymerization time. The proportion of the polymerization time can be adjusted according to the required product performance.

[0012] Preferably, the first stage polymerization time t1 accounts for 20%-58% of the total polymerization time; the second stage polymerization time t2 accounts for 12%-50% of the total polymerization time; and the third stage polymerization time t3 accounts for 8%-30% of the total polymerization time. The proportion of the polymerization time can be adjusted according to the required product performance.

[0013] Preferably, the first stage polymerization time t1 accounts for 20%-58% of the total polymerization time; the second stage polymerization time t2 accounts for 12%-50% of the total polymerization time; and the third stage polymerization time t3 accounts for 8%-30% of the total polymerization time. The proportion of the polymerization time can be adjusted according to the required product performance.

[0014] According to some embodiments of the present application, the polyolefin product prepared by the process has the characteristic of a gradient distribution of comonomer content, and the high, medium and low distribution of comonomer content along the molecular chain can be diversified and adjusted according to the process.

[0015] The decay rate of the comonomer content along the molecular chain with the increase of the molecular weight is W. According to some embodiments of the present application, the decay rate W of the comonomer content between adjacent blocks along the molecular chain in the multi-block polyolefin product is 5-30 mol% per 1000 main chain C, that is, the comonomer content in the next block decreases by W of 5-30 mol% per 1000 main chain C compared with the previous block along the molecular chain, preferably 8-25 mol% per 1000 main chain C.

[0016] According to some embodiments of the present application, the polyolefin product prepared by the process has a weight average molecular weight Mw = 5-30 x 10 4 g / mol; and a molecular weight distribution index MWD = 2.0-6.0.

[0017] According to some embodiments of the present application, the polyolefin catalyst is at least one of a Ziegler-Natta catalyst, a metallocene catalyst, a post-transition metal catalyst, a FI catalyst, a chromium-based catalyst, and a post-metallocene catalyst, which is particularly suitable for a catalyst system that is sensitive to the copolymerization ability and the comonomer content. 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. The molar ratio of the cocatalyst to the main catalyst is in the range of 1-3000, preferably 2-2000, and more preferably 2-1200.

[0018] According to some embodiments of the present application, the solvent is selected from one or more of toluene, xylene, ethylbenzene, diethylbenzene, hexane, heptane, pentane, cyclohexane, octane, nonane, decane, and Isopar E. The solvent can be blended in different proportions according to the characteristics of the copolymer to improve the solubility of the copolymer in the solvent, so that the reaction is more uniform and efficient.

[0019] According to some embodiments of the present application, the first comonomer, the second comonomer, and the third comonomer are 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, pentadiene, and isoprene, and the first comonomer, the second comonomer, and the third comonomer can be the same comonomer or different comonomers. More preferably, the first comonomer, the second comonomer, and the third comonomer are one or more of 1-butene, 1-hexene, and 1-octene. In this way, an olefin copolymer with long-chain branches in the side chains can be prepared, and the olefin polymer has better elasticity and toughness. The main monomer participating in the polymerization can be at least one of ethylene or propylene.

[0020] According to some embodiments of the present application, the preset temperature T is in the range of 90-200°C, preferably 110-170°C, and the temperature of the polymerization reaction is controlled by circulating water or oil outside the reactor.

[0021] According to some embodiments of the present application, the preset pressure P is in the range of 1.0-5.0 MPa, preferably 1.5-4.0 MPa.

[0022] According to some embodiments of the present application, the prepared multi-block olefin copolymer product has high mechanical strength, enhanced toughness, enhanced peel strength with glass or backplane, increased crosslinking degree, and improved light transmittance. The above product properties can be adjusted according to the concentration of the comonomer in each segment and the polymerization time ratio. The multi-block olefin copolymer can be applied not only to photovoltaic film materials, but also to the modification and enhancement of ethylene-based or propylene-based polymers in various fields.

[0023] Compared with the prior art, the present application has the following advantages:

[0024] On the one hand, the mechanical strength, toughness, light transmittance, and peel strength of the olefin copolymer are closely related to the molecular chain structure. The multi-block olefin copolymer prepared by the method of the present application (see schematic diagram 5) is prepared by gradient distribution of comonomer content. The low comonomer chain segment part can promote the crystallization of the ethylene segment, thereby improving the mechanical strength and the glass strength of the copolymer with glass or backplane. In addition, the high comonomer chain segment part can inhibit the crystallization behavior of the chain segment and promote the crosslinking effect of the crosslinking agent, thereby obtaining an olefin copolymer film material with high crosslinking degree, increased amorphous region content, and improved light transmittance. Benefiting from the aggregate structure of the alternating coexistence of crystalline regions and amorphous regions, the multi-block molecular chain with gradient distribution of comonomer can promote the alternating coexistence of crystalline regions and amorphous regions, and obtain an aggregate structure with smaller crystalline region size and larger number. As is known, the existence of crystalline regions as physical entanglement points can significantly improve the elongation at break and toughness of the copolymer material. In addition, the mechanical strength, toughness, light transmittance, and glass strength can be controlled and adjusted by the molecular weight of the copolymer, the type of comonomer, the content of comonomer, and the distribution gradient of comonomer on the molecular chain.

[0025] On the other hand, the multi-block olefin copolymer with gradient distribution of comonomer content can be prepared in a single reactor by controlling the concentration, type, and polymerization time of the comonomer, avoiding the complex catalyst and chain shuttling agent screening in the Dow chain shuttling polymerization system. The gradient concentration also gives the product more excellent performance. This preparation method can obtain a multi-block olefin copolymer with elastic properties, processing properties, mechanical properties, and high and low temperature stability close to the Dow OBC product. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings in the following brief description are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0027] Figure 1 : The polymerization flow chart of the present invention;

[0028] Figure 2 : Dowlex solution polymerization process;

[0029] Figure 3 : Structure diagram of the metallocene catalyst used in Example 5;

[0030] Figure 4 : Schematic diagram of multi-block polyolefin products;

[0031] Figure 5 : Schematic diagram of multi-block polyolefin products. DETAILED DESCRIPTION

[0032] The embodiments of the present invention will be described in detail below with reference to the examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present invention and should not be construed as limiting the scope of the invention. Where specific implementation conditions are not specified in the examples, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. Where the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased on the market.

[0033] The characterization methods of the polymer structure and properties in this embodiment are as follows:

[0034] (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.

[0035] (2) Density: measured according to GB / 1033-1986.

[0036] (3) Tensile strength, Young's modulus and elongation at break: measured according to GB / T 1040-2006.

[0037] (4) Weight average molecular weight and molecular weight distribution: determined by high temperature gel permeation chromatography (HT-GPC).

[0038] (5) Comonomer insertion rate: According to 13 C-NMR measurements and calculations.

[0039] (6) Melting point and crystallinity: measured by differential scanning calorimeter (DSC).

[0040] (7) Light transmittance: measured by light transmittance tester.

[0041] (8) Glass strength: measured by adhesive tape peeling strength tester.

[0042] Example 1

[0043] In a 10L reactor, the temperature in the reactor was raised to 130°C by circulating oil heating / heat removal, 2L of heptane solution, 1L of 1-octene comonomer, and methylaluminoxane co-catalyst were added into the reactor, and the reactor was stirred for 10 min to remove impurities in the reactor, and then metallocene catalyst (CAS: 135072-61-6) and ethylene monomer were added, and the pressure in the reactor was raised to 2.8 MPa, and the first-stage polymerization reaction started; after 20 min, 500 mL of 1-hexene was introduced, and the second-stage polymerization reaction started; after 10 min, 250 mL of 1-octene was introduced again, and the third-stage polymerization reaction started, which lasted for 10 min, and then the product in the reactor was discharged, and after desolventization and granulation, a multi-block polyolefin product with a gradient distribution of comonomer content was obtained (see Figure 1 ) for the polymerization process.

[0044] The multi-block polyolefin product prepared in this example is numbered as A, and the properties of the product are shown in Table 1. The comonomer content between adjacent blocks decreases at a rate W of 10 mol% per 1000 main chain C. The polyolefin product prepared in this example is shown in Figure 4 and Figure 5 .

[0045] Example 2

[0046] In a 10L reactor, the temperature in the reactor was raised to 140°C by circulating oil heating / heat removal, 2L of toluene solution, 1L of 1-hexene comonomer, and trifluorophenyl boron co-catalyst were added into the reactor, and the reactor was stirred for 10 min to remove impurities in the reactor, and then metallocene catalyst (CAS: 135072-61-6) and ethylene monomer were added, and the pressure in the reactor was raised to 3.8 MPa, and the first-stage polymerization reaction started; after 25 min, 600 mL of 1-hexene was introduced, and the second-stage polymerization reaction started; after 12 min, 200 mL of 1-octene was introduced again, and the third-stage polymerization reaction started, which lasted for 8 min, and then the product in the reactor was discharged, and after desolventization and granulation, a multi-block polyolefin product with a gradient distribution of comonomer content was obtained (see Figure 1 ) for the polymerization process.

[0047] The multi-block polyolefin product prepared in this example is numbered B, and the properties of the product are shown in Table 1. The comonomer content between adjacent blocks decays at a rate W of 12 mol% per 1000 main chain C.

[0048] Example 3

[0049] In a 10 L reactor, the temperature in the reactor was raised to 160°C by circulating oil heating / cooling, 3 L of n-hexane solution, 2 L of 1-hexene comonomer, and methylaluminoxane co-catalyst were added into the reactor, and the reactor was stirred for 10 min to remove impurities in the reactor. A metallocene catalyst ([Ph2C(Cp)(2-Me2N-Flu)]ZrCl2) and ethylene monomer were added, and the pressure in the reactor was raised to 3.5 MPa to start the first stage of polymerization. After 15 min, 800 mL of 1-octene was introduced to start the second stage of polymerization. After 15 min, 300 mL of 1-octene was introduced again to start the third stage of polymerization, which lasted for 10 min. Finally, the product in the reactor was discharged, and the product was obtained by desolventizing and granulating. The polymerization process is shown in Figure 1 ).

[0050] The multi-block polyolefin product prepared in this example is numbered C, and the properties of the product are shown in Table 1. The comonomer content between adjacent blocks decays at a rate W of 15 mol% per 1000 main chain C.

[0051] Example 4

[0052] In a 10 L reactor, the temperature in the reactor was raised to 130°C by circulating oil heating / cooling, 2 L of n-hexane solution, 900 mL of 1-octene comonomer, and modified methylaluminoxane co-catalyst were added into the reactor, and the reactor was stirred for 10 min to remove impurities in the reactor. A metallocene catalyst ([Ph2C(Cp)(2-Me2N-Flu)]ZrCl2) and ethylene monomer were added, and the pressure in the reactor was raised to 3.3 MPa to start the first stage of polymerization. After 18 min, 450 mL of 1-octene was introduced to start the second stage of polymerization. After 15 min, 150 mL of 1-octene was introduced again to start the third stage of polymerization, which lasted for 10 min. Finally, the product in the reactor was discharged, and the product was obtained by desolventizing and granulating. The polymerization process is shown in Figure 1 ).

[0053] The multi-block polyolefin product prepared in this example is numbered D, and the properties of the product are shown in Table 1. The comonomer content between adjacent blocks decays at a rate W of 11 mol% per 1000 main chain C.

[0054] Example 5

[0055] In a 10 L reactor, the temperature in the reactor was raised to 130 °C by circulating oil heating / cooling, 4.5 L of n-hexane solution, 2 L of 1-octene comonomer, and methylaluminoxane co-catalyst were added into the reactor, stirred for 10 min to remove impurities in the reactor, and then the metallocene catalyst (catalyst structure as shown in Figure 3 ) and propylene monomer were added. The pressure in the reactor was raised to 4.0 MPa, and the first stage of polymerization began. After 30 min, 900 mL of 1-octene was introduced, and the second stage of polymerization began. After 20 min, 350 mL of 1-hexene was introduced again, and the third stage of polymerization began, which lasted for 15 min. Finally, the product in the reactor was discharged, and after desolventizing and granulating, a multi-block polyolefin product with a gradient distribution of comonomer content was obtained (polymerization process is shown in Figure 1 ).

[0056] The multi-block polyolefin product prepared in this example is numbered E, and the properties of the product are shown in Table 1. The comonomer content between adjacent blocks decays at a rate W of 13 mol% per 1000 main chain C.

[0057] Comparative Example 1:

[0058] Comparative Example 1 used a two-reactor series polymerization process to produce a polyolefin elastomer, and the polymerization process is shown in Figure 2 Dowlex solution polymerization process. The catalyst used was CGC catalyst (CAS: 135072-61-6), the co-catalyst was borane, and the solvent was Isopar E isomeric alkanes. Both reactors were 10 L high-pressure reactors, the temperature of the first reactor was 120 °C, the pressure was 2.5 MPa, the residence time was 17 min, the amount of solvent added was 5 L, and the amount of 1-octene added was 1 L; the temperature of the second reactor was 135 °C, the pressure was 2.8 MPa, the residence time was 13 min, the amount of solvent added was 6 L, and the amount of 1-octene added was 1.3 L.

[0059] This comparative example was based on a two-reactor series polymerization process, and the specific process was as follows:

[0060] (1) The CGC catalyst, co-catalyst borane, and comonomer 1-octene were first pre-mixed, dissolved, and activated in the Isopar E solvent, and then charged into the first reactor under the action of pressurized ethylene;

[0061] (2) After 17 min of polymerization in the first reactor, the reaction was transferred to the second reactor, and an appropriate amount of 1-octene and ethylene was added into the second reactor, and the polymerization in the second reactor lasted for 13 min.

[0062] (3) After the polymerization in the second reactor was completed, the reaction material was introduced into a degassing and desolventizing device, and then passed through a granulating device to obtain the final product. The schematic diagram of the product is shown in Figure 5 .

[0063] The polyolefin product prepared in this example is numbered F, and the properties of the product are shown in Table 1.

[0064] Comparative Example 2:

[0065] In a 10 L reactor, the temperature in the reactor was raised to 130°C by circulating oil heating / cooling, 2 L of n-hexane solution, 1.5 L of 1-octene comonomer, and methylaluminoxane cocatalyst were added into the reactor, and the reactor was stirred for 10 min to remove impurities in the reactor. The metallocene catalyst (the structure of the catalyst is shown in Figure 3 ) and propylene monomer were added, and the pressure in the reactor was raised to 3.3 MPa to start the first stage of polymerization. After 10 min, 800 mL of 1-octene was introduced, and the second stage of polymerization started. After 10 min, 800 mL of 1-hexene was introduced again, and the third stage of polymerization started, which lasted for 10 min. Finally, the product in the reactor was discharged, and after desolventizing and granulating, a multi-block polyolefin product with a gradient distribution of comonomer content was obtained (the polymerization process is shown in Figure 1 ). The multi-block polyolefin product prepared in this comparative example is numbered G, and the properties of the product are shown in Table 1.

[0066] Comparative Example 3:

[0067] In a 10 L reactor, the temperature in the reactor was raised to 130°C by circulating oil heating / cooling, 5 L of n-hexane solution, 1 L of 1-octene comonomer, and methylaluminoxane cocatalyst were added into the reactor, and the reactor was stirred for 10 min to remove impurities in the reactor. The metallocene catalyst (the structure of the catalyst is shown in Figure 3 ) and ethylene monomer were added, and the pressure in the reactor was raised to 3.3 MPa to start the first stage of polymerization. After 15 min, 200 mL of 1-octene was introduced, and the second stage of polymerization started. After 20 min, 50 mL of 1-hexene was introduced again, and the third stage of polymerization started, which lasted for 10 min. Finally, the product in the reactor was discharged, and after desolventizing and granulating, a multi-block polyolefin product with a gradient distribution of comonomer content was obtained (the polymerization process is shown in Figure 1 ). The multi-block polyolefin product prepared in this comparative example is numbered H, and the properties of the product are shown in Table 1.

[0068] Table 1 Properties of the products in Examples 1-4 and Comparative Examples 1-3

[0069]

[0070]

[0071] As can be seen from Table 1, when the single reactor is used to adjust the multi-block polyolefin copolymer by adjusting the comonomer content, the comonomer type and the corresponding stage polymerization time, the catalyst has high catalytic activity, the product has low melting point, low crystallinity and high comonomer insertion rate (e.g. Examples 1-5). Due to the step distribution adjustment of the comonomer content, the elongation at break and toughness of the multi-block olefin copolymer product are greatly improved, and the product has better light transmittance and peel strength than the olefin copolymers in Comparative Examples 1-3. At the same time, due to the limitation of the comonomer concentration in the reactor, the balance of the product processing performance, mechanical properties and use performance is ensured while the polymerization activity is ensured, and the performance defects caused by too high or too low comonomer concentration are avoided.

[0072] It should be noted that the above-described examples are only used to explain the present application and do not constitute any limitation on the present application. The present application is described by referring to typical examples, but it should be understood that the words used therein are descriptive and explanatory words, rather than limiting words. The present application can be modified as specified within the scope of the claims of the present application, and the present application can be revised without departing from the scope and spirit of the present application. Although the present application described therein relates to specific methods, materials and examples, it does not mean that the present application is limited to the specific examples disclosed therein, on the contrary, the present application can be extended to all other methods and applications with the same function.

Claims

1. A method for preparing a block copolymer with a stepwise distribution of comonomer content, characterized in that: The following steps are involved: In a single reactor at a preset temperature T and pressure P, a solvent, a first comonomer and a co-catalyst component are added, and then a main catalyst and an olefin monomer are introduced to carry out a first-stage polymerization, wherein the initial content of the first comonomer in the reactor is ω1; after a reaction time t1, a second comonomer is added to the reactor again to carry out a second-stage polymerization, wherein the initial content of the second comonomer in the reactor is ω2; after a reaction time t2, a third comonomer is added to the reactor for a third time to carry out a third-stage polymerization, wherein the initial content of the third comonomer in the reactor is ω3; after the total polymerization time reaches t1+t2+t3, the polymerization in the reactor is terminated, the product is discharged, and a multi-block olefin copolymer with a step-by-step distribution of comonomer content is obtained through desolvation and granulation; The first polymerization time t1 accounts for 15%-60% of the total polymerization time; the second polymerization time t2 accounts for 8%-55% of the total polymerization time; the third polymerization time t3 accounts for 5%-32% of the total polymerization time; the comonomer concentration ω1 ranges from 30-60 mol%, and the comonomer concentrations ω2 and ω3 in the second and third stages are 30%-60% of the comonomer concentrations in the previous stage; The first comonomer, the second comonomer, and the third comonomer are 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, pentadiene, and isoprene, and the first comonomer, the second comonomer, and the third comonomer can be the same comonomer or different comonomers; the olefin monomer is at least one of ethylene or propylene.

2. The method according to claim 1, wherein: The main catalyst is at least one of a Ziegler-Natta catalyst, a metallocene catalyst, a late transition metal catalyst, a chromium-based catalyst, and a late metallocene catalyst.

3. The method according to claim 2, wherein: The main catalyst is a Ziegler-Natta catalyst or a metallocene catalyst.

4. The method according to claim 1, wherein: 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.

5. The method according to claim 1, wherein The solvent is selected from one or more of toluene, xylene, ethylbenzene, diethylbenzene, hexane, heptane, pentane, cyclohexane, octane, nonane, decane, and Isopar E.

6. The method according to claim 1, characterized in that The first polymerization time t1 accounts for 20%-58% of the total polymerization time; the second polymerization time t2 accounts for 12%-50% of the total polymerization time; and the third polymerization time t3 accounts for 8%-30% of the total polymerization time.

7. The method according to claim 1, wherein The comonomer concentration ω1 ranges from 35 to 55 mol %; and the comonomer concentrations ω2 and ω3 in the second and third stages are 35% to 55% of the comonomer concentration in the previous stage.

8. The method according to claim 1, wherein The preset temperature T ranges from 90°C to 200°C; the preset pressure P ranges from 1.0 MPa to 5.0 MPa.

9. A multi-block olefin copolymer product obtained by the method according to any one of claims 1 to 8, characterized in that: The weight average molecular weight Mw of the multi-block olefin copolymer product is 5 × 10 4 -30 × 10 4 g / mol; molecular weight distribution index MWD = 2.0-6.

0.

10. The multi-block olefin copolymer product according to claim 9, characterized in that: The comonomer content in the multi-block olefin copolymer product is distributed in a stepped manner, presenting a high, medium and low variety of comonomer distribution as the molecular chain grows, and the high, medium and low variety of comonomer distribution can be variably adjusted according to polymerization process parameters.

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