A crystalline ethylene-styrene monomer random copolymer and a preparation method thereof

Abstract

The present invention discloses a crystalline ethylene-styrene monomer random copolymer and a preparation method thereof, belonging to the technical field of olefin polymer preparation. In the present invention, a bridged bis(cyclopentadienyl) rare earth compound is combined with a cocatalyst organic boron salt and a main group alkyl reagent as a catalytic system to catalyze the random copolymerization of ethylene and styrene monomers, so that the bridged bis(cyclopentadienyl) rare earth compound, which shows low catalytic activity or no catalytic activity for the copolymerization of ethylene and styrene monomers, exhibits high catalytic activity for the copolymerization of ethylene and styrene monomers and has a preferential selectivity for ethylene polymerization, and a crystalline ethylene-styrene monomer random copolymer containing a polyethylene chain segment is prepared, and the copolymer has a low styrene content, specifically containing 2.0 mol% to 20.0 mol% of styrene.

Description

Technical Field

[0001] The present invention relates to a crystalline ethylene-styrene monomer random copolymer and a preparation method thereof, belonging to the technical field of olefin polymer preparation. Background Art

[0002] Ethylene and styrene and its derivatives are two types of monomers with very different properties, and it is impossible to copolymerize them using free radical polymerization methods and traditional Ziegler-Natta catalytic systems to prepare copolymers of ethylene-styrene monomers. The invention of single-site catalytic systems has made the copolymerization of these two types of monomers possible. However, so far, only a few single-site catalytic systems can effectively catalyze the copolymerization of ethylene and styrene monomers. For example, Nomura et al. in Japan found that the random copolymerization of ethylene and styrene was catalyzed by a titanium metal complex chelated with a cyclopentadienyl group and a non-cyclopentadienyl ligand to obtain a sequence-random ethylene-styrene copolymer, in which the styrene continuous structural units are stereorandom (Macromolecules 2000, 33, 8122; Macromolecules 2002, 35, 5388; Dalton Trans., 2007, 1802; J. Am. Chem. Soc. 2005, 127, 9364; Macromolecules 2006, 39, 5266). Dow Chemical Company used a constrained geometry titanium catalyst for the copolymerization of ethylene and styrene to prepare a non-crystalline quasi-random ethylene-styrene copolymer (EP 0416815A2, 1991). Hou Zhaomin et al. used a single-cyclopentadienyl scandium metal catalytic system to catalyze the random copolymerization of styrene and ethylene to prepare an ethylene-styrene sequence-random copolymer containing syndiotactic polystyrene segments (J. Am. Chem. Soc. 2004, 126, 13910). ZL201710122863.X reported the copolymerization of ethylene and styrene catalyzed by a constrained geometry rare earth catalyst to prepare a quasi-random ethylene-styrene copolymer. Organometallics 2013, 32, 1445 used a fluorenyl scandium dialkyl compound to catalyze the copolymerization of ethylene and styrene to prepare an ethylene-styrene copolymer containing syndiotactic polystyrene segments. Carpentier et al. used a bridged bis-cyclopentadienyl rare earth allyl catalyst to catalyze the copolymerization of ethylene and styrene to prepare a syndiotactic ethylene-styrene copolymer with a high styrene content (Chem. Eur. J. 2007, 13, 5548, CN200580013508.4). However, how to control the content of styrene monomers in the ethylene-styrene copolymer at a reasonable level so that it retains the crystallization properties of polyethylene and contains a certain proportion of styrene monomer structural units is still a challenging task. Summary of the Invention

[0003] The present invention provides a catalytic system which can efficiently prepare a random copolymer of ethylene and styrene monomer containing a crystalline polyethylene segment, and can control the styrene monomer content in the ethylene-styrene copolymer within the range of 2.0 mol% to 20.0 mol%.

[0004] The technical method of the present invention:

[0005] One of the objectives of the present invention is to provide a method for preparing a crystalline random copolymer of ethylene and styrene monomer. The method is as follows: under anhydrous and anaerobic conditions, in the presence of an organic solvent, a catalytic system composed of a bridged bis(cyclopentadienyl) rare earth metal compound, an organic borate salt, and a main group alkyl reagent catalyzes the copolymerization of ethylene and styrene monomer to obtain a copolymer containing 2.0 mol% to 20.0 mol% of styrene, and the copolymer is a crystalline random copolymer of ethylene and styrene monomer containing a polyethylene segment.

[0006] Further defined, the general formula of the bridged bis(cyclopentadienyl) rare earth metal compound is (Flu-R-Cp)LnR’(Lewis base)n, where Flu is a substituted or unsubstituted fluorenyl group, Cp is a substituted or unsubstituted cyclopentadienyl group, Ln is scandium, yttrium or any rare earth element from lanthanum to lutetium except promethium, R is a bridging group between Flu and Cp, R’ is hydrogen or a hydrocarbon group, silyl group, amino group, borohydride group, tetramethylaluminum group having 1 to 20 carbon atoms, the Lewis base is a neutral coordination solvent molecule, and n is an integer of 0 to 2.

[0007] Further defined, Flu is a fluorenyl group, 2,7-di-tert-butylfluorenyl group or 3,6-di-tert-butylfluorenyl group.

[0008] Further defined, Cp is cyclopentadiene, methylcyclopentadienyl group, ethylcyclopentadienyl group, n-butylcyclopentadienyl group, n-octylcyclopentadienyl group or trimethylsilylcyclopentadienyl group.

[0009] Further defined, R is Me 2 C,Me 2 Si,MeHSi、Et 2 Si or PhMeSi.

[0010] Further defined, R’ is an alkyl group having 1 to 16 carbon atoms, a silyl group having 4 to 16 carbon atoms, an amino group having 2 to 16 carbon atoms, a silylamino group having 4 to 20 carbon atoms, an arylamino group having 6 to 20 carbon atoms, an allyl group having 3 to 10 carbon atoms, a benzyl group having 7 to 20 carbon atoms, a borohydride group, a tetramethylaluminum group or hydrogen.

[0011] Further defined, R' is an alkyl group with 1 to 10 carbon atoms, a silyl group with 4 to 12 carbon atoms, an amino group with 2 to 10 carbon atoms, a silylamino group with 4 to 12 carbon atoms, an arylamino group with 6 to 16 carbon atoms, an allyl group with 3 to 9 carbon atoms, or a benzyl group with 7 to 12 carbon atoms.

[0012] Further defined, R' is trimethylsilylmethylene, bis(trimethylsilyl)methylene, allyl, 2-methylallyl, 1,3-bis(trimethylsilyl)allyl, hexamethyldisilazide, tetramethyldisilazide, methyl, benzyl, 4-methylbenzyl, or 2-N,N'-dimethylbenzyl.

[0013] Further defined, Ln is scandium, yttrium, lutetium, neodymium, gadolinium, holmium, thulium, erbium, ytterbium, or lanthanum.

[0014] Further defined, the Lewis base is tetrahydrofuran, diethyl ether, pyridine, or dimethylether.

[0015] Further defined, n is 0 or 1.

[0016] Further defined, the structure of the bridged bis(cyclopentadienyl) rare earth metal compound is as follows:

[0017]

[0018] Further defined, the organic borate is an organic compound containing a boron anion [B(C 6 F 5 ) 4 -.

[0019] Further defined, the organic borate is one or a mixture of [PhNMe 2 H][B(C 6 F 5 ) 4 , [Ph 3 C][B(C 6 F 5 ) 4 , [N(C 18 H 37 ) 2 Me][B(C 6 F 5 ) 4 .

[0020] Further defined, the main group alkyl reagent is aluminoxane, alkylaluminum, alkylzinc, or alkylmagnesium.

[0021] Further defined, the main group alkyl reagent is one or a mixture of trimethylaluminum, triethylaluminum, tri-n-butylaluminum, tri-n-propylaluminum, triisobutylaluminum, triisopropylaluminum, tripentylaluminum, trihexylaluminum, trioctylaluminum, diethylaluminum hydride, diisobutylaluminum hydride, MAO, DMAO, MMAO, diethylzinc, diethylmagnesium, di-n-propylmagnesium, diisopropylmagnesium, dibutylmagnesium, butylethylmagnesium.

[0022] Further defined, the styrene monomer is styrene, p-methylstyrene, p-ethylstyrene, p-isopropylstyrene, p-tert-butylstyrene, p-fluorostyrene, p-chlorostyrene, p-bromostyrene, preferably styrene, p-methylstyrene, p-ethylstyrene, p-isopropylstyrene, p-tert-butylstyrene, and more preferably one or a mixture of styrene and p-methylstyrene.

[0023] Further defined, the molar ratio of the bridged bis(cyclopentadienyl) rare earth metal compound, the organoborate, and the main group alkyl reagent is 1:(0.1 - 1.1):(1 - 1000).

[0024] Further defined, the molar ratio of the bridged bis(cyclopentadienyl) rare earth metal compound, the organoborate, and the main group alkyl reagent is 1:1:(10 - 500).

[0025] Further defined, the molar ratio of the bridged bis(cyclopentadienyl) rare earth metal compound, the organoborate, and the main group alkyl reagent is 1:1:(20 - 100).

[0026] Further defined, the molar ratio of the styrene monomer to the bridged bis(cyclopentadienyl) rare earth metal compound is (1000 - 100000):1.

[0027] Further defined, the molar ratio of the styrene monomer to the bridged bis(cyclopentadienyl) rare earth metal compound is (4000 - 60000):1.

[0028] Further defined, the specific preparation method is as follows: under anhydrous and anaerobic conditions, dissolve the bridged bis(cyclopentadienyl) rare earth metal compound and the organoborate in toluene, add them to a toluene solution containing the styrene monomer and the main group alkyl reagent and saturated with ethylene at a certain temperature, keep a certain ethylene pressure constant, react at a certain temperature for a certain time, then add an ethanol solution to terminate the reaction, and then pour the reaction solution into ethanol containing a small amount of hydrochloric acid and a stabilizer for precipitation. Place the obtained polymer in a vacuum drying oven for drying to obtain a crystalline ethylene-styrene monomer random copolymer.

[0029] Further defined, the polymerization temperature is 20 - 200 °C, and the time is 0.17 - 24 h.

[0030] Further defined, the polymerization temperature is 50 - 150 °C.

[0031] Further limitation: the polymerization temperature is 60 to 120 °C

[0032] Further limitation: the polymerization time is 0.5 h to 10 h.

[0033] Further limitation: the polymerization time is 1 to 6 h.

[0034] Further limitation: the polymerization time is 2 to 4 h.

[0035] Further limitation: the ethylene pressure is 0.1 to 10 MPa.

[0036] Further limitation: the ethylene pressure is 0.2 to 6 MPa.

[0037] Further limitation: the ethylene pressure is 0.4 to 1 MPa.

[0038] Further limitation: the concentration of styrene monomer in the reaction system is 1 to 90 g / 100 mL

[0039] Further limitation: the concentration of styrene monomer in the reaction system is 10 to 62 g / 100 mL.

[0040] The present invention has the following beneficial effects compared with the prior art:

[0041] The present invention uses a bridged bis(cyclopentadienyl) rare earth compound combined with a cocatalyst organic boron salt and a main group alkyl reagent as a catalytic system to catalyze the random copolymerization of ethylene and styrene monomers, enabling a bridged bis(cyclopentadienyl) rare earth compound that exhibits low or no catalytic activity for the copolymerization of ethylene and styrene monomers to show high catalytic activity for the copolymerization of ethylene and styrene monomers and having a preferential selectivity for ethylene polymerization, and preparing a crystalline ethylene-styrene monomer random copolymer containing polyethylene segments, and the copolymer has a low styrene content, specifically containing 2.0 mol% to 20.0 mol% of styrene. Description of the Drawings

[0042] Figure 1 DSC spectrum of the polymer prepared in Example 1;

[0043] Figure 2 DSC spectrum of the polymer prepared in Example 2;

[0044] Figure 3 DSC spectrum of the polymer prepared in Example 4;

[0045] Figure 4 1H NMR spectrum of the polymer prepared in Example 2;

[0046] Figure 5 1H NMR spectrum of the polymer prepared in Example 4. Detailed Description of the Invention

[0047] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and understandable, the following specifically describes the specific implementation manners of the present invention in conjunction with the embodiments of the specification.

[0048] In the following description, many specific details are set forth in order to fully understand the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art can make similar generalizations without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0049] Secondly, the so-called "one embodiment" or "embodiment" herein refers to a specific feature, structure or characteristic that may be included in at least one implementation manner of the present invention. The "in one embodiment" that appears in different places in this specification does not all refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments.

[0050] The experimental methods used in the following embodiments are all conventional methods unless otherwise specified. The materials, reagents, methods and instruments used, unless otherwise specified, are all conventional materials, reagents, methods and instruments in this field, and those skilled in the art can obtain them through commercial channels.

[0051] Compound 1 and Compound 3 used in the following embodiments were synthesized by the method described in the literature Chem. Eur. J. 2007, 13, 5548 to prepare bridged bis(cyclopentadienyl) rare earth compounds. The specific preparation method is as follows:

[0052] Preparation of Compound 1

[0053] Dissolve 2 mmol of the bis(cyclopentadienyl) ligand Cp-SiMe 2 -Flu in 20 mL of diethyl ether solvent, and then dropwise add 4 mmol of n-butyllithium hexane solution in an ice-water bath, and then react at room temperature for 4 hours. Then, quickly pour the reaction solution into the diethyl ether suspension of ScCl 3 (THF) 3 at -20 °C, and continue to stir the reaction at room temperature for 12 hours. Finally, filter through a glass sand funnel, collect the filtrate, dry it by evaporation, and recrystallize it in toluene to obtain the product (Cp-SiMe 2 -Flu)ScCl(THF). Subsequently, dropwise add the n-hexane solution containing 1.5 mmol of LiCH 2 SiMe 3 at room temperature to 1.5 mmol of (Cp-SiMe 2In a toluene solution of -Flu)ScCl(THF), after stirring the reaction at room temperature for 2 hours, it was filtered through a glass sand filter, the filtrate was collected, the solvent used was removed under vacuum, and then the solid product was redissolved in n-hexane. After concentration, it was recrystallized at -30 °C to obtain a light yellow compound 1. The yield was 56%.

[0054] Preparation of Compound 3

[0055] Dissolve 2 mmol of the bis-cyclopentadienyl ligand Cp-CMe 2 -Flu in 20 mL of diethyl ether solvent, then dropwise add 4 mmol of a n-butyllithium hexane solution in an ice-water bath, and then react at room temperature for 4 hours. After that, the reaction solution was quickly poured into a diethyl ether suspension of ScCl 3 (THF) 3 at -20 °C, and the reaction was continued with stirring at room temperature for 12 hours. Finally, it was filtered through a glass sand funnel, the filtrate was collected and dried, and recrystallized in toluene to obtain the product (Cp-CMe 2 -Flu)ScCl(THF). Subsequently, 1.5 mmol of the red solid KCH 2 Ph was added portionwise at room temperature to a toluene solution of 1.5 mmol (Cp-SiMe 2 -Flu)ScCl(THF). After stirring the reaction at room temperature for 2 hours, it was filtered through a glass sand filter, the filtrate was collected, concentrated under vacuum, and recrystallized at -30 °C to obtain a yellow compound 3. The yield was 62%.

[0056] Example 1

[0057] Under anhydrous and anaerobic conditions, compound 1 (10 μmol) and [Ph 3 C][B(C 6 F 5 ) 4 (abbreviation A, 10 μmol) were added to a toluene solution (2 mL), and at 60 °C, it was added to a solution containing styrene monomer (10 mmol) and Ai i Bu 3 (0.2 mmol) and a toluene solution (10 mL) saturated with ethylene. Then, while maintaining a constant ethylene pressure of 4 bar, after reacting for 10 min, a small amount of ethanol solution was added to terminate the polymerization reaction. Then the reaction solution was poured into ethanol (100 mL) containing a small amount of hydrochloric acid and stabilizer BHT for precipitation. Finally, the obtained polymer was dried in a vacuum drying oven at 50 °C for 48 h to obtain 0.62 g of polymer with a net weight. The polymer had M n = 1600, M w / M n = 1.57, T m = 116, as shown in Table 1 below. The DSC spectrum of this polymer is as Figure 1as shown

[0058] Example 2

[0059] The difference between this example and Example 1 is that the styrene monomer is 20 mmol, the reaction time is 20 min, and the rest of the operation process and parameter settings are the same as those in Example 1. The characteristics of the obtained polymer are shown in Table 1 below, and the DSC spectrum of this polymer is as Figure 2 as shown

[0060] Example 3

[0061] The difference between this example and Example 1 is that the styrene monomer is 20 mmol, the toluene solution saturated with ethylene is 20 mL, the reaction time is 20 min, and the rest of the operation process and parameter settings are the same as those in Example 1. The characteristics of the obtained polymer are shown in Table 1 below.

[0062] Example 4

[0063] The difference between this example and Example 1 is that the styrene monomer is 40 mmol, the reaction time is 30 min, and the rest of the operation process and parameter settings are the same as those in Example 1. The characteristics of the obtained polymer are shown in Table 1 below, and the DSC spectrum of this polymer is as Figure 4 as shown

[0064] Example 5

[0065] The difference between this example and Example 1 is that the styrene monomer is 50 mmol, the reaction time is 120 min, and the rest of the operation process and parameter settings are the same as those in Example 1. The characteristics of the obtained polymer are shown in Table 1 below.

[0066] Example 6

[0067] The difference between this example and Example 1 is that Ai i Bu 3 is 0.5 mmol, the styrene monomer is 100 mmol, the toluene solution saturated with ethylene is 30 mL, the reaction temperature is 120 °C, the reaction time is 60 min, and the rest of the operation process and parameter settings are the same as those in Example 1. The characteristics of the obtained polymer are shown in Table 1 below.

[0068] Example 7

[0069] The difference between this example and Example 1 is that Ai i Bu 3 is 1 mmol, the styrene monomer is 600 mmol, the toluene solution saturated with ethylene is 100 mL, keeping the ethylene pressure at 10 bar unchanged, the reaction temperature is 70 °C, the reaction time is 240 min, and the rest of the operation process and parameter settings are the same as those in Example 1. The characteristics of the obtained polymer are shown in Table 1 below.

[0070] Example 8

[0071] The difference between this example and Example 1 is as follows: Compound 3 is used to replace Compound 1. The operation process and parameter settings are the same as those in Example 1. The characteristics of the obtained polymer are shown in Table 1 below.

[0072] Table 1

[0073]

[0074] Comparative Example 1

[0075] Under anhydrous and anaerobic conditions, rare earth compound 1 (10 μmol) was added to toluene solution (2 mL). At 60 °C, it was added to a toluene solution (10 mL) containing styrene (10 mmol) monomer and toluene solution saturated with ethylene. Then, after maintaining a constant ethylene pressure of 4 bar for 10 min, a small amount of ethanol solution was added to terminate the polymerization reaction. Then the reaction solution was poured into ethanol (100 ml) containing a small amount of hydrochloric acid and stabilizer BHT for precipitation. The obtained polymer was dried in a vacuum drying oven at 50 °C for 48 h to obtain 1.04 g of polymer by net weight. After testing, no styrene structural unit was inserted, and T m = 130 °C.

[0076] Comparative Example 2

[0077] Under anhydrous and anaerobic conditions, rare earth compound 1 (10 μmol) was added to toluene solution (2 mL), and then added to a toluene solution (10 mL) containing styrene (3 mmol). After reacting at 60 °C for 10 min, a small amount of ethanol solution was added to terminate the polymerization reaction. Then the reaction solution was poured into ethanol (100 mL) containing a small amount of hydrochloric acid and stabilizer BHT for precipitation, and no polymer was separated.

[0078] Comparative Example 3

[0079] Under anhydrous and anaerobic conditions, rare earth compound 1 (10 μmol) and Ai i Bu 3 (0.2 mmol) were added to toluene solution (2 mL), and then added to a toluene solution (10 mL) containing styrene (3 mmol). After reacting at 60 °C for 10 min, a small amount of ethanol solution was added to terminate the polymerization reaction. Then the reaction solution was poured into ethanol (100 mL) containing a small amount of hydrochloric acid and stabilizer BHT for precipitation, and no polymer was separated.

[0080] Comparing Example 1 with Comparative Examples 1 to 3, it can be seen that by using a bridged bis(cyclopentadienyl) rare earth compound in combination with a cocatalyst organic boron salt and a main group alkyl reagent as a catalytic system for the random copolymerization of ethylene and styrene monomers, a bridged bis(cyclopentadienyl) rare earth compound that shows low or no catalytic activity for the copolymerization of ethylene and styrene monomers exhibits high catalytic activity for the copolymerization of ethylene and styrene monomers, realizing the copolymerization of ethylene and styrene monomers.

[0081] Analyze the DSC spectra of the polymers prepared in the above examples. As Figures 1 - 3 shown, it can be seen from Figures 1 - 3 that the melting point of the copolymer is between 106 °C and 123 °C, which belongs to the crystallization melting peak of long polyethylene chain segments. No melting peak is observed at about 270 °C, indicating that there is no syndiotactic polystyrene long chain segment present.

[0082] Analyze the nuclear magnetic resonance hydrogen spectrum of the polymers prepared in the above examples. As Figure 4 and Figure 5 shown, it can be seen from Figure 4 and Figure 5 that the resonance peak with a chemical shift between 6.5 and 7.5 ppm is the resonance peak of the hydrogen on the benzene ring of the styrene structural unit in the copolymer. The resonance peak with a chemical shift between 0.95 and 1.92 ppm is the signal peak of the backbone alkane hydrogen.

[0083] The molar content of the styrene structural unit in the copolymer = (I 6.5-7.5 / 5) / [(I 6.5-7.5 / 5)+(I 0.95-1.92 -3(I 6.5-7.5 / 5) / 4)].

[0084] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing examples, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing examples, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing a crystalline ethylene-styrene monomer random copolymer, characterized in that, the copolymer contains 2.0 mol% to 20.0 mol% of styrene and is a crystalline ethylene-styrene monomer copolymer containing polyethylene chain segments; the preparation method is: under anhydrous and anaerobic conditions, in the presence of an organic solvent, the copolymerization of ethylene and styrene monomers is catalyzed by a catalytic system composed of a bridged bis(cyclopentadienyl) rare earth metal compound, an organic borate salt, and a main group alkyl reagent; The general formula of the bridged bis(cyclopentadienyl) rare earth metal compound is (Flu-R-Cp)LnR’(Lewis base)n, where Flu is fluorenyl, 2,7-di-tert-butylfluorenyl or 3,6-di-tert-butylfluorenyl, Cp is cyclopentadienyl, methylcyclopentadienyl, ethylcyclopentadienyl, n-butylcyclopentadienyl, n-octylcyclopentadienyl or trimethylsilylcyclopentadienyl, Ln is scandium, yttrium, lutetium, neodymium, gadolinium, holmium, thulium, erbium, ytterbium or lanthanum, R is the bridging group between Flu and Cp and is Me 2 C, Me 2 Si, MeHSi, Et 2 Si or PhMeSi, R’ is an alkyl group with 1 to 16 carbon atoms, a silyl group with 4 to 16 carbon atoms, an amino group with 2 to 16 carbon atoms, a silylamino group with 4 to 20 carbon atoms, an arylamino group with 6 to 20 carbon atoms, an allyl group with 3 to 10 carbon atoms, a benzyl group with 7 to 20 carbon atoms, a borohydride group, a tetramethylaluminum group or hydrogen, the Lewis base is tetrahydrofuran, diethyl ether, pyridine or dimethyl ether, and n is 1 or 2.

2. The method for preparing a crystalline ethylene-styrene monomer random copolymer according to claim 1, characterized in that, the structure of the bridged bis(cyclopentadienyl) rare earth metal compound is as follows:

3. The method for preparing a crystalline ethylene-styrene monomer random copolymer according to claim 1, characterized in that, The organoborate is an organic compound containing a boron anion [B(C 6 F 5 ) 4 ˉ.

4. The method for preparing a crystalline ethylene-styrene monomer random copolymer according to claim 1, characterized in that, the main group alkyl reagent is aluminoxane, alkylaluminum, alkylzinc, or alkylmagnesium.

5. The method for preparing a crystalline ethylene-styrene monomer random copolymer according to claim 4, characterized in that, the main group alkyl reagent is one or a mixture of trimethylaluminum, triethylaluminum, tri-n-butylaluminum, tri-n-propylaluminum, triisobutylaluminum, triisopropylaluminum, tripentylaluminum, trihexylaluminum, trioctylaluminum, diethylaluminum hydride, diisobutylaluminum hydride, MAO, DMAO, MMAO, diethylzinc, diethylmagnesium, di-n-propylmagnesium, diisopropylmagnesium, dibutylmagnesium, butylethylmagnesium.

6. The method for preparing a crystalline ethylene-styrene monomer random copolymer according to claim 1, characterized in that, the styrene monomer is one or a mixture of styrene, p-methylstyrene, p-ethylstyrene, p-isopropylstyrene, p-tert-butylstyrene, p-fluorostyrene, p-chlorostyrene, p-bromostyrene.

7. The method for preparing a crystalline ethylene-styrene monomer random copolymer according to claim 1, characterized in that, the molar ratio of the bridged bis(cyclopentadienyl) rare earth metal compound, the organic borate salt, and the main group alkyl reagent is 1:(0.1 - 1.1):(1 - 1000); the molar ratio of the styrene monomer to the bridged bis(cyclopentadienyl) rare earth metal compound is (1000 - 100000):1; the polymerization temperature is 20 - 200 °C, and the time is 0.17 - 24 h.

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