Method for preparing syndiotactic polystyrene through transition metal catalysis

Abstract

The invention discloses a method for preparing syndiotactic polystyrene through transition metal catalysis. According to the method, an aryl ether-transition metal chromium compound is adopted to catalyze styrene to polymerize so as to prepare syndiotactic polystyrene. According to the preparation method of the compound, an aryl ether compound reacts with tetrahydrofuran chromium trichloride to obtain a chromium complex, then the chromium complex and aluminum alkyl form a catalytic system, bulk polymerization is performed in styrene to obtain syndiotactic polystyrene, and the syndiotactic polystyrene has the advantages of good stereoselectivity and high activity.

Description

Technical Field

[0001] This invention relates to a method for preparing syndiotactic polystyrene using transition metal catalysis. Background Technology

[0002] Syntactic polystyrene (SPS) is a novel thermoplastic engineering plastic. Due to controlled stereoregularity, its molecular chains have uniformly spaced side-chain benzene rings, resulting in significantly improved properties compared to ordinary polystyrene. It possesses superior properties unlike those of general polystyrene, including a high melting point, rapid crystallization, high elastic modulus, excellent electrical properties, and good chemical resistance. These superior properties make it a promising candidate for applications in the automotive, electronics, and industrial packaging industries.

[0003] Since Ishihara from Japan first synthesized syndiotactic polystyrene using a metallocene catalyst in 1986, significant progress has been made in the synthesis of metallocene catalysts and their application in the syndiotactic polymerization of styrene. Titanium-based catalysts, due to their unique structure and properties, exhibit high activity in styrene polymerization and produce products with high syndiotacticity, thus gaining widespread attention and application in this field.

[0004] In the field of chromium-based catalysts, a large number of patents focus on ethylene polymerization and ethylene oligomerization. US5856257 uses a chromium-based catalyst to catalyze the selective trimerization of ethylene. CN1025581074A prepares a chromium-based catalyst for the production of 1-hexene. CN102107146B describes a catalyst composed of a P and N-containing compound, an electron donor, a chromium compound, a support, and a promoter, used for the catalytic trimerization of ethylene to hexene-1 with high activity and high selectivity. CN107597191B relates to a catalyst for the trimerization of ethylene to 1-hexene, comprising a bisphosphine ligand with a biphenyl or binaphthalene skeleton, a chromium compound, and an activator. CN102407159B provides a chromium coordination complex containing a multidentate mixed heteroatom ligand as an ethylene trimerization catalyst. CN 114225968A uses chromium isooctanoate, chromium acetylacetone, and / or tetrahydrofuran chromium chloride as an ethylene trimerization catalyst. Several patents have also been reported on the preparation of syndiotactic polystyrene using metallocene catalysts. In 1986, Ishihara reported the preparation of syndiotactic polystyrene using a catalytic system formed by CpTiCl3 and the co-catalyst MAO (EP210615). CN 103030721B provides a polymerization method for preparing syndiotactic polystyrene, in which the reaction is carried out under the catalysis of a monometallocene compound main catalyst with sulfur-containing ligands and a methylaluminoxane co-catalyst. CN107903346B invented a method for preparing syndiotactic polystyrene using a binuclear rare earth catalyst. This catalyst contains the general formula [(R2LnLLnR2)(S)]. n A trivalent dinuclear rare earth complex of [ ]; wherein, L is a cyclopentadienyl derivative, indenyl, indenyl derivative, fluorenyl, fluorenyl derivative or amidyl derivative bridged with ferrocene; Ln is a rare earth metal; R is an alkyl, amino or halogen group connected to a rare earth metal; S is selected from diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether or tetramethylethylenediamine. CN 110343199 uses styrene as a monomer, a metallocene zirconium compound as the main catalyst, a mixture of methylaluminoxane (MAO) and triethylaluminum as a cocatalyst, and isopentane as a heat remover, at atmospheric pressure and a temperature of 110-130℃, for a reaction time of 0.5-2h; to obtain syndiotactic polystyrene with a molecular weight distribution of 5-10. CN117126315A provides a catalyst for catalyzing syndiotactic polystyrene, comprising a rare earth complex having the structure shown in Formula I. This invention provides a catalyst combination for catalyzing the polymerization of styrene, which can achieve highly active and highly syndiotactic polymerization of styrene. The monomer conversion rate can reach up to 100%. The number-average molecular weight of the prepared syndiotactic polystyrene is adjustable between 84,000 and 935,000 depending on the molar ratio of styrene monomer to catalyst. The molecular weight distribution is narrow, with a minimum of 1.21. The melting point is in the range of 266-273℃. The catalyst has good adaptability in the polymerization temperature range of -20-60℃.

[0005] Most existing syndiotactic polymerization catalyst systems for styrene are metallocene complexes. While transition metal chromium compounds are a research hotspot in the field of ethylene oligomerization, there are few reports on their use in styrene syndiotactic polymerization. For styrene syndiotactic polymerization catalytic systems, activity, syndiotacticity, and molecular weight are key factors in evaluating the advancement of this technology. Summary of the Invention

[0006] Based on the above background, this invention provides a catalytic system for the highly active and selective preparation of 1-hexene from ethylene trimerization. This catalytic system utilizes an aryl ether-transition metal chromium-PNP complex in conjunction with alkyl aluminum to catalyze the trimerization of ethylene to 1-hexene, effectively improving catalytic activity and resulting in a high 1-hexene content in the oligomerization product.

[0007] The aryl ether-transition metal chromium complex used in this catalytic system has the structure shown in formula (1).

[0008]

[0009] In formula (1), R is an alkyl group such as methyl, ethyl, propyl, n-butyl, tert-butyl, etc. R′ is an alkyl group such as methyl, ethyl, propyl, n-butyl, tert-butyl, etc., or a halogen group such as F, Cl, Br, I, etc.

[0010] The molar ratio of chromium alkyl aluminum auxiliaries in this catalytic system is 1:100-1000, preferably 1:500.

[0011] In the catalyst system, the components aryl ether-transition metal chromium compound and alkyl aluminum can be pre-mixed before being added to the reaction system, or they can be added directly to the reaction system in batches.

[0012] The catalytic trimerization of ethylene in this system proceeds as follows: Before the reaction, the reactor is heated to 180°C. Within one hour, a vacuum is applied three times followed by nitrogen replenishment. Then, the temperature is lowered to a predetermined level, and the reactor is evacuated twice while maintaining an ethylene environment. Styrene is added, and the stirrer is turned on. Once the temperature is constant, alkylaluminum auxiliaries and chromium compounds are added. Alternatively, the alkylaluminum auxiliaries and chromium compounds can be pre-mixed and added all at once. The syndiotactic polymerization of styrene is carried out at a specific temperature. After a certain reaction time, the temperature is lowered to room temperature, and the reaction is terminated with 5% acidified ethanol. The product is filtered and washed several times alternately with alcohol and water. It is then vacuum dried at 80°C to constant weight, weighed, and the polymerization activity is calculated. The syndiotacticity is calculated after extraction using a Soxhlet extractor.

[0013] More specifically, in the method of the present invention, the solvent for dissolving the catalyst is one or a mixture of two or more of toluene, hexane, cyclohexane, and methylcyclohexane, preferably toluene; the reaction temperature range is 50-70°C, preferably 50-60°C; and the reaction time is 6-60 min, preferably 10-60 min.

[0014] More specifically, the alkyl aluminum promoter used in this catalytic system is triethylaluminum, trimethylaluminum, or triisobutylaluminum, preferably triisobutylaluminum.

[0015] Compared with the prior art, the advantages and positive effects of the present invention are:

[0016] (1) In this invention, the CO bond in the aryl ether-transition metal chromium compound has a mild stabilizing effect on the chromium ion at the metal center. The active center of the catalyst is well-defined, and the ligand environment around the central metal can be adjusted by changing the ligand. The stereostructure, molecular weight and molecular weight distribution of polystyrene are controllable.

[0017] (2) The alkyl aluminum used in this invention is isobutyl aluminum, which avoids the use of expensive alkylaluminoxane and reduces application costs. Detailed Implementation

[0018] The present invention will be further described in detail below through specific embodiments. The following embodiments are merely descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0019] Example 1

[0020] 1.8 g NaH, 125 mL THF, and 36 mL LDMMF were added to a 500 mL flask and stirred to form a gray suspension of NaH. 49.7 mmol of 2-bromo-4-methylbenzyl alcohol was slowly added dropwise, and after reacting for 2 h, 14.2 g CH3I was added dropwise, and the reaction was continued for 12 h. The mixture was extracted with diethyl ether and distilled. It was then reacted with 0.21 g magnesium powder for 2 h. At 0 °C, 50 mL of a 0.792 g CrCl3(THF)3THF solution was added dropwise, followed by 1.2 mL of 1,4-dioxane. The reaction was continued for 20 h to obtain the yellow product Cr(o-(CH3OC6H4-CH3)3(Cr-1).

[0021] Example 2

[0022] 1.8 g NaH, 125 mL THF, and 36 mL LDMMF were added to a 500 mL flask and stirred to form a gray suspension of NaH. 49.7 mmol o-bromobenzyl alcohol was slowly added dropwise, and after reacting for 2 h, 14.2 g CH3I was added dropwise, and the reaction was continued for 12 h. The mixture was extracted with diethyl ether and distilled. It was then reacted with 0.21 g magnesium powder for 2 h. At 0 °C, 50 mL of a 0.792 g CrCl3(THF)3THF solution was added dropwise, followed by 1.2 mL of 1,4-dioxane. The reaction was continued for 20 h to obtain the yellow product Cr(o-(CH3OCH2-C6H4)3(Cr-2).

[0023] Example 3

[0024] 1.8 g NaH, 125 mL THF, and 36 mL LDMMF were added to a 500 mL flask and stirred to form a gray suspension of NaH. 49.7 mmol o-bromobenzyl alcohol was slowly added dropwise, and after reacting for 2 h, 50 mmol CH3CH2I was added dropwise, and the reaction was continued for 12 h. The mixture was extracted with diethyl ether and distilled. It was then reacted with 0.21 g magnesium powder for 2 h. 50 mL of a 0.792 g CrCl3(THF)3THF solution was added dropwise at 0 °C, followed by 1.2 mL of 1,4-dioxane. The reaction was continued for 20 h to obtain the red product Cr(o-(CH3CH2OCH2-C6H4)3(Cr-3).

[0025] Example 4

[0026] A dry 250ml reactor equipped with a magnetic stirrer was purged with nitrogen three times. The oil bath was heated to 50°C, and 100ml of styrene and 0.5mmol of triisobutylaluminum were added. Stirring was started, and 1μmol of chromium compound catalyst Cr-1 was added to initiate styrene polymerization. The reaction was terminated with 5% acidified ethanol after 30 minutes. The product was filtered and washed several times alternately with alcohol and water, then dried under vacuum at 80°C to constant weight. The product was weighed, and the polymerization activity was calculated. The syndiotacticity was calculated after extraction using a Soxhlet extractor. Catalytic activity and syndiotacticity are shown in Table 1.

[0027] Example 5

[0028] A dry 250ml reactor equipped with a magnetic stirrer was purged with nitrogen three times. The oil bath was heated to 50°C, and 100ml of styrene and 0.5mmol of triisobutylaluminum were added. Stirring was started, and 1μmol of chromium compound catalyst Cr-2 was added to initiate styrene polymerization. The reaction was terminated with 5% acidified ethanol after 30 minutes. The product was filtered and washed several times alternately with alcohol and water, dried under vacuum at 80°C to constant weight, weighed, and the polymerization activity was calculated. The syndiotacticity was calculated after extraction using a Soxhlet extractor. Catalytic activity and syndiotacticity are shown in Table 1.

[0029] Example 6

[0030] A dry 250ml reactor equipped with a magnetic stirrer was purged with nitrogen three times. The oil bath was heated to 50°C, and 100ml of styrene and 0.5mmol of triisobutylaluminum were added. Stirring was started, and 1μmol of chromium compound catalyst Cr-3 was added to initiate styrene polymerization. The reaction was terminated with 5% acidified ethanol after 30 minutes. The product was filtered and washed several times alternately with alcohol and water, then dried under vacuum at 80°C to constant weight. The product was weighed, and the polymerization activity was calculated. The syndiotacticity was calculated after extraction using a Soxhlet extractor. Catalytic activity and syndiotacticity are shown in Table 1.

[0031] Example 7

[0032] A dry 250ml reactor equipped with a magnetic stirrer was purged with nitrogen three times. The oil bath was heated to 50°C, and 100ml of styrene and 1mmol of triisobutylaluminum were added. Stirring was started, and 1μmol of chromium compound catalyst Cr-1 was added to initiate styrene polymerization. The reaction was terminated with 5% acidified ethanol after 30 minutes. The product was filtered and washed several times alternately with alcohol and water, then dried under vacuum at 80°C to constant weight. The product was weighed, and the polymerization activity was calculated. The syndiotacticity was calculated after extraction using a Soxhlet extractor. Catalytic activity and syndiotacticity are shown in Table 1.

[0033] Example 8

[0034] A dry 250ml reactor equipped with a magnetic stirrer was purged with nitrogen three times. The oil bath was heated to 50°C, and 100ml of styrene and 1mmol of triisobutylaluminum were added. Stirring was started, and 1μmol of chromium compound catalyst Cr-2 was added to initiate styrene polymerization. The reaction was terminated with 5% acidified ethanol after 30 minutes. The product was filtered and washed several times alternately with alcohol and water, dried under vacuum at 80°C to constant weight, weighed, and the polymerization activity was calculated. The syndiotacticity was calculated after extraction using a Soxhlet extractor. Catalytic activity and syndiotacticity are shown in Table 1.

[0035] Example 9

[0036] A dry 250ml reactor equipped with a magnetic stirrer was purged with nitrogen three times. The oil bath was heated to 50°C, and 100ml of styrene and 1mmol of triisobutylaluminum were added. Stirring was started, and 1μmol of chromium compound catalyst Cr-3 was added to initiate styrene polymerization. The reaction was terminated with 5% acidified ethanol after 30 minutes. The product was filtered and washed several times alternately with alcohol and water, then dried under vacuum at 80°C to constant weight. The product was weighed, and the polymerization activity was calculated. The syndiotacticity was calculated after extraction using a Soxhlet extractor. Catalytic activity and syndiotacticity are shown in Table 1.

[0037] Example 10

[0038] A dry 250ml reactor equipped with a magnetic stirrer was purged with nitrogen three times. The oil bath was heated to 50°C, and 100ml of styrene and 0.1mmol of triisobutylaluminum were added. Stirring was started, and 1μmol of chromium compound catalyst Cr-1 was added to initiate styrene polymerization. The reaction was terminated with 5% acidified ethanol after 30 minutes. The product was filtered and washed several times alternately with alcohol and water, dried under vacuum at 80°C to constant weight, weighed, and the polymerization activity was calculated. The syndiotacticity was calculated after extraction using a Soxhlet extractor. Catalytic activity and syndiotacticity are shown in Table 1.

[0039] Table 1 Catalytic performance of syndiotactic polymerization of styrene

[0040]

[0041] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several modifications and improvements can be made without departing from the inventive concept, and these all fall within the protection scope of the present invention.

Claims

1. A method for preparing syndiotactic polystyrene by catalyzing polymerization of styrene with aryl ether-transition metal chromium compound.

2. The transition metal chromium compound as claimed in claim 1 has the structure shown in formula (1). In the formula, R is methyl, ethyl, propyl, n-butyl, t-butyl and the like alkyl group. R' is methyl, ethyl, propyl, n-butyl, t-butyl and the like alkyl group or F, Cl, Br, I and the like halogen group.

3. The catalytic system of claim 1, characterized in that, A solution is prepared with an inert solvent such as toluene, styrene is added in the presence of alkyl aluminum and reacted at 50-70°C for 0.1-1 hour to obtain syndiotactic polystyrene.

4. The polystyrene of claim 1, characterized by The content of syndiotactic polystyrene component is more than 90%.

5. The catalytic system for the polymerization of styrene according to claim 1, characterized in that, The molar ratio of the chromium compound to the alkyl aluminum promoter is 1:100-1000.

6. The alkyl aluminum promoter as claimed in claim 3 is triethyl aluminum, trimethyl aluminum, triisobutyl aluminum.

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