Preparation method of vinyl ether polymer with high stereoregularity

Abstract

The invention relates to the technical field of polymer preparation, and discloses a preparation method of a high-stereoregularity vinyl ether polymer. According to the method, organic phosphoric acid and zirconium tetrachloride are subjected to concerted catalytic polymerization to prepare the high-stereoregularity vinyl ether polymer, and the specific method is as follows: in an inert gas protection atmosphere, one or more vinyl ether monomers are subjected to a reaction under the action of a selected organic phosphoric acid and zirconium chloride catalyst system, and the high-stereoregularity vinyl ether polymer is prepared. And carrying out cationic polymerization reaction at a certain temperature to obtain the alkenyl ether polymer with high stereoregularity. The method has the advantages that the dosage of the metal catalyst is small, the organic phosphoric acid can be recycled, a reaction solvent is not needed, and the vinyl ether polymer with controllable molecular weight, narrow distribution and high stereoregularity can be prepared.

Description

Technical Field

[0001] The invention relates to the technical field of polymer preparation, and in particular to a method for preparing high stereoregular vinyl ether polymers through catalytic polymerization. Background Art

[0002] Vinyl ether polymers (Polyvinyl ethers) are a class of polymers formed by the polymerization of vinyl ether monomers (RO-CH=CH2). Due to their unique chemical structure and physical properties, these polymers have broad application prospects in the fields of coatings, adhesives, medical materials, and electronic materials. However, the vinyl ether polymers prepared by traditional synthesis methods often have irregular molecular structures, resulting in the instability of their physical and chemical properties, which limits their application in high-performance fields. High stereoregularity means that the polymer chain has higher regularity, which usually leads to better material properties. For example, improving the crystallinity of the polymer and enhancing its mechanical strength, thermal stability, and chemical stability. This is of great significance for the manufacture of high-performance materials such as high-strength fibers and heat-resistant materials. By controlling the stereoregularity of the polymer, the properties of the polymer, such as glass transition temperature, melting point, etc., can be finely controlled to meet the needs of different application scenarios. For example, in biomedical materials, the mechanical properties and degradation rate of the material can be optimized by regulating the stereoregularity.

[0003] The methods for preparing high stereoregular vinyl ether polymers mainly consider the following points. The first is selective catalytic polymerization: using a catalyst system with high selectivity, such as a specific metallocene catalyst or a single-center metal catalyst, it is expected to stereoselectively polymerize the vinyl ether monomer. The second is ligand design: it is expected to control the stereoselectivity of the polymerization reaction by designing a specific ligand structure and regulating the steric hindrance and electronic effect of the catalyst. The last is the optimization of reaction conditions: exploring the effects of different reaction conditions (such as temperature, solvent, monomer concentration, etc.) on the stereoregularity of the polymer, and optimizing the reaction system to obtain a polymer with high regularity. However, in the traditional sense, cationic polymerization is characterized by rapid initiation and rapid propagation, resulting in significant heat release during the reaction. This phenomenon often makes the polymerization process uncontrollable, thus posing a challenge to achieving high stereoselectivity control in the cationic polymerization of vinyl ethers. For example, the previously reported methods of phenol titanium complexes and in-situ complexes of binaphthylphosphonic acid and titanium tetrachloride all require extremely low monomer concentrations and high catalyst loadings, limiting the application of highly isotactic polyvinyl ethers in industrial production. Relevant known journal literature reports on methods for preparing highly stereoregular vinyl ether polymers: Macromolecules 1999, 32, 6407; Journal Of Polymer Science Part a-Polymer Chemistry 2001, 39, 1060; Science 2019, 363, 1439; Journal Of the American Chemical Society 2021, 143, 16388; Polymer Chemistry 2020, 11, 3398; Polymer Chemistry 2024, 15, 1062; Journal Of the American Chemical Society 2022, 144, 679; Science China-Chemistry 2022, 65, 304; Chinese Journal Of Polymer Science 2024, 42, 711; Journal Of the American Chemical Society 2024, 146, 6449. Patent documents include CN114262399A and US20210324121A1. Despite this, it is still necessary and industrially practical to develop a bulk, low catalyst loading polymerization system. The development of a preparation method for highly stereoregular vinyl ether polymers not only helps to improve the application performance of vinyl ether polymers, but also promotes the development of catalytic chemistry and polymer synthesis technology.Developing new preparation methods, achieving fine control of material properties, and promoting the development and application of high-performance materials are of great practical significance. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a vinyl ether polymer with high stereoregularity in view of the shortcomings of the prior art. The stereoregularity of the polymer prepared by the method can often be higher than 85%.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A method for preparing a high stereoregular vinyl ether polymer comprises: in an inert gas protective atmosphere, adding organic phosphoric acid and zirconium tetrachloride to a reaction kettle in proportion and cooling them to a polymerization temperature, then adding one or more vinyl ether monomers cooled to the polymerization temperature in advance to the reaction kettle in proportion, stirring at the polymerization temperature, and causing cationic polymerization reaction for a certain period of time to obtain a high stereoregular vinyl ether polymer;

[0007] Polymerization reaction formula:

[0008]

[0009] The structural formula R is selected from C1~C 12 One or more of alkyl, cycloalkyl or -CH2CH2OY, wherein Y is C1~C 12 Alkyl, cycloalkyl or aryl or acetyl or arylformyl; the aryl may be phenyl or substituted phenyl, wherein the substituent may be C1-C6 alkyl or alkoxy;

[0010] The organophosphoric acid may be one or more selected from the following structural formulas: SPA1, TMSPA2, OSPA3 or LSPA4:

[0011]

[0012] In the above structure, R 1 1-4 and R 2 1-4 Respectively represent 4 independent substituent groups, namely R 1 1. R 1 2. R 1 3. R 1 4 and R 2 1. R 2 2. R 2 3. R 2 4. These substituents can be independently selected from hydrogen, chlorine, fluorine, C1-C4 alkyl or alkoxy; the organic phosphoric acid can be a racemate or an enantiomer;

[0013] Furthermore, the polymerization temperature is -78 to -20°C, preferably -78 to -60°C.

[0014] Furthermore, the molar ratio of the vinyl ether monomer, the organic phosphoric acid and the zirconium tetrachloride is 3500:(3-10):(0.01-1), preferably 3500:5:(0.1-1).

[0015] Furthermore,

[0016] The polymerization reaction time is controlled to be 10 minutes to 24 hours;

[0017] Furthermore, the inert gas is nitrogen or argon or a mixture of the two gases in any proportion.

[0018] Preferably, after the reaction is completed, the step of terminating and washing the obtained reaction mixture with an alkaline solution, dissolving the obtained polymer in an organic solvent, and then precipitating in methanol, filtering and vacuum drying is further included. The organic solvent may be dichloromethane or the like. In addition, the filtrate from all polymer purification processes may be collected, and the organic phosphoric acid may be recovered and reused therefrom. Specifically, after the reaction is completed and the polymer is obtained, all the filtrate used to purify the polymer may be collected, concentrated to dryness under reduced pressure, and then dissolved with a solvent such as ethyl acetate. After washing and acidification, the organic phase is dried with anhydrous magnesium sulfate, and then concentrated in vacuum, followed by purification by silica gel column chromatography. The organic phosphoric acid may be recovered after desolventizing to dryness, and the recovery rate may be as high as over 95%.

[0019] The possible principle of the method of the present invention is as follows: organic phosphoric acid and zirconium tetrachloride are continuously complexed in situ during the polymerization reaction, the acidity of phosphoric acid protons is enhanced to react with vinyl isobutyl ether to generate active cations to initiate polymerization, and the phosphoric acid anions interact with the active cations at the chain ends to achieve controllable polymerization, and further the large steric hindrance of organic phosphoric acid limits the directional insertion of monomers to achieve control of polymer stereoselectivity. The speed of complex formation will affect the control of polymer stereoselectivity.

[0020] The method of the present invention has the following advantages: less metal catalyst is used, organic phosphoric acid can be recycled, no polymerization solvent is required, and vinyl ether polymers with controllable molecular weight, narrow distribution and high stereoregularity can be prepared. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is the carbon spectrum of polyvinyl isobutyl ether 94% m. obtained using the organic phosphoric acid R-SPA-4 in Table 1;

[0022] Figure 2 is the TGA of polyvinyl isobutyl ether 94% m. obtained using the organic phosphoric acid R-SPA-4 in Table 1;

[0023] Figure 3 This is the DSC spectrum of polyvinyl isobutyl ether 94% m. obtained using the organic phosphoric acid R-SPA-4 in Table 1. DETAILED DESCRIPTION

[0024] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the preferred embodiments of the present invention are described in detail with the accompanying drawings. The specific implementation methods of the present invention are further described in detail below in conjunction with the accompanying drawings and embodiments. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention. Comparative examples are implemented to further illustrate the novelty, creativity and practicality of the method of the present invention.

[0025] In the following embodiments of the present invention, the nuclear magnetic proton spectrum ( 1 H NMR), carbon spectrum ( 13 C NMR) was measured by Bruker 400MHz NMR, with the sample to be tested dissolved in CDCl3 or CD2 Cl2 as solvent and tetramethylsilane (TMS) as internal standard; the relative molecular weight and molecular weight distribution of the polymer were measured by Waters 1515 series gel permeation chromatograph (GPC), using a differential refractive index detector Waters 2414 gel column HR 4THF (7.8×300mm) in series, and the molecular weight range of the column was 10 2 -10 6 g / mol, CHCl3 as mobile phase, flow rate of 1.0mL / min, manual GPC sample, measured at 40℃, molecular weight calculated based on Shodex polystyrene standard. Decomposition temperature of polymer (T d ) was measured using a TA Q50 instrument. The sample was heated from 40°C to 500°C at a rate of 10°C per minute in a nitrogen atmosphere. The temperature at which the mass loss reached 5% was considered to be T d The differential scanning calorimetry (DSC) measurements of the polymers were performed on a TA Q200 instrument with a heating / cooling rate of 10°C per minute. The samples were heated from -80°C to 180°C in a nitrogen atmosphere. The reported data are from the second heating cycle. According to a specific embodiment of the present invention, the general catalytic polymerization process of polyvinyl ether is generally as follows:

[0026] The polymerization reactions were carried out in 8 mL reaction bottles with septum caps, which were prepared in a glove box filled with nitrogen. A stir bar was added to a dried 8 mL reaction bottle with a septum cap, and solid ZrCl4 (0.0022 mmol) and organophosphoric acid (0.011 mmol) were added without stirring. Vinyl isobutyl ether monomer (7.7 mmol) was added to another separate 2 mL reaction bottle with a septum cap. Both reaction bottles were taken out of the glove box. The reaction bottle containing the catalyst was treated with ultrasound for one minute, then cooled to -78°C in a low temperature bath and allowed to stand for 30 minutes without stirring; the reaction bottle containing the vinyl isobutyl ether monomer was also cooled to -78°C in a low temperature bath and allowed to stand for 30 minutes. The vinyl isobutyl ether monomer was then transferred to the reaction bottle containing the catalyst via a syringe, and the reaction was stirred at -78°C at a speed of 600 rpm until the solution became too thick to continue stirring. Then, 5.0 mL of Et3N / MeOH solution (5% by volume) was added to terminate the polymerization reaction. After warming to room temperature, the reaction mixture was washed with 1N HCl and all volatiles were removed in vacuo. The crude polymer was dissolved in 5 mL of dichloromethane and poured into 100 mL of MeOH at 0°C to precipitate; this process was repeated twice. The purified polymer was dried in vacuo for at least 12 hours to constant weight. The yield was calculated by weighing.

[0027] In some other embodiments of the present invention, the vinyl ether monomer may be any of the following structures:

[0028]

[0029] Where R is selected from C1~C 12 One or more of alkyl, cycloalkyl or -CH2CH2OY, wherein Y is C1~C 12 Alkyl, cycloalkyl or aryl or acetyl or arylformyl; the aryl may be phenyl or substituted phenyl, wherein the substituent may be C1-C6 alkyl or alkoxy; the polymerization temperature may be any value between -78 and -20°C; the molar ratio of the vinyl ether monomer, the organic phosphoric acid and the zirconium tetrachloride may be any value between 3500:(3-10):(0.01-1).

[0030] Embodiment 1:

[0031] Table 1: Effects of different structures of organic phosphoric acid on the isotacticity of polyvinyl isobutyl ether

[0032]

[0033]

[0034] a The regularity of a polymer is determined by13 C NMR spectroscopy. b The polymer yield was determined gravimetrically. c Determined by GPC in CHCl3 and calibrated with polystyrene standards. NA means no reaction.

[0035] In the above table, the organophosphate number starts with R, indicating a right-handed optically active molecular structure, while rac-SPA-10 represents a racemic chiral organophosphate.

[0036] According to the general catalytic polymerization process of polyvinyl ether, the combination of organic phosphoric acid and zirconium tetrachloride with different structures is used. The comparison of the results in the above table shows that the organic phosphoric acid R-SPA-4 and rac-SPA-10 with a trifluoromethylphenyl side chain give polyvinyl isobutyl ether with a tacticity greater than 90%, which is unexpected. The carbon spectrum, TGA and DSC spectra of polyvinyl isobutyl ether with a tacticity of 94% m. obtained by using the organic phosphoric acid R-SPA-4 are as follows: Figure 1 , 2 , as shown in Figure 3.

[0037] Example 2

[0038] According to the general catalytic polymerization process of polyvinyl ether, organic phosphoric acids with different structures are used in combination with zirconium tetrachloride respectively, while other conditions remain unchanged. The organic phosphoric acids with the following structures TMSPA2-1, OSPA3-1 and LSPA4-1 and TMSPA2-2 are used instead, and the isotacticity of the corresponding polyvinyl isobutyl ether can be obtained to be 94%, 88%, 85% and 90% respectively.

[0039]

[0040] Example 3

[0041] According to the general catalytic polymerization process of polyvinyl ether, organophosphoric acid R-SPA-4 is used, zirconium tetrachloride is replaced by other metal Lewis acids, and other parameters remain unchanged. The reaction results are shown in Table 2 below, which shows that the type of metal Lewis acid has a huge impact on the reaction results, which is unexpected. Titanium tetrachloride, tin tetrachloride and ferric chloride are highly active and can catalyze polymerization, and even obtain polyvinyl isobutyl ether with a yield of 99%, but the isotacticity does not exceed 60%. Zinc chloride, titanium tetrachloride tetrahydrofuran complex, zirconocene chloride, etc. are ineffective for this reaction and will not initiate the polymerization process.

[0042] Table 2: Effect of metal Lewis acid on the isotacticity of polyvinyl isobutyl ether

[0043]

[0044] Example 4

[0045] According to the general catalytic polymerization process of polyvinyl ether, a combination of organic phosphoric acid R-SPA-4 and zirconium tetrachloride is used, but the reaction temperature is -60°C, and other conditions remain unchanged, and the corresponding polyvinyl isobutyl ether with an isotacticity of 90% can be obtained.

[0046] Example 5

[0047] According to the general catalytic polymerization process of polyvinyl ether, a combination of organic phosphoric acid R-SPA-4 and zirconium tetrachloride is used, but the ratio between the two is changed, that is, solid ZrCl4 (0.0022mmol) and different ratios of organic phosphoric acid and vinyl isobutyl ether monomer (7.7mmol) are used, and other conditions remain unchanged. As can be seen from Table 3, the ratio of organic phosphoric acid R-SPA-4 and zirconium tetrachloride affects the isotacticity of the corresponding polyvinyl isobutyl ether. Only when the ratio of organic phosphoric acid R-SPA-4 and zirconium tetrachloride is above 3:1, can an isotacticity greater than 90% be obtained.

[0048] Table 3: Effect of the ratio of organophosphate R-SPA-4 and zirconium tetrachloride on the isotacticity of polyvinyl isobutyl ether

[0049]

[0050] Example 6

[0051] The recovery of organic phosphoric acid was investigated. According to the general catalytic polymerization process of polyvinyl ether, a combination of organic phosphoric acid R-SPA-4 and zirconium tetrachloride was used. After the reaction was completed and the polymer was obtained, all the filtrates used to purify the polymer were collected, concentrated to dryness under reduced pressure, and then dissolved with 20 ml of ethyl acetate, washed and acidified three times with 4M HCl. The organic phase was dried with anhydrous magnesium sulfate, then concentrated in vacuo, and then purified by silica gel column chromatography (mobile phase n-hexane: ethyl acetate = volume ratio 1:2). After desolventizing to dryness, 98% of organic phosphoric acid R-SPA-4 can be recovered.

Claims

1. A method for preparing a high stereoregularity vinyl ether polymer, characterized in that: Methods include: In an inert gas atmosphere, organic phosphoric acid and zirconium tetrachloride are added to a reaction kettle in proportion and cooled to a polymerization temperature, and then one or more vinyl ether monomers cooled to a polymerization temperature in advance are added to the reaction kettle in proportion, and the polymerization temperature is maintained and stirred to allow a cationic polymerization reaction to occur for a certain period of time, thereby obtaining a vinyl ether polymer with high stereoregularity; Polymerization reaction formula: The structural formula R is selected from C1~C 12 One or more of alkyl, cycloalkyl or -CH2CH2OY, wherein Y is C1~C 12 Alkyl, cycloalkyl or aryl or acetyl or arylformyl; the aryl is selected from phenyl, substituted phenyl, wherein the substituent is C1-C6 alkyl or alkoxy; The organophosphoric acid is selected from one or more of the following structural formulas: SPA1, TMSPA2, OSPA3 or LSPA4: In the above structure, R 1 1-4 and R 2 1-4 Respectively represent 4 independent substituent groups, namely R 1 1. R 1 2. R 1 3. R 1 4 and R 2 1. R 2 2. R 2 3. R 2 4. The substituents are independently selected from hydrogen, chlorine, fluorine, C1-C4 alkyl or alkoxy; the organic phosphoric acid may be a racemate or an enantiomer.

2. The method for preparing a high stereoregularity vinyl ether polymer according to claim 1, characterized in that: The polymerization temperature is -78 to -20°C, preferably -78 to -60°C.

3. The method for preparing a high stereoregularity vinyl ether polymer according to claim 1, characterized in that: The molar ratio of the vinyl ether monomer, the organic phosphoric acid and the zirconium tetrachloride is 3500:(3-10):(0.01-1), preferably 3500:5:(0.1-1).

4. The method for preparing a high stereoregularity vinyl ether polymer according to claim 1, characterized in that: The polymerization reaction time is controlled to be 10 minutes to 24 hours.

5. The method for preparing a high stereoregularity vinyl ether polymer according to claim 1, characterized in that: The inert gas is nitrogen or argon or a mixture of the two gases in any proportion.

6. The method for preparing a high stereoregularity vinyl ether polymer according to claim 1, characterized in that: After the reaction is completed and the polymer is obtained, all the filtrates used to purify the polymer are collected, concentrated to dryness under reduced pressure, and then dissolved with a solvent. After washing and acidification, the organic phase is dried over anhydrous magnesium sulfate and then concentrated in vacuo, followed by purification by silica gel column chromatography, and the organic phosphoric acid can be recovered by desolventizing to dryness.

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