A method for preparing a vinyl ether polymer with high stereoregularity

Abstract

The present invention relates to the technical field of polymer preparation and discloses a method for preparing a highly stereoregular vinyl ether polymer. This method utilizes the synergistic catalytic polymerization of organophosphoric acid and zirconium tetrachloride to prepare a highly stereoregular vinyl ether polymer. Specifically, in an inert gas atmosphere, one or more vinyl ether monomers undergo cationic polymerization at a specific temperature under the action of a selected organophosphoric acid and zirconium chloride catalyst system to obtain a highly stereoregular vinyl ether polymer. Advantages of this method include: low metal catalyst usage, recyclable organophosphoric acid, no need for a reaction solvent, and the ability to produce a highly stereoregular vinyl ether polymer with a controllable molecular weight and narrow molecular weight distribution.

Description

Technical Field

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

[0002] Vinyl ether polymers (PVEs) 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 hold broad application prospects in coatings, adhesives, medical materials, and electronic materials. However, conventional synthetic methods often produce PVEs with irregular molecular structures, resulting in unstable physical and chemical properties, limiting their application in high-performance applications. High stereoregularity, meaning greater regularity in the polymer chain, generally leads to superior material properties. For example, increasing the crystallinity of a polymer enhances its mechanical strength, thermal stability, and chemical stability. This is crucial for the manufacture of high-performance materials such as high-strength fibers and heat-resistant materials. By controlling the stereoregularity of a polymer, its properties, such as glass transition temperature and melting point, can be finely tuned to meet the needs of diverse applications. For example, in biomedical materials, mechanical properties and degradation rates can be optimized by manipulating stereoregularity.

[0003] The preparation of highly stereoregular vinyl ether polymers primarily involves the following considerations. First, selective catalytic polymerization: Using highly selective catalyst systems, such as specific metallocene catalysts or single-site metal catalysts, one aims to achieve stereoselective polymerization of vinyl ether monomers. Second, ligand design: By designing specific ligand structures, one aims to manipulate the steric hindrance and electronic effects of the catalyst, thereby controlling the stereoselectivity of the polymerization reaction. Finally, reaction condition optimization: The effects of various reaction conditions (such as temperature, solvent, and monomer concentration) on polymer stereoregularity are explored to optimize the reaction system for obtaining highly stereoregular polymers. However, cationic polymerization is traditionally characterized by rapid initiation and propagation, resulting in significant heat release during the reaction. This phenomenon often renders the polymerization process uncontrollable, posing a challenge to achieving high stereoselectivity during cationic polymerization of vinyl ethers. For example, previously reported methods using titanium phenolate complexes and in situ complexes of binaphthylphosphonic acid and titanium tetrachloride require extremely low monomer concentrations and high catalyst loadings, limiting the industrial application of highly stereoregular vinyl ethers. 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 PolymerScience 2024, 42, 711; Journal Of the American Chemical Society 2024, 146, 6449. Patent documents include CN114262399A and US20210324121A1. Despite this, the development of bulk, low-catalyst-loaded polymerization systems remains necessary and industrially practical. The development of methods for preparing highly stereoregular vinyl ether polymers not only helps 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 address the deficiencies of the prior art and provide a method for preparing a vinyl ether polymer with high stereoregularity. The stereoregularity of the polymer prepared by this method can often be higher than 85%.

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

[0006] A method for preparing a high-stereoregularity vinyl ether polymer comprises: in an inert gas atmosphere, adding organic phosphoric acid and zirconium tetrachloride in proportion to a reactor and cooling the mixture to a polymerization temperature; then adding one or more vinyl ether monomers cooled to the polymerization temperature in advance to the reactor in proportion; maintaining the polymerization temperature while stirring and allowing cationic polymerization to occur for a predetermined period of time, thereby obtaining a high-stereoregularity vinyl ether polymer;

[0007] Polymerization reaction formula:

[0008]

[0009] Wherein 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 Represent 4 independent substituent groups, respectively 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 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] Further,

[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 these two gases in any proportion.

[0018] Preferably, after the reaction is complete, the step of terminating the obtained reaction mixture with an alkaline solution and washing it, dissolving the obtained polymer in an organic solvent, and then precipitating it in methanol, filtering it, and drying it in a vacuum oven is further performed. 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 for polymer purification is 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 over anhydrous magnesium sulfate, then concentrated in a vacuum oven, and then purified by silica gel column chromatography. The organic phosphoric acid can be recovered by desolvation to dryness, and the recovery rate can be as high as over 95%.

[0019] The method of the present invention may work as follows: Organophosphoric acid and zirconium tetrachloride continuously form an in-situ complex during the polymerization reaction, enhancing the acidity of the phosphoric acid protons, which react with vinyl isobutyl ether to form active cations that initiate polymerization. The phosphate anions interact with the active cations at the chain ends, enabling controlled polymerization. Furthermore, the large steric hindrance of the organophosphoric acid limits the directional insertion of monomers, enabling control of the polymer stereoselectivity. The rate of complex formation influences the control of polymer stereoselectivity.

[0020] The advantages of the method of the present invention are: low metal catalyst usage, recyclable organic phosphoric acid, no need for polymerization solvent, and the ability to prepare vinyl ether polymers with controllable molecular weight, narrow distribution and high stereoregularity. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0022] Figure 2 This is the TGA of polyvinyl isobutyl ether 94% m. obtained using the organophosphoric 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 to implement it according to the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. The specific embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings and examples. 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 spectrum ( 1 H NMR), carbon spectrum ( 13 C NMR was measured using a Bruker 400 MHz nuclear magnetic resonance spectrometer, with the sample dissolved in CDCl3 or CD2 Cl2 as the solvent and tetramethylsilane (TMS) as the internal standard. The relative molecular weight and molecular weight distribution of the polymers were determined using a Waters 1515 series gel permeation chromatograph (GPC) using a differential refractive index detector and a Waters 2414 gel column HR 4THF (7.8 × 300 mm) in series. The molecular weight range of the column was 10 2 -10 6 g / mol, CHCl3 was used as the mobile phase at a flow rate of 1.0 mL / min, and the GPC sample was manually introduced and measured at 40°C. The molecular weight was calculated using Shodex polystyrene as the standard. The decomposition temperature of the 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 Differential scanning calorimetry (DSC) measurements of the polymers were performed on a TA Q200 instrument at a heating / cooling rate of 10°C per minute. The samples were heated from -80°C to 180°C under a nitrogen atmosphere. The reported data are from the second heating cycle. According to one embodiment of the present invention, a general catalytic polymerization reaction process for polyvinyl ether is generally as follows:

[0026] Polymerization reactions were performed in 8 mL septum-capped reaction vials, which were prepared in a nitrogen-filled glove box. A stir bar was placed in one oven-dried 8 mL septum-capped reaction vial, followed by the addition of solid ZrCl₄ (0.0022 mmol) and organophosphoric acid (0.011 mmol) without stirring. A separate 2 mL septum-capped reaction vial was charged with vinyl isobutyl ether monomer (7.7 mmol). Both reaction vials were removed from the glove box. The reaction vial containing the catalyst was ultrasonicated for one minute, then cooled to -78°C in a cryogenic bath and allowed to stand for 30 minutes without stirring. The reaction vial containing the vinyl isobutyl ether monomer was also cooled to -78°C in a cryogenic bath and allowed to stand for 30 minutes. The vinyl isobutyl ether monomer was then transferred to the reaction vial containing the catalyst via syringe, and the reaction was stirred at -78°C at 600 rpm until the solution became too thick to continue stirring. The polymerization reaction was then terminated by the addition of 5.0 mL of a 5% by volume Et₃N / MeOH solution. 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 0°C MeOH to precipitate; this process was repeated twice. The resulting purified polymer was dried in vacuo for at least 12 hours to a constant weight. The yield was calculated gravimetrically.

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

[0028]

[0029] Wherein 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 group can be phenyl or substituted phenyl, wherein the substituent can be C1-C6 alkyl or alkoxy; the polymerization temperature can be any value between -78 and -20°C; the molar ratio of vinyl ether monomer, organic phosphoric acid and zirconium tetrachloride can be any value between 3500:(3-10):(0.01-1).

[0030] Example 1:

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

[0032]

[0033]

[0034] a The regularity of the polymer is determined by13 C NMR spectroscopy determination. b Polymer yields were 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 begins with R, indicating a right-handed optically active molecular structure, while rac-SPA-10 represents a racemic chiral organophosphate.

[0036] Following the general catalytic polymerization process for polyvinyl ether, using combinations of organophosphoric acids with different structures and zirconium tetrachloride, a comparison of the results in the table above shows that the organophosphoric acids R-SPA-4 and rac-SPA-10, each with a trifluoromethylphenyl side chain, unexpectedly yield polyvinyl isobutyl ether with a 94% m / s isotacticity. The carbon, TGA, and DSC spectra of the polyvinyl isobutyl ether obtained using the organophosphoric acid R-SPA-4 are shown in Table 1. Figure 1 、 2 , as shown in 3.

[0037] Example 2

[0038] According to the general catalytic polymerization reaction process of polyvinyl ether, different organic phosphoric acids with different structures are combined with zirconium tetrachloride, and other conditions remain unchanged. Instead, the organic phosphoric acids with the following structures TMSPA2-1, OSPA3-1 and LSPA4-1 and TMSPA2-2 are used to obtain the corresponding polyvinyl isobutyl ethers with isotacticities of 94%, 88%, 85% and 90%, respectively.

[0039]

[0040] Example 3

[0041] Following the typical catalytic polymerization process for polyvinyl ether, using the organophosphoric acid R-SPA-4, the zirconium tetrachloride was replaced with another metal Lewis acid, with all other parameters remaining unchanged. The reaction results, as shown in Table 2 below, demonstrate the surprising impact of the type of metal Lewis acid on the reaction outcome. While titanium tetrachloride, tin tetrachloride, and ferric chloride are highly active and can catalyze polymerization, even yielding polyvinyl isobutyl ether in a 99% yield, their isotacticity does not exceed 60%. Zinc chloride, titanium tetrachloride in tetrahydrofuran, and zirconocene chloride are ineffective in this reaction and fail to initiate polymerization.

[0042] Table 2: Effect of metal Lewis acids 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, the corresponding polyvinyl isobutyl ether with an isotacticity of 90% can be obtained.

[0046] Example 5

[0047] Following the standard catalytic polymerization process for polyvinyl ether, a combination of organophosphate R-SPA-4 and zirconium tetrachloride was employed, but the ratio between the two was varied. Specifically, solid ZrCl4 (0.0022 mmol) was used with varying ratios of organophosphate and vinyl isobutyl ether monomer (7.7 mmol), while other conditions remained unchanged. Table 3 shows that the ratio of organophosphate R-SPA-4 to zirconium tetrachloride affects the isotacticity of the resulting polyvinyl isobutyl ether. An isotacticity exceeding 90% was achieved only when the ratio of organophosphate R-SPA-4 to zirconium tetrachloride was above 3:1.

[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 organophosphoric acid was investigated. Following the standard catalytic polymerization process for polyvinyl ether, a combination of organophosphoric acid R-SPA-4 and zirconium tetrachloride was employed. After the reaction was completed and the polymer was obtained, all filtrates used for polymer purification were collected and concentrated to dryness under reduced pressure. The filtrate was then dissolved in 20 ml of ethyl acetate, washed and acidified three times with 4M HCl, and the organic phase was dried over anhydrous magnesium sulfate and concentrated in vacuo. Purification followed by silica gel column chromatography (mobile phase: n-hexane:ethyl acetate = 1:2 by volume). After desolventizing to dryness, 98% of the organophosphoric acid R-SPA-4 was recovered.

Claims

1. A method for preparing a highly stereoregular vinyl ether polymer, characterized in that: Methods include: In an inert gas atmosphere, organic phosphoric acid and zirconium tetrachloride are added to a reactor in proportion and cooled to a polymerization temperature. Then, one or more vinyl ether monomers, which have been cooled to the polymerization temperature in advance, are added to the reactor in proportion. The polymerization temperature is maintained with stirring, and cationic polymerization occurs for a predetermined time to obtain a highly stereoregular vinyl ether polymer. The molar ratio of the vinyl ether monomer, organic phosphoric acid, and zirconium tetrachloride is 3500:(3-10):(0.01-1). Polymerization reaction formula: ， wherein the structural formula R is selected from one or more of C1-C12 alkyl, cycloalkyl or -CH2CH2OY, wherein Y is C1-C12 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 represent 4 independent substituent groups, respectively 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 are independently selected from hydrogen, chlorine, fluorine, C1-C4 alkyl or alkoxy; and the organic phosphoric acid is a racemate or enantiomer.

2. The method for preparing a highly stereoregular vinyl ether polymer according to claim 1, wherein: The polymerization temperature is -78 to -20°C.

3. The method for preparing a highly stereoregular vinyl ether polymer according to claim 1, wherein: The polymerization temperature is -78 to -60°C.

4. The method for preparing a highly stereoregular vinyl ether polymer according to claim 1, wherein: The molar ratio of the vinyl ether monomer, the organic phosphoric acid and the zirconium tetrachloride is 3500:5:(0.1-1).

5. The method for preparing a highly stereoregular vinyl ether polymer according to claim 1, wherein: The polymerization reaction time is controlled to be 10 minutes to 24 hours.

6. The method for preparing a highly stereoregular vinyl ether polymer according to claim 1, wherein: The inert gas is nitrogen or argon or a mixture of the two gases in any proportion.

7. The method for preparing a highly stereoregular vinyl ether polymer according to claim 1, wherein: 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. Then, it is purified by silica gel column chromatography and desolventized to dryness to recover the organic phosphoric acid.

Images