A vinyl alcohol-vinyl acetate-vinyl medium alkyl carboxylate copolymer and a method for preparing the same

Abstract

This invention discloses an ethylene alcohol-vinyl acetate-medium-long alkyl carboxylic acid vinyl ester copolymer and its preparation method, belonging to the technical field of preparation of copolymers containing ethylene alcohol structural units. The copolymer has a number average molecular weight of 5,000 to 500,000 and is composed of ethylene alcohol-based structural units (a), vinyl acetate-based structural units (b), and medium-long alkyl carboxylic acid vinyl ester-based structural units (c). The preparation method provided by this invention has mild reaction conditions, simple operation, and is easy to industrialize.

Description

Technical Field

[0001] This invention belongs to the field of preparation technology of copolymers containing ethylene alcohol structural units, and particularly relates to an ethylene alcohol-vinyl acetate-medium-long alkyl carboxylic acid ethylene ester copolymer and its preparation method. Background Technology

[0002] Copolymers containing vinyl alcohol structural units are widely used in coatings and adhesives, polyurethane polyols, and hydrophilic modifiers. For example, water-soluble polyvinyl alcohol (PVA), prepared by polymerization and subsequent hydrolysis of vinyl acetate (VAc) monomers, is often used as a dispersant. Ethylene-vinyl alcohol copolymers (EVOH), prepared from ethylene and VAc copolymers, are widely used in food, cosmetics, and pharmaceutical packaging. In recent years, EVOH has regained interest due to its great potential in protein separation, drug release, and battery separators.

[0003] Generally, the production of EVOH involves two steps: 1. Free radical polymerization to synthesize ethylene-vinyl acetate copolymer (EVA); 2. High-temperature alcoholysis of EVA in toluene to prepare EVOH. EVA not only needs to be prepared under high temperature and high pressure conditions, but its VAc content is generally no higher than 40 wt%, which limits the hydroxyl content in EVOH and hinders further improvement of its performance. Currently, it is still difficult to prepare EVOH with high hydroxyl content. Patent literature with publication number CN115651112A also requires the addition of appropriate amounts of organic epoxy compounds or organic oligomers with molecular weights of 100-50000 g / mol containing epoxy bonds during the alcoholysis process to prepare EVOH with a hydroxyl molar content of 10-99%.

[0004] Therefore, how to prepare a high-performance EVOH-like material with adjustable hydroxyl content more conveniently and efficiently remains an urgent problem to be solved. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a vinyl alcohol (VA)-vinyl acetate-middle-long alkyl vinyl carboxylate copolymer (PVVOH) with controllable VA content and its preparation method. The copolymer composition of the vinyl acetate-middle-long alkyl vinyl carboxylate copolymer (PVV) is controlled by adjusting the feed ratio of VAc and the polymerization of the middle-long alkyl vinyl carboxylate. Since the middle-long alkyl vinyl carboxylate (VV) does not undergo alcoholysis and inhibits the alcoholysis of adjacent VAc, the hydroxyl content in PVVOH can be further controlled by adjusting the copolymer composition of PVV.

[0006] To achieve the above objectives, the present invention provides a vinyl alcohol-vinyl acetate-medium-long alkyl carboxylic acid vinyl ester copolymer (PVVOH) with a number average molecular weight of 5,000 to 500,000, which is composed of vinyl alcohol-based structural units (a), vinyl acetate-based structural units (b), and medium-long alkyl carboxylic acid vinyl ester-based structural units (c), with the following general formula:

[0007]

[0008] Where x = 22-8100, y = 2-1000, z = 5-1100, and R is selected from straight-chain or branched alkyl groups with 7 or more carbon atoms.

[0009] The hydroxyl content of the PVVOH prepared by this invention can be distributed in a wide range of 50 mol% to 85 mol%.

[0010] Further, in the vinyl alcohol-vinyl acetate-medium-long alkyl carboxylate copolymer, the medium-long alkyl carboxylate in structural unit (c) is selected from at least one of ethylene carbonates in which the alkyl group has 7 or more carbon atoms. The medium-long alkyl carboxylate remains stable in the subsequent alcoholysis reaction and has good compatibility with LDPE. Further, in the vinyl alcohol-vinyl acetate-medium-long alkyl carboxylate copolymer, the medium-long alkyl carboxylate in structural unit (c) is selected from at least one of vinyl 2-ethylhexanoate, vinyl neononanoate, and vinyl neodecanoate.

[0011] The present invention also provides a method for preparing the vinyl alcohol-vinyl acetate-medium-long alkyl carboxylic acid vinyl ester copolymer, comprising the following steps:

[0012] In the presence of at least one free radical initiator, vinyl acetate and ethylene alkyl carboxylate are copolymerized at a temperature above 45°C to obtain a vinyl acetate-ethylene alkyl carboxylate copolymer.

[0013] The vinyl acetate-middle-length alkyl carboxylic acid vinyl ester copolymer was subjected to alcoholysis to obtain vinyl alcohol-vinyl acetate-middle-length alkyl carboxylic acid vinyl ester copolymer.

[0014] Furthermore, the free radical initiator includes azo initiators or peroxide initiators, specifically azobisisobutyronitrile or benzoyl peroxide.

[0015] Furthermore, in preparing the vinyl acetate-medium-long alkyl carboxylic acid vinyl ester copolymer, the percentage of medium-long alkyl carboxylic acid vinyl ester in the monomer mixture is 5-50 mol%, ensuring the required hydrophilicity and compatibility of the modified LDPE. Furthermore, the preparation of the vinyl acetate-medium-long alkyl carboxylic acid vinyl ester copolymer is carried out in a solvent, wherein the solvent is dimethyl carbonate or ethyl acetate.

[0016] Furthermore, vinyl acetate and alkyl carboxylic acid vinyl ester are copolymerized at 65°C or 75°C.

[0017] Furthermore, the vinyl alcohol structural unit accounts for 50-85 mol% of the vinyl alcohol-vinyl acetate-medium-long alkyl carboxylic acid vinyl ester copolymer.

[0018] Further, the alcoholysis is carried out by completely dissolving the vinyl acetate-medium-long alkyl carboxylic acid vinyl ester copolymer in an alcohol solution, adding a catalyst, and reacting at a temperature of 30°C or above.

[0019] Furthermore, the alcoholysis temperature is 40°C.

[0020] Furthermore, the alcohol solution is methanol or n-butanol.

[0021] Furthermore, the catalyst is potassium hydroxide (KOH).

[0022] The present invention also provides the application of the aforementioned vinyl alcohol-vinyl acetate-medium-long alkyl carboxylic acid vinyl ester copolymer in improving the hydrophilicity of low-density polyethylene (LDPE).

[0023] Compared with the prior art, the present invention has the following advantages and technical effects:

[0024] The copolymerization behavior of vinyl acetate and alkyl carboxylic acid vinyl ester in this invention conforms to ideal constant ratio copolymerization, and the copolymer composition and degree of alcoholysis can be controlled by simply adjusting the feed ratio.

[0025] The hydroxyl content of the PVVOH prepared by this invention can be distributed in a wide range of 50 mol% to 85 mol%, and the preparation method is simple, easy to operate, and conducive to industrial production. Detailed Implementation

[0026] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0027] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0028] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0029] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0030] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0031] The raw materials and reagents used in this invention are all obtained through purchase.

[0032] The technical solution of the present invention will be further illustrated by the following embodiments.

[0033] Example 1

[0034] 5.40 g of vinyl acetate, 0.60 g of vinyl neodecanoate, 0.06 g of azobisisobutyronitrile initiator, and 14 g of dimethyl carbonate were added to a reaction vessel and reacted at 65 °C for 12 h. After the reaction was completed, the mixture was washed and dried to obtain 5.8 g of vinyl acetate-vinyl neodecanoate copolymer PVV, with a vinyl acetate content of 94.6 mol%.

[0035] 1 g of PVV was dissolved in 3.5 g of methanol solution, and while stirring at 40 °C, it was added dropwise to a methanol solution containing 0.025 g of KOH and 0.01 g of water, for a total of 0.5 g. After reacting for 3 h, the mixture was washed and dried to obtain 0.93 g of PVVOH, a copolymer of vinyl alcohol, vinyl acetate, and vinyl neodecanoate, with a number-average molecular weight of 61,500, a molecular weight distribution index of 2.91, and a degree of alcoholysis of 83.5%. The structural formula is as follows:

[0036]

[0037] The product obtained by alcoholysis of 10 g of the vinyl alcohol-vinyl acetate-vinyl neononanoate copolymer PVVOH obtained in this example was mixed with 30 g of LDPE and then compressed into tablets to obtain a 1 mm thick sheet. The water contact angle of the sheet was measured to be 59.5° using a contact angle meter.o The surface water contact angle was 60.8 after soaking in water for 30 days. o The water contact angle of LDPE is 107.9°. o The surface water contact angle was 100.1 after soaking in water for 30 days. o .

[0038] Example 2

[0039] 2.4 g of vinyl acetate, 3.6 g of vinyl nonanoate, 0.06 g of azobisisobutyronitrile initiator, and 14 g of ethyl acetate were added to a reaction vessel and reacted at 65 °C for 12 h. After the reaction was completed, the mixture was washed and dried to obtain 5.3 g of vinyl acetate-vinyl nonanoate copolymer PVV, with a vinyl acetate content of 59.8 mol%.

[0040] 1 g of PVV was dissolved in 3.5 g of n-butanol solution. Then, 0.5 g of a n-butanol solution containing 0.025 g of KOH and 0.01 g of water was added dropwise while stirring at 40 °C. The reaction was continued for 3 h, followed by washing and drying to obtain 0.92 g of PVVOH, a copolymer of vinyl alcohol, vinyl acetate, and vinyl neononanoate. Its number-average molecular weight was 54200, its molecular weight distribution index was 2.02, and its degree of alcoholysis was 50.0%. The structural formula is as follows:

[0041]

[0042] The product obtained by alcoholysis of 10 g of the vinyl alcohol-vinyl acetate-vinyl neononanoate copolymer PVVOH obtained in this example was mixed with 30 g of LDPE and then compressed into tablets to obtain a 1 mm thick sheet. The water contact angle of the sheet was measured to be 85.8° using a contact angle meter. o The surface water contact angle was 83.5° after immersion in water for 30 days. o .

[0043] Example 3

[0044] 5.40 g of vinyl acetate, 0.60 g of vinyl 2-ethylhexanoate, 0.06 g of azobisisobutyronitrile initiator, and 14 g of dimethyl carbonate were added to a reaction vessel and reacted at 65 °C for 12 h. After the reaction was completed, the mixture was washed and dried to obtain 5.9 g of vinyl acetate-2-ethylhexanoate copolymer PVV, with a vinyl acetate content of 93.7 mol%.

[0045] 1 g of PVV was dissolved in 3.5 g of methanol solution. While stirring at 40 °C, 0.5 g of methanol solution containing 0.025 g of KOH and 0.01 g of water was added dropwise. The reaction was continued for 3 h, followed by washing and drying to obtain 0.91 g of PVVOH, a copolymer of vinyl alcohol-vinyl acetate-2-ethylhexanoate. Its number-average molecular weight was 49400, molecular weight distribution index was 3.16, and degree of alcoholysis was 82.3%. The structural formula is as follows:

[0046]

[0047] The product obtained by alcoholysis of 10 g of the vinyl alcohol-vinyl acetate-vinyl neononanoate copolymer PVVOH obtained in this example was mixed with 30 g of LDPE and then compressed into tablets to obtain a 1 mm thick sheet. The water contact angle of the sheet was measured to be 60.1° using a contact angle meter. o The surface water contact angle was 60.8 after soaking in water for 30 days. o .

[0048] Example 4

[0049] 4.80 g of vinyl acetate, 0.60 g of vinyl decanoate, 0.60 g of vinyl nonanoate, 0.06 g of azobisisobutyronitrile initiator, and 14 g of dimethyl carbonate were added to a reaction vessel and reacted at 65 °C for 12 h. After the reaction was completed, the mixture was washed and dried to obtain 5.8 g of vinyl acetate-vinyl decanoate-vinyl nonanoate copolymer (PVV), with a vinyl acetate content of 89.6 mol%.

[0050] 1 g of PVV was dissolved in 3.5 g of methanol solution. Then, 0.5 g of a methanol solution containing 0.025 g of KOH and 0.01 g of water was added dropwise while stirring at 40 °C. The reaction was continued for 3 h, followed by washing and drying to obtain 0.90 g of PVVOH, a copolymer of vinyl alcohol, vinyl acetate, vinyl neodecanoate, and vinyl neononanoate. Its number-average molecular weight was 58,600, its molecular weight distribution index was 2.64, and its degree of alcoholysis was 72.7%. The structural formula is as follows:

[0051]

[0052] The product obtained by alcoholysis of 10 g of the vinyl alcohol-vinyl acetate-vinyl neononanoate copolymer PVVOH obtained in this example was mixed with 30 g of LDPE and then compressed into tablets to obtain a 1 mm thick sheet. The water contact angle of the sheet was measured to be 83.9° using a contact angle meter. o The surface water contact angle was 75.6 after immersion in water for 30 days. o .

[0053] Example 5

[0054] 4.20 g of vinyl acetate, 0.60 g of vinyl 2-ethylhexanoate, 0.60 g of vinyl neodecanoate, 0.60 g of vinyl neononanoate, 0.06 g of azobisisobutyronitrile initiator, and 14 g of dimethyl carbonate were added to a reaction vessel and reacted at 65 °C for 12 h. After the reaction was completed, the mixture was washed and dried to obtain 5.7 g of vinyl acetate-vinyl neodecanoate copolymer PVV, with a vinyl acetate content of 83.1 mol%.

[0055] 1 g of PVV was dissolved in 3.5 g of methanol solution. Then, 0.5 g of a methanol solution containing 0.025 g of KOH and 0.01 g of water was added dropwise while stirring at 40 °C. The reaction was continued for 3 h, followed by washing and drying to obtain 0.94 g of PVVOH, a copolymer of vinyl alcohol-vinyl acetate-2-ethylhexanoate-vinyl neodecanoate-vinyl neononanoate. Its number-average molecular weight was 52,200, molecular weight distribution index was 2.50, and degree of alcoholysis was 68.2%. The structural formula is as follows:

[0056]

[0057] 10 g of the alcoholysis product was mixed with 30 g of LDPE and then compressed into tablets to obtain a 1 mm thick tablet. The water contact angle of the tablet surface was measured to be 91.4° using a contact angle meter. o The surface water contact angle after immersion in water for 30 days was 81.2°. o .

[0058] Example 6

[0059] 5.40 g of vinyl acetate, 0.60 g of vinyl neodecanoate, 0.06 g of benzoyl peroxide initiator, and 14 g of dimethyl carbonate were added to a reaction vessel and reacted at 75 °C for 12 h. After the reaction was completed, the mixture was washed and dried to obtain 5.7 g of vinyl acetate-vinyl neodecanoate copolymer PVV, with a vinyl acetate content of 93.9 mol%.

[0060] 1 g of PVV was dissolved in 3.5 g of methanol solution, and while stirring at 40 °C, it was added dropwise to a methanol solution containing 0.025 g of KOH and 0.01 g of water, totaling 0.5 g. After reacting for 3 h, the mixture was washed and dried to obtain 0.91 g of PVVOH, a copolymer of vinyl alcohol, vinyl acetate, and vinyl neodecanoate, with a number-average molecular weight of 64,200, a molecular weight distribution index of 2.74, and a degree of alcoholysis of 82.7%. The structural formula is as follows:

[0061]

[0062] 10 g of the vinyl alcohol-vinyl acetate-vinyl neononanoate copolymer PVVOH obtained in this example was mixed with 30 g of LDPE and then compressed into a sheet with a thickness of 1 mm. The water contact angle of the sheet was measured to be 59.2° using a contact angle meter. o The surface water contact angle was 59.9 after immersion in water for 30 days. o .

[0063] Example 7

[0064] 4.8 g of vinyl acetate, 1.2 g of vinyl neononanoate, 0.06 g of benzoyl peroxide initiator, and 14 g of dimethyl carbonate were added to a reaction vessel and reacted at 75 °C for 12 h. After the reaction, the mixture was washed and dried to obtain 5.7 g of vinyl acetate-vinyl neononanoate copolymer (PVV), with a vinyl acetate content of 88.7 mol%.

[0065] 1 g of PVV was dissolved in 3.5 g of methanol solution. Then, 0.5 g of a methanol solution containing 0.025 g of KOH and 0.01 g of water was added dropwise while stirring at 40 °C. The reaction was continued for 3 h, followed by washing and drying to obtain 0.92 g of PVVOH, a copolymer of vinyl alcohol, vinyl acetate, and vinyl neononanoate. Its number-average molecular weight was 61,700, molecular weight distribution index was 2.28, and degree of alcoholysis was 71.0%. The structural formula is as follows:

[0066]

[0067] 10 g of the vinyl alcohol-vinyl acetate-vinyl neononanoate copolymer PVVOH obtained in this example was mixed with 30 g of LDPE and then compressed into a sheet with a thickness of 1 mm. The water contact angle of the sheet was measured to be 79.6° using a contact angle meter. o The surface water contact angle was 77.1 after immersion in water for 30 days. o .

[0068] As can be seen from the above examples, the copolymer composition of vinyl acetate-middle-length alkyl carboxylic acid vinyl ester copolymer (PVV) can be controlled by controlling the feed ratio of VAc and alkyl carboxylic acid vinyl ester polymerization, and the content of hydroxyl groups in PVVOH can also be controlled.

[0069] Comparative Example 1 (without the addition of medium-long alkyl carboxylic acid vinyl ester)

[0070] Specific preparation method:

[0071] 6.00 g of vinyl acetate, 0.06 g of azobisisobutyronitrile initiator, and 14 g of dimethyl carbonate were added to a reaction vessel and reacted at 65 °C for 12 h. After the reaction was completed, the mixture was washed and dried to obtain 5.7 g of vinyl acetate homopolymer PVAc.

[0072] 1 g of PVAc was dissolved in 3.5 g of methanol solution, and while stirring at 40 °C, it was added dropwise to a methanol solution containing 0.025 g of KOH and 0.01 g of water, for a total of 0.5 g. After reacting for 3 h, the mixture was washed and dried to obtain 0.94 g of ethylene alcohol-vinyl acetate copolymer, with a number-average molecular weight of 48,900, a molecular weight distribution index of 3.39, and a degree of alcoholysis of 94.5%. The structural formula is as follows:

[0073]

[0074] 10 g of the ethylene alcohol-vinyl acetate copolymer obtained in this comparative example was mixed with 30 g of LDPE and then compressed into a sheet with a thickness of 1 mm. The water contact angle of the sheet was measured to be 41.2° using a contact angle meter. o The surface water contact angle was 100.7 after immersion in water for 30 days. o .

[0075] Comparative Example 2 (Short-chain alkyl ethylene carbonate)

[0076] Specific preparation method:

[0077] 5.70 g of vinyl acetate, 0.30 g of vinyl propionate, 0.06 g of azobisisobutyronitrile initiator, and 14 g of dimethyl carbonate were added to a reaction vessel and reacted at 65 °C for 12 h. After the reaction was completed, the mixture was washed and dried to obtain 5.6 g of vinyl acetate-vinyl isobutyrate copolymer PVV, with a vinyl acetate content of 95.5 mol%.

[0078] 1 g of PVV was dissolved in 3.5 g of methanol solution. While stirring at 40 °C, 0.5 g of methanol solution containing 0.025 g of KOH and 0.01 g of water was added dropwise. The reaction was continued for 3 h, followed by washing and drying to obtain 0.94 g of vinyl alcohol-vinyl acetate-vinyl propionate copolymer. Its number-average molecular weight was 52400, molecular weight distribution index was 2.98, and degree of alcoholysis was 92.7%. The structural formula is as follows:

[0079]

[0080] 10 g of vinyl alcohol-vinyl acetate-vinyl propionate copolymer was mixed with 30 g of LDPE and then compressed into sheets to obtain a 1 mm thick sheet. The water contact angle of the sheet was measured to be 43.1° using a contact angle meter.o The surface water contact angle was 101.3 after immersion in water for 30 days. o .

[0081] Comparative Example 3 (Short-chain alkyl ethylene carbonate)

[0082] 5.70 g of vinyl acetate, 0.30 g of vinyl isobutyrate, 0.06 g of azobisisobutyronitrile initiator, and 14 g of dimethyl carbonate were added to a reaction vessel and reacted at 65 °C for 12 h. After the reaction was completed, the mixture was washed and dried to obtain 5.8 g of vinyl acetate-vinyl isobutyrate copolymer PVV, with a vinyl acetate content of 94.9 mol%.

[0083] 1 g of PVV was dissolved in 3.5 g of methanol solution. While stirring at 40 °C, 0.5 g of methanol solution containing 0.025 g of KOH and 0.01 g of water was added dropwise. The reaction was continued for 3 h, followed by washing and drying to obtain 0.96 g of vinyl alcohol-vinyl acetate-vinyl isobutyrate copolymer. Its number-average molecular weight was 51700, molecular weight distribution index was 2.66, and degree of alcoholysis was 90.8%. The structural formula is as follows:

[0084]

[0085] 10 g of vinyl alcohol-vinyl acetate-vinyl isobutyrate copolymer was mixed with 30 g of LDPE and then compressed into sheets to obtain a 1 mm thick sheet. The water contact angle of the sheet was measured to be 44.0° using a contact angle meter. o The surface water contact angle after immersion in water for 30 days was 101.2°. o .

[0086] Comparative Example 4

[0087] 0.06 g vinyl acetate, 5.94 g vinyl nonanoate, 0.06 g azobisisobutyronitrile initiator, and 14 g ethyl acetate were added to a reaction vessel and reacted at 65 °C for 12 h. After the reaction was completed, the mixture was washed and dried to obtain 5.1 g of vinyl acetate-vinyl nonanoate copolymer PVV, with a vinyl acetate content of 2.0 mol%.

[0088] 1 g of PVV was dissolved in 3.5 g of n-butanol solution. Then, 0.5 g of a n-butanol solution containing 0.025 g of KOH and 0.01 g of water was added dropwise while stirring at 40 °C. The reaction was continued for 3 h, followed by washing and drying to obtain 0.92 g of PVVOH, a copolymer of vinyl alcohol, vinyl acetate, and vinyl neononanoate. Its number-average molecular weight was 43,100, its molecular weight distribution index was 2.02, and its degree of alcoholysis was 1.0%. The structural formula is as follows:

[0089]

[0090] The product obtained by alcoholysis of 10 g of the vinyl alcohol-vinyl acetate-vinyl neononanoate copolymer PVVOH obtained in this example was mixed with 30 g of LDPE and then compressed into tablets to obtain a 1 mm thick sheet. The water contact angle of the sheet was measured to be 98.8° using a contact angle meter. o The surface water contact angle was 97.5° after immersion in water for 30 days. o Materials prepared under these conditions are no longer hydrophilic.

[0091] As can be seen from the above, the change in contact angle is mainly related to the migration and rearrangement of hydroxyl groups in the added blend. Blends with fewer medium- and long alkyl chain units have better water solubility and will migrate during water immersion, leading to a decrease in contact angle. Blends with more medium- and long alkyl chain units are insoluble in water and will not migrate during water immersion. Furthermore, the hydroxyl groups tend to distribute on the surface in contact with water, causing a decrease in contact angle. Therefore, the copolymer in the comparative example shows severe migration, and the increase in contact angle after water immersion is more pronounced.

[0092] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A vinyl alcohol-vinyl acetate-vinyl medium alkyl carboxylate copolymer, characterized in that, Its number-average molecular weight is between 5,000 and 500,000, and it is composed of structural units based on vinyl alcohol (a), structural units based on vinyl acetate (b), and structural units based on medium-long alkyl carboxylic acids (c), with the following general formula: The medium-long alkyl carboxylic acid vinyl ester in the structural unit (c) is selected from at least one of 2-ethylhexanoate, neononanoate, and neodecanoate; Where x = 22 - 8100, y = 2 - 1000, z = 5 - 1100; When preparing vinyl acetate-medium-long alkyl carboxylic acid vinyl ester copolymers, the percentage of medium-long alkyl carboxylic acid vinyl esters in the monomer mixture is 5-50 mol%. The vinyl alcohol-vinyl acetate-medium-long alkyl carboxylic acid vinyl ester copolymer has a vinyl alcohol structural unit content of 50~85 mol.

2. A process for producing the ethylene-vinyl alcohol-vinyl medium alkyl carboxylate copolymer according to claim 1, characterized by, Includes the following steps: In the presence of a free radical initiator, vinyl acetate and ethylene alkyl carboxylate are copolymerized at a temperature above 45°C to obtain a vinyl acetate-ethylene alkyl carboxylate copolymer. The vinyl acetate-middle-length alkyl carboxylic acid vinyl ester copolymer was subjected to alcoholysis to obtain vinyl alcohol-vinyl acetate-middle-length alkyl carboxylic acid vinyl ester copolymer.

3. The process for producing a vinyl alcohol-vinyl acetate- medium long alkyl vinyl carboxylate copolymer according to claim 2, characterized by, The alcoholysis is carried out by completely dissolving the vinyl acetate-medium-long alkyl carboxylic acid vinyl ester copolymer in an alcohol solution, adding a catalyst, and reacting at a temperature of 30°C or above.

4. The method for preparing the vinyl alcohol-vinyl acetate-medium-long alkyl carboxylic acid vinyl ester copolymer according to claim 2, characterized in that, The alcoholysis temperature is 40°C.

5. The application of the vinyl alcohol-vinyl acetate-medium-long alkyl carboxylic acid vinyl ester copolymer according to claim 1 in improving the hydrophilicity of polyethylene.

Images