Method for producing ethylene-vinyl acetate copolymer

Abstract

The invention discloses a method for preparing an ethylene-vinyl acetate copolymer, and particularly relates to a method for preparing ethylene-vinyl acetate, which comprises the following steps: adding a monomer containing ethylene and vinyl acetate and a solvent containing alkyl acetate into a reactor and polymerizing.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of Korean Patent Application No. 10-2023-0130543 filed in the Korean Intellectual Property Office on September 27, 2023, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] Embodiments of the present disclosure are directed to a method of preparing ethylene-vinyl acetate copolymer. Background Art

[0004] Ethylene-vinyl acetate copolymer is a copolymer in which ethylene and vinyl acetate are randomly copolymerized and exhibit properties comparable to rubber due to its excellent flexibility and elasticity. This ethylene-vinyl acetate copolymer exhibits different physical properties depending on the molecular weight or vinyl acetate content, and has excellent transparency and adhesion, and is therefore commonly used in various applications, such as sealants for solar cells, soles, coated paper, and agricultural films. In addition, vinyl acetate with a high molecular weight can be used for specific applications, such as submarine cables, and ethylene-vinyl acetate copolymers with a high vinyl acetate content can be converted into ethylene-vinyl alcohol with excellent gas barrier properties by additional saponification. The ethylene-vinyl alcohol thus converted can be used in a wide range of fields, such as films, containers, and fibers, due to its excellent gas barrier properties and chemical resistance, and is particularly used as an essential component in fields requiring gas barrier properties, such as fresh food packaging and automotive fuel tanks.

[0005] Generally, the industrial preparation of ethylene-vinyl acetate copolymers is carried out by high-temperature and high-pressure gas phase polymerization or low-temperature and low-pressure solution polymerization using vinyl acetate monomer, ethylene and initiator as raw materials. Among them, the method for preparing ethylene-vinyl acetate copolymers with high vinyl acetate content is generally low-temperature and low-pressure solution polymerization. In this case, C1 to C4 alcohols are used as additional solvents.

[0006] The additional solvent used for solution polymerization is generally present in an amount of 2 to 20 wt % of the total reaction medium to reduce the viscosity in the polymerization reactor and effectively remove the polymerization heat generated during the polymerization of ethylene-vinyl acetate. Depending on the type of alcohol used, a chain transfer reaction occurs in which the active point of polymerization moves to the alcohol, and the chain transfer reaction causes termination or branching of polymer growth, thereby playing a role in hindering the increase in molecular weight of linear polymers.

[0007] In order to prevent this phenomenon, a method of using an alcohol having a low chain transfer coefficient (e.g., tert-butyl alcohol) alone or in combination has been proposed, but it is not applicable due to higher cost, higher boiling point and reduced separation efficiency in the subsequent process, especially in the recovery process of unreacted monomers due to the formation of an azeotropic mixture with the monomers.

[0008] The information disclosed in this section is only for enhancement of understanding of the background of the present disclosure and therefore it may contain information that does not constitute prior art. Summary of the invention

[0009] Embodiments of the present disclosure provide a method for preparing an ethylene-vinyl acetate copolymer using an alkyl acetate as a solvent, the alkyl acetate having a low chain transfer constant and being easily separated from the monomers in the ethylene-vinyl acetate polymerization process.

[0010] Embodiments of the present disclosure provide a method for preparing an ethylene-vinyl acetate copolymer, which is easy to control the molecular weight of the ethylene-vinyl acetate copolymer and is applicable to an ultra-high molecular weight ethylene-vinyl acetate copolymer rubber.

[0011] A method for preparing ethylene-vinyl acetate according to one embodiment of the present disclosure includes adding monomers containing ethylene and vinyl acetate and a solvent containing alkyl acetate into a reactor and performing polymerization.

[0012] The boiling point of the alkyl acetate may be from 57°C to 126°C.

[0013] The alkyl acetate may include at least one selected from the group consisting of ethyl acetate, methyl acetate, propyl acetate, butyl acetate, and dimethyl acetate.

[0014] The solvent may be added in an amount of 2.5 wt % to 50 wt % based on the total amount of the monomer and the solvent.

[0015] The polymerization may further include adding an initiator including an azodiyl compound, benzoyl peroxide (BPO), or a combination thereof, and the azodiyl compound may include azobisisobutyronitrile (AIBN), azobisisoheptanenitrile (ADVN), or a combination thereof.

[0016] The ethylene-vinyl acetate copolymer may have a weight average molecular weight (Mw) of 150,000 g / mol to 500,000 g / mol.

[0017] The ethylene-vinyl acetate copolymer may contain 40 mol % to 80 mol % of vinyl acetate. DETAILED DESCRIPTION

[0018] The following embodiments are provided in order to more fully explain the present disclosure to those of ordinary skill in the art, the following embodiments may be modified in various other forms, and the scope of the present disclosure is not limited to the following embodiments.

[0019] The method for preparing ethylene-vinyl acetate according to one embodiment includes polymerizing monomers in a solvent in a reactor. In this case, the monomers include ethylene and vinyl acetate, and the solvent includes alkyl acetate.

[0020] Typically, C1 to C4 alcohols such as methanol are used as solvents in polymerization reactions to prepare ethylene-vinyl acetate copolymers. In this case, it is difficult to obtain high molecular weight resins due to defects in controlling the molecular weight of ethylene-vinyl acetate (EVA) copolymers, and unreacted vinyl acetate often forms an azeotropic mixture with alcohols, making it difficult to separate.

[0021] As used herein, the term "azeotropic mixture" has the commonly known meaning in the art.

[0022] In other words, it refers to a liquid having a specific composition ratio in which the composition ratio does not change at a constant temperature like a pure liquid, and when boiling, the composition ratio of the solution and the vapor is equal. The equilibrium temperature, which is the boiling point of the azeotropic mixture, is called the "azeotropic point", and the azeotropic state, in which the composition ratio of the solution and the vapor is equal, changes depending on the pressure, and the azeotropic point has a minimum or maximum value on a boiling point curve showing the relationship between the composition ratio and the boiling point.

[0023] On the other hand, according to one embodiment, when polymerization is performed using an alkyl acetate having a low chain transfer constant as a solvent, an ethylene-vinyl acetate (EVA) copolymer having a high molecular weight can be obtained, physical properties of the product can be improved, and thus the ethylene-ethyl acetate (EVA) copolymer can be easily separated because unreacted vinyl acetate does not form an azeotropic mixture with the alkyl acetate.

[0024] The boiling point of the alkyl acetate used as a solvent may be 57 to 126° C., for example, 57 to 102° C. or 57 to 80° C. When an alkyl acetate having a boiling point within the above range is used as a solvent, an ethylene-vinyl acetate (EVA) copolymer having a high molecular weight can be obtained.

[0025] The alkyl acetate used as the solvent may include, for example, at least one selected from ethyl acetate, methyl acetate, propyl acetate, butyl acetate, and dimethyl acetate. Specifically, the alkyl acetate may be ethyl acetate or methyl acetate.

[0026] Based on the total amount of monomer and solvent, the solvent can be added in an amount of 2.5 wt % to 50 wt %, for example, 5 wt % to 30 wt %, 9 wt % to 30 wt %, or 9 wt % to 15 wt %. When the solvent is added within this content range, an ethylene-vinyl acetate (EVA) copolymer having a high molecular weight can be obtained during the polymerization process.

[0027] An initiator may be further added during the polymerization.

[0028] The initiator may include an azodiyl compound, benzoyl peroxide (BPO), or a combination thereof, and the azodiyl compound may include azobisisobutyronitrile (AIBN), azobisisoheptanenitrile (ADVN), or a combination thereof.

[0029] The weight average molecular weight (Mw) of the ethylene-vinyl acetate copolymer obtained by polymerization may be 150,000 g / mol to 500,000 g / mol, for example, 150,000 g / mol to 400,000 g / mol, 250,000 g / mol to 400,000 g / mol or 350,000 g / mol to 400,000 g / mol. The ethylene-vinyl acetate copolymer having a weight average molecular weight (Mw) within the above range may have improved physical properties and may also be suitable for ultra-high molecular weight ethylene-ethyl acetate copolymer rubber.

[0030] The ethylene-vinyl acetate copolymer obtained by polymerization may contain 40 mol % to 80 mol % of vinyl acetate, for example, 56 mol % to 72 mol % of vinyl acetate. The ethylene-vinyl acetate copolymer containing vinyl acetate within this range may have improved physical properties and may also be suitable for ultra-high molecular weight ethylene-vinyl acetate copolymer rubber.

[0031] Hereinafter, specific examples of the present disclosure will be described. However, the examples described below are only used to illustrate or explain the present disclosure in detail and should not be construed as limiting the scope of the present disclosure. In addition, other details that may be fully thought of by those skilled in the art will not be described.

[0032] (Preparation of ethylene-vinyl alcohol copolymer)

[0033] Example 1

[0034] 21.5 wt% of ethylene, 69.3 wt% of vinyl acetate and 9.2 wt% of ethyl acetate with a boiling point of 77°C as a solvent were added to the reactor and heated at 60°C and

[0035] 40kg / cm 2The polymerization was carried out under an ethylene pressure of 1.5 % to prepare an ethylene-vinyl acetate (EVA) copolymer containing 71.3 mol % of vinyl acetate.

[0036] Example 2

[0037] An ethylene-vinyl acetate (EVA) copolymer was prepared in the same manner as in Example 1, except that methyl acetate having a boiling point of 57° C. was used as a solvent instead of ethyl acetate.

[0038] Comparative Example 1

[0039] An ethylene-vinyl acetate (EVA) copolymer was prepared in the same manner as in Example 1, except that ethanol was used as a solvent instead of ethyl acetate.

[0040] Comparative Example 2

[0041] An ethylene-vinyl acetate (EVA) copolymer was prepared in the same manner as in Example 1, except that methanol was used as a solvent instead of ethyl acetate.

[0042] Test 1: Determination of Molecular Weight of Ethylene Vinyl Acetate (EVA) Copolymer

[0043] In order to determine the molecular weight of the ethylene-vinyl acetate (EVA) copolymers prepared in Examples 1 and 2 and Comparative Examples 1 and 2, the weight average molecular weight (Mw) was determined using a gel permeation chromatography (GPC) apparatus, and the results are shown in Table 1 below.

[0044] [Table 1]

[0045] Example 1 Example 2 Comparative Example 1 Comparative Example 2 Weight average molecular weight (Mw) 359,395 394,573 116,281 91,539

[0046] As can be seen from Table 1, the molecular weight of the ethylene-vinyl acetate (EVA) copolymers prepared according to Examples 1 and 2 is higher than that of the copolymers of Comparative Examples 1 and 2. Therefore, according to one embodiment, it can be seen that the physical properties of the product can be improved by obtaining a sufficiently high molecular weight to be suitable for ethylene-vinyl acetate copolymer rubber.

[0047] Test 2: Determining whether an azeotropic mixture of vinyl acetate and solvent is formed It was determined whether the solvents used in Examples 1 and 2 and Comparative Examples 1 and 2 did not form an azeotropic mixture with vinyl acetate and could be separated by simple distillation, or whether the solvents formed an azeotropic mixture and required separation using an extractant, etc., and the results are shown in Table 2 below.

[0048] [Table 2]

[0049]

[0050] Table 2 shows that Examples 1 and 2 do not form azeotropes and can therefore be separated by simple distillation, whereas all of the comparative examples form azeotropes and require a separate separation process.

[0051] As is apparent from the above description, the method according to the embodiment can prepare an ethylene-vinyl acetate copolymer having a high molecular weight, improves the physical properties of the product, and is suitable for ultra-high molecular weight ethylene-vinyl acetate copolymer rubber. In addition, according to the method, unreacted vinyl acetate does not form an azeotropic mixture with the solvent alkyl acetate, making it easy to perform the subsequent separation process.

[0052] Although the preferred embodiments of the present disclosure have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the disclosure as disclosed in the accompanying claims.

Claims

1. A method for preparing ethylene-vinyl acetate, the method comprising adding monomers comprising ethylene and vinyl acetate and a solvent comprising an alkyl acetate into a reactor and performing polymerization.

2. The method according to claim 1, wherein the boiling point of the alkyl acetate is 57°C to 126°C.

3. The method according to claim 1, wherein the alkyl acetate comprises at least one selected from the group consisting of ethyl acetate, methyl acetate, propyl acetate, butyl acetate and dimethyl acetate. 4 . The method according to claim 1 , wherein the solvent is added in an amount of 2.5 wt % to 50 wt % based on the total amount of the monomer and the solvent.

5. The method of claim 1, wherein the polymerization further comprises adding an initiator, the initiator comprising an azodiyl compound, benzoyl peroxide (BPO), or a combination thereof, and The azobisyl compound includes azobisisobutyronitrile (AIBN), azobisisoheptanenitrile (ADVN), or a combination thereof.

6. The method of claim 1, wherein the ethylene-vinyl acetate copolymer has a weight average molecular weight (Mw) of 150,000 g / mol to 500,000 g / mol.

7. The method of claim 1, wherein the ethylene-vinyl acetate copolymer comprises 40 mol% to 80 mol% of vinyl acetate.

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