Ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer and preparation method thereof

Abstract

The invention discloses an ethylene-vinyl acetate copolymer (EVA), an ethylene-vinyl alcohol copolymer (EVOH) and a preparation method of the ethylene-vinyl acetate copolymer (EVA) and the ethylene-vinyl alcohol copolymer (EVOH). The EVA is prepared by the following steps: mixing an initiator, a chain transfer agent, a solvent and vinyl acetate, blowing nitrogen to remove oxygen, introducing ethylene gas, and carrying out pressurized polymerization to obtain the ethylene-vinyl acetate copolymer, the chain transfer agent is selected from at least one of perfluorohexyl iodoalkane, 1, 6-diiodo-dodecafluorohexane, iodine hexane and perfluorobutyl iodoalkane. The reaction rate of the initiator is matched with the activity of the chain transfer agent, so that a moderate chain transfer rate can be kept while stable growth of a polymer chain can be ensured, the molecular weight of EVA is improved, transfer of active species to macromolecular chains is inhibited to a great extent, and the branching degree of the product EVA is reduced. And the EVOH with specific number-average molecular weight and molecular weight distribution is further prepared by taking the EVOH as a raw material.

Description

Technical Field

[0001] The invention belongs to the technical field of organic material preparation, and specifically relates to an ethylene-vinyl acetate copolymer, an ethylene-vinyl alcohol copolymer and a preparation method thereof. Background Art

[0002] Ethylene-vinyl acetate copolymer (EVA) is a thermoplastic resin obtained by copolymerization of ethylene and vinyl acetate monomers. It has excellent mechanical properties, low temperature resistance and hot melt processability. It is widely used as a hot melt adhesive and elastomer in packaging materials, electronics, medical and automobile manufacturing. The ethylene-vinyl alcohol copolymer (EVOH) obtained by saponification of EVA copolymer in an organic solvent with a strong base such as NaOH as a catalyst has excellent gas barrier properties, fragrance retention, oil resistance, chemical corrosion resistance and other characteristics. It is the most widely used high barrier material. The structure of EVA polymer directly affects the structure and properties of the saponified product EVOH. The core application properties of EVA such as mechanical strength are mainly affected by key structures such as vinyl acetate unit content, relative molecular weight, and degree of branching. However, during the solution polymerization process, carbon free radicals are prone to chain transfer to the methyl end of the EVA side chain to form a branch, and the degree of branching of EVA increases. During the alcoholysis process, the branch will be separated from the polymer main chain with the ester bond breaking, resulting in problems such as decreased EVOH molecular weight and low vinyl acetate utilization. Reversible chain transfer polymerization regulates the polymerization system through the reversible chain transfer equilibrium reaction between the growing free radical and the chain transfer agent. In recent years, controlled free radical polymerization has been used to reduce the branching degree of the polymer. However, due to the large difference in the polymerization activity of ethylene and vinyl acetate, how to select, design and synthesize efficient chain transfer agents to achieve controllable preparation of EVA, promote rapid reversible dynamic equilibrium between active species and dormant species, inhibit the transfer of active species to macromolecular chains, and reduce the branching degree of EVA has important research significance and application prospects.

[0003] In the prior art, chain transfer agents are generally aliphatic mercaptans, dodecyl mercaptan, etc., and the research on chain transfer agents is generally controlled free radical polymerization. For example, there are literature reports that azobisisobutyronitrile (AIBN) is used as an initiator, iodide such as tert-butyl iodide and perfluorohexyl iodide is used as a chain transfer agent to carry out copolymerization of ethylene and vinyl acetate to achieve controlled free radical polymerization. The prepared EVA polymer has a narrow molecular weight distribution (<1.9), but the number average molecular weight Mn is generally low (<25000). The Mn of commercial EVOH is generally between 30,000 and 50,000. If the EVA prepared by the scheme of this document is used and the EVOH prepared by saponification reaction is further reduced, it has no application value. The prior art research on chain transfer agents rarely involves EVA with extremely low branching degree, and it does not involve research: whether the initiator and chain transfer agent can cooperate to obtain EVA with extremely low branching degree and high molecular weight. It is expected to develop a free radical initiation system with synergistic initiators and chain transfer agents, in which the active species generated by the reaction only interact with the active center of the polymer main chain, but cannot undergo chain transfer with the side chain methyl end of the polymer, so as to prepare EVA with extremely low branching degree and high molecular weight. Summary of the invention

[0004] The present invention develops a novel and efficient free radical initiation system based on iodine transfer polymerization by selecting specific components and specific ratios of initiators and chain transfer agents, and prepares an EVA copolymer with extremely low branching degree and high molecular weight (Mn between 30,000 and 50,000). Specifically, the present invention uses dodecyl peroxide (or benzoyl peroxide) as an initiator, perfluorohexyl iodide (or 1,6-diiododecyl fluorohexane, iodide hexane, perfluorobutyl iodide) as a chain transfer agent, and methanol as a solvent to carry out the copolymerization of ethylene and vinyl acetate. The reaction rate of the initiator dodecyl peroxide (or benzoyl peroxide) and the activity matching of the chain transfer agent perfluorohexyl iodide (or 1,6-diiododecyl fluorohexane, iodide hexane, perfluorobutyl iodide) can ensure the stable growth of the polymer chain while maintaining a moderate chain transfer rate, increase the molecular weight of EVA, and also greatly inhibit the transfer of active species to the macromolecular chain, thereby reducing the branching degree of the product EVA. And EVOH with specific number average molecular weight and molecular weight distribution is further prepared using this as raw material.

[0005] According to one aspect of the present application, a method for preparing an ethylene-vinyl acetate copolymer is provided, wherein the ethylene-vinyl acetate copolymer is obtained by the following steps:

[0006] An initiator, a chain transfer agent, a solvent and vinyl acetate are mixed, nitrogen bubbling is used to remove oxygen, and then ethylene gas is introduced to polymerize under pressure to obtain the ethylene-vinyl acetate copolymer;

[0007] The initiator is selected from at least one of dodecyl peroxide and benzoyl peroxide;

[0008] The chain transfer agent is at least one selected from perfluorohexyl iodide, 1,6-diiododecafluorohexane, iodine hexane, and perfluorobutyl iodide.

[0009] The solvent is selected from at least one of methanol, ethanol, tert-butanol, n-butanol and isopropanol.

[0010] The molar ratio of the initiator to the chain transfer agent is 1:10 to 10:1;

[0011] Optionally, the molar ratio of the initiator to the chain transfer agent is 1:4 to 4:1;

[0012] The molar ratio of the initiator to vinyl acetate is 1:100000 to 1:1000.

[0013] The volume ratio of the solvent to vinyl acetate is 1:10 to 1:2;

[0014] The ethylene gas is introduced to make the pressure reach 1-10Mpa;

[0015] The polymerization temperature is 20 to 100° C.

[0016] The polymerization time is 0.1 to 10 hours.

[0017] According to another aspect of the present application, there is provided an ethylene-vinyl acetate copolymer prepared by the above-mentioned preparation method, wherein the number average molecular weight of the ethylene-vinyl acetate copolymer is 20000-100000 g / mol;

[0018] Optionally, the number average molecular weight of the ethylene-vinyl acetate copolymer is 30,000 to 60,000 g / mol;

[0019] The branching degree of the ethylene-vinyl acetate copolymer is 0.01 to 0.3;

[0020] Optionally, the degree of branching of the ethylene-vinyl acetate copolymer is 0.01 to 0.2;

[0021] The molecular weight distribution of the ethylene-vinyl acetate copolymer is 1.0 to 3.0;

[0022] Optionally, the molecular weight distribution of the ethylene-vinyl acetate copolymer is 1.0 to 2.0.

[0023] The ethylene content in the ethylene-vinyl acetate copolymer is 20 to 50 mol%.

[0024] According to another aspect of the present application, a method for preparing an ethylene-vinyl alcohol copolymer is provided, wherein the ethylene-vinyl alcohol copolymer is obtained by the following steps:

[0025] The ethylene-vinyl acetate copolymer, an organic solvent and a catalyst are mixed, and alcoholysis reaction is carried out, and the mixture is washed with water, filtered and dried to obtain the ethylene-vinyl alcohol copolymer.

[0026] The organic solvent is selected from at least one of methanol and ethanol;

[0027] The catalyst is selected from at least one of sodium hydroxide, potassium hydroxide and alkali metal alcoholates.

[0028] The mass ratio of the ethylene-vinyl acetate copolymer, the solvent and the catalyst is 1:50:1 to 1:2:0.01.

[0029] The temperature of the alcoholysis reaction is 20 to 100° C.

[0030] The alcoholysis reaction time is 1 to 10 hours.

[0031] According to another aspect of the present application, there is provided an ethylene-vinyl alcohol copolymer prepared by the above-mentioned preparation method, wherein the number average molecular weight of the ethylene-vinyl alcohol copolymer is 20000 to 100000 g / mol;

[0032] The molecular weight distribution of the ethylene-vinyl alcohol copolymer is 1.0 to 3.0;

[0033] The number average molecular weight of the ethylene-vinyl alcohol copolymer is 30,000 to 60,000 g / mol, and the molecular weight distribution is 1.0 to 2.0.

[0034] The ethylene content in the ethylene-vinyl alcohol copolymer is 20 to 50 mol%.

[0035] The beneficial effects of this application include:

[0036] 1) The present invention adopts a combination of dodecanoyl peroxide (or benzoyl peroxide) as an initiator and perfluorohexyl iodide (or 1,6-diiododecafluorohexane, iodide hexane, or perfluorobutyl iodide) as a chain transfer agent to carry out a copolymerization reaction of ethylene and vinyl acetate. The active species generated by the reaction of dodecanoyl peroxide (or benzoyl peroxide) and perfluorohexyl iodide (or 1,6-diiododecafluorohexane, iodide hexane, or perfluorobutyl iodide) only interact with the active center of the polymer main chain due to the influence of steric hindrance or electronic effect, and cannot chain transfer with the side chain methyl end of the polymer. Therefore, the chain transfer can be effectively inhibited and the controllable growth of the polymer chain can be achieved, and finally EVA with a higher molecular weight and extremely low branching degree can be obtained with a high yield.

[0037] 2) The molecular weight and distribution of EVOH obtained after saponification of the above EVA are not much different from those of the corresponding EVA precursor, indicating that the use of dodecyl peroxide (or benzoyl peroxide) as an initiator and perfluorohexyl iodide (or 1,6-diiododecafluorohexane, iodine hexane, perfluorobutyl iodide) as a chain transfer agent successfully inhibits the transfer of active species to macromolecular chains.

[0038] 3) In addition, the present invention can directly estimate the molecular weight of EVOH obtained by saponification of EVA through the molecular weight of EVA with a low degree of branching, thereby achieving a simple measurement of the molecular weight of EVOH. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is the GPC chart of EVA obtained in Example 1.

[0040] Figure 2 This is the H-NMR spectrum of the EVA obtained in Example 1.

[0041] Figure 3 This is the GPC chart of EVA obtained in Example 2.

[0042] Figure 4 This is the H-NMR spectrum of the EVA obtained in Example 2.

[0043] Figure 5 This is the infrared spectrum of EVOH obtained in Example 13.

[0044] Figure 6 This is the GPC chart of EVOH obtained in Example 13.

[0045] Figure 7 This is the infrared spectrum of EVOH obtained in Example 14.

[0046] Figure 8 This is the GPC chart of EVOH obtained in Example 14. DETAILED DESCRIPTION

[0047] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0048] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0049] The experimental methods used in the following examples are conventional methods unless otherwise specified. 1HNMR) is used to characterize the ethylene content of EVA. The structure of EVOH is characterized by infrared spectroscopy (FT-IR). Gel permeation chromatography (GPC) is used to characterize the molecular weight and molecular weight distribution of EVA and EVOH. Since EVOH is poorly soluble in conventional solvents such as tetrahydrofuran, the molecular weight of EVOH is difficult to measure directly at room temperature. It can be inferred by the R-EVA polymer obtained by acetylation of EVOH. The branching degree of EVA is calculated by the formula:

[0050] Branching degree BD value = (EVA molecular weight - R-EVA molecular weight) / R-EVA molecular weight.

[0051] The BD value can be regarded as the ratio of the molecular weight of the branched chain to the molecular weight of the linear part in the EVA structure.

[0052] Examples 1 to 12 are preparation examples of EVA.

[0053] Example 1

[0054] 30mL of vinyl acetate and 6mL of anhydrous methanol were added to a 100mL stainless steel autoclave with a tetrafluoroethylene liner, and then a chain transfer agent (perfluorohexyl iodide, 67mg, 150μmol) and an initiator (dodecyl peroxide, 20mg, 50μmol) were added to the reactor, and nitrogen was replaced three times, and then replaced three times with ethylene gas. The stirring speed of the reactor was controlled to be 150rpm, and then 3.5MPa of ethylene was charged into the reactor, and after heating to 70°C, the reaction was carried out for 4h, cooled to room temperature, and the pressure was released. The product was transferred to a vacuum oven and dried at 50°C for 12 hours to obtain 12.8g of EVA. The ethylene content was 33.3% as measured by nuclear magnetic resonance, and the weight average molecular weight Mw of EVA was 69900g / mol, the number average molecular weight Mn was 36000g / mol, the molecular weight distribution was 1.94, and the degree of branching was 0.06 as measured by gel permeation chromatography.

[0055] Example 2

[0056] 30mL of vinyl acetate and 6mL of anhydrous methanol were added to a 100mL stainless steel autoclave with a tetrafluoroethylene liner, and then a chain transfer agent (perfluorohexyl iodide, 33mg, 75μmol) and an initiator (dodecyl peroxide, 10mg, 25μmol) were added to the reactor, and nitrogen was replaced three times, and then replaced three times with ethylene gas. The stirring speed of the reactor was controlled to be 150rpm, and then 3.5MPa of ethylene was charged into the reactor, and after heating to 70°C, the reaction was carried out for 4h, cooled to room temperature, and the pressure was released. The product was transferred to a vacuum oven and dried at 50°C for 12 hours to obtain 3.8g of EVA. The ethylene content was 33.8% as measured by nuclear magnetic resonance, and the weight average molecular weight Mw of EVA was 67900g / mol, the number average molecular weight Mn was 35600g / mol, the molecular weight distribution was 1.90, and the degree of branching was 0.03 as measured by gel permeation chromatography.

[0057] Example 3

[0058] 30mL of vinyl acetate and 6mL of anhydrous methanol were added to a 100mL stainless steel autoclave with a tetrafluoroethylene liner, and then a chain transfer agent (perfluorohexyl iodide, 33mg, 75μmol) and an initiator (dodecyl peroxide, 20mg, 50μmol) were added to the reactor, and nitrogen was replaced three times, and then replaced three times with ethylene gas. The stirring speed of the reactor was controlled to be 150rpm, and then 3.5MPa of ethylene was charged into the reactor, and after heating to 70°C, the reaction was carried out for 4h, cooled to room temperature, and the pressure was released. The product was transferred to a vacuum oven and dried at 50°C for 12 hours to obtain 14.6g of EVA. The ethylene content was 32.8% as measured by nuclear magnetic resonance, and the weight average molecular weight Mw of EVA was 82900g / mol, the number average molecular weight Mn was 40700g / mol, the molecular weight distribution was 2.04, and the degree of branching was 0.16 as measured by gel permeation chromatography.

[0059] Example 4

[0060] 30mL of vinyl acetate and 6mL of anhydrous methanol were added to a 100mL stainless steel autoclave with a tetrafluoroethylene liner, and then a chain transfer agent (perfluorohexyl iodide, 105mg, 235μmol) and an initiator (dodecyl peroxide, 20mg, 50μmol) were added to the reactor, and nitrogen was replaced three times, and then replaced three times with ethylene gas. The stirring speed of the reactor was controlled to be 300rpm, and then 3.5MPa of ethylene was charged into the reactor, and after heating to 70°C, the reaction was carried out for 4h, cooled to room temperature, and the pressure was released. The product was transferred to a vacuum oven and dried at 50°C for 12 hours to obtain 6.5g of EVA. The ethylene content was 33.1% as measured by nuclear magnetic resonance, and the weight average molecular weight Mw of EVA was 46600g / mol, the number average molecular weight Mn was 30100g / mol, the molecular weight distribution was 1.55, and the degree of branching was 0.02 as measured by gel permeation chromatography.

[0061] Example 5

[0062] 30mL of vinyl acetate and 6mL of anhydrous methanol were added to a 100mL stainless steel autoclave with a tetrafluoroethylene liner, and then a chain transfer agent (perfluorohexyl iodide, 67mg, 150μmol) and an initiator (dodecyl peroxide, 20mg, 50μmol) were added to the reactor, and nitrogen was replaced three times, and then replaced three times with ethylene gas. The stirring speed of the reactor was controlled to be 150rpm, and then 4.5MPa of ethylene was charged into the reactor, and after heating to 60°C, the reaction was carried out for 4h, cooled to room temperature, and the pressure was released. The product was transferred to a vacuum oven and dried at 50°C for 12 hours to obtain 8.5g of EVA. The ethylene content was 41.2% as measured by nuclear magnetic resonance, and the weight average molecular weight Mw of EVA was 75800g / mol, the number average molecular weight Mn was 40300g / mol, the molecular weight distribution was 1.88, and the degree of branching was 0.05 as measured by gel permeation chromatography.

[0063] Example 6

[0064] 30mL of vinyl acetate and 6mL of anhydrous methanol were added to a 100mL stainless steel autoclave with a tetrafluoroethylene liner, and then a chain transfer agent (perfluorohexyl iodide, 67mg, 150μmol) and an initiator (dodecyl peroxide, 20mg, 50μmol) were added to the reactor, and nitrogen was replaced three times, and then ethylene gas was replaced three times. The stirring speed of the reactor was controlled to be 150rpm, and then 1.5MPa of ethylene was charged into the reactor, and after heating to 80°C, the reaction was carried out for 4h, cooled to room temperature, and the pressure was released. The product was transferred to a vacuum oven and dried at 50°C for 12 hours to obtain 6.3g of EVA. The ethylene content was 20.5% as measured by nuclear magnetic resonance, and the weight average molecular weight Mw of EVA was 58600g / mol, the number average molecular weight Mn was 30500g / mol, the molecular weight distribution was 1.92, and the degree of branching was 0.10 as measured by gel permeation chromatography.

[0065] Example 7

[0066] 30mL of vinyl acetate and 6mL of anhydrous methanol were added to a 100mL stainless steel autoclave with a tetrafluoroethylene liner, and then a chain transfer agent (perfluorohexyl iodide, 67mg, 150μmol) and an initiator (dodecyl peroxide, 20mg, 50μmol) were added to the reactor, and nitrogen was replaced three times, and then replaced three times with ethylene gas. The stirring speed of the reactor was controlled to be 150rpm, and then 3.5MPa of ethylene was charged into the reactor, and after heating to 70°C, the reaction was performed for 1h, cooled to room temperature, and the pressure was released. The product was transferred to a vacuum oven and dried at 50°C for 12 hours to obtain 4.0g of EVA. The ethylene content was 31.8% as measured by nuclear magnetic resonance, and the weight average molecular weight Mw of EVA measured by gel permeation chromatography was 54100g / mol, the number average molecular weight Mn was 30400g / mol, the molecular weight distribution was 1.78, and the degree of branching was 0.04.

[0067] Example 8

[0068] 30mL of vinyl acetate and 6mL of anhydrous methanol were added to a 100mL stainless steel autoclave with a tetrafluoroethylene liner, and then a chain transfer agent (perfluorohexyl iodide, 67mg, 150μmol) and an initiator (dodecyl peroxide, 20mg, 50μmol) were added to the reactor, and nitrogen was replaced three times, and then replaced three times with ethylene gas. The stirring speed of the reactor was controlled to be 150rpm, and then 3.5MPa of ethylene was charged into the reactor, and after heating to 70°C, the reaction was carried out for 2h, cooled to room temperature, and the pressure was released. The product was transferred to a vacuum oven and dried at 50°C for 12 hours to obtain 7.9g of EVA. The ethylene content was 32.5% as measured by nuclear magnetic resonance, and the weight average molecular weight Mw of EVA measured by gel permeation chromatography was 57300g / mol, the number average molecular weight Mn was 30900g / mol, the molecular weight distribution was 1.85, and the degree of branching was 0.05.

[0069] Example 9

[0070] 30mL of vinyl acetate and 6mL of anhydrous methanol were added to a 100mL stainless steel autoclave with a tetrafluoroethylene liner, and then a chain transfer agent (perfluorohexyl iodide, 67mg, 150μmol) and an initiator (dodecyl peroxide, 20mg, 50μmol) were added to the reactor, and nitrogen was replaced three times, and then replaced three times with ethylene gas. The stirring speed of the reactor was controlled to be 150rpm, and then 3.5MPa of ethylene was charged into the reactor, and after heating to 70°C, the reaction was carried out for 6h, cooled to room temperature, and the pressure was released. The product was transferred to a vacuum oven and dried at 50°C for 12 hours to obtain 14.5g of EVA. The ethylene content was 33.8% as measured by nuclear magnetic resonance, and the weight average molecular weight Mw of EVA was 71500g / mol, the number average molecular weight Mn was 36100g / mol, the molecular weight distribution was 1.98, and the degree of branching was 0.08 as measured by gel permeation chromatography.

[0071] Example 10

[0072] 30mL of vinyl acetate and 6mL of anhydrous methanol were added to a 100mL stainless steel autoclave with a tetrafluoroethylene liner, and then a chain transfer agent (perfluoroiodobutane, 52mg, 150μmol) and an initiator (dodecyl peroxide, 20mg, 50μmol) were added to the reactor, and nitrogen was substituted three times, and then ethylene gas was substituted three times. The stirring speed of the reactor was controlled to be 150rpm, and then 3.5MPa of ethylene was charged into the reactor, and after heating to 70°C, the reaction was performed for 4h, cooled to room temperature, and the pressure was released. The product was transferred to a vacuum oven and dried at 50°C for 12 hours to obtain 14.0g of EVA. The ethylene content measured by nuclear magnetic resonance was 33.2%, and the weight average molecular weight Mw of EVA measured by gel permeation chromatography was 86400g / mol, the number average molecular weight Mn was 40700g / mol, the molecular weight distribution was 2.12, and the degree of branching was 0.20.

[0073] Embodiment 11

[0074] 30mL of vinyl acetate and 6mL of anhydrous methanol were added to a 100mL stainless steel autoclave with a tetrafluoroethylene liner, and then a chain transfer agent (iodine hexane, 32mg, 150μmol) and an initiator (dodecyl peroxide, 20mg, 50μmol) were added to the reactor, and nitrogen was replaced three times, and then ethylene gas was replaced three times. The stirring speed of the reactor was controlled to be 150rpm, and then 3.5MPa of ethylene was charged into the reactor, and after heating to 70°C, the reaction was performed for 4h, cooled to room temperature, and the pressure was released. The product was transferred to a vacuum oven and dried at 50°C for 12 hours to obtain 14.6g of EVA. The ethylene content measured by nuclear magnetic resonance was 33.5%, and the weight average molecular weight Mw of EVA measured by gel permeation chromatography was 95000g / mol, the number average molecular weight Mn was 40600g / mol, the molecular weight distribution was 2.34, and the degree of branching was 0.26.

[0075] Example 12

[0076] 30 mL of vinyl acetate and 6 mL of anhydrous methanol were added to a 100 mL stainless steel autoclave with a PTFE lining, and then a chain transfer agent (1,6-diiododecafluorohexane, 83 mg, 150 μmol) and an initiator (dodecyl peroxide, 20 mg, 50 μmol) were added to the reactor, and nitrogen was used to replace the reactor three times, and then ethylene gas was used to replace the reactor three times. The stirring speed of the reactor was controlled to be 150 rpm, and then 3.5 MPa of ethylene was filled into the reactor. After heating to 70 ° C, the reaction was carried out for 4 hours, cooled to room temperature, and the pressure was released. The product was transferred to a vacuum oven and dried at 50 ° C for 12 hours to obtain 13.1 g of EVA. The ethylene content was measured by nuclear magnetic resonance to be 33.2%, and the weight average molecular weight Mw of EVA was measured by gel permeation chromatography to be 71400 g / mol, the number average molecular weight Mn was 37600 g / mol, the molecular weight distribution was 1.90, and the degree of branching was 0.10.

[0077] Examples 13 to 22 are preparation examples of EVOH

[0078] Example 13

[0079] In a 100mL round-bottom flask, add 2.0g EVA obtained in Example 1 and 10mL methanol, heat to 60°C, add 2.5mL sodium hydroxide methanol solution (concentration 0.4mol / L) after EVA is completely dissolved, heat to 65°C for 1h, then add 5mL sodium hydroxide methanol solution for 2h, then add 2.5mL sodium hydroxide methanol solution for 1h, then transfer the product to 100mL deionized water for precipitation, filter and wash the crude product with deionized water and ethanol three times each, and dry at 50°C for 12 hours to obtain EVOH resin. The weight average molecular weight Mw of EVOH is 70800g / mol, the number average molecular weight Mn is 41600g / mol, and the molecular weight distribution is 1.70.

[0080] Embodiment 14

[0081] In a 100mL round-bottom flask, add 2.0g EVA obtained in Example 2 and 10mL methanol, heat to 60°C, add 2.5mL sodium hydroxide methanol solution (concentration is 0.4mol / L) after EVA is completely dissolved, heat to 65°C for reaction for 1h, then add 5mL sodium hydroxide methanol solution for reaction for 2h, then add 2.5mL sodium hydroxide methanol solution for reaction for 1h, then transfer the product to 100mL deionized water for precipitation, filter and wash the crude product with deionized water and ethanol three times each, and dry at 50°C for 12 hours to obtain EVOH resin. The weight average molecular weight Mw of EVOH is 70100g / mol, the number average molecular weight Mn is 39600g / mol, and the molecular weight distribution is 1.77.

[0082] Embodiment 15

[0083] In a 100mL round-bottom flask, add 2.0g EVA obtained in Example 3 and 10mL methanol, heat to 60°C, add 2.5mL sodium hydroxide methanol solution (concentration is 0.4mol / L) after EVA is completely dissolved, heat to 65°C for reaction for 1h, then add 5mL sodium hydroxide methanol solution for reaction for 2h, then add 2.5mL sodium hydroxide methanol solution for reaction for 1h, then transfer the product to 100mL deionized water for precipitation, filter and wash the crude product with deionized water and ethanol three times each, and dry at 50°C for 12 hours to obtain EVOH resin. The weight average molecular weight Mw of EVOH is 66700g / mol, the number average molecular weight Mn is 37000g / mol, and the molecular weight distribution is 1.80.

[0084] Example 16

[0085] In a 100mL round-bottom flask, add 2.0g EVA obtained in Example 10 and 10mL methanol, heat to 60°C, add 2.5mL sodium hydroxide methanol solution (concentration 0.4mol / L) after EVA is completely dissolved, heat to 65°C for 1h, then add 5mL sodium hydroxide methanol solution for 2h, then add 2.5mL sodium hydroxide methanol solution for 1h, then transfer the product to 100mL deionized water for precipitation, filter and wash the crude product with deionized water and ethanol three times each, and dry at 50°C for 12 hours to obtain EVOH resin. The weight average molecular weight Mw of EVOH is 69000g / mol, the number average molecular weight Mn is 38300g / mol, and the molecular weight distribution is 1.80.

[0086] Embodiment 17

[0087] In a 100mL round-bottom flask, add 2.0g EVA obtained in Example 11 and 10mL methanol, heat to 60°C, add 2.5mL sodium hydroxide methanol solution (concentration of 0.4mol / L) after EVA is completely dissolved, heat to 65°C for reaction for 1h, then add 5mL sodium hydroxide methanol solution for reaction for 2h, then add 2.5mL sodium hydroxide methanol solution for reaction for 1h, then transfer the product to 100mL deionized water for precipitation, filter and wash the crude product with deionized water and ethanol three times each, and dry at 50°C for 12 hours to obtain EVOH resin. The weight average molecular weight Mw of EVOH is 71800g / mol, the number average molecular weight Mn is 39200g / mol, and the molecular weight distribution is 1.83.

[0088] Embodiment 18

[0089] In a 100mL round-bottom flask, add 2.0g EVA obtained in Example 12 and 10mL methanol, heat to 60°C, add 2.5mL sodium hydroxide methanol solution (concentration 0.4mol / L) after EVA is completely dissolved, heat to 65°C for reaction for 1h, then add 5mL sodium hydroxide methanol solution for reaction for 2h, then add 2.5mL sodium hydroxide methanol solution for reaction for 1h, then transfer the product to 100mL deionized water for precipitation, filter and wash the crude product with deionized water and ethanol three times each, and dry at 50°C for 12 hours to obtain EVOH resin. The weight average molecular weight Mw of EVOH is 60200g / mol, the number average molecular weight Mn is 34400g / mol, and the molecular weight distribution is 1.75.

[0090] Embodiment 19

[0091] In a 100mL round-bottom flask, add 2.0g EVA obtained in Example 1 and 10mL methanol, heat to 60°C, add 2.5mL potassium hydroxide methanol solution (concentration 0.4mol / L) after EVA is completely dissolved, heat to 65°C for 1h, then add 5mL potassium hydroxide methanol solution for 2h, then add 2.5mL potassium hydroxide methanol solution for 1h, then transfer the product to 100mL deionized water for precipitation, filter and wash the crude product with deionized water and ethanol three times each, and dry at 50°C for 12 hours to obtain EVOH resin. The weight average molecular weight Mw of EVOH is 71200g / mol, the number average molecular weight Mn is 35400g / mol, and the molecular weight distribution is 2.01.

[0092] Embodiment 20

[0093] In a 100mL round-bottom flask, add 2.0g EVA obtained in Example 1 and 10mL methanol, heat to 60°C, and after EVA is completely dissolved, add 10mL sodium hydroxide methanol solution (concentration is 0.4mol / L) at one time, heat to 65°C for 4h, then transfer the product to 100mL deionized water for precipitation, filter and wash the crude product with deionized water and ethanol three times respectively, and dry at 50°C for 12 hours to obtain EVOH resin. The weight average molecular weight Mw of EVOH is 70500g / mol, the number average molecular weight Mn is 42500g / mol, and the molecular weight distribution is 1.66.

[0094] Embodiment 21

[0095] In a 100mL round-bottom flask, add 2.0g EVA obtained in Example 1 and 10mL methanol, heat to 60°C, add 2.5mL sodium hydroxide methanol solution (concentration 0.4mol / L) after EVA is completely dissolved, heat to 65°C for 2h, then add 5mL sodium hydroxide methanol solution for 2h, then add 2.5mL sodium hydroxide methanol solution for 2h, then transfer the product to 100mL deionized water for precipitation, filter and wash the crude product with deionized water and ethanol three times each, and dry at 50°C for 12 hours to obtain EVOH resin. The weight average molecular weight Mw of EVOH is 71200g / mol, the number average molecular weight Mn is 40500g / mol, and the molecular weight distribution is 1.76.

[0096] Embodiment 22

[0097] In a 100mL round-bottom flask, add 2.0g EVA obtained in Example 1 and 10mL methanol, heat to 60°C, add 5mL sodium hydroxide methanol solution (concentration 0.4mol / L) after EVA is completely dissolved, heat to 65°C for reaction for 1h, then add 5mL sodium hydroxide methanol solution for reaction for 2h, then add 5mL sodium hydroxide methanol solution for reaction for 1h, then transfer the product to 100mL deionized water for precipitation, filter and wash the crude product with deionized water and ethanol three times each, and dry at 50°C for 12 hours to obtain EVOH resin. The weight average molecular weight Mw of EVOH is 72500g / mol, the number average molecular weight Mn is 41600g / mol, and the molecular weight distribution is 1.74.

[0098] Comparative Example 1

[0099] 30mL of vinyl acetate and 6mL of anhydrous methanol were added to a 100mL stainless steel autoclave with a tetrafluoroethylene liner, and then an initiator (dodecyl peroxide, 20mg, 50μmol) was added to the reactor, and nitrogen was substituted three times, and then ethylene gas was substituted three times. The stirring speed of the reactor was controlled to be 150rpm, and then 3.5MPa of ethylene was charged into the reactor, and after heating to 70°C, the reaction was performed for 4h, cooled to room temperature, and the pressure was released. The product was transferred to a vacuum oven and dried at 50°C for 12 hours to obtain 19.8g of EVA. The ethylene content measured by nuclear magnetic resonance was 33.5%, and the weight average molecular weight Mw of EVA measured by gel permeation chromatography was 78500g / mol, the number average molecular weight Mn was 32900g / mol, the molecular weight distribution was 2.39, and the degree of branching was 0.64.

[0100] Comparative Example 2

[0101] 30 mL of vinyl acetate and 6 mL of anhydrous methanol were added to a 100 mL stainless steel autoclave with a PTFE liner, and then a chain transfer agent (perfluorohexyl iodide, 70 mg, 150 μmol) was added to the autoclave, and the atmosphere was replaced three times with nitrogen and then replaced three times with ethylene gas. The stirring speed of the autoclave was controlled to be 150 rpm, and then 3.5 MPa of ethylene was charged into the autoclave, and the temperature was raised to 70°C, and the reaction was carried out for 4 hours, and then the pressure was released to release the pressure, and no polymer was generated.

[0102] Comparative Example 3

[0103] 30mL of vinyl acetate and 6mL of anhydrous methanol were added to a 100mL stainless steel autoclave with a tetrafluoroethylene liner, and then a chain transfer agent (perfluorohexyl iodide, 70mg, 150μmol) and an initiator (azobisisobutyronitrile, 8mg, 50μmol) were added to the reactor, and nitrogen was used for replacement three times, and then ethylene gas was used for replacement three times. The stirring speed of the reactor was controlled to be 150rpm, and then 3.5MPa of ethylene was charged into the reactor, and after heating to 60°C, the reaction was carried out for 4h, cooled to room temperature, and the pressure was released. The product was transferred to a vacuum oven and dried at 50°C for 12 hours to obtain 3.5g of EVA. The ethylene content was 32.6% as measured by nuclear magnetic resonance, and the weight average molecular weight Mw of EVA was 71500g / mol, the number average molecular weight Mn was 35900g / mol, the molecular weight distribution was 1.99, and the degree of branching was 0.65 as measured by gel permeation chromatography.

[0104] Comparative Example 4

[0105] In a 100mL round-bottom flask, add 2.0g EVA obtained in Comparative Example 3 and 10mL methanol, heat to 60°C, add 2.5mL sodium hydroxide methanol solution (concentration 0.4mol / L) after EVA is completely dissolved, heat to 65°C for 1h, then add 5mL sodium hydroxide methanol solution for 2h, then add 2.5mL sodium hydroxide methanol solution for 1h, then transfer the product to 100mL deionized water for precipitation, filter and wash the crude product with deionized water and ethanol three times each, and dry at 50°C for 12 hours to obtain EVOH resin. The weight average molecular weight Mw of EVOH is 43300g / mol, the number average molecular weight Mn is 23800g / mol, and the molecular weight distribution is 1.82.

[0106] From the results of the comparative example, it can be seen that the copolymerization of ethylene and vinyl acetate using a combination of dodecyl peroxide as an initiator and perfluorohexyl iodide as a chain transfer agent in the present invention can obtain EVA with a high molecular weight and extremely low branching degree in high yield.

[0107] The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing an ethylene-vinyl acetate copolymer, characterized in that: The ethylene-vinyl acetate copolymer is obtained by the following steps: An initiator, a chain transfer agent, a solvent and vinyl acetate are mixed, nitrogen bubbling is used to remove oxygen, and then ethylene gas is introduced to polymerize under pressure to obtain the ethylene-vinyl acetate copolymer; The initiator is selected from at least one of dodecyl peroxide and benzoyl peroxide; The chain transfer agent is at least one selected from perfluorohexyl iodide, 1,6-diiododecafluorohexane, iodine hexane, and perfluorobutyl iodide.

2. The preparation method according to claim 1, characterized in that: The molar ratio of the initiator to the chain transfer agent is 1:10 to 10:1; Preferably, the molar ratio of the initiator to the chain transfer agent is 1:4 to 4:1; The molar ratio of the initiator to vinyl acetate is 1:100000 to 1:1000.

3. The preparation method according to claim 1, characterized in that: The solvent is selected from at least one of methanol, ethanol, tert-butanol, n-butanol and isopropanol.

4. The preparation method according to claim 1, characterized in that: The volume ratio of the solvent to vinyl acetate is 1:10 to 1:2; The ethylene gas is introduced to make the pressure reach 1-10Mpa; The polymerization temperature is 20 to 100° C. The polymerization time is 0.1 to 10 hours.

5. An ethylene-vinyl acetate copolymer prepared by the preparation method according to any one of claims 1 to 4, characterized in that: The number average molecular weight of the ethylene-vinyl acetate copolymer is 20000-100000 g / mol; Preferably, the number average molecular weight of the ethylene-vinyl acetate copolymer is 30,000 to 60,000 g / mol; The branching degree of the ethylene-vinyl acetate copolymer is 0.01 to 0.3; Preferably, the degree of branching of the ethylene-vinyl acetate copolymer is 0.01 to 0.2; The molecular weight distribution of the ethylene-vinyl acetate copolymer is 1.0 to 3.0; Preferably, the molecular weight distribution of the ethylene-vinyl acetate copolymer is 1.0 to 2.

0.

6. A method for preparing an ethylene-vinyl alcohol copolymer, characterized in that: The ethylene-vinyl alcohol copolymer is obtained by the following steps: The ethylene-vinyl acetate copolymer according to claim 5, an organic solvent and a catalyst are mixed, and alcoholysis reaction is carried out, and the mixture is washed with water, filtered and dried to obtain the ethylene-vinyl alcohol copolymer.

7. The preparation method according to claim 6, characterized in that The organic solvent is selected from at least one of methanol and ethanol; The catalyst is selected from at least one of sodium hydroxide, potassium hydroxide and alkali metal alcoholates.

8. The preparation method according to claim 6, characterized in that: The mass ratio of the ethylene-vinyl acetate copolymer, the solvent and the catalyst described in claim 5 is 1:50:1 to 1:2:0.

01.

9. The preparation method according to claim 6, characterized in that: The temperature of the alcoholysis reaction is 20 to 100° C. The alcoholysis reaction time is 1 to 10 hours.

10. An ethylene-vinyl alcohol copolymer prepared by the preparation method according to any one of claims 6 to 10, characterized in that: The number average molecular weight of the ethylene-vinyl alcohol copolymer is 20,000 to 100,000 g / mol; The molecular weight distribution of the ethylene-vinyl alcohol copolymer is 1.0 to 3.0; The number average molecular weight of the ethylene-vinyl alcohol copolymer is 30,000 to 60,000 g / mol, and the molecular weight distribution is 1.0 to 2.0.

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