Initiator for preparing EVOH as well as preparation method and application of initiator

Abstract

The invention relates to an initiator for preparing EVOH as well as a preparation method and application thereof, the initiator is a cyclic bisazo compound, and the structural formula of the cyclic bisazo compound is shown as a formula A. Compared with the prior art, the initiator provided by the invention has a ring rigid structure and two azo groups, can rapidly initiate generation of free radicals with a certain concentration, is high in polymerization efficiency, and effectively improves the performance of an EVOH product.

Description

Technical Field

[0001] This invention relates to the field of ethylene-vinyl alcohol copolymer technology, and in particular to an initiator for preparing EVOH, its preparation method, and its application. Background Technology

[0002] Ethylene-vinyl alcohol copolymer (EVOH) is a high-end polymer barrier material. Its internal structure contains ethylene and vinyl alcohol segments. The ethylene segments provide EVOH with excellent processability, while the vinyl alcohol segments provide excellent gas barrier properties. Currently, EVOH is widely used in food packaging, medical packaging, and electronic component sealing. The rapid development of cold chain logistics and pharmaceutical packaging has further driven the demand for EVOH, with the current annual market growth rate at approximately 5.8%. To meet this growing demand, researchers have made numerous efforts to improve the production capacity and performance of EVOH.

[0003] Since EVOH cannot be directly polymerized, all current manufacturers use a two-step process. The first step involves polymerizing ethylene and vinyl acetate using a free radical initiator to produce ethylene-vinyl acetate copolymer (EVA). The EVA is then saponified in an alcohol solution to obtain the final product, EVOH. Currently, the large-scale application of EVOH faces certain limitations, primarily due to the limited molecular weight of produced EVOH, generally concentrated in the tens or hundreds of thousands. Further increases in molecular weight are not possible because the free radical initiator has low initiation efficiency, failing to produce a sufficient number of free radicals for the polymerization reaction. Lower molecular weight EVOH exhibits significant performance weaknesses, such as lower tensile strength and melting point, hindering its expansion in industries like food packaging films and hoses. Secondly, many studies have found that EVOH production equipment frequently experiences pipe blockage during operation. Analysis revealed this is due to the production of large quantities of high-viscosity, low-molecular-weight EVOH. Further research has shown that the half-life of the free radical initiator and the initial free radical concentration significantly affect the early stages of polymerization of low-molecular-weight EVOH. In conclusion, the selection of free radical initiators is of great significance to both the product quality and the continuity of EVOH production.

[0004] Commonly available free radical initiators mainly fall into three categories: azo initiators, peroxide initiators, and redox initiators. Azo initiators primarily include azobisisobutyronitrile (AIBN), azobisisovalerate (AMBN), and 2,2'-azobis(2,4-dimethyl-4-methoxyvalerate). The decomposition reactions of azo initiators are almost entirely first-order reactions, forming only one type of free radical. They exhibit no induced decomposition, have a low decomposition rate, and are considered low-activity initiators, typically suitable for reaction temperatures of 50℃ to 65℃. Peroxide initiators mainly include benzoyl peroxide (BPO), dicumyl peroxide (DCP), and tert-butyl hydroperoxide. Peroxide initiators have a high decomposition rate and are considered high-activity initiators. Their decomposition reaction involves the homolytic cleavage of the peroxide group under thermal or light conditions to generate initiating free radicals, making them suitable for higher reaction temperatures. Besides the azo compounds and peroxides mentioned above, redox reaction systems can also be used to provide free radicals. These systems consist of peroxide oxidants and a small amount of reducing agents, generating intermediate free radicals through electron transfer reactions for free radical polymerization. These systems have low activation energies and can polymerize at relatively low temperatures. However, unfortunately, the aforementioned common free radical initiators cannot simultaneously meet the requirements of low activation energy and high free radical generation, which is extremely detrimental to the EVOH generation process, leading to low molecular weight EVOH products and production blockages. Summary of the Invention

[0005] The purpose of this invention is to provide an initiator for preparing ethylene-vinyl alcohol copolymers, a method for preparing the same, and its application in order to solve the above-mentioned problems.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] An initiator for preparing EVOH, the initiator being a cyclic diazo compound having an aromatic ring as the intermediate structure of the compound, with a pair of 3,4,5,6-tetrahydropyridazines coupled to the aromatic ring, wherein the aromatic ring includes benzene, and the structural formula of the cyclic diazo compound is as follows:

[0008]

[0009] In formula A, R1 and R2 are each individually selected from H, C1-C6 alkyl, C1-C6 alkoxy, nitro, halogen, amide, C6-C6, and C6-C6 alkyl groups, respectively. 12 Aromatic hydrocarbons.

[0010] More preferably, in formula A, R1 and R2 are each individually selected from H, C1-C3 alkyl groups, C1-C3 alkoxy groups, and C6 aromatic hydrocarbons.

[0011] In a preferred embodiment of the present invention, the cyclic diazo compound is selected from any of the following structures:

[0012]

[0013] The preparation method of the initiator described above is as follows: the cyclic diazo compound is formed by oxidation of compound I, which has two sets of adjacent imino groups, wherein compound I is an aromatic amine derivative with two sets of adjacent imino groups.

[0014] Further, compound I comprises one of benzene-1,2,4,5-tetramethyltetramethylamine, (3,6-dimethylbenzene-1,2,4,5-tetramethyl)tetramethylamine, and 1,1'-biphenyl-2,3,5,6-tetraalkyltetramethylamine, with the following specific structural formula:

[0015]

[0016] Furthermore, compound I can be oxidized into a cyclic diazo compound by sodium hypochlorite intramolecularly or extramolecularly. The specific steps are as follows: dissolve compound I in a solvent, add sodium hypochlorite aqueous solution dropwise, after the reaction is completed, remove the solvent and water, and purify the product by column chromatography.

[0017] Further, compound I is obtained by hydrogenation of compound II, which has two adjacent cyano groups, wherein compound II is an aromatic derivative having two adjacent cyano groups, and compound II includes one of 1,2,4,5-tetracyanobenzene, 1,2,4,5-tetracyano-3,6-dimethylbenzene, and 1,1'-biphenyl-2,3,5,6-tetranitrile, with the specific structural formula as follows:

[0018]

[0019] Further, the specific steps of hydrogenation of compound II are as follows: compound II and methanol-treated RaneyNi are added together to a solution (such as tetrahydrofuran), the mixture is stirred and reacted, and after the reaction is completed, the product is washed with methanol to obtain the product.

[0020] The application of the initiator described above involves preparing EVOH using the aforementioned cyclic diazo compound as the initiator, and ethylene and vinyl acetate as raw materials for free radical polymerization to generate EVA, followed by hydrolysis of EVA under alkaline conditions to obtain EVOH.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] This invention provides a novel cyclic diazo compound as an initiator. It possesses a certain degree of cyclic rigidity, enabling rapid initiation of a specific concentration of free radicals, thus improving the ease and rate of initiation and regulating the initial free radical concentration. The compound structure contains two azo groups, resulting in superior initiation efficiency compared to single-radical initiators. This leads to a larger molecular weight product, effectively improving EVOH product performance. Furthermore, the introduction of multiple free radical initiator groups avoids the formation of low-molecular-weight polymers, preventing pipe blockage during EVOH production. Detailed Implementation

[0023] The following description is provided to disclose the invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples and are not intended to limit the scope of the invention; other obvious variations will occur to those skilled in the art. The basic principles of the invention defined in the following description can be applied to other embodiments, modifications, improvements, equivalents, and other technical solutions that do not depart from the spirit and scope of the invention.

[0024] Unless otherwise specified, the instruments or reagents used in the embodiments of this invention are all conventional commercial instruments or reagents.

[0025] The main reagents used in the examples are as follows:

[0026] Ethylene (CAS: 74-85-1 Shanghai Air Liquide)

[0027] Vinyl acetate (CAS: 108-05-4Sigma-Aldrich)

[0028] Hydrogen (CAS: 1333-74-0 Shanghai Air Liquide)

[0029] 1,2,4,5-Tetracyanobenzene (CAS: 712-74-3 Bailingwei Reagent)

[0030] 1,2,4,5-Tetracyano-3,6-Dimethylbenzene (CAS: 80717-49-3 Pusai Chemical)

[0031] 1,1'-Biphenyl-2,3,5,6-Tetranitrile (CAS: 1802172-30-0 Jilin Zhongke Research Institute)

[0032] Raney Nickel (CAS:7440-02-0Sigma-Aldrich)

[0033] Sodium hydroxide (CAS: 1310-73-2Sigma-Aldrich)

[0034] Tetrahydrofuran (CAS: 109-99-9Sigma-Aldrich)

[0035] Sodium hypochlorite (CAS: 7681-52-9Sigma-Aldrich)

[0036] Methanol (CAS: 67-56-1Sigma-Aldrich)

[0037] Dimethyl sulfoxide (CAS: 67-68-5Sigma-Aldrich)

[0038] tert-Butanol (CAS: 75-65-OSigma-Aldrich)

[0039] Unless otherwise specified, all organic solvents must be anhydrous, and ultrapure water must be used.

[0040] Example 1

[0041] Preparation of initiator A1.

[0042] The synthesis route is as follows:

[0043]

[0044] 1,2,4,5-Tetracyanobenzene (1 mmol, 178.2 mg) and Raney Ni catalyst (10 mg) treated with methanol were added to a tetrahydrofuran solution and placed in a three-necked flask. A hydrogen balloon was attached to the top of the flask, and the mixture was stirred at 40 °C for 12 hours. After the reaction was completed, the mixture was washed with methanol to obtain benzene-1,2,4,5-tetramethyltetramethylamine in 98% yield.

[0045] The obtained benzene-1,2,4,5-tetramethyltetramethylamine (1 mmol, 194.3 mg) was dissolved in 100 mL of water stirred at 25 °C. Then, an aqueous solution of sodium hypochlorite (5 mmol, 372 mg, c = 0.95 mol / L) was slowly added dropwise over 0.5 hours. After the reaction was complete, the solvent water was removed by rotation. The product was then purified by column chromatography using basic alumina as the stationary phase and methanol:HEX = 2:1 as the mobile phase. The resulting product was dried under vacuum and stored in a brown glass bottle for later use. The yield was approximately 45%. 1 H 300MHz, DMSO): 7.01(s,2H,-Ar-H); 2.62(s,8H,-CH2). C 10 H 10 N4: Calculated values ​​(%) by elemental analysis: C, 64.50; H, 5.41; N, 30.09. Experimental values ​​(%): C, 64.53; H, 5.50; N, 30.13.

[0046] Example 2

[0047] Prepare initiator A2.

[0048] The synthesis route is as follows:

[0049]

[0050] 1,2,4,5-Tetracyano-3,6-dimethylbenzene (1 mmol, 206.2 mg) and Raney Ni catalyst (10 mg) treated with methanol were added to a tetrahydrofuran solution and placed in a three-necked flask. A hydrogen balloon was attached to the top of the flask, and the mixture was stirred at 40 °C for 12 hours. After the reaction was completed, the mixture was washed with methanol to obtain (3,6-dimethylbenzene-1,2,4,5-tetramethyl)tetramethylamine in 97% yield.

[0051] (3,6-Dimethylphenyl-1,2,4,5-tetramethyl)tetramethylamine (1 mmol, 222.2 mg) was dissolved in 100 mL of water stirred at 25 °C. Then, sodium hypochlorite aqueous solution (5 mmol, 372 mg, c = 0.95 mol / L) was slowly added dropwise over 0.5 hours. After the reaction was complete, the solvent water was removed by rotation. The product was then purified by column chromatography using basic alumina as the stationary phase and methanol:HEX = 2:1 as the mobile phase. The resulting product was dried under vacuum and stored in a brown glass bottle for later use. The yield was approximately 55%. 1 H 300MHz, DMSO): 2.63(s,8H,-CH2); 2.11(s,6H,-CH3). C 12 H 14 N4: Elemental analysis calculated values ​​(%): C, 67.27; H, 6.59; N, 26.15. Experimental measured values ​​(%): C, 67.30; H, 6.59; N, 26.18.

[0052] Example 3

[0053] Prepare initiator A3.

[0054] The synthesis route is as follows:

[0055]

[0056] 1,1'-Biphenyl-2,3,5,6-tetranitrile (1 mmol, 254.3 mg) and methanol-treated Raney Ni (10 mg) were added to a tetrahydrofuran solution and placed in a three-necked flask. A hydrogen balloon was attached to the top of the flask, and the mixture was stirred at 40 °C for 12 hours. After the reaction was complete, the mixture was washed with methanol to obtain 1,1'-biphenyl-2,3,5,6-tetraalkyltetramethylamine in 95% yield.

[0057] 1,1'-Biphenyl-2,3,5,6-tetraalkyltetramethylamine (1 mmol, 270.4 mg) was dissolved in 100 mL of water stirred at 25 °C. Then, sodium hypochlorite aqueous solution (2 mmol, 148.8 mg, c = 0.95 mol / L) was slowly added dropwise over 0.5 hours. After the reaction was complete, the solvent water was removed by rotation. The product was then purified by column chromatography using basic alumina as the stationary phase and methanol:HEX = 2:1 as the mobile phase. The resulting product was dried under vacuum and stored in a brown glass bottle for later use. The yield was 55%. 1 H 300MHz, DMSO): 7.62-7.36(m,5H,-Ar-H); 7.05(s,1H,-Ar-H); 2.60(s,8H,-CH2). C 16 H 14 N4: Elemental analysis calculated values ​​(%): C, 73.26; H, 5.38; N, 21.36. Experimental measured values ​​(%): C, 73.33; H, 5.42; N, 21.37.

[0058]

Application Examples

[0059] The initiators obtained above were used in EVOH preparation experiments to evaluate their performance.

[0060] The specific reaction conditions were as follows: a 200 mL stainless steel reactor was heated under vacuum at 100 °C for 2 hours, and then cooled to ambient temperature. First, 66 g of vinyl acetate and 22 g of a mixed solution of tert-butanol and methanol (V) were added to the reactants. 叔丁醇 V 甲醇 =1:1). Then, N2 was introduced to raise the temperature to 60℃ and stirred for 30 minutes. Next, a cyclic diazo initiator (approximately 0.25% wt% of vinyl acetate) was added through the ethylene inlet, and ethylene was introduced again, maintaining the pressure at 3.6 MPa. The reaction was carried out at 60℃ for 2.5 hours, and then allowed to cool naturally after the reaction. The resulting EVA tert-butanol solution was poured into another reactor, and 25 mL of sodium hydroxide methanol solution (20 wt% sodium hydroxide concentration) was added. The reaction was stirred at 60℃ for 4 hours. After the reaction, a large amount of acetic acid solution was added to neutralize the unreacted alkali. Finally, the solution was transferred to a metal container and left at room temperature for 24 hours. After cooling and hardening, a paste was obtained. After centrifugation, the paste was washed with plenty of water and vacuum dried at 60℃ for 48 hours to obtain the product EVOH.

[0061] In addition, the cyclic bisazo initiator was replaced with azobisisobutyronitrile (AIBN) and benzoyl oxide (BPO), respectively, with the amount of azobisisobutyronitrile (AIBN) and benzoyl oxide (BPO) being 0.5 wt% of vinyl acetate.

[0062] The yield of EVOH was calculated, and the molar fraction of ethylene was tested according to GB / T 41877.2-2022. The content of vinyl acetate was calculated according to SN / T2333-2009. The results are shown in Table 1.

[0063] EVA conversion rate = (m 初始EVA -m 剩余EVA ) / m 初始EVA *100%

[0064] Table 1. Test results of EVOH yield and ethylene content

[0065]

[0066] As shown in Table 1, the EVOH preparation efficiency of the examples is higher than that of the comparative examples. This is because the diazo group and rigid cyclic structure of the initiator can rapidly generate free radicals, resulting in a better initiation rate and free radical concentration, thus obtaining more EVOH products in a shorter time. The ethylene fragment content in the EVOH obtained by this invention is maintained within the range of 31% to 34%, which meets the processing requirements while possessing high gas barrier properties, indicating that the cyclic diazo initiator of this invention can effectively regulate the ethylene fragment content in EVOH.

[0067]

EVOH Performance Test

[0068] Molecular weight was determined by gel permeation chromatography according to GB / T 27843-2011;

[0069] Impact strength and tensile strength were tested according to GB / T 1043.2-2018.

[0070] The O2 transmittance (GTR) of EVOH was tested according to GBT41877.2-2022.

[0071] The test results are detailed in Table 2.

[0072] Table 2 EVOH Performance Test Results

[0073]

[0074] As shown in Table 2, compared with the comparative example using a single functional group initiator, the EVOH product obtained in this invention has a larger molecular weight, exhibiting superior tensile strength and impact strength, as well as better gas barrier properties (low oxygen permeability). The performance of the EVOH product is superior to that of traditional initiator products. More importantly, the reduction in high and low molecular weight EVOH helps to reduce the occurrence of pipe blockage during production.

[0075] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. An initiator for preparing EVOH, characterized in that, The initiator is a cyclic diazo compound, and the structural formula of the cyclic diazo compound is as follows: In formula A, R1 and R2 are each individually selected from H, C1-C6 alkyl, C1-C6 alkoxy, nitro, halogen, amide, C6-C6, and C6-C6 alkyl groups, respectively. 12 Aromatic hydrocarbons.

2. The initiator for preparing EVOH according to claim 1, characterized in that, In Formula A, R1 and R2 are each individually selected from H, C1-C3 alkyl groups, C1-C3 alkoxy groups, and C6 aromatic hydrocarbons.

3. The initiator for preparing EVOH according to claim 1, characterized in that, The cyclic diazo compound is selected from any of the following structures:

4. A method for preparing an initiator as described in any one of claims 1 to 3, characterized in that, The cyclic diazo compound is formed by oxidation of compound I, which has two sets of adjacent imino groups, wherein compound I is an aromatic amine derivative with two sets of adjacent imino groups.

5. The method for preparing the initiator according to claim 4, characterized in that, Compound I includes one of benzene-1,2,4,5-tetramethyltetramethylamine, (3,6-dimethylbenzene-1,2,4,5-tetramethyl)tetramethylamine, and 1,1'-biphenyl-2,3,5,6-tetraalkyltetramethylamine.

6. The method for preparing the initiator according to claim 5, characterized in that, The compound I is oxidized into a cyclic diazo compound by sodium hypochlorite intramolecularly or extramolecularly. The specific steps are as follows: dissolve compound I in a solvent, add sodium hypochlorite aqueous solution dropwise, remove the solvent and water after the reaction is completed, and purify the product by column chromatography.

7. The method for preparing the initiator according to claim 4, characterized in that, Compound I is obtained by hydrogenation of compound II, which has two sets of adjacent cyano groups. Compound II is an aromatic derivative with two sets of adjacent cyano groups, and includes one of 1,2,4,5-tetracyanobenzene, 1,2,4,5-tetracyano-3,6-dimethylbenzene, and 1,1'-biphenyl-2,3,5,6-tetranitrile.

8. The method for preparing the initiator according to claim 7, characterized in that, The specific steps for hydrogenating compound II are as follows: compound II and methanol-treated Raney Ni are added to the solution, stirred and reacted, and after the reaction is completed, the mixture is washed with methanol to obtain the product.

9. An application of the initiator as described in any one of claims 1 to 3, characterized in that, The initiator is used to prepare EVOH.

10. The application of the initiator according to claim 9, characterized in that, Using the aforementioned cyclic diazo compound as an initiator, ethylene and vinyl acetate were used as raw materials for free radical polymerization to generate EVA, which was then hydrolyzed under alkaline conditions to obtain EVOH.

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