Vinyl Alcohol Based Copolymer, Method for Preparing the Same and Gas Barrier Film Comprising the Same

Abstract

In the present disclosure, there are provided a vinyl alcohol-based copolymer including a first repeating unit derived from an olefin, a second repeating unit containing a hydroxyl group, and a third repeating unit containing a cyanoalkyloxy group formed by a reaction of the repeating unit containing a hydroxyl group and an unsaturated nitrile-based compound, wherein the third repeating unit is included in an amount of 2 mol % or more and less than 10 mol % with respect to 100 mol % of a total amount of the second repeating unit and the third repeating unit; a method for preparing the same; and a gas barrier film including the same. The vinyl alcohol-based copolymer has excellent moisture stability, thereby exhibiting excellent gas barrier properties even in a humid environment.

Claims

1. A vinyl alcohol-based copolymer, comprising a first repeating unit derived from an olefin; a second repeating unit represented by the following Chemical Formula 1 containing a hydroxyl group; and a third repeating unit represented by the following Chemical Formula 2 containing a cyanoalkyloxy group; wherein the third repeating unit is comprised in an amount of 2 mol % or more and less than 10 mol % with respect to 100 mol % of a total amount of the second repeating unit and the third repeating unit: ##STR00005## in Chemical Formula 2, L is C.sub.1-10 alkylene.

2. The vinyl alcohol-based copolymer of claim 1, wherein the third repeating unit is comprised in an amount of 2 to 9 mol % with respect to 100 mol % of a total amount of the second repeating unit and the third repeating unit.

3. The vinyl alcohol-based copolymer of claim 1, wherein in Chemical Formula 2, L is ethylene, 1-methylethylene, or n-propylene.

4. The vinyl alcohol-based copolymer of claim 1, wherein the third repeating unit has a structure represented by the following Chemical Formula 2-1: ##STR00006##

5. The vinyl alcohol-based copolymer of claim 1, wherein the first repeating unit is included in an amount of 10 to 70 mol % with respect to 100 mol % of a total amount of repeating units in the copolymer.

6. The vinyl alcohol-based copolymer of claim 1, wherein the first repeating unit is a repeating unit derived from ethylene.

7. The vinyl alcohol-based copolymer of claim 1, wherein the second repeating unit is comprised in an amount of 25 to 85 mol % with respect to 100 mol % of a total amount of repeating units in the copolymer.

8. The vinyl alcohol-based copolymer of claim 1, wherein the copolymer further comprises a repeating unit derived from a vinyl carboxylate-based compound.

9. The vinyl alcohol-based copolymer of claim 8, wherein the vinyl carboxylate-based compound is vinyl acetate.

10. A method for preparing the vinyl alcohol-based copolymer of claim 1, comprising the step of: performing hydrolysis by a saponification reaction by adding a basic substance to a copolymer of an olefin-vinyl carboxylate-based compound, wherein an unsaturated nitrile-based compound is added when the saponification reaction proceeds at least 95%, and reacted such that a cyanoalkyl substitution ratio according to the following Equation 1 is 2 mol % or more and less than 10 mol %:
Cyanoalkyl substitution ratio=[(mol % of third repeating unit)/(mol % of second repeating unit+mol % of third repeating unit)]×100  [Equation 1] in Equation 1, the mol % of second repeating unit and the mol % of third repeating unit are values based on 100 mol % of a total amount of repeating units in the vinyl alcohol-based copolymer.

11. The method for preparing the vinyl alcohol-based copolymer of claim 10, wherein the copolymer of an olefin-vinyl carboxylate-based compound has a weight average molecular weight of 100,000 to 350,000 g/mol and a molecular weight distribution of 1.5 to 2.5, and first repeating unit derived from an olefin is included in an amount of 10 to 70 mol % with respect to 100 mol % of a total amount of repeating units in the copolymer of an olefin-vinyl carboxylate-based compound.

12. The method for preparing the vinyl alcohol-based copolymer of claim 10, further comprising the step of preparing a copolymer of an olefin-vinyl carboxylate-based compound by adding an olefin and a vinyl carboxylate-based compound in a molar ratio of 5:95 to 40:60 and polymerizing them in an alcohol-based solvent in the presence of a radical initiator, before the hydrolysis of the copolymer of an olefin-vinyl carboxylate-based compound, and the radical initiator is used in a molar ratio of 0.001 to 1 with respect to 100 mol of a total amount of monomers comprising the olefin and the vinyl carboxylate-based compound.

13. The method for preparing the vinyl alcohol-based copolymer of claim 10, wherein the copolymer of an olefin-vinyl carboxylate-based compound is an ethylene-vinyl acetate copolymer.

14. The method for preparing the vinyl alcohol-based copolymer of claim 10, wherein the unsaturated nitrile-based compound comprises at least one selected from the group consisting of acrylonitrile, methacrylonitrile, 1-cyanopropene, and 3-cyanopropene.

15. The method for preparing the vinyl alcohol-based copolymer of claim 10, wherein the hydrolysis is performed by adding the basic substance in a molar ratio of 5 to 15 with respect to 100 mol of the copolymer of an olefin-vinyl carboxylate-based compound.

16. The method for preparing the vinyl alcohol-based copolymer of claim 10, wherein the basic substance comprises sodium hydroxide.

17. A composition for forming a gas barrier film comprising the vinyl alcohol-based copolymer according to claim 1.

18. A gas barrier film comprising the vinyl alcohol-based copolymer according to claim 1.

19. The vinyl alcohol-based copolymer of claim 6, wherein the first repeating unit further includes at least one repeating unit derived from propylene, butylene, pentene, hexene, or octene.

20. The vinyl alcohol-based copolymer of claim 8, wherein the repeating unit derived from a vinyl carboxylate-based compound is included in an amount of 1 mol % or less and 0.1 mol % or more, with respect to 100 mol % of a total amount of repeating units in the copolymer.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0091] Hereinafter, the function and effect of the present invention will be described in more detail through specific examples. However, these examples are for illustrative purposes only, and the invention is not intended to be limited by these examples.

[0092] The copolymers prepared in Examples and Comparative Examples were analyzed in the following manner:

[0093] (1) Weight average molecular weight (Mw) and molecular weight distribution (MWD; Mw/Mn)

[0094] <Analysis Condition> [0095] Column: PL mixed B×2 [0096] Solvent: DMF/0.05M LiBr (0.45 μm filtered) [0097] Flow rate: 1.0 ml/min [0098] Sample concentration: 1.0 mg/ml [0099] Injection volume: 100 μl [0100] Column temperature: 65° C. [0101] Detector: Refractive index detector by Waters [0102] Standard: Polystyrene (PS) (corrected by cubic function) [0103] 6 kinds of polystyrene standard were used with the molecular weight (g/mol) of 9,600/31,420/113,300/327,300/1,270,000/4,230,000. [0104] Data processing:

[0105] 1) A copolymer sample was dissolved in dimethylformamide (DMF) at a concentration of 1 mg/ml and filtered through a 0.45 μm syringe filter. 2) GPC chromatogram was obtained by injecting the sample solution. 3) GPC chromatogram was obtained by injecting a standard solution. 4) A calibration curve and an equation were obtained from the chromatogram of the standard solution, and a retention time of the sample solution was substituted into the equation to obtain a weight average molecular weight and a number average molecular weight of the sample, respectively. A molecular weight distribution (Mw/Mn) was calculated from the weight average molecular weight (Mw) and the number average molecular weight (Mn).

[0106] (2) Cyanoethyl Substitution Ratio

[0107] The cyanoethyl substitution ratio of the prepared copolymer was derived by obtaining a nitrogen content by the Kjeldahl method, and calculating the cyanoethyl substitution ratio, which is a content of the third repeating unit (mol %) containing a cyanoalkyloxy group with respect to 100 mol % of a total amount of the second repeating unit containing a hydroxyl group and the third repeating unit containing a cyanoalkyloxy group in the vinyl alcohol-based copolymer to be finally produced, from the value according to the following Equation 1.

Cyanoalkyl substitution ratio=[(mol % of third repeating unit)/(mol % of second repeating unit+mol % of third repeating unit)]×100  [Equation 1]

[0108] In Equation 1, the mol % of the second repeating unit and the mol % of the third repeating unit are values based on 100 mol % of a total amount of repeating units in the vinyl alcohol-based copolymer to be finally produced.

[0109] (3) Content of ethylene-derived repeating unit in copolymer: After dissolving a sample in a tetrahydrofuran solvent (THF-d8), 1H-NMR spectrum was measured at room temperature using a Bruker Avance III HD 700 Mhz 1H-NMR analyzer. As 4 protons of ethylene monomer and 5 protons of vinyl acetate (VA) monomer appeared at peaks between 0.74 and 2.1 ppm, and one proton of VA monomer appeared at 4.78 ppm, the content (mol %) of ethylene-derived repeating unit in the copolymer was determined using the following Equation 2.

Content of ethylene-derived repeating unit (mol %)=[r/(r+1)]×100  [Equation 2]

[0110] In Equation 2,

[00001]$r=\frac{n\left(\mathrm{ethylene}\right)}{n\left(\mathrm{VAc}\right)}=\frac{I_{0.74-2.1\mathrm{ppm}}-5I_{4.78\mathrm{ppm}}}{4I_{4.78\mathrm{ppm}}},$

[0111] wherein n(ethylene) is a molar content of ethylene-derived repeating unit, n(VAc) is a molar content of vinyl acetate-derived repeating unit, I.sub.0.74-2.1 ppm is an integral value of a peak area appearing between 0.74 and 2.1 ppm, and I.sub.4.78 ppm is an integral value of a peak area appearing at 4.78 ppm.

[0112] (4) 95% RH oxygen permeability: MOCON OX-TRAN 2/20 manufactured by Modern Control was used for measuring the oxygen permeability. The oxygen permeability (unit: cc.Math.20 μm/m.sup.2.Math.24 hr.Math.atm) was measured for 5 samples taken at arbitrary positions on the film under the conditions of a temperature of 20° C., a humidity of 95% RH and an oxygen pressure of 2.5 kg/cm.sup.2, and the minimum value of these was listed as the oxygen permeability.

Preparation of Vinyl Alcohol-Based Copolymer

Example 1-1

[0113] Step 1

[0114] After mixing 8.9 mol % of ethylene and 91.1 mol % of vinyl acetate, 45 parts by weight of t-butanol based on 100 parts by weight of a total amount of ethylene and vinyl acetate as a solvent and 0.043 mol of 2,2′-azobis(2,4-dimethylvaleronitrile) (ADMVN) based on 100 mol of a total amount of ethylene and vinyl acetate as an initiator were used to copolymerize at 60 to 70° C. The solvent and unreacted substances were volatilized and removed from the resulting polymerization solution to obtain an ethylene-vinyl acetate copolymer.

[0115] The obtained ethylene-vinyl acetate polymer had a Mw of 263,000 g/mol, a molecular weight distribution (MWD) of 2.09, and a content of ethylene-derived repeating unit in the copolymer of 27.6 mol %.

[0116] Step 2

[0117] After 20 g of the ethylene-vinyl acetate copolymer prepared in step 1 was dissolved in 180 g of methanol to make a 10% concentration solution, a sodium hydroxide catalyst was dissolved in 180 g of methanol in a content of 9 mol with respect to 100 mol of the copolymer, and then added to perform hydrolysis at 60° C. Subsequently, 10 g of acrylonitrile was added 3 hours after completion of adding the reactant, at which the saponification reaction was confirmed to proceed at least 95%, and the reaction was performed at 60° C. for 24 hours.

[0118] After completion of the reaction, the reaction solution was neutralized with acetic acid, and water vapor was blown to volatilize alcohol, followed by precipitation of particles dispersed in water. The obtained particles were washed with a large amount of water, and then dried to obtain a vinyl alcohol-based copolymer containing a 2-cyanoethyl group.

Example 1-2

[0119] After 20 g of the polymer prepared in step 1 of Example 1-1 was dissolved in 180 g of methanol to make a 10% concentration solution, a sodium hydroxide catalyst was dissolved in 180 g of methanol in a content of 9 mol with respect to 100 mol of the polymer, and then added to perform hydrolysis at 60° C. Subsequently, 5 g of acrylonitrile was added 3 hours after completion of adding the reactant, at which the saponification reaction was confirmed to proceed at least 95%, and the reaction was performed at 60° C. for 24 hours.

[0120] After completion of the reaction, the reaction solution was neutralized with acetic acid, and water vapor was blown to volatilize alcohol, followed by precipitation of particles dispersed in water. The obtained particles were washed with a large amount of water, and then dried to obtain a vinyl alcohol-based copolymer containing a 2-cyanoethyl group.

Example 1-3

[0121] Step 1

[0122] After mixing 18.5 mol % of ethylene and 81.5 mol % of vinyl acetate, 45 parts by weight of t-butanol based on 100 parts by weight of a total amount of ethylene and vinyl acetate as a solvent and 0.048 mol of 2,2′-azobis(2,4-dimethylvaleronitrile) (ADMVN) based on 100 mol of a total amount of ethylene and vinyl acetate as an initiator were used to copolymerize at 60 to 70° C. The solvent and unreacted substances were volatilized and removed from the resulting polymerization solution to obtain an ethylene-vinyl acetate copolymer.

[0123] The obtained ethylene-vinyl acetate polymer had a Mw of 240,000 g/mol, a molecular weight distribution (MWD) of 2.1, and a content of ethylene-derived repeating unit in the copolymer of 44.1 mol %.

[0124] Step 2

[0125] After 20 g of the ethylene-vinyl acetate copolymer prepared in step 1 was dissolved in 180 g of methanol to make a 10% concentration solution, a sodium hydroxide catalyst was dissolved in 180 g of methanol in a content of 9 mol with respect to 100 mol of the copolymer, and then added to perform hydrolysis at 60° C. Subsequently, 10 g of acrylonitrile was added 3 hours after completion of adding the reactant, at which the saponification reaction was confirmed to proceed at least 95%, and the reaction was performed at 60° C. for 24 hours.

[0126] After completion of the reaction, the reaction solution was neutralized with acetic acid, and water vapor was blown to volatilize alcohol, followed by precipitation of particles dispersed in water. The obtained particles were washed with a large amount of water, and then dried to obtain a vinyl alcohol-based copolymer containing a 2-cyanoethyl group.

Comparative Example 1-1

[0127] After 20 g of the copolymer prepared in step 1 of Example 1-1 was dissolved in 180 g of methanol to make a 10% concentration solution, a sodium hydroxide catalyst was dissolved in 180 g of methanol in a content of 9 mol with respect to 100 mol of the copolymer, and then added to perform hydrolysis at 60° C. Subsequently, 10 g of acrylonitrile was added 3 hours after completion of adding the reactant, at which the saponification reaction was confirmed to proceed at least 95%, while gradually adding acetone for increasing the solubility of the copolymer and the substitution ratio, and the reaction was performed at 60° C. for 24 hours.

[0128] After completion of the reaction, the reaction solution was neutralized with acetic acid, and water vapor was blown to volatilize alcohol, followed by precipitation of particles dispersed in water. The obtained particles were washed with a large amount of water, and then dried to obtain a vinyl alcohol-based copolymer containing a 2-cyanoethyl group.

Comparative Example 1-2

[0129] After 20 g of the polymer prepared in step 1 of Example 1-1 was dissolved in 180 g of methanol to make a 10% concentration solution, a sodium hydroxide catalyst was dissolved in 180 g of methanol in a content of 9 mol with respect to 100 mol of the polymer, and then added to perform hydrolysis at 60° C.

[0130] After completion of the reaction, the reaction solution was neutralized with acetic acid, and water vapor was blown to volatilize alcohol, followed by precipitation of particles dispersed in water. The obtained particles were washed with a large amount of water, and then dried to obtain a vinyl alcohol-based copolymer.

Comparative Example 1-3

[0131] After 20 g of the polymer prepared in step 1 of Example 1-1 was dissolved in 180 g of methanol to make a 10% concentration solution, a sodium hydroxide catalyst was dissolved in 180 g of methanol in a content of 9 mol with respect to 100 mol of the polymer, and then added to perform hydrolysis at 60° C. Subsequently, 5 g of acrylonitrile was added 1 hour after completion of adding the reactant, at which the saponification reaction was confirmed to proceed about 50%, and the reaction was performed at 60° C. for 24 hours.

[0132] After completion of the reaction, the reaction solution was neutralized with acetic acid, and water vapor was blown to volatilize alcohol, followed by precipitation of particles dispersed in water. The obtained particles were washed with a large amount of water, and then dried to obtain a vinyl alcohol-based copolymer containing a 2-cyanoethyl group.

Comparative Example 1-4

[0133] After 20 g of the copolymer prepared in step 1 of Example 1-1 was dissolved in 180 g of methanol to make a 10% concentration solution, a sodium hydroxide catalyst was dissolved in 180 g of methanol in a content of 9 mol with respect to 100 mol of the copolymer, and then added to perform hydrolysis at 60° C. Subsequently, 5 g of acrylonitrile was added 3 hours after completion of adding the reactant, at which the saponification reaction was confirmed to proceed at least 95%, while gradually adding acetone for increasing the solubility of the copolymer and the substitution ratio, and the reaction was performed at 60° C. for 24 hours.

[0134] After completion of the reaction, the reaction solution was neutralized with acetic acid, and water vapor was blown to volatilize alcohol, followed by precipitation of particles dispersed in water. The obtained particles were washed with a large amount of water, and then dried to obtain a vinyl alcohol-based copolymer containing a 2-cyanoethyl group.

Comparative Example 1-5

[0135] A sodium hydroxide catalyst was dissolved in 30 g of water in a content of 9 mol with respect to 100 mol of the vinyl alcohol-based copolymer prepared in Comparative Example 1-2. While stirring the resulting solution, 10 g of acrylonitrile and 20 g of the vinyl alcohol-based copolymer prepared in Comparative Example 1-2 were added and reacted at 60° C. for 5 hours. At this time, the vinyl alcohol-based copolymer was made into a film, cut into small pieces, and then gradually added thereto.

[0136] After completion of the reaction, the reaction solution was neutralized with acetic acid. Thereafter, the reaction residue was volatilized under vacuum, dissolved in acetone and precipitated in water to obtain particles. The obtained particles were washed with a large amount of water, and then dried to obtain a vinyl alcohol-based copolymer containing a 2-cyanoethyl group.

Preparation of Film

Example 2-1

[0137] A film was prepared using the vinyl alcohol-based copolymer containing a 2-cyanoethyl group prepared in Example 1-1 above.

[0138] Specifically, 0.5 g of the vinyl alcohol-based copolymer of Example 1-1 was compressed at 190° C. for 3 minutes using a compression molding machine to prepare a film.

Examples 2-2 to 2-3 and Comparative Examples 2-1 to 2-5

[0139] Films were prepared in the same manner as in Example 2-1, except that one of the vinyl alcohol-based copolymers prepared in Examples 1-2 to 2-3 and Comparative Examples 1-1 to 1-5 was used.

Experimental Example 1

[0140] 1H-nuclear magnetic resonance spectroscopy analysis was performed on the vinyl alcohol-based copolymer prepared in Example 1-1.

[0141] As a result, a peak of the cyanoethyl group bonded to the side chain (—CH.sub.2—CN) of the vinyl alcohol-based copolymer appeared at 2.7 ppm, and the proton peak of —CH.sub.2—CN was observed to be higher than the proton peak of —CH.sub.2—CN, which usually appears when acrylonitrile is polymerized as a comonomer. This difference in peak structure is because the amount of proton in —CH.sub.2—CN is twice as large as —CH(CN)—.

Experimental Example 2

[0142] 10 g of the vinyl alcohol-based copolymer prepared in each of Examples and Comparative Examples was added together with 100 g of toluene, and stirred for 1 hour at 70° C. Thereafter, the copolymer was removed, and GC (Gas Chromatography) analysis was performed on by-products dissolved in the toluene layer. Then, a content of by-product was estimated from a relative area of each by-product peak based on the toluene peak.

Experiment Method

[0143] A sample, which is a stock solution, was analyzed by GC/MS (EQC-0291) under the following conditions, and toluene was used as a standard solution.

[0144] Column: HP-5MS (0.25 mm ID×30 mL, 0.25 m d.f. capillary)

[0145] Injector: split/splitless

[0146] Gas Flow rate: Column (He): 1 mL/min

[0147] Oven temperature: Initial Value & Time: 50° C., 5 min

[0148] Program Rate: 15° C./min

[0149] Final Value & Time: 300° C., 20 min

[0150] Injector temperature: 300° C.

[0151] Interface temperature: 300° C.

[0152] Ionization mode: EI

[0153] Mass range: 20-700 m/z

[0154] Injector Split ratio: 1/100

[0155] Injection volume: 0.2 μL

TABLE-US-00001 TABLE 1 Dicyanoeth- Type of Cyano- Cyano- 2-Cyanoethyl ylated by-product ethanol hexanone ether acetone Example 1-1 5 5 5 5 Example 1-2 4 3 5 0 Comp. Ex. 1-1 5 6 5 7 Comp. Ex. 1-3 57 48 60 56 Comp. Ex. 1-5 105 108 130 120

[0156] In Table 1, the content of each by-product is in wt % based on a total weight of the vinyl alcohol copolymer.

[0157] As a result of the experiment, in the case of Comparative Example 1-3 in which acrylonitrile was added when the saponification reaction proceeded 50% and Comparative Examples 1-5 using a polymer in which the saponification reaction was already completed, the amount of by-products generated was greatly increased, compared to Examples 1-1, 1-2 and Comparative Example 1-1 in which acrylonitrile was added when the saponification reaction proceeded at least 95%.

[0158] From this, it could be confirmed that the amount of by-products generated can be reduced by controlling the timing for adding the acrylonitrile.

Experimental Example 3

[0159] The cyanoethyl substitution ratio of each copolymer used in preparing the films of Examples 2-1 to 2-3 and Comparative Examples 2-1 to 2-5 was calculated. The results are shown in Table 2 below.

[0160] In addition, oxygen permeability was measured for the films prepared in Examples 2-1 to 2-3 and Comparative Examples 2-1 to 2-5, and the results are shown in Table 2 below.

TABLE-US-00002 TABLE 2 Comparative Examples Examples 2-1 2-2 2-3 2-4 2-5 Type of 2-1 2-2 2-3 Comp. Comp. Comp. Comp. Comp. copolymer Ex. 1-1 Ex. 1-2 Ex. 1-3 Ex. 1-1 Ex. 1-2 Ex. 1-3 Ex. 1-4 Ex. 1-5 Cyanoethyl 8 3 7 19 0 1 11 10 substitution ratio (mol %) Content of 27.6 27.6 44.1 27.6 27.6 27.6 27.6 27.6 ethylene-derived repeating unit (mol %) 95% RH oxygen 0.02 0.01 0.03 0.14 0.08 — 0.12 0.18 permeability (cc .Math. 20 μm/m.sup.2 .Math. 24 hr .Math. atm)

[0161] In Table 2, the content of ethylene-derived repeating unit is based on 100 mol % of a total amount of repeating units constituting the vinyl alcohol-based copolymer.

[0162] Also, “-” means that it was not measured.

[0163] The films of Examples 2-1 to 2-3 prepared using the copolymer containing a cyanoethyl group according to the present disclosure exhibited excellent oxygen barrier properties even in a humid environment due to improved hygroscopicity, compared to Comparative Examples 2-1 to 2-5. From this, it could be confirmed that the films are useful as a packaging material in a humid environment.