Vinyl alcohol-vinyl acetate copolymer

Abstract

The present invention provides a vinyl alcohol-vinyl acetate copolymer having excellent solubility and a method for producing a vinyl alcohol-vinyl acetate copolymer. Provided is a vinyl alcohol-vinyl acetate copolymer including a unit of vinyl alcohol and a unit of vinyl acetate, the vinyl alcohol-vinyl acetate copolymer having a randomness value R of 0.5 or higher, the randomness value R being obtained using the following equation (1): $\begin{array}{cc}R=\frac{1}{L_A}+\frac{1}{L_O}& \left(1\right)\end{array}$
where L.sub.O represents a mean chain length of the unit of vinyl alcohol and L.sub.A represents a mean chain length of the unit of vinyl acetate.

Claims

1. A method for producing a vinyl alcohol-vinyl acetate copolymer comprising a unit of vinyl alcohol and a unit of vinyl acetate, wherein the vinyl alcohol-vinyl acetate copolymer has a randomness value R of 0.5 or higher, and wherein the randomness value R is obtained using the following equation (1): $\begin{array}{cc}R=\frac{1}{L_A}+\frac{1}{L_O}& \left(1\right)\end{array}$ where L.sub.O represents a mean chain length of the unit of vinyl alcohol and L.sub.A represents a mean chain length of the unit of vinyl acetate, the method comprising the step of: transesterification of polyvinyl acetate or a raw material vinyl alcohol-vinyl acetate copolymer using a dianionic zincate complex represented by the following formula (2):
t-Bu.sub.nR.sub.4-nZnM.sub.m(2) where n represents an integer of 1 to 4, m represents 1 or 2, Rs may be the same as or different from one another when n represents 1 or 2 and each represent a C1-C8 alkyl, alkenyl, aryl, or arylalkyl group, and M represents lithium or magnesium.

2. The method for producing the vinyl alcohol-vinyl acetate copolymer according to claim 1, wherein the dianionic zincate complex is dilithium tetra-t-butylzincate.

3. The method for producing the vinyl alcohol-vinyl acetate copolymer according to claim 1, wherein the transesterification is performed in a homogeneous system.

4. The method for producing the vinyl alcohol-vinyl acetate copolymer according to claim 1, wherein the transesterification is performed in a heterogeneous system.

5. The method for producing the vinyl alcohol-vinyl acetate copolymer according to claim 1, wherein the vinyl alcohol-vinyl acetate copolymer has a mean chain length L.sub.O of the unit of vinyl alcohol of 1 or longer.

6. The method for producing the vinyl alcohol-vinyl acetate copolymer according to claim 1, wherein the vinyl alcohol-vinyl acetate copolymer has a mean chain length L.sub.A of the unit of vinyl acetate of 1 or longer.

7. The method for producing the vinyl alcohol-vinyl acetate copolymer according to claim 1, wherein the vinyl alcohol-vinyl acetate copolymer comprises the unit of vinyl alcohol in an amount of 0.2 to 99.8 mol %.

8. The method for producing the vinyl alcohol-vinyl acetate copolymer according to claim 2, wherein the vinyl alcohol-vinyl acetate copolymer has a mean chain length L.sub.O of the unit of vinyl alcohol of 1 or longer.

9. The method for producing the vinyl alcohol-vinyl acetate copolymer according to claim 2, wherein the vinyl alcohol-vinyl acetate copolymer has a mean chain length L.sub.A of the unit of vinyl acetate of 1 or longer.

10. The method for producing the vinyl alcohol-vinyl acetate copolymer according to claim 2, wherein the vinyl alcohol-vinyl acetate copolymer comprises the unit of vinyl alcohol in an amount of 0.2 to 99.8 mol %.

Description

DESCRIPTION OF EMBODIMENTS

(1) Embodiments of the present invention are more specifically described with reference to, but not limited to, the following examples.

Example 1

(2) An amount of 0.5 g (5.8 mmol) of polyvinyl acetate was dissolved in 22.5 mL of dimethyl sulfoxide (DMSO), and to the solution was added 2.5 mL of methanol and then 0.15 mL (1.5 mol %) of dilithium tetra-t-butylzincate (TBZL) as a catalyst.

(3) The mixture was stirred at 30 C. for five minutes, and hydrochloric acid was added thereto to terminate the reaction. Then, the resulting mixture was subjected to dialysis using acetone and concentration, thereby obtaining a product material (vinyl alcohol-vinyl acetate copolymer).

Example 2

(4) An amount of 0.5 g (5.8 mmol) of polyvinyl acetate was dissolved in 25 mL of methanol, and to the solution was added 0.38 mL (2.5 mol %) of dilithium tetra-t-butylzincate (TBZL) as a catalyst.

(5) The mixture was stirred at 30 C. for 45 minutes, and hydrochloric acid was added thereto to terminate the reaction. Then, the resulting mixture was subjected to dialysis using acetone and concentration, thereby obtaining a product material (vinyl alcohol-vinyl acetate copolymer).

Example 3

(6) An amount of 0.5026 g (11.4 mmol) of polyvinyl alcohol [degree of saponification: >99 mol %] was dissolved in a solvent mixture of acetic acid and water (acetic acid:water=5:5) to prepare 10.5 g of a 5% by weight solution of polyvinyl alcohol.

(7) The obtained polyvinyl alcohol solution was stirred at 100 C. for 24 hours and subjected to reprecipitation using acetone, thereby obtaining a product material (reacetylation).

(8) The obtained product material was subjected to similar operation (reacetylation) using a solvent mixture of acetic acid and water (acetic acid:water=7:3) and then using a solvent mixture of acetic acid and water (acetic acid:water=9:1), thereby obtaining a product material. After the reacetylation using a solvent mixture of acetic acid and water (acetic acid:water=9:1), concentration was carried out to recover a product material (vinyl alcohol-vinyl acetate copolymer).

Example 4

(9) A product material (vinyl alcohol-vinyl acetate copolymer) was obtained as in Example 1, except that the stirring time (reaction time) was changed to 10 minutes.

Example 5

(10) A product material (vinyl alcohol-vinyl acetate copolymer) was obtained as in Example 2, except that the stirring time (reaction time) was changed to 90 minutes.

Example 6

(11) The vinyl alcohol-vinyl acetate copolymer obtained in Example 4 was dissolved in DMSO to a concentration of 2% by weight, and to the solution was added 5 mol % of dilithium tetra-t-butylzincate (TBZL). The mixture was stirred at 30 C. for 24 hours so that transesterification was carried out. The resulting mixture was then subjected to dialysis using acetone and concentration, thereby obtaining a product material (vinyl alcohol-vinyl acetate copolymer).

Example 7

(12) A product material (vinyl alcohol-vinyl acetate copolymer) was obtained as in Example 6, except that the raw material used was the vinyl alcohol-vinyl acetate copolymer obtained in Example 5.

Example 8

(13) A product material (vinyl alcohol-vinyl acetate copolymer) was obtained as in Example 4, except that the stirring time (reaction time) was changed to 15 minutes.

Example 9

(14) A product material (vinyl alcohol-vinyl acetate copolymer) was obtained as in Example 5, except that the stirring time (reaction time) was changed to 180 minutes.

Example 10

(15) An amount of 0.5 g (5.8 mmol) of polyvinyl acetate was dissolved in a mixture of 35.4 mL of dimethyl sulfoxide (DMSO) and 8.9 mL of water, and to the solution was added 0.21 g (5.1 mmol) of NaOH. After stirring at 60 C. for 120 minutes, the mixture was subjected to dialysis using methanol and concentration, thereby obtaining a product material (vinyl alcohol-vinyl acetate copolymer).

(16) The obtained vinyl alcohol-vinyl acetate copolymer was dissolved in DMSO to a concentration of 2% by weight, and to the solution was added 5 mol % of dilithium tetra-t-butylzincate (TBZL). The mixture was stirred at 30 C. for 24 hours so that transesterification was carried out. Then, the resulting mixture was subjected to dialysis using acetone and concentration, thereby obtaining a product material (vinyl alcohol-vinyl acetate copolymer).

Example 11

(17) A product material (vinyl alcohol-vinyl acetate copolymer) was obtained as in Example 10, except that the amount of NaOH was changed to 0.16 g (3.9 mmol).

Comparative Example 1

(18) An amount of 0.5 g (5.8 mmol) of polyvinyl acetate was dissolved in a mixture of 35.4 mL of acetone and 8.9 mL of water, and to the solution was added 0.12 g (2.9 mmol) of NaOH.

(19) The mixture was stirred at 60 C. for 120 minutes and then subjected to concentration using an evaporator, thereby obtaining a product material (vinyl alcohol-vinyl acetate copolymer).

Comparative Example 2

(20) An amount of 0.5 g (5.8 mmol) of polyvinyl acetate was dissolved in 22.5 mL of DMSO (dimethyl sulfoxide), and to the solution was added 2.5 mL of methanol and then 4.8 mg (1.5 mol %) of CH.sub.3ONa as a catalyst.

(21) The mixture was stirred at 30 C. for 80 minutes, and an excessive amount of acetic acid was added thereto to terminate the reaction. The resulting mixture was then subjected to dialysis using acetone and concentration, thereby obtaining a product material (vinyl alcohol-vinyl acetate copolymer).

Comparative Example 3

(22) An amount of 0.5 g (5.8 mmol) of polyvinyl acetate was dissolved in 25 mL of methanol, and to the solution was added 8.6 mg (2.5 mol %) of CH.sub.3ONa as a catalyst.

(23) The mixture was stirred at 30 C. for 17 hours, and an excessive amount of acetic acid was added thereto to terminate the reaction. The resulting mixture was then subjected to dialysis using acetone and concentration, thereby obtaining a product material (vinyl alcohol-vinyl acetate copolymer).

Comparative Example 4

(24) An amount of 0.5 g (5.8 mmol) of polyvinyl acetate was dissolved in a mixture of 35.4 mL of DMSO (dimethyl sulfoxide) and 8.9 mL of water, and to the solution was added 0.12 g (2.9 mmol) of NaOH.

(25) The mixture was stirred at 60 C. for 120 minutes and then subjected to dialysis using methanol and concentration, thereby obtaining a product material (vinyl alcohol-vinyl acetate copolymer).

(26) (Evaluation Method)

(27) The product materials obtained above were evaluated by the following methods. Table 1 shows the results.

(28) (.sup.1H-NMR Analysis)

(29) Each obtained product material was subjected to .sup.1H-NMR analysis for determination of the composition ratio (VOH:vinyl alcohol, Vac:vinyl acetate) thereof.

(30) In addition, the triad content ratio between the vinyl alcohol-centered triads (AOA, AOO, and OOO) and the vinyl acetate-centered triads (AAA, AAO, OAO) was measured. It is to be noted that AOO and OOA are both represented as AOO, and AAO and OAA are both represented as AAO.

(31) Moreover, the mean chain lengths and randomness values of the unit of vinyl alcohol and the unit of vinyl acetate were calculated.

(32) (Evaluation on Gel Formation Temperature)

(33) Each obtained product material was dissolved in a solvent mixture of water and THF (water/THF=3/7) to prepare a 0.1% by weight solution. The obtained solution was put in a sample bottle and warmed on a hotplate from room temperature to 60 C. Then, the temperature was further gradually increased, and the temperature at which clouding of the solution was visually observed was determined as a gel formation temperature.

(34) Direct saponification as in Comparative Example 4 was carried out in which the amount of NaOH was changed. Based on the result, a calibration curve (gelling temperature line) indicating a relation between the composition ratio of VOH and Vac and the gel formation temperature was constructed. The obtained gelling temperature line was represented by the following equation.
Gel formation temperature ( C.)=0.2759VOH composition ratio (mol %)+56.057

(35) Next, the difference between the gel formation temperature obtained in each of the examples and comparative examples and the gel formation temperature at the same composition ratio as above determined from the constructed gelling temperature line (control gel formation temperature) was evaluated based on the following criteria.

(36) oo (Excellent): The obtained gel formation temperature is higher than the control gel formation temperature by 3 C. or more.

(37) o (Good): The obtained gel formation temperature is higher than the control gel formation temperature by 1 C. or more but less than 3 C.

(38) x (Poor): The difference between the obtained gel formation temperature and the control gel formation temperature is less than 1 C.

(39) (Lower Critical Solution Temperature Property)

(40) Each obtained product material was dissolved in a solvent mixture of water and THF (water/THF=3/7) to prepare a 0.1% by weight solution. The obtained solution was put in a Peltier temperature control cell (optical path length: 10 mm), and the temperature was increased and decreased three times within a temperature range from 60 C. to 100 C. at 2 C./min, during which transmittance of light at a wavelength of 500 nm was continuously measured using a spectrophotometer (V550 type available from Jasco Corp.).

(41) Assuming that the transmittance at 60 C. is 100%, the average of the temperatures at which the transmittance at 60 C. dropped to 50% or lower for the second and the third times was taken as the lower critical solution temperature.

(42) Direct saponification as in Comparative Example 4 was carried out, while the amount of NaOH was changed. Based on the result, a calibration curve (lower critical solution temperature curve) indicating a relation between the composition ratio of VOH and Vac and the lower critical solution temperature was constructed. The obtained lower critical solution temperature curve was indicated by the following equation.
Critical solution temperature ( C.)=58.332e{circumflex over ()}(0.0036VOH composition ratio (mol %))

(43) Next, the difference between the lower critical solution temperature obtained in each of the examples and comparative examples and the lower critical solution temperature in the case of the same composition obtained from the constructed lower critical solution temperature curve (control lower critical solution temperature) was evaluated based on the following criteria.

(44) oo (Excellent): The lower critical solution temperature is higher than the control lower critical solution temperature by 3 C. or more.

(45) o (Good): The lower critical solution temperature is higher than the control lower critical solution temperature by 1 C. or more but less than 3 C.

(46) x (Poor): The difference between the lower critical solution temperature and the control lower critical solution temperature is less than 1 C.

(47) TABLE-US-00001 TABLE 1 Composition ratio Preparation method (mol %) Triad content ratio (mol %) Raw material Additive Reaction system Reaction method VOH Vac AOA AOO OOO Example 1 Polyvinyl acetate TBZL Homogenious Transesterification 51.0 49.0 6.6 14.7 16.3 Example 2 Polyvinyl acetate TBZL Heterogenious Transesterification 46.0 54.0 5.4 11.6 32.7 Example 3 Polyvinyl alcohol Acetic acid Homogenious Reacetylation 47.3 52.7 9.1 19.5 18.7 Example 4 Polyvinyl acetate TBZL Homogenious Transesterification 88.5 11.5 3.7 2.9 4.9 Example 5 Polyvinyl acetate TBZL Heterogenious Transesterification 87.0 13.0 4.5 3.2 5.3 Example 6 VOH-Vac copolymer TBZL Homogenious Intramolecular 90.9 9.1 7.3 1.5 0.0 transesterification Example 7 VOH-Vac copolymer TBZL Homogenious Intramolecular 91.6 8.4 6.8 1.3 0.3 transesterification Example 8 Polyvinyl acetate TBZL Homogenious Transesterification 90.5 9.5 2.4 3.8 3.4 Example 9 Polyvinyl acetate TBZL Heterogenious Transesterification 93.9 6.1 2.7 1.5 1.9 Example 10 VOH-Vac copolymer TBZL Homogenious Intramolecular 88.7 11.3 7.4 3.9 0.0 transesterification Example 11 VOH-Vac copolymer TBZL Homogenious Intramolecular 66.4 33.6 19.0 12.7 1.9 transesterification Comparative Polyvinyl acetate NaOH Heterogenious Direct saponification 50.0 50.0 6.1 5.6 39.3 Example 1 Comparative Polyvinyl acetate CH.sub.3ONa Homogenious Transesterification 49.0 51.0 4.3 9.4 16 Example 2 Comparative Polyvinyl acetate CH.sub.3ONa Heterogenious Transesterification 46.0 54.0 4.3 7.6 45.4 Example 3 Comparative Polyvinyl acetate NaOH Homogenious Direct saponification 50.0 50.0 3.1 8.2 40.6 Example 4 Evaluation Lower critical OOO AAA mean chain Acetyl solution Triad content ratio (mol %) content content length Randomness chain Gel formation temperature AAA AAO OAO ratio*1 ratio*2 L.sub.O L.sub.A value R ratio temperature property Example 1 45.7 17.3 4.7 43.4% 67.5% 2.7 5.1 0.57 2.48 Example 2 18.4 20.1 11.8 65.8% 36.6% 4.4 2.3 0.66 1.24 Example 3 7.4 26.4 18.7 39.5% 14.1% 2.5 1.6 1.01 0.87 Example 4 81.7 4.1 2.7 42.6% 92.3% 18.6 2.2 0.50 0.26 Example 5 81.5 3.5 2.0 40.8% 93.7% 23.2 2.1 0.51 0.28 Example 6 83.1 5.9 1.9 0.0% 91.4% 18.7 1.1 0.97 0.10 Example 7 86 4.5 1.2 3.6% 93.8% 26.6 1.1 0.92 0.09 Example 8 81.1 4.3 5.1 35.4% 89.6% 12.5 2.2 0.53 0.21 Example 9 88.2 3.4 2.4 31.1% 93.8% 22.9 1.8 0.61 0.11 Example 10 76.1 11 1.6 0.0% 85.8% 12.5 1.2 0.91 0.14 Example 11 50.5 13.7 2.2 5.7% 76.1% 7.3 1.3 0.89 0.45 Comparative 35.1 9 4.9 77.1% 71.6% 5.7 5.2 0.37 2.61 x x Example 1 Comparative 55.3 12.1 2.8 53.9% 78.8% 3.3 7.9 0.43 4.05 x x Example 2 Comparative 29.8 9.9 2.9 79.2% 70.0% 7.1 5.4 0.33 2.93 x x Example 3 Comparative 34.3 10.3 3.5 78.2% 71.3% 7.2 5.6 0.32 2.78 x x Example 4 *1Proportion of OOO in the total of AOA, AOO, and OOO *2Proportion of AAA in the total of AAA, AAO, and OAO

INDUSTRIAL APPLICABILITY

(48) The present invention can provide a vinyl alcohol-vinyl acetate copolymer having excellent solubility and a method for producing a vinyl alcohol-vinyl acetate copolymer.