JPH0463884B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a polyvinyl alcohol polymer having a mercapto group at one end. More specifically, it is represented by the general formula ()P.SH, where P contains the following structural units A and B, the content of A is 50 to 100 mol%, and the degree of polymerization is 3500 or less, with a mercapto group at one end. The present invention relates to a method for producing a polyvinyl alcohol polymer having the following properties. [Here, R ¹ =H or a hydrocarbon group having 1 to 6 carbon atoms. R ² = H or carbon number 1
Represents hydrocarbon groups from to 20. ] Mercapto groups in polymers play an important role in secondary structure and activity through the formation of disulfide bonds, as seen in cysteine-containing proteins and enzymes, and are an extremely interesting problem in the field of biochemistry. It is. In the field of synthetic polymers, many attempts have been made to synthesize polymers having mercapto groups, with the aim of producing polymers with oxidation-reduction ability that have the ability to capture heavy metals through mercaptide formation. In addition, attempts have been made to modify polymers through polymer reactions that take advantage of the high reactivity of mercapto groups, and there are many research examples. However, on the other hand, mercapto groups are extremely easily oxidized, and polymers with a certain amount of mercapto groups are oxidized in the air, forming disulfide bonds.
Due to the drawback of crosslinking and insolubilization, it is not used industrially except in a few cases. The present inventors investigated the production of polyvinyl alcohol-based polymers having highly reactive mercapto groups and mercapto groups that do not become insolubilized by oxidation. A polyvinyl alcohol having a mercapto group at one end and represented by the general formula () P・SH (), which is characterized by saponifying a polyvinyl ester polymer obtained by polymerizing a vinyl monomer mainly composed of We have discovered a method for producing a polymer based on this and have completed the present invention. [However, P: consists of the following structural units A and B, the content of A is 50 to 100 mol%, and the degree of polymerization is 3500 or less 1
polyvinyl alcohol-based polymer. Here, R ¹ =H or a hydrocarbon group having 1 to 6 carbon atoms, and R ² =H or a hydrocarbon group having 1 to 20 carbon atoms. ] The polyvinyl alcohol-based polymer obtained in this way has a mercapto group only at one end of the molecule, so even if a disulfide bond is formed by oxidation, the mercapto group will not be randomly distributed in the main chain of the molecule as previously known. It is easy to handle because it does not become insolubilized unlike polymers having mercapto groups distributed in . General formula ()P obtained by the production method of the present invention
The polymer represented by SH has a structural unit A content of 50
The content of A is preferably 70 mol% or more from the viewpoint of water solubility. Specifically, the structural unit A is vinyl alcohol,
α-Methyl vinyl alcohol, α-ethyl vinyl alcohol, α-propyl vinyl alcohol, α
-Butyl vinyl alcohol, α-hexyl vinyl alcohol, etc. as the structural unit B include vinyl acetate, vinyl propionate, vinyl laurate, vinyl stearate, and α-substituted products thereof. Furthermore, although it is essential that the polyvinyl alcohol-based polymer in the present invention contains the above-mentioned structural units A and B, there is no problem with containing structural units other than structural units A and B, and as structural units in the polymer. The presence of other structural units poses no problem as long as it contains A and B and the content of A is 50 mol% or more, but from the viewpoint of water solubility, it is preferably 70 mol% or more. Other structural units include, for example, ethylene, propylene, isobutene, acrylic acid, methacrylic acid or salts thereof, or alkyl esters thereof, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide,
Trimethyl (3-acrylamido-3-dimethylpropyl) ammonium chloride, ethyl vinyl ether, butyl vinyl ether, N-vinylpyrrolidone, vinyl chloride, vinyl bromide, vinyl fluoride, vinylidene chloride, vinylidene fluoride, tetrafluoroethylene, structural unit B Other examples include vinyl esters. The degree of polymerization of the polyvinyl alcohol polymer in the present invention is determined from the viewpoint of making the mercapto group that exists only at one end of the molecule effectively act.
It is 3500 or less, preferably 2000 or less, more preferably 1000 or less. The polyvinyl alcohol polymer obtained by the present invention can of course be used for conventional purposes such as paper processing,
Although it fully exhibits its effects when used in fiber processing, etc., the reactivity of the mercapto group at one end, which is a feature of the polymer of the present invention, such as addition to a compound with a double bond, substitution with a halogen compound, etc. It is a highly reactive new material that can be used in an extremely wide range of applications by utilizing reactions, redox decomposition reactions in combination with oxidizing agents, etc. For example, by radically polymerizing monomers capable of radical polymerization in the presence of the polyvinyl alcohol polymer of the present invention by utilizing the fact that it has a mercapto group only at one end, a block copolymer containing the polyvinyl alcohol polymer as one component can be produced. Polymers can be obtained. The following two methods are known as methods for introducing mercapto groups into polymers. The first method is to copolymerize a vinyl monomer with a protected mercapto group, such as an isothiuronium salt or a thiol acid ester, and decompose the resulting polymer with an acid or base to form a mercapto group. The second method is a method of introducing a so-called polymer reaction, in which a polymeric alcohol or halide is used as a starting material and converted into a mercapto group. However, although it is possible to introduce a mercapto group into a polymer by these methods, it is not possible to selectively introduce a mercapto group only at one end of the molecule. Under these circumstances, the present inventors investigated a method of selectively introducing a mercapto group only at one end of the molecule, and as a result, they polymerized vinyl esters in the presence of thiol acid and obtained a polymer. The inventors discovered that a polyvinyl alcohol polymer having a mercapto group only at one end of the molecule can be obtained by saponifying the polyvinyl alcohol, and completed the production method of the present invention. The production method of the present invention is characterized by polymerizing vinyl monomers mainly composed of vinyl esters such as vinyl acetate in the presence of thiol acid to produce a polyvinyl ester polymer having a thioester group at one end. The purpose of this method is to saponify the polymer to produce a polyvinyl alcohol polymer having a mercapto group at one end. Thiol acids used in the present invention include organic thiol acids having a -COSH group. For example, thiol acetic acid, thiol propionic acid, thiol butyric acid,
Examples include thiolvaleric acid, among which thiolacetic acid is the most preferred because it has good decomposition of the thiol acid ester at one end of the polymer. Furthermore, any vinyl ester that can be radically polymerized can be used. Examples include vinyl formate, vinyl acetate, trifluorovinyl acetate, vinyl propionate, vinyl versatate, vinyl laurate, and vinyl stearate, among which vinyl acetate is preferred because it has the best polymerizability. Further, a monomer copolymerizable with these vinyl esters can also be copolymerized. For example, ethylene, propylene, isobutylene, acrylic acid, methacrylic acid or their salts or alkyl esters thereof, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, trimethyl (3-acrylamido-3-dimethylpropyl) ammonium chloride, ethyl vinyl ether, butyl Examples include vinyl ether, N-vinylpyrrolidone, vinyl chloride, vinyl bromide, vinyl fluoride, vinylidene chloride, vinylidene fluoride, and tetrafluoroethylene. The polymerization of vinyl monomers mainly consisting of vinyl esters such as vinyl acetate in the presence of thiol acid according to the present invention can be carried out by any method such as bulk polymerization, solution polymerization, pearl polymerization, emulsion polymerization, etc. in the presence of a radical polymerization initiator. The solution polymerization method using methanol as a solvent is industrially most advantageous. There are no particular limitations on the amount of thiol acid added to the polymerization system and the method of addition, and should be appropriately determined depending on the physical properties of the intended polyvinyl ester polymer. As the polymerization method, known methods such as a batch method, a semi-continuous method, and a continuous method can be employed. As the radical polymerization initiator, known radical polymerization initiators such as 2,2'-azobisisobutyronitrile, benzoyl peroxide, and carbonate peroxide can be used. Azo initiators are preferred because they are easy to handle. Furthermore, radiation, electron beams, etc. can also be used. The polymerization temperature is preferably selected from a range of 30 to 90°C, although it is desirable to select an appropriate temperature depending on the type of initiator used. After polymerization for a predetermined period of time, unpolymerized vinyl esters are removed by a conventional method to obtain a polyvinyl ester polymer having a thiol acid ester group at one end. The reason why a polyvinyl ester polymer having a thiol acid ester group at one end is obtained in the polymerization method of the present invention is considered to be due to the following polymerization mechanism. Between thiol acid and vinyl ester, thiol acid is easier to convert into radicals. In other words, in the polymerization of vinyl ester in the presence of thiol acid, thiol acid radicals are first generated, and vinyl ester monomers are successively added to the thiol acid radicals, resulting in a growth reaction (this growth reaction is a growth reaction of the chain carrier). This continues until the radical is deactivated by chain transfer to the remaining thiol acid.)
As a result, a polyvinyl ester polymer having a thiol acid ester group at one end is obtained. The polyvinyl ester polymer thus obtained is saponified by conventional methods, but it is usually advantageous to carry out the saponification of the polymer as an alcohol solution, particularly a methanol solution. Not only anhydrous alcohols but also those containing a small amount of water can be used depending on the purpose, and organic solvents such as methyl acetate and ethyl acetate may be optionally contained. The saponification temperature is usually selected from the range of 10 to 70°C. As the saponification catalyst, alkaline catalysts such as sodium hydroxide, potassium hydroxide, sodium methylate, potassium methylate, etc. are preferable, and the amount of the catalyst to be used is appropriately determined depending on the degree of saponification and water content. It is desirable to use a molar ratio of 0.001 or more, preferably 0.002 or more.
On the other hand, if the amount of alkali is too large, it will be difficult to remove the residual alkali from the polymer, and the polymer will be colored, which is undesirable.
It is desirable to do the following. In addition, if the polyvinyl ester polymer contains copolymerized components such as carboxyl groups and their ester groups that react with alkali catalysts and consume alkali, it is necessary to use the amount of alkali catalyst in addition to that amount. be. Through this saponification reaction, the thiol acid ester at one end of the polyvinyl ester polymer having a thiol acid ester group at one end and the vinyl ester bond in the main chain are saponified, and one end of the polymer becomes a mercapto group, and the main chain becomes a vinyl alcohol. However, the degree of saponification of the vinyl ester unit in the main chain can be changed depending on the purpose of use. The polymer precipitated after the saponification reaction is purified by a known method, such as washing with methanol, to remove impurities such as residual alkali and alkali metal salts of acetate, and then dried to obtain usually a white powder. The present invention will be specifically explained below with reference to Examples, but the present invention is not limited by these in any way. It should be noted that both the middle part of the example and the percentage are based on weight. Example 1 2400 parts of vinyl acetate (hereinafter abbreviated as VAc), 580 parts of methanol, and 0.93 parts of thiol acetic acid were placed in a reaction vessel, the inside was sufficiently replaced with nitrogen, and the outside temperature was lowered.
Raise the temperature to 65℃, and when the internal temperature reaches 60℃, 2.
20 parts of methanol containing 0.868 parts of 2'-azobisisobutyronitrile was added. Immediately thiol acetic acid
60 parts of a methanol solution containing 17.4 parts was added uniformly over a period of 5 hours. The polymerization rate after 5 hours was 50.4%. After 5 hours, the container was cooled and the remaining VAc was expelled from the system together with methanol under reduced pressure while adding methanol to obtain a methanol solution of PVAc (concentration 64.5%). Take a part of this methanol solution, 50% PVAc concentration,
A methanol solution of NaOH was added so that [NaOH]/[VAc] = 0.05 (molar ratio), and the mixture was saponified at 40°C to obtain PVA. This PVA was purified by Soxhlet washing with methanol and then washed in water at 30°C.
[η] was measured, and the degree of polymerization was calculated as [η] = 7.51×10 ^-3 × ^0.64, and it was found to be 130, and the degree of saponification was measured to be 98.6 mol%. Next, using this purified PVA, the amount of mercapto groups contained in PVA was determined by a method using iodine oxidation, and the presence of mercapto groups of 1.87×10 ^-4 equivalent/g-PVA was confirmed. Thus, the viscosity average degree of polymerization is 130, and the number average degree of polymerization calculated from the titration value of [SH] is 127, and considering the polymerization mechanism as well, it can be said that the mercapto group exists only at one end of the molecule. Example 2 2,400 parts of vinyl acetate (hereinafter abbreviated as VAc) and 580 parts of methanol were placed in a reaction vessel, the inside was sufficiently replaced with nitrogen, the external temperature was raised to 65°C, and when the internal temperature reached 60°C, After adding 5 parts of nitrogen-substituted thiol acetic acid, 20 parts of methanol containing 0.868 parts of 2,2'-azobisisobutyronitrile were added to initiate polymerization. Polymerization rate after 2 hours: 20.5
%, and the remaining VAc was expelled from the system together with methanol under reduced pressure while adding methanol to obtain a methanol solution of PVAc (concentration 45.2%). Take a part of this methanol solution, PVAc concentration 30%, [NaOH]/
A methanol solution of NaOH was added so that [VAc] = 0.05 (molar ratio), and the mixture was saponified at 40°C to obtain PVA. After this PVA was purified by Soxhlet washing with methanol, the degree of polymerization was measured in the same manner as in Example 1 and found to be 90, and the degree of saponification was 99.0 mol%. Next, using this purified PVA, the amount of mercapto groups contained in PVA was determined by a method using iodine oxidation, and the presence of mercapto groups of 2.90×10 ⁻⁴ equivalent/g-PVA was confirmed. Examples 3 to 5 Polymerization was carried out in the same manner as in Example 1 by changing the amount of thiol acetic acid, and then saponification was performed to obtain PVAc and PVA. Table 1 summarizes the polymerization conditions for these productions and the amount of mercapto groups in the products.
It was shown to.

[Table] Example 6 2400 parts of vinyl formate and 580 parts of methanol were placed in a reactor, the inside was sufficiently replaced with nitrogen, and the outside temperature was raised to 65%.
I raised it to ℃. When the internal temperature reached 60℃, add 6.3 parts of thiol acetic acid which had been substituted with nitrogen in advance, and then add 2,2'-azobisisobutyronitrile.
20 parts of methanol containing 0.868 parts were added to initiate polymerization. After 2 hours, when the polymerization rate reached 19.7%, the system was cooled and the remaining VAc was expelled from the system together with methanol under reduced pressure while adding methanol to obtain a methanol solution of PVAc (concentration:
39.8%). Take a portion of this methanol solution and
PVAc concentration 30%, [NaOH]/[vinyl formate] =
A methanol solution of NaOH was added so that the molar ratio was 0.05, and the mixture was saponified at 40°C to obtain PVA. After this PVA was purified by Soxhlet washing with methanol, the degree of polymerization was measured in the same manner as in Example 1 and found to be 92, and the degree of saponification was 98.7 mol%. Next, using this purified PVA, the amount of mercapto groups contained in PVA was determined by a method using iodine oxidation, and the presence of mercapto groups of 3.05×10 ⁻⁴ equivalent/g-PVA was confirmed. Example 7 2400 parts of vinyl acetate (hereinafter abbreviated as VAc), 580 parts of methanol, and 1.10 parts of thiolpropionic acid were placed in a reactor, and the inside was sufficiently replaced with nitrogen.
Raise the external temperature to 65℃, and when the internal temperature reaches 60℃, 2,2'-azobisisobutyronitrile 0.868
20 parts of methanol were added. Immediately, 60 parts of a methanol solution containing 20.6 parts of thiolpropionic acid was added uniformly over 5 hours. The polymerization rate after 5 hours was 49.6%. After 5 hours, the solution was cooled and the remaining VAc was expelled from the system together with methanol under reduced pressure while adding methanol to obtain a methanol solution of PVAc (concentration:
65.3%). Take a portion of this methanol solution and
A methanol solution of NaOH was added so that the PVAc concentration was 50% and [NaOH]/[VAc] = 0.05 (molar ratio), and the mixture was saponified at 40°C to obtain PVA. This PVA
After purification by Soxhlet washing with methanol, the degree of polymerization was measured in the same manner as in Example 1 and found to be 120, and the degree of saponification was 99.0 mol%. Next, using this purified PVA, the amount of mercapto groups contained in PVA was determined by a method using iodine oxidation, and the presence of mercapto groups of 1.85×10 ⁻⁴ equivalent/g-PVA was confirmed.

Claims (1)

[Claims] 1 General formula () P・SH characterized by saponifying a polyvinyl ester polymer obtained by polymerizing vinyl monomers mainly composed of vinyl ester monomers in the presence of thiol acid A method for producing a polyvinyl alcohol polymer having a mercapto group at one end represented by (). [However, P: consists of the following structural units A and B, the content of A is 50 to 100 mol%, and the degree of polymerization is 3500 or less 1
polyvinyl alcohol-based polymer. Here, R ¹ =H or a hydrocarbon group having 1 to 6 carbon atoms, and R ² =H or a hydrocarbon group having 1 to 20 carbon atoms. 2. The method for producing a polyvinyl alcohol polymer according to claim 1, wherein the thiol acid is thiol acetic acid.