JPH0571603B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to aromatic vinyl polymers. More specifically, it has a reactive active halogen atom,
The present invention relates to aromatic vinyl polymers into which basic, acidic, and other functional groups can be easily introduced, and which can be converted into polymers useful for adsorption, ion exchange, or immobilization of various enzymes. Conventionally, attempts to introduce various functional groups into polymers and use these polymers as ion exchange resins and adsorbents have been made, for example, in JP-A-49-11791, JP-A-49-35284, and Many proposals have been made, such as in Japanese Patent Application Laid-Open No. 54-110274. However, conventional polymers into which functional groups exhibiting ion-exchange or adsorption abilities have been introduced have a certain performance. Even if it is possible to introduce a functional group that exhibits cation exchange ability, it may not be possible to introduce a functional group that exhibits cation exchange ability, and polymers that have adsorption and enzyme immobilization functions cannot be modified in principle. In many cases, it could not be said to be a versatile polymer. The present inventors have conducted extensive research into functional polymers that can be easily converted into functional groups that exhibit various functions such as ion exchange, adsorption, and enzyme immobilization.
This is what led us to discover the present invention. In other words, the object of the present invention is to be able to convert into any polymer that has a functional group that has not only cation exchange ability but also anion exchange ability, and to obtain other functions such as adsorption performance and enzyme immobilization from the same polymer. Another purpose is to provide a synthetic polymer that can be converted into a polymer having a functional group derived from the above polymer, which exhibits particularly excellent performance in immobilizing enzymes and bacterial cells and adsorbing and desorbing macromolecules. The purpose of the present invention is to provide a polymer having the following properties. Another objective is to provide functional adsorbent fibers that are superior in handling properties based on the fiber morphology and have greater fixation and adsorption capacity by using fiber-forming polymers such as polyolefin, polyamide, or polyester in combination. be. The present invention has the following configuration. (1) Repeating unit represented by the following general formula ()
A homopolymer consisting of M ₁ or a copolymer of the repeating unit M ₁ and the repeating unit M ₂ represented by the following general formula (), in which the abundance ratio of M ₁ is at least 1 mol %, Molecular weight is 2000
3,000,000.

[ka]

In the above formula, R ₀ and R ₀ ' represent a hydrogen atom or a methyl group, and A represents a benzene ring, a benzene ring having one or two methyl groups, or a benzene ring having a chloro group. Further, Y represents a functional group represented by the following general formula () or ().

[ka]

embedded image In the above formula, X represents a halogen atom, R′ and R″ represent a hydrogen atom, a lower alkyl group, an aryl group, or an aralyl group, and R′ and R″ may be the same or different. Moreover, R ₁ and R ₂ represent a hydrogen atom or an alkyl group. The present invention will be explained in detail below. Starting materials for the aromatic vinyl polymer of the present invention include vinyls having an aromatic nucleus in their side chains, such as polystyrene, polyα-methylstyrene, polyp-chlorostyrene, polyvinyltoluene, and polyvinylxylene, which are known as raw materials for ion exchange resins. Polymers are used, especially polystyrene or polyα-
Methylstyrene is preferred. The polymer of the present invention is characterized in that the aromatic nucleus has a group represented by the general formula (), ie, a haloacetamidomethyl group, as a functional group. The functional group represented by the general formula () has an active halogen atom, and this halogen atom can be easily converted into a basic group, an acidic group, or other various functional groups. Specific examples of such convertible groups include 1
Various functionalities such as conversion to aminoglycyl group or ammonium glycyl group by reaction with primary, secondary, and tertiary amino compounds, phenoxyglycyl group by reaction with phenolate, and introduction of sulfonic acid group by reaction with sodium sulfite. It is possible to introduce groups. In particular, the reaction with the various amino compounds described above can be carried out at a low temperature of room temperature to 100°C. A polymer in which haloacetamidomethyl groups are converted to aminoacetamidomethyl groups through this reaction exhibits excellent performance in immobilizing enzymes and bacterial cells and adsorbing and desorbing macromolecules. Here, the repeating unit shown by the general formula ()
M ₁ is preferably contained in an amount of at least 1 mol % or more, preferably in the range of 10 to 100 mol %, based on all the repeating units in the polymer, and if it is less than 1 mol %, various functional groups for the final purpose The amount is small, and practical performance such as ion exchange, enzyme, and bacterial cell immobilization or adsorption is not satisfied. The molecular weight of the aromatic vinyl polymer of the present invention is usually 2,000 to 3,000,000, since it is not preferable to have a molecular weight that is too small or too large from the viewpoint of moldability.
In particular, those with a number of 50,000 to 1,000,000 are preferably employed. Further, the polymer of the present invention is preferably crosslinked with methylene or methoxymethylene bonds to be insolubilized. Next, when the polymer of the present invention is used for ion exchange, enzyme immobilization, adsorption, etc., it is molded into various shapes such as powder and particles, but preferably known polymers such as polyolefin, polyamide, polyester, etc. mixed spinning with a fiber-forming polymer of
It is preferable to use a method such as composite spinning to form a fiber shape. That is, as will be described later, the polymer of the present invention can be produced by using an uncrosslinked, meltable raw material polymer as a starting material, and by a polymer reaction, functionalities represented by the general formulas () and () can be obtained. Since a group is to be introduced therein, this uncrosslinked starting material before introduction of the functional group can be made into fibers by mixed spinning, composite spinning, etc. with the fiber-forming polymer. Among these, polypropylene or its copolymer, which the present inventors previously proposed in JP-A-54-15019, is used as a core component, and starting materials for the polymer of the present invention such as polystyrene and polyα-methylstyrene are used. A multicore sea-island type composite fiber with a sheath component of which has a functional group represented by the general formula () introduced through a polymer reaction has excellent adsorption performance and is easy to handle due to its mechanical properties. It is extremely advantageous because it can be knitted or woven into a form adapted to the purpose of use, or can be made into short fibers of a certain size. Among the functional polymers obtained from aromatic vinyl polymers having repeating units represented by the general formulas () and () of the present invention, groups represented by the general formula (), that is, aminoacetamide in the side chain Aromatic vinyl polymers into which methyl groups have been introduced exhibit excellent performance as adsorbents for immobilizing enzymes and bacterial cells and adsorbing macromolecules. That is, as is clear from the general formula (), this group has a hydrophilic amide group in the middle of the side chain directly connected to the polymer main chain, and an active amino group at the carbon atom at the α position of the amide carbonyl group. have. In general, amino groups have the ability to act as active sites during ion exchange and adsorption; If it is, ion exchange and adsorption of medium- and high-molecular weight substances cannot be performed sufficiently due to steric hindrance.
In addition, even if the amino group is bonded to the tip of a long and flexible side chain, if the side chain is hydrophobic, ion exchange of hydrophilic medium- and high-molecular weight substances
It cannot exhibit sufficient adsorption ability. Furthermore, even when the amino group is attached to the tip of a hydrophilic side chain of appropriate length, the chemical and thermal stability of the amino group is poor due to the positional relationship between the hydrophilic group and the amino group. Sometimes. For example, in the side chain, the amino group is β of the amide carbonyl group.
If a hydrogen atom is bonded to a carbon atom at the α-position and a hydrogen atom is bonded to a carbon atom at the α-position, the amino group is likely to be removed. Adsorbents with such chemical structures are, for example,
When used in applications that require sterilization, there is a drawback that steam sterilization, which is the safest and most convenient method, cannot be used. On the other hand, in the polymer of the present invention, the amino group is bonded to the aromatic nucleus bonded to the polymer main chain via a linear chain consisting of four atoms, and a hydrophilic group is present in the middle of the linear chain. Since there is an amide group,
It exhibits excellent ability in ion exchange and adsorption of medium and high molecular weight substances, as well as adsorption of enzymes and bacterial cells. Furthermore, since the amino group is bonded to the carbon atom located at the α-position with respect to the carbonyl group of the amide, it is thermally stable, and the polymer of the present invention can be subjected to steam sterilization. The method for producing the aromatic vinyl polymer of the present invention involves a polymer reaction using a homopolymer of an aromatic vinyl monomer represented by styrene, α-methylstyrene, etc. or a copolymer containing these as the main component as a starting material. Manufactured by. Furthermore, since the starting materials are polymers, it is preferable to use these polymers that have been molded in advance so that the polymer reaction can be easily carried out and that they can be used as they are as final products. Hereinafter, as mentioned above, the method for producing the polymer of the present invention will be explained using as an example a raw material polymer molded into a fiber that is easy to handle as a reaction material and a product and can be used as a product as it is. The raw materials used in the production of the polymer of the present invention include homopolymers of vinyl monomers having aromatic nuclei such as styrene, α-methylstyrene, vinyltoluene, etc., or copolymers mainly composed of these. Fibers made of a mixture of polymers and reinforcing polymers such as polyolefins are preferably used. For example, it is used in the form of staples, filaments, punched felt, paper, woven fabrics, knitted fabrics, and the like. There is no particular limit to the thickness of the fiber, but it is usually 0.01 to 500 deniers, especially
A denier of 0.1 to 50 deniers is preferably used from the viewpoint of mechanical properties and practical properties. Formaldehyde used in the production of the polymer of the present invention is a gas at room temperature, so it may be blown into the reaction solution as a gas and dissolved, or it may be supplied in the form of paraformaldehyde, trioxane, tetraoxane, etc. Alternatively, it may be supplied as a compound that is easily decomposed by acid to generate formaldehyde, such as methylal or methylene diacetate. The amount of formaldehyde used is the most important factor determining the crosslink density of the molded product; if the amount is too small, the polymer will dissolve, while if it is too large, the crosslink density will become too high. Therefore, it becomes difficult to introduce a haloacetamidomethyl group. The amount of formaldehyde used depends on the type of polymonovinyl aromatic compound, the size of the molded product, the thickness of the fiber, the type and amount of the acid catalyst, haloacetamide methylating agent, solvent, and the target performance of the product. The amount varies, but approximately 0.001 to 10 mol,
In particular, 0.01 to 2 moles per aromatic nucleus are used. The haloacetaminomethylating agent used in the production of the polymer of the present invention is typified by N-methylol chloroacetamide, N-methylol-α-bromopropionamide, N-methylol-α-iodobutyrylamide, etc. N-methylol-
Examples include α-halocarboxylic acid amides, their alkyl ether compounds or ester compounds, and halogen-substituted hydroxyl groups, but from the viewpoint of economy and stability, N-methylol-α-halocarboxylic acid amides, especially ,
N-methylol-α-chlorocarboxylic acid amide,
Particularly preferred is N-methylol-α-chloroacetamide. Note that the chloro groups introduced into the fibers can be easily converted into iodine groups or bromine groups by treating the fibers with a solution of potassium iodide or potassium bromide. Acid catalysts used in the preparation of the polymers of the present invention include zinc chloride, aluminum chloride, tin tetrachloride, ferric chloride, Friedel-Crafts catalysts, organic acids such as methane, benzene, toluene, sulfonic acids, etc. Examples include strong inorganic acids such as sulfonic acid and sulfuric acid (concentrated or fuming sulfuric acid). In particular, sulfuric acid is optimal in terms of reactivity, operability, economy, stability, etc. The amount of the acid catalyst can be varied over a wide range of 1 mole or more of the haloacetamide methylating agent, but the optimum amount used varies depending on the type and amount of the swelling agent used. The swelling agent used in the production of the polymer of the present invention is an inert solvent that has a swelling effect on the linear or crosslinked polymonovinyl aromatic compound and has solubility for the haloacetamide methylating agent and the acid catalyst. Any suitable solvent may be used, including nitroalkanes such as nitropropane, aromatic nitro compounds such as nitrobenzene, chlorinated hydrocarbons such as 1,2-dichloroethane, and aprotic polar organic solvents such as sulfolane. These can be used individually or mixed with each other or with other inert solvents. The reaction in the present invention is generally carried out at a temperature range of 0 to 100°C, particularly 0 to 30°C to suppress side reactions. In carrying out the production of the polymer of the present invention, it is very important to select the type and amount of the haloacetaminomethylating agent, acid catalyst, and formaldehyde.
Furthermore, combining the reaction solutions to form a homogeneous solution is advantageous in terms of product homogeneity and operability. In this sense, when sulfuric acid is combined with a nitro compound solvent, it is easy to form a homogeneous solution and easy to handle. Furthermore, the aromatic vinyl polymer having an aminoacetamidomethyl group represented by the general formula () of the present invention can be easily obtained by treating the aromatic vinyl polymer having the haloacetamidomethyl group with an amino compound. Obtainable. The amino compounds used in the present invention include ammonia, hydroxylamine, and hydrazine, as well as organic amino compounds having a primary or secondary amino group or a tertiary amino group. Specific examples thereof include methylamine, Examples include ethylamine, n-butylamine, dimethylamine, diethylamine, hexamethylenediamine, polyethyleneimine, trimethylamine, triethylamine, and pyridine. The reaction between the amino compound and the haloacetyl group in the raw fiber in the production of the polymer of the present invention is a reaction that proceeds well at a reaction temperature around room temperature even if the halogen atom is the least reactive chlorine atom. The amount of the amino compound to be used is equal to or more than the amount of amino groups required in the fiber. In this case, when the amino compound is a secondary or tertiary amine, the crosslink density in the fiber does not change, but when the amino compound has _-NH2 groups or multiple secondary amino groups, The amino compound reacts with multiple haloacetyl groups, increasing the crosslink density of the fiber.
This increase in crosslink density is suppressed by increasing the amount of amino compound used. As the solvent used in the reaction of the raw material fiber and the amino compound, water, lower alcohols such as methanol, ethanol, n-butanol, and ethers such as dioxane and tetrahydrofuran are preferably used. Furthermore, when the amino compound is a low boiling point compound, the reaction time can be shortened by reacting under pressure. Molded products of the polymer of the present invention, such as fibers, can be used for ion exchange of low molecular weight anions, adsorption of high molecular weight substances, etc.
Although it can be used for a wide range of applications, including ion exchange and immobilization of enzymes and microbial cells, it is preferable to select and use the most suitable standard according to the individual application. For applications requiring high mechanical strength of the fibers, fibers containing reinforcing polymers are preferably used. The reinforcing fiber polymer is not particularly limited as long as it is physically and chemically inert during the manufacturing process of the molded product of the polymer of the present invention and can maintain mechanical strength. Specific examples of particularly preferred reinforcing polymers include crystalline polyα-olefins represented by polyethylene, polypropylene, poly(3-methylbutene-1), poly(4-methylpentene-1), and the like. For example, fibers that are molded products of the polymer of the present invention are
The reinforcing polymer is arranged inside the fiber in the form of a simple mixed fiber in which an inert aminoacetamidomethylated polymonovinyl aromatic compound (hereinafter referred to as the "base polymer") and the reinforcing polymer are finely dispersed in a disordered manner; There are core-sheath type composite fibers in which the core polymer is the core and the base polymer is placed on the outside, and there are also core-sheath type composite fibers in which the base polymer is the sea component and the reinforcing polymer is the island component dispersed in large numbers in the sea component. There are core-sea-island composite fiber types, and each of these has its own characteristics and can be used effectively. In the simple mixed fiber format, the reinforcing polymer is exposed to the outside at a proportion of the mixing ratio, so the adsorption performance is slightly inferior, but it has the advantage of low swelling and shrinkage, while the core-sheath composite fiber format Although it has the advantage of high adsorption capacity, it has the disadvantage of large swelling and shrinking, and the core and sheath are likely to separate during repeated swelling and shrinking. The multicore sea-island composite fiber format is
It maintains the advantages of both while improving the disadvantages of both, and is particularly excellent because it has high adsorption capacity and high peeling resistance. In this case, if 1 to 30% of a chemically stable reinforcing polymer is mixed in the sea component, swelling and shrinkage will be reduced and peeling resistance will be further improved. Further, the larger the number of islands, the better, but there are technical constraints, and 5 to 50 islands are usually preferred, and 10 to 30 islands are particularly preferred. Hereinafter, the present invention will be explained more specifically using Examples. In the Examples, the haloacetamidomethyl group and groups derived therefrom were identified by the following measurement method. (1) Elemental analysis Carbon, hydrogen, and nitrogen were determined by simultaneous quantitative determination using the thermal conduction method, and halogen was determined by the flask combustion method. (2) Infrared absorption spectrum A sample strip was measured by the KBr tablet method using a Hitachi infrared spectrophotometer model EPI-G3. Examples will be described below. Example 1 Polypropylene (Mitsui “Noprene” J3HG)
40 parts as an island component, polystyrene (“Styron”)
666) 50 parts, polypropylene (Sumitomo “Noprene”)
WF-727-F) 10g of multicore sea-island type composite fiber (number of islands: 16, single fiber fineness: 26 denier, tensile strength: 2.9 g/d, elongation: 55%, number of filaments: 42), with the sea component being a mixture of 1.5 parts of WF-727-F) , in a solution consisting of 10 g of N-methylolchloroacetamide, 80 g of nitrobenzene, 80 g of 98% sulfuric acid and 0.17 g of paraformaldehyde at 20 °C for 15 hours, the reaction was stopped by adding water, and then the fibers were washed with water. Then, nitrobenzene adhering to the fibers was extracted and removed with methanol. The fibers were dried at 60°C to obtain 14.5g. The results of elemental analysis of this fiber are 71.4% carbon, 8.7% hydrogen, and nitrogen.
4.2%, and chlorine 10.6%. Furthermore, the infrared absorption spectrum showed absorptions characteristic of amide groups at 3400 cm ^-1 , 3280 cm ^-1 , 1655 cm ^-1 and 1520 cm ^-1 .
From these results and the reactivity described below, it was found that this fiber had an aromatic nucleus substituted with approximately 92% chloroacetamidomethyl groups. Soak this fiber in a 10% dimethylamine aqueous solution,
After heating at 70° C. for 4 hours, it was washed with water, then washed with a 1N aqueous solution of caustic soda, and then washed with water until the washing solution became neutral. A part of this fiber was subjected to elemental analysis.
One part was used for exchange capacity measurement, and the other part was subjected to hydrolysis treatment. Elemental analysis results: 76.5% carbon, hydrogen
10.2%, nitrogen 8.5%, and no halogen was observed. In the infrared absorption spectrum, 1670 cm ^-1 and
It exhibits an absorption characteristic of amide groups at 1545 cm ^-1 , and
The exchange capacity was 2.42 milliequivalents per gram of hydrochloric acid type fiber. In addition, the exchange capacity of fibers heated under reflux in 6N hydrochloric acid for 15 hours is per gram of hydrochloride type fibers.
The amount was 3.32 milliequivalents, and the absorption at 1670 cm ^-1 disappeared in the infrared absorption spectrum of this fiber, confirming that the dimethylacetyl group had disappeared. Example 2 Polypropylene (Mitsui “Noprene” J3HG)
with polystyrene (“Styron”) as the island component.
666) 49.5 parts, low molecular weight polystyrene (“Hima”)
ST-120) 1.5 parts, polypropylene 7.5 parts and low molecular weight polypropylene (“Viscoll” 550P) 1.5 parts
The sea/island ratio is sea:island=
After melt-spinning to a ratio of 60:40 and then drawing 4 times, a multicore sea-island composite fiber (single fineness 3.7 denier, tensile strength 3.4 g/d, elongation 39%) is produced.
I got it. Next, a tube knit was made using this fiber (156 denier/42 filament) using a 4 inch φ-24 gauge flat knitting machine. Dissolve 3 parts of paraformaldehyde in a mixed solution of 475 parts of nitrobenzene and 475 parts of 98% sulfuric acid at 20°C, then cool the solution to 0°C and adjust the temperature from 0 to 5.
While maintaining the temperature at °C, 50 parts of N-methylolchloroacetamide was added and dissolved. 70 parts of the multi-core sea-island type composite fiber tubular knitted fibers were immersed in the resulting solution and heated at 20℃ for 20 minutes.
Allowed time to react. The obtained cylindrical knit was sufficiently washed with water and methanol, and then vacuum dried at 50°C to obtain 103 parts of chloroacetamidomethylated fiber cylindrical knit. Next, 1 part of the chloroacetamidomethylated fiber tube obtained above was immersed in 20 parts of water or ethanol solution containing various amino compounds shown in Table 1 at a concentration of 10%, heated at 70°C for 5 hours, and then After washing with water and drying, aminoacetamidomethylated insoluble polystyrene (polypropylene reinforced) fiber tube knits of Samples 1 to 4 in the table were obtained. In addition, the chlorcetamide methylated fiber tube knit obtained above was heated at 70°C for 6 hours in a solution consisting of 10% potassium iodide, 80% ethanol, and 10% water to convert the chloro groups to iodine groups. ,
This cylindrical knitted fiber was placed in a 10% trimethylamine aqueous solution.
It was heated at 70° C. for 6 hours to obtain a trimethylammonium acetamidomethylated fiber tube knitted sample 5 in the table. Elemental analysis, exchange capacity measurements, water content, and bilirubin adsorption capacity measurements were performed on these samples. The results are shown in Table 1. However, the nitrogen content in the table is the analytical value for samples 1 to 4 in the free amine type, and for sample 5 in the hydrochloride type. The exchange capacity in the table is the value for the hydrochloride type,
Samples 1-4 show weak anion exchange capacity, and sample 5 shows neutral salt decomposition capacity. Moreover, the water content was calculated from the following formula by sufficiently swelling 4 g (W ₀ ) of a dry sample in water, centrifuging it to remove surface moisture, and then measuring the weight (W). Water content = W - W ₀ / W ₀ The amount of bilirubin adsorbed is the dry weight (W ₁ ).
The bilirubin concentration in the aqueous solution before and after adsorption was determined using a calibration curve from the absorbance at 450 mμ. , calculated from the following formula. Adsorption amount of bilirubin = C ₁ − C ₂ /W ₁ ×V [mg/g] However, in the formula, C ₁ indicates the bilirubin concentration before adsorption, C ₂ indicates the bilirubin concentration after adsorption, and V indicates the amount of aqueous solution used. . The exchange capacity is determined by regenerating the sample with a 1N aqueous sodium hydroxide solution, treating it with 1N hydrochloric acid, calculating the number of equivalents of consumed hydrochloric acid from the amount of remaining hydrochloric acid, and calculating the value by calculating the dry weight of the sample in the hydrochloride form. It is the value divided by the number of grams. Example 3 Polypropylene (Mitsui “Noprene” J3HG)
is the island component and polyvinyltoluene (a mixture of 60% meta and 40% para. After bulk thermal polymerization at 125℃ for 24 hours,
A mixture of 50 parts of polypropylene (with a number average molecular weight of approximately 200,000), 7.5 parts of polypropylene, and 1.5 parts of low molecular weight polypropylene ("Viscoll" 550P) as a sea component, dissolved in benzene and purified by reprecipitation with methanol.
After melt-spinning so that the sea-island ratio is 60:40, and then drawing it 3.5 times, a multicore sea-island composite fiber (single fineness 4.1 denier, tensile strength 3.0
g/d, elongation 35%). Next, using this fiber (160 denier/42 filaments), a tube knit was made using a 4 inch φ-24 gauge flat knitting machine. Dissolve 3 parts of paraformaldehyde in a mixed solution of 475 parts of nitrobenzene and 475 parts of 98% sulfuric acid at 20°C, then cool the solution to 0°C and adjust the temperature from 0 to 5.
While maintaining the temperature at °C, 50 parts of N-methylol chloroacetamide was added and dissolved. 70 parts of the multicore sea-island type composite fiber tubular knitted fibers were immersed in the resulting solution and heated at 20℃ for 20 minutes.
Allowed time to react. The obtained cylindrical knit was thoroughly washed with water and methanol, and then vacuum dried at 50°C to obtain 95 parts of chloroacetamidomethylated fiber cylindrical knit. Next, 10 parts of the chloroacetamide methylated fiber tube obtained above were immersed in a 50% dimethylamine aqueous solution, heated at 50°C for 5 hours, and then washed with water and dried to obtain a dimethylaminoacetamide methylated fiber tube. Ta. When this product was evaluated in the same manner as in Example 2, the exchange capacity was 1.92 meq/g, the water content was 0.9, and the bilirubin adsorption amount was 8.3 mg/g.

【table】

Claims (1)

[Claims] 1. A repeating unit represented by the following general formula ()
A homopolymer consisting of M ₁ or the repeating unit
M ₁ and the repeating unit shown by the general formula () below
A copolymer with M ₂ in which the abundance ratio of M ₁ is at least 1 mol% and the molecular weight is 2000 to 2000.
3,000,000. [Formula] [Formula] In the above formula, R ₀ and R ₀ ' represent a hydrogen atom or a methyl group, and A represents a benzene ring, a benzene ring having one or two methyl groups, or a benzene ring having a chloro group. show. Moreover, Y represents a functional group represented by the following general formula () or (). [Chemical formula] [Chemical formula] In the above formula, X is a halogen atom, R' and R'' represent a hydrogen atom, a lower alkyl group, an aryl group, or an aralyl group, and R' and R'' may be the same or different. . Moreover, R ₁ and R ₂ represent a hydrogen atom or an alkyl group.