JP2684150B2 - Method for producing high molecular weight aliphatic polyester - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an aliphatic polyester, and more specifically, a melt polycondensation reaction between an aliphatic dihydric carboxylic acid di-lower alkyl ester and an aliphatic dihydric alcohol to obtain practical physical properties. To a method for producing a biodegradable aliphatic polyester having.

[0002]

2. Description of the Related Art The characteristics of plastics are that they are light and strong, and that they are difficult to decompose. In particular, general-purpose plastics are industrially mass-produced and widely used in daily life and industrial fields, and the amount of use thereof has been remarkably increasing. Since many plastics are not decomposed in the natural environment, environmental destruction due to the disposal of plastics has become a problem in recent years. Therefore, in recent years, expectations for the development of polymers that are decomposed by microorganisms in the environment, that is, biodegradable polymers, are increasing. Aliphatic polyesters are considered promising as biodegradable polymers,
Recently, some have been developed, but each has the following problems.

Although some microbially produced aliphatic polyesters represented by polyhydroxybutyrate (PHB) have been developed, the productivity is low and the cost is high at this stage, and PHB has a melting point and a thermal decomposition temperature. Has a small temperature difference with the polymer, thermal decomposition of the polymer occurs during molding, and there are problems such as deterioration of polymer performance and odor. Currently, applications to medical materials and the like are being studied. Polycaprolactone is one of the few aliphatic polyesters industrially produced and is a biodegradable polymer having a melting point of 60 ° C.
Its use is limited because it is low. Although polylactides are used in the medical field as bioabsorbable materials, they are expensive and their manufacturing process is complicated. Therefore, in order to improve the problems of the above-mentioned polymer, a condensation type aliphatic polyester has been newly noticed and studied.

Regarding the method of synthesizing an aliphatic polyester by the polycondensation method, many studies on the synthesis of polymers have been reported, including the study by Carosas et al. (Journal of American Chemical Society, 51).
Volume, 2560, (1929), 54, 1559 (1932), Dee Macromolecule Chemie, 5
Vol. 5, p. (1950)). However, a polymer which can be formed into a film and has practical physical properties satisfying mechanical strength equivalent to that of polyethylene or polyethylene terephthalate was not obtained. In addition, the synthetic method of the aliphatic polyester has the following problems. The aliphatic polyester is synthesized by a dehydration reaction and a deglycolization reaction using an aliphatic dibasic acid and glycol as starting materials. The equilibrium constant of this reaction is small. Therefore, unless the water or glycol produced in the reaction system by the dehydration reaction or deglycolization reaction is removed out of the system, the reaction will be in equilibrium and the molecular weight will not improve. In addition, the reverse reaction causes a decomposition reaction to reduce the molecular weight of the polymer. If a large amount of catalyst is used to promote the polycondensation reaction and improve the molecular weight, or if the reaction is carried out at high temperature, side reactions such as dimerization and cyclization of the monomer, thermal decomposition reaction of the polymer and crosslinking are caused. This not only causes a decrease in molecular weight, but also causes coloration and deterioration of polymer performance.

In the polymerization of polyethylene terephthalate (PET), which is known as a typical polyester, ethylene glycol is used in a large excess of 2 equivalents or more with respect to terephthalic acid or dimethyl terephthalate, and bishydroxyethyl terephthalate is removed by dehydration or demethanol. It is well known to synthesize a high molecular weight polymer by deglycolization via (BHT). However, even if the same method is used for the polymerization of the aliphatic polyester, it is difficult to improve the molecular weight because the deglycolization reaction is slow and the transesterification reaction under high vacuum tends to break the molar balance. Furthermore, aliphatic dilcarboxylic acids such as succinic acid and adipic acid and their acid anhydrides cause a decrease in the activity of the catalyst. Since these have different acid strengths from terephthalic acid, they cannot be directly applied as PET polymerization catalysts even if they are highly active. Further, it is known that the activity of the catalyst is also reduced by the water generated by the dehydration reaction, and thus the progress of the reaction is significantly suppressed and it is difficult to obtain a high molecular weight polymer. In addition, the side reaction as described above occurs when the decrease in catalyst activity is compensated for by increasing the amount of catalyst. Regarding the physical properties of the aliphatic polyester, the melting point is generally low, but some have a melting point of around 100 ° C. However, since a high-molecular weight polymer cannot be obtained, the mechanical strength is low, and it has been considered that the film or sheet is brittle and is not suitable for practical use. Since there is a limit to the increase in the molecular weight of the fatty acid polyester, the low molecular weight (number average molecular weight: 5,000 to 15,000) has recently been obtained in the presence of a catalyst from an aliphatic dibasic acid and glycol.
There has been proposed a method for obtaining a high molecular weight aliphatic polyester by synthesizing the aliphatic polyester (0) and reacting hydroxy groups at both ends of the polymer with diisocyanate (JP-A-4-189822). However, this method has a drawback that the number of reaction steps increases and a urethane bond is formed in the polymer chain.

Since the aliphatic polyester produced by the polycondensation method has the above-mentioned problems in the synthetic method and physical properties, the aliphatic polyester is a high molecular weight compound (polymer).
Widely used as a low molecular weight compound (oligomer) or as a reactive oligomer having functional groups such as hydroxyl groups at both ends, as an additive for plasticizers, lubricating oils, and as a base resin for paints and adhesives. Has been. Therefore, industrially, in contrast to research on aromatic polyesters such as polyethylene terephthalate and polybutylene terephthalate, research on increasing the molecular weight of aliphatic polyesters has not been much studied.

[0007]

DISCLOSURE OF THE INVENTION The present invention provides a method for solving the above-mentioned problems found in the prior art, that is, a method for producing a high molecular weight aliphatic polyester having practical physical properties and biodegradability. The task is to provide.

[0008]

The present inventors have completed the present invention as a result of intensive studies to solve the above problems. That is, according to the present invention, an aliphatic dihydric carboxylic acid di-lower alkyl ester and an aliphatic dihydric alcohol are subjected to polycondensation reaction in the presence of a catalyst to give a number average molecular weight of 20,0.
In the method for producing an aliphatic polyester having a number of 00 or more, the content of the free carboxylic acid compound in the aliphatic divalent carboxylic acid di-lower alkyl ester is kept at 0.1 wt% or less, and the raw material charging molar ratio is represented by the formula 1. .0 <A / B ≦ 2.1 (I) (wherein A represents the number of moles of the aliphatic dihydric alcohol, and B represents the number of moles of the aliphatic divalent carboxylic acid di-lower alkyl ester) The method for producing a high molecular weight aliphatic polyester is provided.

The aliphatic dicarboxylic acid (aliphatic dibasic acid) di-lower alkyl ester used in the present invention is hydroesterified from carbon monoxide and alcohol using an olefin as a starting material without passing through the aliphatic dicarboxylic acid. The reaction allows direct synthesis in good yield, which is more cost effective than the aliphatic divalent carboxylic acid. Moreover, this aliphatic divalent carboxylic acid di-lower alkyl ester has a lower melting point than the aliphatic divalent carboxylic acid, has a large compatibility with dihydric alcohols, has thermal stability, and is heavy under mild conditions. It is possible to proceed with the condensation reaction. By allowing the polycondensation reaction to proceed under such reaction conditions, a high molecular weight aliphatic polyester having practical physical properties can be produced.

The aliphatic divalent carboxylic acid di-lower alkyl ester (hereinafter also simply referred to as divalent carboxylic acid ester) used in the present invention is a straight or branched di-lower alkyl of divalent alkyl carboxylic acid. Esters are included. Also,
In this case, the divalent carboxylic acid component may contain an ether bond, and may also contain a substituent such as a keto group or an alkoxy group. Specific examples of these dicarboxylic acid esters include, for example, oxalic acid, malonic acid, succinic acid, adipic acid, pimelic acid, suberic acid,
Azelaic acid, sebacic acid, dodecanoic acid, glutaric acid,
Examples thereof include di-lower alkyl esters of divalent carboxylic acids such as methylmalonic acid, α-methylglutaric acid, α-ethylsuccinic acid, propylmalonic acid, cyclohexylylenedicarboxylic acid, diglycolic acid, corkic acid and γ-ketopimelic acid.

The content of the free carboxylic acid compound in the divalent carboxylic acid ester used in the present invention is 0.1 wt% or less,
It is preferably 0.05 wt% or less. It has been found that when the content of the monovalent or divalent carboxylic acid compound exceeds 0.1 wt%, not only the catalytic activity is remarkably lowered but also the catalyst is deactivated. Therefore, it is difficult to obtain a high molecular weight polymer. This has never been found before. In the aliphatic divalent carboxylic acid di-lower alkyl ester used in the present invention, the lower alkyl group is an alkyl group having 1 to 6 carbon atoms, preferably a methyl group or an ethyl group.

In the present invention, the aliphatic dihydric alcohol (hereinafter also simply referred to as alcohol) used as a reaction component for the divalent carboxylic acid ester is a straight chain, branched chain or cyclic group having 2 to 10 carbon atoms. The dihydric alcohol of is used. Further, this dihydric alcohol may contain an ether bond or may contain a substituent such as a keto group or an alkoxy group. Specific examples of such a dihydric alcohol include, for example, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 2-methyl-propanediol, 1,4-butanediol. , Neopentyl glycol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, diethylene glycol, cyclohexanedimethanol, and the like. These may be used alone or in combination of two or more. Further, a small amount of trifunctional alcohol such as 1,1-tris (hydroxymethyl) propane may be used.

Preferred aliphatic divalent carboxylic acid esters used in the present invention include (i) succinic acid di-lower alkyl ester, (ii) adipic acid di-lower alkyl ester, and (iii) oxalic acid di-lower alkyl ester. It contains at least one selected from alkyl esters. As the other divalent carboxylic acid ester (B) used in combination with these divalent carboxylic acid ester (A), di-lower alkyl ester of various aliphatic divalent carboxylic acid is used, and straight chain, branched chain Di-lower alkyl esters of linear and cyclic aliphatic dicarboxylic acids are included. Further, the divalent carboxylic acid component in this case may contain an ether bond, or may contain a substituent such as a keto group or an alkoxy group. Specific examples of these divalent carboxylic acid esters (B) include, for example, pimelic acid, γ-ketopimelic acid, glutaric acid, α-methylglutaric acid, α.
-Di-lower alkyl esters such as ethylsuccinic acid, propylmalonic acid, suberic acid, azelaic acid, sebacic acid, cyclohexylylenedicarboxylic acid, diglycolic acid, malonic acid and corkic acid.

Next, specific examples of the divalent carboxylic acid ester preferably used as the reaction component in the present invention are shown below. (A) A succinic di-lower alkyl ester obtained by subjecting an acrylic acid lower-alkyl ester to a hydroesterification reaction with carbon monoxide and a lower alcohol, wherein methyl malonic acid di-lower alkyl ester and γ-ketopimelic acid di-lower Those containing 1 to 10% by weight of an alkyl ester. (B) Adipic acid di-lower alkyl ester obtained by subjecting butadiene to a hydroesterification reaction with carbon monoxide and a lower alcohol, such as α-methylglutaric acid di-lower alkyl ester and α-ethylsuccinic acid di-lower alkyl ester. , And / or 1 to 20% by weight of propylmalonic acid di-lower alkyl ester. The succinic acid di-lower alkyl ester preferably used in the present invention can be synthesized by using methyl acrylate as a starting material (Chemical Technology Research Report Vol. 75, No. 10, Supplement, 419 (1980)). The adipic acid di-lower alkyl ester can be synthesized by using butadiene as a starting material (Japanese Patent Publication No. 50-7579, JP-A-4-26).
652). As shown in the formulas (1) and (2), these compounds do not undergo aliphatic divalent carboxylic acid, respectively, and carbon monoxide and methanol in the presence of a catalyst of Co ₂ (CO) ₈ respectively. A hydroesterification reaction of the starting material can be directly obtained in good yield. CH ₂ = CHCOOCH ₃ + CO + CH ₃ OH → CH ₃ OOC (CH ₂ ) ₂ COOCH ₃ (1) CH ₂ = CHCH = CH ₂ + CO + CH ₃ OH → CH ₃ OOC (CH ₂ ) ₄ COOCH ₃ ( 2)

In the reaction of the formula (1), in addition to the main product, dimethyl succinate, as a by-product,
A total of 1 to 10% by weight of methylmalonic acid dimethyl ester and γ-ketopimelic acid dimethyl ester are produced.
In the present invention, the purified succinic acid dimethyl ester may be used alone, or the succinic acid dimethyl ester containing these by-products may be used as it is, and in any case, a high molecular weight raw material having practical physical properties is used. A degradable aliphatic polyester can be obtained. In addition, by containing these by-products, not only the advantage of being able to obtain a flexible film having low crystallinity but also its biodegradability is improved. The content of by-products is usually in the range of 1 to 10% by weight, preferably 1 to 5% by weight. Further, in the present invention, a divalent carboxylic acid ester corresponding to the above by-product or another divalent carboxylic acid ester can be added to the purified dialkyl succinate.

In the reaction of the formula (2), in addition to the main product, adipic acid diethyl ester, as a by-product,
A total of 1 to 30% by weight of α-methylglutaric acid dimethyl ester, α-ethylsuccinic acid dimethyl ester, and propylmalonic acid dimethyl ester is produced. In the present invention, the purified adipic acid dimethyl ester may be used alone, or the adipic acid dimethyl ester containing a by-product may be used as it is, and in any case, a high molecular weight compound having practical physical properties and biodegradability is used. An aliphatic polyester can be obtained. Further, by containing these by-products, not only the advantage that a flexible film having low crystallinity can be obtained but also the biodegradability thereof is improved. The content of by-products is usually 1 to 20% by weight, preferably 1 to 10% by weight. Further, in the present invention, a divalent carboxylic acid ester corresponding to the above by-product or another divalent carboxylic acid ester can be added to the purified adipic acid di-lower alkyl ester.

As described above, the by-products produced in the reactions of both the formulas (1) and (2) can be effectively used as a polymer raw material and must be completely separated from the main product. In addition, there are advantages that the refining process of the raw material can be simplified and that the physical properties of the polymer can be improved.
As the divalent carboxylic acid ester to be used as an additive component for the above-mentioned divalent carboxylic acid ester component, various divalent carboxylic acid esters having 2 to 12 carbon atoms such as diethyl sebacate and dimethyl diglycolate other than the above-mentioned ones Esters of acids can be used.

In the present invention, as the divalent carboxylic acid ester (A), in addition to the succinic acid di-lower alkyl ester and adipic acid di-lower alkyl ester, oxalic acid di-lower alkyl ester is used. For example, butyl oxalate is synthesized by the following reaction formula. 2CO + C ₂ H ₄ OH → C ₂ H ₄ OOC-COOC ₂ H ₄ (3) The oxalic acid diester thus obtained may be used alone or may be added with another divalent carboxylic acid ester. It can also be added and used. The amount of the dicarboxylic acid ester (B) added to the oxalic acid diester is 0 to
It is 50 mol%, preferably 1 to 40 mol%. In addition,
Oxalic acid is obtained by hydrolyzing the oxalic acid diester, so using the oxalic acid diester
This hydrolysis step can be omitted, which is industrially advantageous.

According to the present invention, by performing a melt polycondensation reaction between a divalent carboxylic acid ester and a dihydric alcohol,
A polymer having practical physical properties can be obtained. A polymer having practical physical properties in this specification has a melting point of 70 ° C.
With the above, the difference between the melting point and the thermal decomposition temperature is at least 100 ° C.
This is what is mentioned above and is capable of forming a tough film.
The molecular weight of the high molecular weight aliphatic polyester obtained in the present invention is determined by gel permeation chromatography (G
It has a number average molecular weight of 20,000 or more in terms of polystyrene based on the PC) method. If it is less than 20,000, a tough film cannot be obtained.

In synthesizing the polymer of the present invention,
The charging ratio of the monomer was more than 1 mol of dihydric alcohol and 2.1 mol per 1 mol of divalent carboxylic acid ester.
It is preferable to define it in the range of mol or less, preferably 1.01 to 1.1 mol. This raw material charging molar ratio is different from the conventional polyester polymerization methods.

In the present invention, a catalyst is used in producing a polymer, and a preferable catalyst is a compound containing an element having Pauling electronegativity of the element of 1.0 to 1.8. Especially, among them, periodic table IIa group, IV
Compounds containing an element selected from group a, group Va, group VIIa, group IIb, and group Vb are preferred. More preferably, the group IIa element is magnesium and calcium, and the group IVa element is titanium, zirconium, V
Vanadium and niobium are the elements of group a, manganese is the element of group VIIa, zinc is the element of group IIb,
Cadmium includes silicon, germanium, tin, and lead as the IVb group element, and antimony and bismuth as the Vb group element. Examples of compounds containing these elements include acetates, acetylacetonates, oxalates, carbonates, borates, oxides, hydroxides and alcoholates. These catalysts may contain water of crystallization.

Specific examples of the compound containing a Group IIa element include magnesium acetate, magnesium oxide, magnesium stearate, calcium acetate, calcium oxide and the like. Examples of the compound containing a Group IVa element include titanium tetraisopropoxide, titanium tetrabutoxide, titanium tetrabutoxide trimer, titanium oxyacetylacetonate, titanium di-n-butoxide-bis-acetylacetonate, titanium oxide and shushu. Examples thereof include potassium acid titanate dihydrate, zirconium oxide, zirconium acetylacetonate, zirconium acetate and the like. Examples of the compound containing a Va group element include vanadium acetylacetonate, vanadium oxide, vanadium oxide bisacetylacetonate, niobium acetate, niobium oxide, and triisopropoxide niobium. Examples of the compound containing a Group VIIa element include:
Examples thereof include manganese acetate, manganese oxalate, manganese oxide, manganese acetylacetonate, and manganese stearate. Examples of the compound containing a Group IIb element include zinc acetate, zinc oxalate, zinc acetylacetonate, zinc chloride, zinc sulfate, zinc carbonate, zinc stearate, zinc hydroxide, cadmium acetate, cadmium oxalate, cadmium oxide and stearin. Examples thereof include cadmium acid. Examples of the compound containing a group IVb element include silicon oxide, silica alumina, germanium oxide,
Germanium hydroxide, stannous acetate, stannous oxalate, tin octylate, stannous chloride, stannic chloride, stannous oxide, stannic oxide, dibutyltin oxide, lead acetate, lead borate, citric acid Examples thereof include lead acid, lead hydroxide, lead oxide, lead phosphate, lead phthalate, and lead stearate. Examples of the compound containing a Vb group element include antimony acetate, antimony oxalate, triphenyl antimony,
Examples thereof include antimony pentafluoride, antimony oxide, antimony pentaoxide, bismuth acetate, bismuth carbonate oxide, bismuth oxalate, and bismuth oxide.

These catalysts may be used alone or in combination of two or more. Further, the catalyst amount is 10 ^{-8 with} respect to 1 mol of the divalent carboxylic acid ester used as a raw material
It is in the range of 10 ⁻² mol, preferably 10 ⁻⁷ to 2 × 10 ⁻³ mol. If the amount is less than this range, the reaction does not proceed well, the reaction takes a long time, and it becomes difficult to obtain a high molecular weight polymer. On the other hand, if the amount exceeds this range, thermal decomposition of the polymer during polymerization will be promoted. Further, it causes coloration, cross-linking is not likely to occur, and apparently the molecular weight is large, but the molecular weight distribution is broad, so that the obtained polymer becomes brittle and the performance of the polymer is deteriorated.

The production of the high molecular weight polyester by the reaction of the divalent carboxylic acid ester and the dihydric alcohol in the present invention is carried out in a two-step reaction process. In the reaction step of the first stage, a polycondensation reaction between the divalent carboxylic acid ester and the dihydric alcohol is performed. In this case, since the charged mole numbers of the dihydric carboxylic acid ester and the dihydric alcohol are specified within the above range, the obtained product contains a polyester having a dihydric alcohol residue at its end. In addition, in the reaction step of the first step, the alkyl alcohol that is the ester constituent component is desorbed from the divalent carboxylic acid ester. In the reaction step of the second step, the reaction product containing the polyester having a dihydric alcohol residue at the terminal obtained in the reaction step of the first step is subjected to a condensation reaction to increase the molecular weight. In this case, the dihydric alcohol residue bonded to the end of the polyester is eliminated, and the dihydric alcohol is by-produced.

The reaction step of the first stage of the present invention is 80 to 2
It is carried out at a temperature of 50 ° C, preferably 100 to 220 ° C, more preferably 120 to 200 ° C. The reaction time is 0.
It is 5 to 5 hours, preferably 1 to 3 hours. Also,
The reaction atmosphere is preferably an inert gas atmosphere such as nitrogen. In this reaction, the by-produced alkyl alcohol is preferably removed from the reaction system. For this purpose, a method can be adopted in which an inert gas is passed through the reaction system and the gaseous alkyl alcohol present in the reaction system is discharged together with the inert gas to the outside of the reaction system. The number average molecular weight of the polyester obtained in the reaction step of the first step is usually 500 to 10,000, preferably 1,000 to 10,000.

The second step of the reaction step of the present invention is the first step.
The reaction product obtained in the reaction step of the step is performed at a reaction temperature higher than the reaction temperature of the first step while removing the dihydric alcohol produced as a by-product. For this purpose, the reaction is preferably carried out under reduced pressure or while circulating an inert gas. The reaction temperature is usually 150 to 270 ° C, preferably 170 to 250 ° C. The reaction temperature of the second stage is maintained at 20 ° C. or higher, preferably about 30 to 40 ° C. higher than the reaction temperature of the first stage. When reducing the pressure of the reaction system of the second stage, the pressure of the reaction system is 3 Torr or less, preferably 1 Torr or less, more preferably 0.5 Torr or less. Further, when an inert gas is circulated in the reaction system, as the inert gas,
Examples of the gas that do not participate in the reaction include nitrogen gas, argon gas, and helium gas. The reaction step of the second step can be continuously performed using the reaction vessel used in the reaction step of the first step. In this case, after the completion of the reaction in the first step, the reaction temperature is raised while the pressure of the reaction system is reduced or the inert gas is passed through the reaction system. When the second stage reaction is carried out in another reaction vessel, a reactive distillation column having a structure in which the reaction vessel and the distillation column are connected can be used as the reaction vessel. In the case of this method, the reaction product obtained in the reaction step of the first step is introduced into the reaction vessel of the reactive distillation column, and the divalent divalent by-product is produced while performing the reaction of the second step in the reaction vessel. Alcohol is distilled out of the reaction system through the distillation column. The inside of the reaction vessel is preferably depressurized or an inert gas is introduced.

[0027]

According to the present invention, when an aliphatic polyester is produced by a polycondensation reaction, a divalent carboxylic acid di-lower alkyl ester is used in place of the divalent carboxylic acid,
By carrying out the two-step reaction with the dihydric alcohol at a specific ratio, it becomes possible to proceed the reaction under relatively mild conditions. As a result, a high molecular weight aliphatic polyester can be easily produced. The polymer synthesized according to the present invention is an aliphatic polyester having practical physical properties.

[0028]

Next, the present invention will be described in more detail with reference to examples. The physical properties of the aliphatic polyester obtained in the following examples were measured as follows. (Molecular weight and molecular weight distribution) A calibration curve was prepared from standard polystyrene using gel permeation chromatography (GPC), and the number average molecular weight (Mn), weight average molecular weight (Mw), and molecular weight distribution (Mw / Mn) were determined. Was. As an eluent, chloroform was used. (Thermal property) The melting point and the glass transition point were measured by a differential scanning calorimeter (DSC). Further, the thermal decomposition temperature was measured by a thermogravimetric analyzer (TG).

The biodegradability of the aliphatic polyester obtained in the examples was measured as follows. (Evaluation of biodegradability) The biodegradability test was performed by a method of embedding in soil. The test method is described below. (Soil embedding test) 1) Test method: An embedding test of a polymer press sheet was conducted for 4 weeks using a commercially available compost soil. 2) Test conditions: (1) Soil: Commercial compost soil (2) Sample form: 40 × 40 × 0.15mm press sheet (3) Test temperature: 30 ° C (4) Test period: 4 weeks 3) Decomposition rate calculation Method (Decomposition rate is the weight reduction rate of the press sheet) A: Sample weight before test (g) B: Sample weight after test (g)

Example 1 In a glass four-necked flask having an internal volume of 200 ml, 50 g of dimethyl succinate having a succinic acid content of substantially 0%, 42 g of ethylene glycol, and 100 mg of calcium acetate dihydrate as a catalyst. After charging, the reaction was started at 150 ° C. under a nitrogen atmosphere. After 3 hours, while gradually increasing the reaction temperature, depressurization was started, and finally the reaction temperature 2
After reaching a temperature of 00 ° C. and a vacuum degree of 1 Torr, the reaction was further continued for 3 hours. The polymer obtained had a Mn of 25,000,
It has a molecular weight and a molecular weight distribution of Mw: 45,100 and Mw / Mn: 1.8, and has a melting point of 100 ° C and a thermal decomposition temperature of 305 ° C.
The thermal properties of Since the molecular weight distribution is as narrow as 1.8, this polycondensation reaction proceeds promptly. The obtained polymer was film-moldable, and the film was tough. As a result of a biodegradability test, the degradation rate of the press sheet was 30% in the soil embedding method.

Comparative Example 1 An experiment was conducted in the same manner as in Example 1 except that 40 g of succinic acid was used instead of dimethyl succinate. In this case, the reaction proceeds slowly and the polymer obtained is M
n: 14,800, Mw: 24,200, Mw / Mn:
Since the molecular weight was as low as 1.7, film formation was possible, but only a brittle film was given.

Example 2 An experiment was conducted in the same manner as in Example 1 except that 60 g of 1,4-butanediol and 100 mg of zinc acetate dihydrate were used as a catalyst instead of ethylene glycol. The polymer obtained had Mn: 34,200 and Mw: 58,54.
It had a thermal property of 0, Mw / Mn: 1.71 and a molecular weight distribution, a melting point of 117 ° C. and a thermal decomposition temperature of 302 ° C. In addition, a tough film that can be formed into a film and has almost no coloring could be obtained. As a result of a biodegradability test, the rate of decomposition of the press sheet was 25% by the earth embedding method.

Example 3 Dicobalt octacarbonyl 4 mmol, 3, 5 was added to a stainless steel autoclave equipped with a stirrer and having an inner volume of 300 ml.
-Dimethylpyridine 10 mmol, methanol 0.5 m
mol and 0.5 mmol of methyl acrylate were charged.
Pressurize the autoclave with carbon monoxide and heat to 16
The reaction was allowed to proceed for 2 hours under the conditions of 0 Kg / cm ² and 110 ° C. As a result, the total yield of dicarboxylic acid ester from methyl acrylate was 91.1%. 120 g of N-hexane was added to the product, and the mixture was shaken to separate the dicarboxylic acid ester and the catalyst complex, and further purified by distillation. The composition of the obtained dicarboxylic acid ester was succinic acid dimethyl ester: 94% by weight, methylmalonic acid dimethyl ester: 5% by weight, and γ-ketopimelic acid dimethylester: 1% by weight. Polymerization reaction was carried out as follows using the dicarboxylic acid ester containing succinic acid dimethyl ester thus obtained as a main component. Using a glass four-necked flask having an inner volume of 200 ml, 38 g of the carboxylic acid ester containing dimethyl succinate as a main component and 40 g of 1,4-butanediol obtained above were used.
g, and the same experiment as in Example 1 except that zinc acetate dihydrate 100 mg was used as the catalyst. The obtained polymer has Mn: 32,940, Mw: 58,010, Mw /
It had a molecular weight and a molecular weight distribution of Mn: 1.76, the melting point was 114.2 ° C, and the thermal decomposition starting temperature was 300 ° C. In addition, a tough and flexible film could be formed. As a result of a biodegradability test, the degradation rate of the press sheet was 35% by the soil embedding method.

Example 4 0.01 mmol of dicobalt octacarbonyl was added to a stainless steel autoclave equipped with a stirrer and having an inner volume of 300 ml.
Pyridine 0.8 mmol, methanol 0.4 mmol,
Acetone 0.17 mmol, butadiene 0.17 mmo
l was charged. The autoclave was pressurized with carbon monoxide containing 5% hydrogen and heated to 250 Kg / cm ² , 1
When the first stage reaction was carried out for 6.5 hours under a constant condition of 20 ° C., gas absorption was completed. Next, a part of the residual gas is extracted and further heated to 200 Kg / cm ² , 1
The second stage reaction was carried out for 3.5 hours under constant conditions of 80 ° C. As a result, the yield of dicarboxylic acid ester from butadiene was 80.1%. N-hexane 1 for product
20 g was added, and the mixture was shaken to separate the dicarboxylic acid ester and the catalyst complex, and further purified by distillation. The composition of the obtained dicarboxylic acid ester was as follows: adipic acid dimethyl ester: 85.4% by weight, α-methylglutaric acid dimethyl ester: 12.1% by weight, ethylsuccinic acid dimethyl ester: 2.1% by weight, propylmalonic acid dimethyl ester. Ester: 0.4% by weight. Polymerization reaction was carried out as follows using the dicarboxylic acid ester containing dimethyl diapate thus obtained as a main component. Using a glass four-necked flask having an internal volume of 200 ml, 13 g of a dicarboxylic acid ester containing adipic acid dimethyl ester as a main component obtained above, 26 g of succinic acid dimethyl ester, 46 g of 1,4-butanediol,
As a catalyst, 50 mg of zinc acetate dihydrate and 30 mg of antimony trioxide were charged, and the reaction was started at 140 ° C. under a nitrogen atmosphere. After 2 hours, the reaction temperature was gradually raised and the pressure reduction was started. Finally, the reaction temperature was 200 ° C and the degree of vacuum was 1
After reaching torr to 0.5 torr, the reaction was allowed to proceed for an additional 3 hours. The polymer obtained had Mn: 27,000,
Mw: 44,000, Mw / Mn: 1.6, melting point 77
It had physical properties of ° C and thermal decomposition temperature of 308 ° C, and could be formed into a film. As a result of a biodegradability test, the degradation rate of the press sheet was 45% in the soil embedding method.

Example 5 Instead of using calcium acetate dihydrate as a catalyst, 50 mg of zinc acetate dihydrate and 30 mg of antimony trioxide were used.
An experiment was conducted in the same manner as in Example 1 except that was used. The obtained polymer has Mn: 36,400 and Mw: 59,20.
0, Mw / Mn: 1.63, melting point was 117 ° C., thermal decomposition temperature was 310 ° C., and a tough film was formed. As a result of a biodegradability test, the degradation rate of the press sheet was 28% by the soil embedding method.

Example 6 Instead of succinic acid dimethyl ester, succinic acid dimethyl ester 26 having a succinic acid content of substantially 0%
g, 13 g of adipic acid dimethyl ester, 46 g of 1,4-butanediol instead of ethylene glycol,
An experiment was conducted in the same manner as in Example 1 except that 50 mg of zinc acetate dihydrate was used as the catalyst instead of calcium acetate dihydrate, and 30 mg of antimony trioxide was further used. The polymer obtained has Mn: 27,650, M
w: 49,440, Mw / Mn: 1.8, melting point 82
It had a physical property of 316 ° C. and a thermal decomposition temperature of 316 ° C., was a film-formable and tough film. As a result of a biodegradability test, the degradation rate of the press sheet was 40% in the soil embedding method.

Example 7 Instead of ethylene glycol, 46 g of 1,4-butanediol and 14 of 2-methyl-1,3-propanediol were used.
An experiment was performed in the same manner as in Example 1 except that g was used, 70 mg of zinc acetate dihydrate was used as the catalyst instead of calcium acetate dihydrate, and 30 mg of antimony trioxide was used. The polymer obtained has Mn: 25,500, M
w: 41,800, Mw / Mn: 1.6, melting point 105
The thermal decomposition temperature was 322 ° C and the physical properties were 322 ° C. It also provided a tough, flexible film that was film-formable. As a result of a biodegradability test, the degradation rate of the press sheet by the soil embedding method was 32%.

Example 8 Using a glass four-necked flask having an inner volume of 200 ml, 45 g of adipic acid dimethyl ester having an adipic acid content of substantially 0%, 26 g of p-dihydroxymethylcyclohexane and 1,4-butanediol. 9 g and 50 mg of zinc acetate dihydrate as a catalyst were charged, and the reaction was started at 160 ° C. in a nitrogen atmosphere using 30 mg of antimony trioxide. After 2 hours, decompression was started while gradually increasing the reaction temperature, and after finally reaching a reaction temperature of 210 ° C. and a degree of vacuum of 0.5 Torr, the reaction was further continued for 4 hours. The polymer obtained had Mn of 19,500 and Mw of 33,20.
0, Mw / Mn: 1.7, the melting point was 80 ° C., the thermal decomposition temperature was 330 ° C., and film forming was possible.
As a result of a biodegradability test, the degradation rate of the press sheet was 17% by the soil embedding method.

Example 9 In a glass four-necked flask having an internal volume of 200 ml, 22.5 g of adipic acid dimethyl ester having an adipic acid content of substantially 0%, P-dihydroxymethylcyclohexane 19.5 g, and acetic acid as a catalyst were used. 50 mg of calcium
Was charged and the reaction was started at 160 ° C. in a nitrogen atmosphere. After 2 hours, decompression was started while gradually increasing the reaction temperature, and finally, the reaction temperature of 220 ° C. and the degree of vacuum of 1 Torr were reached, and then the reaction was further performed for 6 hours. The obtained polymer has Mn: 16,600, Mw: 76,750, Mw / M.
n: 4.6, the melting point was 97 ° C., the thermal decomposition temperature was 302 ° C., and the film could be formed. Moreover, as a result of a biodegradability test, the soil embedding method showed a decomposition rate of the press sheet of 5%, and it was biodegradable.

Example 10 In a glass four-necked flask having an internal volume of 200 ml, 43.84 g of dimethyl succinate having a succinic acid content of substantially 0% and 28.39 of 1,4-butanediol were used.
22 g (0.1 mmol) of zinc acetate dihydrate as a catalyst were charged, and the reaction was started at 160 ° C. under a nitrogen atmosphere. After 1 hour, the reaction temperature was gradually raised to 200 ° C., depressurization was started, and finally the reaction was performed at a reaction temperature of 210 ° C. and a vacuum degree of 0.5 Torr for 5 hours. The obtained polymer has a molecular weight of Mn: 34,700, Mw: 62,400,
The molecular weight distribution is Mw / Mn: 1.8, the melting point is 118 ° C.,
It exhibited thermal properties with a thermal decomposition temperature of 335 ° C. Since the molecular weight distribution is as narrow as 1.8, this polycondensation reaction proceeds promptly. The obtained polymer was film-moldable, and the film was tough. As a result of a biodegradability test, the degradation rate of the press sheet was 30% in the soil embedding method.

Example 11 Manganese acetate tetrahydrate 50 instead of zinc acetate dihydrate
In the same manner as in Example 10 except that mg (0.2 mmol) was used, the reaction temperature was 210 ° C. and the vacuum degree was 0.1.
The reaction was carried out at 4 torr for 6 hours. The polymer obtained had a molecular weight of Mn: 24,000, Mw: 45,600, a molecular weight distribution of Mw / Mn: 1.9, and showed thermal properties of a melting point of 117 ° C and a thermal decomposition temperature of 318 ° C. Molecular weight distribution is 1.9
Since it is narrow, this polycondensation reaction is proceeding promptly. The obtained polymer was film-moldable, and the film was tough.

Example 12 65 mg of lead acetate trihydrate instead of zinc acetate dihydrate
(Reaction temperature: 210 ° C., vacuum degree: 0.4)
The reaction was carried out with tall for 5 hours. The obtained polymer had a molecular weight of Mn: 31,000, Mw: 56,000, a molecular weight distribution of Mw / Mn: 1.8, and showed thermal properties of a melting point of 118 ° C and a thermal decomposition temperature of 328 ° C. Since the molecular weight distribution is as narrow as 1.8, this polycondensation reaction proceeds promptly. The obtained polymer was film-moldable, and the film was tough.

Example 13 Example 10 except 52 mg (0.2 mmol) of magnesium acetate tetrahydrate was used instead of zinc acetate dihydrate.
In the same manner as above, the reaction was finally performed under reduced pressure at a reaction temperature of 210 ° C. and a vacuum degree of 0.3 torr for 6 hours. The obtained polymer has a molecular weight of Mn: 29,500, Mw: 59,000,
Molecular weight distribution Mw / Mn: 2.0, melting point 117 ° C.,
It exhibited thermal properties with a thermal decomposition temperature of 325 ° C. Since the molecular weight distribution is as narrow as 2.0, this polycondensation reaction proceeds promptly. The obtained polymer was film-moldable, and the film was tough.

Example 14 Titanium di-n-butoxide-bis-acetylacetonate 20 mg (0.05) instead of zinc acetate dihydrate
In the same manner as in Example 10 except that the reaction temperature is 220 ° C. and the degree of vacuum is 0.3 Torr.
Allowed to react for hours. The obtained polymer has a molecular weight of Mn: 3.
1,500, Mw: 60,100, molecular weight distribution Mw / M
n: 1.8, melting point 117 ° C., thermal decomposition temperature 314 ° C.
The thermal properties of Since the molecular weight distribution is as narrow as 1.8, this polycondensation reaction proceeds promptly. The obtained polymer was film-moldable, and the film was tough.

Example 15 In the same manner as in Example 10 except that 13 mg (0.05 mmol) of titanium oxyacetylacetonate was used instead of zinc acetate dihydrate, the reaction temperature was finally set to 220.
The reaction was carried out at 0 ° C. and a vacuum degree of 0.3 torr for 5 hours. The obtained polymer has a molecular weight of Mn: 34,500, Mw: 62,
100, molecular weight distribution Mw / Mn: 1.8, melting point 1
It exhibited thermal properties of 17.5 ° C and a thermal decomposition temperature of 334 ° C.
Since the molecular weight distribution is as narrow as 1.8, this polycondensation reaction proceeds promptly. The obtained polymer was film-moldable, and the film was tough.

Example 16 In a glass four-neck flask having an inner volume of 200 ml, 43.84 g of dimethyl succinate having a succinic acid content of substantially 0%, 20.48 g of ethylene glycol,
50 mg of zinc acetylacetonate hydrate as a catalyst
(0.18 mmol) was charged and the temperature was 160 ° C. in a nitrogen atmosphere.
Then the reaction started. After 1 hour, gradually increase the reaction temperature to 200 ° C.
Then, depressurization is started until the reaction temperature reaches 2
The reaction was carried out at 20 ° C. and a vacuum degree of 0.4 torr for 5 hours. The obtained polymer has a molecular weight of Mn: 32,400, Mw: 6
The molecular weight distribution was 1,600, the molecular weight distribution was Mw / Mn: 1.9, and the melting point was 102 ° C and the thermal decomposition temperature was 325 ° C.
Since the molecular weight distribution is as narrow as 1.9, this polycondensation reaction proceeds promptly. The obtained polymer was film-moldable, and the film was tough.

Example 17 In a glass four-necked flask having an inner volume of 200 ml, 43.84 g of dimethyl succinate having a succinic acid content of substantially 0%, and cyclohexanedimethanol 43.84.
67 g, 33 mg of zinc acetate anhydrous as a catalyst (0.18
(Mmol) and charged at 160 ° C. under a nitrogen atmosphere to start the reaction. After 1 hour, the reaction temperature was gradually raised to 200 ° C., depressurization was started, and finally the reaction was performed at a reaction temperature of 210 ° C. and a vacuum degree of 0.3 Torr for 6 hours. The obtained polymer had a molecular weight Mn of 28,000 and Mw of 54,60.
0, molecular weight distribution Mw / Mn: 1.9, melting point 119
C., thermal decomposition temperature of 322.degree. Since the molecular weight distribution is as narrow as 1.9, this polycondensation reaction proceeds promptly. The obtained polymer was film-moldable, and the film was tough.

Example 18 In a glass four-necked flask having an inner volume of 200 ml, 52.26 g of adipic acid dimethyl ester having an adipic acid content of substantially 0% and cyclohexanedimethanol 4 were added.
3.67 g, 36 mg of anhydrous zinc acetate as a catalyst (0.
(20 mmol) was charged and the reaction was started at 160 ° C. under a nitrogen atmosphere. After 1 hour, the reaction temperature was gradually raised to 200 ° C., depressurization was started, and finally the reaction temperature of 210
The reaction was carried out at 0 ° C. and a vacuum degree of 0.3 torr for 6 hours. The obtained polymer has a molecular weight of Mn: 26,500, Mw: 47,
700, molecular weight distribution Mw / Mn: 1.8, melting point 1
It exhibited thermal properties of 01 ° C and a thermal decomposition temperature of 314 ° C. Since the molecular weight distribution is as narrow as 1.8, this polycondensation reaction proceeds promptly. The obtained polymer was film-moldable, and the film was tough.

Example 19 In a glass four-necked flask having an inner volume of 200 ml, 30.69 g of dimethyl succinate having a succinic acid content of substantially 0% and an adipic acid content of substantially 0% were used.
Adipic acid dimethyl ester 15.68 g, 1,
28.39 g of 4-butanediol and 33 mg (0.18 mmol) of zinc acetate anhydride as a catalyst were charged, and the reaction was started at 160 ° C. under a nitrogen atmosphere. After 1 hour, the reaction temperature was gradually raised to 200 ° C., depressurization was started, and finally the reaction was performed at a reaction temperature of 210 ° C. and a vacuum degree of 0.3 Torr for 6 hours. The obtained polymer has a molecular weight Mn: 31,4.
00, Mw: 59,600, molecular weight distribution Mw / Mn:
1.9, the melting point was 84 ° C, and the thermal decomposition temperature was 322 ° C. Since the molecular weight distribution is as narrow as 1.9, this polycondensation reaction proceeds promptly. The obtained polymer was film-moldable, and the film was tough.

Example 20 In a glass four-necked flask having an internal volume of 200 ml, 39.45 g of dimethyl succinate having a succinic acid content of substantially 0% and an adipic acid content of substantially 0% were used.
Then, 5.22 g of dimethyl adipic acid ester, 20.48 g of ethylene glycol, and 33 mg (0.18 mmol) of zinc acetate anhydride as a catalyst were charged, and the reaction was started at 160 ° C. under a nitrogen atmosphere. After 1 hour, the reaction temperature was gradually raised to 200 ° C., depressurization was started, and finally the reaction was performed at a reaction temperature of 210 ° C. and a vacuum degree of 0.4 Torr for 6 hours. The obtained polymer has a molecular weight Mn: 28,000,
It had an Mw of 54,600 and a molecular weight distribution of Mw / Mn: 1.9, and showed thermal properties with a melting point of 105 ° C and a thermal decomposition temperature of 322 ° C. Since the molecular weight distribution is as narrow as 1.9, this polycondensation reaction proceeds promptly. The obtained polymer was film-moldable, and the film was tough.

Example 21 In a glass four-necked flask having an internal capacity of 200 ml, 35.07 g of dimethyl succinate having a succinic acid content of substantially 0% and a sebacic acid content of substantially 0% were used.
13.82 g of dimethyl sebacate ester, 1,
27.58 g of 4-butanediol and 28 mg (0.15 mmol) of zinc acetate anhydride as a catalyst were charged, and the reaction was started at 160 ° C. under a nitrogen atmosphere. After 1 hour, the reaction temperature was gradually increased to 200 ° C., depressurization was started, and finally the reaction was performed at a reaction temperature of 210 ° C. and a vacuum degree of 0.5 Torr for 6 hours. The obtained polymer has a molecular weight of Mn: 34.5.
00, Mw: 65,600, molecular weight distribution Mw / Mn:
The melting point was 1.9, indicating a thermal property with a melting point of 107 ° C and a thermal decomposition temperature of 319 ° C. Since the molecular weight distribution is as narrow as 1.9, this polycondensation reaction proceeds promptly. The obtained polymer was film-moldable, and the film was tough.

Example 22 43.84 g of dimethyl succinate having a succinic acid content of substantially 0% and 1,4-butanediol 22.06 were placed in a glass four-necked flask having an internal volume of 200 ml.
g, 1,6-hexanediol (7.21 g) and zinc acetate anhydrous 28 mg (0.15 mmol) as a catalyst were charged, and the reaction was started at 160 ° C. under a nitrogen atmosphere. After 1 hour, the reaction temperature was gradually increased to 200 ° C., depressurization was started, and finally the reaction was performed at a reaction temperature of 210 ° C. and a vacuum degree of 0.5 Torr for 6 hours. The polymer obtained has a molecular weight M
n: 41,500, Mw: 74,800, molecular weight distribution M
w / Mn: 1.9, melting point 107 ° C., thermal decomposition temperature 3
It exhibited a thermal property of 29 ° C. Since the molecular weight distribution is as narrow as 1.9, this polycondensation reaction proceeds promptly. The obtained polymer was film-moldable, and the film was tough.

Example 23 In a glass four-neck flask having an inner volume of 200 ml, 43.84 g of succinic acid dimethyl ester having a succinic acid content of substantially 0% and cyclohexanedimethanol 34.
59 g, 1,4-butanediol 5.95 g, and zinc acetate anhydrous 33 mg (0.18 mmol) as a catalyst were charged, and the reaction was started at 160 ° C. under a nitrogen atmosphere. After 1 hour, the reaction temperature was gradually raised to 200 ° C., depressurization was started, and finally the reaction was performed at a reaction temperature of 210 ° C. and a vacuum degree of 0.3 Torr for 6 hours. The polymer obtained has a molecular weight M
n: 31,000, Mw: 60,600, molecular weight distribution M
w / Mn: 1.9, melting point 107 ° C., thermal decomposition temperature 3
It exhibited a thermal property of 22 ° C. Since the molecular weight distribution is as narrow as 1.9, this polycondensation reaction proceeds promptly. The obtained polymer was film-moldable, and the film was tough.

Comparative Example 2 The same experiment as in Example 10 was carried out except that 43.84 g of succinic acid dimethyl ester containing 0.2 wt% of succinic acid as a free carboxylic acid in succinic acid dimethyl ester was used. . The polymer obtained has Mn: 1
Since the molecular weight was as low as 1,800 and Mw: 20,400, film formation was difficult.

Comparative Example 3 43.84 g of succinic acid dimethyl ester containing 1.0% by weight of succinic acid as a free carboxylic acid in succinic acid dimethyl ester, and lead acetate trihydrate 65 mg (0.18 mmol) as a catalyst. The experiment was conducted in the same manner as in Example 10 except that The polymer obtained is M
Since the molecular weight was as low as n: 10,100 and Mw: 19,100, film formation was difficult.

Comparative Example 4 An experiment was conducted in the same manner as in Example 10 except that 67.6 g of 1,4-butanediol was used. As a result, the obtained polymer had a low molecular weight of Mn: 12,800 and Mw: 24,400, and a film could not be obtained.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Ikuo Takahashi 2-8-11 Nishi-Shimbashi, Minato-ku, Tokyo 7th Toyo Kaiji Building 8th floor Research Institute for Global Environmental Industrial Technology CO2 fixation etc. Project room (72 ) Inventor Kenji Kawamoto 2-8-11 Nishi-Shimbashi, Minato-ku, Tokyo 8th floor, 7th Toyo Kaiji Building Research Institute for Global Environmental Industrial Technology CO2 fixation etc. project room (72) Inventor Takashi Masuda East Tsukuba, Ibaraki Prefecture 1-1-1 Industrial Technology Institute of Materials Engineering and Industrial Technology (72) Inventor Akio Matsuda 1-1-1 Higashi Tsukuba City, Ibaraki Prefectural Institute of Materials Engineering Industrial Technology Kenji Sato (56) Reference JP-A-6 -107935 (JP, A)

Claims (6)

(57) [Claims] 1. A method for producing an aliphatic polyester having a number average molecular weight of 20,000 or more by subjecting an aliphatic divalent carboxylic acid di-lower alkyl ester and an aliphatic dihydric alcohol to a polycondensation reaction in the presence of a catalyst, The content of the free carboxylic acid compound in the aliphatic divalent carboxylic acid di-lower alkyl ester is maintained at 0.1 wt% or less, and the molar ratio of the raw material charged is expressed by the formula 1.0 <A / B ≦ 2.1 (the formula Where A is the number of moles of the aliphatic dihydric alcohol and B is the number of moles of the aliphatic dihydric carboxylic acid di-lower alkyl ester), the production of a high molecular weight aliphatic polyester characterized in that Method. 2. An (i) succinic acid di-lower alkyl ester,
(ii) an adipic acid di-lower alkyl ester and (iii) an oxalic acid di-lower alkyl ester, and an aliphatic divalent carboxylic acid di-lower alkyl ester containing at least one selected from the main components; 2. The method according to claim 1, which comprises subjecting an aliphatic dihydric alcohol to a polycondensation reaction. 3. A succinic acid di-lower alkyl ester is obtained by subjecting an acrylic acid ester to a hydroesterification reaction using carbon monoxide and a lower alcohol, and is methylmalonic acid dialkyl s ester and / or γ- 3. The method according to claim 2, which comprises 1 to 10% by weight of a dialkyl ketopimelic acid ester. 4. An adipic acid dialkyl ester obtained by subjecting butadiene to a hydroesterification reaction with carbon monoxide and a lower alcohol, wherein α-methylglutaric acid di-lower alkyl ester and α-ethylsuccinic acid diester are used. The method according to claim 2, which comprises a lower alkyl ester and / or propylmalonic acid di-lower alkyl ester in an amount of 1 to 20% by weight. 5. The method according to claim 2, wherein the alkyl group of succinic acid di-lower alkyl ester, adipic acid di-lower alkyl ester or oxalic acid di-lower alkyl ester is a methyl group or an ethyl group. 6. A raw material charging molar ratio A / B of 1.01 to
The method according to any one of claims 1 to 5, which is in the range of 1.1.