JPH0753684A - Continuous polymerization of aliphatic polyester - Google Patents

Abstract

PURPOSE:To efficiently obtain the subject high-molecular weight polymer useful as a biodegradable material, etc., by feeding an alpha-oxyacid cyclic dimer to an initial polymerization process together with a catalyst to carry out polymerization, and then, continuously carrying out post-polymerization using a multiaxial kneader. CONSTITUTION:An alpha-oxyacid cyclic dimer (e.g. cyclic dimer of lactic acid) which is a raw material is continuously fed to an initial polymerization process together with a catalyst (tin octylate) and polymerization is carried out, preferably at a temperature not lower than melting point of the cyclic dimer and not higher than 220 deg.C. Then, an oligomer obtained by the initial polymerization process is continuously fed to a multiaxial kneader and post-polymerization process is carried out to provide the objective polymer having units of the formula (R<1> and R<2> are H or 1-5C alkyls). Furthermore, the initial polymerization process is preferably carried out under conditions where melt viscosity of produced oligomer is <=1000 poise at the polymerization temperature and reduced viscosity is 0.1-1. As the multiaxial kneader, a twin shaft kneader capable of carrying out mixing, advancing and retreating by control of a paddle is preferably used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for continuously polymerizing an aliphatic polyester starting from an .alpha.-oxy acid cyclic dimer, and more specifically to efficiently obtain the aliphatic polyester as a high molecular weight product. Regarding the method.

[0002]

2. Description of the Related Art Conventionally, aliphatic polyesters represented by polylactic acid and polyglycolic acid have been used for biodegradable medical materials such as surgical sutures and microcapsules for injection. Further, in recent years, plastic waste has become a problem, and attention has been paid to it as a biodegradable plastic that is expected to be decomposed by enzymes and microorganisms, and research and development is proceeding. By the way, generally, as a method for obtaining a high molecular weight product of the aliphatic polyester, a method of heating a cyclic dimer of an α-oxy acid in the presence of a catalyst to perform ring-opening polymerization is known.

[0003]

However, since the above-mentioned method is a ring-opening polymerization, it is difficult to control the degree of polymerization, a rapid increase in viscosity occurs, and it is difficult to mix and stir the polymer or take out the polymer. Further, there are problems that it takes a long time to take out the polymer after the polymerization, and the recovery rate of the polymer is low, which is not a satisfactory method.

[0004]

Therefore, in view of the above situation, the present inventors have conducted extensive studies to obtain an aliphatic polyester more efficiently than an α-oxyacid cyclic dimer, and as a result, α
-It was found that the polymerization of the oxyacid cyclic dimer can be divided into an initial polymerization which requires a relatively long time and a latter polymerization which causes a rapid viscosity increase. By efficiently supplying the compounds with the catalyst to the initial polymerization step, performing the initial polymerization over a relatively long time, and then continuously supplying the latter polymerization step consisting of a multi-screw kneader. The present inventors have found that the aliphatic polyesters capable of being continuously polymerized can reach the present invention. That is, the present invention is a general formula -OR ¹ CR ² -CO-
(Wherein R ¹ and R ² represent H or an alkyl group having 1 to 5 carbon atoms) as a main repeating unit in the method for producing an α-oxy acid cyclic dimer, The dimer is continuously supplied to the initial polymerization step together with the catalyst, and the melt viscosity after completion of the initial polymerization is 1
000 poise or less and a reduced viscosity of 0.1-1.
It is a continuous polymerization method of an aliphatic polyester characterized in that it is adjusted so as to be in the range of 0 and polymerized, and then continuously fed to a latter-stage polymerization step comprising a multi-axial kneader.

In the present invention, the α-oxy acid cyclic dimer as a starting material is a cyclic dimer such as glycolic acid, lactic acid, 2-hydroxyisobutyric acid, 2-hydroxyhexanoic acid, 2-hydroxy-2-methylbutyric acid. However, the present invention is not limited to these. They can be used alone or in a mixture. The substance having an asymmetric carbon may be any of D-form, L-form and racemic form, and the state may be solid, liquid or solution.

In the present invention, the kind and amount of the catalyst are not particularly limited, but those usable as the ring-opening polymerization catalyst are
Metal compounds such as Sn, Ti, Sb and Zn. These are oxides, chlorides, carboxylates and the like, and are used alone or in a suitable amount in the form of a mixture. As a method of addition, it may be added to the cyclic dimer before the introduction of the initial polymerization step, or may be added directly in the initial polymerization step. The form of the catalyst used is not particularly limited, but a method in which the catalyst is dissolved in a low boiling point solvent such as hydrocarbon, ether, alcohol and the like and added is preferable. Further, primary alcohols, oxyalkylene glycols, epoxides, dialkyl carbonates, carbodiimides, metal compounds capable of reacting with carboxylic acid groups, etc., alone or as a mixture, as polymerization degree regulators for reaction with chain or chain extension It may be used in the form of. Specifically, n-butyl alcohol, isobutyl alcohol, 1-pentanol, 3-methyl-1-butanol, 1-hexanol, 1-heptanol, 1-
Octanol, ethylene glycol, propylene glycol, butylene glycol, polyethylene glycol,
Polypropylene glycol, dimethyl carbonate, diethyl carbonate, phenyl glycidyl ether, calcium oxide, aluminum hydroxide and the like can be used.

In the initial polymerization step, the reaction may be carried out under an atmosphere of inert gas such as nitrogen, carbon dioxide gas, argon gas or the like under normal pressure or under reduced pressure. The polymerization temperature in the initial polymerization step is preferably at least the melting point of the cyclic dimer and 220 ° C. or less. The α-oxy acid cyclic dimer is continuously supplied to this polymerization vessel. The mode of stirring and mixing is not particularly limited, but mechanical stirring with a stirring blade, static stirring with a threshold inside, or the like can be used. The initial polymerization time is not particularly limited, but if it is too short, the degree of polymerization in the latter polymerization step does not increase, and if it is too long, the degree of polymerization increases in the initial polymerization step and it becomes difficult to take it out. Therefore, the polymerization time, temperature, holding time, etc. are adjusted so that the melt viscosity at the polymerization temperature is 1000 poise or less and the reduced viscosity is in the range of 0.1 to 1.0.

In the latter polymerization step, the oligomer quantitatively fed from the initial polymerization step is fed to a multi-screw kneader having at least one mixing shaft. The polymerization temperature is preferably higher than the melting point of the polymer and lower than 260 ° C., and the reaction may be carried out in an atmosphere of an inert gas such as nitrogen, carbon dioxide gas, argon gas or the like under normal pressure, or under reduced pressure. Since the initial polymerization requires a relatively long time, it is preferable to perform polymerization so that it is at least twice as long as the average residence time in the latter polymerization step, and then continuously feed to the latter polymerization step comprising a multi-screw kneader. . The timing of the initial polymerization step and the late polymerization step is important, and if the initial polymerization step is too long, the degree of polymerization will be too high, and it will be difficult to stir or take out the polymer. On the contrary, if it is too short, the degree of polymerization does not increase. As the multi-axis kneading machine, a kneading machine having two mixing axes and capable of mixing, propelling and retracting by adjusting the paddle is preferable. The melt viscosity of the polymer after the polymerization in the latter polymerization step is several thousand poise or more and several hundred thousand poise, preferably tens of thousands poise.

[0009]

By adopting the method of the present invention having the above-mentioned constitution, it has been difficult to control the degree of polymerization in the conventional method, and it has been difficult to mix and stir the polymer and take out the polymer due to the rapid increase in viscosity. Polymerization of an aliphatic polyester from an oxyacid cyclic dimer can be efficiently polymerized. The reason for this is that it is divided into an initial polymerization reaction that requires a relatively long time with a low viscosity and a late polymerization step, and the latter polymerization that causes a rapid increase in viscosity in a relatively short time is carried out by a multi-screw kneader so that It is considered that the problems such as mixing and stirring and taking out due to the increase in viscosity are eliminated and the desired aliphatic polyester can be continuously polymerized efficiently.

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. The reduced viscosity in the examples is 0.12 for the polymer.
5 g was dissolved in chloroform and measured at 25 ° C.

[0011]

【Example】

Example 1 120% (g / min) of a cyclic dimer synthesized from lactic acid in an autoclave at 200 ° C. kept under a nitrogen atmosphere, and 0.036 (g / min) of tin octylate as a catalyst in a 3% solution of toluene. Was continuously supplied. While stirring, the cyclic dimer and the catalyst were continuously supplied at the same temperature under nitrogen flow, and the product was withdrawn from the bottom at 120 (g / min) at an average polymerization time of 20 minutes and supplied to a biaxial kneader. did. After the initial polymerization, the melt viscosity was 250 poise and the reduced viscosity was 0.78. The average residence time of the kneader was about 20 minutes. The reduced viscosity of the produced polymer was 4.85, and the recovery rate was almost quantitative.

Comparative Example 1 480 cyclic dimers were added to the autoclave used in Example 1.
0 g and 1.44 g of tin octylate as a catalyst were added, and stirring was continued at 200 ° C. under a nitrogen atmosphere. After 30 minutes, it became difficult to stir and stopped due to high torque. When the polymer was taken out under nitrogen pressure, the reduced viscosity of the produced polymer was 1.83, and the recovery rate was about 60%.

[0013]

Example 2-4, Comparative Example 2 Polymerization was carried out by changing the polymerization conditions in Example 1. The results are shown in Table 1.

[0014]

[Table 1]

[00015]

By adopting the method of the present invention having the above constitution, it becomes possible to efficiently obtain a high molecular weight aliphatic polyester. The aliphatic polyester thus obtained can be molded into fibers, films, and other molded products from the molten state, and is considered to be particularly useful as a biodegradable material.
Specific applications include fishing lines, fishing nets and non-woven fabrics for fibers, packaging films for films, agricultural mulch films, shopping bags, various tapes, fertilizer bags, separation membranes, etc., and molded products for beverages and cosmetics bottles. Applications include disposable cups, containers such as trays, flowerpots and nursery beds for agriculture, pipes that do not need to be dug out, and temporary fixing materials. Further, as a medical use, sutures, artificial bones, artificial skin, and DDS fields such as microcapsules are considered, and a wide range of applications can be expected, which greatly contributes to industry and environmental protection.

Front page continuation (72) Inventor Keiichi Uno 1-1-1, Katata, Otsu, Shiga Toyobo Co., Ltd. (72) Inventor Kunio Kimura 2-1-1 Katata, Otsu, Shiga Prefecture Toyobo Co., Ltd. Company Research Institute

Claims (2)

[Claims] 1. A general formula —OR ¹ CR ² —CO— (where R is
¹ and R ^{2 each} represent H or an alkyl group having 1 to 5 carbon atoms) as a main repeating unit from the α-oxy acid cyclic dimer.
A continuous polymerization method for an aliphatic polyester, characterized in that the oxyacid cyclic dimer is continuously supplied to the initial polymerization step together with the catalyst, and then continuously supplied to the latter polymerization step comprising a multi-screw kneader. 2. The melt viscosity of the polymer produced after the completion of the initial polymerization is 1000 poise or less at the polymerization temperature and the reduced viscosity is 0.1 in the claim 1.
A method for continuous polymerization of an aliphatic polyester, which comprises adjusting the α-oxy acid cyclic dimer to a value within the range of −1.0.