jp07-118259(1995)-FORPURIFYINGLACTIDEANDFORPOLYMERIZINGTHESAME.doc

PATENT ABSTRACTS OF JAPAN(11)Publication number : 07-118259(43)Date of publication of application : 09.05.1995(51)Int.Cl. C07D319/12 C07B 63/00 (21)Application number : 05-291296(71)Applicant : SHIMADZU CORP(22)Date of filing : 26.10.1993(72)Inventor : OGUCHI MAKOTO(54) METHOD FOR PURIFYING LACTIDE AND METHOD FOR POLYMERIZING THE SAME(57)Abstract:PURPOSE: To obtain a refined lactide having a high purity, readily polymerizing, easily providing a polylactic acid having an extremely high molecular weight, by recrystallizing a lactide with a lower alcohol, then with benzene or an alkyl- substituted group-containing benzene. CONSTITUTION: An unpurified lactide is added to a lower alcohol (e.g. isopropyl alcohol), heated to 70C and completely dissolved. When the solution is cooled to 30C, a crystal is precipitated and filtered. The prepared crystal is washed with water or isopropyl alcohol. The prepared lactide is added to benzene or an alkyl-substituted benzene (e.g. toluene) and heated to 70C to completely dissolve the lactide. The solution is cooled to 30C, a crystal is precipitated and filtered. The prepared crystal is washed with a solvent and dried under reduced pressure to give the high-purity refined lactide providing a polylactic acid having an extremely high molecular weight.CLAIMS Claim(s) Claim 1A purification method of lactide recrystallizing lactide with lower alcohol and recrystallizing with benzene or alkyl substituent benzene subsequently. Claim 2A method of polymerizing lactide polymerizing lactide obtained by recrystallizing lactide with lower alcohol and subsequently recrystallizing with benzene or alkyl substituent benzene. DETAILED DESCRIPTION Detailed Description of the Invention 0001 Industrial ApplicationThis invention relates to the purification method and its polymerizing method of lactide. Especially lactide is useful as manufacturing raw materials of polylactic acid, etc. 0002 Description of the Prior ArtAs a purification method of lactide, the temperature dependence of solubility, such as isopropyl alcohol, is high, and the recrystallizing method using the solvent into which an impurity melts easily is known. For example, to JP,63-101378,A, alcohol of 1-6 carbon numbers and making it precipitate using a non solvent from the recrystallization from isopropyl alcohol or a solution preferably are indicated. However, if it polymerizes using the lactide refined by such a method, the molecular weight of the polylactic acid obtained is 1000 to about 5000, and it is difficult to obtain the with a molecular weights of 100,000 or more amount polylactic acid of polymers. 0003The purpose of this invention has high purity and there is very big polylactic acid of a molecular weight in providing the lactide obtained easily and its polymerizing method. 0004 Means for Solving the ProblemA purification method of lactide, wherein this invention recrystallizes lactide with lower alcohol and subsequently recrystallizes it with benzene or alkyl substituent benzene is provided. A method of polymerizing lactide, wherein this invention polymerizes lactide obtained by the aforementioned purification method is provided. 0005A purification method of this invention is applicable to lactide conventionally obtained by a publicly known method. Lactide is first recrystallized with lower alcohol. As such lower alcohol, methanol, ethanol, n-propyl alcohol, isopropyl alcohol (2-propanol), butanol, a pentanol, etc. are mentioned, and especially isopropyl alcohol is preferred. 0006After it carries out temperature up of the recrystallization by these lower alcohol to about 60-70 * using 1 to 4 times (weight ratio) as many solvents to rough lactide, for example and it dissolves all crystals, it cools to 30 * or less, and it obtains a crystal. Subsequently water, isopropyl alcohol, or these mixed solvents wash a crystal of obtained lactide. Washing is performed at 20-40 * using the above solvent in equivalent amount. 0007Furthermore, benzene or alkyl substituent benzene is recrystallized for a crystal of lactide as a recrystallization solvent. As such a solvent, although benzene, toluene, xylene, ethylbenzene, isopropylbenzene, etc. are mentioned, especially toluene is preferred. Recrystallization using a solvent of these aromatic system is performed like recrystallization by said lower alcohol. That is, after carrying out temperature up from a room temperature to about 60-70 * using a solvent more than one to 4 times (weight ratio) to rough lactide and dissolving all crystals, it cools to 30 * or less, and a crystal is obtained. Subsequently, a crystal of obtained lactide is washed by one sort of said aromatic system solvent, or two sorts or more. Washing is performed at 20-40 * using the above solvent in equivalent amount. 0008Thus, obtained lactide has dramatically low concentration of isopropyl alcohol, and is below a detection limit. 0009The lactide obtained by a purification method of this invention can polymerize as usual. For example, after making it react using a device which has churning and a feed function of a 2 axis extruding kneading machine with a vent, etc., performing churning, mixing, movement, and deaeration, polymer is taken out continuously. As a polymerization catalyst, an organozinc compound derived from an organic tin compound derived from halogenation tin or with a carbon number of 20 or less carboxylic acid or zinc dust, zinc halide, or with a carbon number of 20 or less carboxylic acid is used, and especially tin octylate is preferred in the end of tin. The amount of catalyst used polymerizes being about 0.1 to 1.0 % of the weight, and temperature of 130-230 * supplying continuously it is desirable and to a kneading machine at 160-200 * to lactide. 0010Thus, obtained polylactic acid has a molecular weight a molecular weight very as high as 100,000 or more. That is, there is remains isopropyl alcohol in lactide by the conventional purification method, and it is presumed that this has checked a polymerization reaction. On the other hand, it is thought that lactide obtained in this invention has little remains isopropyl alcohol, and is easy to polymerize. 0011 ExampleThis invention is explained still more concretely based on an example below. 0012Example 1 To 3 kg of unrefined lactide, 3 kg of isopropyl alcohol was added, it heated to 70 *, and lactide was dissolved thoroughly. Subsequently, this solution was cooled to 30 *, the crystal was deposited, and it filtered. It washed using about 10 more kg of water, and 3 kg of isopropyl alcohol. 0013Thus, the obtained lactide was refined further. That is, about 3.5 kg of toluene was added, it heated to 70 *, and lactide was dissolved thoroughly. Subsequently, this toluene solution was cooled to 30 *, the crystal was deposited, and it filtered. It washed with about 6 more kg of toluene. The crystal of the obtained lactide was dried under decompression (yield of about 1.9 kg). 0014Tin octylate was added to the obtained lactide 0.24%, and when it polymerized continuously with the kneading machine at 190 *, the polylactic acid of the weight average molecular weight 150,000 was obtained. 0015Example 2 To 1.9 kg of unrefined lactide, 2.8 kg of isopropyl alcohol was added, it heated to 70 *, and lactide was dissolved thoroughly. Subsequently, this solution was cooled to 30 *, the crystal was deposited, and it filtered. It washed using about 8.4 more kg of isopropyl alcohol. 0016Thus, the obtained lactide was refined further. That is, 2.8 kg of toluene was added, it heated to 70 *, and lactide was dissolved thoroughly. Subsequently, this toluene solution was cooled to 30 *, the crystal was deposited, and it filtered. It washed with about 5.6 more kg of toluene. The crystal of the obtained lactide was dried under decompression (yield of about 0.95 kg). 0017Tin octylate was added to the obtained lactide 0.24%, and when it polymerized continuously with the kneading machine at 190 *, the polylactic acid of the weight average molecular weight 150,000 was obtained. 0018Comparative example 1 To 1.0 kg of unrefined lactide, 1.0 kg of isopropyl alcohol was added, it heated to 70 *, and lactide was dissolved thoroughly. Subsequently, this solution was cooled to 30 *, the crystal was deposited, and it filtered. It washed using about 9.0 more kg of water, and 1.0 kg of isopropyl alcohol. The same operation was dried under decompression of the crystal of the lactide obtained by carrying out a total of 3 times twice further (yield of about 0.52 kg). Tin octylate was added to the obtained lactide 0.24%, and when it polymerized continuously with the kneading machine at 190 *, a polymerization hardly progressed. 0019 Effect of the InventionThe lactide obtained by the purification method of this invention has high purity, and since it is easy to follow a polymerization, the very big polylactic acid of a molecular weight is obtained easily. TECHNICAL FIELD Industrial ApplicationThis invention relates to the purification method and its polymerizing method of lactide. Especially lactide is useful as manufacturing raw materials of polylactic acid, etc.EFFECT OF THE INVENTION Effect of the InventionThe lactide obtained by the purification method of this invention has high purity, and since it is easy to follow a polymerization, the very big polylactic acid of a molecular weight is obtained easily.TECHNICAL PROBLEM Description of the Prior ArtAs a purification method of lactide, the temperature dependence of solubility, such as isopropyl alcohol, is high, and the recrystallizing method using the solvent into which an impurity melts easily is known. For example, to JP,63-101378,A, alcohol of 1-6 carbon numbers and making it precipitate using a non solvent from the recrystallization from isopropyl alcohol or a solution preferably are indicated. However, if it polymerizes using the lactide refined by such a method, the molecular weight of the polylactic acid obtained is 1000 to about 5000, and it is difficult to obtain the with a molecular weights of 100,000 or more amount polylactic acid of polymers. 0003The purpose of this invention has high purity and there is very big polylactic acid of a molecular weight in providing the lactide obtained easily and its polymerizing method.MEANS Means for Solving the ProblemA purification method of lactide, wherein this invention recrystallizes lactide with lower alcohol and subsequently recrystallizes it with benzene or alkyl substituent benzene is provided. A method of polymerizing lactide, wherein this invention polymerizes lactide obtained by the aforementioned purification method is provided. 0005A purification method of this invention is applicable to lactide conventionally obtained by a publicly known method. Lactide is first recrystallized with lower alcohol. As such lower alcohol, methanol, ethanol, n-propyl alcohol, isopropyl alcohol (2-propanol), butanol, a pentanol, etc. are mentioned, and especially isopropyl alcohol is preferred. 0006After it carries out temperature up of the recrystallization by these lower alcohol to about 60-70 * using 1 to 4 times (weight ratio) as many solvents to rough lactide, for example and it dissolves all crystals, it cools to 30 * or less, and it obtains a crystal. Subsequently water, isopropyl alcohol, or these mixed solvents wash a crystal of obtained lactide. Washing is performed at 20-40 * using the above solvent in equivalent amount. 0007Furthermore, benzene or alkyl substituent benzene is recrystallized for a crystal of lactide as a recrystallization solvent. As such a solvent, although benzene, toluene, xylene, ethylbenzene, isopropylbenzene, etc. are mentioned, especially toluene is preferred. Recrystallization using a solvent of these aromatic system is performed like recrystallization by said lower alcohol. That is, after carrying out temperature up from a room temperature to about 60-70 * using a solvent more than one to 4 times (weight ratio) to rough lactide and dissolving all crystals, it cools to 30 * or less, and a crystal is obtained. Subsequently, a crystal of obtained lactide is washed by one sort of said aromatic system solvent, or two sorts or more. Washing is performed at 20-40 * using the above solvent in equivalent amount. 0008Thus, obtained lactide has dramatically low concentration of isopropyl alcohol, and is below a detection limit. 0009The lactide obtained by a purification method of this invention can polymerize as usual. For example, after making it react using a device which has churning and a feed function of a 2 axis extruding kneading machine with a vent, etc., performing churning, mixing, movement, and deaeration, polymer is taken out continuously. As a polymerization catalyst, an organozinc compound derived from an organic tin compound derived from halogenation tin or with a carbon number of 20 or less carboxylic acid or zinc dust, zinc halide, or with a carbon number of 20 or less carboxylic acid is used, and especially tin octylate is preferred in the end of tin. The amount of catalyst used polymerizes being about 0.1 to 1.0 % of the weight, and temperature of 130-230 * supplying continuously it is desirable and to a kneading machine at 160-200 * to lactide. 0010Thus, obtained polylactic acid has a molecular weight a molecular weight very as high as 100,000 or more. That is, there is remains isopropyl alcohol in lactide by the conventional purification method, and it is presumed that this has checked a polymerization reaction. On the other hand, it is thought that lactide obtained in this invention has little remains isopropyl alcohol, and is easy to polymerize.EXAMPLE ExampleThis invention is explained still more concretely based on an example below. 0012Example 1 To 3 kg of unrefined lactide, 3 kg of isopropyl alcohol was added, it heated to 70 *, and lactide was dissolved thoroughly. Subsequently, this solution was cooled to 30 *, the crystal was deposited, and it filtered. It washed using about 10 more kg of water, and 3 kg of isopropyl alcohol. 0013Thus, the obtained lactide was refined further. That is, about 3.5 kg of toluene was added, it heated to 70 *, and lactide was dissolved thoroughly. Subsequently, this toluene solution was cooled to 30 *, the crystal was deposited, and it filtered. It washed with about 6 more kg of toluene. The crystal of the obtained lactide was dried under decompression (yield of about 1.9 kg). 0014Tin octylate was added to the obtained lactide 0.24%, and when it polymerized continuously with the kneading machine at 190