KR100255038B1 - Preparation of Poly(lactic acid-co-caprolactone) - Google Patents

Abstract

PURPOSE: Provided is a production process of polylactate-polycaprolactone copolymer which is processed through polycondensation reaction of lactate and ring opening reaction of ε-caprolactone so that it produces the wanted product easily. CONSTITUTION: The production process of polylactate-polycaprolactone copolymer comprises the steps of: (i) pre-polycondensing lactate solution to prepare lactate oligomer; (ii) purifying lactate oligomer to be less than 0.5wt.% in unreacted lactate content wherein oligomer is dissolved in chloroform or methylene chloride, precipitated in methanol to be crystallized or oligomer powder is washed in isopropylene ether to eliminate unreacted lactate; and (iii) mixing the purified lactate oligomer and ε -caprolactone to polycondensate and polymerize with ring opened.

Description

Preparation method of polylactic acid-polycaprolactone copolymer {Preparation of Poly (lactic acid-co-caprolactone)}

The present invention relates to a method for producing a polylactic acid-polycaprolactone copolymer, and more particularly, to make a lactic acid oligomer from an aqueous lactic acid solution, purify the lactic acid oligomer, and then polymerize with ε-caprolactone to conduct a medical material or general purpose. A method for producing a polylactic acid-polycaprolactone copolymer, which is a biodegradable polymer useful as a substitute for a resin.

Polylactic acid and polycaprolactone, which are a kind of polyhydroxy acid, are generally produced by ring-opening polymerization of lactide and ε-caprolactone, which are cyclic dimers of lactic acid.

In the conventional production method of polylactic acid, the oligomerized D, L-lactic acid is once oligomerized and thermally decomposed under the reduced pressure at 200-500 ° C. to form lactic acid, a cyclic dimer of lactic acid, and recrystallized several times with ethyl acetate to give a melting point of 120 ° C. The method of ring-opening polymerization of the above racemic lactide to produce poly D, L-lactic acid having an inherent viscosity of 0.45 dl / g or more, thereby making a strong film and a fiber (US Pat. No. 2,703,316). However, such polylactic acid has superior physical properties than polyester-based biodegradable polymers of similar series, but has disadvantages of poor heat resistance, moisture resistance, and fragility in processing.

Meanwhile, polycaprolactones include Union Carbide (UCC) products (TONE ™) and Daicel Chemical Industries (Puracel H ™) products in Japan, which are mainly used as medical supplies, adhesives, and release agents.

As a method of preparing polylactide and polycaprolactone copolymers, a method of ring-opening polymerization by mixing L-lactide and ε-caprolactone in a weight ratio of about 3: 1 is known [US Pat. No. 4,057,537], but the annularity In order to use the dimer, lactide, as a polymer raw material, there is a problem that requires a lot of effort and cost in the manufacturing method such as distillation, recrystallization.

In the present invention, by synthesizing the polymer by direct de-shrinkment polymerization and ring-opening polymerization, not only can much effort and cost be reduced, such as distillation and recrystallization according to the conventional manufacturing method, but also ε-caprolactone is copolymerized with the purified lactic acid oligomer. The purpose of the present invention is to provide a method for producing a polylactic acid-polycaprolactone copolymer which can reduce the effect on degradability to a minimum and have a longer aliphatic chain in the lactic acid main chain and thus increase the flexibility.

The present invention provides a method for producing a polylactic acid-polycaprolactone copolymer, comprising the steps of precondensing lactic acid to prepare lactic acid oligomers, removing and purifying unreacted lactic acid in the oligomer, the purified lactic acid oligomer and ε It is characterized by consisting of a process of condensation polymerization and ring-opening polymerization by mixing caprolactone.

Referring to the present invention in more detail as follows.

The present invention condenses lactic acid to form lactic acid oligomers, and then, in order to sufficiently remove unreacted lactic acid from the oligomers, the lactic acid oligomers are dissolved in chloroform or methylene chloride and precipitated in methanol or purified directly with isopropyl ether. A polylactic acid-polycaprolactone copolymer is prepared by condensation polymerization and ring-opening polymerization by mixing lactic acid oligomer with ε-caprolactone.

In the method of preparing a copolymer according to the present invention, the one-step process is a synthesis process of lactic acid oligomer.

The aqueous solution of 90% L-lactic acid is added to the reactor together with the catalyst and dehydrated and condensation polymerization is carried out for several hours under a reduced pressure of not less than 90 ° C and not more than 50 mmHg while stirring.

Lactic acid used in the present invention exists as isomers and is L-lactic acid, D-lactic acid or mixtures thereof. The catalysts include zinc oxide, antimony oxide, antimony chloride, lead oxide, calcium oxide, aluminum oxide, iron oxide, calcium chloride, zinc acetate, p-toluenesulfonic acid, stannous chloride, stannous sulfate, stannous oxide, and oxidant2. Tin, stannous octanoate, tetraphenyltin, tin powder, titanium tetrachloride, and the like, and these catalysts are used in an amount of 0.0005 to 5% by weight, preferably 0.003 to 1% by weight, based on the amount of lactic acid used. If the amount of the catalyst used is less than 0.0005% by weight, the molecular weight of the oligomer is less than 3,000 or the oligomer generation time is very long, and if it exceeds 5% by weight, the depolymerization reaction is severe and there is a problem that an oligomer having a molecular weight of 3,000 or more cannot be obtained. When the esterification condensation polymerization of lactic acid is carried out under such reaction conditions, the molecular weight of the oligomer increases in proportion to the reaction time.

In the present invention, the molecular weight of the lactic acid oligomer is to be 3,000 or more, if the oligomer molecular weight is less than 3,000, a copolymer having a molecular weight of 50,000 or more cannot be produced.

The next two step process is the purification to remove unreacted lactic acid from the lactic acid oligomer. Since the polycondensation water generated in the polymerization process acts to lower the molecular weight of the polymer by hydrolysis, the water produced must be removed out of the system, and the content of unreacted lactic acid contained in the lactic acid oligomer synthesized above The more, the slower the polymerization reaction rate and promotes the depolymerization and pyrolysis, so it is necessary to control their content to 0.5% by weight or less. If the lactic acid oligomer is not sufficiently purified, the average molecular weight of the polylactic acid-polycaprolactone copolymer obtained is reduced to 40,000 or less. Therefore, in order to solve the above problems, a purification process must be performed. The present invention utilizes a method in which the lactic acid oligomer is dissolved in chloroform or methylene chloride and then precipitated in methanol or directly purified with isopropyl ether.

In the three-step process, the purified lactic acid oligomer from which the unreacted lactic acid is sufficiently removed in the two-step process is mixed with ε-caprolactone, polycondensation and ring-opening polymerization together with a catalyst and a heat stabilizer, thereby performing polylactic acid-polycaprolactone air. It is the process of obtaining coalescence. This copolymerization reaction is carried out at the same time the dehydration condensation reaction between the lactic acid oligomer and the ring-opening reaction of ε-caprolactone, the reaction temperature is adjusted to 130 ~ 190 ℃, preferably 160 ~ 180 ℃. If the reaction temperature is less than 130 ℃ during condensation polymerization and ring-opening polymerization, there is a problem that the molecular weight of the copolymer is less than 50,000 or the polymerization time is too long, if it exceeds 190 ℃ is accompanied by the thermal decomposition of the copolymer to a high molecular weight copolymer It is not preferable because there is a problem such as not being able to make.

Ε-caprolactone used in the condensation polymerization and ring-opening polymerization is contained 5 to 30% by weight based on the total amount of the purified lactic acid oligomer and ε-caprolactone, if the content is less than 5% or more than 30% by weight Even if the average molecular weight of the polylactic acid-polycaprolactone copolymer is 50,000 or more, it does not have sufficient mechanical properties.

In addition, the catalyst used for the condensation polymerization and the ring-opening polymerization of the present invention is selected from the catalysts that can be used in the production of the oligomer, which is 0.0005 to 5% by weight, preferably with respect to the total amount of the purified lactic acid oligomer and ε-caprolactone Is used by 0.003 to 1% by weight.

In addition, a thermal stabilizer is used to prevent thermal decomposition, which uses 0.0001 to 5% by weight, preferably 0.001 to 2% by weight, based on the total amount of the purified lactic acid oligomer and ε-caprolactone.

As a result, the average molecular weight of the polylactic acid-polycaprolactone obtained by the method of the present invention is about 50,000 to 200,000, and the molecular weight is the molecular weight of the lactic acid oligomer, the content of the unreacted lactic acid in the lactic acid oligomer, the type and amount of the catalyst used, the reaction temperature. It depends on the reaction time, and thus, by controlling this, there is an advantage of easily obtaining a molecular weight suitable for a use.

In particular, if the average molecular weight of the polymer for film forming is less than 50,000, the tensile strength and elongation are insufficient, so that it is difficult to use as a film. Generally, the average molecular weight of the copolymer is required to be 50,000 or more, more preferably 100,000 or more. As a result, the polylactic acid-polycaprolactone copolymer prepared by the production method of the present invention can be easily used for film molding. In addition, the high molecular weight polylactic acid-polycaprolactone copolymer can be subjected to secondary processing such as stretching, blowing, and vacuum molding. Therefore, the high molecular weight polylactic acid-polycaprolactone copolymer obtained by the method of the present invention can be used as a substitute for conventional general purpose resins such as medical materials, foams, and reticular bodies.

Although this invention is demonstrated in detail based on an Example, this invention is not limited by an Example.

Example 1

33.0 g of an aqueous 90% L-lactic acid solution and 0.06 g of antimony trioxide were put together in a reactor, followed by dehydration and condensation polymerization for 3 hours under a reduced pressure of 150 ° C and 40 mmHg. The reaction was then sufficiently dissolved in 200 mL of methylene chloride and poured into 200 mL of methanol to obtain crystals. The crystals were filtered, washed three times or more with methanol, and sufficiently dried to obtain a white lactic acid oligomer. The molecular weight of the lactic acid oligomer was 12,500 and the content of unreacted lactic acid contained was 0.05% by weight.

27 g of lactic acid oligomer and 3 g of ε-caprolactone were mixed in a reactor, and 0.06 g of antimony trioxide as a catalyst and 0.0091 g of Irganox 1010 (IRGANOX 1010, manufactured by Ciba-Gaikai Co., Ltd.) as a thermal stabilizer were added thereto and stirred at 170 ° C. The polymerization was carried out while heating under reduced pressure of 2 mmHg for 7 hours. After completion of the polymerization reaction, the polylactic acid-polycaprolactone copolymer was taken out from the reactor, pulverized and placed in a vacuum oven at 50 ° C., and dried for 24 hours at a reduced pressure of 0.3 mmHg. The molecular weight of the dried copolymer was 200,000. The polylactic acid-polycaprolactone copolymer was dissolved in a chloroform solution, and the solution was cast into a film having a thickness of 40 μm, and the mechanical properties thereof were measured. The tensile strength was 550 kg / cm 2 and the elongation was 22%.

Example 2

33.0 g of an aqueous 90% L-lactic acid solution and 0.06 g of antimony trioxide were put together in a reactor, followed by dehydration and condensation polymerization for 2 hours under reduced pressure at 150 ° C and 40 mmHg. The reaction is then sufficiently dissolved in 200 ml of methylene chloride and poured into 200 ml of methanol to obtain crystals. The crystals were filtered, washed three times or more with methanol, and sufficiently dried to obtain a white lactic acid oligomer. The molecular weight of the lactic acid oligomer was 3,000 and the content of unreacted lactic acid contained was 0.4% by weight.

Then, as a result of preparing the polylactic acid-polycaprolactone copolymer in the same manner as in Example 1, the molecular weight of the polylactic acid-polycaprolactone copolymer was 54,000, the tensile strength and elongation as a result of the film production using this Excellent at 390 kg / cm 2 and 15%, respectively.

Example 3

33.0 g of an aqueous 90% L-lactic acid solution and 0.06 g of antimony trioxide were put together in a reactor, followed by dehydration and polycondensation at 150 ° C. and 50 mmHg for 2 hours while stirring. The reaction was then ground to form lactic acid oligomers in powder form, and then washed three more times with isopropyl ether. The powder was fully dried to obtain a white lactic acid oligomer. The molecular weight of the lactic acid oligomer was 3,800 and the content of unreacted lactic acid was 0.5% by weight. Then, a polylactic acid-polycaprolactone copolymer was prepared in the same manner as in Example 1, and the molecular weight was 51,000. As a result, a film was manufactured using the same, the tensile strength and the elongation were 350 kg / cm 2 and 17%, respectively. Excellent.

Example 4

28.5 g of lactic acid oligomer (molecular weight 12,500, unreacted lactic acid content 0.05% by weight) and 1.5 g of ε-caprolactone obtained in the same manner as in Example 1 were mixed into a reactor, and the same amount of catalyst and thermal stabilizer as in Example 1 Next, the molecular weight of the polylactic acid-polycaprolactone copolymer prepared by the polymerization, purification and drying in the same manner as in Example 1 was 155,000, and the tensile strength and elongation of the film were 490 kg, respectively. / Cm 2, which was excellent at 11%.

Example 5

21 g of lactic acid oligomer (molecular weight 12,500, unreacted lactic acid content 0.05% by weight) obtained by the same method as in Example 1 was mixed with 9 g of ε-caprolactone, except that the mixing ratio was different, and the polylactic acid-polycapro was prepared in the same manner as in Example 4. Lactone copolymers were prepared. As a result, the molecular weight was 119,000, and the tensile strength and elongation of the film were 270 kg / cm 2 and 17%, respectively.

Comparative Example 1

Polylactic acid-poly was prepared in the same manner as in Example 1 by adding 27 g of lactic acid oligomer (molecular weight 12,500, unreacted lactic acid content 0.05% by weight) and 0.5% by weight of lactic acid and 3 g of ε-caprolactone obtained in the same manner as in Example 1. Caprolactone copolymers were prepared.

As a result, the molecular weight was 24,000, the tensile strength and elongation were 110 kg / ㎠, 3%, respectively, as a result of the film production using this, the mechanical properties were not good.

Comparative Example 2

33.0 g of an aqueous 90% L-lactic acid solution and 0.06 g of antimony trioxide were put together in a reactor, followed by dehydration and polycondensation reaction under a reduced pressure of 100 ° C. and 40 mmHg for 1 hour and 30 minutes. The reaction is then sufficiently dissolved in 200 ml of methylene chloride and then poured into 200 ml of methanol to obtain crystals. The crystals were filtered off, washed three times or more with methanol, and sufficiently dried to obtain a white lactic acid oligomer. The molecular weight of the resulting lactic acid oligomer was 2,700 and the content of unreacted lactic acid contained was 0.4% by weight.

Then, a polylactic acid-polycaprolactone copolymer was prepared in the same manner as in Example 1. As a result, the molecular weight was 46,000, and the tensile strength and elongation of the film were 130 kg / cm 2 and 5%, respectively, resulting in poor mechanical properties.

Comparative Example 3

28.8 g of lactic acid oligomer (molecular weight 12,500, unreacted lactic acid content 0.05% by weight) and 1.2 g of ε-caprolactone obtained in the same manner as in Example 1 were mixed into a reactor, and a catalyst and a thermal stabilizer were added in the same amount as in Example 1. Next, the molecular weight of the polylactic acid-polycaprolactone copolymer prepared by the polymerization, purification and drying in the same manner as in Example 1 was 163,000, and the tensile strength and elongation of the film were 470 kg, respectively. / ㎠, 1% too hard and not flexible, the mechanical properties were not good.

Comparative Example 4

20.7 g of lactic acid oligomer (molecular weight 12,500, unreacted lactic acid content 0.05% by weight) obtained in the same manner as in Example 1 was mixed with 9.3 g of ε-caprolactone, and the same amount of catalyst and thermal stabilizer as in Example 1 was added. Next, the molecular weight of the polylactic acid-polycaprolactone copolymer prepared by the polymerization, purification and drying in the same manner as in Example 1 was 78,000, and the tensile strength and elongation of the film were 126 kg. / Cm 2, 13% was not good mechanical properties.

As described above, the present invention relates to a method for preparing a polylactic acid-polycaprolactone copolymer, which is a biodegradable polymer by direct dehydration polycondensation of lactic acid and ring-opening reaction of ε-caprolactone, and according to the present invention. Compared to the conventional manufacturing method, the solution not only reduces distillation and recrystallization, but also reduces costs, and solves problems of conventional polymers such as pyrolysis at once, and also has flexible physical properties with better tensile strength and elongation at the time of film production. It works.

Claims (4)

In the method for producing a polylactic acid-polycaprolactone copolymer, Preparing a lactic acid oligomer by precondensing lactic acid aqueous solution, The amount of unreacted lactic acid in the lactic acid oligomer is purified to be 0.5% by weight or less, and the oligomer is dissolved in chloroform or methylene chloride and precipitated in methanol to obtain crystals or the oligomer powder is washed with isopropyl ether to give unreacted lactic acid. The process of removing and refining, Method for producing a polylactic acid-polycaprolactone copolymer, characterized in that the condensation polymerization and ring-opening polymerization by mixing the purified lactic acid oligomer and ε-caprolactone. The method of claim 1, wherein the lactic acid oligomer has an average molecular weight of 3,000 or more. The method of claim 1, wherein the ε-caprolactone is used in the range of 5 to 30% by weight based on the total amount of the purified lactic acid oligomer and ε-caprolactone. . The method of claim 1, wherein the polylactic acid-polycaprolactone copolymer has an average molecular weight of 50,000 to 200,000.