CN-117580890-B - Method for preparing polylactic acid polymer

Abstract

The present disclosure relates to a method for preparing a polylactic acid polymer, and more particularly, to a method for preparing a polylactic acid polymer having a desired high molecular weight by using a specific catalyst in a lactide ring-opening polymerization reaction.

Inventors

• Yu Yuanxi
• Wu Wankui
• AN WEIJIN

Assignees

• 株式会社LG化学

Dates

Publication Date

20260508

Application Date

20220704

Priority Date

20210705

Claims (8)

1. 1. A method of preparing a polylactic acid polymer, the method comprising: Ring-opening polymerization of lactide is performed in the presence of SnHPO 3 catalyst to prepare polylactic acid polymer, Wherein the weight average molecular weight change rate defined by the following equation 1 has a positive value: [ mathematics 1] Weight average molecular weight change rate= (M (t+30) –M (t) )/M (t) ×100 (%) M (t) is the weight average molecular weight of the polylactic acid polymer prepared according to the ring-opening polymerization at t DEG C, M (t+30) is the weight average molecular weight of the polylactic acid polymer prepared according to the ring-opening polymerization at a temperature of t+30℃, and T is 150 ℃ to 250 ℃.
2. 2. The method for producing a polylactic acid polymer according to claim 1, wherein: the weight average molecular weight change rate defined by the mathematical formula 1 is 10% to 80%.
3. 3. The method for producing a polylactic acid polymer according to claim 1, wherein: the ring-opening polymerization is carried out at 150 ℃ to 240 ℃.
4. 4. The method for producing a polylactic acid polymer according to claim 1, wherein: The SnHPO 3 catalyst is contained in an amount of 100ppm mol to 1000ppm mol with respect to the lactide.
5. 5. The method for producing a polylactic acid polymer according to claim 1, wherein: The lactide and SnHPO 3 catalyst are each independently pretreated at 50 ℃ to 70 ℃ and 7 mbar to 10 mbar for 1 hour to 3 hours.
6. 6. The method for producing a polylactic acid polymer according to claim 1, wherein: The weight average molecular weight of the polylactic acid polymer is 20,000 to 50,000.
7. 7. The method for producing a polylactic acid polymer according to claim 1, wherein: The polylactic acid polymer has a number average molecular weight of 18,000 to 33,000.
8. 8. The method for producing a polylactic acid polymer according to claim 1, wherein: the polylactic acid polymer has a PDI of 1.18 to 1.5.

Description

Method for preparing polylactic acid polymer [ Field of technology ] Cross Reference to Related Applications The present application claims priority from korean patent application No. 10-2021-0087959 filed on 7/5 of 2021, the disclosure of which is incorporated herein in its entirety. The present disclosure relates to a method for preparing a polylactic acid polymer, and more particularly, to a method for preparing a polylactic acid polymer having a desired high molecular weight by using a specific catalyst in a ring-opening polymerization reaction of lactide. [ Background Art ] Polylactic acid (PLA) is a plant-derived resin extracted from plants such as corn, and has been attracting attention as an environment-friendly material having biodegradability and excellent tensile strength and elastic modulus. Unlike petroleum resins such as polystyrene resins, polyvinyl chloride resins, and polyethylene resins, which have been conventionally used, polylactic acid has effects of preventing depletion of petroleum resources, suppressing emission of carbon dioxide, and the like, and thus can reduce environmental pollution, which is a disadvantage of petroleum plastic products. Therefore, since the problem of environmental pollution caused by waste plastics has become a social problem, efforts are being made to expand the application range to the product fields using general plastics (petroleum-based resins) such as food packaging materials, containers, and electronic product cases. Meanwhile, polylactic acid is produced by polymerizing lactic acid produced by fermentation of microorganisms, but direct polymerization of lactic acid only produces low molecular weight polymers. For synthesizing high molecular weight polylactic acid, a method of polymerizing polylactic acid having a higher molecular weight from low molecular weight polylactic acid obtained by direct polymerization of lactic acid using a chain coupling agent is known, but has a disadvantage in that a process is complicated, and the coupling agent is used together with an organic solvent, thus being not easily removed. In the current commercial high molecular weight polylactic acid production process, a chemical synthesis method is adopted in which lactic acid is converted into lactide, and the polylactic acid is synthesized through the ring-opening reaction of the lactide. However, even in this case, there is a problem that it is difficult to realize a high molecular weight suitable for commercial use. In the case of the Sn (Oct) 2 catalyst conventionally used to achieve a high molecular weight, there are problems in that it has a high viscosity as a liquid catalyst, is difficult to measure accurately, and is fragile to oxygen and moisture, so that the stability of the catalyst itself is lowered. In particular, there is a problem in that the Sn (Oct) 2 catalyst is rapidly decomposed at high temperature, which adversely affects the color of the prepared resin and also reduces economic efficiency. Therefore, there is a need to develop a method for preparing a polylactic acid polymer having excellent physical properties and easily realizing a high molecular weight so as to be applicable to various industries. [ Invention ] [ Problem ] It is an object of the present disclosure to provide a method for preparing a polylactic acid polymer having a high molecular weight to a desired extent by using a specific catalyst in a lactide ring-opening polymerization reaction and controlling a rate of change of a polymer molecular weight with a polymerization temperature in a specific range. Another object of the present disclosure is to provide a method for preparing a polylactic acid polymer, which facilitates removal and reuse of a catalyst after completion of a reaction and is excellent in economical efficiency by using a catalyst exhibiting excellent stability even under high temperature polymerization reaction conditions, and does not cause a change in physical properties of the polymer due to catalyst decomposition. [ Technical solution ] In order to achieve the above object, according to the present disclosure, there is provided a method for preparing a polylactic acid polymer, comprising the steps of: First, the method includes a step of performing ring-opening polymerization of lactide in the presence of SnHPO 3 catalyst to prepare polylactic acid polymer, and The weight average molecular weight change rate defined by the following equation 1 has a positive value: [ mathematics 1] Weight average molecular weight change rate= (M (t+30)–M(t))/M(t) ×100 (%) M (t) is the weight average molecular weight of the polylactic acid polymer prepared according to the ring-opening polymerization at t DEG C, M (t+30) is the weight average molecular weight of the polylactic acid polymer prepared according to the ring-opening polymerization at a temperature of t+30℃, and T is 150 ℃ to 250 ℃. Unless specifically mentioned herein, the terms "comprises" or "comprising" are intended