A polylactic acid-based block copolymer and a method for preparing the same

Abstract

The application provides a kind of block copolymer based on polylactic acid and preparation method thereof, first by random copolymerization to cyclic carbonate monomer and oxadelta-hexalactone monomer, will obtain random copolymer as first block polymer, and then first block polymer and lactide monomer (LA) copolymerization obtains double block polymer.In the double block polymer, cyclic carbonate monomer and oxadelta-hexalactone monomer are random copolymerization, PLA and first block polymer are block copolymerization.The application can well solve the problem of hard and brittle polylactic acid by introducing cyclic carbonate monomer and oxadelta-hexalactone monomer into polylactic acid, improve the strength and toughness of polylactic acid, at the same time, by adjusting the type of cyclic carbonate monomer, oxadelta-hexalactone monomer and the ratio between LA, the comprehensive performance of product can be adjusted, greatly widen the application range of polylactic acid series materials.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically, it relates to a block copolymer based on polylactic acid and its preparation method. Background Technology

[0002] Polylactic acid (PLA), as a renewable and green plastic, has received increasing attention in recent years due to the stimulus of plastic bans, and its application is expected to become more widespread in the coming years. Due to its biodegradability and biocompatibility, PLA is considered an important material in biodegradable plastics and the medical and pharmaceutical fields. Although PLA has high tensile strength and tensile modulus, its low elongation at break and relatively high brittleness limit its application in everyday consumer goods (plastic bags, lunch boxes) or medical fields (absorbable implants, staples, and surgical sutures).

[0003] To address the hardness and brittleness of polylactic acid (PLA), the main methods currently used in academia and industry are melt blending modification and copolymerization modification. Melt blending modification typically involves adding starch, polycaprolactone (PCL), polybutylene adipate / terephthalate (PBAT), etc., to PLA. Physical blending modification can achieve some effect, but it has limitations in terms of effectiveness and efficiency. Chemical copolymerization modification introduces components such as glycolide, ε-caprolactone, and trimethylene carbonate into PLA segments through copolymerization reactions. Among these, the copolymerization of lactide and 1,3-trimethylene carbonate (TMC) is a relatively mature method that can simultaneously improve its mechanical properties and biodegradability. Therefore, some copolymers based on LA and TMC have successfully enabled the preparation of high-performance medical biomaterials. Patent CN113501942B involves a random copolymer of lactide and ε-caprolactone, and the resulting copolymer exhibits good elongation at break and light transmittance.

[0004] Therefore, this invention addresses the problems of poor toughness and high brittleness currently existing in PLA by copolymer modification, thereby solving the above-mentioned shortcomings of PLA and greatly expanding the application of PLA in the fields of daily necessities and biomedical materials. Summary of the Invention

[0005] The purpose of this invention is to address the problems of poor flexibility, hardness, brittleness, and poor impact resistance of polylactic acid (PLA) molecular chains by providing a PLA-based block copolymer and its preparation method, which improves the toughness of PLA while maintaining its biodegradability. The block copolymer of this invention possesses biodegradability and good flexibility, which greatly expands the application fields of PLA and is of great significance in enhancing the value of PLA.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A novel block copolymer based on polylactic acid is represented by the following structural formula:

[0008]

[0009] Where x, y, and z represent the degree of aggregation, which ranges from 10 to 1000.

[0010] The block polymer has a molecular weight between 10 kDa and 500 kDa, and its strength and toughness are much higher than those of lactide self-polymers.

[0011] This invention adopts the following technical solution: a block copolymer based on polylactic acid, composed of the following raw material formulation (molar ratio):

[0012] First monomer (cyclic carbonate monomer): 100-1000

[0013] Second monomer (oxaδ-caprolactone monomer): 100-1000

[0014] Third monomer (lactide): 1000-3000

[0015] Initiator: 0-10

[0016] Catalyst: 1

[0017] Solvent: 1000-6000.

[0018] The first monomer is a cyclic carbonate monomer selected from trimethylene carbonate.

[0019] The second monomer is an oxaδ-caprolactone monomer selected from 1,4-dioxane-2-one.

[0020] The initiator is one or more of the following: n-butanol, n-dodecanol, propylene glycol, pentaerythritol, 1-fluoroacetic acid, and trichloroacetic acid.

[0021] The catalyst is one or more of stannous octoate, stannous chloride, tetrabutyl titanate, tetrabutoxyzirconium, etc.

[0022] The solvent is one or more of benzene, toluene, trimethylbenzene, tetrahydrofuran, pyridine, etc.

[0023] This invention provides a method for preparing a block polymer, comprising the following steps:

[0024] Step 1: Prepare the following ingredients according to the molar ratio:

[0025] First monomer (cyclic carbonate monomer): 100-1000

[0026] Second monomer (oxaδ-caprolactone monomer): 100-1000

[0027] Third monomer (lactide): 1000-3000

[0028] Initiator: 0-10

[0029] Catalyst: 1

[0030] Solvent: 1000-6000

[0031] Step 2: Add the cyclic carbonate monomer, oxaδ-caprolactone monomer, catalyst, and solvent sequentially into the polymerization tube under anhydrous and oxygen-free conditions. Stir the mixture magnetically in an oil bath at 120-160℃ for 2-6 hours. After the reaction is complete, a transparent solution is obtained, which is the solution of the first block copolymer of the cyclic carbonate monomer and the oxaδ-caprolactone monomer.

[0032] Step 3: After the first block copolymer solution has cooled to room temperature, add lactide monomer to the polymerization tube containing the first block copolymer solution. Stir magnetically in an oil bath at 120-160°C for 2-6 hours. After the reaction is complete, precipitate the product with ethanol, remove the solvent by vacuum, and obtain a white solid, which is the polylactic acid-based block copolymer.

[0033] Step 4: After uniformly mixing the obtained polylactic acid-based block copolymer with the chain extender (initiator), the mixture is fed into a twin-screw extruder for co-extrusion to obtain a block copolymer with a larger molecular weight.

[0034] As an advantage of the present invention, the toughness of the block copolymer is greatly improved compared to polylactic acid, and as a new application of the present invention, the block copolymer can broaden the application of polylactic acid (PLA) in the medical field.

[0035] Compared with the prior art, the advantages and positive effects of the present invention are:

[0036] This invention introduces both cyclic carbonate monomers and oxaδ-caprolactone monomers into the polylactic acid (PLA) structure. Because the copolymer blocks of cyclic carbonate and oxaδ-caprolactone monomers exhibit good flexibility, they effectively mitigate the high brittleness of PLA, thus expanding the applications of the prepared copolymers. The preparation process disclosed in this invention is simple, highly operable, and allows for the preparation of copolymers at a low cost, enabling large-scale industrial production.

[0037] The summary section introduces a series of simplified concepts, which will be further explained in detail in the detailed description section. This summary section is not intended to limit the key features and essential technical features of the claimed technical solution, nor is it intended to determine the scope of protection of the claimed technical solution.

[0038] The advantages and features of the present invention will be described in detail below with reference to the accompanying drawings. Attached Figure Description

[0039] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings:

[0040] Figure 1 This is a gel permeation chromatogram of the copolymer synthesized in Example 1 of the present invention;

[0041] Figure 2 The above is the 1H NMR spectrum of the copolymer synthesized in Example 1 of this invention;

[0042] Figure 3 The above is the 1H NMR spectrum of the copolymer synthesized in Example 2 of this invention;

[0043] Figure 4 The image shows the 1H NMR spectrum of the copolymer synthesized in Example 3 of this invention. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the embodiments described herein are merely illustrative and not intended to limit the invention.

[0045] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention can be practiced without one or more of these details. In other instances, certain technical features well-known in the art have not been described in order to avoid obscuring the invention.

[0046] To fully understand the present invention, a detailed structure will be presented in the following description. Obviously, the implementation of the present invention is not limited to the specific details familiar to those skilled in the art. Preferred embodiments of the present invention are described in detail below; however, in addition to these detailed descriptions, the present invention may have other embodiments.

[0047] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0048] The embodiments of the present invention employ a two-step method to prepare block copolymers, and involve the chain extension behavior of the block copolymers using chain extenders.

[0049] This invention discloses a preparation process for a polylactic acid (PLA)-based block copolymer, specifically addressing the effect of different component ratios on the polymer. During polymerization, commonly used additives in existing PLA synthesis techniques, such as nucleating agents, antioxidants, and initiators, can be added. The amount, type, and method of application of these additives are not particularly limited. This invention also relates to the chain-extending behavior of chain extenders on this block copolymer. The type of chain extender is not particularly limited; commonly used types in existing PLA chain-extending techniques can be referenced. This preparation process is simple and convenient, yielding a block copolymer with better toughness than PLA, thus offering broader application prospects in the biomedical materials field. Specific examples are provided below.

[0050] Example 1

[0051] 1) The formulation of the block copolymer is as follows:

[0052]

[0053] 2) Preparation process of block copolymers

[0054] In an anhydrous and oxygen-free environment, 72g of trimethylene carbonate monomer, 72g of 1,4-dioxane-2-one monomer, 0.25g of catalyst, and 200ml of anhydrous toluene were sequentially added to a pressure-resistant polymerization tube.

[0055] The pressure-resistant polymerization tube was magnetically stirred in an oil bath at 150°C for 2 hours. After the reaction was completed, the polymer solution was cooled to room temperature, and 100g of lactide monomer was added to the pressure-resistant polymerization tube in an anhydrous and oxygen-free environment.

[0056] The pressure-resistant polymerization tube was magnetically stirred in an oil bath at 150°C for 2 hours. After the reaction was complete, the product was precipitated with ethanol, and the solvent was removed under vacuum to obtain a pale white, slightly transparent solid, which was the diblock polymer. The molecular weight and molecular structure of the polymer sample were characterized using GPC and 1H NMR spectroscopy.

[0057] Example 2

[0058] 1) The formulation of the block copolymer is as follows:

[0059]

[0060] 2) Preparation process of block copolymers

[0061] In an anhydrous and oxygen-free environment, 36g of trimethylene carbonate monomer, 36g of 1,4-dioxane-2-one monomer, 0.25g of catalyst, and 200ml of anhydrous toluene were sequentially added to a pressure-resistant polymerization tube.

[0062] The pressure-resistant polymerization tube was magnetically stirred in an oil bath at 150°C for 2 hours. After the polymer solution cooled to room temperature, 100g of lactide monomer was added to the pressure-resistant polymerization tube in an anhydrous and oxygen-free environment.

[0063] The pressure-resistant polymerization tube was magnetically stirred in an oil bath at 150°C for 2 hours. After the reaction was complete, the product was precipitated with ethanol, and the solvent was removed under vacuum to obtain a pale white, slightly transparent solid, which was the diblock polymer. The molecular weight and molecular structure of the polymer sample were characterized using GPC and 1H NMR spectroscopy.

[0064] Example 3

[0065] 1) The formulation of the block copolymer is as follows:

[0066]

[0067] 2) Preparation process of block copolymers

[0068] In an anhydrous and oxygen-free environment, 20g of 5-vinyltrimethylene carbonate monomer, 19.6g of 1,4-dioxane-2-one monomer, 0.25g of catalyst, and 200ml of anhydrous toluene were sequentially added to a pressure-resistant polymerization tube.

[0069] The pressure-resistant polymerization tube was magnetically stirred in an oil bath at 160°C for 3 hours. After the polymer solution cooled to room temperature, 100g of lactide monomer was added to the pressure-resistant polymerization tube in an anhydrous and oxygen-free environment.

[0070] The pressure-resistant polymerization tube was reacted with magnetic stirring in an oil bath at 160°C for 3 hours. After the reaction was complete, the product was precipitated with ethanol, and the solvent was removed by vacuum to obtain a pale white, slightly transparent solid, which was the diblock polymer. The molecular weight of the polymerized sample was characterized using GPC.

[0071] Comparative Example 1

[0072] 1) The formulation of the block copolymer is as follows:

[0073]

[0074] 2) Preparation process of block copolymers

[0075] In an anhydrous and oxygen-free environment, 18g of trimethylene carbonate monomer, 18g of 1,4-dioxane-2-one monomer, 50g of lactide monomer, 0.1g of catalyst, and 100ml of anhydrous toluene were sequentially added to a pressure-resistant polymerization tube.

[0076] The pressure-resistant polymerization tube was magnetically stirred in an oil bath at 150°C for 2 hours. After the reaction was complete, the product was precipitated with ethanol, and the solvent was removed under vacuum to obtain a pale white, slightly transparent solid, which was the random copolymer. The molecular weight and molecular structure of the polymerized sample were characterized using GPC and 1H NMR spectroscopy.

[0077] The polymer prepared in Comparative Example 1 is a random copolymer of three monomers: trimethylene carbonate monomer, 1,4-dioxane-2-one monomer, and lactide monomer. In contrast, Examples 1 and 2 are block polymers of two copolymers: a random polymer of trimethylene carbonate and 1,4-dioxane-2-one, and a lactide self-polymer. In Comparative Example 1, the trimethylene carbonate and 1,4-dioxane-2-one units in the random copolymer do not provide a good toughening effect due to their uncertain positions. However, in Examples 1 and 2, by first polymerizing the 1,4-dioxane-2-one and trimethylene carbonate blocks as compliant segments into a single chain segment, a better toughening effect can be achieved, thus highlighting the advantages of this invention.

[0078] Example 4

[0079] The block polymer prepared in Example 1 was subjected to a chain extension experiment, and the specific operation was as follows:

[0080] 50g of block polymer and 1wt% chain extender were premixed together, and then the sample was kneaded on a torque rheometer for 360s at a temperature of 180℃. The molecular weight of the kneaded sample was characterized using GPC.

[0081] Table 1. Molecular weight information for each example and comparative example.

[0082]

[0083] Table 2 Mechanical property tests of each embodiment and comparative example

[0084]

[0085] The comparison of mechanical properties between copolymers with different component contents shows that introducing trimethylene carbonate monomer and 1,4-dioxane-2-one monomer into the copolymer using this method significantly improves the elongation at break, indicating that the introduction of these two monomers effectively enhances the toughness of the copolymer. Furthermore, the higher the content of trimethylene carbonate monomer and 1,4-dioxane-2-one monomer, the greater the increase in toughness. Comparison with Comparative Example 1 shows that the block copolymer of trimethylene carbonate monomer, 1,4-dioxane-2-one monomer, and lactide monomer exhibits superior toughness compared to the random copolymer of trimethylene carbonate monomer, 1,4-dioxane-2-one monomer, and lactide monomer.

[0086] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A block copolymer based on polylactic acid, characterized in that, The raw materials for the block copolymer include, in molar amounts: First monomer: cyclic carbonate monomer: 100-1000 Second monomer, oxa-δ-caprolactone monomer: 100-1000 Third monomer lactide: 1000-3000 Catalyst: 1 Solvent: 1000-6000; The first monomer is selected from trimethylene carbonate, the second monomer is selected from 1,4-dioxane-2-one, and the molecular weight of the block copolymer is between 10 kDa and 500 kDa; The method for preparing the polylactic acid-based block copolymer specifically includes the following steps: Step 1: Prepare raw materials according to the molar ratio; Step 2: Add the cyclic carbonate monomer, oxaδ-caprolactone monomer, catalyst, and solvent sequentially into the polymerization tube under anhydrous and oxygen-free conditions. Stir the mixture magnetically in an oil bath at 120-160℃ for 2-6 hours. After the reaction is complete, a transparent solution is obtained, which is the solution of the first-stage copolymer of the cyclic carbonate monomer and oxaδ-caprolactone monomer. Step 3: After the first-stage copolymer solution has cooled to room temperature, add lactide monomer to the polymerization tube containing the first-stage copolymer solution. Stir the reaction magnetically in an oil bath at 120-160°C for 2-6 hours. After the reaction is complete, precipitate the product with ethanol, remove the solvent by vacuum, and obtain a white solid, which is the polylactic acid-based block copolymer.

2. The block copolymer according to claim 1, characterized in that, The catalyst is one or more of stannous octoate, stannous chloride, tetrabutyl titanate, and tetrabutoxyzirconium.

3. The block copolymer according to claim 1, characterized in that, The solvent is one or more of benzene, toluene, trimethylbenzene, tetrahydrofuran, and pyridine.

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