Modified polylactic-co-glycolic acid copolymer, preparation method therefor, and use thereof

Abstract

The present invention relates to a modified polylactic-co-glycolic acid (PLGA) copolymer, a preparation method therefor, and a use thereof. The preparation method comprises: mixing and reacting a glycolic acid monomer, a lactic acid monomer, a functional branching agent, and a catalyst to prepare a PLGA polymer melt, the functional branching agent comprising one or more of the following substances: a hyperbranched polyhydroxy polymer, a polyamine compound, and a hyperbranched polycarboxylic polymer; after the PLGA polymer melt cools down, subjecting it to crushing to obtain a crushed material; melt-blending the crushed material, a chain extender, and a functional additive, and after a chain extension reaction, obtaining the modified polylactic-co-glycolic acid copolymer. Compared with the prior art, the preparation method of the present invention has the advantages of easily obtainable starting materials and environmental friendliness, and is suitable for industrial-scale production. The prepared modified polylactic-co-glycolic acid copolymer has relatively high molecular weight and strength, and exhibits good mechanical properties, heat resistance, and complete biodegradability.

Description

A modified polylactic acid-glycolic acid copolymer, its preparation method and application Technical Field

[0001] This invention relates to the field of chemical modification technology, and in particular to a modified polylactic acid-hydroxyacetic acid copolymer, its preparation method, and its application. Background Technology

[0002] Poly(lactic-co-glycolic acid) copolymer (PLGA) is a biodegradable material with excellent mechanical properties, heat resistance, and barrier properties, and it has important applications in medical devices, oilfield plugging agents, and high-end membrane materials. Existing one-step processes can only yield low molecular weight PLGA, while the two-step process requires the preparation of intermediates glycolide and lactide before ring-opening polymerization to form high-performance PLGA. This process is cumbersome, and the purification of glycolide and lactide requires large amounts of organic solvents, which is inconsistent with the modern development concept of "green and low-carbon".

[0003] In existing technologies, PLGA prepared by a one-step process is modified to further increase its molecular weight. For example, CN103864999A describes modifying lactic acid-glycolic acid copolymer with maleic anhydride. First, crude polylactic acid-glycolic acid copolymer is prepared, then purified and dried. The purified product is then reacted with maleic anhydride to obtain the final product. The above preparation process requires the initial purification of the crude copolymer, which still requires a large amount of organic solvent.

[0004] Therefore, there is an urgent need for a method to prepare modified polylactic acid-glycolic acid copolymers that are readily available, environmentally friendly, and easy to scale up industrially, so as to obtain modified polylactic acid-glycolic acid copolymers with good performance. Summary of the Invention

[0005] The purpose of this invention is to provide a modified polylactic acid-glycolic acid copolymer, its preparation method, and its application in order to solve the above-mentioned problems. This invention uses glycolic acid monomers and lactic acid monomers as raw materials, and prepares PLGA polymers through esterification / transesterification and polycondensation reactions under the action of catalysts and functional branching agents. Then, the PLGA polymers are pulverized and modified by melt chain extension and blending to obtain the modified polylactic acid-glycolic acid copolymer. The raw materials are readily available, environmentally friendly, and easy to scale up for industrial production.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] The first objective of this invention is to provide a method for preparing a modified polylactic acid-glycolic acid copolymer, the method comprising the following steps:

[0008] (1) Mix and react glycolic acid monomers, lactic acid monomers, functional branching agents and catalysts, and prepare PLGA polymer melt through transesterification or esterification reaction and polycondensation reaction;

[0009] (2) After the PLGA polymer melt cools down, it is pulverized to obtain pulverized material;

[0010] (3) The pulverized material, chain extender and functional additives are melt-blended and then subjected to chain extension reaction to obtain modified polylactic acid-hydroxyacetic acid copolymer.

[0011] Furthermore, the glycolic acid monomer can be one or more of glycolic acid, methyl glycolate, ethyl glycolate, propyl glycolate, isopropyl glycolate, and butyl glycolate.

[0012] Furthermore, the lactic acid monomer can be one or more of lactic acid, methyl lactate, ethyl lactate, propyl lactate, isopropyl lactate, and butyl lactate.

[0013] Furthermore, the catalyst includes, but is not limited to, one or more of the following: tetrabutyl titanate, isopropyl titanate, stannous chloride, stannous octoate, zinc acetate dihydrate, titanium glycolate, antimony glycolate, magnesium oxide, antimony trioxide, and antimony acetate.

[0014] Furthermore, the functional branching agent includes one or more of the following substances: hyperbranched polyhydroxy polymers, polyamine compounds, and hyperbranched polycarboxylic polymers.

[0015] Furthermore, the hyperbranched polyhydroxy polymer includes one or more of hyperbranched polyester polyols with a molecular weight of 500 to 10,000 or hyperbranched polyether polyols with a molecular weight of 500 to 10,000.

[0016] Further, the polyamine compound includes one or more of hexamethylenetetramine, tris(2-aminoethyl)amine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, low-methyleneimine with a molecular weight of 200 to 20000, and amination-treated nanoparticles with a molecular weight of 200 to 20000.

[0017] Furthermore, the hyperbranched polycarboxylated polymer comprises a hyperbranched polyamide with carboxyl groups capped at molecular weight of 300 to 30,000.

[0018] As a preferred embodiment, the functional branching agent is a hyperbranched polyester polyol with a molecular weight of 500 to 10,000, which is prepared by the following method:

[0019] (s1) Add equimolar amounts of diacid and diol, as well as esterification catalyst, to a reaction flask and stir magnetically at 60-80°C. Simultaneously add 0.1%-2% of polyol in molar ratio to diacid, and the amount of esterification catalyst is 0.01wt%-0.2wt% of diacid.

[0020] (s2) The temperature is increased under a nitrogen atmosphere, and the reaction is carried out at 80-150℃ for 2-6 hours;

[0021] (s3) Reduce the pressure of the reaction system and continue the reaction for 2 to 10 hours within the range of 50 kPa to 50 Pa;

[0022] (s4) Stop the reaction, pour out the product while it is hot and cool it, crush it into 10-100 mesh particles and dry it to obtain hyperbranched polyester polyols with a molecular weight of 500-10000.

[0023] More preferably, the molecular weight of the hyperbranched polyester polyol is 5000-10000.

[0024] Furthermore, the esterification catalyst can be a tin salt, zinc salt, titanium salt, sulfur salt, tin oxide, zinc oxide, titanium oxide, sulfur oxide, or a combination thereof, preferably the same as the catalyst in step (1).

[0025] Furthermore, the dicarboxylic acid can be one or more of succinic acid, glutaric acid, adipic acid, pepinoic acid, octanoic acid, azelaic acid, sebacic acid, etc.

[0026] Furthermore, the diol may be one or more of ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, etc.

[0027] Furthermore, the polyol may be selected from one or more of glycerol, pentaerythritol, dipentaerythritol, glycerol, xylitol, mannitol, sorbitol, etc.

[0028] As a preferred embodiment, the functional branching agent is an amination-treated nanoparticle with a molecular weight of 200–20000. The nanoparticles can be selected from siloxane nanoparticles with a particle size of 10–500 nm. The amination-treated nanoparticles are prepared by the following method:

[0029] (s1) Add a silane coupling agent (e.g., silane coupling agent KH550, γ-aminopropyltriethoxysilane) and concentrated hydrochloric acid (37%) with a molar fraction of 0.05% to 0.5% (relative to the silane coupling agent) to a low-carbon alcohol solvent and stir magnetically.

[0030] (s2) The reaction system is continuously stirred magnetically for 3 to 15 days at room temperature and pressure. The excess solvent is removed by rotary evaporation until flocculent to granular precipitate appears. The precipitate is filtered and dried at 50 to 70°C (preferably 60°C) to obtain white granules.

[0031] (s3) The resulting white particles were fully dissolved in a low-carbon alcohol solvent and then passed through a column filled with anion exchange resin to obtain a nanoparticle mixed solution.

[0032] The nanoparticle mixture obtained by (s4) is dried by rotary evaporation at 30-50℃ (preferably 40℃) to obtain aminated siloxane nanoparticles with a molecular weight of 200-20000.

[0033] Furthermore, the low-carbon alcohol solvent is selected from one or more of methanol, ethanol, isopropanol, n-propanol, etc.

[0034] More preferably, the molecular weight of the amination-treated siloxane nanoparticles is 5000 to 20000.

[0035] As a preferred embodiment, the functional branching agent is a carboxyl-terminated hyperbranched polyamide with a molecular weight of 300–30000. The carboxyl-terminated hyperbranched polyamide with a molecular weight of 300–30000 is prepared by the following method:

[0036] (s1) Under a nitrogen atmosphere, a polar aprotic solvent (one or more of NMP, DMF, DMSO, and DMAC), triphenyl phosphite in a molar ratio of 1:1, and pyridine are added to a reaction flask and dissolved by magnetic stirring.

[0037] (s2) Add the polybasic acid / anhydride and the diamine to the reaction flask at a molar ratio of 0.5% to 5% excess carboxyl group, mix them evenly at 60 to 90°C, the molar ratio of the sum of the molar amounts of triphenyl phosphite and pyridine to the molar amount of the diamine is 0.01% to 0.1%, and the mass of the solvent accounts for 50% to 80% of the total mass.

[0038] (s3) Heat the reaction system to 130-150℃ (preferably 140℃) and continue the reaction for 4-10 hours;

[0039] (s4) After the reaction is complete, the reaction solution is poured into water to precipitate, filtered and dried to obtain carboxyl-terminated hyperbranched polyamide with a molecular weight of 300 to 30,000.

[0040] More preferably, the molecular weight of the carboxyl-terminated hyperbranched polyamide is 5000-30000. Further, the polybasic acid / anhydride is selected from one or more of 2,2-hydroxymethylpropionic acid, 2,2-hydroxymethylbutyric acid, trimalonic acid, trimellitic acid, trimellitic anhydride, pyromellitic acid, pyromellitic anhydride, and pyromellitic acid.

[0041] Furthermore, the diamine is selected from one or more of ethylenediamine, propylenediamine, hexamethylenediamine, p-phenylenediamine, o-phenylenediamine, m-phenylenediamine, and benzidine.

[0042] As a preferred embodiment, the molar ratio of glycolic acid monomers to lactic acid monomers is 50:50 to 90:10, and the molar amount of the functional branching agent is 0.1% to 3% of the total molar amount of glycolic acid monomers and lactic acid monomers.

[0043] As a preferred embodiment, the molar amount of the catalyst accounts for 0.005% to 6% of the total molar amount of glycolic acid monomers and lactic acid monomers.

[0044] Furthermore, the chain extender includes, but is not limited to, one or more of the following categories: 1) Isocyanates: such as terephthalic diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, or one or more; 2) Epoxy compounds: such as BASF ADR type, KL-E4370, or one or more; 3) Oxazoline compounds: such as 1,3-PBO dioxazoline, 2,2-bis(2-oxazoline), or one or more.

[0045] As a preferred embodiment, the amount of chain extender added is 1 wt% to 10 wt% of the pulverized material.

[0046] As a preferred option, terephthalic diisocyanate is selected as the chain extender.

[0047] As a preferred embodiment, the functional additives include, but are not limited to, one or more of antioxidants, reinforcing agents, stiffening agents, nucleating agents, flame retardants, and opening agents, and the amount of each functional additive added is 0.01 to 10% of the total molar amount of glycolic acid monomers and lactic acid monomers.

[0048] More preferably, the antioxidant includes, but is not limited to, one or more of hindered phenols and phosphites, such as antioxidant 1010, antioxidant 168 and one or more of their compound products.

[0049] More preferably, the reinforcing agent includes, but is not limited to, one or more of various organic and inorganic nanoparticles, such as NA960, NA21, nano-calcium carbonate, talc powder, etc., commercially available from Shanghai Magic Box New Materials Co., Ltd.

[0050] More preferably, the stiffening agent includes, but is not limited to, one or more of various organic and inorganic nanoparticles, such as NA960, NA21, nano-calcium carbonate, talc powder, etc., which are commercially available from Shanghai Magic Box New Materials Co., Ltd.

[0051] More preferably, the nucleating agent includes, but is not limited to, one or more of various organic and inorganic nanoparticles, such as NA960, NA21, nano-calcium carbonate, talc powder, etc., commercially available from Shanghai Magic Box New Materials Co., Ltd.

[0052] More preferably, the flame retardant includes, but is not limited to, one or more of inorganic hydroxides and their modified hydroxides, phosphorus-nitrogen type flame retardants, and organosilicon flame retardants, such as Doher-998 from Daer Chemical and APP flame retardant from Wanran Technology.

[0053] More preferably, the opening agent includes, but is not limited to, one or more of talc, diatomaceous earth, oleamide, erucamide, and EBS (ethylene bis-stearamide) derivatives, such as one or more of Lingwei Technology's K-80, K-35X, and K-25.

[0054] Furthermore, step (1) specifically includes:

[0055] (s1) Heat the reaction apparatus to 60-100°C, introduce inert gas for protection (for example, circulate / purge inert gas 2-4 times, evacuate to an absolute pressure of less than 200 Pa, and then purge to atmospheric pressure), add glycolic acid monomers, lactic acid monomers, functional branching agents and catalysts, and stir to mix evenly.

[0056] (s2) Perform esterification or transesterification: Increase the temperature of the reaction apparatus and react at 110℃~170℃ for 2~8h. When the volume or weight of the by-product reaches 60~90% of the theoretical volume or weight, the esterification or transesterification reaction is terminated.

[0057] (s3) Perform polycondensation reaction: Vacuum is drawn at a rate of 0.1 to 10 kPa / min, and the polycondensation reaction temperature is increased and controlled at 170 to 220°C and vacuum degree of 30 to 500 Pa. The reaction is continued for 2 to 16 hours until the power of the stirring motor no longer increases, and the PLGA polymer melt is obtained.

[0058] Furthermore, step (2) specifically includes:

[0059] After the PLGA polymer melt is cooled, the cooled PLGA polymer is obtained. The cooled PLGA polymer is then crushed by a pulverizer and screened by a sieve to obtain material with a particle size of 10 to 100 mesh.

[0060] Furthermore, step (3) specifically includes:

[0061] The pulverized materials, functional additives, and chain extenders are melt-blended at 130–220°C for 0.5–5 minutes to obtain modified polylactic acid-glycolic acid copolymer. A suitable melt-blending device can be selected based on the amount of raw materials used. For example, a torque rheometer is used as the melt-blending device in the laboratory stage, while a twin-screw extruder is used in the scale-up production stage.

[0062] The second objective of this invention is to provide a modified polylactic acid-glycolic acid copolymer (modified PLGA copolymer) prepared by the above-described preparation method.

[0063] Furthermore, the modified PLGA copolymer is pale yellow, white, yellow, gray, brown, or black, with a molecular weight of 50,000 to 200,000, an intrinsic viscosity of 0.5 to 1.8 dL / g, a melt index of 100 to 5 g / 10 min (190°C, 2.16 kg), a tensile strength of 20 to 100 MPa, and an elongation at break of 30% to 300%.

[0064] More preferably, the modified PLGA copolymer has a molecular weight of 90,000 to 200,000, an intrinsic viscosity of 1 to 1.8 dL / g, a melt index of 50 to 5 g / 10 min (190°C, 2.16 kg), a tensile strength of 40 to 100 MPa, and an elongation at break of 50% to 300%.

[0065] A third objective of this invention is to provide an application of a modified polylactic acid-glycolic acid copolymer prepared by the above-described preparation method.

[0066] Furthermore, the application fields of the modified PLGA copolymer include, but are not limited to, one or more of the following fields: biodegradable film materials, disposable lunch boxes, disposable straws, disposable packaging bags, disposable knives, disposable forks, disposable spoons, biodegradable logistics packaging, biodegradable tapes, biodegradable gift boxes, recyclable and biodegradable injection molded products, foaming materials, blended modified ingredients, etc.

[0067] Compared with the prior art, the beneficial effects of the present invention are reflected in the following aspects:

[0068] 1) This scheme uses glycolic acid monomers and lactic acid monomers to prepare PLGA polymers through esterification / transesterification and polycondensation reactions under the action of catalysts and functional branching agents. Then, the PLGA polymers are pulverized and modified by melt chain extension and blending to obtain modified polylactic acid-glycolic acid copolymers. Compared with the existing two-step process using glycolide and lactide as raw materials, the raw materials are readily available, environmentally friendly, and easy to scale up for industrial production.

[0069] 2) The functional branching agent is a polyamine compound or a hyperbranched oligomer, which reacts with glycolic acid monomers and lactic acid monomers to form a branched PLGA polymer. The branched structure can increase the crosslinking sites with the chain extender, further improving the molecular weight and strength of the modified polylactic acid-glycolic acid copolymer. The modified polymer has good mechanical properties, heat resistance and biodegradability. Detailed Implementation

[0070] The present invention will now be described in detail with reference to specific embodiments, but this is by no means a limitation thereof. Any preparation methods, materials, structures, or compositional ratios not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0071] Unless otherwise specified, the reagents, methods, instruments, and equipment used in this invention are conventional in the art. Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0072] Comparative Example 1

[0073] This comparative example provides a method for preparing a modified polylactic acid-glycolic acid copolymer, using pentaerythritol as the functional branching agent, and includes the following steps:

[0074] A 250ml two-necked flask was placed in an 80℃ oil bath and heated under N2 protection. 0.85mol of glycolic acid crystals, 0.15mol of lactic acid (70% aqueous solution), 0.0005mol of stannous chloride, and 0.002mol of pentaerythritol were added sequentially, and the mixture was magnetically stirred for 0.5h until homogeneous. The temperature was gradually increased to 130℃, and the reaction was carried out at 130℃ for 1h; the temperature was increased to 150℃, and the reaction was carried out at 150℃ for 1h; the temperature was increased to 170℃, and the reaction was carried out at 170℃ for 1h. Then, a vacuum was applied at 170℃ to 30kPa at a rate of 5kPa / min, and the reaction was carried out for 1h; the vacuum was continued at a rate of 5kPa / min to 5kPa, and the reaction was carried out for 1h; the vacuum was then continued to 50–100Pa, and the temperature was increased to 190℃, and the reaction was carried out for 6h.

[0075] After cooling and removing the material, it is crushed and sieved to obtain a material with a particle size of 50 mesh. The obtained material, along with 2 wt% terephthalic acid diisocyanate and 0.003 mol antioxidant 1010, is added to a torque rheometer and reacted at 190℃ and 100 rpm for 5 min to obtain a modified polylactic acid-hydroxyacetic acid copolymer.

[0076] Example 1

[0077] The method for preparing the modified polylactic acid-glycolic acid copolymer provided in this embodiment uses a hyperbranched polyester polyol with a molecular weight of 500-10000 as the functional branching agent. The preparation method includes the following steps:

[0078] Preparation of hyperbranched polyester polyol: Equimolar amounts of succinic acid and ethylene glycol, along with 0.1 wt% (relative to succinic acid) of stannous chloride, were added to a reaction flask. Under magnetic stirring at 70°C, pentaerythritol (0.5% molar ratio to succinic acid) was added. The mixture was gradually heated to 110°C for 3 hours under a slightly positive nitrogen atmosphere. The reaction system pressure was gradually reduced, and the reaction continued at 1 kPa for 2 hours. After the reaction was complete, the product was poured off while hot, cooled, pulverized into 50-mesh particles, and dried to obtain hyperbranched polyethylene succinate. The molecular weight of the hyperbranched polyethylene succinate was determined to be 8600 g / mol.

[0079] Preparation of modified PLGA copolymer: The preparation method is the same as that of Comparative Example 1, except that 0.002 mol of pentaerythritol is replaced with 0.002 mol of the above-mentioned hyperbranched polyethylene succinate to obtain modified polylactic acid-hydroxyacetic acid copolymer.

[0080] Example 2

[0081] The preparation method of the modified polylactic acid-glycolic acid copolymer provided in this embodiment is the same as that in Example 1, except that the amount of hyperbranched polyethylene succinate added is changed from 0.002 mol to 0.005 mol to obtain the modified polylactic acid-glycolic acid copolymer.

[0082] Example 3

[0083] The preparation method of the modified polylactic acid-glycolic acid copolymer provided in this embodiment is the same as that in Example 1, except that the amount of hyperbranched polyethylene succinate added is changed from 0.002 mol to 0.01 mol to obtain the modified polylactic acid-glycolic acid copolymer.

[0084] Example 4

[0085] This embodiment provides a method for preparing a modified polylactic acid-glycolic acid copolymer. The functional branching agent used is a carboxyl-terminated hyperbranched polyamide with a molecular weight of 300-30000. The preparation method includes the following steps:

[0086] Preparation of carboxyl-terminated hyperbranched polyamide: Under a nitrogen atmosphere, appropriate amounts of the polar aprotic solvent DMSO, triphenyl phosphite and pyridine (molar ratio 1:1, where the sum of the molar amounts of triphenyl phosphite and pyridine is 0.05% of the molar ratio of hexamethylenediamine in subsequent steps) were added to a reaction flask and magnetically stirred to dissolve. Trimeric trioxide and hexamethylenediamine were added to the reaction flask at a molar ratio of 2% carboxyl excess, and mixed thoroughly at 80°C. The DMSO solvent accounted for 60% of the mass of the system. The reaction system was heated to 140°C and the reaction was continued for 6 hours. After the reaction was completed, the reaction solution was poured into water to precipitate, filtered, and dried to obtain the carboxyl-terminated hyperbranched polyamide. The molecular weight of the hyperbranched polyamide was measured to be 12000 g / mol.

[0087] Preparation of modified PLGA copolymer: The preparation method is the same as that of Comparative Example 1, except that 0.002 mol of pentaerythritol is replaced with 0.005 mol of the above hyperbranched polyamide to obtain modified polylactic acid-hydroxyacetic acid copolymer.

[0088] Example 5

[0089] The preparation method of the modified polylactic acid-glycolic acid copolymer provided in this embodiment is the same as that in Example 4, except that the amount of hyperbranched polyamide added is changed from 0.005 mol to 0.01 mol to obtain the modified polylactic acid-glycolic acid copolymer.

[0090] Example 6

[0091] The preparation method of the modified polylactic acid-glycolic acid copolymer provided in this embodiment is the same as that in Example 4, except that the amount of hyperbranched polyamide added is changed from 0.005 mol to 0.02 mol to obtain the modified polylactic acid-glycolic acid copolymer.

[0092] Example 7

[0093] This embodiment provides a method for preparing modified polylactic acid-glycolic acid copolymer, using ammoniated nanoparticles with a molecular weight of 200-20000 as the functional branches. The preparation method includes the following steps:

[0094] Silane coupling agent KH550 and 0.1% molar fraction (relative to silane coupling agent) of concentrated hydrochloric acid (37%) were added to methanol and magnetically stirred. The reaction system was continuously stirred magnetically for 10 days at room temperature and pressure. Excess methanol solvent was removed by rotary evaporation until flocculent to granular precipitate appeared. The precipitate was filtered and dried at 60°C to obtain white particles. The obtained white particles were fully dissolved in methanol again and then passed through a column packed with anion exchange resin to obtain a nanoparticle solution. The obtained nanoparticle solution was dried by rotary evaporation at 40°C to obtain amination-treated nanoparticles with a molecular weight of 15000 g / mol.

[0095] Preparation of modified PLGA copolymer: The preparation method is the same as that of Comparative Example 1, except that 0.002 mol of pentaerythritol is replaced with 0.01 mol of the above-mentioned aminated nanoparticles to obtain modified polylactic acid-glycolic acid copolymer.

[0096] Example 8

[0097] The preparation method of the modified polylactic acid-glycolic acid copolymer provided in this embodiment is the same as that in Example 7, except that the amount of amination-treated nanoparticles added is changed from 0.01 mol to 0.02 mol to obtain the modified polylactic acid-glycolic acid copolymer.

[0098] Comparative Example 2

[0099] This comparative example provides a method for preparing a modified polylactic acid-glycolic acid copolymer. The functional branching agent used is polyethylene succinate. The preparation method of polyethylene succinate is the same as in Example 1, except that pentaerythritol is not added during the preparation of polyethylene succinate. Succinic acid and ethylene glycol are added to the reaction flask at a molar ratio of 2% excess hydroxyl group. The molecular weight of the prepared polyethylene succinate is measured to be 2600 g / mol.

[0100] The modified polylactic acid-glycolic acid copolymer was prepared in the same way as in Example 1, except that the hyperbranched polyethylene succinate was replaced with the above-mentioned polyethylene succinate to obtain the modified polylactic acid-glycolic acid copolymer.

[0101] Comparative Example 3

[0102] The preparation method of the modified polylactic acid-glycolic acid copolymer provided in this comparative example is the same as that in Example 1, except that the amount of hyperbranched polyethylene succinate added is changed from 0.002 mol to 0.05 mol to obtain the modified polylactic acid-glycolic acid copolymer.

[0103] Performance testing:

[0104] The modified polylactic acid-glycolic acid copolymer samples from Examples 1-8 and Comparative Examples 1-3 were subjected to the following performance tests:

[0105] 1. Weight-average molecular weight

[0106] The sample was dissolved in a 5 mmol / L sodium trifluoroacetate solution in hexafluoroisopropanol to prepare a 0.05–0.3 wt% solution. This solution was then filtered through a 0.4 μm PTFE filter. 20 μL of the filtered solution was added to a gel permeation chromatography (GPC) injector to determine the molecular weight of the sample. Five standard molecular weights of methyl methacrylate with different molecular weights were used for molecular weight correction.

[0107] 2. Intrinsic viscosity

[0108] Weigh approximately 0.125 g of the sample and dissolve it in 25 ml of hexafluoroisopropanol, then incubate in a constant temperature water bath at 25°C. Measure the intrinsic viscosity (η) using an Ubbelohde viscometer. Take three average measurements. The outflow time of each measurement should not differ by more than 0.2 seconds.

[0109] 3. Melt Flow Index (MFR) Test

[0110] The melt flow index (MFR) of the copolymer was tested according to the following method: 1) The copolymer was dried in a vacuum drying oven at 105°C; 2) The test temperature of the testing instrument was set to 190°C and the instrument was preheated; 3) 4g of the dried copolymer was loaded into a barrel through a funnel, and a piston was inserted into the barrel to press the dried copolymer into a rod; 4) The dried copolymer was held in the rod for 1 minute with a weight of 2.16kg on top, and then a section was cut every 30s, for a total of five sections; 5) The mass of each sample was weighed and its MFR was calculated. MFR = 600W / t (g / 10min), where W is the average mass of each section and t is the cutting time interval of each section.

[0111] 4. Tensile strength and elongation at break

[0112] The test was conducted according to the GB / T1040.2-2016 test standard, with a tensile speed of 50 mm / min, and the average value of 5 groups of samples was taken.

[0113] Table 1 Performance test results of each embodiment and comparative example

[0114] As shown in Table 1, comparing Example 1 with Comparative Example 1, it can be seen that using hyperbranched polyester polyol as a functional branching agent, compared with the commonly used branching agent pentaerythritol, can effectively improve the weight-average molecular weight, intrinsic viscosity, tensile strength, and elongation at break of the modified polylactic acid-glycolic acid copolymer. Using carboxyl-terminated hyperbranched polyamide or aminated nanoparticles as functional branching agents, compared with the same amount of hyperbranched polyester polyol, the weight-average molecular weight, tensile strength, and elongation at break of the obtained modified polylactic acid-glycolic acid copolymer are slightly improved. Furthermore, the modified polylactic acid-glycolic acid copolymer prepared using commonly used branching agents cannot be detected in the melt index test due to excessively rapid flow, while the modified polylactic acid-glycolic acid copolymer obtained in this application has a melt index between 30 and 5 g / 10 min (190℃, 2.16 kg), exhibiting good hot melt stability.

[0115] In comparison with Comparative Example 2, no polyol was added during the preparation of the polyester polyol. Only succinic acid and ethylene glycol were used for esterification. The resulting polyester polyol had a linear structure. When the linear polyester polyol was used as a functional branching agent, the modified polylactic acid-glycolic acid copolymer could not be detected in the melt index test because it flowed out too quickly, and the tensile strength was low.

[0116] Compared with Comparative Example 3, when the molar amount of the functional branching agent was 5% (greater than 3%) of the total molar amount of glycolic acid monomers and lactic acid monomers, the obtained modified polylactic acid-glycolic acid copolymer was insoluble in a 5 mmol / L sodium trifluoroacetate solution in hexafluoroisopropanol or in hexafluoroisopropanol, indicating excessive crosslinking.

[0117] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a modified polylactic-co-glycolic acid polymer, characterized by, The preparation method includes the following steps: (1) Mix and react glycolic acid monomers, lactic acid monomers, functional branching agents and catalysts to prepare PLGA polymer melt, wherein the functional branching agents include one or more of the following substances: hyperbranched polyhydroxy polymers, polyamine compounds and hyperbranched polycarboxylic polymers. (2) After the PLGA polymer melt cools down, it is pulverized to obtain pulverized material; (3) The pulverized material, chain extender and functional additives are melt-blended and then subjected to chain extension reaction to obtain modified polylactic acid-hydroxyacetic acid copolymer.

2. The method for preparing a modified polylactic acid-glycolic acid copolymer according to claim 1, characterized in that, The hyperbranched polyhydroxy polymer includes one or more of hyperbranched polyester polyols with a molecular weight of 500 to 10,000 or hyperbranched polyether polyols with a molecular weight of 500 to 10,000. The polyamine compound includes one or more of hexamethylenetetramine, tris(2-aminoethyl)amine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, low-methyleneimine with a molecular weight of 200 to 20000, and amination-treated nanoparticles with a molecular weight of 200 to 20000. The hyperbranched polycarboxylated polymer includes hyperbranched polyamides with carboxyl-terminated molecular weights of 300 to 30,000.

3. The method for preparing a modified polylactic acid-glycolic acid copolymer according to claim 2, characterized in that, The functional branching agent is a hyperbranched polyester polyol with a molecular weight of 500-10000, and the preparation of the hyperbranched polyester polyol with a molecular weight of 500-10000 includes the following steps: (s1) Equimolar amounts of diacid and diol, along with the esterification catalyst, are stirred at 60–80 °C, while simultaneously adding a polyol at a molar ratio of 0.1%–2% to the diacid. (s2) The temperature is increased under a nitrogen atmosphere, and the reaction is carried out at 80-150℃ for 2-6 hours; (s3) Reduce the pressure of the reaction system and continue the reaction for 2 to 10 hours within the range of 50 kPa to 50 Pa; (s4) Stop the reaction and wait for the product to cool. Then crush the product into 10-100 mesh particles and dry it to obtain hyperbranched polyester polyol with a molecular weight of 500-10000.

4. The method for preparing a modified polylactic acid-glycolic acid copolymer according to claim 2, characterized in that, The functional branching agent is an amination-treated nanoparticle with a molecular weight of 200-20000. The nanoparticles are selected from siloxane nanoparticles with a particle size of 10-500 nm. The preparation of the amination-treated nanoparticles includes the following steps: (s1) Add the silane coupling agent and concentrated hydrochloric acid at a molar fraction of 0.05% to 0.5% relative to the silane coupling agent to a low-carbon alcohol solvent and stir magnetically; (s2) The reaction system was continuously stirred magnetically for 3 to 15 days at room temperature and pressure. Excess solvent was removed by rotary evaporation until precipitation occurred. The precipitate was filtered and dried at 50 to 70°C to obtain white granules. (s3) The resulting white particles were redissolved in a low-carbon alcohol solvent and then passed through a column filled with anion exchange resin to obtain a nanoparticle mixed solution. The nanoparticle mixture obtained by (s4) is dried by rotary evaporation at 30-50℃ to obtain aminated siloxane nanoparticles with a molecular weight of 200-20000.

5. The method for preparing a modified polylactic acid-glycolic acid copolymer according to claim 2, characterized in that, The functional branching agent is a carboxyl-terminated hyperbranched polyamide with a molecular weight of 300-30000. The preparation of the carboxyl-terminated hyperbranched polyamide with a molecular weight of 300-30000 includes the following steps: (s1) Under a nitrogen atmosphere, a polar aprotic solvent, triphenyl phosphite and pyridine are mixed evenly to obtain a mixture, wherein the molar ratio of triphenyl phosphite and pyridine is 1:1; (s2) Mix the polybasic acid / anhydride and the diamine with the mixture from step (s1) at a molar ratio of 0.5% to 5% excess carboxyl group, and mix them evenly at 60 to 90°C. The molar ratio of the sum of the molar amounts of triphenyl phosphite and pyridine to the molar ratio of the diamine is 0.01% to 0.1%. (s3) Heat the reaction system to 130-150℃ and continue the reaction for 4-10 hours; (s4) After the reaction is complete, the reaction solution is poured into water to precipitate, filtered and dried to obtain carboxyl-terminated hyperbranched polyamides with a molecular weight of 300 to 30,000.

6. The method for preparing a modified polylactic-co-glycolic acid according to any one of claims 1 to 5, characterized in that, The molar ratio of glycolic acid monomers to lactic acid monomers is 50:50 to 90:10, and the molar amount of the functional branching agent is 0.1% to 3% of the total molar amount of glycolic acid monomers and lactic acid monomers. The chain extender includes one or more of the following substances: isocyanates, epoxides, and oxazoline compounds, and the amount of the chain extender added is 1 wt% to 10 wt% of the pulverized material.

7. The method for preparing a modified polylactic acid-glycolic acid copolymer according to claim 6, characterized in that, Step (1) specifically includes: (s1) Heat the reaction apparatus to 60-100°C, introduce an inert gas for protection, add glycolic acid monomers, lactic acid monomers, functional branching agents and catalysts, and stir to mix evenly. (s2) Increase the temperature of the reaction apparatus and react at 110℃~170℃ for 2~8h. When the volume or weight of the by-product reaches 60~90% of the theoretical volume or weight, the esterification reaction or transesterification reaction is terminated. (s3) Vacuum is drawn at a rate of 0.1 to 10 kPa / min, and the polycondensation reaction temperature is increased and controlled at 170 to 220°C and a vacuum degree of 30 to 500 Pa. The reaction is continued for 2 to 16 hours to prepare PLGA polymer melt.

8. The method for preparing a modified polylactic acid-glycolic acid copolymer according to claim 6, characterized in that, The particle size of the pulverized material obtained in step (2) is 10 to 100 mesh; In step (3), the pulverized material, functional additives and chain extender are melt-blended at a temperature of 130 to 220°C and reacted for 0.5 to 5 minutes to obtain modified polylactic acid-hydroxyacetic acid copolymer.

9. A modified polylactic-co-glycolic acid polymer, characterized in that, Prepared using the preparation method described in any one of claims 1-8.

10. Use of the modified polylactic-glycolic acid copolymer prepared by the preparation method according to any one of claims 1 to 8, characterized in that, The modified polylactic acid-glycolic acid copolymer is used in the field of biodegradable and recyclable materials.

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