阅读说明：本技术 一种共聚聚乳酸及其制备方法 (Copolymerized polylactic acid and preparation method thereof ) 是由 李文刚 范红卫 王丽丽 尚束元 孙文路 尹立新 魏存宏 于 2020-12-29 设计创作，主要内容包括：本发明涉及一种共聚聚乳酸及其制备方法,将乳酸、2,4-吡啶二甲酸、乙二醇和氯化锌混合均匀后先后进行酯化反应和缩聚反应制得共聚聚乳酸；制得的共聚聚乳酸包括乳酸链段、2,4-吡啶二甲酸链段和乙二醇链段,且不同2,4-吡啶二甲酸链段之间经Zn～(2+)配位；乳酸链段、2,4-吡啶二甲酸链段和乙二醇链段的摩尔比为1:0.05～0.07:1.30～1.40；2,4-吡啶二甲酸链段参与配位的有羰基上的O原子和吡啶上的N原子。本发明的一种共聚聚乳酸的制备方法,通过Zn～(+2)与吡啶形成配位键增大了交联密度,使得聚乳酸的玻璃化温度从55～60℃增加到68～73℃,减弱了聚乳酸干燥时发粘的程度,扩大了应用范围。(The invention relates to a copolymerized polylactic acid and its preparation method, mix lactic acid, 2, 4-pyridine dicarboxylic acid, ethanediol and zinc chloride, carry on esterification reaction and polycondensation reaction to get copolymerized polylactic acid sequentially; the prepared copolymerized polylactic acid comprises a lactic acid chain segment, a 2, 4-pyridinedicarboxylic acid chain segment and an ethylene glycol chain segment, and Zn is arranged between different 2, 4-pyridinedicarboxylic acid chain segments 2+ Coordination; the molar ratio of the lactic acid chain segment to the 2, 4-pyridinedicarboxylic acid chain segment to the ethylene glycol chain segment is 1: 0.05-0.07: 1.30-1.40; the 2, 4-pyridinedicarboxylic acid segment is coordinated by an O atom on the carbonyl group and an N atom on the pyridine. The invention relates to a preparation method of copolymerized polylactic acid, which is implemented by Zn +2 The coordination bond formed with pyridine increases the crosslinking density, increases the glass transition temperature of the polylactic acid from 55-60 ℃ to 68-73 ℃, weakens the degree of stickiness of the polylactic acid during drying, and expands the application range.)

1. A copolymerized polylactic acid, characterized in that: comprises a lactic acid chain segment, a 2, 4-pyridinedicarboxylic acid chain segment and an ethylene glycol chain segment, and Zn is arranged between different 2, 4-pyridinedicarboxylic acid chain segments²⁺Coordination;

the molar ratio of the lactic acid chain segment to the 2, 4-pyridinedicarboxylic acid chain segment to the ethylene glycol chain segment is 1: 0.05-0.07: 1.30-1.40;

the 2, 4-pyridinedicarboxylic acid chain segment is coordinated with an O atom on a carbonyl group and an N atom on pyridine;

the glass transition temperature of the copolymerized polylactic acid is 68-73 ℃.

2. The polylactic acid copolymer according to claim 1, wherein the segments of different 2, 4-pyridinedicarboxylic acids are Zn-doped²⁺The coordination structure formed by coordination is as follows:

3. a preparation method of copolymerized polylactic acid is characterized in that: lactic acid, 2, 4-pyridinedicarboxylic acid, ethylene glycol and zinc chloride are uniformly mixed and then subjected to esterification reaction and polycondensation reaction in sequence to prepare the copolymerized polylactic acid.

4. The method for preparing copolymerized polylactic acid according to claim 3, wherein the steps of preparing copolymerized polylactic acid are as follows:

(1) performing esterification reaction;

preparing lactic acid, 2, 4-pyridinedicarboxylic acid and ethylene glycol into slurry, adding a catalyst and zinc chloride, uniformly mixing, pressurizing in a nitrogen atmosphere to perform esterification reaction, wherein the pressurizing pressure is 0.3-0.5 MPa, the temperature of the esterification reaction is 220-230 ℃, and the termination condition of the esterification reaction is as follows: the distilled amount of water in the esterification reaction reaches more than 95 percent of a theoretical value;

(2) performing polycondensation reaction;

and after the esterification reaction is finished, starting the polycondensation reaction in a low vacuum stage under the condition of negative pressure, stably pumping the pressure in the stage from normal pressure to below 500Pa in 50-70 min at the reaction temperature of 260-270 ℃ for 80-100 min, then continuously pumping the vacuum to perform the polycondensation reaction in a high vacuum stage, further reducing the reaction pressure to below 50Pa, controlling the reaction temperature of 270-275 ℃ and the reaction time of 100-120 min, and purifying the obtained product to obtain the copolymerized polylactic acid.

5. The method for preparing polylactic acid copolymer according to claim 4, wherein the molar ratio of lactic acid, pyridine dicarboxylic acid and ethylene glycol is 1: 0.05-0.07: 1.30-1.40, the amount of catalyst added is 0.3-0.5 wt% of the amount of terephthalic acid added; the adding amount of the zinc chloride is 0.5-0.6 mol% of the adding amount of the 2, 4-pyridinedicarboxylic acid.

6. The method for preparing copolymerized polylactic acid according to claim 5, wherein the catalyst is stannous chloride.

Technical Field

The invention belongs to the technical field of polylactic acid, and relates to copolymerized polylactic acid and a preparation method thereof.

Background

The polylactic acid is a green functional polymer material with good biocompatibility and biodegradability, which is polymerized by micromolecule lactic acid generated by microbial fermentation of biomass raw materials (such as corn starch and the like), can be completely degraded into water and carbon dioxide, is more consistent with the concepts of circular economy and sustainable development compared with petroleum-based general plastics, is easy to degrade, does not cause environmental pollution, and can fundamentally solve the problems of cost rise caused by petroleum resource exhaustion and environmental pollution treatment. Polylactic acids and their copolymers have received a great deal of attention from textile, biomedical and pharmaceutical industries. The reasons for this are mainly the following, which can be made from renewable resources such as starch; has good mechanical properties, and can be compared favorably with the commercialized high polymer; they can be degraded not only in natural environment but also in human body; the degraded product lactic acid and its oligomer have low toxicity in human body and natural environment.

With the continuous and intensive research of researchers, PLA products have been widely used in the fields of medicine (surgical sutures, bone anchors, surgical adhesives, artificial blood vessels, various biological scaffolds, drug sustained-release carriers, tissue engineering, etc.), packaging materials, textiles, daily necessities, industrial products, etc.

However, in the application and processing process, the polylactic acid is often required to be dried, and the polylactic acid is sticky during drying and difficult to produce due to the low glass transition temperature of the polylactic acid, usually lower than 60 ℃, and more usually about 55 ℃, and the low crystallinity of the polylactic acid.

In order to achieve wider application fields of polylactic acid, the polylactic acid needs to be subjected to copolymerization modification, so that a more convenient method is provided for polylactic acid processing.

Disclosure of Invention

The invention aims to solve the problem that in the prior art, the polylactic acid has a serious sticky phenomenon in the drying process in the application and processing process due to low glass transition temperature, and provides a copolymerized polylactic acid and a preparation method thereof.

The invention adopts the coordination technology to modify the polylactic acid, improves the glass transition temperature, solves the problem of serious stickiness of the polylactic acid when the polylactic acid is dried, and widens the application field of the polylactic acid.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

the copolymerized polylactic acid comprises a lactic acid chain segment, a 2, 4-pyridinedicarboxylic acid chain segment and an ethylene glycol chain segment, wherein Zn is arranged between different 2, 4-pyridinedicarboxylic acid chain segments²⁺Coordination;

the molar ratio of the lactic acid chain segment to the 2, 4-pyridinedicarboxylic acid chain segment to the ethylene glycol chain segment is 1: 0.05-0.07: 1.30-1.40;

the 2, 4-pyridinedicarboxylic acid chain segment is coordinated with an O atom on a carbonyl group and an N atom on pyridine;

the glass transition temperature of the copolymerized polylactic acid is 68-73 ℃.

Zn of the invention⁺²The coordination bond is formed with pyridine, the physical crosslinking point and intermolecular action in the polylactic acid are enhanced, the chain segment movement is restricted with the increase of the crosslinking density, the chain movement is difficult, higher temperature is needed to stimulate the molecular chain movement, the glass transition temperature of the material in the area is increased, the Tg of the polylactic acid is increased to a certain degree, the Tg is increased from 55-60 ℃ to 68-73 ℃, and the drying temperature can be increased when the polylactic acid is dried, so that the degree of stickiness when the polylactic acid is dried is reduced. Meanwhile, the Tg of the polylactic acid is improved, so that the application field of the polylactic acid is wider.

As a preferred technical scheme:

the above-mentioned copolymerized polylactic acid has Zn layers between different 2, 4-pyridinedicarboxylic acid segments²⁺The coordination structure formed by coordination is as follows:

the invention also provides a preparation method of the copolymerized polylactic acid, which is characterized in that lactic acid, 2, 4-pyridinedicarboxylic acid, ethylene glycol and zinc chloride are uniformly mixed and then are subjected to esterification reaction and polycondensation reaction in sequence to prepare the copolymerized polylactic acid.

As a preferred technical scheme:

the preparation method of the copolymerized polylactic acid comprises the following steps:

(1) performing esterification reaction;

preparing lactic acid, 2, 4-pyridinedicarboxylic acid and ethylene glycol into slurry, adding a catalyst and zinc chloride, uniformly mixing, pressurizing in a nitrogen atmosphere to perform esterification reaction, wherein the pressurizing pressure is 0.3-0.5 MPa, the temperature of the esterification reaction is 220-230 ℃, and the termination condition of the esterification reaction is as follows: the distilled amount of water in the esterification reaction reaches more than 95 percent of a theoretical value;

(2) performing polycondensation reaction;

and after the esterification reaction is finished, starting the polycondensation reaction in a low vacuum stage under the condition of negative pressure, stably pumping the pressure in the stage from normal pressure to below 500Pa in 50-70 min at the reaction temperature of 260-270 ℃ for 80-100 min, then continuously pumping the vacuum to perform the polycondensation reaction in a high vacuum stage, further reducing the reaction pressure to below 50Pa, controlling the reaction temperature of 270-275 ℃ and the reaction time of 100-120 min, and purifying the obtained product to obtain the copolymerized polylactic acid.

According to the preparation method of the copolymerized polylactic acid, the molar ratio of the lactic acid to the pyridine dicarboxylic acid to the ethylene glycol is 1: 0.05-0.07: 1.30-1.40, and the addition amount of the catalyst is 0.3-0.5 wt% of that of the terephthalic acid; the adding amount of the zinc chloride is 0.5-0.6 mol% of the adding amount of the 2, 4-pyridinedicarboxylic acid.

In the preparation method of the copolymerized polylactic acid, the catalyst is stannous chloride.

The mechanism of the invention is as follows:

the polylactic acid molecular chains are linearly arranged, and the chain segments of the polylactic acid molecular chains are not supported by firmer cross-linking nodes, so that the mechanical properties of the polylactic acid molecular chains are inevitably influenced when the polylactic acid molecular chains are heated. The cross-linking points can be chemical cross-linking points or physical cross-linking points, wherein the chemical cross-linking structures form stable intramolecular chemical bonds, and the physical cross-linking structures comprise hydrogen bonds, ionic bonds, coordination bonds and the like.

The glass transition temperature is an important characteristic parameter of a material, and many properties of the material change sharply around the glass transition temperature. In the case of high polymer, it is the temperature at which the high polymer changes from a glassy state to a highly elastic state, and at the glass transition temperature, the specific heat capacity, thermal expansion coefficient, viscosity, free volume, and elastic modulus of the high polymer all undergo a sudden change. In terms of molecular structure, the glass transition temperature is a relaxation phenomenon of the amorphous portion of the polymer from a frozen state to a thawed state. Below the glass transition temperature, the polymer is in a glassy state, the molecular chain and the chain segment cannot move, and only the atoms (or groups) forming the molecules vibrate at the equilibrium positions; at the glass transition temperature, the molecular chain cannot move, but the chain starts to move, and the polymer exhibits high elasticity.

Zn of the invention⁺²The coordination bond is formed with pyridine, the physical crosslinking point and intermolecular action in the polylactic acid are enhanced, the chain segment movement is restricted with the increase of the crosslinking density, the chain movement is difficult, higher temperature is needed to stimulate the molecular chain movement, the glass transition temperature of the material in the area is increased, the Tg of the polylactic acid is increased to a certain degree, the Tg is increased from 55-60 ℃ to 68-73 ℃, and the drying temperature can be increased when the polylactic acid is dried, so that the degree of stickiness when the polylactic acid is dried is reduced. Meanwhile, the Tg of the polylactic acid is improved, so that the application field of the polylactic acid is wider.

Has the advantages that:

(1) the invention relates to a preparation method of copolymerized polylactic acid, which is implemented by Zn⁺²Forming a coordination bond with pyridine to increase the crosslinking density, so that the glass transition temperature of the polylactic acid is increased from 55-60 ℃ to 68-73 ℃, and the degree of stickiness of the polylactic acid during drying is weakened;

(2) the copolymerized polylactic acid prepared by the method has wider application field.

Detailed Description

The invention will be further illustrated with reference to specific embodiments. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.

Example 1

A preparation method of copolymerized polylactic acid comprises the following specific steps:

(1) performing esterification reaction;

preparing lactic acid, 2, 4-pyridinedicarboxylic acid and ethylene glycol into slurry according to the molar ratio of 1:0.05:1.30, adding a catalyst (stannous chloride) and zinc chloride, uniformly mixing, wherein the adding amount of the catalyst is 0.3 wt% of the adding amount of the terephthalic acid, the adding amount of the zinc chloride is 0.5 mol% of the adding amount of the 2, 4-pyridinedicarboxylic acid, then pressurizing in a nitrogen atmosphere to carry out esterification reaction, the pressurizing pressure is 0.3MPa, the temperature of the esterification reaction is 220 ℃, and the termination condition of the esterification reaction is as follows: the distilled water amount in the esterification reaction reaches 95 percent of a theoretical value;

(2) performing polycondensation reaction;

after the esterification reaction is finished, starting the polycondensation reaction in the low vacuum stage under the negative pressure condition, stably pumping the pressure in the stage from normal pressure to the absolute pressure of 500Pa within 50min, controlling the reaction temperature to be 260 ℃ and the reaction time to be 80min, then continuing to pump vacuum, carrying out the polycondensation reaction in the high vacuum stage, further reducing the reaction pressure to the absolute pressure of 50Pa, controlling the reaction temperature to be 270 ℃ and the reaction time to be 100min, and purifying the obtained product to obtain the copolymerized polylactic acid.

The prepared copolymerized polylactic acid comprises a lactic acid chain segment, a 2, 4-pyridinedicarboxylic acid chain segment and an ethylene glycol chain segment in a molar ratio of 1:0.05: 1.30; zn is arranged between different 2, 4-pyridine dicarboxylic acid chain segments²⁺The 2, 4-pyridinedicarboxylic acid chain segment is coordinated with O atoms on carbonyl groups and N atoms on pyridine, and the coordination structure formed by coordination is as follows:the glass transition temperature of the copolymerized polylactic acid is 68 ℃.

A preparation method of copolymerized polylactic acid comprises the following specific steps:

(1) performing esterification reaction;

preparing lactic acid, 2, 4-pyridinedicarboxylic acid and ethylene glycol into slurry according to the molar ratio of 1:0.06:1.30, adding a catalyst (stannous chloride) and zinc chloride, uniformly mixing, wherein the adding amount of the catalyst is 0.3 wt% of the adding amount of the terephthalic acid, the adding amount of the zinc chloride is 0.5 mol% of the adding amount of the 2, 4-pyridinedicarboxylic acid, then pressurizing in a nitrogen atmosphere to carry out esterification reaction, the pressurizing pressure is 0.3MPa, the temperature of the esterification reaction is 222 ℃, and the termination condition of the esterification reaction is as follows: the distilled water amount in the esterification reaction reaches 95 percent of a theoretical value;

(2) performing polycondensation reaction;

after the esterification reaction is finished, starting the polycondensation reaction in the low vacuum stage under the negative pressure condition, stably pumping the pressure in the stage from normal pressure to absolute pressure of 490Pa within 53min, controlling the reaction temperature to be 262 ℃, controlling the reaction time to be 83min, then continuing to pump vacuum, carrying out the polycondensation reaction in the high vacuum stage, further reducing the reaction pressure to absolute pressure of 30Pa, controlling the reaction temperature to be 271 ℃, controlling the reaction time to be 102min, and purifying the obtained product to obtain the copolymerized polylactic acid.

The prepared copolymerized polylactic acid comprises a lactic acid chain segment, a 2, 4-pyridinedicarboxylic acid chain segment and an ethylene glycol chain segment in a molar ratio of 1:0.06: 1.30; zn is arranged between different 2, 4-pyridine dicarboxylic acid chain segments²⁺The 2, 4-pyridinedicarboxylic acid chain segment is coordinated with O atoms on carbonyl groups and N atoms on pyridine, and the coordination structure formed by coordination is as follows:the glass transition temperature of the copolymerized polylactic acid is 69 ℃.

A preparation method of copolymerized polylactic acid comprises the following specific steps:

(1) performing esterification reaction;

preparing lactic acid, 2, 4-pyridinedicarboxylic acid and ethylene glycol into slurry according to the molar ratio of 1:0.07:1.30, adding a catalyst (stannous chloride) and zinc chloride, uniformly mixing, wherein the adding amount of the catalyst is 0.4 wt% of the adding amount of the terephthalic acid, the adding amount of the zinc chloride is 0.5 mol% of the adding amount of the 2, 4-pyridinedicarboxylic acid, then pressurizing in a nitrogen atmosphere to carry out esterification reaction, the pressurizing pressure is 0.4MPa, the temperature of the esterification reaction is 224 ℃, and the termination condition of the esterification reaction is as follows: the distilled water amount in the esterification reaction reaches 96 percent of a theoretical value;

(2) performing polycondensation reaction;

after the esterification reaction is finished, starting the polycondensation reaction in the low vacuum stage under the negative pressure condition, stably pumping the pressure in the stage from normal pressure to absolute pressure of 480Pa within 56min, controlling the reaction temperature to 264 ℃ and the reaction time to 85min, then continuing to pump vacuum, carrying out the polycondensation reaction in the high vacuum stage, further reducing the reaction pressure to absolute pressure of 20Pa, controlling the reaction temperature to 272 ℃ and the reaction time to 104min, and purifying the obtained product to obtain the copolymerized polylactic acid.

The prepared copolymerized polylactic acid comprises a lactic acid chain segment, a 2, 4-pyridinedicarboxylic acid chain segment and an ethylene glycol chain segment in a molar ratio of 1:0.07: 1.30; zn is arranged between different 2, 4-pyridine dicarboxylic acid chain segments²⁺The 2, 4-pyridinedicarboxylic acid chain segment is coordinated with O atoms on carbonyl groups and N atoms on pyridine, and the coordination structure formed by coordination is as follows:the glass transition temperature of the copolymerized polylactic acid is 70 ℃.

A preparation method of copolymerized polylactic acid comprises the following specific steps:

(1) performing esterification reaction;

preparing lactic acid, 2, 4-pyridinedicarboxylic acid and ethylene glycol into slurry according to the molar ratio of 1:0.05:1.40, adding a catalyst (stannous chloride) and zinc chloride, uniformly mixing, wherein the adding amount of the catalyst is 0.4 wt% of the adding amount of the terephthalic acid, the adding amount of the zinc chloride is 0.6 mol% of the adding amount of the 2, 4-pyridinedicarboxylic acid, then pressurizing in a nitrogen atmosphere to carry out esterification reaction, the pressurizing pressure is 0.4MPa, the temperature of the esterification reaction is 226 ℃, and the termination condition of the esterification reaction is as follows: the distilled water amount in the esterification reaction reaches 96 percent of a theoretical value;

(2) performing polycondensation reaction;

after the esterification reaction is finished, starting the polycondensation reaction in the low vacuum stage under the negative pressure condition, smoothly pumping the pressure in the stage from normal pressure to absolute pressure of 440Pa within 59min, controlling the reaction temperature to 266 ℃ and the reaction time to 88min, then continuing to pump vacuum, carrying out the polycondensation reaction in the high vacuum stage, further reducing the reaction pressure to absolute pressure of 18Pa, controlling the reaction temperature to 273 ℃ and the reaction time to 106min, and purifying the obtained product to obtain the copolymerized polylactic acid.

The prepared copolymerized polylactic acid comprises a lactic acid chain segment, a 2, 4-pyridinedicarboxylic acid chain segment and an ethylene glycol chain segment in a molar ratio of 1:0.05: 1.40; zn is arranged between different 2, 4-pyridine dicarboxylic acid chain segments²⁺The 2, 4-pyridinedicarboxylic acid chain segment is coordinated with O atoms on carbonyl groups and N atoms on pyridine, and the coordination structure formed by coordination is as follows:the glass transition temperature of the copolymerized polylactic acid is 71 ℃.

A preparation method of copolymerized polylactic acid comprises the following specific steps:

(1) performing esterification reaction;

preparing lactic acid, 2, 4-pyridinedicarboxylic acid and ethylene glycol into slurry according to the molar ratio of 1:0.06:1.4, adding a catalyst (stannous chloride) and zinc chloride, uniformly mixing, wherein the adding amount of the catalyst is 0.45 wt% of the adding amount of the terephthalic acid, the adding amount of the zinc chloride is 0.6 mol% of the adding amount of the 2, 4-pyridinedicarboxylic acid, then pressurizing in a nitrogen atmosphere to carry out esterification reaction, the pressurizing pressure is 0.5MPa, the temperature of the esterification reaction is 228 ℃, and the termination condition of the esterification reaction is as follows: the distilled water amount in the esterification reaction reaches 97 percent of the theoretical value;

(2) performing polycondensation reaction;

after the esterification reaction is finished, starting the polycondensation reaction in the low vacuum stage under the negative pressure condition, stably pumping the pressure in the stage from normal pressure to absolute pressure of 400Pa within 62min, controlling the reaction temperature to 268 ℃ and the reaction time to 90min, then continuing to pump vacuum, carrying out the polycondensation reaction in the high vacuum stage, further reducing the reaction pressure to absolute pressure of 18Pa, controlling the reaction temperature to 274 ℃ and the reaction time to 110min, and purifying the obtained product to obtain the copolymerized polylactic acid.

The copolymer emulsion is preparedAn acid comprising a lactic acid segment, a 2, 4-pyridinedicarboxylic acid segment, and an ethylene glycol segment in a molar ratio of 1:0.06: 1.4; zn is arranged between different 2, 4-pyridine dicarboxylic acid chain segments²⁺The 2, 4-pyridinedicarboxylic acid chain segment is coordinated with O atoms on carbonyl groups and N atoms on pyridine, and the coordination structure formed by coordination is as follows:the glass transition temperature of the copolymerized polylactic acid is 72 ℃.

A preparation method of copolymerized polylactic acid comprises the following specific steps:

(1) performing esterification reaction;

preparing lactic acid, 2, 4-pyridinedicarboxylic acid and ethylene glycol into slurry according to the molar ratio of 1:0.07:1.40, adding a catalyst (stannous chloride) and zinc chloride, uniformly mixing, wherein the adding amount of the catalyst is 0.5 wt% of the adding amount of the terephthalic acid, the adding amount of the zinc chloride is 0.6 mol% of the adding amount of the 2, 4-pyridinedicarboxylic acid, then pressurizing in a nitrogen atmosphere to carry out esterification reaction, the pressurizing pressure is 0.5MPa, the temperature of the esterification reaction is 230 ℃, and the termination condition of the esterification reaction is as follows: the distilled water amount in the esterification reaction reaches 97 percent of the theoretical value;

(2) performing polycondensation reaction;

after the esterification reaction is finished, starting the polycondensation reaction in the low vacuum stage under the negative pressure condition, stably pumping the pressure in the stage from normal pressure to the absolute pressure of 350Pa within 66min, controlling the reaction temperature to 269 ℃, controlling the reaction time to 95min, then continuing to pump vacuum, carrying out the polycondensation reaction in the high vacuum stage, further reducing the reaction pressure to the absolute pressure of 17Pa, controlling the reaction temperature to 274 ℃, controlling the reaction time to 115min, and purifying the obtained product to obtain the copolymerized polylactic acid.

The prepared copolymerized polylactic acid comprises a lactic acid chain segment, a 2, 4-pyridinedicarboxylic acid chain segment and an ethylene glycol chain segment in a molar ratio of 1:0.07: 1.40; zn is arranged between different 2, 4-pyridine dicarboxylic acid chain segments²⁺The 2, 4-pyridinedicarboxylic acid chain segment is coordinated with O atoms on carbonyl groups and N atoms on pyridine, and the coordination structure formed by coordination is as follows:the glass transition temperature of the copolymerized polylactic acid is 73 ℃.

A preparation method of copolymerized polylactic acid comprises the following specific steps:

(1) performing esterification reaction;

preparing lactic acid, 2, 4-pyridinedicarboxylic acid and ethylene glycol into slurry according to the molar ratio of 1:0.07:1.40, adding a catalyst (stannous chloride) and zinc chloride, uniformly mixing, wherein the adding amount of the catalyst is 0.5 wt% of the adding amount of the terephthalic acid, the adding amount of the zinc chloride is 0.6 mol% of the adding amount of the 2, 4-pyridinedicarboxylic acid, then pressurizing in a nitrogen atmosphere to carry out esterification reaction, the pressurizing pressure is 0.5MPa, the temperature of the esterification reaction is 230 ℃, and the termination condition of the esterification reaction is as follows: the distilled water amount in the esterification reaction reaches 98 percent of the theoretical value;

(2) performing polycondensation reaction;

after the esterification reaction is finished, starting the polycondensation reaction in the low vacuum stage under the negative pressure condition, stably pumping the pressure in the stage from normal pressure to absolute pressure of 300Pa within 70min, controlling the reaction temperature to be 270 ℃ and the reaction time to be 100min, then continuing to pump vacuum, carrying out the polycondensation reaction in the high vacuum stage, further reducing the reaction pressure to absolute pressure of 15Pa, controlling the reaction temperature to be 275 ℃ and the reaction time to be 120min, and purifying the obtained product to obtain the copolymerized polylactic acid.

The prepared copolymerized polylactic acid comprises a lactic acid chain segment, a 2, 4-pyridinedicarboxylic acid chain segment and an ethylene glycol chain segment in a molar ratio of 1:0.07: 1.40; zn is arranged between different 2, 4-pyridine dicarboxylic acid chain segments²⁺The 2, 4-pyridinedicarboxylic acid chain segment is coordinated with O atoms on carbonyl groups and N atoms on pyridine, and the coordination structure formed by coordination is as follows:the glass transition temperature of the copolymerized polylactic acid is 73 ℃.