PET-PGA copolyester and preparation method thereof

Abstract

The present invention relates to the technical field of polyester synthesis, and discloses a PET-PGA copolyester and a preparation method thereof, the copolyester is copolymerized from modified PGA, terephthalic acid and ethylene glycol, the modified PGA is prepared from glycollic acid, a catalyst and a chain extender, a benzene ring group in the chain extender can improve the chain segment rigidity of polyglycolic acid, and the polyglycolic acid can improve the rigidity of the polyglycolic acid; the phosphate structure can improve the thermal stability of polyglycolic acid, the combination of the phosphate structure and the polyglycolic acid can significantly reduce the thermal decomposition effect of PGA, the content of PGA in PET-PGA copolyester can be significantly increased, the utilization rate of raw materials is increased, and thus the production cost is reduced; in addition, the modified PGA can also significantly improve the flame retardant property of the PET-PGA copolyester.

Description

Technical Field

[0001] The invention relates to the technical field of polyester synthesis, in particular to a PET-PGA copolyester and a preparation method thereof. Background Art

[0002] Polyethylene terephthalate (PET) is a non-toxic, transparent and thermodynamically stable polymer material, which is widely used in textile, food, packaging, medicine, information and electronics. Although PET is non-toxic, it is extremely difficult to decompose in the natural environment and causes great pollution to the environment. Therefore, it is of great significance to study degradable PET.

[0003] Currently, biodegradable polyesters are produced by copolymerizing or blending easily degradable aliphatic monomers or polymers into the polyester system to adjust the degradation performance. Polyglycolic acid, as an easily degradable aliphatic polymer, is often used in the degradation modification of polymers.

[0004] CN11423569A discloses an antibacterial and degradable polyethylene terephthalate copolyester and a preparation method thereof. The invention first synthesizes low molecular weight polyglycolic acid, and then reacts the low molecular weight polyglycolic acid with dimethyl terephthalate, ethylene glycol, and an antibacterial agent to obtain the copolyester. Although this method achieves the regulation of the degradability of the copolyester by adjusting the amount of polyglycolic acid added, its mechanical properties are poor.

[0005] CN113698585A discloses a method for preparing a biodegradable glycolide-(alicyclic-co-aromatic)-glycolide block copolyester, which is obtained by copolymerizing alicyclic dibasic acid, aromatic dibasic acid and ethylene glycol, and further ring-opening glycolide, taking into account the degradation performance and mechanical properties of the copolyester. However, under high temperature and high vacuum, the polyglycolic acid molecules have poor thermal stability and are easily decomposed into monomer molecules and extracted from the reaction system, resulting in a low content of polyglycolic acid in the copolyester component and low monomer utilization, thereby increasing production costs. In addition, the copolyester has poor flame retardancy, which limits its scope of application. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a PET-PGA copolyester and a preparation method thereof. The copolyester is synthesized by copolymerizing modified PGA, terephthalic acid and ethylene glycol. The modified PGA is made of glycolic acid, a catalyst and a chain extender. The benzene ring group in the chain extender can improve the segment rigidity of polyglycolic acid, and the phosphate structure can improve the thermal stability of polyglycolic acid. The combination of the two can significantly reduce the thermal decomposition of PGA, significantly increase the content of PGA in the PET-PGA copolyester, improve the utilization rate of raw materials, and thus reduce production costs. In addition, the modified PGA can also significantly improve the flame retardant properties of the PET-PGA copolyester.

[0007] The specific technical scheme of the present invention is: A PET-PGA copolyester, the raw materials include modified PGA, terephthalic acid and ethylene glycol, the raw materials of the modified PGA include a chain extender and glycolic acid, the chemical formula of the chain extender is

[0008] Preferably, the mass ratio of the chain extender to glycolic acid is 0.05 to 1:100.

[0009] Preferably, the molar ratio of glycolic acid, terephthalic acid and ethylene glycol is 1:1.0-1.8:1.5-3.

[0010] The invention provides a PET-PGA copolyester. The copolyester is copolymerized with modified PGA, terephthalic acid and ethylene glycol as raw materials, wherein PGA is a polymer synthesized by using a chain extender and glycolic acid. The chain extender used in the invention is a polymer made of a polymerizable low eutectic solvent, and its molecular structure contains a phosphate structure and a benzene ring group. The benzene ring group can significantly improve the rigidity of the PGA chain segment, and the phosphate structure can significantly improve the thermal stability of the PGA chain segment. The combination of the two can significantly reduce the thermal decomposition effect of PGA, significantly improve the utilization rate of PGA, and significantly reduce the production cost. In addition, the modified PGA of the invention can also significantly improve the flame retardant performance of the PET-PGA copolyester, thereby expanding the application range of the PET-PGA copolyester.

[0011] A method for preparing the above-mentioned PET-PGA copolyester comprises the following steps: (1) adding terephthalic acid and ethylene glycol into a reaction vessel and heating the vessel to carry out esterification reaction to generate polymerization monomers; (2) adding glycolic acid and a catalyst into a reaction vessel and heating the vessel to carry out an esterification reaction of PGA to produce low molecular weight PGA, and then adding a chain extender to carry out a polycondensation reaction with the low molecular weight PGA to produce modified PGA; (3) The polymerizable monomers in step (1) and the modified PGA in step (2) are uniformly mixed and subjected to polycondensation reaction to prepare PET-PGA copolyester.

[0012] Preferably, the chain extender comprises the following preparation steps: reacting methyl dichlorophosphate, benzyl alcohol, cyclohexane and stannous chloride at 80-120° C. to prepare an intermediate product, and reacting the intermediate product, ethanol oxide, a catalyst and an inhibitor at 60-90° C. to prepare the chain extender.

[0013] Preferably, the molar ratio of methyl dichlorophosphate to benzyl alcohol is 1:2-4; the molar ratio of the intermediate product to glycidol is 1:1-1.3.

[0014] Preferably, the inhibitor is one or more of 2,4-dimethyl-6-tert-butylphenol, 2,6-di-tert-butyl-tetramethylphenol, tetrachlorobenzoquinone and N-phenyl-α-naphthylamine; and the catalyst is one or more of sodium acetate, potassium acetate and potassium cyanide.

[0015] Preferably, the conditions for the esterification reaction in step (1) include: a temperature of 220 to 260°C.

[0016] Preferably, the conditions for the PGA esterification reaction in step (2) include: a temperature of 150 to 180° C. and a vacuum degree of -50 to 0 KPa; the conditions for the high vacuum polymerization reaction include: a temperature of 180 to 220° C. and a vacuum degree of 0 to 100 Pa.

[0017] Preferably, the conditions for the polycondensation reaction in step (3) include: a temperature of 220 to 250° C. and a vacuum degree of 0 to 60 Pa.

[0018] Compared with the prior art, this application has the following technical effects: (1) The polyglycolic acid synthesized by the phosphoric acid ester chain extender is introduced into the copolyester of the present invention, which improves the biodegradability of the copolyester and the flame retardant property of the copolyester, thereby expanding its application range; (2) The preparation process of the chain extender is simple and convenient for industrial production; (3) A chain extender is synthesized for the chain growth polymerization reaction of polyglycolic acid. The chain extender introduces various functional groups such as aromatic rings and phosphate esters, thereby improving the thermal stability of polyglycolic acid in the copolyester, increasing the utilization rate of polyglycolic acid in the copolyester, and greatly reducing the production cost. DETAILED DESCRIPTION

[0019] The present invention will be further described below in conjunction with the embodiments.

[0020] Embodiment 1: A method for preparing PET-PGA copolyester comprises the following steps: (1) Preparation of a chain extender: 10 g of methyl dichlorophosphate, 15 g of benzyl alcohol and 200 ml of cyclohexane are added to a reaction container, 0.05 g of stannous chloride (catalyst) is added under mechanical stirring, the reaction is heated under reflux for 5 h, the intermediate product is cooled, and the intermediate product is separated by ether extraction, the product is washed three times with saturated sodium bicarbonate and then dried with anhydrous calcium chloride to obtain an intermediate product; the obtained intermediate product is mixed with 5 g of glycidol, 0.05 g of sodium acetate and 0.05 g of 2,4-dimethyl-6-tert-butylphenol, heated for 3 h and then distilled to obtain a chain extender; (2) Preparation of PET-PGA copolyester: 830 g of terephthalic acid and 403 g of ethylene glycol are added to a reaction vessel and heated to 250° C. for esterification reaction to produce ethylene terephthalate; 152 g of glycolic acid and 0.15 g of stannous octoate are added to a reaction vessel and heated to 160° C. for PGA esterification reaction; after the PGA esterification reaction is completed, the vessel is evacuated to -50 KPa for polymerization reaction to produce low molecular weight PGA, and then 0.29 g of a chain extender is added and polymerization reaction is carried out at 220° C. and 50 Pa to produce modified PGA; the prepared ethylene terephthalate and modified PGA are uniformly mixed and subjected to polycondensation reaction at 240° C. and 50 Pa vacuum conditions to produce PET-PGA copolyester.

[0021] Embodiment 2: A method for preparing PET-PGA copolyester comprises the following steps: (1) Preparation of a chain extender: 10 g of methyl dichlorophosphate, 15 g of benzyl alcohol and 200 ml of cyclohexane are added to a reaction container, 0.05 g of stannous chloride (catalyst) is added under mechanical stirring, the reaction is heated under reflux for 5 h, the intermediate product is cooled, and the intermediate product is separated by ether extraction, the product is washed three times with saturated sodium bicarbonate and then dried with anhydrous calcium chloride to obtain an intermediate product; the obtained intermediate product is mixed with 5 g of glycidol, 0.05 g of sodium acetate and 0.05 g of 2,4-dimethyl-6-tert-butylphenol, heated for 3 h and then distilled to obtain a chain extender; (2) Preparation of PET-PGA copolyester: 830 g of terephthalic acid and 403 g of ethylene glycol are added to a reaction vessel and heated to 250° C. for esterification reaction to produce ethylene terephthalate; 152 g of glycolic acid and 0.15 g of stannous octoate are added to a reaction vessel and heated to 160° C. for PGA esterification reaction; after the PGA esterification reaction is completed, the vessel is evacuated to -50 KPa for polymerization reaction to produce low molecular weight PGA; 0.87 g of a chain extender is added and polymerization reaction is carried out under the conditions of 220° C. and 50 Pa to produce modified PGA; the prepared ethylene terephthalate and modified PGA are uniformly mixed and subjected to polycondensation reaction under the conditions of 240° C. and 50 Pa vacuum to produce PET-PGA copolyester.

[0022] Embodiment 3: A method for preparing PET-PGA copolyester comprises the following steps: (1) Preparation of a chain extender: 10 g of methyl dichlorophosphate, 15 g of benzyl alcohol and 200 ml of cyclohexane are added to a reaction container, 0.05 g of stannous chloride (catalyst) is added under mechanical stirring, the reaction is heated under reflux for 5 h, the intermediate product is cooled, and the intermediate product is separated by ether extraction, the product is washed three times with saturated sodium bicarbonate and then dried with anhydrous calcium chloride to obtain an intermediate product; the obtained intermediate product is mixed with 5 g of glycidol, 0.05 g of sodium acetate and 0.05 g of 2,4-dimethyl-6-tert-butylphenol, heated for 3 h and then distilled to obtain a chain extender; (2) Preparation of PET-PGA copolyester: 830 g of terephthalic acid and 403 g of ethylene glycol are added to a reaction vessel and heated to 250° C. for esterification reaction to produce ethylene terephthalate; 152 g of glycolic acid and 0.15 g of stannous octoate are added to a reaction vessel and heated to 160° C. for PGA esterification reaction; after the PGA esterification reaction is completed, the vessel is evacuated to -50 KPa for polymerization reaction to produce low molecular weight PGA; 2.9 g of chain extender is added and polymerization reaction is carried out under the conditions of 220° C. and 50 Pa to produce modified PGA; the prepared ethylene terephthalate and modified PGA are uniformly mixed and subjected to polycondensation reaction under the conditions of 240° C. and 50 Pa vacuum to produce PET-PGA copolyester.

[0023] Embodiment 4: A method for preparing PET-PGA copolyester comprises the following steps: (1) Preparation of a chain extender: 10 g of methyl dichlorophosphate, 15 g of benzyl alcohol and 200 ml of cyclohexane are added to a reaction container, 0.05 g of stannous chloride (catalyst) is added under mechanical stirring, the reaction is heated under reflux for 5 h, the intermediate product is cooled, and the intermediate product is separated by ether extraction, the product is washed three times with saturated sodium bicarbonate and then dried with anhydrous calcium chloride to obtain an intermediate product; the obtained intermediate product is mixed with 5 g of glycidol, 0.05 g of sodium acetate and 0.05 g of 2,4-dimethyl-6-tert-butylphenol, heated for 3 h and then distilled to obtain a chain extender; (2) Preparation of PET-PGA copolyester: 830 g of terephthalic acid and 403 g of ethylene glycol are added to a reaction vessel and heated to 250° C. for esterification reaction to produce ethylene terephthalate; 152 g of glycolic acid and 1.5 g of stannous octoate are added to a reaction vessel and heated to 160° C. for PGA esterification reaction; after the PGA esterification reaction is completed, the vessel is evacuated to -50 KPa for polymerization reaction to produce low molecular weight PGA, and then 0.29 g of a chain extender is added and polymerization reaction is carried out under the conditions of 220° C. and 50 Pa to produce modified PGA; the prepared ethylene terephthalate and modified PGA are uniformly mixed and subjected to polycondensation reaction under the conditions of 240° C. and 50 Pa vacuum to produce PET-PGA copolyester.

[0024] Embodiment 5: A method for preparing PET-PGA copolyester comprises the following steps: (1) Preparation of a chain extender: 10 g of methyl dichlorophosphate, 15 g of benzyl alcohol and 200 ml of cyclohexane are added to a reaction container, 0.05 g of stannous chloride (catalyst) is added under mechanical stirring, the reaction is heated under reflux for 5 h, the intermediate product is cooled, and the intermediate product is separated by ether extraction, the product is washed three times with saturated sodium bicarbonate and then dried with anhydrous calcium chloride to obtain an intermediate product; the obtained intermediate product is mixed with 5 g of glycidol, 0.05 g of sodium acetate and 0.05 g of 2,4-dimethyl-6-tert-butylphenol, heated for 3 h and then distilled to obtain a chain extender; (2) Preparation of PET-PGA copolyester: 830 g of terephthalic acid and 403 g of ethylene glycol are added to a reaction vessel and heated to 250° C. for esterification reaction to produce ethylene terephthalate; 152 g of glycolic acid and 2 g of stannous octoate are added to a reaction vessel and heated to 160° C. for PGA esterification reaction; after the PGA esterification reaction is completed, the vessel is evacuated to -50 KPa for polymerization reaction to produce low molecular weight PGA, and then 0.29 g of a chain extender is added and polymerization reaction is carried out under the conditions of 220° C. and 50 Pa to produce modified PGA; the prepared ethylene terephthalate and modified PGA are uniformly mixed and subjected to polycondensation reaction under the conditions of 240° C. and 50 Pa vacuum to produce PET-PGA copolyester.

[0025] Embodiment 6: A method for preparing PET-PGA copolyester comprises the following steps: (1) Preparation of a chain extender: 10 g of methyl dichlorophosphate, 15 g of benzyl alcohol and 200 ml of cyclohexane are added to a reaction container, 0.05 g of stannous chloride (catalyst) is added under mechanical stirring, the reaction is heated under reflux for 5 h, the intermediate product is cooled, and the intermediate product is separated by ether extraction, the product is washed three times with saturated sodium bicarbonate and then dried with anhydrous calcium chloride to obtain an intermediate product; the obtained intermediate product is mixed with 5 g of glycidol, 0.05 g of sodium acetate and 0.05 g of 2,4-dimethyl-6-tert-butylphenol, heated for 3 h and then distilled to obtain a chain extender; (2) Preparation of PET-PGA copolyester: 830 g of terephthalic acid and 403 g of ethylene glycol are added to a reaction vessel and heated to 250° C. for esterification reaction to produce ethylene terephthalate; 152 g of glycolic acid and 2.5 g of stannous octoate are added to a reaction vessel and heated to 160° C. for PGA esterification reaction; after the PGA esterification reaction is completed, the vessel is evacuated to -50 KPa for polymerization reaction to produce low molecular weight PGA, and then 0.29 g of a chain extender is added and polymerization reaction is carried out under the conditions of 220° C. and 50 Pa to produce modified PGA; the prepared ethylene terephthalate and modified PGA are uniformly mixed and subjected to polycondensation reaction under the conditions of 240° C. and 50 Pa vacuum to produce PET-PGA copolyester.

[0026] Embodiment 7: A method for preparing PET-PGA copolyester comprises the following steps: (1) Preparation of a chain extender: 10 g of methyl dichlorophosphate, 15 g of benzyl alcohol and 200 ml of cyclohexane are added to a reaction container, 0.05 g of stannous chloride (catalyst) is added under mechanical stirring, the reaction is heated under reflux for 5 h, the intermediate product is cooled, and the intermediate product is separated by ether extraction, the product is washed three times with saturated sodium bicarbonate and then dried with anhydrous calcium chloride to obtain an intermediate product; the obtained intermediate product is mixed with 5 g of glycidol, 0.05 g of sodium acetate and 0.05 g of 2,4-dimethyl-6-tert-butylphenol, heated for 3 h and then distilled to obtain a chain extender; (2) Preparation of PET-PGA copolyester: 830 g of terephthalic acid and 403 g of ethylene glycol are added to a reaction vessel and heated to 250° C. for esterification reaction to produce ethylene terephthalate; 152 g of glycolic acid and 2.9 g of stannous octoate are added to a reaction vessel and heated to 160° C. for PGA esterification reaction; after the PGA esterification reaction is completed, the vessel is evacuated to -50 KPa for polymerization reaction to produce low molecular weight PGA, and then 0.29 g of a chain extender is added and polymerization reaction is carried out at 220° C. and 50 Pa to produce modified PGA; the prepared ethylene terephthalate and modified PGA are uniformly mixed and subjected to polycondensation reaction at 240° C. and 50 Pa vacuum conditions to produce PET-PGA copolyester.

[0027] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that no chain extender is added, and the following steps are included: 830 g of terephthalic acid and 403 g of ethylene glycol are added into a reaction container and heated to 250°C for esterification reaction to produce ethylene terephthalate; 152 g of glycolic acid and 0.15 g of stannous octoate are added into a reaction container and heated to 160°C for PGA esterification reaction. After the PGA esterification reaction is completed, a polymerization reaction is carried out at 220°C and 50Pa to produce PGA; the produced ethylene terephthalate and PGA are uniformly mixed and subjected to a condensation reaction at 240°C and 50Pa vacuum conditions to produce PET-PGA copolyester.

[0028] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that the chain extender is added in the form of a blend, comprising the following steps: (1) Preparation of a chain extender: 10 g of methyl dichlorophosphate, 15 g of benzyl alcohol and 200 ml of cyclohexane are added to a reaction container, 0.05 g of stannous chloride (catalyst) is added under mechanical stirring, the reaction is heated under reflux for 5 h, the intermediate product is cooled, and the intermediate product is separated by ether extraction, the product is washed three times with saturated sodium bicarbonate and then dried with anhydrous calcium chloride to obtain an intermediate product; the obtained intermediate product is mixed with 5 g of glycidol, 0.05 g of sodium acetate and 0.05 g of 2,4-dimethyl-6-tert-butylphenol, heated for 3 h and then distilled to obtain a chain extender; (2) Preparation of PET-PGA copolyester: 830 g of terephthalic acid and 403 g of ethylene glycol are added to a reaction vessel and the temperature is raised to 250° C. for esterification reaction to produce ethylene terephthalate; 152 g of glycolic acid and 0.15 g of stannous octoate are added to a reaction vessel and the temperature is raised to 160° C. for PGA esterification reaction; the PGA esterification reaction is polymerized at 220° C. and 50 Pa to produce PGA; the produced ethylene terephthalate, chain extender and PGA are screw blended to produce PET-PGA copolyester.

[0029] Comparative Example 3: The difference between Comparative Example 3 and Example 1 is that a common epoxy chain extender (glycidyl methacrylate) is added, and the following steps are included: 830g of terephthalic acid and 403g of ethylene glycol are added to a reaction container and heated to 250°C for esterification reaction to produce ethylene terephthalate; 152g of glycolic acid and 0.15g of stannous octoate are added to a reaction container and heated to 160°C for PGA esterification reaction. After the PGA esterification reaction is completed, the temperature is evacuated to -50KPa for polymerization reaction to produce low molecular weight PGA, and then 0.29g of epoxy chain extender (glycidyl methacrylate) is added and polymerization reaction is carried out under the conditions of 220°C and 50Pa to produce modified PGA; the prepared ethylene terephthalate and modified PGA are evenly mixed and subjected to polycondensation reaction under the conditions of 240°C and 50Pa vacuum to produce PET-PGA copolyester.

[0030] Test example: The properties of the PET-PGA copolyesters prepared in Examples 1 to 7 and Comparative Examples 1 to 3 were tested; the test items included: intrinsic viscosity, tensile strength, impact strength, glass transition temperature, melting point, degradation rate, flame retardancy and monomer utilization.

[0031] The intrinsic viscosity is tested according to the method disclosed in GB / T 14190-2008 Test method for fiber-grade polyester chips (PET); The tensile strength is tested according to the method disclosed in GB / T 1040-1992 Plastic Tensile Test Method; The impact strength is tested according to the method disclosed in GB / T 1043-1993 Hard Plastic Simply Supported Beam Impact Test Method; The glass transition temperature and melting point are tested according to the method disclosed in GB / T 13464-1992 Thermal Analysis Test Method for Thermal Stability of Materials; The flame retardant performance was tested with reference to the method disclosed in "GB / T 5454-1997 Textile Combustion Performance Test Oxygen Index Method"; the degradation rate test method comprises the following steps: testing the degradation rate of PET-PGA copolyester in a soil burial degradation experiment for 360 days; soil burial degradation experiment: first, each embodiment and comparative example was made into a film with a thickness of 0.02 mm by a flat vulcanizer, and then the film was cut into several squares with a size of 10╳10 mm. Three groups of parallel experiments were set for each sample, and 8 sample films were randomly selected from each group. After weighing, they were buried in the soil at a depth of 30 cm. The soil was watered every 30 days, and the samples were taken out every 60 days, the surface soil was wiped off, washed, and vacuum dried at 40°C for 12 hours, and the changes in the mass of the samples before and after were recorded; the test results are shown in Table 1.

[0032] Table 1 Test results As shown in Table 1, the monomer utilization rate of the PET-PGA copolyester prepared in Example 1 is 82.3%, the limiting oxygen index is 27%, the degradation rate is 79.2%, the glass transition temperature is 44.9°C, the melting point is 165.1°C, and the impact strength is 1.85 KJ / m 2 , tensile strength is 46.8MPa, intrinsic viscosity is 0.59dL / g, compared with comparative example 1 (without using chain extender), the monomer utilization rate of embodiment 1 is significantly improved, and the degradation rate, tensile strength and impact strength are all improved. In addition, the limiting oxygen index of comparative example 1 is 22%, and comparative example 1 is a combustible material, while the limiting oxygen index of embodiment 1 is 29%, which is a flame retardant material. The above results show that the prepared PET-PGA copolyester of the present invention also has excellent flame retardant properties.

[0033] In Comparative Example 2, the chain extender was added to the reaction system in the form of a blend. The results showed that the monomer utilization rate of Comparative Example 2 was only 74.5%, which was significantly lower than that of Example 1, and the limiting oxygen index was only 25%. The flame retardant performance of Comparative Example 2 was also significantly lower than that of Example 1. The above results show that the chain extender participates in the synthesis of copolyester through copolymerization, and its monomer utilization rate and flame retardant effect are better than those of blending, indicating that the chain extender participates in the polymerization in the form of copolymerization, which can directly change the chemical structure of the molecular chain and is evenly distributed. In blending, the chain extender is dispersed in the polymer matrix as independent molecules or aggregates, and the degree of uniform distribution is limited, and it is difficult to change the molecular chain structure as accurately as copolymerization.

[0034] In Comparative Example 3, glycidyl methacrylate was used as a chain extender. The results showed that the monomer utilization rate of the PET-PGA copolyester prepared in Comparative Example 3 was significantly lower than that in Example 1, and the limiting oxygen index of Comparative Example 3 was only 22%, which was a combustible material without flame retardant properties.

[0035] In addition, through the results of Examples 1 to 3, it is found that as the amount of chain extender gradually increases, the thermodynamic properties of the prepared PET-PGA copolyester also decrease. The reason for this phenomenon may be that as the content of the chain extender increases, a branched structure appears in the copolymer structure, which reduces the regularity of the copolyester molecular chain, thereby resulting in a decrease in thermodynamic properties. Therefore, in actual production, it is necessary to control the amount of chain extender according to actual needs.

[0036] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A PET-PGA copolyester, characterized in that: The raw materials include modified PGA, terephthalic acid and ethylene glycol. The raw materials of the modified PGA include a chain extender and glycolic acid. The chemical formula of the chain extender is 2. PET-PGA copolyester according to claim 1, characterized in that, The mass ratio of the chain extender to glycolic acid is 0.05 to 1:

100.

3. PET-PGA copolyester according to claim 1, characterized in that, The molar ratio of glycolic acid, terephthalic acid and ethylene glycol is 1:1.0-1.8:1.5-3.

4. A method for preparing the PET-PGA copolyester according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) adding terephthalic acid and ethylene glycol into a reaction vessel and heating the vessel to carry out esterification reaction to generate polymerization monomers; (2) adding glycolic acid and a catalyst into a reaction vessel and heating the vessel to carry out an esterification reaction of PGA to produce low molecular weight PGA, and then adding a chain extender to carry out a polycondensation reaction with the low molecular weight PGA to produce modified PGA; (3) The polymerizable monomers in step (1) and the modified PGA in step (2) are uniformly mixed and subjected to polycondensation reaction to prepare PET-PGA copolyester.

5. The preparation method according to claim 4, characterized in that: The chain extender comprises the following preparation steps: reacting methyl dichlorophosphate, benzyl alcohol, cyclohexane and stannous chloride at 80-120° C. to prepare an intermediate product; and reacting the intermediate product, ethanol oxide, a catalyst and a polymerization inhibitor at 60-90° C. to prepare the chain extender.

6. The preparation method according to claim 5, characterized in that: The molar ratio of methyl dichlorophosphate and benzyl alcohol is 1:2-4; the molar ratio of the intermediate product and glycidol is 1:1-1.

3.

7. The preparation method according to claim 5, characterized in that: The inhibitor is one or more of 2,4-dimethyl-6-tert-butylphenol, 2,6-di-tert-butyl-tetramethylphenol, tetrachlorobenzoquinone and N-phenyl-α-naphthylamine; the catalyst is one or more of sodium acetate, potassium acetate and potassium cyanide.

8. The preparation method according to claim 4, characterized in that: The conditions for the esterification reaction in step (1) include: a temperature of 220 to 260°C.

9. The preparation method according to claim 4, characterized in that: The conditions for the PGA esterification reaction in step (2) include: a temperature of 150 to 180° C. and a vacuum degree of -50 to 0 KPa; the conditions for the high vacuum polymerization reaction include: a temperature of 180 to 220° C. and a vacuum degree of 0 to 100 Pa.

10. The preparation method according to claim 4, characterized in that: The conditions for the polycondensation reaction in step (3) include: a temperature of 220 to 250° C. and a vacuum degree of 0 to 60 Pa.

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