Modified polyethylene glycol terephthalate and preparation method thereof

Abstract

The invention relates to the technical field of polyethylene glycol terephthalate, and discloses modified polyethylene glycol terephthalate and a preparation method thereof.The method comprises the steps that 1, under the transesterification reaction and / or esterification reaction conditions, ethylene glycol, a monomer A and a monomer B are subjected to the transesterification reaction and / or esterification reaction, and reaction liquid is obtained; wherein the monomer A is terephthalic acid and / or terephthalic acid dialkyl ester; the monomer B is hydroxyl-substituted terephthalic acid and / or hydroxyl-substituted dialkyl terephthalate; the molar dosage of the monomer B accounts for 1-10% of the total molar dosage of the monomer A and the monomer B; and (2) carrying out polycondensation reaction on the reaction liquid under polycondensation reaction conditions. According to the method disclosed by the invention, the high-molecular-weight polyethylene glycol terephthalate can be prepared under the condition of improving the hydrophilicity of the polyethylene glycol terephthalate, so that the mechanical property of the polyethylene glycol terephthalate is improved, and the application in different fields is met.

Description

Technical Field

[0001] The present invention relates to the technical field of polyethylene terephthalate, in particular to modified polyethylene terephthalate and a preparation method thereof. Background Art

[0002] Due to its excellent performance and low production costs, polyethylene terephthalate (PET) is widely used in food and beverage packaging, clothing and textiles, engineering plastics, and other fields. With the rapid development of the domestic economy, demand for PET products has increased significantly. PET fiber accounts for 75% of the total PET production. However, PET material has poor water absorption and dyeability, is prone to static electricity, and has poor biodegradability.

[0003] Today, the world faces a shortage of petroleum resources, and the environmental problems caused by these resources are constantly emerging. In the past decade, the production of bio-based monomers from polysaccharides such as straw and starch through biofermentation and chemical methods has attracted widespread attention. Replacing petroleum-based monomers with bio-based monomers can not only reduce dependence on petroleum resources, but also alleviate the environmental pollution caused by petroleum resources. However, existing PET materials have poor hydrophilicity. Summary of the Invention

[0004] The purpose of the present invention is to overcome the problem of poor hydrophilicity of PET materials in the prior art while ensuring that the molecular weight of the PET material is high, and to provide a modified polyethylene terephthalate and a preparation method thereof.

[0005] The inventors of the present invention have discovered that most prior art methods use hydrophilic additives to improve the hydrophilicity of PET materials. However, over time, these additives can become ineffective or leach out, leading to a decrease in the hydrophilicity of the PET material. The inventors of the present invention have discovered that a copolymerization method, in which ethylene glycol is copolymerized with monomers A and B in specific ratios to prepare modified polyethylene terephthalate, can improve the hydrophilicity of polyethylene terephthalate and increase its molecular weight without the use of hydrophilic additives.

[0006] To achieve the above-mentioned object, the first aspect of the present invention provides a modified polyethylene terephthalate, which comprises a structural unit A and a structural unit B, wherein the structural unit A has a structure represented by formula (3), and the structural unit B has a structure represented by formula (4); the molar content of the structural unit B accounts for 0.8-10% of the total molar content of the structural units A and B;

[0007]

[0008] Wherein, R1, R2, R3 and R4 are each independently a hydroxyl group or H, and at least one of R1, R2, R3 and R4 is a hydroxyl group.

[0009] A second aspect of the present invention provides a method for preparing modified polyethylene terephthalate, the method comprising:

[0010] (1) Under transesterification reaction and / or esterification reaction conditions, ethylene glycol is subjected to transesterification reaction and / or esterification reaction with monomer A and monomer B to obtain a reaction solution; wherein monomer A is terephthalic acid and / or dialkyl terephthalate; monomer B is hydroxy-substituted terephthalic acid and / or dialkyl terephthalate; and the molar amount of monomer B accounts for 1-10% of the total molar amount of monomer A and monomer B;

[0011] (2) Under polycondensation reaction conditions, the reaction solution is subjected to polycondensation reaction.

[0012] The third aspect of the present invention provides modified polyethylene terephthalate prepared by the above-described method.

[0013] Through the above technical solution, the following beneficial effects are achieved:

[0014] (1) The present invention adopts a copolymerization method to copolymerize ethylene glycol with monomer A and monomer B in a specific ratio to prepare modified polyethylene terephthalate. The method of the present invention can prepare high molecular weight polyethylene terephthalate while improving the hydrophilicity of polyethylene terephthalate, thereby improving the mechanical properties of polyethylene terephthalate to meet the application needs of different fields.

[0015] (2) Compared with the polymer blending process or post-processing process (improving the properties of the polymer by using additives), the modified polyethylene terephthalate obtained by the copolymerization method of the present invention has more stable properties, simple synthesis steps, and reduced economic costs.

[0016] (3) According to a preferred embodiment of the present invention, the present invention further adopts a two-stage polycondensation and controls the temperature of the two stages, thereby obtaining polyethylene terephthalate with better hue without adding other additives.

[0017] (4) The modified polyethylene terephthalate synthesized by the present invention can greatly improve the water absorption of polyethylene terephthalate when the content of monomer B is low, which is expected to improve the hygroscopicity of polyester fibers and thus improve the comfort of polyester clothing. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is the infrared spectrum of PET-4 and DPET-1;

[0019] Figure 2 These are the nuclear magnetic resonance spectra of PET-1, PET-2, PET-3, PET-4 and DPET-1. DETAILED DESCRIPTION

[0020] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0021] A first aspect of the present invention provides a modified polyethylene terephthalate, comprising a structural unit A and a structural unit B, wherein the structural unit A has a structure represented by formula (3), and the structural unit B has a structure represented by formula (4); the molar content of the structural unit B accounts for 0.8-10% (preferably 1-9%) of the total molar content of the structural units A and B;

[0022]

[0023] wherein R1, R2, R3, and R4 are each independently a hydroxyl group, H, or an alkyl group (preferably a C1-C4 alkyl group), and at least one of R1, R2, R3, and R4 is a hydroxyl group. For example, any one of R1, R2, R3, and R4 is a hydroxyl group, or any two of R1, R2, R3, and R4 are hydroxyl groups.

[0024] According to the present invention, preferably, the weight average molecular weight of the modified polyethylene terephthalate is 19000-55000 g / mol.

[0025] A second aspect of the present invention provides a method for preparing modified polyethylene terephthalate, the method comprising:

[0026] (1) Under transesterification reaction and / or esterification reaction conditions, ethylene glycol is subjected to transesterification reaction and / or esterification reaction with monomer A and monomer B to obtain a reaction solution; wherein monomer A is terephthalic acid and / or dialkyl terephthalate; monomer B is hydroxy-substituted terephthalic acid and / or dialkyl terephthalate; and the molar amount of monomer B accounts for 1-10% (preferably 2-5%, more preferably 2-4%) of the total molar amount of monomer A and monomer B;

[0027] (2) Under polycondensation reaction conditions, the reaction solution is subjected to polycondensation reaction.

[0028] According to the present invention, preferably, the conditions for the polycondensation reaction include: vacuum degree of 50Pa-1000Pa, temperature of 210-250°C, and time of 0.5-2h.

[0029] According to the present invention, in order to obtain polyethylene terephthalate with a better hue, the polycondensation reaction preferably includes a first polycondensation reaction and a second polycondensation reaction performed sequentially, wherein the temperature of the second polycondensation reaction is 20-40°C higher than that of the first polycondensation reaction. By controlling the temperature difference between the first and second polycondensation reactions, polyethylene terephthalate with a lighter color can be obtained, thereby broadening the application areas of polyethylene terephthalate.

[0030] According to the present invention, preferably, the vacuum degree of the first polycondensation reaction is 300-1000 Pa higher than the vacuum degree of the second polycondensation reaction.

[0031] According to the present invention, in order to further improve the hue, hydrophilicity, absorptivity, surface free energy and weight average molecular weight of polyethylene terephthalate, preferably, the conditions of the first polycondensation reaction include: a vacuum degree of 500 Pa-1000 Pa, a temperature of 210-230° C., and a time of 1-2 h, more preferably 1-1.5 h.

[0032] According to the present invention, in order to further improve the hue, hydrophilicity, absorptivity, surface free energy and weight average molecular weight of polyethylene terephthalate, preferably, the conditions of the second polycondensation reaction include: vacuum degree of 50-200, temperature of 250-270°C and time of 0.5-2h.

[0033] The present invention has further discovered that the hue of polyethylene terephthalate can be further improved without using additives by limiting the temperature of the first polycondensation reaction and the temperature of the second polycondensation reaction to relatively low ranges.

[0034] In the present invention, the time of the first polycondensation reaction and the second polycondensation reaction does not include the time of the temperature rising process, and only refers to the time of maintaining the temperature of the first polycondensation reaction and the temperature of the second polycondensation reaction.

[0035] According to the present invention, preferably, the temperature of the first polycondensation reaction reaches the temperature of the second polycondensation reaction at a heating rate of 0.5-2°C / min (preferably 0.5-1°C / min). Controlling the heating rate within the above range can further improve the hue of the polyethylene terephthalate.

[0036] According to the present invention, preferably, the conditions of the transesterification reaction are such that the transesterification rate is above 95%, for example, the transesterification rate may be 95-99.9%.

[0037] According to the present invention, preferably, the conditions of the esterification reaction are such that the esterification rate is above 95%, for example, the esterification rate can be 95-99.9%.

[0038] In the present invention, when monomer A is a dialkyl terephthalate and monomer B is a hydroxyl-substituted dialkyl terephthalate, ethylene glycol undergoes an ester exchange reaction with monomers A and B. When monomer A is terephthalic acid and monomer B is a hydroxyl-substituted terephthalic acid, ethylene glycol undergoes an esterification reaction with monomers A and B. When preparing the modified polyethylene terephthalate according to the present invention, the ester exchange reaction and esterification reaction can be carried out simultaneously, followed by a polycondensation reaction; alternatively, the ester exchange reaction or esterification reaction can be carried out separately, followed by a polycondensation reaction.

[0039] According to the present invention, preferably, the transesterification reaction includes a first transesterification reaction and a second transesterification reaction performed sequentially, and the temperature of the second transesterification reaction is 20-60° C. higher than that of the first transesterification reaction.

[0040] According to the present invention, preferably, the conditions for the first transesterification reaction include: a temperature of 140-190° C., and a time of 2-3 h, more preferably 2-2.5 h.

[0041] According to the present invention, preferably, the conditions for the second transesterification reaction include: a temperature of 210-230° C., and a time of 0.5-2 h, more preferably 0.5-1 h.

[0042] In the present invention, the first transesterification reaction and the second transesterification reaction are usually carried out under normal pressure.

[0043] According to the present invention, preferably, the conditions of the esterification reaction include: temperature of 160-220° C., time of 3-5 h, and pressure of 0.3-0.5 MPa.

[0044] According to the present invention, preferably, the esterification reaction includes a first esterification reaction and a second esterification reaction carried out sequentially, wherein the temperature of the first esterification reaction is 140-190° C., and the time of the first esterification reaction is 2-3 hours; the temperature of the second esterification reaction is 210-230° C., and the time of the second esterification reaction is 0.5-2 hours.

[0045] The inventors further discovered that by controlling the reaction temperature of transesterification or esterification within a relatively low range, the hydrophilicity, absorptivity, surface free energy, and weight-average molecular weight of polyethylene terephthalate can be further improved.

[0046] According to the present invention, preferably, the transesterification reaction is carried out in the presence of a transesterification catalyst and a first catalyst; more preferably, the transesterification catalyst comprises zinc acetate and / or calcium acetate; more preferably, the first catalyst comprises antimony trioxide and / or antimony glycol.

[0047] According to the present invention, preferably, the ratio of the molar amount of the transesterification catalyst to the total molar amount of monomer A and monomer B is 0.0005-0.001:1.

[0048] According to the present invention, preferably, the ratio of the molar amount of the first catalyst to the total molar amount of monomer A and monomer B is 0.0005-0.0015:1.

[0049] According to the present invention, preferably, the esterification reaction is carried out in the presence of a second catalyst, wherein the second catalyst comprises at least one of antimony trioxide, antimony glycolate, titanium glycolate and tetrabutyl titanate.

[0050] According to the present invention, preferably, the ratio of the molar amount of the second catalyst to the total molar amount of monomer A and monomer B is 0.0005-0.001:1.

[0051] According to the present invention, preferably, the hydroxy-substituted terephthalic acid has the structural formula shown in formula (1):

[0052]

[0053] wherein R'1, R'2, R'3, and R'4 are hydroxyl groups, H, or alkyl groups (preferably C1-C4 alkyl groups), and at least one of R'1, R'2, R'3, and R'4 is a hydroxyl group. For example, any one of R'1, R'2, R'3, and R'4 is a hydroxyl group, or any two of R'1, R'2, R'3, and R'4 are hydroxyl groups.

[0054] According to the present invention, preferably, the hydroxy-substituted terephthalic acid includes at least one of 2-hydroxyterephthalic acid, 2,5-dihydroxyterephthalic acid and 2,6-dihydroxyterephthalic acid.

[0055] According to the present invention, preferably, the hydroxy-substituted dialkyl terephthalate has the structural formula shown in formula (2):

[0056]

[0057] Wherein, R'1, R'2, R'3 and R'4 are hydroxyl groups or H, and at least one of R'1, R'2, R'3 and R'4 is hydroxyl groups; R5 and R6 are each independently selected from C1-C10 alkyl groups.

[0058] According to the present invention, preferably, the hydroxy-substituted dialkyl terephthalate includes at least one of 2-hydroxy dialkyl terephthalate, 2,5-dihydroxy dialkyl terephthalate and 2,6-dihydroxy dialkyl terephthalate.

[0059] According to the present invention, preferably, the alkyl groups in the dialkyl terephthalate and the hydroxy-substituted dialkyl terephthalate are each independently selected from C1-C5 alkyl groups, such as methyl, ethyl, propyl, butyl, and pentyl.

[0060] According to the present invention, preferably, the ratio of the total molar amount of monomer A and monomer B to the molar amount of ethylene glycol is 1:1.3-2; more preferably 1:1.8-2.

[0061] According to the present invention, no other additives may be used in the transesterification reaction and / or esterification reaction. Other additives may be tourmaline or serpentine commonly used in the art.

[0062] The third aspect of the present invention provides modified polyethylene terephthalate prepared by the above-described method.

[0063] According to a particularly preferred embodiment of the present invention, the present invention provides a method for preparing modified polyethylene terephthalate, the method comprising:

[0064] (1) Under a nitrogen atmosphere, ethylene glycol, monomer A (dimethyl terephthalate), monomer B (dimethyl 2-hydroxyterephthalate), zinc acetate, and antimony glycolate were added to a three-necked flask equipped with a mechanical stirrer. The temperature was raised to 165-170° C. (preferably 168-170° C.), and the reaction was carried out for 2-2.5 hours. The fraction collection rate was reduced, and the temperature was gradually raised to 210-220° C. (preferably 218-220° C.), and the reaction was maintained for 0.5-1 hour. The esterification rate reached more than 95%, and the transesterification reaction was terminated. The amount of monomer A used was 0.67-0.693 mol (preferably 0.67-0.672 mol) and the amount of monomer B used was 0.007-0.028 mol (preferably 0.02-0.03 mol) relative to 1.4 mol of ethylene glycol. The ratio of the molar amount of zinc acetate to the total molar amount of monomer A and monomer B is 0.0006-0.0009:1 (preferably 0.0008-0.0009:1), and the ratio of the molar amount of antimony glycol to the total molar amount of monomer A and monomer B is 0.001-0.0012:1.

[0065] (2) The reaction system is gradually evacuated to a low vacuum (500-800 Pa, preferably 700-800 Pa), maintained at 210-220 ° C (preferably 218-220 ° C) for 1-1.5 hours, then evacuated to a high vacuum (less than 200 Pa), and slowly heated to 245-250 ° C at a heating rate of 0.5-1 ° C / min, and reacted for 1-2 hours (preferably 1-1.2 hours) to obtain modified polyethylene terephthalate.

[0066] The present invention will be described in detail below by way of examples.

[0067] Dimethyl 2-hydroxyterephthalate is a commercial product of Damas-Beta with the trademark 013403037;

[0068] Zinc acetate is a commercial product of Aladdin Company with the brand name Z119378;

[0069] Antimony ethylene glycol is a commercial product of MACKLIN under the trade name P836404.

[0070] Example 1

[0071] (1) Under nitrogen atmosphere, ethylene glycol (1.4 mol, 86.8 g), monomer A (dimethyl terephthalate, 0.693 mol, 134.4 g), monomer B (dimethyl 2-hydroxyterephthalate, 0.007 mol, 1.47 g), zinc acetate, and antimony glycolate were added to a three-necked flask equipped with a mechanical stirrer. The temperature was raised to 160°C and the reaction was continued for 2 h. The collection rate of the fraction (e.g., methanol) decreased. The temperature was gradually raised to 210°C and maintained for 0.5 h. The transesterification reaction was terminated when the transesterification rate reached 96.5%. The ratio of the molar amount of zinc acetate to the total molar amount of monomer A and monomer B was 0.0006:1, and the ratio of the molar amount of antimony glycolate to the total molar amount of monomer A and monomer B was 0.001:1.

[0072] (2) The reaction system was gradually evacuated to a low vacuum (500 Pa), maintained at 210 ° C for 1 hour, and then evacuated to a high vacuum (less than 200 Pa), and the temperature was increased to 250 ° C at a heating rate of 1 ° C / min. After reacting for 2 hours, modified polyethylene terephthalate PET-1 was obtained.

[0073] Example 2

[0074] (1) Under nitrogen atmosphere, ethylene glycol (1.4 mol, 86.8 g), monomer A (dimethyl terephthalate, 0.686 mol, 133.1 g), monomer B (dimethyl 2-hydroxyterephthalate, 0.014 mol, 2.94 g), zinc acetate, and antimony glycolate were added to a three-necked flask equipped with a mechanical stirrer. The temperature was raised to 165°C and the reaction was continued for 2 h. The fraction collection rate was reduced, and the temperature was gradually raised to 215°C and maintained for 0.5 h. The esterification rate reached 97.2%, and the transesterification reaction was terminated. The ratio of the molar amount of zinc acetate to the total molar amount of monomer A and monomer B was 0.0007:1, and the ratio of the molar amount of antimony glycolate to the total molar amount of monomer A and monomer B was 0.001:1.

[0075] (2) The reaction system was gradually evacuated to a low vacuum (600 Pa), maintained at 215 ° C for 1 hour, and then evacuated to a high vacuum (less than 200 Pa), and the temperature was increased to 250 ° C at a heating rate of 1 ° C / min, and the reaction was carried out for 1.5 hours to obtain modified polyethylene terephthalate PET-2.

[0076] Example 3

[0077] (1) Under nitrogen atmosphere, ethylene glycol (1.4 mol, 86.8 g), monomer A (dimethyl terephthalate, 0.672 mol, 130.4 g), monomer B (dimethyl 2-hydroxyterephthalate, 0.028 mol, 5.88 g), zinc acetate, and antimony glycolate were added to a three-necked flask equipped with a mechanical stirrer. The temperature was raised to 170°C and the reaction was continued for 2 h. The fraction collection rate was reduced, and the temperature was gradually raised to 220°C and maintained for 0.5 h. The esterification rate reached 95.3%, and the transesterification reaction was terminated. The ratio of the molar amount of zinc acetate to the total molar amount of monomer A and monomer B was 0.0008:1, and the ratio of the molar amount of antimony glycolate to the total molar amount of monomer A and monomer B was 0.001:1.

[0078] (2) The reaction system was gradually evacuated to a low vacuum (800 Pa), maintained at 220 ° C for 1 hour, and then evacuated to a high vacuum (less than 200 Pa), and the temperature was slowly increased to 250 ° C at a heating rate of 1 ° C / min, and the reaction was carried out for 1 hour to obtain modified polyethylene terephthalate PET-3.

[0079] Example 4

[0080] (1) Under nitrogen atmosphere, ethylene glycol (1.4 mol, 86.8 g), monomer A (dimethyl terephthalate, 0.63 mol, 122.2 g), monomer B (dimethyl 2-hydroxyterephthalate, 0.07 mol, 14.7 g), zinc acetate, and antimony glycolate were added to a three-necked flask equipped with a mechanical stirrer. The temperature was raised to 175°C and the reaction was continued for 2 h. The fraction collection rate was reduced, and the temperature was gradually raised to 230°C and maintained for 0.5 h. The transesterification reaction was completed when the esterification rate reached 97.5% or above. The ratio of the molar amount of zinc acetate to the total molar amount of monomer A and monomer B was 0.001:1, and the ratio of the molar amount of antimony glycolate to the total molar amount of monomer A and monomer B was 0.001:1.

[0081] (2) The reaction system was gradually evacuated to a low vacuum (1000 Pa), maintained at 230 ° C for 1 hour, and then evacuated to a high vacuum (less than 200 Pa), and the temperature was increased to 250 ° C at a heating rate of 0.5 ° C / min, and the reaction was carried out for 0.5 h to obtain modified polyethylene terephthalate PET-4.

[0082] PET-4 and DPET-1 were tested by infrared, and the infrared spectra of PET-4 and DPET-1 are as follows Figure 1 As shown, from Figure 1 The characteristic peak of hydroxyl groups appearing at 3500 nm indicates that hydroxyl groups have been successfully introduced into the polymer backbone.

[0083] PET-1, PET-2, PET-3, PET-4 and DPET-1 were subjected to nuclear magnetic resonance testing. The nuclear magnetic resonance testing method was to dissolve the polymer in a mixed solvent of deuterated chloroform / trifluoroacetic acid and test it using a nuclear magnetic resonance spectrometer. The nuclear magnetic spectra of PET-4 and DPET-1 are shown in Figure 2. Figure 2 As shown, from Figure 2 PET-4 exhibits three characteristic peaks between 7.5 and 8.0 ppm, representing the three hydrogen atoms in the benzene ring of dimethyl 2-hydroxyterephthalate, demonstrating the successful incorporation of dimethyl 2-hydroxyterephthalate into the polymer backbone. The NMR spectra of PET-1, PET-2, and PET-3 are similar to that of PET-4 and are not shown here.

[0084] Example 5

[0085] Under a nitrogen atmosphere, ethylene glycol (1.4 mol, 86.8 g), terephthalic acid (0.693 mol, 134.4 g), 2-hydroxyterephthalic acid (0.007 mol, 1.47 g), and antimony glycolate were added to a three-necked flask equipped with a mechanical stirrer. The system pressure was controlled at 0.3-0.5 MPa. The temperature was raised to 190°C and the reaction was allowed to proceed for 2 h. The fraction collection rate was reduced, and the temperature was gradually raised to 210°C and maintained for 0.5 h. The esterification reaction was terminated when the esterification rate reached over 96.7%. The molar ratio of antimony glycolate to the total molar amount of terephthalic acid and 2-hydroxyterephthalic acid was 0.001:1.

[0086] (2) The reaction system was gradually evacuated to a low vacuum (500 Pa), maintained at 210 ° C for 1 hour, and then evacuated to a high vacuum (less than 200 Pa), and the temperature was increased to 250 ° C at a heating rate of 1 ° C / min, and the reaction was carried out for 2 hours to obtain modified polyethylene terephthalate PET-5.

[0087] Example 6

[0088] The method of Example 1 was followed, except that in step (2), the reaction system was gradually evacuated to a low vacuum (500 Pa) and maintained at 290° C. for 3 h to obtain modified polyethylene terephthalate PET-6. Compared with Example 1, the color of the polymer was significantly darker and the hue was worse.

[0089] Example 7

[0090] The method of Example 1 was followed, except that in step (2), "the temperature was raised to 250°C at a heating rate of 1°C / min and the reaction was continued for 2 h" was replaced with "the temperature was raised to 250°C at a heating rate of 2°C / min and the reaction was continued for 2 h." Modified polyethylene terephthalate PET-7 was obtained. Due to the faster heating rate in Example 7, the color was darker and the hue was worse than that in Example 1.

[0091] Example 8

[0092] The method of Example 1 was followed, except that in step (1), "raising the temperature to 160°C and reacting for 2 hours" was replaced by "raising the temperature to 140°C and reacting for 2 hours," and "gradually raising the temperature to 210°C and maintaining it for 0.5 hours" was replaced by "gradually raising the temperature to 190°C and maintaining it for 0.5 hours." Due to the low transesterification temperature, the transesterification reaction was difficult to complete, and the resulting modified polyethylene terephthalate (PET-8) had a low molecular weight and could not be used as a material (e.g., it could not be formed into a film).

[0093] Example 9

[0094] The method of Example 1 was followed, except that the antimony ethylene glycolate was replaced with an equal molar amount of antimony trioxide. The resulting modified polyethylene terephthalate (PET-9) was found to have poorer dispersibility in the polymerization system, lower catalytic activity, and longer polymerization times than that of the antimony ethylene glycolate. The resulting polymer also exhibited a poorer hue than that of Example 1.

[0095] Example 10

[0096] The method of Example 1 was followed, except that 2-hydroxydimethyl terephthalate was replaced with an equal molar amount of 2,5-dihydroxydimethyl terephthalate. Modified polyethylene terephthalate PET-10 was obtained. Compared with Example 1, the resulting polymer was slightly cross-linked, poorly soluble in chloroform, and had lower water absorption, hydrophilicity, and enzymatic degradability than Example 1.

[0097] Comparative Example 1

[0098] The method of Example 1 was followed, except that monomer B was replaced with an equal mole of monomer A to obtain modified polyethylene terephthalate DPET-1.

[0099] Comparative Example 2

[0100] The method of Example 1 was followed, except that 0.49 mol of monomer A and 0.21 mol of monomer B were used. The viscosity of the resulting modified polyethylene terephthalate (DPET-2) increased rapidly during the second polycondensation, and it was difficult to dissolve in all solvents. This is presumably due to extensive cross-linking during the reaction. Due to the severe cross-linking, DPET-2 could not be processed into a film.

[0101] Test Example 1

[0102] The contents of structural unit A and structural unit B in the PET products obtained in the above examples and comparative examples are shown in Table 1. Structural unit A is a structural unit formed by the reaction of monomer A and ethylene glycol, and structural unit B is a structural unit formed by the reaction of monomer B and ethylene glycol.

[0103] The test method for the content of structural unit A and structural unit B in PET products is: dissolve the PET sample in deuterated chloroform / trifluoroacetic acid solution and conduct nuclear magnetic resonance hydrogen spectrum test. The content of structural unit A and structural unit B can be obtained by comparing the integrated areas of the characteristic peaks of structural unit A and structural unit B.

[0104] Table 1

[0105] Structural unit A (mol%) Structural unit B (mol%) Example 1 99.1 0.9 Example 2 98.2 1.8 Example 3 96.6 3.4 Example 4 91.2 8.8 Example 5 99.11 0.89 Example 6 99.2 0.8 Example 7 99.15 0.85 Example 8 —— —— Example 9 99.13 0.87 Example 10 99.12 0.88 Comparative Example 1 100 0 Comparative Example 2 —— ——

[0106] Test Example 2

[0107] The PET products obtained in the above examples and comparative examples were subjected to performance tests, and the test results are shown in Table 2.

[0108] (1) The test method for the water absorption rate of PET is as follows: According to GB / T 1034-2008, the modified PET is hot-pressed (pressure of 10,000 lb, temperature of 280°C) into a polymer sheet of 10 cm*10 cm*0.5 mm, the surface is cleaned with ethanol, and the sheet is placed in a vacuum drying oven at 30°C and dried for 24 hours. The mass of the dried polymer sheet is weighed as M1, and the polymer sheet is immersed in deionized water for 24 hours. After being taken out, the surface water droplets are wiped off with filter paper and weighed immediately to obtain the mass after water absorption M2. The water absorption rate is calculated as follows: Water absorption rate = (M2-M1) / M1.

[0109] (2) The water contact angle and surface free energy of PET films were measured as follows: the modified PET was hot-pressed into a 10 cm x 10 cm x 0.5 mm polymer sheet, the surface was cleaned with ethanol, and the sheet was dried in a vacuum drying oven at 30°C for 24 hours. A Kruss MSA portable contact angle meter was used to measure the contact angle of 15 randomly selected locations on each sample. The average value was then calculated as the contact angle of the PET film. After measuring the contact angle, the instrument automatically generated surface free energy data. The higher the surface free energy, the more hydrophilic the PET film.

[0110] (3) The weight-average molecular weight of PET was determined using an Agilent 1260 gel permeation chromatograph, a refractive index detector, a guard column and a PL HFIPgel 300*7.5mm column connected in series, hexafluoroisopropanol as the mobile phase, a flow rate of 1 mL / min, PMMA as the standard, and a test temperature of 35°C.

[0111] (4) The color test method for PET is as follows: According to the PET color test method in GB / T 14189-2015, the PET sample is dried and crushed and then tested for color using an automatic colorimeter. The results are expressed in the HunterLab color system L, a, b. A higher b value indicates a worse polymer hue.

[0112] (5) The enzymatic degradation of PET is tested as follows: a small amount of PET sample is crushed and dispersed in 10 times its mass in pH 8 phosphate buffer (Mreda, M176437). LCC cutinase is added at a concentration of 0.3% by mass of the PET. The solution is maintained at 70°C for 24 hours. The degradation product content in the solution is quantitatively analyzed by liquid chromatography, and the degree of enzymatic degradation of the PET is calculated. PET enzymatic degradation rate = (mass of TPA + mass of MHET + mass of BHF) / mass of PET; where TPA is terephthalic acid, MHET is monohydroxyethyl terephthalate, and BHF is bishydroxyethyl terephthalate.

[0113] Table 2

[0114]

[0115]

[0116] The results in Table 1 indicate that the method of the present invention can not only improve the hydrophilicity of PET but also increase its weight-average molecular weight. Preferably, the methods of Examples 2-4 of the present invention can achieve even higher hydrophilicity and weight-average molecular weight of PET. Particularly preferably, the methods of Examples 2-3 of the present invention can further enhance the biodegradability of PET.

[0117] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A modified polyethylene terephthalate, characterized in that: The modified polyethylene terephthalate comprises a structural unit A and a structural unit B, wherein the structural unit A has a structure shown in formula (3), and the structural unit B has a structure shown in formula (4); the molar content of the structural unit B accounts for 0.8-10% of the total molar content of the structural unit A and the structural unit B; Wherein, R1, R2, R3 and R4 are each independently a hydroxyl group, H, or an alkyl group, and at least one of R1, R2, R3 and R4 is a hydroxyl group.

2. The modified polyethylene terephthalate according to claim 1, wherein The weight average molecular weight of the modified polyethylene terephthalate is 19000-55000 g / mol.

3. A method for preparing modified polyethylene terephthalate, characterized in that: The method includes: (1) Under transesterification reaction and / or esterification reaction conditions, ethylene glycol is subjected to transesterification reaction and / or esterification reaction with monomer A and monomer B to obtain a reaction solution; wherein monomer A is terephthalic acid and / or dialkyl terephthalate; monomer B is hydroxy-substituted terephthalic acid and / or dialkyl terephthalate; and the molar amount of monomer B accounts for 1-10% of the total molar amount of monomer A and monomer B; (2) Under polycondensation reaction conditions, the reaction solution is subjected to polycondensation reaction.

4. The method according to claim 3, wherein: The conditions of the polycondensation reaction include: vacuum degree of 50Pa-1000Pa, temperature of 210-250°C, and time of 0.5-2h; Preferably, the polycondensation reaction comprises a first polycondensation reaction and a second polycondensation reaction carried out sequentially, wherein the temperature of the second polycondensation reaction is 20-40° C. higher than the temperature of the first polycondensation reaction; More preferably, the conditions for the first polycondensation reaction include: vacuum degree of 500 Pa-1000 Pa, temperature of 210-230° C., and time of 1-2 h; More preferably, the conditions for the second polycondensation reaction include: vacuum degree of 50 Pa-200 Pa, temperature of 250-270° C., and time of 0.5-2 h; More preferably, the temperature of the first polycondensation reaction reaches the temperature of the second polycondensation reaction at a heating rate of 0.5-1°C / min.

5. The method according to claim 3, wherein The conditions of the transesterification reaction are such that the transesterification rate is above 95%; and / or, the conditions of the esterification reaction are such that the esterification rate is above 95%; Preferably, the transesterification reaction includes a first transesterification reaction and a second transesterification reaction carried out sequentially, wherein the conditions for the first transesterification reaction include: a temperature of 140-190° C. and a time of 2-3 hours; the conditions for the second transesterification reaction include: a temperature of 210-230° C. and a time of 0.5-2 hours; Preferably, the esterification reaction conditions include: temperature of 160-220°C, time of 3-5h, and pressure of 0.3-0.5MPa; More preferably, the esterification reaction includes a first esterification reaction and a second esterification reaction carried out sequentially, wherein the temperature of the first esterification reaction is 140-190° C., and the time of the first esterification reaction is 2-3 hours; the temperature of the second esterification reaction is 210-230° C., and the time of the second esterification reaction is 0.5-2 hours.

6. The method according to claim 3, wherein: The transesterification reaction is carried out in the presence of a transesterification catalyst and a first catalyst, wherein the transesterification catalyst comprises zinc acetate and / or calcium acetate; the first catalyst comprises antimony trioxide and / or antimony glycol; Preferably, the ratio of the molar amount of the transesterification catalyst to the total molar amount of monomer A and monomer B is 0.0005-0.001:1; Preferably, the ratio of the molar amount of the first catalyst to the total molar amount of monomer A and monomer B is 0.0005-0.0015:

1.

7. The method according to claim 3, wherein: The esterification reaction is carried out in the presence of a second catalyst, wherein the second catalyst comprises at least one of antimony trioxide, antimony glycolate, titanium glycolate and tetrabutyl titanate; Preferably, the ratio of the molar amount of the second catalyst to the total molar amount of monomer A and monomer B is 0.0005-0.001:

1.

8. The method according to claim 3, wherein: The hydroxy-substituted terephthalic acid includes at least one of 2-hydroxyterephthalic acid, 2,5-dihydroxyterephthalic acid and 2,6-dihydroxyterephthalic acid; and / or, the hydroxy-substituted dialkyl terephthalate comprises at least one of 2-hydroxy dialkyl terephthalate, 2,5-dihydroxy dialkyl terephthalate and 2,6-dihydroxy dialkyl terephthalate; And / or, the alkyl groups in the dialkyl terephthalate and the hydroxy-substituted dialkyl terephthalate are each independently selected from C1-C5 alkyl groups.

9. The method according to claim 3, wherein: The ratio of the total molar amount of monomer A and monomer B to the molar amount of ethylene glycol is 1:1.3-2; And / or, no other additives are used during the transesterification reaction and / or esterification reaction.

10. Modified polyethylene terephthalate prepared by the method according to any one of claims 3 to 9.

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