Degradable polyester and method for preparing the same

Abstract

The present application relates to the technical field of polyester material degradation modification, and particularly relates to a degradable polyester and a preparation method thereof. The degradable polyester is a modified polyethylene terephthalate (PET) containing aromatic diacetic acid structural units and being degradable in an acidic or alkaline environment, and is synthesized by polycondensation reaction of aromatic diacetic acid or aromatic diacetate monomers and dihydric alcohol monomers according to a certain proportion. The present application breaks the conjugate stabilization effect of the PET polyester molecular chain by means of methylene insertion, activates the weak polar bond in the chemical structure, and thus provides a degradable paradigm modified PET which retains the advantageous properties of the PET polyester to different degrees and realizes internal degradation, thereby promoting the sustainable development of polyester materials and the environment.

Description

Technical Field

[0001] The present invention relates to the technical field of degradation and modification of polyester materials, and in particular to a degradable polyester and a preparation method thereof. Background Art

[0002] Polyethylene terephthalate (PET) is a versatile thermoplastic polymer widely used in the textile industry as synthetic fibers and as packaging plastic for food and beverage products. PET's linear polymer chain is composed of terephthalic acid and ethylene glycol structural units, linked by a relatively unstable polar formate group, making the macromolecule highly reactive towards various tertiary recycling options. However, PET is difficult to degrade in nature, and disposal by landfill or incineration poses significant environmental risks, necessitating the urgent need for recycling large quantities of waste PET.

[0003] In recent years, as people pay more attention to environmental protection, the concept of sustainable development has become a hot topic. On June 1, 2022, the two recommended national standards, "Degradation Performance and Labeling Requirements of Biodegradable Plastics and Products" and "Biodegradable Drinking Straws", were officially implemented, which means that the promotion and application of degradable materials and products will be greatly accelerated. Regarding PET degradation, the most studied methods at home and abroad are chemical methods and enzymatic degradation methods. Many scholars believe that the two methods have greater exploration value and more far-reaching development prospects than physical methods; however, the above methods cannot fundamentally solve the problem. High cost, low recycling rate and slow technological development have become important factors currently restricting the industrialization of PET recycling. The present invention uses the basic principle of electronic effect to activate and modify the PET molecular chain structure, insert a methylene group between the benzene ring and the formate group to interrupt the strong conjugated stabilization effect, and make PET polyester an intrinsically degradable sustainable polymer material, thereby solving the environmental pollution problem of PET waste. Summary of the Invention

[0004] In light of this, the present invention aims to provide a biodegradable polyester and a method for its preparation. By inserting a methylene group as a paradigm modification, the present invention disrupts the conjugated stabilization effect of the PET polyester molecular chain and activates the polar weak bonds in its chemical structure. The resulting modified PET polyester is not only inherently biodegradable but also exhibits excellent thermal stability.

[0005] In order to achieve the above object, the technical solution of the present invention is:

[0006] A degradable polyester having the chemical structural formula:

[0007]

[0008] In the formula, 0 represents no group, R Ar For Fang support, R CA is cycloalkylene, (0 / RAr / R CA ) represents no group or an arylene or cycloalkylene group between the two -CH2- groups, and n is a natural number ≥ 25.

[0009] Further, the arylene group is a phenylene group, a biphenylene group, a naphthylene group, a furanylene group, a thienylene group or a pyrrolylene group, and the cycloalkylene group is a cyclopentylene group or a cyclohexylene group.

[0010] The present application also provides a preparation method of the above-mentioned degradable polyester, which comprises the following steps: first, pre-polymerization of aromatic diacetic acid or aromatic diacetate monomers and dihydric alcohol monomers by melt esterification or transesterification, and then post-polycondensation.

[0011] Further, the preparation method of the degradable polyester comprises the following steps:

[0012] Step 1, pre-polymerization: weigh aromatic diacetic acid or aromatic diacetate monomers and dihydric alcohol monomers, and add a catalyst; under a nitrogen atmosphere, heat to 190-200°C, and react under mechanical stirring and distillation condensation; when the first drop of water or alcohol by-product is distilled, start timing; the esterification or transesterification reaction lasts for 2.5-3.5 hours until no by-product is distilled.

[0013] Step 2, post-polycondensation: add a polycondensation catalyst; keep mechanical stirring, close the nitrogen atmosphere, remove the distillation condenser, and vacuum to 200 Pa or less; heat to 200-240°C for polycondensation reaction for 3.0-4.5 hours until no vacuum bubble is extracted; after the reaction, pour the reaction mixture into an evaporating dish while hot, and vacuum dry to obtain a crude polyester product.

[0014] Step 3, refine the crude product: dissolve the crude polyester product in a mixed solvent of trifluoroacetic acid and chloroform, use a mixed precipitant of ethylene glycol and methanol to re-precipitate the polyester product from the mixed solvent, perform suction filtration, wash (preferably three times with the mixed precipitant), and finally vacuum dry to obtain the degradable polyester.

[0015] Preferably, in Step 1, the aromatic diacetate monomer is diethyl terephthalate monomer, and the dihydric alcohol monomer is one of ethylene glycol, terephthalyl alcohol or 4,4'-biphenyl dimethyl alcohol monomer.

[0016] Preferably, in Step 1, the molar ratio of aromatic diacetic acid or aromatic diacetate monomers to dihydric alcohol monomers is 1:(1-2.2).

[0017] Further, in Step 1, the catalyst is one or more metal acetates; and in Step 2, the polycondensation catalyst is one metal acetate.

[0018] Preferably, in step 1, the catalyst is one or more of manganese acetate, magnesium acetate and zinc acetate; and in step 2, the polycondensation catalyst is antimony acetate.

[0019] Preferably, in step 1, the molar ratio of the catalyst to the aromatic diacetic acid or aromatic diacetate monomer is [(5×10 -4 )~(2×10 -3 )]: 1; In the step 2, the molar ratio of the polycondensation catalyst to the aromatic diacetic acid or aromatic diacetate monomer is [0~(8×10 -4 )]:1.

[0020] More preferably, the chemical structure of the degradable polyester is (O / R Ar / R CA ) is 0: in the step 1, the diol monomer is ethylene glycol monomer, the molar ratio of aromatic diacetic acid or aromatic diacetate monomer to diol monomer is 1:2.2, the catalyst is manganese acetate, and the molar ratio of catalyst to aromatic diacetic acid or aromatic diacetate monomer is (5×10 -4 ): 1; In the step 2, the polycondensation catalyst is antimony acetate, and the molar ratio of the polycondensation catalyst to the aromatic diacetic acid or aromatic diacetate monomer is (8×10 -4 ):1.

[0021] More preferably, the chemical structure of the degradable polyester is (O / R Ar / R CA ) is R Ar / R CA When: in the step 1, the diol monomer is one of p-phenylenedimethanol or 4,4'-biphenylenedimethanol monomer, the molar ratio of aromatic diacetic acid or aromatic diacetate monomer to diol monomer is 1:1, the catalyst is a mixture of manganese acetate, magnesium acetate and zinc acetate in a molar ratio of 1:1:1, and the molar ratio of the total amount of catalyst to the aromatic diacetic acid or aromatic diacetate monomer is (2×10 -3 ): 1; in the step 2, the amount of the polycondensation catalyst is 0.

[0022] Preferably, in step 1 and step 2, the heating rate is 5°C min -1 , the mechanical stirring rate is 100-200 rpm.

[0023] Preferably, in step 2 and step 3, the vacuum drying temperature is 80-100° C., and the vacuum drying time is 48 h and 72 h, respectively.

[0024] Preferably, in step 3, the volume ratio of trifluoroacetic acid and chloroform in the mixed solvent and the volume ratio of ethylene glycol and methanol in the mixed precipitant are both 1:4, and the volume ratio of the mixed solvent to the mixed precipitant is 1:20.

[0025] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0026] 1. Compared with the existing technology, the present invention is no longer limited to the study of external degradation methods. Instead, it uses the principle of weakening the conjugation effect to promote the heterolytic cleavage of covalent bonds. A methylene group is inserted between the benzene ring and the formate group, interrupting the strong p-π-large π-π-p conjugation in the PET molecular chain, activating the ester group's CO polar weak bond, and realizing the intrinsic degradation of PET polyester through paradigm molecular modification.

[0027] 2. The degradable modified PET polyester prepared by the present invention is a material matrix resin, which can be used to produce plastics, fibers, films, foams, sheets, etc., which is conducive to the recovery and recycling of these materials and products after they are discarded.

[0028] 3. The present invention adopts bulk polymerization, the product is pure, the operation is simple, no complicated separation and purification process is required, the reactor has a large effective reaction volume, is easy to be continuous, has high production efficiency and low production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 For the synthesis system of Example 1 1 H NMR spectra: (a, d) ethylene glycol monomer; (b, e) diethyl terephthalate monomer; (c, f) modified PET polyester, namely polyethylene terephthalate (PEP).

[0030] Figure 2 For the synthesis system of Example 1 13 C NMR spectra: (a, d) ethylene glycol monomer; (b, e) diethyl terephthalate monomer; (c, f) modified PET polyester PEP.

[0031] Figure 3 For the synthesis system of Example 2 1 H NMR spectra: (a, d) dimethylbenzene monomer; (b, e) diethyl terephthalate monomer; (c, f) modified PET polyester, namely poly(terephthalate) (PTP).

[0032] Figure 4 For the synthesis system of Example 2 13 C NMR spectra: (a, d) terephthalic alcohol monomer; (b, e) diethyl terephthalate monomer; (c, f) modified PET polyester PTP.

[0033] Figure 5 For Example 3 synthesis system1 H NMR spectra: (a, d) 4,4'-diphenylmethanol monomer; (b, e) diethyl terephthalate monomer; (c, f) modified PET polyester, namely poly(4,4'-diphenylmethyl terephthalate) (PBP).

[0034] Figure 6 For the synthesis system of Example 3 13 C NMR spectra: (a, d) 4,4'-biphenyl dimethanol monomer; (b, e) diethyl terephthalate monomer; (c, f) modified PET polyester PBP.

[0035] Figure 7 For the comparative example synthesis system 1 H NMR spectra: (a, d) ethylene glycol monomer; (b, e) dimethyl terephthalate monomer; (c, f) PET polyester.

[0036] Figure 8 For the comparative example synthesis system 13 C NMR spectra: (a, d) ethylene glycol monomer; (b, e) dimethyl terephthalate monomer; (c, f) PET polyester.

[0037] Figure 9 For test example 1, 20℃min -1 Differential scanning calorimetry temperature spectra of the modified PET polyester PEP synthesized in Example 1 compared with the PET polyester synthesized in the comparative example at the heating and cooling rates: (a) second heating cycle; (b) cooling cycle.

[0038] Figure 10 Scanning electron micrographs of the surface morphology of the samples (a, c) of the PET polyester synthesized in the comparative example and (b, d) the modified PET polyester PEP synthesized in Example 1 before and after hydrolysis at 90°C under the strong alkaline conditions of 3.0 M NaOH aqueous solution for 5 h: (a, b) before hydrolysis; (c, d) after hydrolysis.

[0039] Figure 11 Scanning electron micrographs of the surface morphology of the samples (a, c) of the PET polyester synthesized in the comparative example and (b, d) the modified PET polyester PEP synthesized in Example 1 before and after hydrolysis at 120°C under the strong acidic conditions of 3.0 M H2SO4 aqueous solution for 12 h: (a, b) before hydrolysis; (c, d) after hydrolysis.

[0040] Figure 12 In Test Example 1, (a) the modified PET polyester PEP synthesized in Example 1 and (b) the PET polyester synthesized in the comparative example were alkaline hydrolyzed in 3.0M NaOH aqueous solution at 90°C for 5h. 1H NMR spectra, where (a1, a2) and (b1, b2) are enlarged views of (a) and (b), respectively.

[0041] Figure 13 In Test Example 1, (a) the modified PET polyester PEP synthesized in Example 1 and (b) the PET polyester synthesized in the comparative example were alkaline hydrolyzed in 3.0M NaOH aqueous solution at 90°C for 5h. 13 C NMR spectroscopy.

[0042] Figure 14 In Test Example 1, (a) the modified PET polyester PEP synthesized in Example 1 and (b) the PET polyester synthesized in the comparative example were acidically hydrolyzed in a 3.0M H2SO4 aqueous solution at 120°C for 12 hours. 1 H NMR spectrum: (a) white needle-shaped crystalline product precipitated from the degradation solution; (b) degradation solution.

[0043] Figure 15 In Test Example 1, (a) the modified PET polyester PEP synthesized in Example 1 and (b) the PET polyester synthesized in the comparative example were acidically hydrolyzed in a 3.0M H2SO4 aqueous solution at 120°C for 12 hours. 13 C NMR spectrum: (a) white needle-shaped crystalline product precipitated from the degradation solution; (b) degradation solution.

[0044] Figure 16 For test example 1, 10℃min in nitrogen atmosphere -1 Thermogravimetric analysis temperature spectra of the modified PET polyester PEP synthesized in Example 1 compared with the PET polyester synthesized in the comparative example at the heating rate: (a) thermal gravimetric loss curve; (b) thermal gravimetric loss differential curve.

[0045] Figure 17 For test example 2, 20℃min -1 Differential scanning calorimetry thermograms of the modified PET polyesters PTP and PBP synthesized in Examples 2 and 3, respectively, compared with the PET polyester synthesized in the comparative example at the heating and cooling rates: (a) second heating cycle; (b) cooling cycle.

[0046] Figure 18 Scanning electron micrographs of the surface morphology of the samples (a, d) of the PET polyester synthesized in the comparative example, (b, e) the modified PET polyester PTP synthesized in Example 2, and (c, f) the modified PET polyester PBP synthesized in Example 3 before and after hydrolysis at 90°C under the strong alkaline condition of 3.0 M NaOH aqueous solution for 5 h: (a, b, c) before hydrolysis; (d, e, f) after hydrolysis.

[0047] Figure 19Scanning electron micrographs of the surface morphology of the samples (a, d) of the PET polyester synthesized in the comparative example, (b, e) the modified PET polyester PTP synthesized in Example 2, and (c, f) the modified PET polyester PBP synthesized in Example 3 before and after hydrolysis at 120°C under the strong acidic conditions of 3.0 M H2SO4 aqueous solution for 24 hours: (a, b, c) before hydrolysis; (d, e, f) after hydrolysis.

[0048] Figure 20 The degradation liquid of (a) the modified PET polyester PBP synthesized in Example 3, (b) the modified PET polyester PTP synthesized in Example 2, and (c) the PET polyester synthesized in the comparative example was subjected to alkaline hydrolysis in a 3.0M NaOH aqueous solution at 90°C for 5h. 1 H NMR spectra, where (a1), (b1), and (c1) are enlarged views of (a), (b), and (c), respectively.

[0049] Figure 21 The degradation liquid of (a) the modified PET polyester PBP synthesized in Example 3, (b) the modified PET polyester PTP synthesized in Example 2, and (c) the PET polyester synthesized in the comparative example was subjected to alkaline hydrolysis in a 3.0M NaOH aqueous solution at 90°C for 5h. 13 C NMR spectroscopy.

[0050] Figure 22 The results of test example 2 are as follows: (a) the modified PET polyester PBP synthesized in Example 3, (b) the modified PET polyester PTP synthesized in Example 2, and (c) the PET polyester synthesized in the comparative example were acidically hydrolyzed in a 3.0M H2SO4 aqueous solution at 120°C for 24 hours. 1 H NMR spectra: (a, b) white needle-shaped crystalline products precipitated from the degradation solution; (c) degradation solution.

[0051] Figure 23 The results of test example 2 are as follows: (a) the modified PET polyester PBP synthesized in Example 3, (b) the modified PET polyester PTP synthesized in Example 2, and (c) the PET polyester synthesized in the comparative example were acidically hydrolyzed in a 3.0M H2SO4 aqueous solution at 120°C for 24 hours. 13 C NMR spectrum: (a, b) white needle-shaped crystalline product precipitated from the degradation solution; (c) degradation solution.

[0052] Figure 24 For test example 2, 10℃min in nitrogen atmosphere -1 Thermogravimetric analysis temperature spectra of the modified PET polyesters PTP and PBP synthesized in Examples 2 and 3, respectively, compared with the PET polyester synthesized in the comparative example at the heating rate: (a) thermal gravimetric loss curve; (b) thermal gravimetric loss differential curve. DETAILED DESCRIPTION

[0053] In order to better understand the present invention, the following examples are provided to further illustrate the present invention, but the present invention is not limited to the following examples. Those skilled in the art may make various modifications or adjustments to the present invention, and these equivalent forms are also within the scope of the claims listed in this application.

[0054] The present invention uses test examples to compare the degradation efficiency of the modified PET degradable polyester prepared in the examples with that of the PET polyester prepared in the comparative examples. Unless otherwise specified, the drugs and raw materials used in the examples, comparative examples and test examples are all commercially available analytical grade.

[0055] Example 1:

[0056] A method for preparing a modified PET degradable polyester, namely polyethylene terephthalate (PEP), comprises the following steps:

[0057] 1. Preliminary polymerization: weigh 4×10 -2 mol diethyl terephthalate monomer and 8.8×10 -2 10 mol ethylene glycol monomer was placed in a 100 mL four-necked flask (nitrogen atmosphere was introduced into the four flasks respectively, and a mechanical stirrer, thermometer, and distillation condensation device were installed, the same below). Manganese acetate catalyst was added. The molar ratio of the catalyst to diethyl terephthalate monomer was (5×10 -4 ):1; Under nitrogen atmosphere, 5℃min -1 The system was heated at a rate (same below). When the system approached 60°C, the diethyl terephthalate monomer melted. At this time, mechanical stirring was started and the speed was set to 100 rpm to mix the two monomers evenly. When the temperature was continued to rise to 190°C, the stirring speed was increased to 200 rpm. The time when the first drop of ethanol by-product was distilled was used as the starting point for timing. The ester exchange reaction was maintained at 190°C for 3.0 to 3.5 hours until no by-product was distilled, thus completing the early polymerization.

[0058] 2. Late polycondensation: After the early polymerization is completed, antimony acetate catalyst is added. The molar ratio of the catalyst to diethyl terephthalate monomer is (8×10 -4 ): 1; the temperature was raised to 220°C, and the polycondensation reaction was maintained at 200 rpm for 1 hour. The viscosity of the system increased significantly. At this time, the nitrogen atmosphere was turned off, the distillation condensation device was removed, and a vacuum pump was used to evacuate the mixture to a vacuum degree of 200 Pa; the temperature was continued to be raised to 240°C, the vacuum degree was increased to 100-150 Pa, and the reaction was stirred for 3.0-3.5 hours. The viscosity of the system continued to increase until no vacuum bubbles were extracted. The stirring and vacuuming were stopped, and the reactants were poured into an evaporating dish while hot and dried in vacuo at 100°C for 48 hours to obtain a crude modified PET polyester product.

[0059] 3. Refining the crude product: Take trifluoroacetic acid and chloroform (volume ratio of 1:4) and mix them evenly to prepare a polyester solvent; take ethylene glycol and methanol (volume ratio of 1:4) and mix them evenly to prepare a polyester settler; place the dried polyester crude product in a 100mL beaker, add 40mL of polyester solvent thereto, and stir magnetically until the crude product is completely dissolved to form a transparent polyester solution; add 800mL of polyester settler to a 1000mL beaker, and slowly pour the above polyester solution into the polyester settler while stirring with a glass rod, refrigerate and let it stand overnight (4-10℃, 8h, the same below) to allow the polyester to reprecipitate and settle to the bottom of the cup; filter the precipitated polyester, wash the filter cake repeatedly three times with a polyester settler, and finally vacuum dry at 100℃ for 72h to obtain modified PET polyester PEP.

[0060] Example 2:

[0061] A method for preparing a modified PET biodegradable polyester, namely poly(terephthalate) (PTP), comprises the following steps:

[0062] 1. Preliminary polymerization: weigh 4×10 -2 mol diethyl terephthalate monomer and 4×10 -2 mol of terephthalic acid methanol monomer was placed in a 100 mL four-necked flask, and manganese acetate, magnesium acetate and zinc acetate catalysts (the molar number of each catalyst was the same). The molar ratio of the total amount of the three catalysts to diethyl terephthalate monomer was (2×10 -3 ): 1; Under a nitrogen atmosphere, the system was heated. When the system approached 60° C., the diethyl terephthalate monomer melted. At this time, mechanical stirring was started and the speed was set to 100 rpm to uniformly mix the two monomers. When the temperature was further raised to 190° C., the stirring speed was increased to 200 rpm. The time when the first drop of ethanol byproduct was distilled was used as the starting point for the timing. The transesterification reaction was maintained at 190° C. for 2.5 to 3.0 hours. The viscosity of the system gradually increased until no byproduct was distilled, completing the early polymerization.

[0063] 2. Late polycondensation: After the early polymerization is completed, no catalyst is added; the nitrogen atmosphere is turned off, the distillation and condensation device is removed, and a vacuum pump is used to evacuate the mixture to a vacuum degree of 200 Pa; the temperature is raised to 220°C, and the polycondensation reaction is carried out under stirring at 200 rpm for 1 hour, and the viscosity of the system further increases; the temperature is continued to be raised to 240°C, the vacuum degree is increased to 100-150 Pa, and the reaction is stirred for 2.0-2.5 hours, and the viscosity of the system continues to increase until no vacuum bubbles are extracted. Then, stirring and vacuuming are stopped, and the reactants are poured into an evaporating dish while hot, and vacuum dried at 100°C for 48 hours to obtain a crude modified PET polyester product.

[0064] 3. Refining the crude product: Take trifluoroacetic acid and chloroform (volume ratio of 1:4) and mix them evenly to prepare a polyester solvent; take ethylene glycol and methanol (volume ratio of 1:4) and mix them evenly to prepare a polyester settler; place the dried polyester crude product in a 100mL beaker, add 40mL of polyester solvent thereto, and stir magnetically until the crude product is completely dissolved to form a transparent polyester solution; add 800mL of polyester settler to a 1000mL beaker, and slowly pour the above polyester solution into the polyester settler while stirring with a glass rod, refrigerate and let it stand overnight to allow the polyester to precipitate again and settle to the bottom of the cup; filter the precipitated polyester, wash the filter cake repeatedly three times with a polyester settler, and finally vacuum dry at 100°C for 72h to obtain modified PET polyester PTP.

[0065] Example 3:

[0066] A method for preparing a modified PET biodegradable polyester, namely poly (4,4'-biphenyl dimethyl terephthalate) (PBP), comprises the following steps:

[0067] 1. Preliminary polymerization: weigh 4×10 -2 mol diethyl terephthalate monomer and 4×10 -2 mol 4,4'-biphenyl dimethanol monomer was placed in a 100 mL four-necked flask, and manganese acetate, magnesium acetate and zinc acetate catalysts (the molar number of each catalyst was the same). The molar ratio of the total amount of the three catalysts to diethyl terephthalate monomer was (2×10 -3 ): 1; Under a nitrogen atmosphere, the system was heated. When the system approached 60° C., the diethyl terephthalate monomer melted. At this time, mechanical stirring was started and the speed was set to 100 rpm to uniformly mix the two monomers. When the temperature was further raised to 190° C., the stirring speed was increased to 200 rpm. The time when the first drop of ethanol byproduct was distilled was used as the starting point for the timing. The transesterification reaction was maintained at 190° C. for 2.5 to 3.0 hours. The viscosity of the system gradually increased until no byproduct was distilled, completing the early polymerization.

[0068] 2. Late polycondensation: After the early polymerization is completed, no catalyst is added; the nitrogen atmosphere is turned off, the distillation and condensation device is removed, and a vacuum pump is used to evacuate the mixture to a vacuum degree of 200 Pa; the temperature is raised to 220°C, and the polycondensation reaction is carried out under stirring at 200 rpm for 1 hour, and the viscosity of the system further increases; the temperature is continued to be raised to 240°C, the vacuum degree is increased to 100-150 Pa, and the reaction is stirred for 2.0-2.5 hours, and the viscosity of the system continues to increase until no vacuum bubbles are extracted. Then, stirring and vacuuming are stopped, and the reactants are poured into an evaporating dish while hot, and vacuum dried at 100°C for 48 hours to obtain a crude modified PET polyester product.

[0069] 3. Refining the crude product: trifluoroacetic acid and chloroform (volume ratio 1:4) are mixed uniformly to prepare polyester solvent; ethylene glycol and methanol (volume ratio 1:4) are mixed uniformly to prepare polyester precipitant; the dried polyester crude product is placed in a 100 mL beaker, 40 mL of polyester solvent is added, and the crude product is stirred magnetically until it is completely dissolved to form a transparent polyester solution; 800 mL of polyester precipitant is added to a 1000 mL beaker, and the polyester solution is slowly poured into the polyester precipitant under glass rod stirring, and the mixture is refrigerated and left overnight to allow the polyester to re-precipitate and settle at the bottom of the beaker; the precipitated polyester is suction filtered, the filter cake is washed repeatedly three times with polyester precipitant, and finally dried at 100°C under vacuum for 72 h to obtain the modified PET polyester PBP.

[0070] Comparative Example:

[0071] A method for preparing a PET polyester, the method comprising the following steps:

[0072] 1. Pre-polymerization: 4 x 10 -2 mol of dimethyl terephthalate monomer and 8.8 x 10 -2 mol of ethylene glycol monomer are weighed into a 100 mL four-necked flask, and a manganese acetate catalyst is added, the molar ratio of the catalyst to the dimethyl terephthalate monomer being (5 x 10 -4 ): 1; under a nitrogen atmosphere, the system is warmed, and when the dimethyl terephthalate monomer melts at a temperature close to 140°C, mechanical stirring is started at a speed of 100 rpm to mix the two monomers uniformly; the temperature is further increased to 190°C, and the stirring speed is increased to 200 rpm, and the ester exchange reaction is carried out at 190°C for 4.0-4.5 h until no byproduct is distilled out, and the pre-polymerization is completed.

[0073] 2. Post-polymerization: after the pre-polymerization is completed, an antimony acetate catalyst is added, the molar ratio of the catalyst to the dimethyl terephthalate monomer being (8 x 10 -4 ): 1; the temperature is increased to 240°C, and the polymerization is carried out under stirring at 200 rpm for 1 h, and then the nitrogen atmosphere is removed, the distillation condenser is removed, and vacuum is applied using a vacuum pump to achieve a vacuum degree of 200 Pa; the temperature is then increased to 250°C, and the stirring is carried out for 1 h, and the viscosity of the system is further increased; the temperature is then increased to 270°C, the vacuum degree is increased to 100-150 Pa, and the stirring is carried out for 2.0-2.5 h, and the viscosity of the system continues to increase until no vacuum bubble is distilled out, and then the stirring and vacuum are stopped, and the reaction product is poured into an evaporating dish while hot, and dried at 100°C under vacuum for 48 h to obtain the PET polyester crude product.

[0074] 3. Purify the crude product: take trifluoroacetic acid and chloroform (volume ratio of 1:4) and mix them evenly to prepare a polyester solvent; take ethylene glycol and methanol (volume ratio of 1:4) and mix them evenly to prepare a polyester precipitant; place the dried polyester crude product in a 100mL beaker, add 40mL of polyester solvent thereto, and stir magnetically until the crude product is completely dissolved to form a transparent polyester solution; add 800mL of polyester precipitant to a 1000mL beaker, and slowly pour the above polyester solution into the polyester precipitant while stirring with a glass rod, refrigerate and let it stand overnight to allow the polyester to precipitate again and settle to the bottom of the cup; filter the precipitated polyester, wash the filter cake repeatedly three times with a polyester precipitant, and finally vacuum dry at 100°C for 72h to obtain PET polyester.

[0075] Testing and Characterization:

[0076] The structures of the modified PET polyesters PEP, PTP and PBP prepared in Examples 1 to 3 and the PET polyester prepared in the comparative example were characterized, and the characterization included the following steps:

[0077] 1. Utilize 1 H and 13 C nuclear magnetic resonance spectroscopy was used to characterize the chemical structures of the monomers and their polymerization products, namely, comparative characterization of: ethylene glycol monomer, diethyl terephthalate monomer, and PEP in Example 1; terephthalic acid diethyl ester monomer, and PTP in Example 2; 4,4'-biphenyl dimethanol monomer, diethyl terephthalate monomer, and PBP in Example 3; and ethylene glycol monomer, dimethyl terephthalate monomer, and PET polyester in the comparative example.

[0078] Weigh 5-10 mg (for 1 H spectrum test) or 40-50 mg (for 13 C spectrum test) The sample was placed in an NMR tube, and 0.5-0.6 mL of deuterated solvent was added to prepare a solution sample. A Bruker Ascend 400 NMR spectrometer was used to collect the chemical shift (δ) values ​​of the solution sample. 1 H and 13 C nuclear magnetic resonance peak. Before preparing the solution sample, the deuterated solvent was fully dried with molecular sieves. The deuterated solvent used for ethylene glycol monomer, diethyl terephthalate monomer, PEP, PTP and dimethyl terephthalate monomer was deuterated chloroform (CDCl3), the deuterated solvent used for terephthalic acid monomer and 4,4'-biphenyl dimethanol monomer was deuterated dimethyl sulfoxide (C2D6SO), the deuterated solvent used for PET polyester was deuterated trifluoroacetic acid (CF3COOD), and the deuterated solvent used for PBP was CF3COOD (for 1 H spectrum test), CDCl3 (for 13 C spectrum test).

[0079] 2. In accordance with the national standard GB / T23942-2009, the metal element content of the residual catalyst in the polyester and its crude product was determined by inductively coupled plasma optical emission spectrometry: in Example 1 and the comparative example, the manganese and antimony contents in the polyester crude product of step 2 and the polyester of step 3 were compared and determined; in Examples 2 and 3, the manganese, magnesium, and zinc contents in the polyester crude product of step 2 and the polyester of step 3 were compared and determined.

[0080] A 100mg sample was weighed and placed in a polytetrafluoroethylene digestion tube. 5mL of 68wt% concentrated nitric acid, 1mL of 36-38wt% concentrated hydrochloric acid, and 1mL of 40wt% hydrofluoric acid were added, followed by digestion at 200°C for 5h. The sample was then transferred to a 25mL volumetric flask, made up to volume with deionized water, and allowed to stand for 12h to prepare the digestion solution. Using an Agilent ICP-OES 730 inductively coupled plasma optical emission spectrometer, a calibration curve was first determined, followed by testing of the digestion solution. Finally, the concentration of each metal element in the sample was determined based on the calibration curve.

[0081] 3. According to the national standard GB / T1632.1-2008, the intrinsic viscosity method was used to test the degree of polymerization of polyester (viscosity-average degree of polymerization, the same below): comparative tests were conducted on the degree of polymerization of modified PET polyesters PEP, PTP, PBP and PET polyester.

[0082] Weigh 0.2500g, For polyester samples, 50 mL of a mixed solvent of phenol and 1,1,2,2-tetrachloroethane (the mass ratio of phenol to tetrachloroethane is 1:1, the same below) was used to prepare the concentrations of c, (c=0.5g dL -1 ) sample solution. After filtering the solution with a filter head, use an Ubbelohde viscometer (inner diameter 0.5-0.6mm) in a 25°C constant temperature water bath to measure its average outflow time. (The median of five test values, the same below); Similarly, the average elution time of the mixed solvent (ie, 0c) was determined.

[0083] The three concentrations (C, C = c, The same below) The intrinsic viscosity of the sample [η] (dL g -1 ):

[0084]

[0085] The molecular weights of the three concentration samples were estimated using the following Mark-Houwink empirical equation: (g mol -1 ) (viscosity average molecular weight, the same below):

[0086]

[0087] Here, it is assumed that, like PET polyester, the intrinsic viscosity and molecular weight of the polyesters PEP, PTP, and PBP in a mixed solvent of phenol and 1,1,2,2-tetrachloroethane at 25°C approximately conform to the above Mark-Houwink equation, that is, the two constants of the four polyesters are 2.1×10 -4 Finally, the median of the three DP values ​​obtained by dividing the molecular weight by the molar mass of the repeating unit is taken as the DP test value of the sample.

[0088] Test Example 1:

[0089] A comparative test of the degradation efficiency of a modified PET degradable polyester PEP (Example 1) and a PET polyester (Comparative Example) was conducted, wherein the comparative test included the following items in sequence:

[0090] Project 1: Determine the crystallization properties of polyester using differential scanning calorimetry according to GB / T19466-2004 national standard: Compare the thermal transition behaviors of PEP and PET polyesters.

[0091] Using a Netzsch DSC 214 differential scanning calorimeter, the temperature and heat flow were calibrated with indium standard metal and the reaction was carried out at 20 mL min -1 The test was carried out under nitrogen atmosphere. Weigh 5-10 mg of sample, seal it in an aluminum crucible, and place it in the sample chamber; another blank aluminum crucible was sealed and placed in the reference chamber. -1 The rate was raised from room temperature (25℃, the same below) to 300℃ to eliminate the effect of sample preparation history; then the temperature was raised to 20℃min -1 From 300℃ to -60℃; finally at 20℃min -1 From -60℃ to 300℃. In the cooling and second heating cycles, the heat flow (W g -1 ) Temperature spectrum of the temperature change with temperature (℃). In the temperature spectrum of cooling (or second heating), the peak point (℃) and peak area (J g -1 ) are defined as the temperature and enthalpy of crystallization (or melting), respectively; in the second temperature rise spectrum, the inflection point (°C) of the step is defined as the glass transition temperature (or transition temperature).

[0092] Project 2: Conduct polyester degradation experiments: Compare the acidic and alkaline hydrolysis experiments of PEP and PET polyester under the same conditions.

[0093] The alkaline hydrolysis experiment includes the following steps:

[0094] Step 1: Alkaline water degrading agent preparation: weigh 30 g of NaOH into a 500 mL beaker, slowly add 200 mL of deionized water, and stir with a glass rod until completely dissolved; after the solution cools to room temperature, transfer it to a 250 mL volumetric flask, and use deionized water to dilute to volume, stand overnight to prepare a 3.0 M NaOH aqueous solution.

[0095] Step 2: Degrading experiment implementation: use Wuhan Ruiming SZS-20 micro injection molding machine, add sample powder into the barrel, preheat and tamp, inject into the mold cavity at 230°C (for PEP) or 270°C (for PET polyester) under compressed air pressure, and form an injection molded sample strip (the same below); cut the injection molded sample strip into 10 mm x 5 mm x 2 mm rectangular pieces; select four of them, weigh (total) and place them in a 250 mL two-necked flask (both equipped with a mechanical stirrer and a reflux condenser, the same below), add 50 mL of the alkaline water prepared in step 1, and reflux at 90°C under 500 rpm mechanical stirring for 5 hours.

[0096] Step 3: Degrading sample collection: remove the residual sample pieces, wash them repeatedly with deionized water three times, and dry them at 80°C under vacuum for 48 hours; filter the degradation solution, and recover the filtered residual debris and filtrate; the debris is washed repeatedly with deionized water three times, combined with the washed residual sample pieces, and dried at 80°C under vacuum for 48 hours; take 10 mL of the filtrate and seal it in a sample bottle as the degradation liquid sample to be tested.

[0097] The acidic hydrolysis experiment includes the following steps:

[0098] Step 1: Acidic water degrading agent preparation: in a 500 mL beaker, add 200 mL of deionized water, and slowly pour in 41.5 mL of concentrated H2SO4 (mass fraction 98.3%), and stir with a glass rod until well mixed; after the solution cools to room temperature, transfer it to a 250 mL volumetric flask, and use deionized water to dilute to volume, stand overnight to prepare a 3.0 M H2SO4 aqueous solution.

[0099] Step 2: Degrading experiment implementation: cut the injection molded sample strip into 10 mm x 5 mm x 2 mm rectangular pieces; select four of them, weigh (total) and place them in a 250 mL two-necked flask, add 50 mL of the acidic water prepared in step 1, and reflux at 120°C under 500 rpm mechanical stirring for 12 hours.

[0100] Step 3: Degrading sample collection: remove the residual sample pieces, wash them repeatedly with deionized water three times, and dry them at 80°C under vacuum for 48 hours; for PEP, filter the degradation solution, and recover the white needle-shaped crystalline product precipitated therein, which is washed and dried like a sample piece for testing; for PET polyester, no product is precipitated in the degradation solution, directly take 10 mL of the degradation solution and seal it in a sample bottle for testing.

[0101] Item 3, according to the JY / T0584-2020 standard, observe the surface micro-morphology of the polyester in the degradation experiment by scanning electron microscopy: compare and observe the surface of PEP and PET polyesters before and after acid and alkaline hydrolysis experiments respectively.

[0102] The surface morphology of the sample was observed using a Hitachi SU 8010 scanning electron microscope. The sample to be tested was adhered to the sample stage using conductive glue, and after platinum spraying, it was transferred to the microscope sample chamber for observation.

[0103] The samples before acid and alkaline hydrolysis were rectangular samples before reaction in step 2 of the acid and alkaline hydrolysis steps in item 2 degradation experiment, and the samples after acid and alkaline hydrolysis were residual samples after drying in step 3 of the acid and alkaline hydrolysis steps in item 2 degradation experiment.

[0104] Item 4, using the weighing method, determine the mass loss rate of the polyester in the degradation experiment: compare and estimate the weight loss rate of PEP and PET polyesters after hydrolysis compared to before hydrolysis in acid and alkaline hydrolysis experiments.

[0105] The mass loss rate (%) of the polyester sample is estimated by the following equation:

[0106]

[0107] In the formula, m AD (g) is the sample mass before the degradation experiment, m PD (g) is the sample mass after the degradation experiment.

[0108] During acid and alkaline hydrolysis, m AD is the total weight of the four samples before reaction in step 2 of the acid and alkaline hydrolysis steps in item 2 degradation experiment; during alkaline hydrolysis, m PD is the total weight of the residual sample and debris after drying in step 3 of the alkaline hydrolysis step in item 2 degradation experiment, and during acid hydrolysis, m PD is the weight of the residual sample after drying in step 3 of the acid hydrolysis step in item 2 degradation experiment.

[0109] Item 5, using 1 H and 13 C nuclear magnetic resonance spectroscopy, analyze the chemical structure of the polyester after the degradation experiment: compare and analyze the products in the degradation solution of PEP and PET polyesters after acid and alkaline hydrolysis experiments respectively.

[0110] Using a Bruker Ascend 400 nuclear magnetic resonance spectrometer, collect the 1 H and 13C NMR peak. Before preparing solution samples, deuterated solvents were thoroughly dried using molecular sieves.

[0111] After alkaline hydrolysis, 0.1 mL of the degradation solution to be tested encapsulated in step 3 was taken and placed in a nuclear magnetic resonance tube, and 0.6 mL of deuterated water (D2O) was added to prepare a solution sample.

[0112] After acid hydrolysis: For PEP, take 5 mg (for 1 H spectrum test) or 20-30 mg (for 13 C spectrum test) In step 3, the white needle-shaped crystalline product to be tested was recovered by filtration from the degradation solution, dried, placed in an NMR tube, and 0.6 mL of CF3COOD was added to prepare a solution sample; for PET polyester, the sample was prepared similarly to that after alkaline hydrolysis.

[0113] Project 6: Characterize the thermal stability of polyester using thermogravimetric analysis according to GB / T33047-2016 and JY / T0589.5-2020 standards: Comparative test of the thermal decomposition temperatures of PEP and PET polyesters.

[0114] A TA Instruments SDT Q600 thermogravimetric-differential thermal analyzer was used to analyze the -1 The test was carried out under nitrogen atmosphere. Two empty Al2O3 crucibles were placed on the two trays of the balance in the furnace and leveled; 3-5 mg of dried polyester sample was weighed and placed in the outer crucible, and the furnace was closed; the temperature was set at 10℃ min -1 The temperature is raised from room temperature to 800°C, and the weight of the sample and the rate of weight change with temperature are recorded in real time. The temperature corresponding to 5% weight loss is defined as the thermal decomposition temperature.

[0115] Test Example 2:

[0116] A comparative test of the degradation efficiency of a modified PET degradable polyester PTP and PBP (Examples 2 and 3) and a PET polyester (Comparative Example), the comparative test including the following items in sequence:

[0117] Project 1: Determine the crystallization properties of polyester using differential scanning calorimetry according to national standard GB / T19466-2004: Comparative test of the thermal transition behavior of PTP, PBP, and PET polyesters.

[0118] The specific test method is the same as item 1 in test example 1. In addition, the crystallization enthalpy ΔH mc (J g -1 ), the crystallinity of the sample X c (%) is estimated by the following equation:

[0119]

[0120] Where, is the ideal melting enthalpy when the crystallinity reaches 100% theoretically, and assuming that the PTP and PBP Both with PET polyester Literature value (117.6 J g -1 )quite.

[0121] Project 2: Conduct polyester degradation experiments: Compare the acidic and alkaline hydrolysis experiments of PTP, PBP and PET polyester under the same conditions.

[0122] When preparing injection-molded sample strips in the acidic and alkaline hydrolysis experiments, the injection molding temperature of PTP and PBP was 230°C, and the injection molding temperature of PET polyester was 270°C.

[0123] In the alkaline hydrolysis experiment, residual flakes and debris were produced in the degradation solutions of PTP, PBP and PET polyester. In the acidic hydrolysis experiment, white needle-shaped crystalline products were precipitated in the degradation solutions of PTP and PBP, but no products were precipitated in the degradation solution of PET polyester.

[0124] The specific alkaline hydrolysis experimental method is the same as item 2 in test example 1.

[0125] The specific acidic hydrolysis experimental method is similar to that of item 2 in test example 1; the difference is that the reflux reaction time in the corresponding step 2 is 24 hours.

[0126] Project 3: In accordance with the JY / T0584-2020 standard, the surface morphology of polyester in degradation experiments was observed using scanning electron microscopy technology: the surfaces of PTP, PBP, and PET polyesters were compared before and after acidic and alkaline hydrolysis experiments.

[0127] The specific observation method is the same as item 3 in test example 1.

[0128] Project 4: Use the weighing method to determine the mass loss rate of polyester in degradation experiments: Compare and estimate the weight loss rate of PTP, PBP and PET polyesters after hydrolysis compared with before hydrolysis in acidic and alkaline hydrolysis experiments.

[0129] The specific estimation method is the same as item 4 in test example 1.

[0130] Project 5: Utilization 1 H and 13 C nuclear magnetic resonance spectroscopy was used to analyze the chemical structure of polyester after degradation experiments: the products of PTP, PBP and PET polyester in the degradation liquid after acidic and alkaline hydrolysis experiments were compared and analyzed respectively.

[0131] The specific analysis method after alkaline hydrolysis is the same as item 5 in Test Example 1.

[0132] The specific analysis method after acid hydrolysis is similar to item 5 in Test Example 1, wherein the sample preparation of PTP and PBP is similar to that of PEP; the difference is that the deuterated solvent used for sample preparation of PTP and PBP is CDCl3; for PBP, due to the small amount of white needle-shaped crystalline product precipitated in its degradation solution, 2 mg is taken for 1 H spectrum test and 5 mg for 13 C spectrum test.

[0133] Item 6, according to GB / T33047-2016 and JY / T0589.5·2020 standards, the thermal stability of the polyester is characterized by thermal gravimetric analysis method: the thermal decomposition temperatures of PTP, PBP and PET polyesters are compared and tested.

[0134] The specific test method is the same as item 6 in Test Example 1.

[0135] Test results

[0136] 1. NMR spectroscopy results:

[0137] From Figure 1 and Figure 2 It can be seen that the chain chemical structure of the polymerization product (c, f) in Example 1 is clear relative to the monomers (a, d; b, e): 1 H nuclear magnetic resonance spectrum Figure 1 The three resonance peaks in (c) are respectively attributed to the modified PET polyester PEP repeating unit Figure 1 The three chemical environment H atoms in (f); 13 C nuclear magnetic resonance spectrum Figure 2 The five resonance peaks in (c) are respectively attributed to the PEP repeating unit Figure 2 The five chemical environment C atoms in (f); both figures Figure 1 (c, 2c) do not show other impurity peaks; these indicate that the polymerization product is a modified PET polyester PEP with high purity, and the synthesis is successful.

[0138] Similarly, from Figure 3 and Figure 4 It can be seen that the modified PET polyester PTP in Example 2 is successfully synthesized; from Figure 5 and Figure 6 It can be seen that the modified PET polyester PBP in Example 3 is successfully synthesized; from Figure 7 and Figure 8 It can be seen that the PET polyester in the comparative example is successfully synthesized.

[0139] 2. Inductively coupled plasma emission spectroscopy results:

[0140] As can be seen from Table 1, in Examples 1 to 3 and the comparative example, compared with the polyester crude product obtained in step 2, the metal element content of the residual catalyst in the PEP, PTP, PBP and PET polyester obtained in step 3 decreased by nearly two orders of magnitude (from 10 -4 to 10 -6 gg -1 ), indicating that after refining, the residual catalysts in the four polyesters were effectively removed, which eliminated the influence of the catalysts on the subsequent degradation reactions to the greatest extent and increased the comparability of the subsequent comparative degradation experiments.

[0141] Table 1 The metal element content of the residual catalyst in the crude products of the modified PET polyesters PEP, PTP and PBP prepared in Examples 1 to 3 and the PET polyester prepared in the comparative example

[0142]

[0143] 3. Intrinsic viscosity method results:

[0144] As can be seen from Table 2, the degrees of polymerization of the polyesters PEP, PTP and PBP prepared in Examples 1 to 3 and the PET polyester prepared in the comparative example are 29, 32, 30 and 31 (taking the median of the three degrees of polymerization values), respectively. That is, the degrees of polymerization of the four polyesters are equivalent, which eliminates the effect of the degree of polymerization on the subsequent degradation reaction to the greatest extent and increases the comparability of subsequent comparative degradation experiments.

[0145] Table 2 Intrinsic viscosity ([η]), molecular weight of modified PET polyesters PEP, PTP and PBP prepared in Examples 1 to 3 and PET polyester prepared in the comparative example and degree of polymerization

[0146]

[0147]

[0148] Note: In the table, c = 0.5 g dL -1 , “·” indicates not applicable.

[0149] Test case 1 results:

[0150] 1. Before conducting comparative degradation experiments on PEP and PET polyesters, the crystallization performance, an important factor affecting the degradation efficiency, was investigated. Figure 9 It can be seen that compared with PET polyester which undergoes glass transition at 78.0℃ ( Figure 9 a) and obvious crystallization at 204.8℃ ( Figure 9 b), the glass transition temperature of PEP dropped significantly to 6.8℃ ( Figure 9 a) and does not crystallize ( Figure 9b) The researchers revealed that the insertion of methylene groups disrupts the rigid, planar structure formed by strong conjugation, significantly softening the PEP molecular chain to the point that it thermodynamically does not crystallize. As expected, amorphous PEP is more easily penetrated by degradation agents than crystalline PET, leading to increased degradation efficiency.

[0151] 2. By Figure 10 It was observed that before alkaline hydrolysis, PET polyester ( Figure 10 a) and PEP( Figure 10 b) The surface is smooth and crack-free. However, after alkaline hydrolysis etching, the surface morphology of the two polyesters is significantly different: PET polyester ( Figure 10 c) Surface holes and cracks are small and few; but PEP ( Figure 10 d) A large number of holes and cracks are obviously produced on the surface, and the surface layer is completely degraded and peeled off, leaving grooves of varying depths.

[0152] Similarly, by Figure 11 It was observed that before acid hydrolysis, PET polyester ( Figure 11 a) and PEP( Figure 11 b) The surface is smooth and crack-free. However, after acid hydrolysis etching, PET polyester ( Figure 11 c) Only a few superficial fine lines appear on the surface, but PEP ( Figure 11 d) A large number of holes, grooves and even debris are obviously produced on the surface.

[0153] Therefore, during acidic and alkaline hydrolysis, the surface etching degree of PEP is significantly higher than that of PET polyester, that is, the degradation efficiency of modified PET polyester PEP is much higher than that of PET polyester.

[0154] 3. As shown in Table 3, the mass loss rates of PET and PEP during alkaline hydrolysis were 5.9% and 89.3%, respectively, while during acidic hydrolysis, the mass loss rates were 0.3% and 90.6%, respectively. These comparative data indicate that under both acidic and alkaline conditions, significantly more PEP than PET was lost to the degradation solution through hydrolysis, indicating that PEP is much more efficient in degradation than PET.

[0155] Table 3 In the acidic and alkaline hydrolysis experiments, the degradation mass (m) of the modified PET polyester PEP prepared in Example 1 compared with that of the PET polyester prepared in the comparative example AD ), mass after degradation experiment (m PD ) and mass loss rate

[0156]

[0157] 4. In terms of chemical structure, Figure 12It can be seen that after alkaline hydrolysis, the PEP degradation solution showed 6.95, 3.35 and 3.24 ppm 1 H resonance peak ( Figure 12 a: a1, a2), respectively attributed to the 2,3-position C of the benzene ring of terephthaloyloxy, the ethylene H of ethylenedioxy, and the methylene H of terephthaloyloxy; while only 7.60 ppm appeared in the PET polyester degradation liquid. 1 H resonance peak ( Figure 12 b: b1, b2), attributed to the H at the 2,3-position C of the benzene ring of terephthaloyloxy. Figure 13 In the PEP degradation solution after alkaline hydrolysis, 181.11, 135.12, 129.14 and 43.91 ppm appeared 13 C resonance peak ( Figure 13 a), which were attributed to the carbonyl C of terephthaloyloxy, C at positions 1,4 and 2,3 of the benzene ring, and methylene C; while the PET polyester degradation liquid only produced 128.62ppm with a very low signal-to-noise ratio. 13 C resonance peak ( Figure 13 b), C at the 2,3 positions of the benzene ring is attributed to terephthaloyloxy. Figure 12 ,13 Spectral data revealed that the PEP degradation liquid was rich in alkaline hydrolysis products of disodium terephthalate and disodium ethylene glycol, while the PET polyester degradation liquid contained very little alkaline hydrolysis products of disodium terephthalate and disodium ethylene glycol.

[0158] Figure 14 The white needle-shaped crystals precipitated from the PEP degradation solution after acidic hydrolysis occurred at 8.99 and 5.49 ppm. 1 H resonance peak ( Figure 14 a), respectively attributed to the H on the 2nd and 3rd carbon of the benzene ring of terephthaloyloxy and the methylene H; while no H appeared in the PET polyester degradation liquid. 1 H resonance peak ( Figure 14 b) By Figure 15 It can be seen that the white needle-shaped crystalline products precipitated from the PEP degradation solution after acidic hydrolysis appeared at 181.46, 133.41, 131.23 and 41.06 ppm 13 C resonance peak ( Figure 15 a), respectively attributed to the carbonyl C of terephthaloyloxy, C at 1,4 and 2,3 positions of benzene ring, and methylene C; while PET polyester degradation liquid did not 13 C resonance peak ( Figure 15 b). Figure 14 ,15 The spectral data revealed that the PEP degradation liquid was rich in terephthalic acid acid hydrolysis products, and its crystals were precipitated, while the acid hydrolysis products in the PET polyester degradation liquid were so little that they could be ignored.

[0159] Therefore, during acidic and alkaline hydrolysis, the concentration of hydrolysis products in the degradation solution of polyester PEP is much higher than that of PET polyester, that is, the degradation efficiency of PEP is much higher than that of PET polyester.

[0160] In summary, the above comparative degradation experimental test results 2 to 4 (surface morphology, mass loss rate, chemical structure) self-consistently show that compared with the non-degradable PET polyester, the degradation efficiency of the polyester PEP prepared by modification is greatly improved, and it is a degradable polyester.

[0161] The modification of PEP by inserting a methylene group between the benzene ring and the formate group in PET disrupts the strong macroconjugation in the PET molecule, resulting in two primary effects: a significant softening of the molecular chain, preventing crystallization; and a significant reduction in conjugation stability, activating the weak polar C·O bonds in the ester group. The former externally accelerates degradation agent penetration, while the latter intrinsically promotes heterolytic cleavage of the C·O bond; these two effects combine to achieve PEP degradation. Because polyester PEP degrades much more efficiently than PET, while the external factor (amorphous state) plays a significant role, the degradation is essentially due to an internal factor (weak bond activation).

[0162] 5. By Figure 16 It can be seen from a that the thermal decomposition temperature of PEP is 386.2℃, which is not much lower than the thermal decomposition temperature of PET polyester (415.5℃), and still remains above 350℃. Figure 16 As shown in Figure 2, PEP and PET polyester thermally decompose most rapidly at 455.5°C and 460.9°C, respectively, which are comparable. Therefore, compared with non-degradable PET polyester, polyester PEP maintains higher thermal stability while achieving degradation.

[0163] Test case 2 results:

[0164] In order to further confirm that the main essential reason for the degradation achieved by methylene insertion modification is weak bond activation rather than amorphous state, Examples 2 and 3, based on Example 1, respectively insert a benzene ring and biphenyl with increasing rigidity between the two methylene groups of the ethylene glycol monomer, and use 4,4'-biphenyl dimethanol monomers and 4,4'-biphenyl dimethanol monomers to condense with diethyl terephthalate monomers, respectively, to prepare polyesters PTP and PBP with increased chain rigidity and thus restored crystallinity, and then compare the degradation efficiency with the PET polyester prepared in the comparative example.

[0165] 1. Before conducting comparative degradation experiments on PTP, PBP and PET polyester, examine the crystallization properties. Figure 17 The differential scanning calorimetry temperature spectrum of the three was used to obtain the crystallization performance data in Table 4. Figure 9As shown in Table 4, the glass transition temperature increases in the order of PEP, PTP, PBP, and PET polyester (6.8 → 27.7 → 58.7 → 78.0°C), indicating that the chain rigidity of PTP and PBP increases compared to PEP (although still lower than that of PET polyester), and both have indeed restored significant crystallinity. The crystal phase of PTP, PBP, and PET polyester with increasing chain rigidity gradually "hardens", so the crystallization and melting temperatures increase monotonically (T mc :107.8→183.5→204.8℃; T m :175.1→220.1→254.8℃).

[0166] Table 4 Crystallization properties of modified PET polyesters PTP and PBP prepared in Examples 2 and 3 respectively compared with those of PET polyester prepared in the comparative example

[0167]

[0168] Note: In the table, T g is the glass transition temperature, T mc is the crystallization temperature, ΔH mc is the crystallization enthalpy, T m is the melting temperature, ΔH m is the melting enthalpy, X c is the crystallinity.

[0169] In the order of PBP, PTP, and PET polyesters, the repeating units contain three, two, and one rigid bulky benzene ring, respectively, which causes the free volume between the chain segments to decrease and the interaction force to increase. Therefore, as can be seen from Table 4, the crystallization enthalpy and melting enthalpy increase monotonically (ΔH mc :43.9→48.1→53.2J g -1 ; ΔH m :50.9→55.9→57.8J g -1 ), resulting in the test case 2 item 1 The estimated crystallinity also increases in sequence (37.3→40.9→45.2%). Importantly, the three crystallinity values ​​are not much different; in fact, the crystallinity of PBP, PTP, and PET polyesters is not much different. The value also increases gradually, reaching 117.6 J g for PET polyester. -1 Therefore, the actual crystallinity of the three may be closer, all close to 45.2% of PET polyester.

[0170] The crystallinity of PTP, PBP and PET polyester is similar, which further increases the comparability for characterizing the intrinsic degradation activity (the effect of weak bond activation on degradation efficiency) through comparative degradation experiments.

[0171] 2. By Figure 18 It was observed that before alkaline hydrolysis, PET polyester ( Figure 18 a) With PTP( Figure 18 b) PBP( Figure 18 c) The surface is smooth and crack-free. After alkaline hydrolysis etching, the surface morphology of the three polyesters is significantly different: PET polyester ( Figure 18 d) Surface holes and cracks are small and few; PTP ( Figure 18 e) Huge, deep holes are formed on the surface, the surface layer is severely degraded and peeled off, and PBP ( Figure 18 f) The surface etching degree is moderate, resulting in larger and more holes and cracks.

[0172] Similarly, by Figure 19 It was observed that before acid hydrolysis, PET polyester ( Figure 19 a) With PTP( Figure 19 b) PBP( Figure 19 c) The surface is smooth and crack-free. After acid hydrolysis etching: PET polyester ( Figure 19 d) Only a few superficial fine lines appear on the surface; PTP ( Figure 19 e) The surface is rich in holes, cracks and grooves, while PBP ( Figure 19 f) The surface etching degree is moderate, with some obvious holes and cracks.

[0173] Therefore, during acidic and alkaline hydrolysis, the degradation efficiency of modified PET polyesters PTP and PBP is significantly higher than that of PET polyester; among the first two, the degradation efficiency of PTP is significantly higher than that of PBP.

[0174] 3. As shown in Table 5, the mass loss rates of PET polyester, PTP, and PBP during alkaline hydrolysis were 7.0%, 93.0%, and 16.7%, respectively, while during acidic hydrolysis, the mass loss rates of the three materials were 1.0%, 37.6%, and 7.0%, respectively. These comparative data indicate that although the degree of acidic hydrolysis is lower than that of alkaline hydrolysis, both PTP and PBP hydrolyze and lose more of their mass into the degradation solution than PET polyester under both acidic and alkaline conditions. This indicates that the degradation efficiency of polyester PTP and PBP is significantly higher than that of PET polyester. Of the former two, the degradation efficiency of PTP is significantly higher than that of PBP.

[0175] Table 5: The degradation weight (m) of the modified PET polyesters PTP and PBP prepared in Examples 2 and 3, respectively, compared with that of the PET polyester prepared in the comparative example in the acidic and alkaline hydrolysis experiments before the degradation experiment. AD ), mass after degradation experiment (m PD ) and mass loss rate

[0176]

[0177] 4. By Figure 20 It can be seen that after alkaline hydrolysis, the PBP degradation solution produced 7.93ppm1 H resonance peak ( Figure 20 a: a1), attributed to the 3,3′-position C H of the benzene ring of 4,4′-biphenyldimethoxy; PTP degradation solution produces strong 7.11 and 6.95 ppm 1 H resonance peak ( Figure 20 b: b1), which are respectively attributed to the 2,3-position C H of the benzene ring of terephthalyloxy and terephthalyloxy; while the PET polyester degradation liquid only weakly appears 7.13ppm 1 H resonance peak ( Figure 20 c: c1), H at the 2,3-position C of the benzene ring is attributed to terephthaloyloxy. Figure 21 In the alkaline degradation solution of the three polyesters, 17.10, 16.98, 17.14 ppm, and 57.36, 57.11, or 57.32 ppm were observed. 13 The C resonance peaks are attributed to the methyl C and methylene C of the residual ethanol in the molecular sieve, which are the signal peaks of non-hydrolysis products; after alkaline hydrolysis, the PBP degradation solution appears 128.62ppm 13 C resonance peak ( Figure 21 a), C at position 2,2′ of the benzene ring is attributed to 4,4′-biphenyldimethoxy; Figure 21 In b, the PTP degradation solution produced 181.09, 135.11, 129.14 and 43.91 ppm 13 The C resonance peaks are attributed to the carbonyl C of terephthaloyloxy, C at positions 1,4 and 2,3 of the benzene ring, and C at the methylene group, and also occur at 140.57, 127.56, and 63.61 ppm. 13 C resonance peaks are attributed to the 1,4-position C and 2,3-position C of the benzene ring of terephthalylene dimethoxy, and methylene C; PET polyester degradation liquid does not produce 13 C resonance peak ( Figure 21 c). Figure 20 ,21 Spectral data showed that the PTP degradation liquid was rich in alkaline hydrolysis products of disodium terephthalate and disodium terephthalate dimethanol, the PBP degradation liquid contained alkaline hydrolysis products of disodium terephthalate and disodium 4,4'-biphenyl dimethanol, while the PET polyester degradation liquid contained very little alkaline hydrolysis products of disodium terephthalate and disodium ethylene glycol.

[0178] Figure 22 In a and b, the white needle-shaped crystalline products precipitated from the acidic degradation solutions of PBP and PTP were 1.26 ppm. 1 The H resonance peak is attributed to the residual water peak of the sample that was not completely dried, which is the signal peak of the non-hydrolysis product; after acidic hydrolysis, the white needle-shaped crystalline product precipitated in the PBP degradation solution appeared at 5.16, 4.64 and 3.66 ppm. 1 H resonance peak ( Figure 22a), which were attributed to the hydroxyl H and methylene H of 4,4′-biphenyl dimethanol and the methylene H of terephthalic acid respectively; the white needle-shaped crystalline product precipitated in the PTP degradation solution had strong 1 H resonance peak ( Figure 22 b) are respectively attributed to the H on the 2,3 position of the benzene ring of terephthalic acid and terephthalic acid, and the methylene H of terephthalic acid and terephthalic acid; while the PET polyester degradation liquid does not appear 1 H resonance peak ( Figure 22 c) By Figure 23 It can be seen that after acidic hydrolysis, the white needle-shaped crystal product precipitated in the PBP degradation solution did not appear 13 C resonance peak ( Figure 23 a) This may be because most of the degradation products are dissolved in acid water and very little precipitation occurs, resulting in the product in the solution sample 13 C concentration is low and the signal is weak; Figure 23 In b, the white needle-shaped crystal product precipitated from the PTP degradation solution had strong peaks of 171.23, 132.96, 129.48 and 40.96 ppm. 13 The C resonance peaks are attributed to the carbonyl C of terephthalic acid, C at positions 1,4 and 2,3 of the benzene ring, and methylene C, respectively. Strong peaks of 135.95, 128.32, and 66.29 ppm also occur. 13 C resonance peaks are attributed to the 1,4-position C and 2,3-position C and methylene C of the benzene ring of terephthalic alcohol, respectively; while the PET polyester degradation liquid does not produce 13 C resonance peak ( Figure 23 c). Figure 22 ,23 Spectral data showed that the PTP degradation liquid was rich in acidic hydrolysis products of terephthalic acid and terephthalic alcohol, and crystals were precipitated; the PBP degradation liquid contained acidic hydrolysis products of terephthalic acid and 4,4'-biphenyl dimethanol, and crystals were precipitated; while the acidic hydrolysis products in the PET polyester degradation liquid were so few that they could be ignored.

[0179] Therefore, during acidic and alkaline hydrolysis, the concentration of hydrolysis products in the degradation liquid of PTP and PBP is significantly higher than that of PET polyester, that is, the degradation efficiency of polyester PTP and PBP is significantly higher than that of PET polyester; similarly, the degradation efficiency of PTP is significantly higher than that of PBP.

[0180] In summary, the above comparative degradation experimental test results 2 to 4 (surface morphology, mass loss rate, chemical structure) self-consistently reveal that compared with the non-degradable PET polyester, the degradation efficiency of the polyesters PTP and PBP prepared by modification is significantly increased, and they are two degradable polyesters; among them, the degradation efficiency of the degradable PTP is significantly higher than that of the degradable PBP, which may be due to the fact that the steric hindrance of the benzene ring in the diol structural unit of the former is less than that of the biphenyl in the latter.

[0181] Under fully comparable conditions of effective removal of catalysts, equivalent degree of polymerization and similar crystallinity, the chain chemical structure of non-degradable PET polyester was modified to obtain degradable polyesters PTP and PBP, indicating that the insertion of methylene interrupts the strong conjugation stability, thereby activating the ester group's CO polar weak bond, which is the main essential reason for achieving the intrinsic degradability of polyester.

[0182] 5. By Figure 24 It can be seen that the thermal decomposition temperatures of PTP and PBP are 378.1℃ and 373.5℃ respectively, which are not much lower than the thermal decomposition temperature of PET polyester (415.5℃), and both are still maintained above 350℃. Figure 24 In Figure 2b, PTP and PBP thermally decomposed most rapidly at 409.6°C and 425.5°C, respectively, which is lower than the fastest thermal decomposition temperature of PET (460.9°C). Overall, compared to non-degradable PET, polyester PTP and PBP maintain higher thermal stability while achieving degradation.

[0183] Comprehensive results:

[0184] In the results of Test Example 1, the degradation efficiency of amorphous modified PET polyester (PEP) was significantly higher than that of crystalline PET polyester, due to the dual effects of strong conjugation disruption caused by methylene insertion, which activated weak bonds, and amorphization, which facilitated the penetration of the degradation agent. In the results of Test Example 2, the degradation efficiency of crystalline modified PET polyesters (PTP) and PBP) was significantly higher than that of crystalline PET polyester, due primarily to the strong conjugation disruption caused by methylene insertion, which activated weak bonds. Combining the results of the two test examples, compared to non-degradable PET polyester, modified PET polyesters (PEP), PTP, and PBP) are all degradable polyesters. Their degradation efficiencies decrease in descending order, but all maintain a high thermal stability that is not significantly lower than that of PET polyester.

[0185] In summary, the present invention prepares three degradable polyesters with decreasing degradation efficiency and high thermal stability, namely polyethylene terephthalate (PEP), poly(4-methyl terephthalate) (PTP) and poly(4,4'-biphenyl dimethyl terephthalate) (PBP), by inserting methylene into the terephthalic acid structural unit and modifying the PET molecular chain by inserting benzene rings and biphenyls into the ethylene glycol structural unit, thereby realizing the degradable modification of PET polyester.

[0186] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention; simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A degradable polyester, characterized in that The chemical structural formula of the degradable polyester is: In the formula, 0 represents no group, R Ar For Fang support, R CA is cycloalkylene, (0 / R Ar / R CA ) means that there is no group between the two -CH2- groups or that they are arylene or cycloalkylene, and the degree of polymerization n is a natural number ≥25.

2. The degradable polyester according to claim 1, characterized in that The arylene is phenylene, biphenylene, naphthylene, furanylene, thiopheneylene or pyrroleylene, and the cycloalkylene is cyclopentylene or cyclohexylene.

3. A method for preparing the degradable polyester according to claim 1 or 2, characterized in that: The preparation method comprises the following steps: firstly, aromatic diacetic acid or aromatic diacetate monomer and diol monomer are polymerized in the early stage by melt esterification or ester exchange, and then polycondensed in the late stage.

4. The preparation method according to claim 3, characterized in that The steps include: Step 1, preliminary polymerization: weigh aromatic diacetic acid or aromatic diacetate monomer and diol monomer, add catalyst; under nitrogen atmosphere, heat to 190-200°C, react under mechanical stirring, distillation and condensation, start timing when the first drop of water or alcohol byproduct is distilled out, and esterification or transesterification reaction is 2.5-3.5 hours; Step 2, late polycondensation: adding a polycondensation catalyst; maintaining mechanical stirring, turning off the nitrogen atmosphere, removing the distillation condensation, and evacuating to within 200 Pa; heating to 200-240° C. for polycondensation reaction for 3.0-4.5 hours, pouring the reactants into an evaporating dish while hot, and vacuum drying to obtain a crude polyester product; Step 3, refining the crude product: dissolving the crude polyester product in a mixed solvent of trifluoroacetic acid and chloroform, using a mixed precipitant of ethylene glycol and methanol to reprecipitate the polyester product from the mixed solvent, filtering, washing, and finally vacuum drying to obtain a degradable polyester.

5. The preparation method according to claim 4, characterized in that In the step 1, the molar ratio of the aromatic diacetic acid or aromatic diacetate monomer to the diol monomer is 1:(1-2.2).

6. The preparation method according to claim 4, characterized in that In step 1, the catalyst is one or more metal acetates, and the molar ratio of the catalyst to the aromatic diacetic acid or aromatic diacetate monomer is [(5×10 -4 )~(2×10 -3 )]: 1; In the step 2, the polycondensation catalyst is a metal acetate, and the molar ratio of the polycondensation catalyst to the aromatic diacetic acid or aromatic diacetate monomer is [0~(8×10 -4 )]:

1.

7. The preparation method according to claim 4, characterized in that In step 1 and step 2, the heating rate is 5°C min -1 , the mechanical stirring rate is 100-200 rpm.

8. The preparation method according to claim 4, characterized in that In step 2 and step 3, the vacuum drying temperature is 80-100° C., and the vacuum drying time is 48 h and 72 h, respectively.

9. The preparation method according to claim 4, characterized in that In step 3, the volume ratio of trifluoroacetic acid and chloroform in the mixed solvent and the volume ratio of ethylene glycol and methanol in the mixed precipitant are both 1:4, and the volume ratio of the mixed solvent to the mixed precipitant is 1:20.

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