Amorphous copolyesters and their preparation methods

Abstract

This application provides an amorphous copolyester and its preparation method. First, a Ca-SIPM salt containing divalent metal ions is prepared by reacting sodium dimethyl isophthalate-5-sulfonate with CaCl2 in water. Subsequently, the Ca-SIPM salt undergoes an ester exchange reaction with ethylene glycol to obtain a novel polyester precursor, Ca-SIPE. Finally, a novel, completely amorphous polyethylene terephthalate is successfully synthesized by copolymerizing Ca-SIPE with a diacid and a diol. Because of the large molecular structure of Ca-SIPE, its introduction into the molecular chain completely disrupts the regularity of the entire polyester molecular chain, increasing the amorphous regions within the polyester molecular chain. This preparation method not only achieves amorphization of the polyester material but also achieves complete amorphization of the polyester with a minimal addition of a third monomer. Compared to existing technologies where the addition of a third monomer must exceed 9% or 20% to achieve amorphization, this significantly reduces production costs.

Description

Technical Field

[0001] This invention relates to the field of polyester fiber technology, specifically to an amorphous copolyester and its preparation method. Background Technology

[0002] Amorphous polyesters, due to their unique properties, exhibit high transparency, good toughness, and ease of processing. These properties make amorphous polyesters suitable for manufacturing extruded films, packaging materials, and medical device components, and they are also widely used in many high-tech products. Their industrial development and technological innovation continue to drive the advancement of materials science.

[0003] In existing technologies, researchers synthesize amorphous polyethylene terephthalate copolyester by introducing isophthalic acid (IPA) (Journal of Applied Polymer Science, 2019, 136, 47186). However, the amount of IPA added in this synthesis method often needs to exceed 20% to make the polyester material completely amorphous. Another method is to reduce the crystallinity of the polyester by introducing sodium 5-sulfobis(hydroxyethyl)isophthalate (SIPE) into the PET chain segment to make it amorphous. However, this method often requires an addition amount of more than 9% to achieve the amorphous state of the polyester, resulting in higher material costs.

[0004] In view of this, it is necessary to design an economical and efficient amorphous copolyester and its preparation method. Summary of the Invention

[0005] The purpose of this application is to provide a method for preparing an amorphous copolyester. This method involves reacting a specific monomer, sodium dimethyl isophthalate-5-sulfonate (Na-SIPM), with CaCl2 in water to obtain a Ca-SIPM salt containing divalent metal ions. Then, the Ca-SIPM salt undergoes a transesterification reaction with ethylene glycol (EG) to obtain a novel polyester precursor, Ca-SIPE. Finally, a novel, completely amorphous polyethylene terephthalate (PET) is successfully synthesized by copolymerizing Ca-SIPE with a diacid and a diol. This preparation method achieves complete amorphization of the polyester with a minimal amount of a third monomer (0.25–3% of the molar amount of the first monomer), significantly reducing production costs and making this high-performance polyester material more competitive in commercial applications. It also provides new possibilities for the sustainable development and environmentally friendly applications of polyester materials.

[0006] In a first aspect, embodiments of this application provide a method for preparing an amorphous copolyester, comprising the following steps:

[0007] S1, sodium dimethyl isophthalate-5-sulfonate and CaCl2 are dissolved in deionized water in a molar ratio of 2:(1.1-1.4) and mixed in a reactor; the resulting mixture is magnetically stirred at room temperature for 2-3 days, then filtered to collect the precipitate, dried until a constant weight is reached to obtain Ca-SIPM salt;

[0008] S2, under nitrogen atmosphere, Ca-SIPM salt and ethylene glycol are subjected to transesterification reaction in a molar ratio of 1:(10.4-15.4) to obtain a transparent liquid product named Ca-SIPE; the catalyst used in the transesterification reaction is Mn(OAc)2; the mass fraction of Mn(OAc)2 is 0.3%-0.6%;

[0009] S3, using terephthalic acid as the first monomer and ethylene glycol as the second monomer, the first monomer and the second monomer are added to a reactor for esterification reaction; the esterification reaction ends when the amount of water discharged reaches the theoretical amount of water discharged.

[0010] S4. After esterification, the third monomer Ca-SIPE obtained in step S2 is added. After reacting under normal pressure for 0.5 to 1 hour, a polycondensation reaction is carried out. The resulting copolymer is then pelletized to obtain an amorphous copolyester.

[0011] Preferably, in step S4, the amount of the third monomer added is 0.25 to 3% of the molar amount of the first monomer.

[0012] Preferably, in step S3, the molar ratio of the first monomer to the second monomer is 1:(1.2 to 1.6).

[0013] Preferably, in step S2, the reaction temperature of the transesterification reaction is 160–200°C, and the reaction time is 3.5–4.5 h.

[0014] Preferably, in step S2, the transesterification reaction ends when no more methanol is distilled out.

[0015] Preferably, in step S4, the specific process of the polycondensation reaction is as follows: first, the system is slowly evacuated to 80-100 Pa for pre-polycondensation treatment within 1-3 hours, and then the system is heated to 260-280°C and the reaction is continued for 1-2 hours.

[0016] Preferably, in step S3, the esterification reaction is carried out at a temperature of 240–260°C, for a reaction time of 2–4 h, and at a pressure of 100 kPa–360 kPa inside the reactor.

[0017] Preferably, in step S3, the catalyst added to the esterification reaction is Sb2O3, and the amount of the catalyst added is 400-600 ppm.

[0018] Secondly, this application provides an amorphous copolyester, which is prepared using the preparation method described in the foregoing technical solution.

[0019] The beneficial effects of this invention are:

[0020] 1. The method for preparing amorphous copolyester provided by this invention first explores a novel ion exchange technology. By reacting a specific monomer, sodium dimethyl isophthalate-5-sulfonate (Na-SIPM), with CaCl2 in water, a Ca-SIPM salt containing divalent metal ions was successfully prepared. This crucial step lays the foundation for subsequent transesterification reactions, ensuring high reaction efficiency and product purity. Subsequently, the Ca-SIPM salt is transesterified with ethylene glycol (EG) to obtain a novel polyester precursor, Ca-SIPE. The synthesis of this intermediate is crucial for achieving a completely amorphous polyester structure because it introduces special structural features (Ca ions can coordinate with two sulfonate groups, resulting in an ionic structure exhibiting vertical symmetry). Specifically, because the Ca-SIPE molecule is large, its introduction into the molecular chain completely disrupts the regularity of the entire polyester molecular chain, increasing the amorphous region within the polyester molecular chain and helping to suppress the ordered arrangement of the polyester molecular chain. Finally, a novel, completely amorphous polyethylene terephthalate was successfully synthesized by copolymerizing Ca-SIPE with diacids and diols.

[0021] 2. The innovative synthesis route provided by this invention not only achieves the amorphization of polyester materials, but also enables the complete amorphization of polyester with a minimum addition amount of the third monomer (the addition amount of the third monomer is 0.25% to 3% of the molar amount of the first monomer). Compared with the prior art, where the addition amount of the third monomer must exceed 9% or 20% to achieve the amorphization of polyester, this significantly reduces production costs, making this high-performance polyester material more competitive in commercial applications and broadening the application fields of polyester.

[0022] 3. The amorphous copolyester obtained by this invention not only exhibits excellent physical properties, such as high transparency and good mechanical strength, but also significant processing properties, such as rapid molding and excellent thermal stability. This achievement not only reflects our technological progress in the field of materials science, but also provides new possibilities for the sustainable development and environmentally friendly application of polyester materials.

[0023] 4. The copolyester prepared by this invention can be completely amorphous, and the production process matches the traditional polyester production process. No modification of existing equipment is required. The materials are inexpensive, the preparation process is simple, and it has the potential for industrial production.

[0024] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0026] Figure 1 This is a synthetic route diagram of Ca-SIPM and Ca-SIPE salts in this invention.

[0027] Figure 2 This is a synthetic route diagram of the PET-CaSIPE copolyester in this invention.

[0028] Figure 3 The image shows a comparison of the DSC heating curves of the PET-CaSIPE polyester prepared in Example 1 and pure polyester (PET).

[0029] Figure 4 This is a comparison of the TG curves of the PET-CaSIPE polyester prepared in Example 1 and pure polyester (PET).

[0030] Figure 5 This is a comparison chart of the DTG curves of the PET-CaSIPE polyester prepared in Example 1 and pure polyester (PET).

[0031] Figure 6 The images show actual photos of the PET-CaSIPE polyester sheets and pure polyester (PET) sheets prepared in Examples 1-4.

[0032] Figure 7 The image shows a comparison of the tensile stress-strain curves of the PET-CaSIPE polyester prepared in Example 1 and pure polyester (PET).

[0033] Figure 8 The XRD patterns of the PET-CaSIPE polyester sheets prepared in Examples 1-4 and pure polyester (PET) are shown. Detailed Implementation

[0034] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0036] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0037] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0038] Please see Figures 1 to 2 As shown, the present invention provides a method for preparing amorphous copolyester, comprising the following steps:

[0039] S1, sodium dimethyl isophthalate-5-sulfonate (Na-SIPM) and CaCl2 are dissolved in deionized water in a molar ratio of 2:(1.1-1.4) and mixed in a glass reactor; the resulting mixture is magnetically stirred at room temperature for 2-3 days, then filtered to collect the precipitate, dried until a constant weight is reached to obtain Ca-SIPM salt;

[0040] A Ca-SIPM salt containing divalent metal ion coordination was successfully prepared by reacting a specific monomer, sodium dimethyl isophthalate-5-sulfonate (Na-SIPM), with CaCl2 in water. This crucial step lays the foundation for subsequent transesterification reactions, ensuring high reaction efficiency and product purity.

[0041] S2, under nitrogen atmosphere, Ca-SIPM salt and ethylene glycol are subjected to transesterification reaction in a molar ratio of 1:(10.4~15.4) to obtain a transparent liquid product named Ca-SIPE; the catalyst used in the transesterification reaction is Mn(OAc)2; the mass fraction of Mn(OAc)2 is 0.3%~0.6%;

[0042] A novel polyester precursor, Ca-SIPE, was obtained by transesterification of Ca-SIPM salt with ethylene glycol (EG). The synthesis of this intermediate is crucial for achieving a completely amorphous structure in polyesters because it introduces unique structural features (Ca ions can coordinate with two sulfonate groups, resulting in an ionic structure exhibiting vertical symmetry). Specifically, due to the large size of the Ca-SIPE molecule, its introduction into the molecular chain completely disrupts the regularity of the entire polyester molecular chain, increasing the amorphous regions and helping to suppress the ordered arrangement of the polyester molecular chains.

[0043] Specifically, under nitrogen atmosphere, Ca-SIPM salt, EG at a molar ratio of 1:(10.4–15.4), and 0.3%–0.6% Mn(OAc)₂ were mixed in a 500 mL three-necked round-bottom flask and heated to 160–200 °C. When reflux was observed in the reaction flask, the reaction time was started and the reaction was allowed to proceed for 3.5–4.5 h. The reaction was stopped when no more methanol was observed to distill off, yielding a transparent liquid product named Ca-SIPE.

[0044] S3, using terephthalic acid as the first monomer and ethylene glycol as the second monomer, the first monomer and the second monomer are added to a reactor for esterification reaction; the esterification reaction ends when the amount of water discharged reaches the theoretical amount of water discharged.

[0045] During the esterification reaction, the reaction temperature is 240–260℃, the reaction time is 2–4 h, and the pressure inside the reactor is 100 kPa–360 kPa.

[0046] Specifically, after checking the sealing of the reactor, terephthalic acid is used as the first monomer and ethylene glycol as the second monomer, with a molar ratio of 1:(1.2~1.6) to the second monomer in the reactor. Nitrogen gas is introduced into the reactor, and after the pressure reaches 120 kPa, the valve is opened to release pressure. After reaching atmospheric pressure, the valve is closed, and nitrogen gas is introduced into the reactor again. This operation is repeated three times to ensure that the air in the reactor is purged. Then, nitrogen gas is introduced, and the pressure is increased to 100 kPa to carry out the esterification reaction. The reactor temperature is set to 260℃, the process tower temperature is set to 150℃, and the stirrer is used for stirring at a frequency of 30Hz. During this process, the temperature of the material in the reactor slowly rises to 260℃, and the pressure is controlled at 360 kPa. When water begins to drip out, the pressure is released. The esterification reaction can be judged to be over when the amount of water discharged reaches the theoretical amount.

[0047] The catalyst added in the esterification reaction is Sb2O3, and the amount of catalyst added is 400-600 ppm.

[0048] S4, after esterification, the third monomer Ca-SIPE is added, and the reaction is carried out under normal pressure for 0.5 to 1 hour, followed by polycondensation. The resulting copolymer is then pelletized to obtain an amorphous copolyester.

[0049] A novel, completely amorphous polyethylene terephthalate was successfully synthesized by copolymerizing Ca-SIPE with a diacid and a diol.

[0050] The amount of the third monomer added is 0.25 to 3% of the molar amount of the first monomer.

[0051] The specific process of the polycondensation reaction is as follows: First, the system is slowly evacuated to 80-100 Pa for pre-polycondensation treatment within 1-3 hours. Then, the system is heated to 260-280℃ and the reaction is continued for 1-2 hours.

[0052] Specifically, after esterification, the third monomer, Ca-SIPE, is added through the feed port. After reacting at atmospheric pressure for 1–3 hours, the valve between the reactor and the process tower is closed, and the heating switch of the process tower is turned off. The reactor temperature is adjusted to 260–280°C. The valve between the reactor and the polycondensation condenser is opened to enter the polycondensation stage. During polycondensation, the vacuum pump is turned on, and the vacuum level inside the reactor is slowly reduced at a rate of 10 min / 20 kPa using the vacuum fine-tuning valve until it reaches a vacuum state. Polycondensation continues for another 1–2 hours. As the reaction proceeds, the viscosity of the material gradually increases, which will cause the power of the agitator to gradually increase. Therefore, the power of the agitator must be monitored during the polycondensation process. If the power is too high, the agitator frequency should be set to 25 Hz to continue the reaction. Once the agitation power reaches a certain value, the reaction ends, and the material is discharged from the bottom of the reactor and pelletized.

[0053] The present invention also provides an amorphous copolyester, which is prepared by the aforementioned preparation method. This amorphous copolyester not only exhibits excellent physical properties, such as high transparency and good mechanical strength, but also has significant processing properties, such as rapid molding and excellent thermal stability.

[0054] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0055] Example 1

[0056] This embodiment provides a method for preparing amorphous copolyester, including the following steps:

[0057] S1, Na-SIPM and CaCl2 were dissolved in deionized water in a molar ratio of 2:1.1 and mixed in a glass reactor; the resulting mixture was magnetically stirred at room temperature for 3 days, and then the precipitate was collected by filtration. After a thorough drying process until a constant weight was reached, the Ca-SIPM salt was obtained;

[0058] S2, under nitrogen atmosphere, Ca-SIPM, EG in a molar ratio of 1:10.6, and 0.4% Mn(OAc)2 were mixed in a 500 mL three-necked round-bottom flask and heated to 180 °C. When reflux was observed in the reaction flask, the reaction was timed for 4 hours. The reaction was stopped when no more methanol was observed to distill out, yielding a transparent liquid product, named Ca-SIPE.

[0059] S3, using terephthalic acid as the first monomer and ethylene glycol as the second monomer, the first monomer and the second monomer are added to the reactor in a molar ratio of 1:1.3 to carry out the esterification reaction; the esterification reaction ends when the output water reaches the theoretical output water.

[0060] S4. After esterification, a third monomer, Ca-SIPE, is added. The amount of the third monomer added is 3% of the molar amount of the first monomer. After reacting at normal pressure for 0.5 h, a polycondensation reaction is carried out for 1 h. The resulting copolymer is pelletized to obtain an amorphous copolyester.

[0061] Figure 3The image shows a comparison of the DSC heating curves of the amorphous polyester prepared in Example 1 and pure polyester (PET). It can be seen that the DSC heating curve of pure PET shows Tg (glass transition temperature), Tcc (cold crystallization temperature peak), and Tm (melting peak). Since pure PET is a semi-crystalline polyester, it exhibits the specific characteristics of polyester. However, the heating curve of PET-CaSIPE only shows Tg (glass transition temperature), and the cold crystallization and melting peaks disappear. This is attributed to the molecular structure characteristics of Ca-SIPE. Due to its large molecular structure, the introduction of Ca-SIPE into the molecular chain completely disrupts the regularity of the entire polyester molecular chain, increasing the amorphous region within the polyester molecular chain. Therefore, the DSC heating curve shows no crystallization or melting peaks, indicating the successful preparation of an amorphous copolyester.

[0062] Figure 4 This is a comparison of the TG curves of the amorphous polyester prepared in Example 1 and pure polyester (PET).

[0063] Figure 5 This is a comparison chart of the DTG curves of the amorphous polyester prepared in Example 1 and pure polyester (PET).

[0064] The table below shows the thermal data of amorphous polyester tested by TGA.

[0065] Sample <![CDATA[T 5％ (℃)]]> <![CDATA[T 10％ (℃)]]> <![CDATA[T max (℃)]]> Residue (%) PET 395.5 403.2 436.2 10.1 Example 1 382.3 396.3 430.2 12.7

[0066] In the table, T 5％ T 10％ These represent the temperatures at which the weight is reduced by 5% and 10%, respectively.

[0067] As you can see, Figure 4 The TG curves show that the PET-CaSIPE prepared in Example 1 has similar thermal stability and decomposition tendency to PET. With the addition of Ca-SIPE, the initial decomposition temperature of PET-CaSIPE decreases slightly. Similarly, the maximum decomposition temperature of PET-CaSIPE (T0) is also lower. max The temperature also decreased slightly, from 436.2℃ for PET to 430.2℃.

[0068] Furthermore, with the addition of Ca-SIPE, the modified polyester prepared in Example 1 had a maximum temperature residue weight percentage of 12.7%, which is 2.6% higher than the 10.1% of pure polyester. This indicates that sulfonic acid groups can promote the formation of a dense carbon layer in PET. This dense carbon layer can, to some extent, prevent heat and oxygen transfer, thereby improving the flame retardant properties of the material. Simultaneously, the formation of this carbon layer can increase the melt viscosity and strength of the material at high temperatures, reduce dripping during combustion, and improve the mechanical strength of the polyester.

[0069] Comparative Example 1

[0070] This comparative example provides a method for preparing an amorphous copolyester. Compared with Example 1, the only difference is that in the transesterification reaction in step S2, the catalyst Mn(OAc)2 is replaced with Zn(OAc)2. Other experimental parameters and conditions are basically the same as in Example 1, and will not be repeated here.

[0071] The table below shows the experimental data for Example 1 and Comparative Example 1:

[0072] project catalyst Measured transesterification rate / % Example 1 <![CDATA[Mn(OAc)2]]> 96.8 Comparative Example 1 <![CDATA[Zn(OAc)2]]> 72.6

[0073] It can be seen that the transesterification rate of the product obtained by using Zn(OAc)2 as a catalyst is only 72.6%, which is much lower than that of Example 1.

[0074] Examples 2-5 and Comparative Examples 2-7

[0075] Compared with Example 1, the main differences are that the molar ratio of Na-SIPM to CaCl2 in step S1, the molar ratio of Ca-SIPM salt to ethylene glycol in step S2, and the amount of the third monomer Ca-SIPE added in step S4 were changed. Other experimental parameters and conditions are basically the same as in Example 1, and will not be repeated here. The details are shown in the table below.

[0076]

[0077]

[0078] Experiments show that when the molar ratio of Na-SIPM to CaCl2 is less than 1:0.7 (Comparative Example 7), because the molar ratio on both sides is not carried out according to the conventional reaction ratio, the reaction will have an excess of Na-SIPM and an insufficient amount of CaCl2, resulting in incomplete ion exchange on both sides and thus causing the failure of the next reaction.

[0079] When the molar ratio of Na-SIPM to CaCl2 is greater than 2:1.1 (Comparative Example 6), excess substrate may cause side reactions, especially when one of the substrates has completely reacted, the remaining substrate may react undesirably with other reactants or products.

[0080] When the amount of the third monomer added is greater than 3% of the molar amount of the first monomer (Comparative Example 3), specifically when the amount of the third monomer added is 4% of the molar amount of the first monomer, the polyester is also amorphous. However, the excessive addition of the third monomer will cause the melting point and Tg of the material to drop particularly sharply.

[0081] When the amount of the third monomer added is 0.125% of the molar amount of the first monomer, if the amount of the third monomer added is too small, it will not have a significant impact on the crystallinity of the pure polyester. The key point of amorphous polyester is crystallinity. Only when the polyester does not crystallize or has very poor crystallization ability will it be amorphous. That is, if the amount of the third monomer added is too small, amorphous polyester cannot be obtained.

[0082] When the molar ratio of Ca-SIPM salt to ethylene glycol is less than 1:15.4 (Comparative Example 5), the excess EG will lead to inaccurate judgment of the reaction endpoint, and the ethylene glycol molecules will also undergo dehydration reaction, which will greatly reduce the purity of the product.

[0083] When the molar ratio of Ca-SIPM salt to ethylene glycol is 1:8, the substrate ratio affects the position of the chemical equilibrium, causing the reaction to proceed incompletely and affecting the product yield. According to Le Chatelier's principle, if the concentration of reactants increases, the equilibrium will shift towards the forward reaction to reduce the concentration of those reactants; conversely, if the concentration of products increases, the equilibrium will shift towards the reverse reaction.

[0084] The transparency and mechanical strength of the modified polyester prepared in Examples 1-4 were compared with those of pure polyester (PET), and the results are as follows: Figure 6 , Figure 7 As shown.

[0085] The transparency test method is as follows: polyester chips are melt-pressed using a flat vulcanizing machine at an experimental temperature of 260℃, followed by cooling at room temperature. The pressed samples are then compared and analyzed.

[0086] The mechanical strength test method is as follows: The Instron universal testing machine is used to test dumbbell-shaped samples with dimensions of 25 mm (neck length) × 4 mm (neck width) × 2 mm (thickness) at a tensile rate of 50 mm / min. Each sample is tested in parallel for 5 times, and then the average value is taken.

[0087] Figure 6 The images show actual photos of the PET-CaSIPE polyester sheets prepared in Examples 1-4 and pure polyester (PET) sheets. It can be seen that the transparency of the PET-CaSIPE polyester sheets prepared in Examples 1-4 is improved compared to pure polyester (PET).

[0088] Figure 7 The image shows a comparison of the tensile stress-strain curves of the PET-CaSIPE polyester prepared in Example 1 and pure polyester (PET). It can be seen that the tensile strength of the PET-CaSIPE polyester prepared in Example 1 is higher than that of pure polyester (PET).

[0089] Specifically, the tensile strength of the pure polyester sample was 30.4 MPa, and the tensile strength of the modified polyester obtained in Example 1 was higher than that of pure PET, at 36.9 MPa.

[0090] Figure 8 The images show the XRD patterns of the PET-CaSIPE polyester sheets prepared in Examples 1-4 and pure polyester (PET). It can be seen that pure PET has a triclinic crystal structure, and the modified polyester obtained by adding the third monomer Ca-SIPE still maintains the original crystal structure, indicating that the addition of the third monomer does not affect the crystalline shape of the polyester.

[0091] In summary, the method for preparing amorphous copolyester of the present invention first involves reacting sodium dimethyl isophthalate-5-sulfonate with CaCl2 in water to obtain a Ca-SIPM salt containing divalent metal ions. Subsequently, the Ca-SIPM salt undergoes an ester exchange reaction with ethylene glycol to obtain a novel polyester precursor, Ca-SIPE. Finally, a novel, completely amorphous polyethylene terephthalate is successfully synthesized by copolymerizing Ca-SIPE with a diacid and a diol. Because of the large molecular structure of Ca-SIPE, its introduction into the molecular chain completely disrupts the regularity of the entire polyester molecular chain, increasing the amorphous region within the polyester molecular chain. This preparation method not only achieves amorphization of the polyester material but also achieves complete amorphization of the polyester with a minimal addition of a third monomer. Compared to existing technologies where the addition of a third monomer must exceed 9% or 20% to achieve amorphization, this significantly reduces production costs.

[0092] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing an amorphous copolyester, characterized in that, Includes the following steps: S1, dissolve sodium dimethyl isophthalate-5-sulfonate and CaCl2 in deionized water at a molar ratio of 2:(1.1~1.4) and mix in a reactor; stir the resulting mixture magnetically at room temperature for 2~3 days, then filter to collect the precipitate, dry until a constant weight is reached to obtain Ca-SIPM salt; S2, under nitrogen atmosphere, Ca-SIPM salt and ethylene glycol are subjected to transesterification in a molar ratio of 1:(10.4~15.4) to obtain a transparent liquid product, named Ca-SIPE; the catalyst used in the transesterification reaction is Mn(OAc)2; the mass fraction of Mn(OAc)2 is 0.3%~0.6%; S3, using terephthalic acid as the first monomer and ethylene glycol as the second monomer, the first monomer and the second monomer are added to a reactor for esterification reaction; the esterification reaction ends when the amount of water discharged reaches the theoretical amount of water discharged; the molar ratio of the first monomer to the second monomer is 1:(1.2~1.6). S4. After esterification, the third monomer Ca-SIPE obtained in step S2 is added. After reacting under normal pressure for 0.5 to 1 hour, a polycondensation reaction is carried out. The resulting copolymer is pelletized to obtain an amorphous copolyester. The amount of the third monomer added is 0.25 to 3% of the molar amount of the first monomer.

2. The method for preparing amorphous copolyester according to claim 1, characterized in that, In step S2, the transesterification reaction is carried out at a temperature of 160-200°C for 3.5-4.5 h.

3. The method for preparing amorphous copolyester according to claim 1, characterized in that, In step S2, the transesterification reaction ends when no more methanol is distilled out.

4. The method for preparing amorphous copolyester according to claim 1, characterized in that, In step S4, the specific process of the polycondensation reaction is as follows: First, the system is slowly evacuated to 80-100 Pa for pre-polycondensation treatment within 1-3 hours, and then the system is heated to 260-280℃ and the reaction is continued for 1-2 hours.

5. The method for preparing amorphous copolyester according to claim 1, characterized in that, In step S3, during the esterification reaction, the reaction temperature is 240~260℃, the reaction time is 2~4h, and the pressure inside the reactor is 100kPa~360kPa.

6. The method for preparing amorphous copolyester according to claim 1, characterized in that, In step S3, the catalyst added to the esterification reaction is Sb2O3, and the amount of catalyst added is 400~600ppm.

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