Hydrolysis-resistant crystallizable copolyester material as well as preparation method and application thereof

Abstract

The invention discloses a hydrolysis-resistant crystallizable copolyester material as well as a preparation method and application thereof, and belongs to the technical field of high polymer copolymerization modification. The purpose of the invention is to solve the problem of poor hydrolysis resistance of traditional PET. According to the copolyester material, for a chain segment of terephthalic acid (PTA)-ethylene glycol (EG), 1, 4-cyclohexanedimethanol (CHDM) is introduced as a high impedance hydrolysis monomer to form a ternary prepolymer; the preparation method comprises the following steps: firstly, copolymerizing the copolyester with a prepolymer of PTA (Pure Terephthalic Acid) and 1, 5-pentanediol (NG) to form a novel copolymer, and finally, carrying out end-capping stabilization on active hydroxyl and carboxyl of the copolyester at the final stage of final polymerization. According to the preparation method, a double esterification-prepolymerization-mixed polycondensation-later-stage end capping process is adopted, and the obtained copolyester material has excellent hydrolysis resistance and good crystallization capacity and mechanical property and can be applied to the fields of hydrolysis-resistant textile fibers (in the spinning field), medical instruments and engineering plastics.

Description

Technical Field

[0001] This invention belongs to the field of polymer copolymer modification technology, specifically relating to a hydrolysis-resistant and crystallizable copolyester material, its preparation method, and its application. Background Technology

[0002] Polyethylene terephthalate (PET), as the world's most produced single-variety polymer material, has been widely used in core fields such as textile fiber spinning, food packaging containers, and engineering plastics due to its excellent mechanical strength, good thermal stability, and cost advantages. However, traditional PET materials have significant technical shortcomings, especially insufficient hydrolysis resistance, which severely restricts their application under high temperature and high humidity conditions. Traditional PET, after six months of service at 80℃ and 90% relative humidity, experiences a decrease in tensile strength of over 30%; when used in high-temperature sterilization packaging, the material exhibits significant embrittlement and cracking after three sterilization cycles at 121℃.

[0003] The current mainstream PET hydrolysis resistance solutions mainly rely on modification technology using anti-hydrolysis carbonization additives. These additives, such as carbodiimides, consume the terminal carboxyl groups generated during PET hydrolysis and form a physical barrier, reducing the ester bond hydrolysis rate. CN104045980B discloses a carbodiimide-containing anti-hydrolysis PET masterbatch, which can reduce the terminal carboxyl group content by more than 60% and extend the material's service life by 5-8 times. CN111875728A develops a polymeric carbodiimide anti-hydrolysis agent that combines thermal stability and hydrolysis resistance, maintaining stability at PET processing temperatures. CN102344654B confirms that surface modification of nano-silicon carbide significantly improves its compatibility with the PET matrix, synergistically achieving long-term hydrolysis resistance with carbodiimides; however, this external addition method is prone to phase separation during processing, making it unsuitable for applications such as spinning films.

[0004] By introducing CHDM to construct copolyester molecular chain structures such as PETG and PCTG, the hydrolytic activity of ester bonds can be reduced, and its hydrolytic lifespan can be increased by 2 to 3 times compared with traditional PET. CN104693704A discloses a high-transparency PETG copolyester film preparation technology. By adding high-efficiency ultraviolet light absorbers, pigments, modified metal oxides, and antioxidants, the hydrolytic lifespan of the material under 85℃ / 85%RH humid heat conditions is 2.8 times that of PET. CN116693830A further confirms that when the molar ratio of CHDM to ethylene glycol in PCTG copolyester is 6:4, the terminal carboxyl group growth rate is only 1 / 3 of that of PET, and the service life is extended by 2.5 times under 120℃ high-pressure steam environment. However, its price is very high, and it has non-crystallizable properties, making it unsuitable for fiber or other engineering plastic applications.

[0005] Existing technologies have not effectively solved the problem of sealing the active hydroxyl groups at the ends of molecular chains. The terminal hydroxyl groups and carboxylic acid end groups serve as the starting sites for hydrolysis reactions, which will accelerate the degradation process of materials. Low molecular weight end-capping agents have poor heat resistance and are easy to volatilize, resulting in poor end-capping effects and difficulty in achieving long-term hydrolysis resistance.

[0006] In summary, existing hydrolysis-resistant PET modification technologies have multiple limitations: CHDM copolymerization of PETG / PCTG resin results in low crystallinity, reduced spinnability, and low fiber strength; hydrolysis-resistant carbonization additives suffer from poor thermal stability and gas generation during processing. Developing a technology that combines excellent hydrolysis resistance, crystallinity, and mechanical properties for application in core areas such as spinning and high-strength films has become a pressing technical challenge for the PET industry, and is of great significance for expanding PET application scenarios and increasing product added value. Summary of the Invention

[0007] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0008] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0009] Therefore, the purpose of this invention is to overcome the shortcomings of traditional PET in terms of poor hydrolysis resistance and to provide a hydrolysis-resistant and crystallizable copolyester material.

[0010] To solve the above-mentioned technical problems, the present invention provides the following technical solutions, including: The copolyester material uses polyethylene terephthalate as the main chain segment; its structural formula is: R'-NHCOO-[(PTA-EG) m1 -(PTA-CHDM) n -(PTA-EG) m2 ] Q -(PTA-NG) P -OOC-NH-R"

[0011] Where R' represents an HMDI residue, ;R" represents an IPDI residue. R' and R" can coexist or be interchanged depending on the end-capping agent; PTA-EG stands for polyethylene terephthalate unit. ; PTA-NG neopentyl terephthalate unit ; PTA-CHDM stands for terephthalic acid-cyclohexanediethanol unit. ; m1, m2, n, P, and Q are integers. The values ​​of m1 and m2 are 1 to 5, and the value of m1+m2 is 4 to 10. The value of n is 1 to 3. The value of P is 20 to 50. The value of Q is 20 to 50.

[0012] As a preferred embodiment of the hydrolysis-resistant and crystallizable copolyester material of the present invention, the structure of the copolyester material is as follows: , Where: m1, m2, n, P, and Q are integers; m1 and m2 are the number of repeating units in the PTA-EG esterified chain segment, ranging from 1 to 5, and m1+m2 ranges from 4 to 10; n is the number of repeating units in the PTA-CHDM, ranging from 1 to 3; P is the number of repeating units in the PTA-NG crystalline block segment prepolymer, ranging from 20 to 50; and Q is the number of repeating units in the PTA-EG-PTA-CHDM esterified sterically hindered segment-esterified oligomer, ranging from 20 to 50.

[0013] This structure achieves a balance between compatibility and functional independence between chain segments through a multi-block synergistic design. The PTA-EG-PTA-CHDM main chain ensures mechanical strength and thermal stability, while the PNG blocks provide a driving force for rapid crystallization. The dense surface layer formed after IPDI / HMDI end capping effectively inhibits moisture penetration. The three work together to improve the long-term durability of the material in high-temperature and high-humidity environments.

[0014] As a preferred embodiment of the hydrolysis-resistant and crystallizable copolyester material of the present invention, the copolyester material has the following properties: intrinsic viscosity 0.65~0.85 dL / g, crystallinity 20~35%, melting temperature 235~250℃, tensile strength ≥50MPa, and PCT hydrolysis resistance: after accelerated aging at 121℃ / 2.0MPa for 48h, the intrinsic viscosity retention rate is ≥80%, and the tensile strength retention rate is ≥80%.

[0015] Another objective of this invention is to overcome the shortcomings of traditional PET in terms of poor hydrolysis resistance and to provide a method for preparing a hydrolysis-resistant and crystallizable copolyester material, employing a diesterization-prepolymerization-mixed polycondensation-post-capping process, including: PTA, EG, CHDM and polyester catalyst are mixed with stabilizer and subjected to a single esterification reaction until the esterification rate is ≥92% to obtain a ternary esterification product; then the temperature is raised to carry out a prepolymerization reaction to obtain a PTA-EG-CHDM ternary prepolymer, denoted as prepolymer A. PTA, NG, and polyester catalyst were mixed with a stabilizer and subjected to a secondary esterification reaction until the esterification rate was ≥92% to obtain the PNG esterification product; the prepolymerization reaction was carried out by heating to obtain the PTA-NG nucleated block prepolymer, denoted as prepolymer B. Prepolymer A and prepolymer B are preheated and mixed, and then the vacuum is gradually reduced to ≤100Pa. The temperature is then increased to carry out the copolymerization reaction. When the intrinsic viscosity is ≥0.65dL / g, the end-capping agent is injected. After the reaction is fully stirred, the copolymer melt is extruded and granulated under nitrogen pressure of 1~3 atmospheres. When the moisture content is ≤300ppm, it is packaged to obtain a hydrolysis-resistant and crystallizable copolyester material. The copolymerization reaction is carried out under a nitrogen atmosphere at a temperature of 250-270°C for 3-5 hours.

[0016] This invention employs a diesterization-prepolymerization-mixed polycondensation-post-terminal capping process, described as follows: 1. Staged prepolymerization: PTA-EG-CHDM ternary prepolymer (prepolymer A) and PTA-NG oligomer (prepolymer B) are prepared separately to control the intercalation structure and material viscosity relatively precisely, avoiding uneven block distribution caused by single-step polymerization; 2. Prepolymer viscosity control: Prepolymer A and prepolymer B have low viscosities, typically between 0.3 and 0.5 dL / g, to ensure uniform dispersion during mixing and polycondensation and to avoid phase separation;

[0017] 3. Dynamic end-capping: For end-capping agents such as IPDI and HMDI and their mixtures, diluents such as diphenyl phthalate (DPH, boiling point 370℃) or dioctyl terephthalate (DOTP, boiling point 383℃) or their mixtures are used. After sufficient dehydration, the mixing ratio of the diluent with the end-capping agent is 0.5~3:1, in order to reduce the viscosity and activity of the end-capping agent and prevent the end-capping agent from self-polymerizing during storage.

[0018] 4. A dynamic mixing device and a precision metering pump are used to ensure uniform dispersion of the end-capping agent. Simultaneously, a small amount of diluent remaining in the copolyester resin will act as a nucleating agent, promoting the crystallization ability of the polyester. This invention reduces the attack of water molecules on the copolyester backbone and slows down the hydrolysis rate of ester bonds through a synergistic mechanism of steric barrier, end-group closure, and structural stability protection. The specific mechanism is as follows: 1. CHDM steric barrier and reduced ester bond density, slowing down small water molecule attacks on ester bonds: The cyclohexane ring in the CHDM molecule is a rigid ring structure. Introducing it into the copolymer backbone creates a steric barrier around the ester bonds (-CO-O-), and the longer CHDM chain segments also reduce the density of ester bond distribution. Water molecules (H2O) are polar molecules, and their attack on ester bonds follows a reaction pathway of "nucleophilic attack - tetrahedral intermediate formation - bond breaking." The steric hindrance of the cyclohexane ring will: ① increase the steric resistance of water molecules approaching the ester bonds to some extent, reducing the probability of effective collisions; ② distort the electron cloud distribution of the ester bonds, weakening their electrophilicity and reducing the nucleophilic attack of oxygen atoms by water molecules; ③ increase the activation energy of the hydrolysis reaction from 85~90 kJ / mol in traditional PET to 120~130 kJ / mol in pure CHDM-PTA ester bonds, thus reducing the hydrolysis rate; ④ reduce the density of ester bonds in the backbone, thus reducing the probability of ester bond hydrolysis to some extent.

[0019] 2. End-capping agent for end-group blocking: reduces hydrolysis initiation sites.

[0020] The terminal hydroxyl (-OH) and carboxylic acid groups of the copolyester molecular chain are the core initiation sites for hydrolysis: hydroxyl and carboxylic acid groups readily form hydrogen bonds with water molecules, inducing water molecules to activate and attack adjacent ester bonds, triggering unzipping-like hydrolytic degradation. This invention achieves triple protection by sealing the terminal hydroxyl groups with isocyanate end-capping agents: ① Reducing the terminal hydroxyl group as a hydrolysis initiation site, thus reducing the initiation of the hydrolysis reaction; ② The generated urethane end-capping groups (-O-CO-NH-) exhibit excellent hydrolysis resistance, with bond energies (305 kJ / mol) far exceeding those of ester bonds (250 kJ / mol), making them less susceptible to breakage by water molecules; ③ The trace amounts of NCO groups remaining at the end can react with moisture in the environment to form urea bonds (-NH-CO-NH-), further crosslinking to form a dense surface protective layer, hindering water molecules from penetrating into the main chain.

[0021] 3. PNG segment crystallization reinforcement: improves the density of the main chain structure.

[0022] PNG blocks have a regular linear chain structure, a fast crystallization rate, and high crystallinity, which can form uniformly distributed crystalline regions in copolymers. The dense structure of the crystalline regions, the regular arrangement of molecular chains, and high hydrophobicity can: ① reduce the penetration channels of water molecules inside the material and decrease the probability of water molecules contacting the ester bonds of the main chain; ② the strong intermolecular forces in the crystalline regions can stabilize the main chain structure, inhibit the rotation and breakage of ester bonds, and improve the hydrolytic stability of the main chain; ③ the crystalline and amorphous regions form a microphase separation structure, with CHDM steric units and end-capping groups mainly distributed in the amorphous regions, forming a synergistic structure of "crystalline region support - amorphous region protection", further enhancing the hydrolysis resistance.

[0023] 4. Component synergistic stabilization: Optimizing the main chain chemical environment

[0024] The synergistic effect of CHDM, PNG blocks, and end-capping agents optimizes the chemical environment of the main chain, further mitigating hydrolysis: ① The cyclohexane ring of CHDM has a hydrophobic structure, which reduces the ester bond density and hydrophilicity of the material, decreasing the adsorption of water molecules; ② The flexible hydrophobic segments of the PNG blocks also achieve a certain degree of toughening effect, improving the mechanical toughness of the material; ③ The highly thermally stable end-capping agent forms a synergistic steric hindrance effect with the cyclohexane structure of CHDM, constructing a double spatial barrier around the ester bonds; ④ The highly heat-resistant end-capping diluent can act as a nucleating agent to further enhance the crystallinity of the material. Ultimately, this achieves the integrity of the main chain structure, further improving the hydrolytic stability of the copolyester material.

[0025] This invention maintains a certain degree of crystallinity in the novel copolymer through "block synergistic nucleation + structural regularity regulation + heterogeneous nucleation crystallization". 1) The dominant role of PNG block nucleation: 1,5-Pentanediol (NG) is a straight-chain diol. The PNG block formed with PTA has a highly ordered molecular chain structure. Its carbon chain length (5 methylene groups) matches the spacing of the PET host chain (EG contains 2 methylene groups) very well, serving as a "heterogeneous nucleation site". The straight-chain structure of NG reduces the rotational resistance within the molecular chain, making it easier for the PNG block to form ordered crystal nuclei, inducing the directional crystallization of the surrounding PTA-EG host chain, and significantly improving the crystallization rate and crystallinity.

[0026] 2) Control of CHDM content: The cyclohexyl groups of CHDM have a steric hindrance effect. Excessive introduction will disrupt the regular arrangement of PET molecular chains, leading to a sharp drop in crystallinity. This invention controls the CHDM content at ≤8~20% (total molar amount of PTA). Its steric hindrance effect is offset by the nucleation effect of PNG blocks. At the same time, the rigid structure of CHDM can optimize the stability of the crystalline regions, so that the crystallinity of the copolymer is maintained at a high level, such as 20~30%, thus balancing crystallinity and hydrolysis resistance.

[0027] 3) Synergistic technology of dual prepolymerization process and heterogeneous nucleation with end-capping diluent: The prepolymer A (PTA-EG-CHDM) and prepolymer B (PNG) prepared in stages ensure that the PNG blocks are relatively uniformly dispersed in the main chain segments after mixed polycondensation, avoiding crystal nucleus failure caused by block aggregation; at the same time, the high-temperature resistant diluent is introduced as a heterogeneous nucleating agent, which is uniformly dispersed in the copolymer, further ensuring the uniformity of crystallization and stabilizing the copolymer melting temperature at 245~250℃, meeting the requirements of multiple application scenarios.

[0028] In a preferred embodiment of the method for preparing the hydrolysis-resistant and crystallizable copolyester material of the present invention, the following is specified: in the PTA-EG-CHDM ternary prepolymer, the molar ratio of PTA, EG, and CHDM is 1:1~1.15:0.08~0.15; in the PNG esterification product, the molar ratio of PTA to NG is 1:1.05~1.2; and the mass ratio of prepolymer A to prepolymer B is 85~95:5~15.

[0029] In a preferred embodiment of the method for preparing the hydrolysis-resistant and crystallizable copolyester material of the present invention, the polyester catalyst comprises one or more of zinc acetate, cobalt acetate, tetrabutyl titanate, antimony trioxide, isopropyl titanate, antimony trioxide, antimony glycolate, and dibutyltin oxide; the stabilizer is a phosphorus-based compound selected from at least one of phosphate esters, phosphites, and phosphonic acid compounds; the phosphate esters include triphenyl phosphate and triethyl phosphate; the phosphites include triphenyl phosphite and distearate pentaerythritol diphosphite; and the phosphonic acid compounds include 2-carboxyethylphosphonic acid and 2-carboxypropylphosphonic acid.

[0030] In a preferred embodiment of the method for preparing the hydrolysis-resistant and crystallizable copolyester material of the present invention, the prepolymerization reaction is carried out at a temperature of 240~260℃ for 1~2h and a vacuum degree of 1000~200Pa.

[0031] In a preferred embodiment of the method for preparing the hydrolysis-resistant and crystallizable copolyester material of the present invention, the primary esterification reaction is carried out in an inert gas atmosphere at a temperature of 220-250°C and a pressure of 0.2-0.3 MPa for 2-4 hours; the secondary esterification reaction is carried out in an inert gas atmosphere at a temperature of 230-250°C and a pressure of 0.1-0.3 MPa for 3-4 hours.

[0032] In a preferred embodiment of the method for preparing the hydrolysis-resistant and crystallizable copolyester material of the present invention, the end-capping agent is selected from one or more of isophorone diisocyanate (IPDI) and 4,4'-dicyclohexylmethane diisocyanate (HMDI); the amount of end-capping agent is 0.4~0.9% of the copolymer mass.

[0033] This invention uses IPDI or HMDI as a capping agent, which undergoes a nucleophilic addition reaction with the terminal hydroxyl groups of the copolymer precursor to block the active end groups and form a hydrolysis-resistant protective layer. The core reaction is as follows: 1. IPDI undergoes a capping reaction with the terminal hydroxyl groups of the copolymer to obtain an IPDI-modified active copolymer with the following structural formula: , The urethane bonds (-O-CO-NH-) generated in the reaction have high bond energy and excellent hydrolysis resistance. The NCO groups remaining at the ends can further react with trace amounts of water to form urea bonds, enhancing the intermolecular forces.

[0034] 2. The end-capping reaction of HMDI with the hydroxyl groups of the copolymer yields an HMDI-modified active copolymer with the following structural formula: , The cyclohexane structure of HMDI forms a synergistic steric hindrance effect with CHDM, further enhancing the steric hindrance around the ester bond and hindering the attack of water molecules.

[0035] In a preferred embodiment of the preparation method of the hydrolysis-resistant and crystallizable copolyester material of the present invention, the capping agent is diluted and then preheated to 50-90°C, and injected through a precision metering pump and a dynamic mixing device; the diluent for the capping agent includes one or more of diphenyl phthalate and dioctyl terephthalate; the mixing mass ratio of the diluent to the capping agent is 0.5-3:1, and the diluent reduces the viscosity of the capping agent to prevent self-polymerization of the capping agent during storage.

[0036] Another objective of this invention is to address the shortcomings of traditional PET in terms of poor hydrolysis resistance, and to provide a hydrolysis-resistant and crystallizable copolyester material for use in the preparation of textile fibers, high-temperature sterilization packaging materials, or outdoor products suitable for high-temperature and high-humidity environments.

[0037] Beneficial effects of this invention: (1) Significantly improved hydrolysis resistance: Through the multiple effects of CHDM steric hindrance and end-cap protection, after PCT 121℃ / 2.0MPa accelerated aging for 48h, the characteristic viscosity retention rate of the resin is ≥80% and the fracture strength retention rate of the material is ≥80%, which is 20% or more higher than that of traditional PET. The obtained material can adapt to high temperature and high humidity application scenarios.

[0038] (2) Excellent crystallinity and mechanical properties: PNG blocks compensate for the damage to crystallinity caused by CHDM, with a crystallinity of 20~35%, a melting temperature of 235~250℃, and a tensile strength of >50MPa, which can meet the performance requirements of spinning and other engineering plastic application scenarios.

[0039] (3) Good process stability: The staged preparation process of diesterization can accurately control the parameters of each step, so as to achieve controllability of structural design. Attached Figure Description

[0040] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein: Figure 1 The image shows the hydrogen spectrum of the copolyester material prepared in Example 1.

[0041] Figure 2 The above are the DSC enthalpy curves for Example 1, Comparative Examples 1 and 2. Detailed Implementation

[0042] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0043] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0044] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0045] Unless otherwise specified, all raw materials used in this invention are commercially available.

[0046] Terephthalic acid (PTA, purified, 99.5% purity); ethylene glycol (EG, 99.9% purity, boiling range 196.5~197.5℃); 1,4-cyclohexanediethanol (CHDM, 99.5% purity); 1,5-pentanediol (NG, 99.5% purity, boiling point 242℃); phorone diisocyanate (IPDI, 99% purity); 4,4'-dicyclohexylmethane diisocyanate (HMDI, 99% purity); antimony glycolate / catalytic grade; tetrabutyl titanate (TBT); triphenyl phosphate (TPP); diphenyl phthalate (DPH, boiling point 370℃); dioctyl terephthalate (DOTP, boiling point 383℃).

[0047] The materials obtained in the embodiments of the present invention were subjected to performance testing according to the following method: Intrinsic viscosity: Ubbelohde viscometer method, phenol-tetrachloroethane (1:1) as solvent, tested at 25℃.

[0048] Crystallinity and melting temperature: Differential scanning calorimeter (DSC), heating rate 10℃ / min, nitrogen atmosphere.

[0049] Mechanical properties: Using a universal testing machine, type 1A specimens were prepared according to GB / T 1040.3-2006, with a tensile rate of 50 mm / min, and the breaking strength and elongation at break were tested.

[0050] Hydrolysis resistance: PCT accelerated aging chamber, 121℃ / 2.0MPa aging for 48h, molecular weight retention rate was evaluated by intrinsic viscosity, and fracture strength retention rate of the material was tested by universal testing machine.

[0051] The determination of terminal carboxyl groups in copolymers was performed according to GB / T 12008.5-2010, using the phenol-chloroform dissolution-acid-base titration method.

[0052] Example 1

[0053] This embodiment provides a method for preparing a copolyester material, specifically as follows: 1. Preparation of diluent capping agent: The DOTP diluent is fully dehydrated, and the diluent (DOTP) and capping agent (IPDI) are mixed at a mass ratio of 2:1 to obtain a diluent capping agent with a concentration of 33.3%, which is then sealed and ready for use.

[0054] 2. Preparation of Prepolymer A: In a polyester reactor, PTA, EG, CHDM, TBT catalyst (20 ppm effective titanium), and TPP stabilizer (50 ppm) in a molar ratio of 1:1:0.15 were added and mixed for 1 hour. Then, the esterification stage was initiated under nitrogen protection. The esterification temperature was gradually increased from 220℃ to 240℃ to terminate the esterification. The pressure esterification was then increased from 0.1 MPa to 0.2 MPa, controlling the esterification rate to ≥92%. The esterification time was approximately 3-5 hours. Then, the prepolymerization stage was initiated. The vacuum was gradually reduced from 1000 Pa to a medium vacuum of 200 Pa, and the temperature was raised to 255℃. Prepolymerization was carried out for 1.5 hours to obtain prepolymer A, which was then ready for use.

[0055] 3. Preparation of prepolymer B: In a polyester reactor, purified PTA monomer and polymerization-grade NG monomer, 230 ppm antimony glycol catalyst, and 50 ppm TPP stabilizer in a molar ratio of 1:1.1 were mixed by slurrying for 1 hour. Under nitrogen protection, the mixture was heated to enter the esterification stage. Esterification began at 230℃ and gradually increased to 250℃ to terminate the esterification. The esterification pressure started at 0.1 MPa and gradually increased to 0.2 MPa. The reaction lasted for about 4 hours. At this point, the esterification rate reached ≥92%. Then, the prepolymerization stage was entered. The polymerization temperature was gradually increased from 255℃ to 265℃, and the vacuum was gradually increased from 1000 Pa to 200 Pa. The prepolymerization time was about 1.5 hours. The viscosity of the prepolymer was 0.40 dL / g. The prepolymer was extruded under nitrogen, pulverized, cooled, and dried for later use.

[0056] 4. Mixed polycondensation: Add prepolymer B to molten prepolymer A at a mass ratio of 90:10. After mixing evenly, gradually raise the temperature to 260℃ under nitrogen protection and stir for 20 minutes. Stepwise vacuuming is performed until the vacuum is controlled to be less than 100 Pa. The temperature is then gradually raised to 265℃ until it reaches 270℃ to achieve the target viscosity. The reaction takes about 4 hours, which is close to the final polymerization stage, and the copolymer precursor is obtained.

[0057] 5. End-capping modification: Under a vacuum of 800 Pa and a stirring speed of 90 r / min, the diluted IPDI end-capping agent is kept at approximately 70°C and injected into the melt at a rate of 15 mL / min, with dynamic online mixing. The injection time is approximately 10 minutes. The effective content of the diluted IPDI end-capping agent is 0.6% of the polymer melt. Stirring is continued for 15 minutes to carry out the end-capping and polymerization reaction, obtaining the end-capped polymer. Stirring is then stopped. Granulation is performed under nitrogen pressure of 0.2~0.3 MPa, followed by drying at 125°C for 5 hours until the moisture content is below 300 ppm, yielding the copolyester material with the following structural formula: , The hydrogen spectrum of the copolyester material is as follows: Figure 1 As shown, no obvious terminal hydroxyl signals were observed in the overall spectrum, indicating that the esterification polycondensation reaction proceeded relatively completely and the target copolyester product was successfully prepared.

[0058] Example 2

[0059] The difference between this embodiment and Example 1 is that the mass ratio of prepolymer A to prepolymer B in step 4 is adjusted to 95:5. All other preparation processes are the same as in Example 1, yielding a copolyester material. Its structural formula is similar to that of Example 1.

[0060] Example 3

[0061] The difference between this embodiment and Example 1 is that the mass ratio of prepolymer A to prepolymer B in step 4 is adjusted to 85:15. The remaining preparation processes are the same as in Example 1, yielding a copolyester material. Its structural formula is similar to that of Example 1.

[0062] Example 4

[0063] The difference between this embodiment and Example 1 is that the effective content of the diluted IPDI capping agent in step 5 is adjusted to 0.4% of the polymer melt. The remaining preparation process is the same as in Example 1, and a copolyester material is obtained. Its structural formula is similar to that of Example 1.

[0064] Example 5

[0065] The difference between this embodiment and Example 1 is that the effective content of the diluted IPDI capping agent in step 5 is adjusted to 0.9% of the polymer melt. The remaining preparation processes are the same as in Example 1, yielding a copolyester material. Its structural formula is similar to that of Example 1.

[0066] Example 6

[0067] The difference between this embodiment and Embodiment 1 is that the type of end-capping agent in step 5 is changed to HMDI end-capping agent; the rest of the preparation process is the same as in Embodiment 1, yielding a copolyester material. The structural formula is...

[0068] Example 7

[0069] The difference between this embodiment and Example 1 is that the type of end-capping agent in step 5 is changed to IPDI / HMDI (1:1) end-capping agent. The remaining preparation process is the same as in Example 1, yielding a copolyester material. The structural formula is:

[0070] Example 8

[0071] The difference between this embodiment and Example 1 is that the molar ratio of PTA, EG, and CHDM is adjusted to 1:1.15:0.08, while the rest of the preparation process is the same as in Example 1, resulting in a copolyester material. Its structural formula is similar to that of Example 1.

[0072] Comparative Example 1 (no CHDM sterically hindered monomer, only PTA-EG main chain segment)

[0073] The difference between this comparative example and Example 1 is that in step 2, the amount of CHDM monomer added is 0, and the molar ratio of raw material PTA monomer and EG monomer is 1:1.15, so as to obtain PET prepolymer A without CHDM. The rest of the preparation process is the same as in Example 1, and a copolyester material is obtained.

[0074] Comparative Example 2 (no PNG nucleation blocks, only CHDM sterically hindered monomers)

[0075] The difference between this comparative example and Example 1 is that the amount of prepolymer B added in step 4 is adjusted to 0, while the rest of the preparation process is the same as in Example 1, and a copolyester material is obtained.

[0076] Figure 2 The DSC (Differential Scanning Calorimetry) enthalpy curves for Example 1, Comparative Examples 1 and 2 are shown. It can be seen that the present invention significantly improves the high-temperature thermal stability of the copolyester material. The high-temperature endothermic peak temperature (259℃) of Example 1 is much higher than that of Comparative Example 2 (230℃), indicating that the modified material can withstand higher temperatures. Simultaneously, the copolyester material of Example 1 possesses a characteristic melting peak of 146.3℃, while pure PET end-capped material (Comparative Example 1) does not have this peak, indicating a difference in their thermal behavior and suggesting that the present invention forms a unique microstructure. The DSC curves show that the material prepared by the present invention combines specific low-temperature melt processability (146.3℃) with high-temperature service stability (259℃), demonstrating broad application prospects in scenarios requiring a balance between processing efficiency and high-temperature performance, such as the preparation of high-end resin materials and the development of heat-resistant coatings.

[0077] Comparative Example 3 (without post-terminal end-capping modification)

[0078] The difference between this comparative example and Example 1 is that no end-capping modification was performed, but the rest of the preparation process was the same as in Example 1, and a copolyester material was obtained.

[0079] Comparative Example 4 (CHDM Excess)

[0080] The difference between this comparative example and Example 1 is that the excess CHDM was adjusted in step 2, and the molar ratio of PTA, EG, and CHDM was 1:0.85:0.3, so that the CHDM content in the obtained prepolymer A was 30% of the PTA content; the rest of the preparation process was the same as in Example 1, and a copolyester material was obtained.

[0081] Comparative Example 5 (Traditional PET system, no CHDM, no NG, no end-capping)

[0082] This comparative example provides a traditional PET system, specifically: In a polyester reactor, PTA and EG monomers in a molar ratio of 1:1.15, along with a tetrabutyl titanate catalyst (20 ppm effective titanium) and 50 ppm TPP stabilizer, were added and mixed for 1 hour. Then, the esterification stage began under nitrogen protection. Esterification was initiated at 220°C and continued until approximately 240°C. Pressurized esterification was carried out at pressures ranging from 0.1 MPa to 0.2 MPa for about 4 hours, at which point the esterification rate exceeded 92%. The reactor then entered the prepolymerization stage, gradually increasing the vacuum to 1000 Pa and then gradually increasing it to 2... At 00 Pa, the temperature is raised to 255℃ and prepolymerized for about 1.5 hours to obtain CHDM-free PET prepolymer A. Prepolymer B is not required. Under nitrogen protection, the temperature is gradually raised to 260℃ to enter the pre-condensation stage. Vacuum is applied stepwise to less than 100 Pa, preferably reaching 50 Pa. The temperature is then gradually raised to 265℃ and further to 270℃, reacting for about 4 hours. Stirring is stopped when the stirring current in the reactor reaches the target value or stops increasing. Granulation is then performed under nitrogen pressure of 0.2~0.3 MPa, followed by drying at 125℃ for 5 hours, resulting in a moisture content below 300 ppm.

[0083] Comparative Example 6 (using ultra-high IPDI end-capping agent, 1.2%)

[0084] The difference between this comparative example and Example 1 is that the effective content of IPDI end-capping agent was adjusted to 1.2% of the polymer melt content, while the rest of the preparation process was the same as in Example 1, to obtain a copolyester material.

[0085] Comparative Example 7 (using pure IPDI end-capping agent, 0.6% without diluent)

[0086] The difference between this comparative example and Example 1 is that pure, diluent-free IPDI end-capping agent was used, while the rest of the preparation process was the same as in Example 1, to obtain the copolyester material.

[0087] During the injection process, it was found that the resistance of the injection tube was extremely high, and the injection process was unstable.

[0088] The components of the above embodiments and comparative examples are shown in Table 1. Performance tests were conducted on the materials prepared in the above embodiments and comparative examples, and the results compared with Example 1 are shown in Table 2. Performance tests included intrinsic viscosity, crystallinity, melting temperature, fracture strength, intrinsic viscosity retention rate after PCT 48h, fracture strength retention rate, and terminal carboxyl group value.

[0089] Table 1. List of components for examples and comparative examples.

[0090] Table 2 Performance List of Examples and Comparative Examples

[0091] As shown in the table above, Examples 1-3 used a fixed CHDM to PTA molar ratio of 15%, IPDI as the end-capping agent with an effective addition of 0.6%, and only adjusted the addition amount of the fast-crystallizing block PNG (based on the total copolymer amount), which was 5% (Example 2), 10% (Example 1), and 15% (Example 3), respectively. By comparing with Comparative Example 2 (without PNG) and Comparative Example 5 (traditional PET without PNG / CHDM modification), the crystallization-inducing and structure-optimizing effects of PNG were clearly demonstrated. Performance data showed that the crystallinity of Examples 1-3 was 22.6%, 25.9%, and 24.8%, respectively. This range can balance spinning efficiency and fiber strength, avoiding insufficient strength due to excessively low crystallinity or reduced spinnability due to excessively high crystallinity. Comparative Example 2 did not add PNG, and the remaining components were the same as in Example 1. The crystallinity was only 12.0% (far below the target lower limit), and the melting temperature dropped to 230°C. Due to the lack of high crystallinity-induced nucleation effect of PNG, the crystallization ability of the material was significantly deteriorated. Comparative Example 5 had a crystallinity of 27.4%, but its hydrolysis resistance was poor, and the PCT 48h tensile strength retention rate was only 54.5%.

[0092] Examples 4-7 are based on Example 1 (CHDM 15%, PNG 10%), with the variables being the effective amount of end-capping agent added (0.4%, 0.6%, 0.9%) and type (IPDI, HMDI, IPDI / HMDI mixture). Combined with Comparative Example 3 without end-capping agent, Comparative Example 6 with excess end-capping agent (1.20%), and conventional PET (Comparative Example 5), the hydrolysis protection mechanism of end-capping agent is clarified—the terminal carboxyl group is the active site for polyester hydrolysis, and the lower the content, the stronger the hydrolysis resistance. The trend of carboxyl-terminated groups and hydrolysis performance shows that: Example 4 (0.4% capping agent) has 2.3 mmol / t of carboxyl-terminated groups, Example 1 (0.6%) has 2.0 mmol / t, and Example 5 (0.9%) has 1.8 mmol / t. As the amount of capping agent added increases, the content of carboxyl-terminated groups gradually decreases, and the addition of 0.4% can significantly reduce the carboxyl-terminated groups (compared to 29.0 mmol / t in Comparative Example 3 without capping agent). The corresponding PCT 48h characteristic viscosity / tensile strength retention rate are both ≥85%, meeting the market requirement of ≥80%, and there is no obvious performance inflection point, proving that the addition range of 0.4~0.9% is economical and efficient.

[0093] Example 6 uses 0.6% HMDI instead of IPDI, with 2.1 mmol / t of terminal carboxyl groups, and a PCT 48h retention rate of 88.1% / 86.8%, which is close to the performance of Example 1 (IPDI). Example 7 uses a 0.9% IPDI:HMDI=1:1 mixed end-capping agent, with 1.3 mmol / t of terminal carboxyl groups, and a retention rate of 89.3% / 87.2%, with stable performance and no process abnormalities, thus broadening the process adaptability. Comparative Example 3, without end-capping agent, had a carboxyl group retention rate of 29.0 mmol / t and a PCT retention rate of 78.6% / 68.3% after 48 h, showing significant performance degradation after hydrolysis. Comparative Example 6, with 1.20% excess end-capping agent, had a carboxyl group retention rate of 1.4 mmol / t, which, although relatively high, easily led to partial cross-linking or gelation of the molecular chain, affecting processing flowability. Comparative Example 5, without end-capping treatment, had a carboxyl group retention rate of 30.0 mmol / t and a PCT retention rate of approximately 60% after 48 h, further demonstrating that "end-capping protection" is the core element, and an addition amount of 0.4~0.9% can balance hydrolysis performance and processing performance.

[0094] Examples 1 (CHDM molar ratio of PTA 15%) and 8 (CHDM 8%), combined with Comparative Example 1 (no CHDM), Comparative Example 4 (excess CHDM, 30%), and conventional PET (Comparative Example 5), illustrate the steric modification effect of CHDM—by introducing the steric hindrance of the cyclohexane structure, it synergistically regulates crystallization, melting temperature, and hydrolysis resistance. The crystallinity of Examples 8 and 1 were 27.4% and 25.9%, respectively, both within the 20-35% range. Increasing the CHDM content slightly inhibited crystallinity (due to the steric hindrance affecting molecular chain regularity), but it still synergistically maintained a suitable crystallization state with PNG. Comparison shows that: Comparative Example 1, without CHDM, had a crystallinity of 30.6% (meeting the standard, but the molecular chain was easily hydrolyzed and broken); Comparative Example 4, with excess CHDM (30%), had a crystallinity of only 8.2%, severely damaging molecular chain regularity and unable to form high-strength fibers; Comparative Example 5 had a crystallinity of 27.4%, but without steric modification, its hydrolysis resistance was extremely poor.

[0095] Polyester fibers need to meet the temperature resistance requirement of a melting temperature ≥235℃. The melting temperatures of Example 8 and Example 1 were 253℃ and 242℃, respectively, both higher than the standard. Furthermore, within the CHDM content range of 8-15%, the melting temperature decreased slightly with increasing content, but the thermal stability remained good. Comparative experiments showed that: Comparative Example 1, without CHDM, had a melting temperature of 258℃ (meeting the standard but prone to hydrolysis); Comparative Example 4, with excessive CHDM, had a melting temperature reduced to 230℃, exhibiting an amorphous crystalline state that could not meet spinning requirements; Comparative Example 5 had a melting temperature of 259.3℃, but poor hydrolysis resistance, demonstrating that CHDM can achieve a balance between processing performance and hydrolysis resistance.

[0096] Regarding hydrolysis resistance: The steric hindrance of CHDM can prevent water molecules from attacking the ester bonds. The PCT 48h retention rates of Examples 8 and 1 were 87.4% / 87.8% and 87.2% / 87.5%, respectively, both ≥80% and with similar performance, indicating that 8~20% CHDM can effectively exert the steric hindrance effect. Comparative Example 5 (traditional PET) had a retention rate of only 62.2% / 54.5%, exhibiting the worst hydrolysis resistance, further verifying the necessity of CHDM. In summary, 8~20% CHDM content is the optimized range for balancing steric hindrance, crystallinity, and hydrolysis resistance, avoiding the hydrolysis defects caused by the absence of CHDM or the crystallization difficulties caused by excessive CHDM.

[0097] This invention successfully prepared a novel copolyester material with high crystallinity and hydrolysis resistance through a technical route of steric hindrance modification (CHDM), block copolymerization (PNG), and end-capping protection (end-capping agent). Verification was achieved through examples and comparative examples.

[0098] The core component CHDM (8-20%, based on the PTA molar ratio) inhibits hydrolysis through steric hindrance, exhibiting significantly better hydrolysis resistance than traditional PET; PNG (5-15%, based on the total copolymer content) regulates crystallinity to a stable 20-35%, improving spinnability and hydrolysis stability; the end-capping agent (0.4-0.9% effective addition) reduces the end carboxyl content (1.3-2.3 mmol / t), applicable to IPDI, HMDI, and mixed systems, with strong process adaptability, ensuring a stable PCT retention rate of ≥86% over 48 hours.

[0099] The materials prepared by this invention have significant performance advantages. All embodiments meet the core requirements of crystallinity 20-35%, melting temperature ≥235℃, and PCT 48h retention rate ≥80%. In contrast, the comparative examples (without key components or with abnormal content) all have defects such as poor hydrolysis resistance and substandard processing performance. This fully demonstrates the necessity, advancement, and industrial feasibility of this technical solution, and provides a reliable basis for the large-scale production of hydrolysis-resistant copolyester materials.

[0100] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A hydrolysis-resistant, crystallizable copolyester material, characterized in that: The copolyester material uses polyethylene terephthalate as the main chain segment; its structural formula is: R'-NHCOO-[(PTA-EG) m1 -(PTA-CHDM) n -(PTA-EG) m2 ] Q -(PTA-NG) P -OOC-NH-R" Wherein, R' includes HMDI residues and IPDI residues, and R" includes HMDI residues and IPDI residues; The general formula of the HMDI residues is: , The general formula of the IPDI residues is: ; PTA-EG stands for polyethylene terephthalate unit. ; PTA-NG neopentyl terephthalate unit ; PTA-CHDM stands for terephthalic acid-cyclohexanediethanol unit. ; m1, m2, n, P, and Q are integers. The values ​​of m1 and m2 are 1 to 5, and the value of m1+m2 is 4 to 10. The value of n is 1 to 3. The value of P is 20 to 50. The value of Q is 20 to 50.

2. The hydrolysis-resistant crystallizable copolyester material as described in claim 1, characterized in that: The properties of the copolyester material are as follows: intrinsic viscosity 0.65~0.85 dL / g, crystallinity 20~35%, melting temperature 235~250℃, tensile strength ≥50MPa, and PCT hydrolysis resistance: after accelerated aging at 121℃ / 2.0MPa for 48h, the intrinsic viscosity retention rate is ≥80%, and the tensile strength retention rate is ≥80%.

3. A method for preparing a hydrolysis-resistant, crystallizable copolyester material as described in claim 1 or 2, characterized in that: The process employs diesterization-prepolymerization-mixed polycondensation-post-end-capping, including: PTA, EG, CHDM and polyester catalyst are mixed with stabilizer and subjected to a single esterification reaction until the esterification rate is ≥92% to obtain ter esterification product. The prepolymerization reaction was carried out by heating to obtain the PTA-EG-CHDM ternary prepolymer, denoted as prepolymer A; PTA, NG and polyester catalyst were mixed with stabilizer and subjected to a secondary esterification reaction until the esterification rate was ≥92% to obtain PNG esterification product. The prepolymerization reaction was carried out by heating to obtain the PTA-NG nucleated block prepolymer, denoted as prepolymer B; Prepolymer A and prepolymer B are preheated and mixed, and then the vacuum is gradually reduced to ≤100Pa. The temperature is then increased to carry out the copolymerization reaction. When the intrinsic viscosity is ≥0.65dL / g, the end-capping agent is injected. After the reaction is fully stirred, the copolymer melt is extruded and granulated under nitrogen pressure of 1~3 atmospheres. When the moisture content is ≤300ppm, it is packaged to obtain a hydrolysis-resistant and crystallizable copolyester material. The copolymerization reaction is carried out under a nitrogen atmosphere at a temperature of 250-270°C for 3-5 hours.

4. The method for preparing the hydrolysis-resistant crystallizable copolyester material as described in claim 3, characterized in that: In the PTA-EG-CHDM ternary prepolymer, the molar ratio of PTA, EG, and CHDM is 1:1~1.15:0.08~0.15; in the PNG esterification product, the molar ratio of PTA to NG is 1:1.05~1.2; and the mass ratio of prepolymer A to prepolymer B is 85~95:5~15.

5. The method for preparing the hydrolysis-resistant crystallizable copolyester material as described in claim 3 or 4, characterized in that: The polyester catalyst comprises one or more of zinc acetate, cobalt acetate, tetrabutyl titanate, antimony trioxide, isopropyl titanate, antimony trioxide, antimony glycolate, and dibutyltin oxide; the stabilizer is a phosphorus-based compound selected from at least one of phosphate esters, phosphites, and phosphonic acid compounds; the phosphate esters include triphenyl phosphate and triethyl phosphate; the phosphites include triphenyl phosphite and distearate pentaerythritol diphosphite; and the phosphonic acid compounds include 2-carboxyethylphosphonic acid and 2-carboxypropylphosphonic acid.

6. The method for preparing the hydrolysis-resistant crystallizable copolyester material as described in claim 5, characterized in that: The prepolymerization reaction is carried out at a temperature of 240-260°C for 1-2 hours and a vacuum of 1000-200 Pa.

7. The method for preparing the hydrolysis-resistant crystallizable copolyester material as described in claim 3, characterized in that: The primary esterification reaction is carried out in an inert gas atmosphere at a temperature of 220-250°C and a pressure of 0.2-0.3 MPa for 2-4 hours. The secondary esterification reaction is carried out in an inert gas atmosphere at a temperature of 230-250°C and a pressure of 0.1-0.3 MPa for 3-4 hours.

8. The hydrolysis-resistant crystallizable copolyester material as described in claim 7, characterized in that: The end-capping agent is selected from one or more of isophorone diisocyanate and 4,4'-dicyclohexylmethane diisocyanate; the amount of end-capping agent is 0.4~0.9% of the copolymer mass.

9. The method for preparing the hydrolysis-resistant crystallizable copolyester material as described in claim 7 or 8, characterized in that: The capping agent is diluted and then preheated to 50~90°C before injection; the diluent for the capping agent includes one or more of diphenyl phthalate and dioctyl terephthalate; the mass ratio of the diluent to the capping agent is 0.5~3:

1.

10. The application of a hydrolysis-resistant and crystallizable copolyester material as described in claim 1 or 2 in the preparation of textile fibers, high-temperature sterilization packaging materials, or outdoor products suitable for high-temperature and high-humidity environments.

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