Preparation method of high-heat-resistance cyclobutanediol-based copolyester

Abstract

The invention provides a preparation method of high-heat-resistance cyclobutanediol-based copolyester, and belongs to the field of polyester synthesis. The preparation method comprises the following steps: firstly, reacting 2, 2, 4, 4-tetramethyl-1, 3-cyclobutanediol with isocyanate at a relatively low temperature to obtain a hydroxyl-terminated intermediate product, and then carrying out esterification polycondensation reaction on the hydroxyl-terminated intermediate product, dimethyl terephthalate and aliphatic dihydric alcohol to prepare the high-heat-resistance cyclobutanediol copolyester. The 2, 2, 4, 4-tetramethyl-1, 3-cyclobutanediol is modified through isocyanate, the initial reaction temperature and the reaction time of the 2, 2, 4, 4-tetramethyl-1, 3-cyclobutanediol are reduced, the sublimation rate of the 2, 2, 4, 4-tetramethyl-1, 3-cyclobutanediol is reduced, and the heat resistance, the heat stability and the mechanical property of the polyester material are improved by introducing a benzene ring and / or an aliphatic ring structure.

Description

Technical Field

[0001] This invention belongs to the field of polyester synthesis, specifically relating to a method for preparing a high heat-resistant cyclobutanediol-based copolyester. Background Technology

[0002] Terephthalic acid copolyesters derived from sterically hindered diols such as 2,2,4,4-tetramethyl-1,3-cyclobutanediol and isosorbide are important transparent polymers with high heat resistance and safety. They can be used to replace bisphenol A-based polycarbonates in food contact applications because they do not release harmful bisphenol A during use. Among them, the copolyester synthesized by the condensation polymerization of 2,2,4,4-tetramethyl-1,3-cyclobutanediol, cyclohexanediol, and dimethyl terephthalate exhibits transparency exceeding 90% and a heat distortion temperature as high as 109°C. It has been commercialized and has become one of the major transparent thermoplastics used in water cups, baby bottles, and small appliance casings.

[0003] 2,2,4,4-Tetramethyl-1,3-cyclobutanediol and cyclohexanediol appear to be a perfect pair of diol monomers. 2,2,4,4-Tetramethyl-1,3-cyclobutanediol mainly helps to increase the glass transition temperature, while cyclohexanediol imparts balanced mechanical properties to the copolyester and also contributes to heat resistance. However, there are still some shortcomings in the synthesis and processing of its copolyester. For example, in Chinese invention patent CN 113321796 B, 2,2,4,4-tetramethyl-1,3-cyclobutanediol is a solid at room temperature and easily sublimates at higher reaction temperatures. Although cyclohexanediol and dimethyl terephthalate can melt at higher reaction temperatures, the solubility and dissolution rate of 2,2,4,4-tetramethyl-1,3-cyclobutanediol in the melts of both are not high enough. Therefore, the sublimation of 2,2,4,4-tetramethyl-1,3-cyclobutanediol inevitably occurs during the reaction, resulting in monomer loss. On the other hand, due to the sublimation of 2,2,4,4-tetramethyl-1,3-cyclobutanediol, it will condense when it comes into contact with the cooler pipe wall during the synthesis process. The condensed solid will cause blockage of the pipe and affect the polymerization reaction. In summary, it is essential to reduce the sublimation of 2,2,4,4-tetramethyl-1,3-cyclobutanediol during the reaction process. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for preparing a high-heat-resistant cyclobutanediol-based copolyester. The objective of this invention is to reduce the initial reaction temperature and reaction time of 2,2,4,4-tetramethyl-1,3-cyclobutanediol by modifying it with isocyanate, thus solving the problem of reactor pipe blockage caused by the sublimation of 2,2,4,4-tetramethyl-1,3-cyclobutanediol, avoiding monomer loss, and preventing a decrease in the copolyester grafting ratio and the reduction in the effect of improving the glass transition temperature. A further objective of this invention is to further improve the heat resistance and glass transition temperature of the polyester material by introducing benzene rings and / or aliphatic ring structures, while also endowing the polyester material with thermal stability and oxidation resistance.

[0005] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: This invention provides a method for preparing a high heat-resistant cyclobutanediol-based copolyester, comprising the following steps: S1: 2,2,4,4-Tetramethyl-1,3-cyclobutanediol is reacted with isocyanate at 60-130℃ to give a hydroxyl-terminated intermediate. S2: Esterification reaction of dimethyl terephthalate, intermediate product and aliphatic diol; S3: After the esterification reaction has reached 80% of the theoretical amount of methanol, a processing aid is added, and the esterification product is obtained after the esterification is complete. S4: The esterification product is subjected to polycondensation reaction to obtain a high heat-resistant cyclobutanediol-based copolyester.

[0006] Because the polyester esterification reaction temperature is high and the reaction time is long, the sublimation rate of 2,2,4,4-tetramethyl-1,3-cyclobutanediol increases continuously with increasing reaction temperature and time. When the sublimed material comes into contact with the cooler tube wall, it will solidify and block the reaction pipeline, affecting the reaction process. Therefore, this invention reduces the sublimation rate of 2,2,4,4-tetramethyl-1,3-cyclobutanediol by lowering the initial reaction temperature and time, thus avoiding blockage of the reactor pipeline and monomer loss, which affects the copolyester grafting ratio and reduces the effect of increasing the glass transition temperature. This invention also improves the tensile strength of the polyester by introducing isocyanate groups with cyclic structures. At the same time, the urethane bonds formed by the reaction of isocyanate and 2,2,4,4-tetramethyl-1,3-cyclobutanediol also form a large number of hydrogen bonds, effectively improving the heat resistance of the material. In this invention, after the esterification reaction has reached 80% of the theoretical methanol yield, a processing aid is added. The purpose of this addition is to enable the processing aid to be better dispersed in the system, to prevent it from being removed during the vacuuming process of the subsequent polycondensation reaction, and to prevent the processing aid from affecting the esterification reaction.

[0007] Preferably, in step S1, the hydroxyl-terminated intermediate has the following structural formula: CM: CHM: CI: .

[0008] The urethane bonds in the hydroxyl-terminated intermediates can form a large number of intermolecular hydrogen bonds, which can enhance the toughness and impact resistance of polyester materials, provide more stable chemical bonds for the molecular chain, improve the easy hydrolysis properties, and extend the service life.

[0009] Preferably, in step S1, the molar ratio of 2,2,4,4-tetramethyl-1,3-cyclobutanediol to isocyanate is (2-2.5):1; the isocyanate is one of 4,4'-diphenylmethane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, and isoflurane diisocyanate. This invention ensures that the intermediate product is end-capped with hydroxyl groups by controlling the amount of 2,2,4,4-tetramethyl-1,3-cyclobutanediol to be higher than that of isocyanate. Introducing isocyanates with benzene ring and aliphatic ring structures improves the mechanical properties and glass transition temperature of polyester materials through a more rigid molecular ring structure.

[0010] Preferably, in step S2, the intermediate product and the aliphatic diol are total diols; the molar ratio of the intermediate product to the total diol is no more than 0.4:1, and more preferably (0.1-0.3):1; the molar ratio of the total diol to dimethyl terephthalate is (1-2):1.

[0011] Preferably, in step S2, the aliphatic diol is one or more of 1,4-cyclohexanediol, ethylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, neopentanediol, 1,6-hexanediol, 1,7-heptanediol, and 1,8-octanediol.

[0012] Preferably, in step S1, catalyst A is added under a nitrogen atmosphere, and the reaction is carried out for 30-60 minutes. Catalyst A is at least one of tin-based, antimony-based, zinc-based, or titanium-based catalysts. The mass of catalyst A is 100-500 ppm of the mass of 2,2,4,4-tetramethyl-1,3-cyclobutanediol and isocyanate. Because the methyl group in 2,2,4,4-tetramethyl-1,3-cyclobutanediol generates a significant steric hindrance effect, hindering the reaction of isocyanate with it and resulting in a slow reaction rate, this invention promotes the reaction and increases the reaction rate by adding catalyst A.

[0013] Preferably, in step S2, catalyst B is added under a nitrogen atmosphere, the reaction temperature is 210-250℃, and the reaction time is 2-4 hours; catalyst B is at least one of tin-based, antimony-based, zinc-based, titanium-based, or manganese-based catalysts. The mass of catalyst B is 300-1000 ppm of dimethyl terephthalate.

[0014] Preferably, in step S3, the reaction temperature is 210-250℃ and the reaction time is 1-2h.

[0015] Preferably, in step S3, the processing aid includes at least one of a stabilizer and an antioxidant; the stabilizer is one or more of trimethyl phosphate, triphenyl phosphate, and triethyl phosphate, and the mass of the stabilizer is 100-1000 ppm of the mass of dimethyl terephthalate fed into the feed; the antioxidant is one or more of BasfIrganox 1098, BasfIrganox MD1024, BasfIrganox 1076, BasfIrganox 1010, Irganox 1035, PZSTAB 784, Revonox 608, BasfIrganox 168, and Ethanox 398, and the mass of the antioxidant is 100-1000 ppm of the mass of dimethyl terephthalate fed into the feed.

[0016] The stabilizers in this invention include trimethyl phosphate, triphenyl phosphate, and triethyl phosphate. Through the strong coordinating ability of phosphorus atoms, they complex with residual metal ions to form a stable structure, thereby improving the thermal stability of the polyester material during synthesis. The addition of antioxidants reduces oxidative chain reactions, preventing high-temperature thermal oxidative degradation and oxidative discoloration during synthesis or processing.

[0017] Preferably, in step S4, the reaction temperature is 250-280℃ and the reaction time is 2-5h; a low-vacuum polycondensation reaction is carried out first, with the vacuum degree controlled above 100Pa, and then a high-vacuum polycondensation reaction is carried out, with the vacuum degree being 0.1-100Pa.

[0018] Compared with the prior art, the beneficial effects of the present invention are: This invention modifies 2,2,4,4-tetramethyl-1,3-cyclobutanediol with isocyanate, reducing the sublimation rate of 2,2,4,4-tetramethyl-1,3-cyclobutanediol. The resulting copolyester also exhibits a high glass transition temperature, reaching 125°C or higher. Furthermore, this invention enhances the tensile strength of the copolyester by incorporating rigid or aliphatic ring structures, achieving a tensile strength of 48 MPa or higher. The high-heat-resistant cyclobutanediol-based copolyester prepared by this invention not only possesses a high glass transition temperature and tensile strength but also exhibits strong thermal stability and oxidation resistance. Attached Figure Description

[0019] Figure 1 This is a schematic diagram showing the sublimation rate of 2,2,4,4-tetramethyl-1,3-cyclobutanediol at different stirring temperatures. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to specific embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0021] General Implementation Examples A method for preparing a high heat-resistant cyclobutanediol-based copolyester includes the following steps: S1: Under a nitrogen atmosphere, 2,2,4,4-tetramethyl-1,3-cyclobutanediol and isocyanate are added to a reaction vessel and reacted under the action of catalyst A. The molar ratio of 2,2,4,4-tetramethyl-1,3-cyclobutanediol to isocyanate is (2-2.5):1. The mass of catalyst A is 100-500 ppm of the mass of 2,2,4,4-tetramethyl-1,3-cyclobutanediol and isocyanate. The reaction is carried out at 60-130℃ for 30-60 min to obtain a hydroxyl-terminated intermediate. The isocyanate is one of 4,4'-diphenylmethane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, or isoflurane diisocyanate. Catalyst A is at least one of tin-based, antimony-based, zinc-based, or titanium-based catalysts. S2: After the reaction in step S1 is completed, under a nitrogen atmosphere, dimethyl terephthalate, intermediate product, aliphatic diol, and catalyst B are added to a reaction vessel for esterification. After replacing the air with nitrogen, the pressure is increased to 0.1 MPa, and the temperature inside the reaction vessel is controlled at 210-250℃. The esterification reaction is stirred for 2-4 hours. The intermediate product and aliphatic diol are total diols, and the molar ratio of total diol to dimethyl terephthalate is (1-2):1. The molar ratio of intermediate product to total diol does not exceed 0.4:1, preferably (0.1-0.3):1. The mass of catalyst B is 300-1000 ppm of the mass of dimethyl terephthalate. The aliphatic diol is 1,4-cyclohexanediol, ethylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,4-cyclohexanediol, ethylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,4-cyclohexanediol, ethylene glycol, 1,3-propanediol, 2,3-cyclohexanediol, 1,4-propanediol, 2,3-cyclohexanediol, ethylene glycol, 1,3-propanediol, 2,3-cyclohexanediol, 2 ... One or more of butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, neopentanediol, 1,6-hexanediol, 1,7-heptanediol, and 1,8-octanediol, and catalyst B is at least one of tin-based, antimony-based, zinc-based, titanium-based, or manganese-based catalysts; S3: After the esterification reaction reaches 80% of the theoretical methanol yield, add a stabilizer and an antioxidant to the reactor at 100-1000 ppm and 100-1000 ppm of the mass of dimethyl terephthalate, respectively. Control the reactor temperature at 210-250℃ and continue the reaction for 1-2 hours until esterification is complete to obtain the esterification product. The stabilizer is one or more of trimethyl phosphate, triphenyl phosphate, and triethyl phosphate, and the antioxidant is one or more of BasfIrganox 1098, BasfIrganoxMD 1024, BasfIrganox 1076, BasfIrganox 1010, Irganox 1035, PZSTAB 784, Revonox 608, BasfIrganox 168, and Ethanox 398. S4: The esterification product is subjected to polycondensation reaction. The temperature inside the reactor is controlled at 250-280℃. Low vacuum polycondensation reaction is carried out with the vacuum degree controlled above 100Pa. Then, high vacuum polycondensation reaction is carried out with the vacuum degree controlled below 100Pa. The polycondensation reaction is carried out for 2-5 hours and then discharged to obtain high heat-resistant cyclobutanediol-based copolyester.

[0022] After testing, the high heat-resistant cyclobutanediol-based copolyester prepared by reacting 2,2,4,4-tetramethyl-1,3-cyclobutanediol with isocyanate at a low temperature, followed by esterification and polycondensation reaction with dimethyl terephthalate and aliphatic diol, has a glass transition temperature of 110-130℃ and a tensile strength of 44-50 MPa. It has strong heat resistance, mechanical strength and thermal stability, is not easily oxidized and discolored, and is easy to process, produce and apply.

[0023] Example 1 A method for preparing a high heat-resistant cyclobutanediol-based copolyester includes the following steps: S1: Under a nitrogen atmosphere, 2,2,4,4-tetramethyl-1,3-cyclobutanediol and 4,4'-diphenylmethane diisocyanate were added to a reaction vessel and reacted in the presence of catalyst A, dibutyltin dilaurate. The molar ratio of 2,2,4,4-tetramethyl-1,3-cyclobutanediol to 4,4'-diphenylmethane diisocyanate was 2:1, and the mass of catalyst A, dibutyltin dilaurate, was 100 ppm of the mass of 2,2,4,4-tetramethyl-1,3-cyclobutanediol and 4,4'-diphenylmethane diisocyanate. The reaction was carried out at 130°C for 30 min to obtain the hydroxyl-terminated intermediate CM. S2: After the reaction in step S1 is completed, under a nitrogen atmosphere, dimethyl terephthalate, intermediate product CM, aliphatic diol 1,4-cyclohexanediethanol, and catalyst B dibutyltin oxide are added to a reaction vessel for esterification. After replacing the air with nitrogen, the pressure is increased to 0.1 MPa, and the temperature inside the reaction vessel is controlled at 235℃. The esterification reaction is stirred for 2 hours. Among them, the intermediate product and aliphatic diol 1,4-cyclohexanediethanol are total diols. The molar ratio of total diol to dimethyl terephthalate is 1.05:1, the molar ratio of intermediate product to total diol is 0.18:1, and the mass of catalyst B dibutyltin oxide is 500 ppm of the mass of dimethyl terephthalate. S3: After the esterification reaction reaches 80% of the theoretical methanol yield, add the stabilizer triphenyl phosphate, the antioxidant BasfIrganox 1010, and the antioxidant BasfIrganox 168 to the reactor at mass ratios of 100 ppm, 100 ppm, and 200 ppm of the added dimethyl terephthalate, respectively. Control the reactor temperature at 245°C and continue the reaction for 1 hour. After the esterification is complete, the esterified product is obtained. S4: The esterification product is subjected to polycondensation reaction. The temperature inside the reactor is controlled at 255℃ for low-vacuum polycondensation reaction, and the vacuum degree is controlled above 100Pa. Then, the temperature inside the reactor is controlled at 270℃ for high-vacuum polycondensation reaction, and the vacuum degree is controlled below 100Pa. After the polycondensation reaction is carried out for 3 hours, the product is discharged to obtain high heat-resistant cyclobutanediol-based copolyester.

[0024] Example 2 A method for preparing a high heat-resistant cyclobutanediol-based copolyester includes the following steps: S1: Under a nitrogen atmosphere, 2,2,4,4-tetramethyl-1,3-cyclobutanediol and 4,4'-dicyclohexylmethane diisocyanate were added to a reaction vessel and reacted in the presence of catalyst A, dibutyltin dilaurate. The molar ratio of 2,2,4,4-tetramethyl-1,3-cyclobutanediol to 4,4'-dicyclohexylmethane diisocyanate was 2:1. The mass of catalyst A, dibutyltin dilaurate, was 100 ppm of the mass of 2,2,4,4-tetramethyl-1,3-cyclobutanediol and 4,4'-dicyclohexylmethane diisocyanate. The reaction was carried out at 80°C for 45 min to obtain the hydroxyl-terminated intermediate CHM. S2: After the reaction in step S1 is completed, under a nitrogen atmosphere, dimethyl terephthalate, intermediate product CHM, aliphatic diol 1,4-cyclohexanediethanol, and catalyst B dibutyltin oxide are added to the reactor for esterification. After replacing the air with nitrogen, the pressure is increased to 0.1 MPa, and the temperature inside the reactor is controlled at 235℃. The esterification reaction is stirred for 2 hours. Among them, the intermediate product and aliphatic diol 1,4-cyclohexanediethanol are total diols. The molar ratio of total diol to dimethyl terephthalate is 1.05:1, the molar ratio of intermediate product to total diol is 0.18:1, and the mass of catalyst B dibutyltin oxide is 500 ppm of the mass of dimethyl terephthalate. S3: After the esterification reaction reaches 80% of the theoretical methanol yield, add the stabilizer triphenyl phosphate, the antioxidant BasfIrganox 1010, and the antioxidant BasfIrganox 168 to the reactor at mass ratios of 100 ppm, 100 ppm, and 200 ppm of the added dimethyl terephthalate, respectively. Control the reactor temperature at 245°C and continue the reaction for 1 hour. After the esterification is complete, the esterified product is obtained. S4: The esterification product is subjected to polycondensation reaction. The temperature inside the reactor is controlled at 255℃ for low-vacuum polycondensation reaction, and the vacuum degree is controlled above 100Pa. Then, the temperature inside the reactor is controlled at 270℃ for high-vacuum polycondensation reaction, and the vacuum degree is controlled below 100Pa. After the polycondensation reaction is carried out for 3 hours, the product is discharged to obtain high heat-resistant cyclobutanediol-based copolyester.

[0025] Example 3 A method for preparing a high heat-resistant cyclobutanediol-based copolyester includes the following steps: S1: Under a nitrogen atmosphere, 2,2,4,4-tetramethyl-1,3-cyclobutanediol and isoflurane diisocyanate were added to a reaction vessel and reacted in the presence of catalyst A, dibutyltin dilaurate. The molar ratio of 2,2,4,4-tetramethyl-1,3-cyclobutanediol to isoflurane diisocyanate was 2:1, and the mass of catalyst A, dibutyltin dilaurate, was 100 ppm of the mass of 2,2,4,4-tetramethyl-1,3-cyclobutanediol and isoflurane diisocyanate. The reaction was carried out at 70°C for 30 min to obtain the hydroxyl-terminated intermediate CI. S2: After the reaction in step S1 is completed, under a nitrogen atmosphere, dimethyl terephthalate, intermediate product CI, aliphatic diol 1,4-cyclohexanediethanol, and catalyst B dibutyltin oxide are added to a reaction vessel for esterification. After replacing the air with nitrogen, the pressure is increased to 0.1 MPa, and the temperature inside the reaction vessel is controlled at 235℃. The esterification reaction is stirred for 2 hours. Among them, the intermediate product and aliphatic diol 1,4-cyclohexanediethanol are total diols. The molar ratio of total diol to dimethyl terephthalate is 1.05:1, the molar ratio of intermediate product to total diol is 0.18:1, and the mass of catalyst B dibutyltin oxide is 500 ppm of the mass of dimethyl terephthalate. S3: After the esterification reaction reaches 80% of the theoretical methanol yield, add the stabilizer triphenyl phosphate, the antioxidant BasfIrganox 1010, and the antioxidant BasfIrganox 168 to the reactor at mass ratios of 100 ppm, 100 ppm, and 200 ppm of the added dimethyl terephthalate, respectively. Control the reactor temperature at 245°C and continue the reaction for 1 hour. After the esterification is complete, the esterified product is obtained. S4: The esterification product is subjected to polycondensation reaction. The temperature inside the reactor is controlled at 255℃ for low-vacuum polycondensation reaction, and the vacuum degree is controlled above 100Pa. Then, the temperature inside the reactor is controlled at 270℃ for high-vacuum polycondensation reaction, and the vacuum degree is controlled below 100Pa. After the polycondensation reaction is carried out for 3 hours, the product is discharged to obtain high heat-resistant cyclobutanediol-based copolyester.

[0026] Example 4 A method for preparing a high heat-resistant cyclobutanediol-based copolyester includes the following steps: S1: Under a nitrogen atmosphere, 2,2,4,4-tetramethyl-1,3-cyclobutanediol and 4,4'-diphenylmethane diisocyanate were added to a reaction vessel and reacted in the presence of catalyst A, dibutyltin dilaurate. The molar ratio of 2,2,4,4-tetramethyl-1,3-cyclobutanediol to 4,4'-diphenylmethane diisocyanate was 2:1. The mass of catalyst A, dibutyltin dilaurate, was 150 ppm of the mass of 2,2,4,4-tetramethyl-1,3-cyclobutanediol and 4,4'-diphenylmethane diisocyanate. The reaction was carried out at 130°C for 45 min to obtain the hydroxyl-terminated intermediate CM. S2: After the reaction in step S1 is completed, under a nitrogen atmosphere, dimethyl terephthalate, intermediate product CM, aliphatic diol 1,4-cyclohexanediethanol, and catalyst B dibutyltin oxide are added to the reactor for esterification. After replacing the air with nitrogen, the pressure is increased to 0.1 MPa, and the temperature inside the reactor is controlled at 235℃. The esterification reaction is stirred for 2 hours. Among them, the intermediate product and aliphatic diol 1,4-cyclohexanediethanol are total diols. The molar ratio of total diol to dimethyl terephthalate is 1.05:1, the molar ratio of intermediate product to total diol is 0.25:1, and the mass of catalyst B dibutyltin oxide is 550 ppm of the mass of dimethyl terephthalate. S3: After the esterification reaction reaches 80% of the theoretical methanol yield, add the stabilizer triphenyl phosphate, the antioxidant BasfIrganox 1010, and the antioxidant BasfIrganox 168 to the reactor at mass ratios of 100 ppm, 100 ppm, and 200 ppm of the added dimethyl terephthalate, respectively. Control the reactor temperature at 245°C and continue the reaction for 1 hour. After the esterification is complete, the esterified product is obtained. S4: The esterification product is subjected to polycondensation reaction. The temperature inside the reactor is controlled at 255℃ for low-vacuum polycondensation reaction, and the vacuum degree is controlled above 100Pa. Then, the temperature inside the reactor is controlled at 270℃ for high-vacuum polycondensation reaction, and the vacuum degree is controlled below 100Pa. After the polycondensation reaction is carried out for 3 hours, the product is discharged to obtain high heat-resistant cyclobutanediol-based copolyester.

[0027] Comparative Example 1 A method for preparing a cyclobutanediol-based copolyester includes the following steps: S1: Under a nitrogen atmosphere, dimethyl terephthalate, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, aliphatic diol 1,4-cyclohexanediethanol, and catalyst B dibutyltin oxide were added to a reactor for esterification. After replacing the air with nitrogen, the pressure was increased to 0.1 MPa, and the reactor temperature was controlled at 235℃. The esterification reaction was stirred for 2 hours. Among them, 2,2,4,4-tetramethyl-1,3-cyclobutanediol and aliphatic diol 1,4-cyclohexanediethanol were the total diols, and the molar ratio of total diols to dimethyl terephthalate was 1.05:1. The molar ratio of 2,2,4,4-tetramethyl-1,3-cyclobutanediol to total diols was 0.3:1. The mass of catalyst B dibutyltin oxide was 400 ppm of the mass of dimethyl terephthalate. S2: After the esterification reaction reaches 80% of the theoretical methanol yield, add the stabilizer triphenyl phosphate, the antioxidant BasfIrganox 1010, and the antioxidant BasfIrganox 168 to the reactor at mass ratios of 100 ppm, 100 ppm, and 200 ppm of the added dimethyl terephthalate, respectively. Control the reactor temperature at 245°C and continue the reaction for 1 hour. After the esterification is complete, the esterified product is obtained. S3: The esterification product is subjected to polycondensation reaction. The temperature inside the reactor is controlled at 255℃ for low-vacuum polycondensation reaction, and the vacuum degree is controlled above 100Pa. Then, the temperature inside the reactor is controlled at 270℃ for high-vacuum polycondensation reaction, and the vacuum degree is controlled below 100Pa. After the polycondensation reaction is carried out for 3 hours, the product is discharged to obtain cyclobutanediol-based copolyester.

[0028] Comparative Example 2 A method for preparing a cyclobutanediol-based copolyester includes the following steps: S1: Under a nitrogen atmosphere, dimethyl terephthalate, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, aliphatic diol 1,4-cyclohexanediethanol, catalyst B (dibutyltin oxide), and 4,4'-diphenylmethane diisocyanate were added to a reactor for esterification. After replacing the air with nitrogen, the pressure was increased to 0.1 MPa, and the reactor temperature was controlled at 235°C. The esterification reaction was stirred for 2 hours. 2,2,4,4-Tetramethyl-1,3-cyclobutanediol and aliphatic diol 1,4-cyclohexanediethanol were the total diols, with a molar ratio of total diols to dimethyl terephthalate of 1.05:1, and a molar ratio of 1,2,2,4,4-tetramethyl-1,3-cyclobutanediol to total diols of 0.3:1. The molar ratio of 1,2,2,4,4-tetramethyl-1,3-cyclobutanediol to 4,4'-diphenylmethane diisocyanate is 2:1, and the mass of catalyst B oxidizing dibutyltin is 500 ppm of the mass of dimethyl terephthalate. S2: After the esterification reaction reaches 80% of the theoretical methanol yield, add the stabilizer triphenyl phosphate, the antioxidant BasfIrganox 1010, and the antioxidant BasfIrganox 168 to the reactor at mass ratios of 100 ppm, 100 ppm, and 200 ppm of the added dimethyl terephthalate, respectively. Control the reactor temperature at 245°C and continue the reaction for 1 hour. After the esterification is complete, the esterified product is obtained. S3: The esterification product is subjected to polycondensation reaction. The temperature inside the reactor is controlled at 255℃ for low-vacuum polycondensation reaction, and the vacuum degree is controlled above 100Pa. Then, the temperature inside the reactor is controlled at 270℃ for high-vacuum polycondensation reaction, and the vacuum degree is controlled below 100Pa. After the polycondensation reaction is carried out for 3 hours, the product is discharged to obtain cyclobutanediol-based copolyester.

[0029] Comparative Example 3 A method for preparing a cyclobutanediol-based copolyester includes the following steps: S1: Under a nitrogen atmosphere, dimethyl terephthalate, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, aliphatic diol 1,4-cyclohexanediethanol, and catalyst B dibutyltin oxide were added to a reactor for esterification. After replacing the air with nitrogen, the pressure was increased to 0.1 MPa, and the reactor temperature was controlled at 235℃. The esterification reaction was stirred for 2 hours. Among them, 2,2,4,4-tetramethyl-1,3-cyclobutanediol and aliphatic diol 1,4-cyclohexanediethanol were the total diols, and the molar ratio of total diols to dimethyl terephthalate was 1.05:1. The molar ratio of 2,2,4,4-tetramethyl-1,3-cyclobutanediol to total diols was 0.4:1. The mass of catalyst B dibutyltin oxide was 450 ppm of the mass of dimethyl terephthalate. S2: After the esterification reaction reaches 80% of the theoretical methanol yield, add the stabilizer triphenyl phosphate, the antioxidant BasfIrganox 1010, and the antioxidant BasfIrganox 168 to the reactor at mass ratios of 100 ppm, 100 ppm, and 200 ppm of the added dimethyl terephthalate, respectively. Control the reactor temperature at 245°C and continue the reaction for 1 hour. After the esterification is complete, the esterified product is obtained. S3: The esterification product is subjected to polycondensation reaction. The temperature inside the reactor is controlled at 255℃ for low-vacuum polycondensation reaction, and the vacuum degree is controlled above 100Pa. Then, the temperature inside the reactor is controlled at 270℃ for high-vacuum polycondensation reaction, and the vacuum degree is controlled below 100Pa. After the polycondensation reaction is carried out for 3 hours, the product is discharged to obtain cyclobutanediol-based copolyester.

[0030] Test Example 1 The sublimation rate of 2,2,4,4-tetramethyl-1,3-cyclobutanediol was tested at different stirring temperatures, and the results are as follows: Figure 1As shown in the figure. Test results indicate that the sublimation rate of 2,2,4,4-tetramethyl-1,3-cyclobutanediol is very low when stirred at 60-130℃ for 0.5-1h. However, the sublimation rate increases significantly with increasing temperature and time. When stirred at 140℃ for more than 4h, the sublimation rate is significantly greater than 50%, and it also increases significantly with increasing temperature. Therefore, reacting 2,2,4,4-tetramethyl-1,3-cyclobutanediol at 60-130℃ for 0.5-1h is more effective than reacting it directly at a higher esterification temperature for a longer time in avoiding monomer sublimation. This prevents significant loss of monomer during esterification, which could hinder the improvement of the temperature resistance and mechanical strength of polyester materials, and even clog reaction vessel pipes, affecting subsequent reactions and increasing operating costs.

[0031] Test Example 2 The glass transition temperature (Tg), heat distortion temperature, and tensile strength of Examples 1-5 and Comparative Examples 1-3 were tested, and the test results are shown in Table 1 below. As shown in Table 1, the copolyester synthesized by modifying 2,2,4,4-tetramethyl-1,3-cyclobutanediol with isocyanate by lowering the initial reaction temperature has a high glass transition temperature and excellent heat resistance. At the same time, the introduction of rigid ring or aliphatic ring structure improves the tensile strength of the copolyester.

[0032] Isocyanates are highly reactive, but they lack the groups that can directly react with dimethyl terephthalate (DMT), and can only react with alcohols. However, they exhibit competitive polymerization relationships with different alcohols, and at higher reaction temperatures, isocyanates are prone to side reactions, namely dimerization or trimerization, forming urea-formate or biuret structures. Therefore, compared to the uncontrollable nature of the one-step addition method for synthesizing copolyesters in Comparative Example 2, this invention uses a stepwise polymerization method. First, isocyanate-modified 2,2,4,4-tetramethyl-1,3-cyclobutanediol is carried out at a lower temperature, effectively reducing the sublimation rate of 2,2,4,4-tetramethyl-1,3-cyclobutanediol, yielding an intermediate product that can be used as a diol. This intermediate product is then subjected to esterification and polycondensation reactions with other components at high temperatures. This method allows for more effective control of the monomer ratio, reaction process, and product consistency, while also offering significant advantages in performance.

[0033] Comparative Examples 1 and 3 were both cyclobutanediol-based copolyesters obtained by polycondensation after esterification of dimethyl terephthalate, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, and aliphatic diols. According to the test results, compared with Examples 1 and 4, their glass transition temperature and tensile strength were both decreased. Direct esterification of 2,2,4,4-tetramethyl-1,3-cyclobutanediol at temperatures exceeding 140°C resulted in a significantly increased sublimation rate, easily causing monomer loss and affecting the grafting ratio of the copolyester, making it difficult to achieve the desired glass transition temperature. Simultaneously, its ability to improve the heat resistance of polyester materials was significantly lower than that of the intermediate product formed by the reaction of isocyanate and 2,2,4,4-tetramethyl-1,3-cyclobutanediol. The intermediate product forms numerous hydrogen bonds between the urethane bonds, which can significantly improve the heat resistance and enhance the mechanical properties of the polyester material.

Claims

1. A method for preparing a high heat-resistant cyclobutanediol-based copolyester, characterized in that, Includes the following steps: S1: 2,2,4,4-Tetramethyl-1,3-cyclobutanediol is reacted with isocyanate at 60-130℃ to give a hydroxyl-terminated intermediate. S2: Esterification reaction of dimethyl terephthalate, intermediate product and aliphatic diol; S3: After the esterification reaction has reached 80% of the theoretical amount of methanol, a processing aid is added, and the esterification product is obtained after the esterification is complete. S4: The esterification product is subjected to polycondensation reaction to obtain a high heat-resistant cyclobutanediol-based copolyester.

2. The method for preparing a high heat-resistant cyclobutanediol-based copolyester according to claim 1, characterized in that, In step S1, the structural formula of the hydroxyl-terminated intermediate includes: CM: CHM: CI: 。 3. The method for preparing a high heat-resistant cyclobutanediol-based copolyester according to claim 1 or 2, characterized in that, In step S1, the molar ratio of 2,2,4,4-tetramethyl-1,3-cyclobutanediol to isocyanate is (2-2.5):

1. The isocyanate is one of 4,4'-diphenylmethane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, and isoflurone diisocyanate.

4. The method for preparing a high heat-resistant cyclobutanediol-based copolyester according to claim 1, characterized in that, In step S2, the intermediate product and the aliphatic diol are total diols; The molar ratio of the intermediate product to the total diol does not exceed 0.4:1; The molar ratio of total diol to dimethyl terephthalate is (1-2):

1.

5. The method for preparing a high heat-resistant cyclobutanediol-based copolyester according to claim 4, characterized in that, In step S2, the aliphatic diol is one or more of the following: 1,4-cyclohexanediol, ethylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, neopentanediol, 1,6-hexanediol, 1,7-heptanediol, and 1,8-octanediol.

6. The method for preparing a high heat-resistant cyclobutanediol-based copolyester according to claim 1 or 2, characterized in that, In step S1, catalyst A is added under a nitrogen atmosphere and the reaction is carried out for 30-60 minutes. The catalyst A is at least one of tin-based, antimony-based, zinc-based, or titanium-based catalysts.

7. The method for preparing a high heat-resistant cyclobutanediol-based copolyester according to claim 2 or 4, characterized in that, In step S2, catalyst B is added under a nitrogen atmosphere, the reaction temperature is 210-250℃, and the reaction time is 2-4h. Catalyst B is at least one of tin-based, antimony-based, zinc-based, titanium-based, or manganese-based catalysts.

8. The method for preparing a high heat-resistant cyclobutanediol-based copolyester according to claim 1, characterized in that, In step S3, the reaction temperature is 210-250℃ and the reaction time is 1-2h.

9. A method for preparing a high heat-resistant cyclobutanediol-based copolyester according to claim 2 or 8, characterized in that, In step S3, the processing aids include at least one of stabilizers and antioxidants; The stabilizer is one or more of trimethyl phosphate, triphenyl phosphate, and triethyl phosphate; The antioxidant is one or more of BasfIrganox 1098, BasfIrganoxMD 1024, BasfIrganox 1076, BasfIrganox 1010, Irganox 1035, PZSTAB 784, Revonox 608, BasfIrganox 168, and Ethanox 398.

10. A method for preparing a high heat-resistant cyclobutanediol-based copolyester according to claim 1 or 2, characterized in that, In step S4, the reaction temperature is 250-280℃ and the reaction time is 2-5h; First, a low-vacuum polycondensation reaction is carried out, with the vacuum level controlled above 100 Pa, and then a high-vacuum polycondensation reaction is carried out, with the vacuum level being 0.1-100 Pa.

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