A methyl propylene glycol-modified polyester and its preparation method

Abstract

This application relates to the technical field of polymer synthesis, specifically disclosing a methyl propylene glycol-modified polyester and its preparation method. A methyl propylene glycol-modified polyester is prepared by esterification-polymerization of raw materials in the following molar ratio: terephthalic acid and a diol; the diol includes ethylene glycol, diethylene glycol, and methyl propylene glycol; the methyl propylene glycol is subjected to cyclodextrin inclusion treatment before use; the molar ratio of terephthalic acid, ethylene glycol, diethylene glycol, and methyl propylene glycol is 1:(0.7~0.9):(0.01~0.05):(0.2~0.6). The methyl propylene glycol-modified polyester obtained by this application has a low melting point and good mechanical properties.

Description

Technical Field

[0001] This application relates to the technical field of polymer material synthesis, and more specifically, to a methylpropanediol modified polyester and its preparation method. Background Technology

[0002] Polyester is a semi-crystalline thermoplastic polymer with excellent overall performance and low cost, and it has found wide application in fibers, bottle flakes, films, and engineering plastics. This is mainly due to its good mechanical strength, chemical resistance, insulation, spinnability, and excellent processing and molding properties. However, the relatively high melting point (~255℃) and crystallization rate of standard PET pose limitations in certain applications, such as low-temperature hot-melt processing, lamination with heat-sensitive substrates, and applications requiring high transparency and low molding shrinkage. Therefore, chemically modifying the chain structure of PET to obtain novel polyester materials with lower melting points and slower crystallization rates has become an important and active research direction in the field of polymer science.

[0003] Copolymerization modification is an effective way to achieve this goal. This method involves introducing one or more third, or even fourth, monomers different from the original components during polymerization. By co-condensation, the symmetry and regularity of the molecular chains are altered, thereby fundamentally adjusting the final properties of the polymer. Copolymerization modification can be divided into two main categories: acid modification and alcohol modification. The former involves introducing dicarboxylic acid monomers such as isophthalic acid (IPA) and adipic acid to disrupt the regularity of the chain structure; the latter achieves a similar purpose by introducing diol monomers with different structures.

[0004] Patent application CN110684184A discloses a diol-modified PETG polyester chip made from the following raw materials: terephthalic acid, neopentyl glycol, diethylene glycol, and ethylene glycol in a molar ratio of 1:(0.1~0.5):(0.05~0.1):(0.6~0.8).

[0005] In this scheme, neopentyl glycol is used to modify polyester. Its molecular structure is a highly symmetrical quaternary carbon center. In the polyester modification process, this structure promotes the regular arrangement of polyester molecular chains, which significantly improves the crystallinity of polyester and thus gives the material high hardness. However, this structure also restricts the movement of molecular chains, making it prone to brittle fracture under impact load. At the same time, the high crystallinity leads to a relatively high melting point and a narrower processing window. Summary of the Invention

[0006] In order to effectively balance mechanical properties while lowering the melting point of polyester, this application provides a methyl propylene glycol modified polyester and its preparation method.

[0007] In a first aspect, this application provides a methyl propylene glycol-modified polyester, which adopts the following technical solution:

[0008] A methyl propylene glycol-modified polyester is produced by esterification-polymerization of raw materials in the following molar ratio:

[0009] Including terephthalic acid and diols;

[0010] The diols include ethylene glycol, diethylene glycol, and methylpropanediol;

[0011] The methylpropanediol is encapsulated with cyclodextrin before use.

[0012] The molar ratio of terephthalic acid, ethylene glycol, diethylene glycol and methyl propylene glycol is 1:(0.7~0.9):(0.01~0.05):(0.2~0.6).

[0013] In this technical solution, cyclodextrin is used to encapsulate methylpropanediol, which effectively increases the apparent boiling point of methylpropanediol, thus protecting it effectively during the subsequent high-temperature esterification process. The volatility is significantly reduced, ensuring that the amount of methylpropanediol participating in the reaction is close to the feed amount. As a result, the molecular chain structure of the final polymer is highly accurate to the design expectation, and the batch stability of the product is greatly improved.

[0014] The side methyl groups of 2-methyl-1,3-propanediol create strong steric hindrance, effectively disrupting the regularity and close packing of polyester molecular chains, which is the main reason for the reduced crystallinity and melting point. A small amount of diethylene glycol's ether bonds introduce flexibility, further contributing to the lower melting point. Furthermore, methylpropanediol itself is a short-chain diol, which can achieve a low melting point while preserving as much rigidity as possible in the base polyester, providing fundamental support for mechanical properties.

[0015] Preferably, the molar ratio of terephthalic acid to diol is 1:(1.1~1.35).

[0016] In this technical solution, the molar ratio ensures that a sufficient amount of cyclodextrin effectively includes some methylpropanediol molecules. These included molecules have increased apparent boiling points, thus being preferentially protected during the high-temperature phase of the esterification reaction, significantly reducing overall volatilization loss.

[0017] Preferably, the amount of diethylene glycol used is 0.9% to 2.5% of the molar number of the diol.

[0018] Preferably, the molar ratio of cyclodextrin to methylpropanediol is 1:(1~1.5).

[0019] This technical solution ensures that methyl propylene glycol molecules are fully encapsulated to form a stable inclusion complex, effectively suppressing volatilization during the esterification reaction.

[0020] Preferably, the diol further includes a diol containing an indole ring or a diol containing a naphthalene ring.

[0021] Preferably, the amount of the indole ring-containing diol is 2% to 4% of the molar number of the diol.

[0022] Preferably, the diol containing the indole ring is 1H-indole-5,6-diol.

[0023] This technical solution introduces 1H-indole-5,6-diol as a rigid modifying monomer. The indole ring in its molecular structure has a large rigid planar structure and a lactam structure, which can effectively enhance the rigidity of the molecular chain and significantly compensate for the modulus and strength that may be lost due to the introduction of methylpropanediol.

[0024] Preferably, the amount of the naphthalene-containing diol is 2.5% to 4.5% of the molar number of the diol.

[0025] Preferably, the naphthalene-containing diol is 1,3-naphthalenedimethanol.

[0026] This technical solution introduces 1,3-naphthalenedimethanol, whose naphthalene ring structure has a larger conjugated system and steric hindrance than that of benzene ring. When it is embedded in the polyester backbone, it can more effectively restrict the movement of molecular chain segments, reduce chain segment slippage under external force, and thus significantly improve the impact resistance of polyester.

[0027] Preferably, the methyl propylene glycol modified polyester further includes a catalyst, the amount of which is 0.04% to 0.08% of the total molar amount of terephthalic acid.

[0028] Preferably, the catalyst includes titanium-based catalysts and antimony-based catalysts.

[0029] Preferably, the cyclodextrin is hydroxypropyl-β-cyclodextrin.

[0030] Secondly, this application provides a method for preparing methyl propylene glycol modified polyester, comprising the following steps:

[0031] S1: Hydroxypropyl-β-cyclodextrin, methylpropanediol and a portion of ethylene glycol are mixed evenly to obtain a pre-inclusion complex;

[0032] S2: Mix the catalyst and the remaining diol evenly, then add the pre-encapsulated compound, diethylene glycol and terephthalic acid and mix evenly to obtain a slurry;

[0033] S3: Transfer the slurry into the reactor and proceed with the following reactions in sequence:

[0034] S3a: React at 245~255℃ and 75~85kPa for 3~4h;

[0035] S3b: React at 255~260℃ and 15~25kPa for 1~2 hours;

[0036] S3c: React for 60-90 min under a vacuum of 5000~8000 Pa and 260~265℃;

[0037] S3d: React for 50-70 min under a vacuum of 500-800 Pa and a temperature of 265-270 °C.

[0038] S3e: React for 3-4 hours under a vacuum of 90-200 Pa and 260-265 °C;

[0039] The material is discharged, pressurized, separated into solid and liquid components, granulated, and dried to obtain methyl propylene glycol modified polyester.

[0040] In step S1, the mixing temperature is 40~60℃ and the mixing time is 30~60min.

[0041] Preferably, in step S2, after adding diethylene glycol, the step further includes adding a diol containing a naphthalene ring or a diol containing an indole ring.

[0042] In summary, this application has the following beneficial effects:

[0043] 1. This application pretreats methylpropanediol using cyclodextrin inclusion technology, which effectively solves the problem of its easy volatility during high-temperature esterification, ensuring the accuracy of the formulation and the stability of the product structure.

[0044] 2. This application achieves a clever balance of mechanical properties by using the synergistic effect of methyl propylene glycol and diethylene glycol, and optionally introducing rigid diol monomers, to effectively reduce the melting point of polyester. Detailed Implementation

[0045] The present application will be further described in detail below with reference to the embodiments.

[0046] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this application are all commercially available.

[0047] Example 1

[0048] The preparation method of methyl propylene glycol modified polyester in this embodiment includes the following steps:

[0049] S1: Add 0.15 mol hydroxypropyl-β-cyclodextrin, 0.2 mol methyl propylene glycol and 0.15 mol ethylene glycol to a container, heat to 50℃, and stir at 350 r / min for 40 min to obtain the pre-inclusion complex;

[0050] S2: Add 0.25 mol of ethylene glycol, 0.0002 mol of antimony glycol, and 0.0001 mol of tetrabutyl titanate to a reaction vessel and stir at 250 r / min for 5 min. Then add the pre-inclusion compound and 0.015 mol of diethylene glycol and stir at 350 r / min for 5 min. Add 0.5 mol of terephthalic acid in 3 portions and stir for 5 min each time. Heat to 40℃ and maintain the temperature for 45 min to obtain the slurry.

[0051] S3: Increase the temperature of the reactor jacket to 250℃ at 8℃ / min, and adjust the pressure inside the reactor to 80kPa through the nitrogen buffer tank. Maintain the temperature for 3.5h. Slowly reduce the pressure inside the reactor to 20kPa, and increase the temperature to 255℃. Maintain the temperature for 1.5h. Start the vacuum pump to evacuate the vacuum inside the reactor to 7000Pa, adjust the temperature to 260℃, and react for 80min. Continue to evacuate the vacuum to 700Pa, adjust the temperature to 265℃, and maintain the temperature for 60min. Continue to evacuate the vacuum to 150Pa, adjust the temperature to 260℃, and maintain the temperature for 3.5h. After the melt is discharged from the reactor, pressurize it to 10MPa through the melt gear pump, filter to remove impurities, and extrude it into strips through a single-hole casting die (255~260℃). Cool the strips to 60℃ in a 50℃ water bath, slice them underwater, and vacuum dry them at 120℃ to obtain methyl propylene glycol modified polyester.

[0052] Example 2

[0053] The preparation method of methyl propylene glycol modified polyester in this embodiment includes the following steps:

[0054] S1: Add 0.2 mol hydroxypropyl-β-cyclodextrin, 0.3 mol methyl propylene glycol and 0.2 mol ethylene glycol to a container, heat to 60℃, and stir at 350 r / min for 60 min to obtain the pre-inclusion complex;

[0055] S2: Add 0.15 mol ethylene glycol, 0.0001 mol antimony glycol, and 0.0001 mol tetrabutyl titanate to a reaction vessel and stir at 250 r / min for 5 min. Then add the pre-encapsulated compound and 0.025 mol diethylene glycol and stir at 350 r / min for 5 min. Add 0.5 mol terephthalic acid in 3 portions and stir for 5 min each time. Heat to 50℃ and maintain the temperature for 30 min to obtain the slurry.

[0056] S3: Increase the temperature of the reactor jacket to 245℃ at 8℃ / min, and adjust the pressure inside the reactor to 75kPa through the nitrogen buffer tank. Maintain the temperature for 4 hours. Slowly reduce the pressure inside the reactor to 15kPa and increase the temperature to 255℃. Maintain the temperature for 2 hours. Start the vacuum pump to evacuate the vacuum inside the reactor to 5000Pa. Adjust the temperature to 260℃ and react for 90 minutes. Continue to evacuate the vacuum to 500Pa and adjust the temperature to 265℃. Maintain the temperature for 70 minutes. Continue to evacuate the vacuum to 90Pa and adjust the temperature to 260℃. Maintain the temperature for 4 hours. After the melt is discharged from the reactor, pressurize it to 10MPa through the melt gear pump, filter to remove impurities, and extrude it into strips through a single-hole casting die (255~260℃). Cool the strips to 60℃ in a 50℃ water bath, slice them underwater, and vacuum dry them at 120℃ to obtain methyl propylene glycol modified polyester.

[0057] Example 3

[0058] The preparation method of methyl propylene glycol modified polyester in this embodiment includes the following steps:

[0059] S1: Add 0.1 mol hydroxypropyl-β-cyclodextrin, 0.1 mol methyl propylene glycol and 0.2 mol ethylene glycol to a container, heat to 40℃, and stir at 350 r / min for 30 min to obtain the pre-inclusion complex;

[0060] S2: Add 0.25 mol of ethylene glycol, 0.0002 mol of antimony glycol, and 0.0002 mol of tetrabutyl titanate to a reactor and stir at 250 r / min for 5 min. Then add the pre-encapsulated compound and 0.005 mol of diethylene glycol and stir at 350 r / min for 5 min. Add 0.5 mol of terephthalic acid in 3 portions and stir for 5 min each time. Heat to 45℃ and maintain the temperature for 60 min to obtain the slurry.

[0061] S3: Increase the temperature of the reactor jacket to 255℃ at 8℃ / min, and adjust the pressure inside the reactor to 85kPa through the nitrogen buffer tank. Maintain the temperature for 3 hours. Slowly reduce the pressure inside the reactor to 25kPa, and increase the temperature to 260℃. Maintain the temperature for 1 hour. Start the vacuum pump to evacuate the vacuum inside the reactor to 8000Pa, adjust the temperature to 265℃, and react for 60 minutes. Continue to evacuate the vacuum to 800Pa, adjust the temperature to 270℃, and maintain the temperature for 50 minutes. Continue to evacuate the vacuum to 200Pa, adjust the temperature to 265℃, and maintain the temperature for 3 hours. After the melt is discharged from the reactor, pressurize it to 10MPa through the melt gear pump, filter to remove impurities, and extrude it into strips through a single-hole casting die (255~260℃). Cool the strips to 60℃ in a 50℃ water bath, slice them underwater, and vacuum dry them at 120℃ to obtain methyl propylene glycol modified polyester.

[0062] Example 4

[0063] The difference between this embodiment and Embodiment 1 is that:

[0064] S2: Add 0.25 mol of ethylene glycol, 0.0002 mol of antimony glycol, and 0.0001 mol of tetrabutyl titanate to a reaction vessel and stir at 250 r / min for 5 min. Then add the pre-inclusion compound, 0.015 mol of diethylene glycol, and 0.012 mol of 1H-indole-5,6-diol and stir at 350 r / min for 5 min. Add 0.5 mol of terephthalic acid in three portions and stir for 5 min each time. Heat to 40℃ and maintain the temperature for 45 min to obtain the slurry.

[0065] Everything else is the same as in Example 1.

[0066] Example 5

[0067] The difference between this embodiment and embodiment 4 is that:

[0068] The amount of 1H-indole-5,6-diol used was 0.25 mol;

[0069] The rest is the same as in Example 4.

[0070] Example 6

[0071] The difference between this embodiment and Embodiment 1 is that:

[0072] S2: Add 0.25 mol of ethylene glycol, 0.0002 mol of antimony glycol, and 0.0001 mol of tetrabutyl titanate to a reaction vessel and stir at 250 r / min for 5 min. Then add the pre-inclusion compound, 0.015 mol of diethylene glycol, and 0.016 mol of 1,3-naphthalenedimethanol and stir at 350 r / min for 5 min. Add 0.5 mol of terephthalic acid in three portions and stir for 5 min each time. Heat to 40℃ and maintain the temperature for 45 min to obtain the slurry.

[0073] Everything else is the same as in Example 1.

[0074] Example 7

[0075] The difference between this embodiment and embodiment 6 is that:

[0076] The amount of 1,3-naphthalenedimethanol used was 0.029 mol.

[0077] The rest is the same as in Example 6.

[0078] Comparative Example 1

[0079] The preparation method of the methyl propylene glycol modified polyester in this comparative example includes the following steps:

[0080] S1: Add 0.4 mol of ethylene glycol, 0.0002 mol of antimony glycol, and 0.0001 mol of tetrabutyl titanate to a reactor and stir at 250 r / min for 5 min. Then add 0.2 mol of methyl propylene glycol and 0.015 mol of diethylene glycol and stir at 350 r / min for 5 min. Add 0.5 mol of terephthalic acid in 3 portions and stir for 5 min each time. Heat to 40℃ and maintain the temperature for 45 min to obtain the slurry.

[0081] S2: Increase the temperature of the reactor jacket to 250℃ at 8℃ / min, and adjust the pressure inside the reactor to 80kPa through the nitrogen buffer tank. Maintain the temperature for 3.5h. Slowly reduce the pressure inside the reactor to 20kPa, and increase the temperature to 255℃. Maintain the temperature for 1.5h. Start the vacuum pump to evacuate the vacuum inside the reactor to 7000Pa, adjust the temperature to 260℃, and react for 80min. Continue to evacuate the vacuum to 700Pa, adjust the temperature to 265℃, and maintain the temperature for 60min. Continue to evacuate the vacuum to 150Pa, adjust the temperature to 260℃, and maintain the temperature for 3.5h. After the melt is discharged from the reactor, pressurize it to 10MPa through the melt gear pump, filter to remove impurities, and extrude it into strips through a single-hole casting die (255~260℃). Cool the strips to 60℃ in a 50℃ water bath, slice them underwater, and vacuum dry them at 120℃ to obtain methyl propylene glycol modified polyester.

[0082] Comparative Example 2

[0083] The preparation method of the modified polyester in this comparative example includes the following steps:

[0084] S1: Add 0.6 mol of ethylene glycol, 0.0002 mol of antimony glycol, and 0.0001 mol of tetrabutyl titanate to a reactor and stir at 250 r / min for 5 min. Then add 0.015 mol of diethylene glycol and stir at 350 r / min for 5 min. Add 0.5 mol of terephthalic acid in three portions and stir for 5 min each time. Heat to 40℃ and maintain the temperature for 45 min to obtain a slurry.

[0085] S2: Increase the temperature of the reactor jacket to 250℃ at 8℃ / min, and adjust the pressure inside the reactor to 80kPa through the nitrogen buffer tank. Maintain the temperature for 3.5h. Slowly reduce the pressure inside the reactor to 20kPa, and increase the temperature to 255℃. Maintain the temperature for 1.5h. Start the vacuum pump to evacuate the vacuum inside the reactor to 7000Pa, adjust the temperature to 260℃, and react for 80min. Continue to evacuate the vacuum to 700Pa, adjust the temperature to 265℃, and maintain the temperature for 60min. Continue to evacuate the vacuum to 150Pa, adjust the temperature to 260℃, and maintain the temperature for 3.5h. After the melt is discharged from the reactor, pressurize it to 10MPa through the melt gear pump, filter to remove impurities, and extrude it into strips through a single-hole casting die (255~260℃). Cool the strips to 60℃ in a 50℃ water bath, slice them underwater, and vacuum dry them at 120℃ to obtain the modified polyester.

[0086] Comparative Example 3

[0087] The preparation method of methyl propylene glycol modified polyester in this embodiment includes the following steps:

[0088] S1: Add 0.15 mol hydroxypropyl-β-cyclodextrin, 0.2 mol methyl propylene glycol and 0.15 mol ethylene glycol to a container, heat to 50℃, and stir at 350 r / min for 40 min to obtain the pre-inclusion complex;

[0089] S2: Add 0.25 mol of ethylene glycol and 0.0003 mol of antimony glycol to the reactor and stir at 250 r / min for 5 min. Then add the pre-encapsulated compound and 0.015 mol of diethylene glycol and stir at 350 r / min for 5 min. Add 0.5 mol of terephthalic acid in 3 portions and stir for 5 min each time. Heat to 40℃ and maintain the temperature for 45 min to obtain the slurry.

[0090] S3: Increase the temperature of the reactor jacket to 250℃ at 8℃ / min, and adjust the pressure inside the reactor to 80kPa through the nitrogen buffer tank. Maintain the temperature for 3.5h. Slowly reduce the pressure inside the reactor to 20kPa, and increase the temperature to 255℃. Maintain the temperature for 1.5h. Start the vacuum pump to evacuate the vacuum inside the reactor to 7000Pa, adjust the temperature to 260℃, and react for 80min. Continue to evacuate the vacuum to 700Pa, adjust the temperature to 265℃, and maintain the temperature for 60min. Continue to evacuate the vacuum to 150Pa, adjust the temperature to 260℃, and maintain the temperature for 3.5h. After the melt is discharged from the reactor, pressurize it to 10MPa through the melt gear pump, filter to remove impurities, and extrude it into strips through a single-hole casting die (255~260℃). Cool the strips to 60℃ in a 50℃ water bath, slice them underwater, and vacuum dry them at 120℃ to obtain methyl propylene glycol modified polyester.

[0091] Performance testing

[0092] The modified polyesters prepared in Examples 1-7 and Comparative Examples 1-3 were subjected to performance tests according to the following standards. The specific details are shown in Table 1.

[0093] Melting point: GB / T 19466.3-2004;

[0094] Color (b value / L value): GB / T 3979-2008;

[0095] Intrinsic viscosity: GB / T 14190-2008;

[0096] Tensile strength: GB / T 1040-2006;

[0097] Impact resistance: GB / T 1843-2008.

[0098] Table 1. Performance test data of the modified polyesters prepared in Examples 1-7 and Comparative Examples 1-3

[0099]

[0100] As can be seen from the test data in Table 1, the simultaneous improvement of intrinsic viscosity and mechanical properties in Example 1 compared with Comparative Example 1 indicates that the inclusion treatment of hydroxypropyl-β-cyclodextrin can effectively suppress the volatilization of methyl propylene glycol, ensure its full participation in the reaction, and promote the formation of higher molecular weight polymers.

[0101] Compared with Comparative Example 2, Example 1 has higher intrinsic viscosity and tensile strength due to its regular molecular chain, but its melting point is too high and its impact strength is significantly lower. This indicates that the introduction of methyl propylene glycol disrupts the chain regularity, but achieves a balance between low melting point and good toughness.

[0102] The significant advantage in intrinsic viscosity between Example 1 and Comparative Example 3 demonstrates that the titanium-antimony composite catalyst system can more effectively promote polycondensation reactions, generating polymers with higher molecular weights. Although a single antimony catalyst may achieve acceptable tensile strength, its lower molecular weight directly leads to insufficient product toughness.

[0103] As can be seen from Examples 1-3, by precisely controlling the amount of methyl propylene glycol, the melting point of polyester can be effectively adjusted within a certain range, indicating that methyl propylene glycol, as a modifying monomer, can effectively disrupt the regularity of polyester molecular chains through its side methyl groups.

[0104] As can be seen from Examples 4-7, the introduction of diols with rigid aromatic rings can significantly improve the mechanical properties of copolyesters and their impact strength is partially improved compared with the basic formulation. At the same time, the tensile strength remains at a high level. This indicates that the rigid monomer, as an effective reinforcing unit, is likely to achieve toughening by restricting molecular chain movement and inducing crimping. While compensating for the rigidity loss caused by the introduction of methyl propylene glycol, it also improves the impact toughness.

[0105] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A methylpropanediol-modified polyester characterized by, The raw materials including terephthalic acid and dihydric alcohol are esterified and polycondensed to obtain the methylpropylene glycol modified polyester, wherein the molar ratio of the raw materials is as follows: terephthalic acid: dihydric alcohol: methylpropylene glycol: hydroxypropyl-β-cyclodextrin = 1: (0.7-0.9): (0.01-0.05): (0.2-0.6). The dihydric alcohol includes ethylene glycol, diethylene glycol and methylpropylene glycol. The methylpropylene glycol is treated by cyclodextrin inclusion before use. The molar ratio of the terephthalic acid, ethylene glycol, diethylene glycol and methylpropylene glycol is 1: (0.7-0.9): (0.01-0.05): (0.2-0.6). The methylpropylene glycol modified polyester further includes a catalyst, and the catalyst includes a titanium-based catalyst and an antimony-based catalyst. The cyclodextrin is hydroxypropyl-β-cyclodextrin.

2. The methylpropanediol-modified polyester according to claim 1, characterized by, The molar ratio of the terephthalic acid and dihydric alcohol is 1: (1.1-1.35).

3. The methylpropanediol-modified polyester according to claim 1, characterized by, The molar ratio of the cyclodextrin and methylpropylene glycol is 1: (1-1.5).

4. The methylpropanediol-modified polyester according to claim 1, characterized by, The dihydric alcohol further includes an indole ring-containing dihydric alcohol or a naphthalene ring-containing dihydric alcohol.

5. The methylpropanediol-modified polyester according to claim 4, characterized by The amount of the indole ring-containing dihydric alcohol is 2%-4% of the molar amount of the dihydric alcohol.

6. The methylpropanediol-modified polyester according to claim 4, characterized by The amount of the naphthalene ring-containing dihydric alcohol is 2.5%-4.5% of the molar amount of the dihydric alcohol.

7. The methylpropanediol-modified polyester according to claim 1, characterized by The amount of the catalyst is 0.04%-0.08% of the total molar amount of the terephthalic acid.

8. A process for producing the methylpropanediol-modified polyester as claimed in any one of claims 1 to 3, characterized by, The method includes the following steps: S1: uniformly mixing hydroxypropyl-β-cyclodextrin, methylpropylene glycol and part of ethylene glycol to obtain a pre-inclusion compound; S2: uniformly mixing a catalyst and the remaining ethylene glycol, then uniformly mixing the pre-inclusion compound, diethylene glycol and terephthalic acid to obtain a slurry; S3: transferring the slurry into a reaction kettle and sequentially performing the following reactions: S3a: reacting at 245-255℃ and 75-85kPa for 3-4h; S3b: reacting at 255-260℃ and 15-25kPa for 1-2h; S3c: reacting at a vacuum degree of 5000-8000Pa and 260-265℃ for 60-90min; S3d: reacting at a vacuum degree of 500-800Pa and 265-270℃ for 50-70min; S3e: reacting at a vacuum degree of 90-200Pa and 260-265℃ for 3-4h; discharging, pressurizing, solid-liquid separation, granulation, drying to obtain the methylpropylene glycol modified polyester.

9. The method of preparing a methylpropanediol-modified polyester according to claim 8, characterized by, In step S2, after adding the diethylene glycol, the method further includes the steps of adding the naphthalene ring-containing dihydric alcohol or the indole ring-containing dihydric alcohol.

Images