Copolyesters and their use

Abstract

This invention relates to the field of polyesters and discloses a copolyester and its applications. The copolyester exhibits a storage modulus versus angular frequency curve with a slope K1 not exceeding 1.7, a loss modulus versus angular frequency curve with a slope K2 not exceeding 1, and a K1 / K2 ratio 2 not exceeding 1.5. The difference between the flow activation energy of the copolyester at 230°C and at 240°C is not higher than 3 kJ / mol. This copolyester demonstrates low temperature sensitivity, small change in melt flow activation energy, and good stability.

Description

Technical Field

[0001] This invention relates to the field of polyesters, and more specifically, to a copolyester and its applications. Background Technology

[0002] Polyether ester elastomer (TPEE) is a block copolyester containing hard polyester segments and soft polyether segments. The soft segments impart elasticity, while the hard segments provide processability. Compared to rubber, TPEE offers better processability and a longer service life; compared to engineering plastics, TPEE exhibits higher strength, better flexibility, and superior dynamic mechanical properties. Due to its outstanding mechanical strength, excellent resilience, wide operating temperature range, and superior processability, TPEE is widely used in automotive parts, hydraulic hoses, cables, and wires.

[0003] When TPEE is used for high-speed extrusion of small-diameter tubes (0.5-2cm), high uniformity of tube diameter is required, with diameter deviation controlled within ±0.10mm. High melt stability during processing is also crucial; fluctuations in screw temperature must not alter the melt flow properties and affect the uniformity of the tube diameter. Conventional TPEE has high melt flowability but low melt viscosity and strength, which cannot meet the stability requirements for extruded tubes. For example, CN101492542A obtained a high molecular weight polyether ester copolymer through solid-state polymerization, achieving a high molecular weight; CN113621132A used the addition of various chain extenders to TPEE resin to obtain a product with high melt strength and low melt index; CN104520379A disclosed the preparation of blow-molding grade polyether ester elastomer by first solid-state thickening of TPEE and PBT respectively and then blending them with chain extenders; CN114933784A used epoxy chain extenders to add to TPEE elastomer to prepare large-diameter (Diameter≥25mm) TPEE rods; CN103788584A reduced the melt index of the material by adding isocyanate and extruding it with polyether ester elastomer; CN1281658C also prepared polyether ester elastomer with a melt index of less than 3 by directly adding chain extenders such as polyisocyanate and epoxy resin through twin-screw reactive extrusion. However, none of the above patents take into account the product's temperature sensitivity. In practical applications, the high temperature sensitivity of TPEE elastomers can still easily affect the uniformity of the tube diameter. Summary of the Invention

[0004] The purpose of this invention is to overcome the problem in the prior art that when the extrusion diameter of TPEE elastomer is small, the TPEE elastomer is highly sensitive to temperature, which affects the uniformity of the tube diameter. The invention provides a copolyester and its application, which has low temperature sensitivity, small change in melt flow activation energy, and good stability.

[0005] To achieve the above objectives, the first aspect of the present invention provides a copolyester, wherein the slope K1 of the storage modulus versus angular frequency curve of the copolyester is not higher than 1.7, the slope K2 of the loss modulus versus angular frequency curve is not higher than 1, and the ratio of K1 / K2 is not higher than 1.5; the difference between the flow activation energy of the copolyester at 230°C and at 240°C is not higher than 3 kJ / mol.

[0006] The second aspect of the present invention provides the application of the copolyester described in the first aspect in tubular products.

[0007] A third aspect of the present invention provides a tubular product prepared using the copolyester described in the first aspect above.

[0008] Through the above technical solution, the copolyester provided by this invention, based on specific slopes K1 of the storage modulus versus angular frequency curve, K2 of the loss modulus versus angular frequency curve, the K1 / K2 ratio, and the difference in flow activation energy at 230℃ and 240℃, can effectively improve the melt strength of the copolyester, reduce its temperature sensitivity, and enhance the stability of the copolyester product. In particular, when this copolyester is used to extrude pipe products with diameters of 0.5-2.0 cm, the pipe diameter error is less than 0.1 mm, significantly improving the uniformity of the pipe products while ensuring the mechanical properties of the pipe diameter, thus demonstrating significant market potential. Detailed Implementation

[0009] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0010] In a first aspect, the present invention provides a copolyester, wherein the slope K1 of the storage modulus versus angular frequency curve of the copolyester is not higher than 1.7, the slope K2 of the loss modulus versus angular frequency curve is not higher than 1, and the ratio of K1 / K2 is not higher than 1.5; the difference between the flow activation energy of the copolyester at 230°C and at 240°C is not higher than 3 kJ / mol.

[0011] During their research, the inventors of this invention unexpectedly discovered that by modifying the copolyester to obtain specific slopes K1 of the storage modulus versus angular frequency curve, K2 of the loss modulus versus angular frequency curve, the K1 / K2 ratio, and the difference in flow activation energy at 230°C and 240°C, the melt strength of the copolyester can be effectively improved, its temperature sensitivity reduced, and thus the stability of the copolyester product enhanced. In particular, when this copolyester is used to extrude pipe products with diameters of 0.5-2.0 cm, the pipe diameter error is less than 0.1 mm. This significantly improves the uniformity of the pipe products while ensuring the mechanical properties of the pipe diameter, demonstrating significant market potential.

[0012] According to the present invention, in order to further improve the melt strength of the copolyester and reduce its temperature sensitivity, preferably, the slope K1 of the storage modulus versus angular frequency curve of the copolyester is not higher than 1, the slope K2 of the loss modulus versus angular frequency curve is not higher than 0.8, and the difference between the flow activation energy of the copolyester at 230°C and at 240°C is not higher than 1 kJ / mol.

[0013] According to the present invention, preferably, the copolyester has a flow activation energy of 35-60 kJ / mol at a temperature of 230°C, specifically 35 kJ / mol, 40 kJ / mol, 45 kJ / mol, 50 kJ / mol, 55 kJ / mol, 60 kJ / mol, or any value between the aforementioned two. The inventors have found that, under this preferred embodiment, the copolyester having the above-mentioned flow activation energy has higher melt strength, which can further reduce the temperature sensitivity of the copolyester and thus improve the stability of the copolyester product. More preferably, the copolyester has a flow activation energy of 40-50 kJ / mol at a temperature of 230°C.

[0014] According to the present invention, preferably, under conditions of a load of 2.16 kg and a temperature of 230°C, the melt index of the copolyester is 0.8-5 g / min, specifically 0.8 g / min, 2 g / min, 3 g / min, 4 g / min, 5 g / min, or any value between the aforementioned two. This copolyester possesses both high melt strength and a low melt index, which further reduces the temperature sensitivity of the copolyester and thus improves the stability of the copolyester product. More preferably, under conditions of a load of 2.16 kg and a temperature of 230°C, the melt index of the copolyester is 2-5 g / min.

[0015] In this invention, the method for testing the flow activation energy of copolyester includes: calculating the flow activation energy E of the melt using the Arrhenius equation based on the relationship between melt index MFI and temperature; the flow activation energy E is derived from lnMFI and T. -1The slope of the curve is calculated.

[0016] In this invention, K1 of the copolyester is the slope of the copolyester's storage modulus (G') versus angular frequency (ω) curve, and K2 of the copolyester is the slope of the copolyester's loss modulus (G'') versus angular frequency (ω) curve. The storage modulus (G') and loss modulus (G'') of the copolyester are tested using a rotational rheometer under the following conditions: temperature 220-250℃, parallel plate clamp spacing 1mm, and angular frequency (ω) 0.1-100rad / s.

[0017] According to the present invention, preferably, the copolyester contains structural unit A as shown in formula (I) and structural unit B formed of hydroxy acid; Formula (I); Wherein, R1 is a C2-C10 alkylene group, which can be a straight-chain C2-C10 alkylene group, a branched C2-C10 alkylene group, or a C3-C10 cycloalkylene group. For example, R1 can be ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene, etc.; n is an integer from 5 to 40, specifically 5, 10, 20, 30, 40, or any value between the two aforementioned values. The inventors discovered that, in this preferred embodiment, structural unit A and structural unit B participate in the construction and rearrangement of polyester macromolecular chain segments. Through the synergistic effect between structural unit A and structural unit B, the slope K1 of the storage modulus versus angular frequency curve, the slope K2 of the loss modulus versus angular frequency curve, the K1 / K2 ratio, and the difference in flow activation energy at 230°C and 240°C are controlled within a specific range. This can further improve the melt strength of the copolyester and reduce its temperature sensitivity, thereby improving the stability of the copolyester product.

[0018] According to the present invention, preferably, the weight ratio of structural unit A to structural unit B is 350-1000:1, specifically 350:1, 500:1, 750:1, 1000:1, or any value between the aforementioned two values. The inventors have found that, in this preferred embodiment, structural unit A and structural unit B, in a specific ratio, participate in the construction and rearrangement of polyester macromolecular chain segments. Through the synergistic effect between structural unit A and structural unit B, the slope K1 of the storage modulus versus angular frequency curve, the slope K2 of the loss modulus versus angular frequency curve, the K1 / K2 ratio, and the difference in flow activation energy at 230°C and 240°C are controlled within a specific range, which can further improve the melt strength of the copolyester, reduce its sensitivity to temperature, and thus further improve the stability of the copolyester product. More preferably, the weight ratio of structural unit A to structural unit B is 550-750:1.

[0019] According to the present invention, in order to further control the slope K1 of the energy storage modulus versus angular frequency curve, the slope K2 of the loss modulus versus angular frequency curve, the K1 / K2 ratio, and the difference in flow activation energy at 230°C and 240°C within a specific range, thereby improving the stability of the copolyester product, preferably, R1 is a C2-C4 alkylene group; n is an integer from 10 to 25, specifically 10, 15, 20, 25, or any value between the two aforementioned values.

[0020] According to the present invention, in order to further control the slope K1 of the storage modulus versus angular frequency curve, the slope K2 of the loss modulus versus angular frequency curve, the K1 / K2 ratio, and the difference in flow activation energy at 230°C and 240°C within a specific range, and to improve the stability of the copolyester product, preferably, m is 3.

[0021] In this invention, the hydroxy acid is a compound containing both hydroxyl and carboxyl groups, with ≥3 functional groups. To further improve the stability of the copolyester product by controlling the slope K1 of the storage modulus versus angular frequency curve, the slope K2 of the loss modulus versus angular frequency curve, the K1 / K2 ratio, and the difference in flow activation energy at 230°C and 240°C within specific ranges, the hydroxy acid is preferably selected from at least one of citric acid, glyceric acid, malic acid, and tartaric acid, and more preferably citric acid and / or glyceric acid.

[0022] In this invention, all of the above-mentioned substances can be obtained commercially or prepared in-house.

[0023] According to the present invention, preferably, the content of structural unit A in the copolyester is 20-40 wt%, specifically 20 wt%, 30 wt%, 40 wt%, or any value between the two aforementioned values; the content of structural unit B is 0.02-0.1 wt%, specifically 0.02 wt%, 0.05 wt%, 0.1 wt%, or any value between the two aforementioned values. The inventors have found that, under this preferred embodiment, controlling the content of both structural unit A and structural unit B within their respective ranges can improve the interaction effect between structural unit A and structural unit B. Furthermore, controlling the slope K1 of the storage modulus versus angular frequency curve, the slope K2 of the loss modulus versus angular frequency curve, the K1 / K2 ratio, and the difference in flow activation energy at 230°C and 240°C within specific ranges can improve the melt strength of the copolyester, reduce its temperature sensitivity, and thus further improve the stability of the copolyester product.

[0024] According to the present invention, in order to further improve the stability and polyester properties of the copolyester product, preferably, the copolyester contains structural unit C shown in formula (II) and structural unit D shown in formula (III).

[0025] Formula (II); Formula (III); Wherein, R2, R3, R4 and R5 are each independently selected from hydrogen or C1-C4 alkyl, and R6 is a C2-C10 alkylene; the C1-C4 alkyl can be a straight-chain alkyl or a cycloalkyl, and by way of example, the C1-C4 alkyl can be methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, isobutyl, tert-butyl or other feasible C1-C4 alkyl; R6 is a C2-C10 alkylene, and by way of example, R6 is ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene or decylene.

[0026] According to the present invention, in order to further improve the stability and polyester properties of the copolyester product, preferably, R2, R3, R4 and R5 are each independently methyl or hydrogen, and R6 is a C2-C4 alkylene, specifically ethylene, propylene or butylene.

[0027] According to the present invention, in order to further improve the stability and polyester properties of the copolyester product, preferably, the content of structural unit C in the copolyester is 36-48 wt%, specifically 36 wt%, 42 wt%, 48 wt%, or any value between the two aforementioned values; the content of structural unit D is 24-32 wt%, specifically 24 wt%, 28 wt%, 32 wt%, or any value between the two aforementioned values.

[0028] In this invention, the contents of structural units A, C, and D in the copolyester are obtained through infrared and nuclear magnetic resonance (NMR) analysis; the specific composition can be obtained through gas / liquid chromatography (GC). Specifically, the GC method involves methanol hydrolysis of the copolyester, with tetraethylene glycol dimethyl ether as an internal standard, and detection using an HP5890 GC. FTIR spectroscopy primarily utilizes a Fourier transform infrared spectrometer to rapidly compare and analyze the chemical composition and molecular structure of the particulate polyester by measuring its infrared spectrum.

[0029] According to the present invention, preferably, the copolyester contains titanium. The inventors have found that, under this preferred embodiment, the stability of the copolyester product can be further improved, and it exhibits better polyester properties.

[0030] According to the present invention, in order to further improve the stability and polyester properties of the copolyester product, preferably, the titanium content in the copolyester is 80-150 ppm.

[0031] The content of titanium can be determined by elemental content detection method.

[0032] According to a particularly preferred embodiment of the present invention, a copolyester is provided, wherein the slope of the storage modulus versus angular frequency curve of the copolyester is not higher than 1.7, the slope of the loss modulus versus angular frequency curve is not higher than 1, and the K1 / K2 ratio is not higher than 1.5; the difference between the flow activation energy of the copolyester at 230°C and at 240°C is not higher than 3 kJ / mol; the flow activation energy of the copolyester at 230°C is 35-60 kJ / mol; and under the conditions of a load of 2.16 kg and a temperature of 230°C, the melt index of the copolyester is 0.8-5 g / min. The copolyester contains structural unit A as shown in formula (I) and structural unit B formed from hydroxy acids; Formula (I); Wherein, R1 is a C2-C4 alkylene group, and n is an integer from 10 to 25; the hydroxy acid is glyceric acid and / or citric acid; the weight ratio of structural unit A to structural unit B is 350-1000:1; the content of structural unit A in the copolyester is 20-40 wt%, and the content of structural unit B is 0.02-0.1 wt%. The copolyester contains structural unit C as shown in formula (II) and structural unit D as shown in formula (III); Formula (II); Formula (III); In this copolyester, R2, R3, R4, and R5 are each independently hydrogen or methyl, and R6 is a C2-C4 alkylene group; the content of structural unit C in the copolyester is 36-48 wt%, and the content of structural unit D is 24-32 wt%. The copolyester contains titanium; the titanium content in the copolyester is 80-150 ppm.

[0033] In the above-mentioned preferred embodiments, by controlling the slope K1 of the storage modulus versus angular frequency curve, the slope K2 of the loss modulus versus angular frequency curve, the K1 / K2 ratio, and the difference in flow activation energy at 230°C and 240°C within a specific range, the melt strength of the copolyester can be effectively improved, the temperature sensitivity of the copolyester can be reduced, and the stability of the copolyester product can be improved.

[0034] In this invention, the preparation method of the copolyester is not limited, as long as the slope K1 of the storage modulus versus angular frequency curve of the obtained copolyester is not higher than 1.7, the slope K2 of the loss modulus versus angular frequency curve is not higher than 1, the ratio of K1 / K2 is not higher than 1.5, and the difference between the flow activation energy at 230°C and the flow activation energy at 240°C is not higher than 3 kJ / mol. Those skilled in the art can use any method capable of obtaining a copolyester with the above properties to prepare this copolyester. As a preferred embodiment of the preparation method of the copolyester with the above properties, the preparation method of the copolyester includes the following steps: (1) Under esterification reaction conditions, a diacid monomer, a diol monomer, a modified monomer having the structure shown in formula (I), a hydroxy acid, an antioxidant and a catalyst are mixed and reacted in the first stage to obtain a prepolymer; (2) Under polycondensation reaction conditions, the prepolymer is subjected to a second-stage reaction to obtain a polyester base material; (3) The polyester base material is subjected to solid-state polycondensation reaction, or the polyester base material and chain extender are mixed and reacted; Formula (I); Wherein, R1 is a C2-C10 alkylene group, which can be a straight-chain C2-C10 alkylene group, a branched C2-C10 alkylene group, or a C3-C10 cycloalkylene group. For example, R1 can be ethylene, propyleneene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene, etc.; n is an integer from 5 to 40, specifically 5, 10, 20, 30, 40, or any value between the aforementioned two values. The preparation method of this copolyester is simple and suitable for industrial production.

[0035] According to the present invention, in order to further control the slope K1 of the storage modulus versus angular frequency curve, the slope K2 of the loss modulus versus angular frequency curve, the K1 / K2 ratio, and the difference in flow activation energy at 230°C and 240°C within a specific range, and to improve the stability of the copolyester product, preferably, R I and R II Each of the modified monomers is independently hydrogen or methyl, and the number average molecular weight is 1000-3000 g / mol.

[0036] According to the present invention, in order to further improve the stability and polyester properties of the copolyester product, preferably, the diacid monomer is a diacid having the structure shown in formula (II); the diol monomer is a diol having the structure shown in formula (III); Formula (II); Formula (III); Wherein, R2, R3, R4 and R5 are each independently selected from hydrogen or C1-C4 alkyl, and R6 is a C2-C10 alkylene; the C1-C4 alkyl can be a straight-chain alkyl or a cycloalkyl, and by way of example, the C1-C4 alkyl can be methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, isobutyl, tert-butyl or other feasible C1-C4 alkyl; R6 is a C2-C10 alkylene, and by way of example, R6 is ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene or decylene.

[0037] According to the present invention, in order to further improve the stability and polyester properties of the copolyester product, preferably, R2, R3, R4 and R5 are each independently methyl or hydrogen, and R6 is a C2-C4 alkylene, specifically ethylene, propylene or butylene.

[0038] According to the present invention, in order to control the slope K1 of the storage modulus versus angular frequency curve, the slope K2 of the loss modulus versus angular frequency curve, the K1 / K2 ratio, and the difference in flow activation energy at 230°C and 240°C within a specific range, thereby further improving the melt strength of the copolyester and reducing its temperature sensitivity, the hydroxy acid is selected from at least one of citric acid, glyceric acid, malic acid, and tartaric acid, and is more preferably citric acid and / or glyceric acid.

[0039] According to the present invention, in order to further improve the polyester properties and stability of the copolyester, the catalyst is preferably at least one selected from isopropyl titanate, titanium glycolate, nano-titanium dioxide, and tetrabutyl titanate.

[0040] According to the present invention, in order to further improve the polyester properties and stability of the copolyester, the antioxidant is preferably a hindered phenolic antioxidant and / or a phosphite antioxidant, more preferably at least one selected from 1,3,5,tris(3,5-di-tert-butyl,4-hydroxybenzyl)triazine (antioxidant 3114), β-(4-hydroxy-3,5-di-tert-butylphenyl)propionate n-octadecyl alcohol ester (antioxidant 1076), tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] pentaerythritol ester (antioxidant 1010), 2,4,6-tris(3',5'-di-tert-butyl-4'-hydroxybenzyl)trimethylbenzyl (antioxidant 330) and tris[2,4-di-tert-butylphenyl]phosphite (antioxidant 168).

[0041] According to the present invention, in order to further improve the efficiency and yield of the reaction, preferably, in step (1), the molar ratio of the diol monomer to the diacid monomer is 2-5:1; based on the theoretical yield of the copolyester, the amount of the modified monomer is 20-40%, and the amount of the hydroxy acid is 300-1000ppm; compared to 1000g of the diacid monomer, the amount of the antioxidant is 3-5g, and the amount of the catalyst is 1-3g.

[0042] According to the present invention, in order to further improve the melt strength of the copolyester and reduce the temperature sensitivity of the copolyester, preferably, the weight ratio of the modified monomer to the hydroxy acid is 500-800:1.

[0043] According to the present invention, preferably, in step (1), the conditions for the esterification reaction include at least: a temperature of 190-230°C, specifically 190°C, 200°C, 210°C, 220°C, 230°C, or any value between the two aforementioned values; a gauge pressure of 0-0.4 MPa, specifically 0 MPa, 0.1 MPa, 0.2 MPa, 0.3 MPa, 0.4 MPa, or any value between the two aforementioned values; and the conditions for the termination of the esterification reaction process include at least: the amount of water produced is greater than 90% of the theoretical amount of water produced.

[0044] According to the present invention, preferably, in step (2), the conditions for the polycondensation reaction include at least: a temperature of 240-260°C, specifically 240°C, 250°C, 260°C, or any value between the two aforementioned values; an absolute pressure of 0-100 Pa, specifically 0 Pa, 50 Pa, 100 Pa, or any value between the two aforementioned values; and the conditions for the end of the polycondensation reaction process include at least: the stirring power reaching a preset value. The inventors have found that, under this preferred embodiment, the product of the esterification reaction has a better polycondensation effect, improving the stability of the structure and properties of the copolyester.

[0045] In this invention, both the first-stage reaction and the second-stage reaction are carried out under stirring conditions, with the stirring speed controlled at 25-50 rpm.

[0046] It should be noted that the preset stirring power in this invention is 130-200% of the rated power of the reactor used. Different reactors have different rated power values.

[0047] According to the present invention, in order to control the slope K1 of the energy storage modulus versus angular frequency curve, the slope K2 of the loss modulus versus angular frequency curve, the K1 / K2 ratio, and the difference in flow activation energy at 230°C and 240°C within a specific range, thereby improving the stability of the copolyester product, preferably, in step (3), when the polyester base material is subjected to a solid-state polycondensation reaction, the conditions of the solid-state polycondensation reaction include at least: a temperature of 190-200°C, specifically 190°C, 195°C, 200°C, or any value between the two aforementioned values; a time of 4-8h, specifically 4h, 6h, 8h, or any value between the two aforementioned values; or, when the polyester base material and the chain extender are mixed and reacted, the conditions of the mixing reaction include at least: a temperature of 200-230°C and a time of 5-20min.

[0048] According to the present invention, in order to control the slope K1 of the storage modulus versus angular frequency curve, the slope K2 of the loss modulus versus angular frequency curve, the K1 / K2 ratio, and the difference in flow activation energy at 230°C and 240°C within a specific range, thereby improving the stability of the copolyester product, preferably, the chain extender is at least one of epoxy chain extenders, isocyanate chain extenders, and oxazoline chain extenders.

[0049] In this invention, all of the above-mentioned substances can be obtained commercially or prepared in-house.

[0050] Secondly, the present invention provides the application of the copolyester described in the first aspect in pipe products.

[0051] Thirdly, the present invention provides a tubular product prepared using the copolyester described in the first aspect above.

[0052] Pipe products prepared using the copolyester described in the first aspect above have low temperature sensitivity and small changes in flow activation energy, which can significantly improve the uniformity of pipe products while ensuring the mechanical properties of the pipe diameter.

[0053] In this invention, the method for preparing pipe products using the copolyester described in the first aspect is not limited, and the product can be prepared using a screw reactor conventionally selected in the art.

[0054] According to the present invention, preferably, the diameter of the pipe product is 5-20 mm, and the diameter error of the pipe product is less than 0.1 mm.

[0055] In this invention, the method for testing the pipe diameter error of pipe products includes: the maximum difference in pipe diameter (Y) has a certain functional relationship with the ratio of K1 / K2 (X) of the product, and the relationship is y=0.3225x. 2 -0.5838x + 0.2733, with a correlation coefficient of 0.990.

[0056] The present invention will be described in detail below with reference to embodiments, but this does not limit the scope of the invention.

[0057] In the following examples, polytetrahydrofuran (PTF) with a molecular weight of 1000 was purchased from Hangzhou Sanlong New Materials Co., Ltd., and was classified as polymerization grade; PTF with a molecular weight of 1800 was purchased from Hangzhou Sanlong New Materials Co., Ltd., and was classified as polymerization grade; PTF with a molecular weight of 2000 was purchased from Hangzhou Sanlong New Materials Co., Ltd., and was classified as polymerization grade; PTF with a molecular weight of 3000 was purchased from Hangzhou Sanlong New Materials Co., Ltd., and was classified as polymerization grade. Unless otherwise specified, all other raw materials or reagents were conventional commercially available products.

[0058] In the following embodiments, the method for testing the flow activation energy of the copolyester includes: calculating the flow activation energy E of the melt using the Arrhenius equation based on the relationship between the melt index MFI and temperature; the flow activation energy E is derived from lnMFI and T. -1 The slope of the curve is calculated.

[0059] K1 represents the slope of the copolyester's storage modulus (G') versus angular frequency (ω) curve, and K2 represents the slope of the copolyester's loss modulus (G'') versus angular frequency (ω) curve. The storage modulus (G') and loss modulus (G'') of the copolyester were tested using a rotational rheometer under the following conditions: temperature 220-250℃, parallel plate clamp spacing 1mm, and angular frequency (ω) 0.1-100 rad / s.

[0060] The contents of structural units A, C, and D in the copolyester were obtained through infrared and nuclear magnetic resonance (NMR) analysis; the specific composition was obtained through gas / liquid chromatography (GC). Specifically, the GC method involved methanol hydrolysis of the copolyester, with tetraethylene glycol dimethyl ether as an internal standard, and detection using an HP5890 GC. Fourier transform infrared (FTIR) spectroscopy was primarily used to rapidly compare and analyze the chemical composition and molecular structure of the particulate polyester by measuring its infrared spectrum.

[0061] The titanium content in copolyesters can be determined by elemental content detection methods.

[0062] The test method for pipe diameter error of pipe products includes: the maximum difference in pipe diameter (Y) has a certain functional relationship with the ratio of K1 / K2 (X) of the product, and the relationship is y=0.3225x. 2 -0.5838x + 0.2733, with a correlation coefficient of 0.990.

[0063] Example 1 2.64 kg of terephthalic acid, 4.5 kg of 1,4-butanediol (BDO), 1.50 kg of polytetrahydrofuran (molecular weight 1000), 2.0 g of glyceric acid, 2.9 g of tetrabutyl titanate, and 10 g of antioxidant 1010 were added to a reactor and subjected to esterification reaction at a temperature of 190-230℃ and a pressure of 0-0.4 MPa. Esterification was terminated when the esterification rate was ≥90%. Polycondensation reaction was then carried out at a temperature of 240-260℃ and a pressure of 0-100 Pa. After the stirring current reached the rated value, the product was discharged to obtain polyester base material. The obtained polyester base material was dried and subjected to solid-state polycondensation at a temperature of 190℃ and a vacuum of 20 Pa for 7 hours to obtain copolyester.

[0064] Example 2 3 kg of terephthalic acid, 4.5 kg of 1,4-butanediol (BDO), 1 kg of polytetrahydrofuran (molecular weight 1000), 2.0 g of glyceric acid, 3.5 g of isopropyl titanate, and 10 g of antioxidant 168 were added to a reactor and esterified at 190-230℃ and 0-0.4 MPa. Esterification was terminated when the esterification rate was ≥90%. Polycondensation was then carried out at 240-260℃ and 0-100 Pa. After the stirring current reached the rated value, the product was discharged to obtain polyester base material. The obtained polyester base material was dried and then subjected to solid-state polycondensation at 190℃ and 20 Pa for 5 hours to obtain copolyester.

[0065] Example 3 2.35 kg of terephthalic acid, 4.5 kg of 1,4-butanediol (BDO), 2.05 kg of polytetrahydrofuran (molecular weight 2000), 3.5 g of citric acid, 5 g of tetrabutyl titanate, and 10 g of antioxidant 1010 were added to a reactor and subjected to esterification reaction at a temperature of 190-230℃ and a pressure of 0-0.4 MPa. Esterification was terminated when the esterification rate was ≥90%. Polycondensation reaction was then carried out at a temperature of 240-260℃ and a pressure of 0-100 Pa. After the stirring current reached the rated value, the product was discharged to obtain polyester base material. The obtained polyester base material was dried and subjected to solid-state polycondensation at a temperature of 200℃ and a vacuum of 30 Pa for 6 hours to obtain copolyester.

[0066] Example 4 2.35 kg of terephthalic acid, 4.5 kg of 1,4-butanediol (BDO), 2.05 kg of polytetrahydrofuran (molecular weight 2000), 3.5 g of citric acid, 5.5 g of isopropyl titanate, and 10 g of antioxidant 168 were added to a reactor and esterified at 190-230℃ and 0-0.4 MPa. Esterification was terminated when the esterification rate was ≥90%. Polycondensation was then carried out at 240-260℃ and 0-100 Pa. After the stirring current reached the rated value, the product was discharged to obtain polyester base material. The obtained polyester base material was dried and 1.5 g of epoxy chain extender ADR4468 (BASF) was added to obtain copolyester.

[0067] Example 5 The copolyester was prepared according to the method of Example 1, except that the molecular weight of polytetrahydrofuran was replaced with 650.

[0068] Example 6 The copolyester was prepared according to the method of Example 1, except that the amount of glyceric acid was replaced with 1.6g.

[0069] Example 7 The copolyester was prepared according to the method of Example 1, except that the amount of glyceric acid was replaced with 3.5g.

[0070] Example 8 The copolyester was prepared according to the method of Example 1, except that glyceric acid was replaced with malic acid.

[0071] Comparative Example 1 2.64 kg of terephthalic acid, 4.5 kg of 1,4-butanediol (BDO), 1.50 kg of polytetrahydrofuran (molecular weight 1000), 5 g of tetrabutyl titanate, and 10 g of antioxidant 1010 were added to a reactor and subjected to esterification reaction at a temperature of 190-230℃ and a pressure of 0-0.4 MPa. Esterification was terminated when the esterification rate was ≥90%. Polycondensation reaction was then carried out at a temperature of 240-260℃ and a pressure of 0-100 Pa. After the stirring current reached the rated value, the product was discharged to obtain polyester base material. The obtained polyester base material was subjected to solid-state polycondensation at a temperature of 190℃ and a vacuum degree of 20 Pa for 20 hours to obtain copolyester.

[0072] Comparative Example 2 2.64 kg of terephthalic acid, 4.5 kg of 1,4-butanediol (BDO), 1.50 kg of polytetrahydrofuran (molecular weight 1000), 5 g of tetrabutyl titanate, and 10 g of antioxidant 1010 were added to a reactor and subjected to esterification reaction at a temperature of 190-230℃ and a pressure of 0-0.4 MPa. Esterification was terminated when the esterification rate was ≥90%. Polycondensation reaction was then carried out at a temperature of 240-260℃ and a pressure of 0-100 Pa. After the stirring current reached the rated value, the product was discharged to obtain polyester base material. After drying the obtained polyester base material, 3 g of epoxy chain extender ADR4468 (BASF) was added to obtain copolyester.

[0073] Comparative Example 3 The copolyester was prepared according to the method of Example 1, except that glyceric acid was replaced with glycerol.

[0074] Comparative Example 4 2.64 kg of terephthalic acid, 4.5 kg of 1,4-butanediol (BDO), 1.50 kg of polyester diol (purchased from Wanhua Chemical, model 405), 2.0 g of glyceric acid, 2.9 g of tetrabutyl titanate, and 10 g of antioxidant 1010 were added to a reactor and subjected to esterification reaction at a temperature of 190-230℃ and a pressure of 0-0.4 MPa. Esterification was terminated when the esterification rate was ≥90%. Polycondensation reaction was then carried out at a temperature of 240-260℃ and a pressure of 0-100 Pa. After the stirring current reached the rated value, the product was discharged to obtain polyester base material. After drying the obtained polyester base material, 1.5 g of epoxy chain extender ADR4468 (BASF) was added to obtain copolyester.

[0075] Test Example 1 The contents of structural unit A (as shown in formula (I), structural unit B (as shown in formula (II), structural unit C (as shown in formula (III)), and titanium element content in the copolyesters prepared in Examples 1-8 and Comparative Examples 1-4 were tested. The results are shown in Table 1.

[0076] Table 1

[0077] Test Example 2 The storage modulus (G') and angular frequency (ω) curves (K1), loss modulus (G'') and angular frequency (ω) curves (K2), and melt index (230℃, 2.16kg) of the polyester base materials and copolyesters prepared in Examples 1-8 and Comparative Examples 1-4 were tested, and the results are shown in Table 2. The flow activation energy at 230°C, the flow activation energy at 240°C, the difference between the flow activation energies at 230°C and 240°C, the tensile strength and the elongation at break of the copolyesters prepared in Examples 1-8 and Comparative Examples 1-4 were tested, and the results are shown in Table 3. The copolyesters obtained in Examples 1-8 and Comparative Examples 1-4 were extruded through a screw reactor to prepare pipe products with a diameter of 12 cm. The maximum error of the pipe diameter was tested, and the results are shown in Table 3.

[0078] Table 2

[0079] Table 3

[0080] As can be seen from the results in Tables 2 and 3, compared with Comparative Examples 1-4, Examples 1-8 can prepare copolyesters with K1, K2, K1 / K2 ratio and activation energy difference that meet the application requirements by using the method provided by the present invention. They have good melt stability, and the maximum error of the pipe diameter of the pipe products made is less than 0.10 mm, which has significant market prospects.

[0081] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A copolyester characterized in that, The slope K1 of the energy storage modulus versus angular frequency curve of the copolyester is not higher than 1.7, the slope K2 of the loss modulus versus angular frequency curve is not higher than 1, and the ratio of K1 / K2 is not higher than 1.

5. The difference between the flow activation energy of the copolyester at 230°C and at 240°C is no higher than 3 kJ / mol.

2. The copolyester according to claim 1, characterized in that, The copolyester has a flow activation energy of 35-60 kJ / mol at a temperature of 230°C.

3. The copolyester according to claim 1, characterized in that, Under conditions of a load of 2.16 kg and a temperature of 230 °C, the melt index of the copolyester is 0.8-5 g / min.

4. The copolyester according to any one of claims 1 to 3, characterized in that, The copolyester contains structural unit A as shown in formula (I) and structural unit B formed from hydroxy acids; Equation (I); Wherein, R1 is a C2-C10 alkylene group, and n is an integer from 5 to 40; Preferably, the weight ratio of structural unit A to structural unit B in the copolyester is 350-1000:

1.

5. The copolyester according to claim 4, characterized in that, R1 is a C2-C4 alkylene group, and n is an integer from 10 to 25; Preferably, the hydroxy acid is selected from at least one of citric acid, glyceric acid, malic acid and tartaric acid, and more preferably citric acid and / or glyceric acid.

6. The copolyester according to claim 4, characterized in that, In the copolyester, the content of structural unit A is 20-40 wt%, and the content of structural unit B is 0.02-0.1 wt%.

7. The copolyester according to any one of claims 1 to 3, characterized in that, The copolyester contains structural unit C as shown in formula (II) and structural unit D as shown in formula (III); Formula (II); Formula (III); R2, R3, R4 and R5 are each independently selected from hydrogen or C1-C4 alkyl, and R6 is a C2-C10 alkylene.

8. The copolyester according to claim 7, characterized in that, R2, R3, R4 and R5 are each independently methyl or hydrogen, and R6 is a C2-C4 alkylene group; Preferably, the content of structural unit C in the copolyester is 36-48 wt%, and the content of structural unit D is 24-32 wt%.

9. The use of the copolyester according to any one of claims 1 to 8 in tubular products.

10. A tubular product, characterized in that, It is prepared using the copolyester described in any one of claims 1 to 8; Preferably, the diameter of the pipe product is 0.5-2.0 cm, and the diameter error of the pipe product is less than 0.1 mm.

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