Modified copolyesters, their preparation methods and applications

Abstract

This invention relates to polyesters and discloses a modified copolyester. The modified copolyester contains structural unit A as shown in formula (I), and the content of structural unit A in the modified copolyester is 4.5-33 wt%, wherein R1, R4, and R5 are each independently C0-C4 alkylene groups, R2 and R3 are each independently C1-C4 alkyl groups, n and m are each independently natural numbers from 1 to 4, and m+n≤4. Furthermore, this invention also discloses a method for preparing the modified copolyester and its applications. This modified copolyester can improve its glass transition temperature and tensile strength while maintaining its toughness. Formula (I).

Description

Technical Field

[0001] This invention relates to polyesters, and more specifically to a modified copolyester. Furthermore, this invention also discloses a method for preparing the modified copolyester and its applications. Background Technology

[0002] Polybutylene terephthalate (PBT) is an engineering plastic with excellent overall properties. PBT can be rapidly molded at relatively low temperatures, and its products exhibit good electrical conductivity, temperature resistance, high mechanical strength, high surface hardness, and good dimensional stability. Therefore, it is widely used in electronics, automotive, and machinery industries.

[0003] The main products of modified PBT polyester include flame-retardant, glass fiber reinforced, flame-retardant glass fiber reinforced, and blended alloy grades. Market demand for flame-retardant glass fiber reinforced PBT accounts for over 70% of modified PBT demand. Its wide range of applications makes flame-retardant glass fiber reinforced PBT a key research focus both domestically and internationally.

[0004] CN104119519B discloses a method for preparing reinforced modified PBT copolyester, which is a copolyester that can be used in the fields of films and engineering plastics. The method involves liquid-phase polymerization of dimethyl 2,6-naphthalenedicarboxylate or 2,6-naphthalenedicarboxylic acid, an inorganic nucleating agent, terephthalic acid or dimethyl terephthalate, and 1,4-butanediol to obtain the reinforced modified PBT polyester in one step. In this technical solution, replacing part of the terephthalic acid with dimethyl 2,6-naphthalenedicarboxylate or 2,6-naphthalenedicarboxylic acid results in only a small improvement in tensile strength and temperature resistance. Furthermore, the addition of an inorganic nucleating agent leads to a decrease in toughness and impact strength.

[0005] CN102321349A discloses a glass fiber reinforced halogen-free flame-retardant PBT and its preparation method. The method is characterized by the following raw material mass distribution: PBT 40-50 parts, halogen-free flame retardant 10-20 parts, acrylate copolymer 2-8 parts, nano-grade PET 1-5 parts, antioxidant 1-5 parts, and glass fiber 20-40 parts, wherein the halogen-free flame retardant is melamine salt. The product prepared from the glass fiber reinforced halogen-free flame-retardant PBT of this invention is low-smoke, environmentally friendly, and not easily broken, making it easy to process and mold. However, this technical solution uses glass fiber reinforcement or inorganic filler-modified PBT polyester, which reduces the toughness of the PBT product. This reduced toughness increases the product's brittleness and significantly enhances its moisture absorption, causing significant wear and corrosion to the injection molding machine screw and injection mold.

[0006] In summary, existing technologies mainly prepare reinforced heat-resistant PBT copolyesters by using glass fiber and adding aromatic diacids and their derivatives. Glass fiber-modified products suffer from reduced toughness, significantly increased moisture absorption, and poor processability. The improvement in tensile strength and heat distortion temperature of PBT products modified with aromatic diacids and their derivatives is limited, making it difficult to meet the demands of high-performance products in electronics, automobiles, and machinery. Summary of the Invention

[0007] The purpose of this invention is to overcome the problem that the existing technology increases tensile strength and glass transition temperature while reducing toughness, and to provide a modified copolyester, its preparation method and application. This modified copolyester can improve the glass transition temperature and tensile strength while ensuring its toughness, and has good processing performance.

[0008] To achieve the above objectives, a first aspect of the present invention provides a modified copolyester containing structural unit A as shown in formula (I), wherein the content of structural unit A in the modified copolyester is 4.5-33 wt%. Formula (I), Among them, R1, R4 and R5 are each independently C0-C4 alkylene, R2 and R3 are each independently C1-C4 alkyl, n and m are each independently natural numbers from 1 to 4, and m+n≤4.

[0009] A second aspect of the present invention provides a method for preparing a modified copolyester, the method comprising the following steps: S1. Under esterification reaction conditions I, the dicarboxylic acid shown in formula (IV), the diol shown in formula (V), and catalyst I are subjected to contact reaction I to obtain reactant I. Under esterification reaction conditions II, aliphatic diol monomers, aromatic dicarboxylic acid monomers, and catalyst II are subjected to contact reaction II to obtain reactant II; under prepolymerization reaction conditions, reactant II is reacted to obtain a prepolymer. S2. Under polycondensation reaction conditions, reactant I and prepolymer are subjected to contact reaction III, wherein the mass ratio of reactant I to prepolymer is 0.05-0.5:1; Formula (IV), Formula (V); Among them, R1, R4 and R5 are each independently C1-C4 alkylene groups, R2 and R3 are each independently C1-C4 alkyl groups, n and m are each independently natural numbers from 1 to 4, and m+n≤4.

[0010] A third aspect of the present invention provides a modified copolyester prepared by the above-described preparation method.

[0011] A fourth aspect of the present invention provides the application of the above-mentioned modified copolyester in electronic and electrical materials and automotive parts materials.

[0012] Through the above technical solution, the modified copolyester provided by the present invention contains structural unit A as shown in formula (I), and the content of structural unit A in the modified copolyester is controlled at 4.5-33 wt%, which can improve the glass transition temperature and tensile strength of the modified copolyester while ensuring its toughness. Furthermore, it has a low terminal carboxyl group, good processing performance, and can be used in fields such as electronic appliances and automotive parts. Detailed Implementation

[0013] 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.

[0014] As previously stated, the modified copolyester contains structural unit A as shown in formula (I), and the content of structural unit A in the modified copolyester is 4.5-33 wt%. Formula (I), Among them, R1, R4 and R5 are each independently C0-C4 alkylene, R2 and R3 are each independently C1-C4 alkyl, n and m are each independently natural numbers from 1 to 4, and m+n≤4.

[0015] According to the present invention, in the modified copolyester, the content of structural unit A can be 4.5 wt%, 9 wt%, 13.5 wt%, 18 wt%, 22.5 wt%, 27 wt%, 30 wt%, 33 wt%, or any value between these values. "R1, R4, and R5 are each independently C0-C4 alkylene" means that R1, R4, and R5 can be the same or different; specifically, R1 can be absent or be a C1-C4 alkylene, R4 can be absent or be a C1-C4 alkylene, and R5 can be absent or be a C1-C4 alkylene. "R2 and R3 are each independently C1-C4 alkyl" means that R2 and R3 can be the same or different; specifically, R2 can be a C1-C4 alkyl, and R3 can be a C1-C4 alkyl. R2 and R3 can each independently be methylene, ethylene, methylmethylene, propylene, methylethylene, ethylmethylene, butylene, 1-methylpropylene, 2-methylpropylene, 1,1-dimethylethylene, 1,2-dimethylethylene, ethylethylene, or propylethylene. C1-C4 alkyl groups can be methyl, ethyl, propyl, 1-methylethyl, butyl, 1-methylpropyl, 2-methylpropyl, or 1,1-dimethylbutyl. m and n can be the same or different, and m and n can each independently be 1, 2, 3, or 4, with m+n≤4.

[0016] According to the present invention, structural unit A can be qualitatively tested using infrared spectroscopy, and quantitatively tested using gas chromatography after methanol hydrolysis. Infrared FTIR spectroscopy mainly utilizes a Fourier transform infrared spectrometer to rapidly compare and analyze the chemical composition and molecular structure of particulate polyester by measuring its infrared spectrum. The copolyester is subjected to methanol hydrolysis, with tetraethylene glycol dimethyl ether as an internal standard, and detected by an HP5890 gas chromatograph.

[0017] During their research, the inventors unexpectedly discovered that the presence of structural unit A, as shown in formula (I), in the copolyester at a content of 4.5-33 wt%, can improve the glass transition temperature and tensile strength of the modified copolyester while maintaining its toughness. Furthermore, the low end carboxyl group content results in good processing performance, making it suitable for applications in electronics, automobiles, and machinery.

[0018] Preferably, n and m are both 0, and the copolyester containing the above-mentioned structural units has better glass transition temperature and tensile strength. Further preferably, considering the potential to further improve the glass transition temperature and tensile strength of the copolyester, R1, R4, and R5 are each independently a C0-C2 alkyl group. More preferably, R4 and R5 are the same.

[0019] Preferably, in the modified copolyester, the content of structural unit A is 22-33 wt%. Studies have found that controlling the content of structural unit A within the above range can further improve the glass transition temperature and tensile strength of the copolyester.

[0020] In structural unit A, the substituents on the benzene ring, excluding R2 and R3, can be para, meta, or ortho. Para placement is preferred.

[0021] In a relatively preferred embodiment of the present invention, the structure of structural unit A is as shown in formula (VI); Formula (VI), In this study, R1 is absent or is a C1-C4 alkylene group. The study found that copolyesters containing structural unit A as shown in formula (VI) can further improve their glass transition temperature and tensile strength.

[0022] Preferably, the modified copolyester further contains structural unit B as shown in formula (II) and structural unit C as shown in formula (III). Equation (II), Formula (III) R6 is a C1-C4 alkylene group. Through the interaction between structural units A, B, and C, the glass transition temperature and tensile strength of the copolyester can be further improved.

[0023] According to the present invention, in structural unit B, the groups on the benzene ring can be arranged in the para, meta, or ortho positions. Para arrangement is preferred. Specifically, the structure of structural unit B is shown in formula (VII); Equation (VII).

[0024] Preferably, in the modified copolyester, the content of structural unit B is 37-54 wt%, which can be 37 wt%, 40 wt%, 45 wt%, 50 wt%, 54 wt%, or any value between these values; the content of structural unit C is 29-42 wt%, which can be 29 wt%, 35 wt%, 40 wt%, 42 wt%, or any value between these values. The above-mentioned contents of structural units B, C, and A have a better synergistic effect, thereby further improving the glass transition temperature and tensile strength of the copolyester. Further preferably, considering the ability to further improve the glass transition temperature and tensile strength of the copolyester, the content of structural unit B is 37-44 wt%, and the content of structural unit C is 29-34 wt%.

[0025] Preferably, the modified copolyester further contains a metal element, namely tin and titanium. The simultaneous presence of titanium and tin in the polyester can further improve its glass transition temperature and tensile strength. More preferably, considering the ability to further improve the glass transition temperature and tensile strength of the polyester, the content of the metal in the modified copolyester is 150-300 ppm, which can be 150 ppm, 200 ppm, 250 ppm, 300 ppm, or any value between these values.

[0026] According to the present invention, the contents of titanium and tin in the copolyester can be determined by elemental analysis.

[0027] Preferably, the mass ratio of tin to titanium is 1:0.9-12. More preferably, considering the potential to further improve the glass transition temperature and tensile strength of the polyester, the mass ratio of tin to titanium is 1:1.2-2.8.

[0028] Preferably, the modified copolyester has an end carboxyl group value of 18-25 mol / t, a glass transition temperature of 62-105℃, a tensile strength of 55-90 MPa, and an elongation at break of 160-320%.

[0029] According to the present invention, the glass transition temperature is obtained by thermogravimetric analysis according to the national standard GB / T14190-2017; the tensile strength and elongation at break are obtained according to GB / T 1040-2006 Determination of tensile properties of plastics.

[0030] Secondly, the present invention provides a method for preparing a modified copolyester, the method comprising the following steps: S1. Under esterification reaction conditions I, the dicarboxylic acid shown in formula (IV), the diol shown in formula (V), and catalyst I are subjected to contact reaction I to obtain reactant I. Under esterification reaction conditions II, aliphatic diol monomers, aromatic dicarboxylic acid monomers, and catalyst II are subjected to contact reaction II to obtain reactant II; under prepolymerization reaction conditions, reactant II is reacted to obtain a prepolymer. S2. Under polycondensation reaction conditions, reactant I and prepolymer are subjected to contact reaction III, wherein the mass ratio of reactant I to prepolymer is 0.05-0.5:1; Formula (IV), Formula (V); Among them, R1, R4 and R5 are each independently C1-C4 alkylene groups, R2 and R3 are each independently C1-C4 alkyl groups, n and m are each independently natural numbers from 1 to 4, and m+n≤4.

[0031] The above preparation method can introduce the structural unit A shown in formula (I) into the polyester, so that the prepared copolyester has the structural unit A shown in formula (I), and can control the structural unit A in the polyester to 4.5-33wt%, thereby improving the glass transition temperature and tensile strength of the modified copolyester while ensuring its toughness.

[0032] Preferably, both n and m are 0, which can further improve the glass transition temperature and tensile strength of the obtained copolyester. Further preferably, considering the ability to further improve the glass transition temperature and tensile strength of the copolyester, R1 is a C2-C4 alkyl group, and R4 and R5 are each independently a C1-C2 alkyl group. More preferably, R4 and R5 are the same.

[0033] In formula (V), the substituents on the benzene ring, excluding R2 and R3, can be para, meta, or ortho. Para is preferred.

[0034] As a specific embodiment of the present invention, the diol represented by formula (V) is terephthalic acid.

[0035] Preferably, the mass ratio of reactant I to the prepolymer is 0.28-0.5:1. Studies have found that controlling the mass ratio of reactant I to the prepolymer within the above range can further improve the glass transition temperature and tensile strength of the obtained copolyester.

[0036] In formula (V), the two substituents containing the hydroxyl group can be arranged in the para, meta, or ortho positions. The para position is preferred.

[0037] Preferably, the aliphatic diol monomer is a diol containing the structure shown in formula (III), and the aromatic diacid monomer is a diacid containing the structure shown in formula (II). Equation (II), Formula (III) R6 is a C1-C4 alkylene group. The copolyester obtained by the above monomer synthesis has a high glass transition temperature and tensile strength.

[0038] Preferably, catalyst I is an organotin catalyst and catalyst II is an organotitanium catalyst. Using the above catalysts enables the prepared copolyester to have a high glass transition temperature and tensile strength. Considering the potential to further improve the glass transition temperature and tensile strength of the prepared copolyester, preferably, based on 1 kg of the dicarboxylic acid represented by formula (IV), the amount of the organotin catalyst added is 1-2.5 g, which can be 1 g, 1.5 g, 2 g, 2.5 g, or any value between these values; based on 1 kg of the aromatic dicarboxylic acid monomer, the amount of the organotitanium catalyst added is 1.5-2 g, which can be 1.5 g, 1.6 g, 1.7 g, 1.8 g, 1.9 g, 2 g, or any value between these values.

[0039] Preferably, the organotin catalyst is dibutyltin dilaurate and / or dibutyltin diacetate, and the organotitanium catalyst is a titanate ester. More preferably, the organotitanium catalyst is tetrabutyl titanate; Preferably, the degree of polymerization of the prepolymer is 2-5. Controlling the polymer within this range can further improve the glass transition temperature and tensile strength of the resulting copolyester.

[0040] Preferably, in step S1, the esterification reaction conditions I include at least: a temperature of 140-150℃ and a time of 3-4 hours; the esterification reaction conditions II include at least: a temperature of 190-230℃ and a time of 1-3 hours; the pre-condensation reaction conditions include at least: a temperature of 235-245℃ and a time of 1.5-2.5 hours; and in step S2, the condensation reaction conditions include at least: a temperature of 240-250℃ and a time of 1-2 hours. This invention first performs the esterification reaction of terephthalic acid and aliphatic dicarboxylic acid at a lower temperature, which can effectively introduce the structure of terephthalic acid into the polyester, improving its thermal decomposition temperature, glass transition temperature, and tensile strength.

[0041] Thirdly, the present invention provides a modified copolyester prepared by the above-described preparation method.

[0042] Fourthly, the present invention provides an application of the above-mentioned modified copolyester in electrical materials and / or automotive parts materials.

[0043] According to a particularly preferred embodiment of the present invention, a method for preparing a modified copolyester is provided, comprising the following steps: S1. Esterify the dicarboxylic acid shown in formula (IV), the diol shown in formula (V), and the tin lauryl catalyst at a temperature of 140-150℃ for 3-4 hours to obtain reactant I. Aliphatic diol monomers, aromatic dicarboxylic acid monomers, and titanate esters are reacted at 190-230°C for 1-3 hours to obtain reactant II; reactant II is then reacted at 235-245°C for 1.5-2.5 hours to obtain a prepolymer. S2. React the reactant I and the prepolymer at a temperature of 240-250°C for 1-2 hours, wherein the mass ratio of the reactant I to the prepolymer is 0.28-0.5:1; The aliphatic diol monomer is a diol containing the structure shown in formula (III), and the aromatic diacid monomer is a diacid containing the structure shown in formula (II). Equation (II), Formula (III) Formula (IV), Formula (V); Wherein, R6 is a C1-C4 alkylene group, R1 is a C2-C4 alkyl group, R4 and R5 are each independently C1-C2 alkyl groups, R2 and R3 are each independently C1-C4 alkyl groups, n and m are each independently natural numbers from 1 to 4, and m+n≤4; based on 1 kg of the dicarboxylic acid represented by formula (IV), the amount of the organotin catalyst added is 1-2.5 g; based on 1 kg of the aromatic dicarboxylic acid monomer, the amount of the organotitanium catalyst added is 1.5-2 g.

[0044] The copolyester prepared by the above method has high glass transition temperature and tensile strength, as well as high toughness.

[0045] In the following examples, the content of metal elements in the copolyester was determined by elemental analysis.

[0046] The contents of structural units B and C in the copolyester were obtained by gas / liquid chromatography. The copolyester was subjected to methanol alcoholysis, and tetraethylene glycol dimethyl ether was used as an internal standard for detection by an HP5890 gas chromatograph. The limiting oxygen index of the copolyester was tested according to the "FZ / T 50017-2011 Test Method for Flame Retardant Properties of Polyester Fibers - Oxygen Index Method". The test procedure included: fixing the sample vertically in a transparent combustion tube with an upward flow of oxygen and nitrogen mixed gas, igniting the top of the sample, observing the combustion characteristics of the sample, comparing the burning length of the sample with a given criterion, and estimating the minimum oxygen concentration through a series of tests at different oxygen concentrations; each sample was tested three times, and the average value was taken.

[0047] The tensile strength and elongation at break of the copolyester were tested in accordance with GB / T 1040-2006 Test of Tensile Properties of Plastics.

[0048] Intrinsic viscosity, end carboxyl group content, and glass transition temperature were all tested in accordance with the national standard GB / T14190-2017 "Test Methods for Fiber Grade Polyester (PET) Chips".

[0049] Example 1 S1. Esterify 2.3 kg of oxalic acid, 3.6 kg of terephthalic acid and 9 g of dibutyltin dilaurate catalyst at 150 °C for 3 h to obtain terephthalic acid esterified product.

[0050] S2. Add 3.7 kg of terephthalic acid, 3.6 kg of 1,4-butanediol and 7.4 g of tetrabutyl titanate to a reactor, esterify at 210°C for 2 h, and then react at 240°C for 1 h to obtain a butylene terephthalate prepolymer with a degree of polymerization of 5.

[0051] S3. Add 2.5 kg of terephthalic acid esterified methanol obtained in step S1 to the butylene terephthalate prepolymer in step S2, and after nitrogen purging, continue polycondensation at 250°C for 1 h to obtain modified PBT copolyester.

[0052] Example 2 S1. Esterify 2.3 kg of oxalic acid, 4.3 kg of terephthalic acid and 4.3 g of dibutyltin dilaurate catalyst at 145 °C for 3.5 h to obtain terephthalic acid esterified product.

[0053] S2. Add 3.7 kg of terephthalic acid, 6 kg of 1,4-butanediol and 5.6 g of tetrabutyl titanate to a reactor. Esterify at 190°C for 3 h, then react at 235°C for 1.5 h to obtain a terephthalic acid butanediol prepolymer with a degree of polymerization of 5.

[0054] S3. Add 2 kg of terephthalic acid terephthalic acid ester obtained in step S1 to the butylene terephthalate prepolymer in step S2, and after nitrogen purging, continue polycondensation at 245°C for 1.5 h to obtain modified PBT copolyester.

[0055] Example 3 S1. Esterify 2.3 kg of oxalic acid, 4 kg of terephthalic acid and 6 g of dibutyltin dilaurate catalyst at 140 °C for 4 h to obtain terephthalic acid esterified product.

[0056] S2. Add 3.7 kg of terephthalic acid, 4.5 kg of 1,4-butanediol and 6.5 g of tetrabutyl titanate to a reactor, esterify at 230°C for 1 h, and then react at 245°C for 2.5 h to obtain a butylene terephthalate prepolymer with a degree of polymerization of 5.

[0057] S3. Add 1.5 kg of terephthalic acid terephthalic acid ester obtained in step S1 to the butylene terephthalate prepolymer in step S2. After nitrogen purging, continue polycondensation at 250°C for 1 h to obtain modified PBT copolyester.

[0058] Example 4 PBT copolyester was prepared according to the method described in Example 3, except that in step S3, the amount of oxalic acid terephthalic acid esterified product was 1 kg.

[0059] Example 5 PBT copolyester was prepared according to the method described in Example 1, except that in step S3, the amount of 255g of terephthalic acid esterified product was used.

[0060] Example 6 PBT copolyester was prepared according to the method described in Example 1, except that in step S2, the amount of tetrabutyl titanate used was 5.6 g.

[0061] Example 7 PBT copolyester was prepared according to the method described in Example 3, except that in step S1, the amount of dibutyltin dilaurate catalyst used was 4.3g.

[0062] Example 8 The PBT copolyester was prepared according to the method described in Example 2, except that in step S2, the reaction was carried out at 235°C for 1 hour, and the degree of polymerization of the resulting butylene terephthalate prepolymer was 3.

[0063] Example 9 The PBT copolyester was prepared according to the method described in Example 2, except that in step S2, the reaction was carried out at 235°C for 0.5 h, and the degree of polymerization of the resulting butylene terephthalate prepolymer was 2.

[0064] Example 10 PBT copolyester was prepared according to the method described in Example 1, except that in step S2, the reaction was carried out at 240°C for 1 hour, and the degree of polymerization of the resulting butylene terephthalate prepolymer was 10.

[0065] Example 11 The copolyester was prepared according to the method described in Example 1, except that terephthalic acid was replaced with isophthalic acid (CAS No.: 626-18-6).

[0066] Example 12 The copolyester was prepared according to the method described in Example 1, except that 3.6 kg of terephthalic acid was replaced with 3.2 kg of 4-hydroxybenzyl alcohol (CAS No.: 623-05-2), and 2.3 kg of oxalic acid was replaced with 3.0 kg of 1,4-succinic acid (CAS No.: 110-15-6).

[0067] Example 13 The copolyester was prepared according to the method described in Example 1, except that 2.3 kg of oxalic acid was replaced with 3.4 kg of 1,5-heptanediol (CAS No.: 111-16-0).

[0068] Example 14 The copolyester was prepared according to the method described in Example 1, except that 4.5 kg of 1,4-butanediol was replaced with 3.0 kg of 1,3-propanediol, and terephthalic acid was replaced with isophthalic acid.

[0069] Example 15 The PBT copolyester was prepared according to the method described in Example 12, except that in step S3, the amount of the esterified product obtained in step S1 was 255g.

[0070] Example 16 S1. Esterify 2.3 kg of oxalic acid, 4.0 kg of 2-methylterephthalic acid (CAS No.: 5156-01-4) and 9 g of dibutyltin dilaurate catalyst at 150 °C for 3 h to obtain terephthalic acid esterified product.

[0071] S2. Add 3.7 kg of terephthalic acid, 3.6 kg of 1,4-butanediol and 7.4 g of tetrabutyl titanate to a reactor, esterify at 210°C for 2 h, and then react at 240°C for 1 h to obtain a butylene terephthalate prepolymer with a degree of polymerization of 5.

[0072] S3. Add 2.5 kg of terephthalic acid terephthalic acid ester obtained in step S1 to the butylene terephthalate prepolymer in step S2, and after nitrogen purging, continue polycondensation at 250°C for 1 h to obtain the modified copolyester.

[0073] Comparative Example 1 PBT copolyester was prepared according to the method described in Example 1, except that in step S3, the amount of 3 kg of oxalic acid terephthalic acid ester was used.

[0074] Comparative Example 2 PBT copolyester was prepared according to the method described in Example 1, except that in step S3, the amount of 220g of terephthalic acid ester was used.

[0075] Comparative Example 3 Esterification of 3.7 kg terephthalic acid, 3.6 kg terephthalic acid and 9 g dibutyltin dilaurate catalyst at 150 °C for 3 h did not produce esterification water.

[0076] Comparative Example 4 PBT copolyester was prepared according to the method described in Example 12, except that in step S3, the amount of 3 kg of oxalic acid terephthalic acid ester was used.

[0077] Comparative Example 5 PBT copolyester was prepared according to the method described in Example 12, except that in step S3, the amount of 220g of terephthalic acid ester was used.

[0078] Comparative Example 6 2.3 kg of oxalic acid, 3.6 kg of terephthalic acid, 9 g of dibutyltin dilaurate catalyst, 3.7 kg of terephthalic acid, 3.6 kg of 1,4-butanediol, and 14.8 g of tetrabutyl titanate were added to a reaction vessel and esterified at 210 °C for 2 h. The resulting ester was black. Tests showed that the ester contained virtually no structural units formed by terephthalic acid.

[0079] Test case The performance parameters of the copolyesters obtained in the examples and comparative examples are shown in Tables 1 and 2.

[0080] Table 1

[0081] Table 2

[0082] As can be seen from the results in Table 2, the glass transition temperature, tensile strength, and elongation at break of the embodiment are all better than those of the corresponding comparative example. This indicates that the polyester provided by the present invention has a high glass transition temperature and good mechanical properties. At the same time, the intrinsic viscosity and end carboxyl group content of the polyester also meet the application requirements and have significant market prospects.

[0083] 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 modified copolyester, characterized in that, The modified copolyester contains structural unit A as shown in formula (I), and the content of structural unit A in the modified copolyester is 4.5-33 wt%. Equation (I), Among them, R1, R4 and R5 are each independently C0-C4 alkylene, R2 and R3 are each independently C1-C4 alkyl, n and m are each independently natural numbers from 1 to 4, and m+n≤4.

2. The modified copolyester according to claim 1, characterized in that, Both n and m are 0; Preferably, R1, R4 and R5 are each independently a C0-C2 alkyl group; Preferably, R4 and R5 are the same; Preferably, in the modified copolyester, the content of structural unit A is 22-33 wt%.

3. The modified copolyester according to claim 1 or 2, characterized in that, The modified copolyester also contains structural unit B as shown in formula (II) and structural unit C as shown in formula (III). Equation (II), Formula (III) R6 is a C1-C4 alkylene group; Preferably, in the modified copolyester, the content of structural unit B is 37-54 wt%, and the content of structural unit C is 29-42 wt%.

4. The modified copolyester according to claim 1 or 2, characterized in that, The modified copolyester also contains metal elements, namely tin and titanium. Preferably, in the modified copolyester, the content of the metal element is 150-300 ppm; Preferably, the mass ratio of tin to titanium is 1:0.9-12, and more preferably 1:1.2-2.

8.

5. The modified copolyester according to claim 1 or 2, characterized in that, The modified copolyester has an end carboxyl group value of 18-25 mol / t, a glass transition temperature of 62-105℃, a tensile strength of 55-90 MPa, and an elongation at break of 160-320%.

6. A method for preparing a modified copolyester, characterized in that, The preparation method includes the following steps: S1. Under esterification reaction conditions I, the dicarboxylic acid shown in formula (IV), the diol shown in formula (V), and catalyst I are subjected to contact reaction I to obtain reactant I. Under esterification reaction conditions II, aliphatic diol monomers, aromatic dicarboxylic acid monomers and catalyst II are subjected to contact reaction II to obtain reactant II; Under prepolymerization reaction conditions, reactant II is reacted to obtain a prepolymer; S2. Under polycondensation reaction conditions, reactant I and prepolymer are subjected to contact reaction III, wherein the mass ratio of reactant I to prepolymer is 0.05-0.5:1; Formula (IV), Formula (V); Among them, R1, R4 and R5 are each independently C1-C4 alkylene groups, R2 and R3 are each independently C1-C4 alkyl groups, n and m are each independently natural numbers from 1 to 4, and m+n≤4.

7. The preparation method according to claim 6, characterized in that, Both n and m are 0; Preferably, R1 is a C2-C4 alkyl group, and R4 and R5 are each independently a C1-C2 alkyl group; Preferably, R4 and R5 are the same; Preferably, the mass ratio of reactant I to the prepolymer is 0.28-0.5:1; Preferably, the aliphatic diol monomer is a diol containing the structure shown in formula (III), and the aromatic diacid monomer is a diacid containing the structure shown in formula (II). Equation (II), Formula (III) R6 is a C1-C4 alkylene group.

8. The preparation method according to claim 6 or 7, characterized in that, Catalyst I is an organotin catalyst, and catalyst II is an organotitanium catalyst; Preferably, based on 1 kg of the dicarboxylic acid represented by formula (IV), the amount of the organotin catalyst added is 1-2.5 g; Based on 1 kg of the aromatic dicarboxylic acid monomer, the amount of the organotitanium catalyst added is 1.5-2 g; Preferably, the organotin catalyst is dibutyltin dilaurate and / or dibutyltin diacetate; The organic titanium catalyst is a titanate, more preferably tetrabutyl titanate; Preferably, the degree of polymerization of the prepolymer is 2-5; Preferably, in step S1, the esterification reaction conditions I include at least: a temperature of 140-150°C and a time of 3-4 hours; The esterification reaction conditions II include at least the following: temperature of 190-230℃ and time of 1-3h; The pre-polymerization reaction conditions include at least the following: a temperature of 235-245℃ and a time of 1.5-2.5h; In step S2, the polycondensation reaction conditions include at least the following: a temperature of 240-250°C and a time of 1-2 hours.

9. The modified copolyester prepared by the preparation method according to any one of claims 6 to 8.

10. The use of the modified copolyester according to any one of claims 1-5 and 9 in electronic and electrical materials and / or automotive parts materials.

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