Low-shrinkage PBT material and preparation method thereof

Abstract

The invention relates to the technical field of high polymer materials, in particular to a low-shrinkage PBT (polybutylene terephthalate) material and a preparation method thereof. The low-shrinkage PBT material is based on terephthalic acid and 1, 4-butanediol, and a rigid monomer 1, 5-bis (2-hydroxyethoxy) naphthalene and carboxyl-terminated hyperbranched polyester are introduced for copolymerization modification. Wherein a plane structure of a naphthalene ring inhibits regular crystallization of a molecular chain through a steric hindrance effect, and the shrinkage rate is reduced; the carboxyl-terminated hyperbranched polyester constructs a three-dimensional network through a controllable cross-linking reaction, the crystallization behavior is further regulated and controlled, and the shrinkage rate of the material is reduced through synergism of the two. A hydrogen bond network is formed by a hydroxyethoxy side chain and a branched structure of hyperbranched polyester, so that the mechanical and thermal stability of the material is enhanced. The low-shrinkage PBT material prepared by the invention solves the problem of balancing the shrinkage rate with mechanical and thermal stability and other properties of the traditional PBT material, and has a wide application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, and particularly relates to a low-shrinkage PBT material and a preparation method thereof. Background Art

[0002] Polybutylene terephthalate (PBT), as a semi-crystalline thermoplastic engineering plastic, is widely used in the fields of electronic appliances, automotive parts, and precision molds due to its excellent mechanical properties, heat resistance, and processing fluidity. However, PBT materials have significant volume shrinkage during the injection molding process (conventional shrinkage rate is 1.5%-2.0%), resulting in problems such as poor dimensional stability of products, warpage deformation, and surface defects of products, which severely limit the scope of its application.

[0003] Currently, the main methods to reduce the shrinkage rate of PBT include adding inorganic fillers (such as glass fiber, mineral powder) or introducing blending modifiers (such as elastomers, other polymers). For example, the addition of glass fiber can significantly reduce the shrinkage rate, but it will increase the brittleness of the material, decrease the surface finish, and the fiber orientation during the processing process is likely to cause anisotropic shrinkage. In addition, although chemical modification methods (such as introducing cross-linking agents or functional monomers) can improve the shrinkage problem, they are often accompanied by complex processes, increased costs, or loss of material toughness.

[0004] In terms of thermal stability, the heat distortion temperature (HDT) of traditional PBT is limited by its crystallization behavior, and the molecular chains are prone to slip and cause deformation at high temperatures. Although the high-temperature performance can be improved by increasing the crystallinity or adding heat-resistant additives, these strategies often conflict with shrinkage rate control. For example, high crystallinity can improve thermal stability, but it will exacerbate the molding shrinkage; and the excessive use of heat-resistant additives may introduce interfacial defects and weaken the overall performance of the material. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a low-shrinkage PBT material and a preparation method thereof to solve the balance problem of the shrinkage rate, mechanical properties, heat distortion temperature, and water absorption rate of existing PBT materials.

[0006] Based on the above purpose, the present invention provides a low-shrinkage PBT material, which is prepared from the following raw materials: 1,5-bis(2-hydroxyethoxy)naphthalene, carboxyl-terminated hyperbranched polyester, terephthalic acid, 1,4-butanediol, tetrabutyl titanate;

[0007] The preparation method of the 1,5-bis(2-hydroxyethoxy)naphthalene is as follows: Under nitrogen protection, 1,5-naphthalenediol, 2-chloroethanol, and potassium carbonate are added to N,N-dimethylformamide, and then tetrabutylammonium bromide is added. The temperature is raised to 110-130 °C, and the reaction is carried out for 6-8 h. After cooling to room temperature, the reaction solution is added to deionized water at 5 °C, and extracted three times with dichloromethane. The organic phases are combined and washed successively with a 5% NaOH solution and deionized water. After drying, it is concentrated under reduced pressure to obtain a crude product, which is separated by gradient elution on a silica gel column chromatography, and the eluent is removed by distillation under reduced pressure to obtain 1,5-bis(2-hydroxyethoxy)naphthalene;

[0008] The preparation method of the carboxyl-terminated hyperbranched polyester is as follows: Under nitrogen protection, pentaerythritol and tetrahydrofuran are added to a 2 mol / L NaOH solution to form solution A; terephthaloyl chloride is added to dichloromethane to form solution B; at 0-5 °C, solution B is added to solution A. After the addition is complete, the temperature is raised to room temperature, and the reaction is carried out for 1-3 h. Dilute hydrochloric acid is added to adjust the pH to neutral, and it is stirred in methanol for 20-30 min, filtered, washed, and dried to obtain the carboxyl-terminated hyperbranched polyester.

[0009] Preferably, the preparation reaction equation of the 1,5-bis(2-hydroxyethoxy)naphthalene is as follows:

[0010]

[0011] The product was characterized by 1H NMR. 1H NMR (400 MHz, Chloroform-d) δ 7.95 (dt, J = 7.9, 0.8 Hz, 2H), 7.21 (t, J = 7.9 Hz, 2H), 7.05-6.85 (m, 2H), 4.08 (t, J = 4.7 Hz, 4H), 3.74 (dt, J = 6.2, 4.6 Hz, 4H), 3.06 (t, J = 6.2 Hz, 2H).

[0012] Preferably, in the preparation method of the 1,5-bis(2-hydroxyethoxy)naphthalene, the weight ratio of 1,5-naphthalenediol, 2-chloroethanol, potassium carbonate, tetrabutylammonium bromide, and N,N-dimethylformamide is 1:2-2.5:1-1.4:0.08-0.12:8-12.

[0013] Preferably, in the preparation method of the 1,5-bis(2-hydroxyethoxy)naphthalene, the weight ratio of deionized water at 5 °C to N,N-dimethylformamide is 3:1; extracting three times with dichloromethane means that the weight of dichloromethane used for each extraction is one-third of the weight of deionized water at 5 °C, and extracting three times; the weight ratio of the 5% NaOH solution, deionized water, and deionized water at 5 °C is 1:1:1.

[0014] Preferably, in the preparation method of 1,5-bis(2-hydroxyethoxy)naphthalene, gradient elution separation refers to the use of gradient elution method, and the volume ratio of petroleum ether to ethyl acetate in each eluent is successively from 1:0, 20:1, 10:1 to 5:1.

[0015] Preferably, the schematic diagram of the preparation reaction of the terminal carboxyl hyperbranched polyester is as follows:

[0016]

[0017] The product reacts through the hydroxyl group of compound A and the acyl chloride group of compound B to form a hyperbranched structure. Excessive compound B ensures that the end group of the hyperbranched structure is an acyl chloride group, which can be converted into a terminal carboxyl group by hydrolysis reaction. The product was characterized by FTIR infrared spectroscopy, and C=O vibration peaks in ester groups and carboxyl groups were observed at 1750-1850 cm -1 C=O vibration peaks in ester groups were observed at 1000-1300 cm -1 C-O-C vibration peaks in ester groups were observed at 3800-3900 cm -1 Free O-H vibration peaks of terminal carboxyl groups were observed, and at the same time, C=C vibration peaks in benzene rings were observed at 1400-1450 cm -1 C=C vibration peaks in benzene rings were observed, reflecting the structural characteristics of the terminal carboxyl hyperbranched polyester.

[0018] Preferably, in the preparation method of the terminal carboxyl hyperbranched polyester, the weight ratio of pentaerythritol, tetrahydrofuran, 2 mol / L NaOH solution, terephthaloyl chloride, dichloromethane and methanol is 1:0.3-0.7:8-12:2.1-2.3:5-9:10-14, and the dilute hydrochloric acid refers to a hydrochloric acid solution with a concentration of 10%.

[0019] Furthermore, the present invention also provides a preparation method of the above low-shrinkage PBT material, including the following steps:

[0020] S1. Add terephthalic acid, 1,4-butanediol, 1,5-bis(2-hydroxyethoxy)naphthalene and tetrabutyl titanate into a reaction kettle. Under stirring, heat up to 170-190 °C and react for 1-3 h, then continue to heat up to 230-250 °C and reduce the pressure to 400-600 Pa, react for 2-3 h, cool to room temperature, add a 5% NaOH solution to adjust the PH to neutral, filter, wash and dry to obtain a low-shrinkage PBT intermediate;

[0021] S2. Add the low-shrinkage PBT intermediate, terminal carboxyl hyperbranched polyester and tetrabutyl titanate obtained in S1 into a reaction kettle. Under stirring, heat up to 250-260 °C and reduce the pressure to 30-50 Pa, react for 3-5 h, cool to room temperature, add a 3% NaOH solution to adjust the PH to neutral, filter, wash and dry to obtain the low-shrinkage PBT material;

[0022] S3. Add the low-shrinkage PBT material into an injection molding machine, set the parameters, fill different mold cavities through the injection molding machine, and demold after pressure holding and cooling to obtain low-shrinkage PBT products with various shapes and uses.

[0023] Preferably, the preparation reaction equation of the low-shrinkage PBT intermediate in S1 is as follows:

[0024]

[0025] The product was characterized by FTIR infrared spectroscopy. A C=O vibration peak in the ester group was observed at 1850 - 1950 cm -1 A C-O-C and ether bond vibration peak in the ester group was observed at 1000 - 1300 cm -1 A C=C vibration peak in the benzene ring and naphthalene ring was observed at 1350 - 1450 cm -1 An O-H vibration peak was observed at 3200 - 3400 cm -1 which reflected the structural characteristics of the low-shrinkage PBT intermediate.

[0026] Preferably, in S1, the weight ratio of terephthalic acid, 1,4-butanediol, 1,5-bis(2-hydroxyethoxy)naphthalene, and tetrabutyl titanate is 0.7 - 0.9:1.8 - 2.2:0.15 - 0.25:0.01 - 0.03.

[0027] Preferably, the preparation reaction schematic diagram of the low-shrinkage PBT material in S2 is as follows:

[0028]

[0029] The end-carboxyl hyperbranched polyester and the low-shrinkage PBT intermediate are polycondensed through an esterification reaction to obtain a product. The water generated in the reaction is removed by high-temperature and reduced pressure to promote the forward progress of the reaction.

[0030] Preferably, in S2, the weight ratio of the low-shrinkage PBT intermediate, end-carboxyl hyperbranched polyester, and tetrabutyl titanate is 1:0.08 - 0.12:0.01 - 0.03.

[0031] Preferably, the parameters set in S3 refer to the rear section temperature of the injection molding machine: 230 - 240 °C, the middle section temperature: 240 - 250 °C, the front section temperature: 250 - 260 °C, the nozzle temperature: 255 - 265 °C, the injection pressure: 80 - 100 MPa, the pressure holding pressure: 40 - 50 MPa, the pressure holding time: 15 - 25 s; the mold temperature: 60 - 80 °C.

[0032] The beneficial effects of the present invention:

[0033] 1. The present invention solves the contradiction between the reduction of shrinkage rate and the deterioration of mechanical properties in the modification of traditional PBT by introducing the synergistic effect of naphthalene ring rigid units and hyperbranched cross-linked structures. The naphthalene ring in 1,5-bis(2-hydroxyethoxy)naphthalene molecules serves as a rigid comonomer, restricting the regular arrangement of PBT molecular chains through π-π conjugation effects, significantly inhibiting the volume shrinkage caused by high crystallinity. At the same time, its symmetric dihydroxy structure participates in the polycondensation reaction to form a polymer backbone with enhanced main-chain rigidity, fundamentally improving the intrinsic strength of the material. The introduction of carboxyl-terminated hyperbranched polyester forms physical entanglements of molecular chains through a three-dimensional network structure. While inhibiting crystal growth, a dynamic hydrogen bond network is formed between the carboxyl groups at the hyperbranched terminals and the hydroxyl groups at the PBT terminals, which can not only disperse stress and improve toughness but also limit the slippage of molecular chains through cross-linking points. The synergistic effect of the two enables the material to maintain good tensile strength when the shrinkage rate decreases, breaking through the "seesaw" effect of shrinkage rate and mechanical properties in the traditional filler-reinforced system.

[0034] 2. A multi-level heat-resistant protection mechanism from chemical bonds to micro-morphology is constructed through structural innovation at the molecular level. The rigid planar structure of the naphthalene ring endows the material with higher thermal stability, and the intermolecular forces generated by its conjugated system effectively resist the segmental movement at high temperatures. The three-dimensional network of carboxyl-terminated hyperbranched polyester not only forms physical cross-linking points, but the carboxyl groups at its terminals also form stable ester bond cross-links with the PBT chain ends, significantly enhancing the melt strength. More importantly, the steric hindrance effect of the hyperbranched structure hinders the orientation crystallization of molecular chains, forming an interpenetrating structure of uniformly distributed microcrystalline regions and amorphous regions. This micro-morphology enables the material to achieve dimensional stability in a wide temperature range through the synergistic effect of crystal region anchoring and viscoelastic response of the amorphous region, overcoming the single dependence of the high-temperature performance of traditional PBT on crystallinity.

[0035] 3. The present invention solves the problem that the physical blending of hyperbranched polyester and PBT materials cannot balance water absorption and other properties through the chemical structure design of the hyperbranched structure and chemical cross-linking. First, through chemical cross-linking, the esterification reaction occurs between the carboxyl groups at the terminals of carboxyl-terminated hyperbranched polyester and the hydroxyl groups at the PBT chain ends, converting the highly polar hydroxyl groups on the material surface into hydrophobic ester groups, reducing the content of free hydroxyl groups and weakening the chemical driving force for water molecules to adsorb through hydrogen bonds. Secondly, the three-dimensional network structure of hyperbranched polyester forms a water-repellent barrier in the matrix, and its dense branched nodes block the penetration of water molecules. Finally, the rigid naphthalene ring units on the branched chains enhance the molecular chain packing density through π-π stacking, forming a low-polarity dense structure layer inside the material, reducing the water absorption rate of the material. Particularly importantly, this water absorption control mechanism stems from the innovation of the intrinsic structure of the material, enabling the material to have good performance in other aspects while maintaining a low water absorption rate, greatly broadening the scope of use of this PBT material. Description of the Drawings

[0036] Figure 1 1H NMR spectrum of 1,5-bis(2-hydroxyethoxy)naphthalene prepared in Example 2;

[0037] Figure 2 FTIR infrared spectrogram of carboxyl-terminated hyperbranched polyester prepared in Example 2;

[0038] Figure 3 FTIR infrared spectrogram of low-shrinkage PBT material prepared in Example 2. Detailed implementation manners

[0039] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with specific embodiments.

[0040] The sources of the reagent raw materials used in the embodiments of the present invention are as follows:

[0041] 1,5-Naphthalenediol was purchased from Shanghai Haohong Biopharmaceutical Technology Co., Ltd., with a purity of 98%; 2-chloroethanol was purchased from Wuxi Yinxing Plastics Industry Technology Co., Ltd., with a purity of 99%; tetrabutylammonium bromide was purchased from Shanghai Macklin Biochemical Co., Ltd., with a purity of 99%; pentaerythritol was purchased from Yunnan Yuntianhua Co., Ltd., with a purity of 98%; terephthaloyl chloride was purchased from Shanghai Macklin Biochemical Co., Ltd., with a purity of 99%; terephthalic acid was purchased from Shanghai Macklin Biochemical Co., Ltd., with a purity of 99%; 1,4-butanediol was purchased from Shanghai Macklin Biochemical Co., Ltd., with a purity of 99%; tetrabutyl titanate was purchased from Shanghai Macklin Biochemical Co., Ltd., with a purity of 98%.

[0042] Example 1: A low-shrinkage PBT material and its preparation method, including the following process:

[0043] (1) Under nitrogen protection, 30 g of 1,5-naphthalenediol, 60 g of 2-chloroethanol, and 30 g of potassium carbonate were added to 240 g of N,N-dimethylformamide, and then 2.4 g of tetrabutylammonium bromide was added. The temperature was raised to 110 °C and the reaction was carried out for 6 h. After cooling to room temperature, the reaction solution was added to 720 g of deionized water at 5 °C, and extracted three times with 240 g of dichloromethane each time. The organic phases were combined and washed successively with 720 g of 5% NaOH solution and 720 g of deionized water. After drying, it was concentrated under reduced pressure. The obtained crude product was separated by gradient elution on a silica gel column, and the eluent was removed by distillation under reduced pressure to obtain 1,5-bis(2-hydroxyethoxy)naphthalene;

[0044] (2) Under nitrogen protection, 30 g of pentaerythritol and 9 g of tetrahydrofuran were added to 240 g of a 2 mol / L NaOH solution to form solution A; 63 g of terephthaloyl chloride was added to 150 g of dichloromethane to form solution B; at 0 °C, solution B was added to solution A. After the addition, the temperature was raised to room temperature, and the reaction was carried out for 1 h. Then, 10% dilute hydrochloric acid was added to adjust the pH to neutral. The mixture was added to 300 g of methanol and stirred for 20 min. After filtration, washing, and drying, a carboxyl-terminated hyperbranched polyester was obtained;

[0045] (3) 210 g of terephthalic acid, 540 g of 1,4-butanediol, 45 g of 1,5-bis(2-hydroxyethoxy)naphthalene, and 3 g of tetrabutyl titanate were added to a reaction kettle. Under stirring, the temperature was raised to 170 °C and the reaction was carried out for 1 h. Then, the temperature was further raised to 230 °C and the pressure was reduced to 400 Pa, and the reaction was carried out for 2 h. After cooling to room temperature, 5% NaOH solution was added to adjust the pH to neutral. After filtration, washing, and drying, a low-shrinkage PBT intermediate was obtained;

[0046] (4) 500 g of the low-shrinkage PBT intermediate obtained in S1, 40 g of the carboxyl-terminated hyperbranched polyester, and 5 g of tetrabutyl titanate were added to a reaction kettle. Under stirring, the temperature was raised to 250 °C and the pressure was reduced to 30 Pa, and the reaction was carried out for 3 h. After cooling to room temperature, 3% NaOH solution was added to adjust the pH to neutral. After filtration, washing, and drying, a low-shrinkage PBT material was obtained;

[0047] (5) The low-shrinkage PBT material was added to an injection molding machine, and different mold cavities were filled through the injection molding machine. After pressure holding and cooling, demolding was carried out to obtain low-shrinkage PBT products of various shapes and uses; The set temperature of the rear section of the injection molding machine was: 230 °C, the middle section temperature was: 240 °C, the front section temperature was: 250 °C, the nozzle temperature was: 255 °C, the injection pressure was: 80 MPa, the pressure holding pressure was: 40 MPa, and the pressure holding time was: 15 s; The mold temperature was: 60 °C.

[0048] Example 2: A low-shrinkage PBT material and its preparation method, including the following process:

[0049] (1) Under nitrogen protection, 40 g of 1,5-naphthalenediol, 90 g of 2-chloroethanol, and 48 g of potassium carbonate were added to 400 g of N,N-dimethylformamide, and then 4 g of tetrabutylammonium bromide was added. The temperature was raised to 120 °C and the reaction was carried out for 7 h. After cooling to room temperature, the reaction solution was added to 1.2 Kg of deionized water at 5 °C, and extracted three times with 400 g of dichloromethane each time. The organic phases were combined and washed successively with 1.2 Kg of 5% NaOH solution and 1.2 Kg of deionized water. After drying, it was concentrated under reduced pressure. The obtained crude product was separated by gradient elution on a silica gel column, and the eluent was removed by distillation under reduced pressure to obtain 1,5-bis(2-hydroxyethoxy)naphthalene;

[0050] (2) Under nitrogen protection, 40 g of pentaerythritol and 20 g of tetrahydrofuran were added to 400 g of a 2 mol / L NaOH solution to form solution A; 88 g of terephthaloyl chloride was added to 280 g of dichloromethane to form solution B; at 3 °C, solution B was added to solution A. After the addition, the temperature was raised to room temperature and the reaction was carried out for 2 h. Then, 10% dilute hydrochloric acid was added to adjust the pH to neutral. The mixture was added to 480 g of methanol and stirred for 25 min. After filtration, washing, and drying, a terminal carboxyl hyperbranched polyester was obtained;

[0051] (3) 200 g of terephthalic acid, 500 g of 1,4-butanediol, 50 g of 1,5-bis(2-hydroxyethoxy)naphthalene, and 5 g of tetrabutyl titanate were added to a reaction kettle. Under stirring, the temperature was raised to 180 °C and the reaction was carried out for 2 h. Then, the temperature was further raised to 240 °C and the pressure was reduced to 500 Pa, and the reaction was carried out for 2.5 h. After cooling to room temperature, 5% NaOH solution was added to adjust the pH to neutral. After filtration, washing, and drying, a low-shrinkage PBT intermediate was obtained;

[0052] (4) 600 g of the low-shrinkage PBT intermediate obtained in S1, 60 g of the terminal carboxyl hyperbranched polyester, and 12 g of tetrabutyl titanate were added to a reaction kettle. Under stirring, the temperature was raised to 255 °C and the pressure was reduced to 40 Pa, and the reaction was carried out for 4 h. After cooling to room temperature, 3% NaOH solution was added to adjust the pH to neutral. After filtration, washing, and drying, a low-shrinkage PBT material was obtained;

[0053] (5) The low-shrinkage PBT material was added to an injection molding machine and filled into different mold cavities through the injection molding machine. After pressure holding and cooling, demolding was carried out to obtain low-shrinkage PBT products of various shapes and uses; the set temperature of the rear section of the injection molding machine was 235 °C, the middle section temperature was 245 °C, the front section temperature was 255 °C, the nozzle temperature was 260 °C, the injection pressure was 90 MPa, the pressure holding pressure was 45 MPa, the pressure holding time was 20 s; the mold temperature was 70 °C.

[0054] Example 3: A low-shrinkage PBT material and its preparation method, including the following process:

[0055] (1) Under nitrogen protection, 30 g of 1,5-naphthalenediol, 75 g of 2-chloroethanol, and 42 g of potassium carbonate were added to 360 g of N,N-dimethylformamide, and then 4.2 g of tetrabutylammonium bromide was added. The temperature was raised to 130 °C and the reaction was carried out for 8 h. After cooling to room temperature, the reaction solution was added to 1.08 Kg of deionized water at 5 °C. Each time, it was extracted three times with 360 g of dichloromethane. The organic phases were combined and washed successively with 1.08 Kg of 5% NaOH solution and 1.08 Kg of deionized water. After drying, it was concentrated under reduced pressure. The obtained crude product was separated by gradient elution on a silica gel column, and the eluent was removed by distillation under reduced pressure to obtain 1,5-bis(2-hydroxyethoxy)naphthalene;

[0056] (2) Under nitrogen protection, 50 g of pentaerythritol and 35 g of tetrahydrofuran were added to 600 g of a 2 mol / L NaOH solution to form solution A; 115 g of terephthaloyl chloride was added to 450 g of dichloromethane to form solution B; at 5 °C, solution B was added to solution A, and after the addition, the temperature was raised to room temperature. The reaction was carried out for 3 h, 10% dilute hydrochloric acid was added to adjust the pH to neutral, and it was stirred in 700 g of methanol for 30 min. After filtration, washing, and drying, a carboxyl-terminated hyperbranched polyester was obtained;

[0057] (3) 180 g of terephthalic acid, 440 g of 1,4-butanediol, 50 g of 1,5-bis(2-hydroxyethoxy)naphthalene, and 6 g of tetrabutyl titanate were added to a reaction kettle. Under stirring, the temperature was raised to 190 °C and the reaction was carried out for 3 h. Then the temperature was further raised to 250 °C and the pressure was reduced to 600 Pa, and the reaction was carried out for 3 h. After cooling to room temperature, 5% NaOH solution was added to adjust the pH to neutral. After filtration, washing, and drying, a low-shrinkage PBT intermediate was obtained;

[0058] (4) 600 g of the low-shrinkage PBT intermediate obtained in S1, 72 g of the carboxyl-terminated hyperbranched polyester, and 20 g of tetrabutyl titanate were added to a reaction kettle. Under stirring, the temperature was raised to 260 °C and the pressure was reduced to 50 Pa, and the reaction was carried out for 5 h. After cooling to room temperature, 3% NaOH solution was added to adjust the pH to neutral. After filtration, washing, and drying, a low-shrinkage PBT material was obtained;

[0059] (5) The low-shrinkage PBT material was added to an injection molding machine, and different mold cavities were filled through the injection molding machine. After pressure holding and cooling, demolding was carried out to obtain low-shrinkage PBT products of various shapes and uses; the set temperature of the rear section of the injection molding machine was 240 °C, the middle section temperature was 250 °C, the front section temperature was 260 °C, the nozzle temperature was 265 °C, the injection pressure was 100 MPa, the pressure holding pressure was 50 MPa, the pressure holding time was 25 s; the mold temperature was 80 °C.

[0060] Comparative Example 1: The difference between Comparative Example 1 and Example 2 is that 1,5-bis(2-hydroxyethoxy)naphthalene was not added during the preparation process of the low-shrinkage PBT material. The specific process is as follows: A low-shrinkage PBT material and its preparation method include the following process:

[0061] (1) Under nitrogen protection, 40 g of pentaerythritol and 20 g of tetrahydrofuran were added to 400 g of a 2 mol / L NaOH solution to form solution A; 88 g of terephthaloyl chloride was added to 280 g of dichloromethane to form solution B; at 3 °C, solution B was added to solution A, and after the addition, the temperature was raised to room temperature. The reaction was carried out for 2 h, 10% dilute hydrochloric acid was added to adjust the pH to neutral, and it was stirred in 480 g of methanol for 25 min. After filtration, washing, and drying, a carboxyl-terminated hyperbranched polyester was obtained;

[0062] (2) Add 200 g of terephthalic acid, 500 g of 1,4-butanediol, and 5 g of tetrabutyl titanate into a reaction kettle. Under stirring, heat up to 180 °C and react for 2 h. Then continue to heat up to 240 °C and reduce the pressure to 500 Pa, and react for 2.5 h. Cool to room temperature, add 5% NaOH solution to adjust the pH to neutral, filter, wash, and dry to obtain the PBT intermediate;

[0063] (3) Add 600 g of the PBT intermediate obtained in S1, 60 g of carboxyl-terminated hyperbranched polyester, and 12 g of tetrabutyl titanate into a reaction kettle. Under stirring, heat up to 255 °C and reduce the pressure to 40 Pa, and react for 4 h. Cool to room temperature, add 3% NaOH solution to adjust the pH to neutral, filter, wash, and dry to obtain the low-shrinkage PBT material;

[0064] (4) Add the low-shrinkage PBT material into an injection molding machine, fill different mold cavities through the injection molding machine, and demold after pressure holding and cooling to obtain low-shrinkage PBT products of various shapes and uses; The set temperature of the rear section of the injection molding machine is: 235 °C, the middle section temperature is: 245 °C, the front section temperature is: 255 °C, the nozzle temperature is: 260 °C, the injection pressure is: 90 MPa, the pressure holding pressure is: 45 MPa, and the pressure holding time is: 20 s; The mold temperature is: 70 °C.

[0065] Comparative Example 2: The difference between Comparative Example 2 and Example 2 is that: in the preparation process of the low-shrinkage PBT material, carboxyl-terminated hyperbranched polyester is not added. The specific process is as follows: A low-shrinkage PBT material and its preparation method include the following processes:

[0066] (1) Under nitrogen protection, add 40 g of 1,5-naphthalenediol, 90 g of 2-chloroethanol, and 48 g of potassium carbonate into 400 g of N,N-dimethylformamide, then add 4 g of tetrabutylammonium bromide, heat up to 120 °C, and react for 7 h. After cooling to room temperature, add the reaction solution into 1.2 Kg of deionized water at 5 °C, extract three times with 400 g of dichloromethane each time, combine the organic phases, wash successively with 1.2 Kg of 5% NaOH solution and 1.2 Kg of deionized water, dry, concentrate under reduced pressure, obtain the crude product, separate by gradient elution on a silica gel column chromatography, and distill off the eluent under reduced pressure to obtain 1,5-bis(2-hydroxyethoxy)naphthalene;

[0067] (2) Add 200 g of terephthalic acid, 500 g of 1,4-butanediol, 50 g of 1,5-bis(2-hydroxyethoxy)naphthalene, and 5 g of tetrabutyl titanate into a reaction kettle. Under stirring, heat up to 180 °C and react for 2 h. Then continue to heat up to 240 °C and reduce the pressure to 500 Pa, and react for 2.5 h. Cool to room temperature, add 5% NaOH solution to adjust the pH to neutral, filter, wash, and dry to obtain the low-shrinkage PBT material;

[0068] (3) Add the low-shrinkage PBT material into an injection molding machine, fill different mold cavities through the injection molding machine, and demold after pressure holding and cooling to obtain low-shrinkage PBT products of various shapes and uses; the set temperature of the rear section of the injection molding machine is 235°C, the middle section temperature is 245°C, the front section temperature is 255°C, the nozzle temperature is 260°C, the injection pressure is 90 MPa, the pressure holding pressure is 45 MPa, and the pressure holding time is 20 s; the mold temperature is 70°C.

[0069] Comparative Example 3: The difference between Comparative Example 3 and Example 2 is that the weight ratio of the low-shrinkage PBT intermediate to the carboxyl-terminated hyperbranched polyester is 1:0.03. The specific process is as follows: A low-shrinkage PBT material and its preparation method include the following processes:

[0070] (1) Under nitrogen protection, add 40 g of 1,5-naphthalenediol, 90 g of 2-chloroethanol, and 48 g of potassium carbonate to 400 g of N,N-dimethylformamide, then add 4 g of tetrabutylammonium bromide, heat to 120°C, react for 7 h, cool to room temperature, add the reaction solution to 1.2 Kg of deionized water at 5°C, extract three times with 400 g of dichloromethane each time, combine the organic phases, wash successively with 1.2 Kg of 5% NaOH solution and 1.2 Kg of deionized water, dry, concentrate under reduced pressure, obtain the crude product, separate by gradient elution on a silica gel column chromatography, and distill off the eluent under reduced pressure to obtain 1,5-bis(2-hydroxyethoxy)naphthalene;

[0071] (2) Under nitrogen protection, add 40 g of pentaerythritol and 20 g of tetrahydrofuran to 400 g of 2 mol / L NaOH solution to form solution A; add 88 g of terephthaloyl chloride to 280 g of dichloromethane to form solution B; at 3°C, add solution B to solution A, after addition, heat to room temperature, react for 2 h, add 10% dilute hydrochloric acid to adjust the pH to neutral, add to 480 g of methanol and stir for 25 min, filter, wash, and dry to obtain the carboxyl-terminated hyperbranched polyester;

[0072] (3) Add 200 g of terephthalic acid, 500 g of 1,4-butanediol, 50 g of 1,5-bis(2-hydroxyethoxy)naphthalene, and 5 g of tetrabutyl titanate to a reaction kettle, stir, heat to 180°C and react for 2 h, continue to heat to 240°C and reduce the pressure to 500 Pa, react for 2.5 h, cool to room temperature, add 5% NaOH solution to adjust the pH to neutral, filter, wash, and dry to obtain the low-shrinkage PBT intermediate;

[0073] (4) Add 600 g of low-shrinkage PBT intermediate, 18 g of carboxyl-terminated hyperbranched polyester, and 12 g of tetrabutyl titanate obtained in S1 into a reaction kettle. While stirring, heat up to 255 °C and reduce the pressure to 40 Pa. React for 4 h, cool to room temperature, add a 3% NaOH solution to adjust the pH to neutral, filter, wash, and dry to obtain the low-shrinkage PBT material;

[0074] (5) Add the low-shrinkage PBT material into an injection molding machine, fill different mold cavities through the injection molding machine, and demold after pressure holding and cooling to obtain low-shrinkage PBT products of various shapes and uses; The set temperature of the rear section of the injection molding machine is: 235 °C, the middle section temperature is: 245 °C, the front section temperature is: 255 °C, the nozzle temperature is: 260 °C, the injection pressure is: 90 MPa, the pressure holding pressure is: 45 MPa, and the pressure holding time is: 20 s; The mold temperature is: 70 °C.

[0075] Comparative Example 4: The difference between Comparative Example 4 and Example 2 is that the weight ratio of the low-shrinkage PBT intermediate and the carboxyl-terminated hyperbranched polyester is 1:0.2. The specific process is as follows: A low-shrinkage PBT material and its preparation method include the following process:

[0076] (1) Under nitrogen protection, add 40 g of 1,5-naphthalenediol, 90 g of 2-chloroethanol, and 48 g of potassium carbonate into 400 g of N,N-dimethylformamide, then add 4 g of tetrabutylammonium bromide, heat up to 120 °C, react for 7 h, after cooling to room temperature, add the reaction solution into 1.2 Kg of deionized water at 5 °C, extract three times with 400 g of dichloromethane each time, combine the organic phases, wash successively with 1.2 Kg of a 5% NaOH solution and 1.2 Kg of deionized water, dry, concentrate under reduced pressure to obtain the crude product, separate by gradient elution on a silica gel column chromatography, and distill off the eluent under reduced pressure to obtain 1,5-bis(2-hydroxyethoxy)naphthalene;

[0077] (2) Under nitrogen protection, add 80 g of pentaerythritol and 40 g of tetrahydrofuran into 800 g of a 2 mol / L NaOH solution to form solution A; add 176 g of terephthaloyl chloride into 560 g of dichloromethane to form solution B; at 3 °C, add solution B into solution A, after adding, heat up to room temperature, react for 2 h, add a 10% dilute hydrochloric acid to adjust the pH to neutral, add it into 960 g of methanol and stir for 25 min, filter, wash, and dry to obtain the carboxyl-terminated hyperbranched polyester;

[0078] (3) Add 200 g of terephthalic acid, 500 g of 1,4-butanediol, 50 g of 1,5-bis(2-hydroxyethoxy)naphthalene, and 5 g of tetrabutyl titanate into a reaction kettle. Under stirring, heat up to 180 °C and react for 2 h. Then continue to heat up to 240 °C and reduce the pressure to 500 Pa, and react for 2.5 h. Cool to room temperature, add 5% NaOH solution to adjust the pH to neutral, filter, wash, and dry to obtain a low-shrinkage PBT intermediate;

[0079] (4) Add 600 g of the low-shrinkage PBT intermediate obtained in S1, 120 g of carboxyl-terminated hyperbranched polyester, and 12 g of tetrabutyl titanate into a reaction kettle. Under stirring, heat up to 255 °C and reduce the pressure to 40 Pa, and react for 4 h. Cool to room temperature, add 3% NaOH solution to adjust the pH to neutral, filter, wash, and dry to obtain a low-shrinkage PBT material;

[0080] (5) Add the low-shrinkage PBT material into an injection molding machine, fill different mold cavities through the injection molding machine, and demold after pressure holding and cooling to obtain low-shrinkage PBT products with various shapes and uses; The set temperature of the rear section of the injection molding machine is: 235 °C, the middle section temperature is: 245 °C, the front section temperature is: 255 °C, the nozzle temperature is: 260 °C, the injection pressure is: 90 MPa, the pressure holding pressure is: 45 MPa, the pressure holding time is: 20 s; The mold temperature is: 70 °C.

[0081] Comparative Example 5: The difference between Comparative Example 5 and Example 2 is that the PBT material used for injection molding is a directly purchased PBT material, purchased from Shenzhen Yuanbang New Materials Co., Ltd., model: CE2055 NC010. The specific preparation process is as follows: Add the purchased PBT material (model: CE2055 NC010) into an injection molding machine, fill different mold cavities through the injection molding machine, and demold after pressure holding and cooling to obtain low-shrinkage PBT products with various shapes and uses; The set temperature of the rear section of the injection molding machine is: 235 °C, the middle section temperature is: 245 °C, the front section temperature is: 255 °C, the nozzle temperature is: 260 °C, the injection pressure is: 90 MPa, the pressure holding pressure is: 45 MPa, the pressure holding time is: 20 s; The mold temperature is: 70 °C.

[0082] Comparative Example 6: The difference between Comparative Example 6 and Example 2 is that the carboxyl-terminated hyperbranched polyester and the low-shrinkage PBT intermediate are used to prepare the low-shrinkage PBT material by blending. The specific preparation process is as follows: A low-shrinkage PBT material and its preparation method include the following process:

[0083] (1) Under nitrogen protection, 40 g of 1,5-naphthalenediol, 90 g of 2-chloroethanol, and 48 g of potassium carbonate were added to 400 g of N,N-dimethylformamide, and then 4 g of tetrabutylammonium bromide was added. The temperature was raised to 120 °C and the reaction was carried out for 7 h. After cooling to room temperature, the reaction solution was added to 1.2 Kg of deionized water at 5 °C, and extracted three times with 400 g of dichloromethane each time. The organic phases were combined and washed successively with 1.2 Kg of 5% NaOH solution and 1.2 Kg of deionized water. After drying, it was concentrated under reduced pressure. The obtained crude product was separated by gradient elution on a silica gel column, and the eluent was removed by distillation under reduced pressure to obtain 1,5-bis(2-hydroxyethoxy)naphthalene;

[0084] (2) Under nitrogen protection, 40 g of pentaerythritol and 20 g of tetrahydrofuran were added to 400 g of 2 mol / L NaOH solution to form solution A; 88 g of terephthaloyl chloride was added to 280 g of dichloromethane to form solution B; at 3 °C, solution B was added to solution A. After the addition was completed, the temperature was raised to room temperature and the reaction was carried out for 2 h. 10% dilute hydrochloric acid was added to adjust the pH to neutral, and then it was added to 480 g of methanol and stirred for 25 min. After filtration, washing, and drying, a carboxyl-terminated hyperbranched polyester was obtained;

[0085] (3) 200 g of terephthalic acid, 500 g of 1,4-butanediol, 50 g of 1,5-bis(2-hydroxyethoxy)naphthalene, and 5 g of tetrabutyl titanate were added to a reaction kettle. Under stirring, the temperature was raised to 180 °C and the reaction was carried out for 2 h. Then the temperature was further raised to 240 °C and the pressure was reduced to 500 Pa, and the reaction was carried out for 2.5 h. After cooling to room temperature, 5% NaOH solution was added to adjust the pH to neutral. After filtration, washing, and drying, a low-shrinkage PBT intermediate was obtained;

[0086] (4) 600 g of the low-shrinkage PBT intermediate obtained in S1 and 60 g of the carboxyl-terminated hyperbranched polyester were added to a twin-screw extruder. The temperature gradient of the extruder was set as follows: zone 1: 230 - 240 °C, zone 2: 240 - 250 °C, zone 3: 250 - 260 °C, die head temperature: 255 - 265 °C, screw speed: 300 - 400 rpm, and melt blending was carried out for 10 - 15 min. The blend was water-cooled and pelletized to obtain a low-shrinkage PBT material;

[0087] (5) The low-shrinkage PBT material was added to an injection molding machine, and different mold cavities were filled through the injection molding machine. After pressure holding and cooling, the mold was removed to obtain low-shrinkage PBT products of various shapes and uses; The temperature of the rear section of the injection molding machine was set at 235 °C, the middle section temperature was 245 °C, the front section temperature was 255 °C, the nozzle temperature was 260 °C, the injection pressure was 90 MPa, the pressure holding pressure was 45 MPa, the pressure holding time was 20 s; the mold temperature was 70 °C.

[0088] Performance test:

[0089] 1. Anti-shrinkage test: The low-shrinkage PBT materials prepared in Examples 1-3 and Comparative Examples 1-6 were used to prepare test specimens according to the test standard of GB / T39818-2021, and the shrinkage rate test was carried out. The experimental results are shown in Table 1.

[0090] 2. Mechanical property test: The low-shrinkage PBT materials prepared in Examples 1-3 and Comparative Examples 1-6 were used to prepare test specimens according to the test standards of ASTM D638 and ASTM D790, and the mechanical property test was carried out. The tensile strength and flexural strength of the specimens were recorded. The experimental results are shown in Table 1.

[0091] 3. Heat distortion temperature test: The low-shrinkage PBT materials prepared in Examples 1-3 and Comparative Examples 1-6 were used to prepare test specimens according to the test standard of GB / T1634.2-2019, and the heat distortion temperature of the test specimens under the flexural stress values of 0.45 MPa and 1.8 MPa was tested. The experimental results are shown in Table 1.

[0092] 4. Water absorption test: The low-shrinkage PBT materials prepared in Examples 1-3 and Comparative Examples 1-6 were used to prepare test specimens according to the test standard of GB / T 1034-2008, and the water absorption test was carried out at 23 °C for 24 h. The water absorption rate was calculated. The experimental results are shown in Table 1.

[0093] Table 1 Test results

[0094]

[0095] Data analysis:

[0096] It can be seen from the data in Table 1 that the low-shrinkage PBT materials prepared in Examples 1-3 by the present invention have good anti-shrinkage performance and mechanical properties, and the change of heat distortion temperature under different pressures is small, which indicates that the materials have certain high-temperature stability and low water absorption rate. Among them, Example 2 has the best comprehensive performance.

[0097] As can be seen from the data in Table 1, the performance of Comparative Example 1 has decreased compared to that of Example 2. This may be because 1,5-bis(2-hydroxyethoxy)naphthalene was added in Example 2. As a rigid group, the naphthalene ring inhibits the excessive crystallization of the molecular chain, reduces the volume shrinkage during material forming. At the same time, the rigid skeleton of the naphthalene ring can enhance the intermolecular force through π-π conjugation, forming a more uniform microstructure, thus improving the mechanical properties of the material. The planar structure of the naphthalene ring can also increase the crystallization temperature of the material, enhance the high-temperature stability. At high temperatures, the material molecules are not prone to slip, enhancing the heat distortion temperature of the material under different pressures. Finally, the rigid planar structure of the naphthalene ring helps the molecules to be closely and orderly arranged, forming a relatively dense structure, reducing the channels for water molecules to enter. If the naphthalene ring is missing in the material, the packing of molecules becomes loose, and the intermolecular voids increase, providing more space for the entry of water molecules, thereby increasing the water absorption rate of the material.

[0098] As can be seen from the data in Table 1, there are differences in the performance of Comparative Example 2 compared to Example 2. This may be because the terminal carboxyl hyperbranched polyester in Example 2 hinders the regular arrangement of PBT molecular chains through its branched structure, inhibiting excessive crystal growth, thereby reducing the shrinkage rate. When not added, the crystallinity of PBT increases and the shrinkage rate rises. At the same time, the three-dimensional network structure of the hyperbranched polyester can enhance the mechanical properties of the material through physical crosslinking. After deletion, the internal defects of the material increase, and stress concentration leads to a decrease in strength. The hyperbranched structure can also enhance the high-temperature creep resistance of the material and increase the heat distortion temperature of the material. When this structure is missing, the high-temperature creep resistance of the material decreases, resulting in a decrease in the heat distortion temperature. Finally, the terminal carboxyl group of the hyperbranched polyester can form hydrogen bonds with the terminal hydroxyl group of PBT, reducing the number of free hydroxyl groups, thereby reducing the water absorption rate and offsetting the problem of increased water absorption rate caused by the reduction of the material's crystallinity due to the hyperbranched structure.

[0099] As can be seen from the data in Table 1, the performance of Comparative Example 3 is inferior to that of Example 2. This may be because the branched structure of the hyperbranched polyester needs to reach a critical concentration to effectively inhibit crystallization. When the addition amount is insufficient, its restrictive effect on molecular chain movement weakens, the crystallinity increases, and the shrinkage rate increases. The branch points of the hyperbranched polyester can serve as stress dispersion centers to enhance the toughness of the material. At low concentrations, the stress dispersion effect is insufficient, resulting in a decrease in strength. The hyperbranched structure can improve the thermal stability of the material through physical crosslinking. When the addition amount is insufficient, the crosslinking density is low, and the molecular chains are prone to slip at high temperatures, resulting in a decrease in heat resistance. Finally, due to the insufficient branched structure, the number of exposed free hydroxyl groups in the material increases, and it cannot offset the problem of increased water absorption rate caused by the reduction of the material's crystallinity due to the hyperbranched structure, resulting in an increase in the water absorption rate of the material.

[0100] As can be seen from the data in Table 1, although Comparative Example 4 is slightly superior to Example 2 in water absorption rate, it is inferior to Example 2 in other properties. This may be because the addition of excessive amounts of terminal carboxyl hyperbranched polyester results in too high a crosslinking degree, a decrease in Tg, and a tendency for the material to transform into a rubbery state. The shrinkage rate of the material increases significantly. The soft structural characteristics cause an increase in the tensile strength of the material, a decrease in the flexural strength, and a decrease in the heat distortion temperature. For the corresponding water absorption rate, due to the increase in the crosslinked structure, the material becomes denser, resulting in a decrease in the water absorption rate.

[0101] As can be seen from the data in Table 1, the unmodified PBT material used in Comparative Example 5 has an extremely low water absorption rate due to its high crystallinity. However, the high crystallinity brings a high shrinkage rate. At the same time, the lack of the rigid structure of the naphthalene ring and the modification effect brought by the hyperbranched crosslinked structure results in inferior mechanical properties compared to Example 2. Finally, due to the lack of the additional support of the rigid structure and the crosslinked structure for the material under high temperature and high pressure, the thermal stability of the material decreases.

[0102] As can be seen from the data in Table 1, the PBT material prepared in Comparative Example 6 fails to achieve a balance among various properties. This may be because the blending method weakens the interfacial bonding force of the material and reduces the mechanical properties; the lack of chemical crosslinking and low crosslinking density may reduce the crystallinity of the material, but the heat distortion temperature and shrinkage rate are still not well controlled; physical blending reduces the crystallinity of the material, causing the molecular chains to be relatively loose. Coupled with the residual polar groups of the unreacted terminal carboxyl hyperbranched polyester, the water absorption rate surges; the chemical crosslinking used in Example 2 increases the density and uniform distribution of the molecular chains to a certain extent, so all aspects of the properties can maintain a good balance.

[0103] Those of ordinary skill in the art should understand that: the discussion of any above embodiments is only exemplary and is not intended to imply that the scope of the present invention is limited to these examples; under the concept of the present invention, the technical features in the above embodiments or different embodiments can also be combined, and the steps can be implemented in any order, and there are many other variations in different aspects of the present invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A low-shrinkage PBT material, characterized in that, It is prepared from the following raw materials: 1,5-bis(2-hydroxyethoxy)naphthalene, carboxyl-terminated hyperbranched polyester, terephthalic acid, 1,4-butanediol, tetrabutyl titanate; The preparation process of the 1,5-bis(2-hydroxyethoxy)naphthalene is as follows: Under nitrogen protection, 1,5-naphthalenediol, 2-chloroethanol, and potassium carbonate are added to N,N-dimethylformamide, and then tetrabutylammonium bromide is added. The temperature is raised to 110-130 °C and the reaction is carried out for 6-8 h. After cooling to room temperature, the reaction solution is added to deionized water at 5 °C, and extracted three times with dichloromethane. The organic phases are combined and washed successively with a 5% NaOH solution and deionized water. After drying, it is concentrated under reduced pressure to obtain a crude product, which is separated by gradient elution on a silica gel column, and the eluent is removed by vacuum distillation to obtain 1,5-bis(2-hydroxyethoxy)naphthalene; The preparation process of the carboxyl-terminated hyperbranched polyester is as follows: Under nitrogen protection, pentaerythritol and tetrahydrofuran are added to a 2 mol / L NaOH solution to form solution A; terephthaloyl chloride is added to dichloromethane to form solution B; at 0-5 °C, solution B is added to solution A. After the addition is complete, the temperature is raised to room temperature and the reaction is carried out for 1-3 h. Dilute hydrochloric acid is added to adjust the pH to neutral, and it is stirred in methanol for 20-30 min. After filtration, washing, and drying, the carboxyl-terminated hyperbranched polyester is obtained.

2. The low-shrinkage PBT material according to claim 1, wherein The weight ratio of the 1,5-naphthalenediol, 2-chloroethanol, potassium carbonate, tetrabutylammonium bromide, and N,N-dimethylformamide is 1:2-2.5:1-1.4:0.08-0.12:8-12.

3. The low-shrinkage PBT material according to claim 1, wherein The weight ratio of the deionized water at 5 °C and N,N-dimethylformamide is 3:1; extracting three times with dichloromethane means that the weight of dichloromethane used for each extraction is one-third of the weight of the deionized water at 5 °C, and it is extracted three times; the weight ratio of the 5% NaOH solution, deionized water, and deionized water at 5 °C is 1:1:

1.

4. The low-shrinkage PBT material according to claim 1, wherein, The gradient elution separation refers to using the gradient elution method, and the volume ratio of petroleum ether and ethyl acetate in each step of the eluent is successively from 1:0, 20:1, 10:1 to 5:

1.

5. The low-shrinkage PBT material according to claim 1, wherein The weight ratio of the pentaerythritol, tetrahydrofuran, 2 mol / L NaOH, terephthaloyl chloride, dichloromethane, and methanol is 1:0.3-0.7:8-12:2.1-2.3:5-9:10-14, and the dilute hydrochloric acid refers to a 10% hydrochloric acid solution.

6. The preparation method of the low-shrinkage PBT material according to any one of claims 1-5, characterized in that, It includes the following steps: S1. Add terephthalic acid, 1,4-butanediol, 1,5-bis(2-hydroxyethoxy)naphthalene, and tetrabutyl titanate to the reaction kettle. Under stirring, the temperature is raised to 170-190 °C and the reaction is carried out for 1-3 h. Then the temperature is further raised to 230-250 °C and the pressure is reduced to 400-600 Pa, and the reaction is carried out for 2-3 h. After cooling to room temperature, a 5% NaOH solution is added to adjust the pH to neutral. After filtration, washing, and drying, a low-shrinkage PBT intermediate is obtained; S2. Add the low-shrinkage PBT intermediate, carboxyl-terminated hyperbranched polyester, and tetrabutyl titanate obtained in S1 into a reaction kettle, heat up to 250 - 260 °C under stirring and reduce the pressure to 30 - 50 Pa, react for 3 - 5 h, cool to room temperature, add a 3% NaOH solution to adjust the pH to neutral, filter, wash, and dry to obtain the low-shrinkage PBT material. S3. Add the low-shrinkage PBT material into an injection molding machine, set the parameters, fill different mold cavities through the injection molding machine, and demold after pressure holding and cooling to obtain low-shrinkage PBT products of various shapes and uses.

7. The preparation method of the low-shrinkage PBT material according to claim 6, characterized in that, In the said S1, the weight ratio of terephthalic acid, 1,4-butanediol, 1,5-bis(2-hydroxyethoxy)naphthalene, and tetrabutyl titanate is 0.7 - 0.9:1.8 - 2.2:0.15 - 0.25:0.01 - 0.

03.

8. The preparation method of the low-shrinkage PBT material according to claim 6, wherein, In the said S2, the weight ratio of the low-shrinkage PBT intermediate, carboxyl-terminated hyperbranched polyester, and tetrabutyl titanate is 1:0.08 - 0.12:0.01 - 0.

03.

9. The preparation method of the low-shrinkage PBT material according to claim 6, characterized in that, In the said S3, setting the parameters refers to setting the temperature of the rear section of the injection molding machine: 230 - 240 °C, the temperature of the middle section: 240 - 250 °C, the temperature of the front section: 250 - 260 °C, the nozzle temperature: 255 - 265 °C, the injection pressure: 80 - 100 MPa, the pressure holding pressure: 40 - 50 MPa, the pressure holding time: 15 - 25 s; the mold temperature: 60 - 80 °C.

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