Low-molecular-weight polyester polyol as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of high polymer materials, and discloses low-molecular-weight polyester polyol as well as a preparation method and application thereof. The preparation method of the low-molecular-weight polyester polyol comprises the following steps: S1, mixing polyfunctional alcohol, cyclic anhydride and an antioxidant, and reacting to obtain a prepolymer; and S2, adding glycidyl tertiary carboxylic ester and a catalyst into the prepolymer, reacting, and adding a diluent to obtain the low-molecular-weight polyester polyol. Through precise design of anhydride types, polyol structures and synthesis processes, the molecular chain structure design can be effectively regulated and controlled, energy consumption and side reactions in the synthesis process are remarkably reduced, VOC emission is strictly controlled, and finally the low-molecular-weight polyester polyol which is low in viscosity, low in molecular weight distribution, high in reaction activity and environmentally friendly is obtained. And the polyurethane coating prepared from the series of polyols shows comprehensive and balanced excellent performance.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a low molecular weight polyester polyol, its preparation method, and its application. Background Technology

[0002] Polyurethane materials, with their tunable mechanical properties, excellent corrosion resistance, high-temperature resistance, abrasion resistance, and good processing flexibility, have become indispensable key materials in modern industrial fields such as aerospace, construction, automotive, electronics, textiles, and medicine. Polyester polyols, as one of the core raw materials for synthesizing polyurethane, typically contain multiple hydroxyl groups in their molecular structure, enabling them to react with isocyanates to form polyester-type polyurethanes. Due to the large number of highly polar ester groups in the polyester chain segments, these polyurethane materials exhibit high cohesive strength and adhesion, thus demonstrating superior abrasion resistance, chemical corrosion resistance, high elasticity, aging resistance, solvent resistance, and mechanical strength.

[0003] Traditional synthesis of polyester polyols often involves high-temperature polycondensation reactions of alcohols with limited functionality and acid anhydrides. This method frequently results in a wide molecular weight distribution and difficulty in precisely controlling the branching degree of the molecular chains, thus failing to meet the precise microstructural requirements of high-performance polyurethane materials. Particularly in environmentally friendly coatings and adhesives systems that pursue high solids content and low volatile organic compounds (VOCs), even higher demands are placed on the low viscosity, low VOC content, and overall coating performance of polyester polyols.

[0004] In existing technologies, there have been some attempts to develop low molecular weight polyester polyols to adapt to high solids content systems. However, the synthesis and application of low molecular weight polyester polyols still face many challenges: First, in terms of synthesis routes, traditional polycondensation processes are extremely sensitive to raw material ratios, reaction temperatures, and catalyst types, easily leading to an increase in side reactions, such as transesterification and thermal oxidative degradation, resulting in a further broadening of the molecular weight distribution and affecting the batch stability and performance consistency of the final product. Second, existing low molecular weight polyester polyols often contain unreacted monomers or low-boiling-point small-molecule byproducts. These residues not only increase VOC emissions from the system but may also cause defects during subsequent film formation or curing, affecting the coating's density, gloss, and chemical resistance. In addition, although existing low molecular weight polyester polyols have improved in terms of viscosity and hardness, they often struggle to achieve an ideal balance in key performance indicators such as VOC content, drying time, gloss, and adhesion.

[0005] Therefore, there is an urgent need to develop a novel low molecular weight polyester polyol and its synthesis method, which can effectively control the molecular chain structure design, significantly reduce energy consumption and side reactions in the synthesis process, strictly control VOC emissions, and ultimately obtain a novel polyester polyol with low viscosity, narrow molecular weight distribution, high reactivity, excellent end-use performance and environmental friendliness, so as to broaden its application prospects in high-end environmentally friendly polyurethane materials. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a low molecular weight polyester polyol, its preparation method and application.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a method for preparing a low molecular weight polyester polyol, comprising the following steps: S1. Mix a multifunctional alcohol, a cyclic anhydride and an antioxidant, and react to obtain a prepolymer; the cyclic anhydride includes alicyclic anhydrides and dodecenyl succinic anhydride in a molar ratio of 1:(0.6-1.8).

[0008] S2. Add glycidyl tert-carbonate and catalyst to the prepolymer, react, add diluent, and obtain low molecular weight polyester polyol.

[0009] This invention provides a method for preparing low molecular weight polyester polyols. Through precise design of the type of acid anhydride, the structure of the polyol, and the synthesis process, effective control is achieved in the molecular chain structure design, significantly reducing energy consumption and side reactions during the synthesis process, strictly controlling VOC emissions, and ultimately obtaining low molecular weight polyester polyols with low viscosity, low molecular weight distribution, high reactivity, and environmental friendliness. First, in the prepolymer construction stage, the ring-opening polymerization of cyclic acid anhydrides directly constructs the main molecular chain of the polyester. This reaction does not produce small molecule byproducts such as water, fundamentally ensuring the low VOC characteristics of the final system. Moreover, the alicyclic structure is introduced into the main chain, giving the polymer skeleton inherent rigidity and good heat resistance. Second, the multifunctional alcohol, as a co-reacting monomer, can initiate branching reactions through multiple hydroxyl sites. This not only effectively limits the unlimited growth of the molecular chain, precisely controls the molecular weight and achieves a narrow distribution, but also inhibits crystallization by disrupting the regularity of the molecular chain through side chain groups. This allows the low molecular weight polyester polyol to obtain the required rigidity while maintaining low viscosity and excellent processing performance. Subsequently, during the end-capping modification stage, the epoxy groups of glycidyl tert-carbonate react with the carboxyl groups at the end of the prepolymer chain to generate a stable β-hydroxy ester structure, which significantly reduces the acid value of the final product, avoids side reactions caused by residual carboxyl groups in subsequent polyurethane synthesis, and improves storage stability. Furthermore, the highly branched structure of the tert-carbonate groups of glycidyl tert-carbonate forms a dense three-dimensional shielding layer at the end of the polyester molecular chain. This protective layer physically blocks the attack of water molecules on the ester bonds through a strong steric hindrance effect, significantly improving the hydrolysis resistance of the polyester polyol and its final coating film.

[0010] Therefore, this invention achieves precise control over both molecular structure and product performance through a stepwise reaction design of a ternary synergistic system involving ring-opening of cyclic anhydrides, branching of polyfunctional alcohols, and end-capping with glycidyl tert-carbonate. This ultimately leads to the successful synthesis of a low-molecular-weight polyester polyol with low viscosity, narrow distribution, low acid value, and high stability. This product is perfectly suited for high-end polyurethane applications requiring weather resistance, flexibility, and extremely low VOC content. Furthermore, the basic raw materials used throughout the preparation process are standardized and widely commercialized products. This design significantly reduces the economic cost barrier to implementing this technology, providing a solid foundation for its industrialization.

[0011] In a preferred embodiment of the method for preparing the low molecular weight polyester polyol of the present invention, the molar ratio of the alicyclic anhydride and the dodecenyl succinic anhydride is 1:(1-1.2).

[0012] In a preferred embodiment of the method for preparing the low molecular weight polyester polyol of the present invention, the molar ratio of the hydroxyl group of the polyfunctional alcohol, the anhydride group of the cyclic anhydride, and the epoxy group of the glycidyl tert-carbonate is 1:(0.5-2):(1-3); and / or, the mass of the antioxidant is 0.02%-0.06% of the total mass of the raw materials; and / or, the mass of the catalyst is 0.03%-0.06% of the total mass of the raw materials; and / or, the mass of the diluent is 10%-30% of the total mass of the raw materials.

[0013] In a preferred embodiment of the method for preparing the low molecular weight polyester polyol of the present invention, the alicyclic anhydride includes at least one of methylhexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, hexahydrophthalic anhydride, and tetrahydrophthalic anhydride.

[0014] As a preferred embodiment of the preparation method of the low molecular weight polyester polyol of the present invention, the polyfunctional alcohol includes at least one of neopentyl glycol, trimethylolpropane, pentaerythritol, and tris(2-hydroxyethyl)isocyanurate; and / or, the antioxidant includes trinonyl phosphite; and / or, the catalyst includes stannous octoate and / or dibutyltin dilaurate; and / or, the diluent includes at least one of butyl acetate, amyl acetate, propylene glycol methyl ether acetate, methyl isobutyl ketone, and methyl amyl ketone.

[0015] In a preferred embodiment of the method for preparing the low molecular weight polyester polyol of the present invention, in step S1, the reaction temperature is 120℃-140℃ and the time is 1h-5h; and / or, in step S2, the reaction temperature is 100℃-115℃ and the time is 3h-6h.

[0016] Secondly, the present invention provides a low molecular weight polyester polyol prepared by the aforementioned preparation method.

[0017] Thirdly, the present invention provides a polyurethane coating made from the following raw materials in parts by weight: 50-70 parts of the low molecular weight polyester polyol, 15-30 parts of the polyisocyanate curing agent, 0.1-0.4 parts of the catalyst, 0.1-0.8 parts of the leveling agent, and 10-30 parts of the organic solvent.

[0018] Fourthly, the present invention provides a method for preparing the polyurethane coating, characterized by comprising the following steps: mixing the low molecular weight polyester polyol, polyisocyanate curing agent, catalyst, leveling agent, and organic solvent, reacting them to obtain the polyurethane coating.

[0019] Fifthly, the present invention provides the application of the aforementioned low molecular weight polyester polyol and the aforementioned polyurethane coating in transportation vehicles, electronic equipment, industrial protective building materials, daily necessities packaging, and furniture products.

[0020] Compared with existing technologies, the beneficial effects of this invention are as follows: Through precise design of the type of acid anhydride, the structure of the polyol, and the synthesis process, this invention successfully prepares low molecular weight polyester polyols with suitable viscosity and low acid value. Polyurethane coatings prepared from this series of polyols exhibit comprehensive and balanced superior performance. Firstly, the polyurethane coatings prepared from the low molecular weight polyester polyols of this invention exhibit extremely high adhesion under both air-drying and oven-drying conditions, demonstrating an extremely strong bond between the coating and the substrate. Simultaneously, the coating hardness is moderate, indicating that the coating has successfully achieved an ideal balance between protection and flexibility, making it very suitable for applications such as wooden furniture and automotive interior parts that require both a certain level of surface hardness and impact and deformation resistance. Secondly, the polyurethane coatings prepared from the low molecular weight polyester polyols of this invention exhibit excellent gloss, with superior gloss under both oven-drying and air-drying conditions. This characteristic allows the coating to meet the special aesthetic requirements of high-gloss surfaces in industrial protection and high-end decoration fields. Furthermore, the coating has a wide application window, facilitating operation, and ensures good leveling properties during application, which is beneficial for forming a smooth and even coating film. Furthermore, the VOC content of the polyurethane coating prepared by the low molecular weight polyester polyol of this invention is much lower than that of conventional solvent-based coatings, fully complying with the national mandatory standard GB24409-2020 "Limits of Hazardous Substances in Vehicle Coatings" and the national recommended standard GB / T 38597-2020 "Technical Requirements for Coating Products with Low Volatile Organic Compound Content", providing a practical solution for the development of high-performance environmentally friendly polyurethane coatings. Detailed Implementation

[0021] To better illustrate the objectives, technical solutions, and advantages of this invention, the invention will be further described below with reference to specific embodiments. Those skilled in the art should understand that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0022] The following description, in conjunction with specific embodiments, illustrates the practical effects of the present invention.

[0023] Unless otherwise specified, the experimental methods used in the examples are conventional methods; the materials, reagents, equipment, etc. used are all commercially available unless otherwise specified.

[0024] Example 1: This embodiment provides a low molecular weight polyester polyol, the preparation method of which includes the following steps: (1) First, add 24.29 g (0.181 mol) of trimethylolpropane, 58.87 g (0.35 mol) of methylhexahydrophthalic anhydride, 56.74 g (0.213 mol) of dodecenylsuccinic anhydride, and 1.46 g of trinonyl phosphite (TNPP) to a 500 mL four-necked flask. Set up the experimental apparatus, turn on the power, and set the initial temperature of the heating mantle to 112 °C. After the sample dissolves, start stirring and adjust the speed to 200 rpm. After maintaining this for 10 min, adjust the reaction temperature to 130 °C and heat at this constant temperature for 2 h.

[0025] (2) Stop heating and lower the material temperature to 95°C. Start adding a mixture of 0.16g stannous octoate and 122.19g (0.535mol) glycidyl tert-carbonate. After the addition is complete, adjust the material temperature to 110°C and heat at a constant temperature for 4.5h. Then add 65.52g BAC to dilute the mixture. Stir for 30min and then cool down to 50°C. Discharge the material to obtain low molecular weight polyester polyol.

[0026] Example 2: This embodiment provides a low molecular weight polyester polyol, the preparation method of which includes the following steps: (1) First, add 27.83g (0.267mol) neopentyl glycol, 45.58g (0.271mol) methylhexahydrophthalic anhydride, 72.19g (0.271mol) dodecenylsuccinic anhydride, and 1.5g TNPP to a 500mL four-necked flask. Set up the experimental apparatus, turn on the power, and set the initial temperature of the heating mantle to 112℃. After the sample dissolves, start stirring and adjust the speed to 200rpm. After maintaining this for 10min, adjust the reaction temperature to 130℃ and heat at this constant temperature for 2h.

[0027] (2) Stop heating and lower the material temperature to 95°C. Start adding a mixture of 0.17g stannous octoate and 124.59g (0.546mol) glycidyl tert-carbonate. After the addition is complete, adjust the material temperature to 110°C and heat at a constant temperature for 4.5h. Then add 67.55g BAC to dilute the mixture. Stir for 30min and then cool down to 50°C. Discharge the material to obtain low molecular weight polyester polyol.

[0028] Example 3: This embodiment provides a low molecular weight polyester polyol, the preparation method of which includes the following steps: (1) First, add 43.28 g (0.155 mol) tris(2-hydroxyethyl) isocyanurate, 30.95 g (0.184 mol) methylhexahydrophthalic anhydride, 85.25 g (0.32 mol) dodecenylsuccinic anhydride, and 1.49 g TNPP to a 500 mL four-necked flask. Set up the experimental apparatus, turn on the power, and set the initial temperature of the heating mantle to 112 °C. After the sample dissolves, start stirring and adjust the speed to 200 rpm. After maintaining this for 10 min, adjust the reaction temperature to 130 °C and heat at this constant temperature for 2 h.

[0029] (2) Stop heating and lower the material temperature to 95°C. Start adding a mixture of 0.15g stannous octoate and 113.29g (0.496mol) glycidyl tert-carbonate. After the addition is complete, adjust the material temperature to 110°C and heat at a constant temperature for 4.5h. Then add 68.19g BAC to dilute the mixture. Stir for 30min and then cool down to 50°C. Discharge the material to obtain low molecular weight polyester polyol.

[0030] Example 4: This embodiment provides a low molecular weight polyester polyol, the preparation method of which includes the following steps: (1) First, add 19.63g (0.144mol) pentaerythritol, 34.31g (0.204mol) methylhexahydrophthalic anhydride, 95.90g (0.36mol) dodecenylsuccinic anhydride, and 1.60g TNPP to a 500mL four-necked flask. Set up the experimental apparatus, turn on the power, and set the initial temperature of the heating mantle to 112℃. After the sample dissolves, start stirring and adjust the speed to 200rpm. After maintaining this for 10min, adjust the reaction temperature to 130℃ and heat at this constant temperature for 2h.

[0031] (2) Stop heating and lower the material temperature to 95°C. Start adding a mixture of 0.21g stannous octoate and 129.56g (0.567mol) glycidyl tert-carbonate. After the addition is complete, adjust the material temperature to 110°C and heat at a constant temperature for 4.5h. Then add 69.85g BAC to dilute the mixture. Stir for 30min and then cool down to 50°C. Discharge the material to obtain low molecular weight polyester polyol.

[0032] Example 5: This embodiment provides a low molecular weight polyester polyol, the only difference between its preparation method and that of Example 1 is that methylhexahydrophthalic anhydride is replaced with the same molar amount of methyltetrahydrophthalic anhydride.

[0033] Example 6: This embodiment provides a low molecular weight polyester polyol, the only difference between its preparation method and that of Example 1 is that methyl hexahydrophthalic anhydride is replaced with the same molar amount of hexahydrophthalic anhydride.

[0034] Example 7: This embodiment provides a low molecular weight polyester polyol, the only difference between its preparation method and that of Example 1 is that the molar ratio of methylhexahydrophthalic anhydride and dodecenylsuccinic anhydride is 1:1.

[0035] Example 8: This embodiment provides a low molecular weight polyester polyol, the only difference between its preparation method and that of Example 1 is that the molar ratio of methylhexahydrophthalic anhydride and dodecenylsuccinic anhydride is 1:1.2.

[0036] Example 9: This embodiment provides a low molecular weight polyester polyol, the only difference between its preparation method and that of Example 1 is that the molar ratio of methylhexahydrophthalic anhydride and dodecenylsuccinic anhydride is 1:1.4.

[0037] Example 10: This embodiment provides a low molecular weight polyester polyol, the only difference between its preparation method and that of Example 1 is that the molar ratio of methylhexahydrophthalic anhydride and dodecenylsuccinic anhydride is 1:1.8.

[0038] Comparative Example 1: This comparative example provides a low molecular weight polyester polyol, the only difference between its preparation method and that of Example 1 is that dodecenyl succinic anhydride is not used.

[0039] Comparative Example 2: This comparative example provides a low molecular weight polyester polyol, the only difference between its preparation method and that of Example 1 is that methylhexahydrophthalic anhydride is not used.

[0040] Comparative Example 3: This comparative example provides a low molecular weight polyester polyol, the preparation method of which differs from that of Example 1 only in that trimethylolpropane is replaced with the same molar amount of glycerol.

[0041] Comparative Example 4: This comparative example provides a low molecular weight polyester polyol, the only difference between its preparation method and that of Example 1 is that methyl hexahydrophthalic anhydride is replaced with the same molar amount of phthalic anhydride.

[0042] Comparative Example 5: This comparative example provides a low molecular weight polyester polyol, the only difference between its preparation method and that of Example 1 is that dodecenyl succinic anhydride is replaced with the same molar amount of maleic anhydride.

[0043] Comparative Example 6: This comparative example provides a low molecular weight polyester polyol, the only difference between its preparation method and that of Example 1 is that the molar ratio of methylhexahydrophthalic anhydride and dodecenylsuccinic anhydride is 1:0.4.

[0044] Comparative Example 7: This comparative example provides a low molecular weight polyester polyol, the only difference between its preparation method and that of Example 1 is that the molar ratio of methylhexahydrophthalic anhydride and dodecenylsuccinic anhydride is 1:2.5.

[0045] Comparative Example 8: This comparative example provides a low molecular weight polyester polyol, the preparation method of which includes the following steps: Add 24.29 g (0.181 mol) trimethylolpropane, 58.87 g (0.35 mol) methylhexahydrophthalic anhydride, 56.74 g (0.213 mol) dodecenylsuccinic anhydride, 1.46 g trinonyl phosphite (TNPP), 0.16 g stannous octoate, and 122.19 g (0.535 mol) glycidyl tert-carbonate to a 500 mL four-necked flask. Assemble the experimental apparatus, turn on the power, and set the initial temperature of the heating mantle to 112 °C. After the sample dissolves, start the stirrer and adjust the speed to 200 rpm. Maintain this temperature for 10 minutes, then adjust the reaction temperature to 130 °C and heat at this temperature for 2 hours. Then, continue to adjust the reaction temperature to 110 °C and maintain this temperature for another 4.5 hours. Add 60.56 g of BAC to dilute the mixture, stir for 30 minutes, then cool to 50 °C and discharge the product to obtain the low molecular weight polyester polyol.

[0046] Application Example 1-10: Application Examples 1-10 respectively prepared polyurethane coatings from the low molecular weight polyester polyols of Examples 1-10. The raw materials for preparation included the following components in parts by weight: 40 parts low molecular weight polyester polyol (Examples 1-10), 11 parts butyl acetate, 0.2 parts dibutyltin dilaurate, 0.4 parts leveling agent 3700, and 14.59 parts curing agent HT100.

[0047] Application Example 1-10: The preparation method of polyurethane coating includes the following steps: (1) Preparation of component A (a) Weighing and mixing: Accurately weigh the low molecular weight polyester polyol, add dibutyltin dilaurate and leveling agent in sequence, and mix evenly; (b) Dispersion: Stir with a glass rod or mechanical stirrer at medium speed (about 400-600 rpm) for 10-15 minutes to ensure that the additives are fully and evenly dispersed; (c) Dilution: Slowly add 80 wt% butyl acetate and continue stirring for 5 min to initially dilute it; (2) Mixing and maturation (a) Accurately weigh HT100 curing agent, slowly pour component A into a beaker containing curing agent, use a mechanical stirrer, start stirring at low speed (300-400 rpm) to avoid introducing too many air bubbles, stir for 15-20 minutes to ensure that the two components are completely and evenly mixed. (b) Clean the beaker containing component A with the remaining 20 wt% butyl acetate, and pour the cleaning solution into the mixed coating to achieve a suitable application viscosity. After mixing evenly, let it stand (mature) for 15-30 minutes to allow the air bubbles to escape, thus obtaining the polyurethane coating.

[0048] Application Comparative Examples 1-8: The only difference between the polyurethane coatings used in Comparative Examples 1-8 and those used in Examples 1-10 is that the low molecular weight polyester polyols used in Comparative Examples 1-8 are employed.

[0049] Test Example 1: The relevant parameters of the low molecular weight polyester polyols in the above embodiments and comparative examples were tested.

[0050] (1) Molecular weight test: Test method: The number-average molecular weight of low molecular weight polyester polyols was determined by gel permeation chromatography.

[0051] (2) Solid content test: Test method: The test was conducted in accordance with the national standard GB / T 1725-2007 "Determination of nonvolatile matter content in paints, varnishes and plastics".

[0052] (3) Acid value test: Test method: The test was conducted in accordance with the national standard GB-T 6743-2008 "Determination of acid value and total acid value of polyester resin for plastics, paints and varnishes".

[0053] (4) Viscosity test: Test method: At 25℃, the time required for a bubble of a specified volume to rise a fixed distance in the sample is determined by the Grignard tube method, thereby characterizing the bubble viscosity of the sample.

[0054] Table 1: Test Results of Performance Indicators of Low Molecular Weight Polyester Polyol in Test Example 1 of the Invention Test Example 2: The relevant properties of the polyurethane coatings in the above application examples and comparative examples were tested.

[0055] (1) Test method for surface drying time and actual drying time: The surface drying time and actual drying time of polyurethane coating at 25℃ are tested according to the test standard of GB / T1728-1979.

[0056] (2) Gel time test method: The gel time of polyurethane coating at 25°C is tested according to the test standard of ASTM D7997-21.

[0057] (3) Test method for drying hardness and air-drying hardness: The drying hardness of polyurethane coating at 80℃ and the air-drying hardness at 25℃ are tested according to the test standard of GB / T6739-2006.

[0058] (4) Drying adhesion and self-drying adhesion test method: The drying adhesion of polyurethane coating at 80℃ and the self-drying adhesion at 25℃ are tested according to the test standard of GB / T9286-2021.

[0059] (5) Test method for drying gloss and air-drying gloss: The drying gloss and air-drying gloss of polyurethane coatings at 60° are tested according to the test standard of GB / T9754-2007.

[0060] (6) VOC content test method: The VOC content (g / L) of polyurethane coatings shall be tested according to the test standard of GB / T23985-2009.

[0061] Table 2: Performance test results of polyurethane coatings in application examples of the present invention Table 3: Performance test results of the comparative polyurethane coatings used in this invention As can be seen from the results in Tables 2 and 3, the polyurethane coatings of the application examples of this invention exhibit excellent comprehensive performance, combining outstanding practicality, excellent adhesion, high decorative properties, and superior environmental characteristics. They can be applied to scenarios requiring a balance between protection and flexibility, such as wooden furniture and automotive interior parts. Firstly, regarding adhesion, whether air-dried or oven-dried, the polyurethane coatings prepared by this invention achieve an A0 grade adhesion, demonstrating excellent adhesion. Secondly, regarding gloss, the coatings prepared by this invention achieve a gloss level of over 132, suitable for special high-gloss applications such as industrial protection and high-end decoration. Furthermore, regarding VOC content, the polyurethane coatings prepared from the low molecular weight polyester polyols in the embodiments of this invention have VOC contents below 336 g / L, which not only meets the national mandatory standard GB24409-2020 "Limits of Hazardous Substances in Vehicle Coatings" but also satisfies the requirements of GB / T38597-2020 "Technical Requirements for Coatings with Low Volatile Organic Compound Content," providing a new solution for developing environmentally friendly, high-performance polyurethane coatings.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a low molecular weight polyester polyol, characterized in that, Includes the following steps: S1. Mix a multifunctional alcohol, a cyclic anhydride and an antioxidant, and react to obtain a prepolymer; the cyclic anhydride includes alicyclic anhydrides and dodecenyl succinic anhydride in a molar ratio of 1:(0.6-1.8); S2. Add glycidyl tert-carbonate and catalyst to the prepolymer, react, add diluent, and obtain low molecular weight polyester polyol.

2. The method for preparing the low molecular weight polyester polyol as described in claim 1, characterized in that, The molar ratio of the alicyclic anhydride and the dodecenyl succinic anhydride is 1:(1-1.2).

3. The method for preparing low molecular weight polyester polyol as described in claim 1, characterized in that, The molar ratio of the hydroxyl group of the polyfunctional alcohol, the anhydride group of the cyclic anhydride, and the epoxy group of the glycidyl tert-carbonate is 1:(0.5-2):(1-3); and / or, the mass of the antioxidant is 0.02%-0.06% of the total mass of the raw materials; and / or, the mass of the catalyst is 0.03%-0.06% of the total mass of the raw materials; and / or, the mass of the diluent is 10%-30% of the total mass of the raw materials.

4. The method for preparing low molecular weight polyester polyol as described in claim 1, characterized in that, The alicyclic anhydride includes at least one of methylhexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, and hexahydrophthalic anhydride.

5. The method for preparing low molecular weight polyester polyol as described in claim 1, characterized in that, The polyfunctional alcohol includes at least one of neopentyl glycol, trimethylolpropane, pentaerythritol, and tris(2-hydroxyethyl)isocyanurate; and / or, the antioxidant includes trinonyl phosphite; and / or, the catalyst includes stannous octoate and / or dibutyltin dilaurate; and / or, the diluent includes at least one of butyl acetate, amyl acetate, propylene glycol methyl ether acetate, methyl isobutyl ketone, and methyl amyl ketone.

6. The method for preparing the low molecular weight polyester polyol as described in claim 1, characterized in that, In step S1, the reaction temperature is 120℃-140℃ and the time is 1h-5h; and / or, in step S2, the reaction temperature is 100℃-115℃ and the time is 3h-6h.

7. The low molecular weight polyester polyol prepared by any of the preparation methods described in claims 1-6.

8. A polyurethane coating, characterized in that, It is made from the following raw materials in parts by weight: 50-70 parts of the low molecular weight polyester polyol as described in claim 7, 15-30 parts of polyisocyanate curing agent, 0.1-0.4 parts of catalyst, 0.1-0.8 parts of leveling agent, and 10-30 parts of organic solvent.

9. The method for preparing the polyurethane coating according to claim 8, characterized in that, Includes the following steps: The low molecular weight polyester polyol, polyisocyanate curing agent, catalyst, leveling agent, and organic solvent are mixed and reacted to obtain the polyurethane coating.

10. The application of the low molecular weight polyester polyol of claim 7 and the polyurethane coating of claim 8 in transportation vehicles, electronic equipment, industrial protective building materials, daily necessities packaging, and furniture products.

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