Polyester polyol, preparation method and application of polyester polyol in preparation of polyurethane

Abstract

The invention provides polyester polyol, a preparation method and application of the polyester polyol in preparation of polyurethane, and relates to the field of polyester polyol. The preparation method of the polyester polyol comprises the following steps: prepolymerization reaction, condensation polymerization reaction and byproduct recycling. According to the preparation method of the polyester polyol, the esterification effect is good, and the acid value of the prepared polyester polyol is low; the polyester polyol prepared in the same batch is small in molecular weight difference and narrow in molecular weight distribution; the side reaction in the preparation process of the polyester polyol can be inhibited, and the product yield is further improved. According to the application of the polyester polyol in preparation of polyurethane, the defect that the stability of a polyurethane product is influenced due to different activities of residual catalyst components in preparation of the polyester polyol in subsequent synthesis of polyurethane can be effectively avoided, and the cold resistance, toughness and softness of the polyurethane prepared from the polyester polyol are further improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of polyester polyols, in particular to a polyester polyol, a preparation method and application thereof in the preparation of polyurethane. BACKGROUND

[0002] Polyester polyols are a kind of polymers prepared from polycarboxylic acid and polyol as raw materials through condensation reaction and other processes. Polyester polyols are the most commonly used and most important synthetic raw materials for polyurethane. Because in the synthesis process of polyurethane, polyester polyols can provide flexible soft segments for polyurethane, thereby endowing polyurethane with excellent performance. As the main source of flexible soft segment structure of polyurethane, the molecular chain structure and relative molecular mass of polyester polyols have a significant influence on the final performance of polyurethane.

[0003] At present, the production methods of polyester polyols mainly include: a first reaction process and a second reaction process. The first reaction process is the dehydration esterification reaction of dicarboxylic acid and dihydric alcohol or trihydric alcohol to generate small molecules with monoester groups. The second reaction process is the condensation reaction of the small molecules with monoester groups generated above at high temperature to generate polyester polyols with a predetermined molecular weight.

[0004] However, the existing polyester polyols still have the following deficiencies in the preparation process: (1) the esterification effect is poor, and the acid value of the polyester polyols is high; (2) the molecular weight of the polyester polyols prepared in the same batch differs greatly, and the molecular weight distribution is wide; (3) there are many side reactions in the preparation process of the polyester polyols, and the product yield needs to be further improved.

[0005] Further, the existing polyester polyols also have the following deficiencies in the subsequent preparation of polyurethane: (1) the residual catalyst components in the preparation of the polyester polyols have different activities in the subsequent synthesis of polyurethane, which not only leads to poor stability of the synthesis of polyurethane, but also affects the stability (such as water resistance, ethanol resistance, etc.) of the polyurethane product; (2) the molecular weight of the polyester polyols differs greatly, and the molecular weight distribution is wide, which directly affects the mechanical properties of the polyurethane, especially limits the improvement of the toughness of the polyurethane; (3) the cold resistance, toughness and softness of the polyurethane prepared by using the existing polyester polyol need to be further improved, which limits the further expansion of the application range of the polyurethane. SUMMARY

[0006] To address the technical problems existing in the prior art, this invention provides a method for preparing polyester polyols to achieve the following objectives: (1) good esterification effect and low acid value of the prepared polyester polyols; (2) small molecular weight difference and narrow molecular weight distribution of polyester polyols prepared in the same batch; (3) suppression of side reactions in the preparation process of polyester polyols, further improving product yield; (4) effective avoidance of the defect that the stability of polyurethane products is affected by the different activities of residual catalyst components in the preparation of polyester polyols during subsequent polyurethane synthesis; (5) further improvement of the cold resistance, toughness and softness of polyurethanes prepared using polyester polyols. This invention also provides polyester polyols prepared by the aforementioned method. This invention also provides the application of the aforementioned polyester polyols in the preparation of polyurethanes.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A method for preparing a polyester polyol includes the following steps: prepolymerization reaction, polycondensation reaction, and by-product recycling; The method for the prepolymerization reaction is as follows: dimethyl glutarate and diol are placed in a reaction vessel, a catalyst is added under stirring conditions, the reaction pressure is controlled at atmospheric pressure, the temperature is raised to 100-200℃ and kept at the temperature to carry out the prepolymerization reaction until no light components are distilled out, thus completing the prepolymerization reaction. The method of polycondensation reaction is as follows: after the prepolymerization reaction is completed, continue stirring and heating to 180-185℃, keep warm and evacuate the reactor, maintain vacuum and keep warm to carry out polycondensation reaction, and obtain polyester polyol.

[0008] Furthermore, the polycondensation reaction method is as follows: after the prepolymerization reaction is completed, the mixture is stirred and heated to 180-185°C, kept at the temperature, and the reactor is evacuated until the vacuum degree inside the reactor is 0.095-0.099 MPa. The vacuum degree is maintained and the temperature is kept to carry out the polycondensation reaction to obtain polyester polyol.

[0009] Preferably, in the prepolymerization reaction, the diol is at least one of the following: ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, diethylene glycol, triethylene glycol, polyethylene glycol, and polytetraethylene glycol.

[0010] Preferably, in the prepolymerization reaction, the molar ratio of dimethyl glutarate to diol is 1:1-5.

[0011] Preferably, the prepolymerization reaction is carried out under heat for 4-5 hours.

[0012] Preferably, in the polycondensation reaction, the rate at which the vacuum level in the reactor is reduced to 0.095-0.099 MPa is 0.02-0.025 MPa every 15 minutes; In the polycondensation reaction, the polycondensation reaction is carried out under vacuum and at a constant temperature for 7-9 hours.

[0013] Preferably, in the prepolymerization reaction, the catalyst is an organotin catalyst and / or an organotitanium catalyst; The organotin catalyst is at least one of the following: dibutyltin dilaurate, dimethyl dinedecanoate, and dibutyltin oxide; the organotitanium catalyst is at least one of the following: tetra-n-butoxide titanium, tetra-n-propoxide titanium, tetraisopropoxide titanium, and tetraisopropyl titanate. The catalyst is added at a rate of 10-100 ppm of the total weight of dimethyl glutarate and diol.

[0014] Furthermore, the methanol generated in the prepolymerization reaction is continuously extracted from the top of the reactor and condensed for recovery, and then used as a by-product for reuse. In the polycondensation reaction, the methanol generated during the process of heat preservation and vacuuming of the reactor is continuously collected from the top of the reactor, condensed and recovered, and used as a by-product for reuse.

[0015] Furthermore, the method for recycling the by-products is as follows: the methanol recovered in the prepolymerization reaction and / or the polycondensation reaction is used for esterification to prepare dimethyl glutarate or dimethyl succinate; the dimethyl succinate is used for hydrogenolysis to prepare butanediol; The dimethyl glutarate and / or butanediol obtained from the by-product recycling process are recycled into the prepolymerization reaction.

[0016] A polyester polyol prepared by the aforementioned method has a molecular weight of 300-10000.

[0017] Preferably, the molecular structure of the polyester polyol is: HO-[(CH2)] m -O-CO-(CH2)3-CO-О] n -(CH2) m -OH; where -(CH2) m - comes from diol, -CO-(CH2)3-CO- comes from dimethyl glutarate, m is any integer from 2 to 12, and n is the number of repeating units.

[0018] An application of the aforementioned polyester polyol in the preparation of polyurethane, wherein the polyurethane is an oil-based polyurethane or a water-based polyurethane.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The method for preparing polyester polyols of the present invention uses dimethyl glutarate and diols as raw materials, and obtains polyester polyols through prepolymerization and polycondensation reactions. The esterification effect is good, the prepared polyester polyols have low acid values, and the polyester polyols are stable and do not easily decompose. The polyester polyols prepared in the same batch have small differences in molecular weight and narrow molecular weight distribution. The molecular weight and viscosity of the polyester polyols prepared in the same batch are similar, the product quality is stable, and the adverse effects on the mechanical properties of polyurethane are effectively avoided. At the same time, it can also suppress side reactions in the preparation process of polyester polyols, further improve the product yield, and reduce impurity residues. Furthermore, the application of the polyester polyols in the preparation of polyurethanes can effectively avoid the defect that the stability of polyurethane products is affected by the different activities of the catalyst components remaining in the preparation of polyester polyols during subsequent polyurethane synthesis, and further improve the cold resistance, toughness and softness of polyurethanes prepared using polyester polyols.

[0020] (2) The polyester polyol preparation method of the present invention has a molecular weight distribution of 1.25-1.30, an acid value of 0.05-0.06 mgKOH / g, and a yield of 90.2-90.8%.

[0021] (3) The oil-based polyurethane film prepared using the polyester polyol of the present invention has a tensile strength of 27-33 MPa and an elongation at break of 475-602%; after being soaked in hot water at 80°C for 10 days, the film retains a flexural strength of 72-78%; after being soaked in anhydrous ethanol at room temperature for 10 days, the film retains a flexural strength of 80-85%; after being stored at a constant temperature of -40°C for 192 hours, the film still has normal elasticity and excellent cold resistance; after being worn by a 1kg weight for 1000 cycles, the film has a wear mass of 53.4-58.9 mg; the muscle-forming index of the film is 0.369-0.628 mm and the solidification speed is 160-200 s; compared with the oil-based polyurethane prepared using commercially available polyhexanediol adipate, the toughness, hydrolysis resistance, ethanol resistance, cold resistance, abrasion resistance and muscle-forming properties of the polyurethane film are significantly improved.

[0022] (4) The waterborne polyurethane prepared using the polyester polyol of the present invention, after being stored in a constant temperature environment of 60°C for 5 days, showed no significant changes in color, uniformity, film-forming properties and pH, indicating good storage stability; the tensile strength of the waterborne polyurethane film was 18-21 MPa and the elongation at break was 567-641%; after being soaked in water for 5 days, the film did not harden or become brittle, indicating excellent water resistance; after being rubbed 100 times with a weight wrapped in a cloth soaked in alcohol, the film did not swell and showed no obvious scratch marks; compared with the waterborne polyurethane prepared using commercially available polyhexamethylene adipate diol, the storage performance of the emulsion was significantly improved, and the toughness, hydrolysis resistance, ethanol resistance and scratch resistance of the polyurethane film prepared using it were significantly improved.

[0023] (5) The application of polyester polyol in the preparation of polyurethane in this invention results in polyurethane with good toughness, cold resistance, water resistance and ethanol resistance, which can be effectively applied to polyurethane adhesives, polyurethane leather, polyurethane waterproof coatings and other fields, further expanding the application scope of polyurethane. Attached Figure Description

[0024] Figure 1 The image shows the 1H NMR spectrum of the polyester polyol prepared in Example 1. Detailed Implementation

[0025] To provide a clearer understanding of the technical features, objectives, and effects of this invention, specific embodiments are now described. It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0026] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, "first," "second," etc., are used to distinguish similar objects and are not used to describe a particular order or sequence. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0027] This invention provides a method for preparing polyester polyols, comprising the following steps: prepolymerization reaction, polycondensation reaction, molecular weight detection, and by-product recycling.

[0028] The prepolymerization reaction method is as follows: dimethyl glutarate and diol are added to a reactor in a certain proportion, stirring is started, a certain amount of catalyst is added according to the feed amount, the reaction temperature is set to 100-200℃ (preferably 175-180℃), the reaction pressure is atmospheric pressure, and after the temperature is raised to the predetermined temperature, the prepolymerization reaction is carried out until no light components are distilled out (the holding time is 4-5 hours), and the prepolymerization reaction is completed; during the prepolymerization reaction, a light component, methanol, is generated, which is continuously collected from the top of the reactor and condensed for recovery.

[0029] In the prepolymerization reaction, the diol is at least one of the following: ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, diethylene glycol, triethylene glycol, polyethylene glycol, polytetraethylene glycol; preferably one of the following: 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol.

[0030] In the prepolymerization reaction, the molar ratio of dimethyl glutarate to diol is 1:1-5 (preferably 1:1.05-1.1).

[0031] In the prepolymerization reaction, the catalyst is an organotin catalyst and / or an organotitanium catalyst; the organotin catalyst is at least one of the following: dibutyltin dilaurate, dimethyl dinedecanoate, dibutyltin oxide; the organotitanium catalyst is at least one of the following: tetra-n-butoxide titanium, tetra-n-propoxide titanium, tetraisopropoxide titanium, tetraisopropyl titanate.

[0032] In the prepolymerization reaction, the amount of catalyst added is 10-100 ppm of the total weight of dimethyl glutarate and diol.

[0033] The method for the polycondensation reaction is as follows: the reactor temperature is controlled to rise to 180-185℃, the temperature is maintained, and the reactor is evacuated. The pressure reduction rate of the evacuation is controlled to be 0.02-0.025 MPa every 15 minutes, and the vacuum degree is evacuated to 0.001-0.1 MPa (preferably 0.095-0.099 MPa). The vacuum is maintained for 1-1.25 hours. During the heat preservation and vacuuming process, methanol is continuously collected from the top of the reactor and condensed and recovered to ensure that the polycondensation reaction proceeds in the forward direction. When the vacuum degree reaches 0.095-0.1 MPa, the polycondensation reaction is carried out for 7-9 hours under heat preservation and pressure to obtain polyester polyol.

[0034] The method for determining the molecular weight is as follows: after the polycondensation reaction is completed, the vacuum of the reaction system is broken, nitrogen is used to fill the system to positive pressure, a sample is taken, and the hydroxyl value of the polyester polyol is determined by the phthalic anhydride pyridine method. The number-average molecular weight of the polyester polyol is then calculated.

[0035] The method for recycling the by-products is as follows: the methanol recovered during the prepolymerization and polycondensation reactions can be used for esterification to prepare dimethyl glutarate or dimethyl succinate; and the obtained dimethyl succinate is hydrogenated (hydrogenolysis) to prepare butanediol; the dimethyl glutarate and butanediol obtained using the by-product methanol can be used as reaction raw materials to continue to be used in the preparation of polyester polyols.

[0036] This invention also provides a polyester polyol prepared by the aforementioned method, wherein the molecular weight of the polyester polyol is 300-10000; and the molecular structure of the polyester polyol is: HO-[(CH2)] m -O-CO-(CH2)3-CO-О] n -(CH2) m -OH, where -(CH2) m - comes from diol, -CO-(CH2)3-CO- comes from dimethyl glutarate, m is any integer from 2 to 12, and n is the number of repeating units.

[0037] The embodiments of the present invention also provide the application of the aforementioned polyester polyols in the preparation of polyurethane.

[0038] The present invention will be further described below with reference to some specific embodiments.

[0039] Example 1 This embodiment provides a method for preparing polyester polyols, specifically as follows: (1) Prepolymerization reaction Dimethyl glutarate and bio-based 1,4-butanediol were added to a reactor in a certain proportion, and stirring was started. A certain amount of dibutyltin dilaurate was added as a catalyst according to the feed amount. The reaction temperature was set to 175°C and the reaction pressure was atmospheric pressure. After the temperature was raised to the predetermined temperature, the prepolymerization reaction was carried out until no light components were distilled out (the holding time was 5 hours), and the prepolymerization reaction was completed. During the prepolymerization reaction, a light component, methanol, was generated, which was continuously collected from the top of the reactor and condensed for recovery.

[0040] The molar ratio of dimethyl glutarate to diol is 1:1.05.

[0041] The amount of dibutyltin dilaurate added is 100 ppm of the total weight of dimethyl glutarate and diol.

[0042] (2) Condensation reaction The reactor temperature was raised to 185°C, maintained at this temperature, and a vacuum was evacuated. The pressure reduction rate during evacuation was controlled at 0.025 MPa every 15 minutes, and evacuation continued for 1 hour until the vacuum level inside the reactor reached 0.099 MPa. During the evacuation and heat preservation process, methanol was continuously collected from the top of the reactor and condensed for recovery to ensure the forward polycondensation reaction. Once the vacuum level reached 0.099 MPa, the polycondensation reaction was maintained at this temperature and pressure for 8.5 hours to obtain the polyester polyol. The 1H NMR spectrum of the polyester polyol prepared in this example is shown below. Figure 1 As shown.

[0043] (3) Molecular weight detection After the polycondensation reaction is completed, the vacuum of the reaction system is broken, nitrogen is used to purge to positive pressure, samples are taken and the hydroxyl value of the polyester polyol is determined by the phthalic anhydride pyridine method, and the number average molecular weight of the polyester polyol is calculated.

[0044] (4) Reuse of by-products Methanol recovered during the prepolymerization and polycondensation processes can be used for esterification to prepare dimethyl glutarate and dimethyl succinate; and the obtained dimethyl succinate can be hydrogenated (hydrogenolysis) to prepare butanediol; the dimethyl glutarate and butanediol obtained using by-product methanol can be used as reaction raw materials in the preparation of polyester polyols.

[0045] This embodiment also provides a polyester polyol prepared by the aforementioned method, with a molecular weight of 2014.36 and a molecular structure of HO-[(CH2)]. m -O-CO-(CH2)3-CO-О] n -(CH2) m -OH, where m is 4.

[0046] Example 2 This embodiment provides a method for preparing polyester polyols, specifically as follows: (1) Prepolymerization reaction Dimethyl glutarate and bio-based 1,4-butanediol were added to a reactor in a certain proportion, and stirring was started. A certain amount of dibutyltin dilaurate was added as a catalyst according to the feed amount. The reaction temperature was set to 177°C and the reaction pressure was atmospheric pressure. After the temperature was raised to the predetermined temperature, the prepolymerization reaction was carried out until no light components were distilled out (the holding time was 4.6 hours), and the prepolymerization reaction was completed. During the prepolymerization reaction, a light component, methanol, was generated, which was continuously collected from the top of the reactor and condensed for recovery.

[0047] The molar ratio of dimethyl glutarate to diol is 1:1.08.

[0048] The amount of dibutyltin dilaurate added is 90 ppm of the total weight of dimethyl glutarate and diol.

[0049] (2) Condensation reaction The reactor temperature was controlled to rise to 182℃, and the reactor was kept at this temperature while being evacuated. The pressure reduction rate of the evacuation was controlled to be 0.025 MPa every 15 minutes. The evacuation was carried out for 1 hour until the vacuum degree inside the reactor reached 0.099 MPa. During the heat preservation and vacuuming process, methanol was continuously collected from the top of the reactor and condensed to ensure that the polycondensation reaction proceeded in the forward direction. When the vacuum degree reached 0.099 MPa, the polycondensation reaction was carried out at this temperature and pressure for 8 hours to obtain polyester polyol.

[0050] (3) Molecular weight detection After the polycondensation reaction is completed, the vacuum of the reaction system is broken, nitrogen is used to purge to positive pressure, samples are taken and the hydroxyl value of the polyester polyol is determined by the phthalic anhydride pyridine method, and the number average molecular weight of the polyester polyol is calculated.

[0051] (4) Reuse of by-products Methanol recovered during the prepolymerization and polycondensation processes can be used for esterification to prepare dimethyl glutarate and dimethyl succinate; and the obtained dimethyl succinate can be hydrogenated (hydrogenolysis) to prepare butanediol; the dimethyl glutarate and butanediol obtained using by-product methanol can be used as reaction raw materials in the preparation of polyester polyols.

[0052] This embodiment also provides a polyester polyol prepared by the aforementioned method, with a molecular weight of 1486.10 and a molecular structure of: HO-[(CH2)] m -O-CO-(CH2)3-CO-О] n -(CH2) m -OH, where m is 4.

[0053] Example 3 This embodiment provides a method for preparing polyester polyols, specifically as follows: (1) Prepolymerization reaction Dimethyl glutarate and bio-based 1,4-butanediol were added to a reactor in a certain proportion, and stirring was started. A certain amount of dibutyltin dilaurate was added as a catalyst according to the feed amount. The reaction temperature was set to 180℃ and the reaction pressure was atmospheric pressure. After the temperature was raised to the predetermined temperature, the prepolymerization reaction was carried out until no light components were distilled out (the holding time was 4.1h), and the prepolymerization reaction was completed. During the prepolymerization reaction, a light component, methanol, was generated, which was continuously collected from the top of the reactor and condensed for recovery.

[0054] The molar ratio of dimethyl glutarate to diol is 1:1.1.

[0055] The amount of dibutyltin dilaurate added is 70 ppm of the total weight of dimethyl glutarate and diol.

[0056] (2) Condensation reaction The reactor was heated to 180°C, kept at that temperature, and evacuated. The pressure reduction rate of the evacuation was controlled at 0.025 MPa every 15 minutes. The evacuation was carried out for 1 hour until the vacuum degree inside the reactor reached 0.099 MPa. During the heat preservation and vacuuming process, methanol was continuously collected from the top of the reactor and condensed to ensure that the polycondensation reaction proceeded in the forward direction. When the vacuum degree reached 0.099 MPa, the polycondensation reaction was carried out at the same temperature and pressure for 7.2 hours to obtain polyester polyol.

[0057] (3) Molecular weight detection After the polycondensation reaction is completed, the vacuum of the reaction system is broken, nitrogen is used to purge to positive pressure, samples are taken and the hydroxyl value of the polyester polyol is determined by the phthalic anhydride pyridine method, and the number average molecular weight of the polyester polyol is calculated.

[0058] (4) Reuse of by-products Methanol recovered during the prepolymerization and polycondensation processes can be used for esterification to prepare dimethyl glutarate and dimethyl succinate; and the obtained dimethyl succinate can be hydrogenated (hydrogenolysis) to prepare butanediol; the dimethyl glutarate and butanediol obtained using by-product methanol can be used as reaction raw materials in the preparation of polyester polyols.

[0059] This embodiment also provides a polyester polyol prepared by the aforementioned method, with a molecular weight of 992.74 and a molecular structure of: HO-[(CH2)] m -O-CO-(CH2)3-CO-О] n -(CH2) m -OH, where m is 4.

[0060] Example 4 Example 4 adopts the technical solution of Example 1, except that in the prepolymerization reaction, equimolar amounts of 1,5-pentanediol are used to replace bio-based butylene glycol.

[0061] This embodiment also provides a polyester polyol prepared by this method, with a molecular weight of 2006.02 and a molecular structure of: HO-[(CH2)] m -O-CO-(CH2)3-CO-О] n -(CH2) m -OH, where m is 5.

[0062] Example 5 Example 5 adopts the technical solution of Example 1, except that in the prepolymerization reaction, equimolar amounts of 1,6-hexanediol are used to replace bio-based butylene glycol.

[0063] This embodiment also provides a polyester polyol prepared by this method, with a molecular weight of 2011.68 and a molecular structure of HO-[(CH2)]. m-O-CO-(CH2)3-CO-О] n -(CH2) m -OH, where m is 6.

[0064] The hydroxyl value, molecular weight, molecular weight distribution, acid value, color number, moisture content, and viscosity (60°C) of the polyester polyols obtained in Examples 1-5 were measured, and the yields of the polyester polyols prepared by each example were statistically analyzed. The specific results are shown in the table below:

[0065] It can be seen that the polyester polyols prepared by the methods in Examples 1-5 have small differences in molecular weight and narrow molecular weight distribution among the same batch; good esterification effect and low acid value; and high yield of polyester polyols.

[0066] Experimental Example 1 Oil-based polyurethanes were prepared using the polyester polyols from Examples 1, 4, and 5, respectively. A control group using commercially available polyhexane adipate diol was also prepared. The specific preparation method for the oil-based polyurethane was as follows: Polyester polyol: 1,4-butanediol (BDO): 4,4'-diphenylmethane diisocyanate (MDI) were prepared in a molar ratio of 1:2:3.1. The polyester diol, BDO, and solvent DMF were added to a four-necked flask and heated to 50°C. After the raw materials dissolved, MDI was added, and the temperature was further increased to 75°C. The reaction was maintained at this temperature until the viscosity met the requirements, and then the mixture was poured out to obtain the corresponding oil-based polyurethane.

[0067] The physical properties of the oil-based polyurethanes corresponding to Examples 1, 4, 5, and the control group were tested. The casting conditions were as follows: each polyurethane film was uniformly coated onto release paper using a 20-micron coating tool, transferred to an oven, and kept at 120°C for 2 hours to obtain the polyurethane film. Physical property testing was conducted using a universal testing machine (Jinjian UTM-1432 universal tensile testing machine). The specific testing method followed GB / T1040-2006. Each polyurethane film was cut into standard strips of 2cm × 15cm as samples. The sample movement speed was controlled at 100mm / min, and the tensile strength and elongation at break of each sample were tested at room temperature. The specific results are shown in the table below.

[0068] Furthermore, water resistance and ethanol resistance tests were conducted on each polyurethane film sample, and the tensile strength was measured after the tests to calculate the tensile strength retention rate. The water resistance test method was as follows: each polyurethane film was immersed in hot water at 80℃ for 10 days, and then the tensile strength was measured. The ethanol resistance test method was as follows: each polyurethane film was immersed in anhydrous ethanol at room temperature for 10 days, and then the tensile strength was measured. Specific results are shown in the table below:

[0069] Furthermore, cold resistance tests were conducted on each polyurethane film sample. Specifically, each polyurethane film was stored at a constant temperature of -40℃, and the elasticity of each polyurethane film was checked at 24h, 48h, 72h, 96h, 120h, 144h, and 192h of storage. The specific results are shown in the table below:

[0070] Furthermore, abrasion resistance tests were conducted on each polyurethane film sample. Specifically, polyurethane films with a thickness of 100 mils were prepared using various oil-based polyurethanes, and abrasion resistance tester with an H-22 grinding wheel was used for testing. The weight of the abrasion resistance tester was controlled at 1 kg, and the running cycle was 1000 cycles. The specific results are shown in the table below:

[0071] Furthermore, a skin-forming test was conducted on each polyurethane film sample. Specifically, each oil-based polyurethane film was coated onto a smooth glass plate, then gently immersed at an angle in a pre-prepared 20wt% DMF aqueous solution for 60 seconds. A small weight was then placed on the surface of the partially solidified polyurethane film, and subsequent small weights were placed every 20 seconds. The solidification rate was recorded based on the marks left by the weights, and the skin-forming properties were observed. The specific results are shown in the table below:

[0072] It can be seen that the oil-based polyurethane prepared using the polyester polyol of the present invention exhibits significantly improved toughness, hydrolysis resistance, ethanol resistance, cold resistance, abrasion resistance, and skin-forming properties compared to the oil-based polyurethane prepared using commercially available polyhexanediol adipate.

[0073] Experimental Example 2 Waterborne polyurethane was prepared using the polyester polyols from Examples 1, 4, and 5, respectively; a control group using polyhexyl adipate diol was also prepared. The specific preparation method for waterborne polyurethane was as follows: 100g of polyester diol was added to a 1000mL four-necked round-bottom flask and heated to 120℃. After vacuum dehydration, the temperature was lowered to 60℃. 41.26g of isophorone diisocyanate (IPDI) and 12μL of dibutyltin dilaurate were added. The temperature was raised to 80℃ and maintained for 2 hours. Then, 9.89g of the hydrophilic agent 2,2-dihydroxypropionic acid (DMPA) was added, and the reaction was carried out for 1 hour. The temperature was then lowered to 50℃, diluted with 100mL of acetone, and 7.46g of the salt-forming agent triethylamine was added. After discharge, water was added to adjust the solid content to 40%, and the mixture was emulsified by high-speed stirring. Finally, the acetone was heated to evaporate, yielding a polyurethane emulsion. A thickener was added to adjust the viscosity to facilitate film formation, thus obtaining waterborne polyurethane.

[0074] Storage stability tests were conducted on each waterborne polyurethane. Specifically, each waterborne polyurethane was placed in a constant temperature environment of 60℃ and stored for 5 days. The changes in color, uniformity, film-forming properties, and pH of the waterborne polyurethane emulsion were then observed. The specific results are shown in the table below:

[0075] Furthermore, the physical properties of the waterborne polyurethane resins corresponding to Examples 1, 4, 5, and the control group were tested. The film coating conditions were as follows: each polyurethane film was uniformly coated onto a glass plate using an 80-micron coating rod, allowed to stand at room temperature for 1 hour, then transferred to an oven and allowed to stand at 40°C for 1 hour, 60°C for 1 hour, and 80°C for 1 hour. The films were then removed and cured to obtain polyurethane films. Physical property testing was performed using a universal testing machine (Jinjian UTM-1432 universal tensile testing machine). The specific testing method followed GB / T1040-2006. Each polyurethane film was cut into standard strips of 2cm × 15cm as samples. The sample movement speed was controlled at 100mm / min. The tensile strength and elongation at break of each sample were tested at room temperature. The specific results are shown in the table below.

[0076] Furthermore, water resistance tests were conducted on the polyurethane films corresponding to Examples 1, 4, and 5, respectively. Specifically, after immersing the polyurethane films corresponding to Examples 1, 4, and 5 in water for 5 days, each polyurethane film exhibited good elasticity and extensibility, without hardening or brittleness, demonstrating excellent water resistance.

[0077] Furthermore, ethanol resistance and scratch resistance tests were conducted on the polyurethane films corresponding to Examples 1, 4, and 5, respectively. Specifically, a 1kg weight, wrapped in cloth and soaked in alcohol, was rubbed back and forth on the surface of each polyurethane film 100 times, and the swelling and scratching performance of each polyurethane film were observed. The specific results are shown in the table below:

[0078] It can be seen that the waterborne polyurethane prepared using the polyester polyol of the present invention has significantly improved storage performance compared with the waterborne polyurethane prepared using commercially available polyhexyl adipate diol, and the toughness, hydrolysis resistance, ethanol resistance and scratch resistance of the polyurethane film prepared using it are also significantly improved.

[0079] Unless otherwise stated, all percentages used in this invention are mass percentages.

[0080] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A process for the preparation of a polyester polyol, characterized in that, The method comprises the following steps: prepolymerization, polycondensation reaction, byproduct recycling; The method of the prepolymerization is as follows: dimethyl glutarate and dihydric alcohol are put into a reaction kettle, a catalyst is added under stirring, the reaction pressure is controlled to be normal pressure, the temperature is raised to 100-200 DEG C under stirring, and the prepolymerization is carried out under insulation until no light components are distilled out, and the prepolymerization is completed. The method of the polycondensation reaction is as follows: after the prepolymerization is completed, the temperature is continuously raised to 180-185 DEG C under stirring, the reaction kettle is vacuumized under insulation, and the polycondensation reaction is carried out under vacuum and insulation to obtain polyester polyol.

2. The method for producing a polyester polyol according to claim 1, characterized by, In the prepolymerization, the dihydric alcohol is at least one of the following: ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, diethylene glycol, triethylene glycol, polyethylene glycol, polytetraethylene glycol.

3. The method of making a polyester polyol according to claim 1, wherein, In the prepolymerization, the molar ratio of dimethyl glutarate to dihydric alcohol is 1:1-5.

4. The method of making a polyester polyol according to claim 1, wherein, In the prepolymerization, the time for carrying out the prepolymerization under insulation is 4-5 h. In the polycondensation reaction, the time for carrying out the polycondensation reaction under vacuum and insulation is 7-9 h.

5. The method of making a polyester polyol according to claim 1, wherein, In the prepolymerization, the catalyst is an organic tin catalyst and / or an organic titanium catalyst. The organic tin catalyst is at least one of the following: dibutyltin dilaurate, dimethyltin dineodecanoate, dibutyltin oxide; the organic titanium catalyst is at least one of the following: titanium tetra-n-butylate, titanium tetra-n-propylate, titanium tetra-isopropylate, titanium isopropylate; The addition amount of the catalyst is 10-100 ppm of the total weight of dimethyl glutarate and dihydric alcohol.

6. The method of making a polyester polyol according to claim 1, wherein, In the prepolymerization, the methanol generated is continuously collected from the top of the reaction kettle and recovered by condensation, and then is used for byproduct recycling. In the polycondensation reaction, the methanol generated in the process of insulation and vacuumization of the reaction kettle is continuously collected from the top of the reaction kettle and recovered by condensation, and then is used for byproduct recycling.

7. The method of making a polyester polyol according to claim 6, wherein, The method of the byproduct recycling is as follows: the recovered methanol in the prepolymerization and / or the polycondensation reaction is used for esterification to prepare dimethyl glutarate or dimethyl succinate; the dimethyl succinate is used for hydrogenolysis to prepare butanediol. The dimethyl glutarate and / or butanediol prepared in the byproduct recycling is recycled to the prepolymerization.

8. A polyester polyol characterized in that, The polyester polyol is prepared by the preparation method of any one of claims 1-7, and has a molecular weight of 300-10000.

9. The polyester polyol according to claim 8, characterized in that, HO-[(CH2) m -O-CO-(CH2)3-CO-О] n -(CH2) m -OH; wherein -(CH2) m - from dihydric alcohol, -CO-(CH2)3-CO- from dimethyl glutarate, m is any integer from 2 to 12, n is the number of repeating units.

10. Use of the polyester polyol according to claim 8 for the production of polyurethanes, characterized in that The polyurethane is an oily polyurethane or an aqueous polyurethane.

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