A method for catalytically synthesizing oligomeric polyester polyols using methyl glycolate as raw material

Abstract

The present invention belongs to the technical field of polyurethane materials, and specifically relates to a method for catalytically synthesizing oligomeric polyester polyols using methyl glycolate as a raw material. To prepare a novel oligomeric polyester polyol with a higher ester group content, the present invention first conducts an ester exchange reaction between methyl glycolate and a small molecule polyol in the presence of a catalyst to produce a glycolic acid polyol ester-based dimeric polyhydroxy compound. The glycolic acid polyol ester-based dimeric polyhydroxy compound then reacts with an organic dicarboxylic acid to produce a novel oligomeric polyester polyol (molecular weight 1,000 to 3,000) with a higher ester group content through esterification and polycondensation. This method is expected to impart stronger polarity and intermolecular hydrogen bonding to the polyurethane material, thereby improving the material's mechanical properties.

Description

Technical Field

[0001] The invention belongs to the technical field of polyurethane materials, and particularly relates to a method for catalytically synthesizing oligomeric polyester polyols by using methyl glycolate as a raw material. Background Art

[0002] Polyurethane (PU) is a class of polymer materials with excellent properties, typically prepared through polymerization reactions using polyols, polyisocyanates, and chain extenders as primary raw materials. Because PU's molecular structure contains repetitive rigid urethane segments (hard segments) and flexible polyol segments, it possesses excellent mechanical properties, wear resistance, flexibility, weather resistance, chemical resistance, processability, and performance adjustability. It can be made into elastomers, foams, fibers, synthetic leather, coatings, and adhesives, and is widely used in a variety of fields, including aerospace, construction and building materials, transportation, textile machinery, sports equipment, clothing and footwear, electrical equipment, and mining. As the scope of polyurethane applications continues to expand, the requirements for its performance are also gradually increasing. Developing new polyurethane raw materials and improving the performance of polyurethane materials to meet diverse application requirements have become a key direction in polyurethane development in recent years.

[0003] Oligomeric polyester polyols are one of the important raw materials for synthesizing polyurethane materials, and are mainly used to synthesize high-performance polyurethane elastomers. The synthesis of polyester polyols is usually prepared by dehydration esterification and polycondensation reaction using small molecule polyols and dicarboxylic acids or anhydrides as raw materials. Because polyester polyols contain highly polar ester groups, the hydrogen bonding effect in the prepared polyurethane material is significantly improved, giving the material better mechanical properties, thermal stability, oil resistance, etc. Compared with polyether polyols, polyester polyols have a wider range of molecular structure design and adjustment due to the rich variety of small molecule polyols and polyacid raw materials, and the categories of related polyurethane products are also more.

[0004] Methyl glycolate (MG) contains two functional groups, hydroxyl and ester, and possesses the chemical properties of both alcohols and esters. It has a wide range of uses, not only as a common chemical intermediate and excellent solvent, but also in organic and pharmaceutical synthesis, particularly in the preparation of the biodegradable material polyglycolic acid, as described in patent CN107177032A. Introducing glycolic acid segments into the molecular chains of polyurethane polymers could theoretically improve the biodegradability of polyurethane materials, but research in this area is limited, with only a few reports. For example, in patent CN112194781A, glycolic acid is mixed with 1,4-butanediol and, in the presence of zinc acetate dihydrate as a catalyst, undergoes a condensation reaction to produce a polyglycolic acid-based polyol containing one butanediol and multiple glycolic acid segments. The reaction process is shown below:

[0005]

[0006] This polyol has been used in polyurethane rigid foam materials, showing good mechanical properties and certain degradability. Although these reports have achieved the application of glycolic acid groups in polyurethane, the synthesized polyols are mainly polyglycolic acid with a molecular weight of about 200 to 300, and their application has only been investigated in the preparation of polyurethane rigid foam materials. The polyols described in the paper "Preparation and Application of Polyglycolic Acid-Based Polyols" have too high hydroxyl and acid values ​​(hydroxyl value 381.32 mgKOH / g, acid value 48.85 mgKOH / g), and are not suitable for the preparation of polyurethane elastomers.

[0007] Therefore, the present invention requires a novel oligomeric polyester polyol with a higher ester content, which can give the polyurethane material stronger polarity and intermolecular hydrogen bonding, thereby improving the mechanical properties of the material. Summary of the Invention

[0008] To address the above-mentioned issues, the present invention provides a method for catalytically synthesizing oligomeric polyester polyols using methyl glycolate as a raw material. Under the action of a catalyst, methyl glycolate first undergoes an ester exchange reaction with a small molecule polyol to produce a glycolate polyol ester-based dimeric polyhydroxy compound. The glycolate polyol ester-based dimeric polyhydroxy compound then reacts with an organic dicarboxylic acid to produce a novel oligomeric polyester polyol (molecular weight 1000-3000) with a higher ester group content through esterification and polycondensation. This method is expected to impart stronger polarity and intermolecular hydrogen bonding to polyurethane materials, thereby improving the material's mechanical properties.

[0009] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions:

[0010] Because MG has a unique hydroxyl and ester structure, it can undergo an ester exchange reaction with small molecular polyols such as ethylene glycol, propylene glycol, butanediol, and hexanediol to produce new ester-containing diols such as ethylene glycol ester. The reaction process is as follows:

[0011]

[0012] Among them, the dotted box is the structural formula of the transesterification product, R = CH2-CH2-O-CH2CH2; CH2-CH2-O-CH2-CH2-O-CH2-CH2; (CH2) n , n=2,3,4,5,6….

[0013] Because the hydroxyl groups on MG are affected by the electron-withdrawing carbonyl group, the rate of transesterification between MG molecules is slower than with diols containing multiple methylene groups, such as 1,4-butanediol. Therefore, by manipulating catalysts and reaction conditions, it is possible to selectively transesterify MG with ethylene glycol, butanediol, and other diols to produce novel diols such as glycolate (HO-CH2-C(O)O-CH2-CH2-OH). The physical properties of this novel diol have not yet been reported. However, the hydroxyl groups at its terminals can be reacted with dicarboxylic acids to produce novel polyester polyols (as shown below), which can then be used to prepare polyurethane materials. Compared to traditional polyester polyols such as polybutylene adipate diol and polyethylene adipate diol, the introduction of specialized glycolate segments is expected to impart superior mechanical properties to the resulting polyurethanes, providing a new avenue for the development of novel polyurethane products.

[0014] The process of synthesizing oligomeric polyester polyols by polycondensation and dehydration of alkyd is as follows:

[0015]

[0016] Where R'=(CH2) n , n=2,3,4,5,6….

[0017] A method for catalytically synthesizing oligomeric polyester polyols using methyl glycolate as a raw material comprises the following steps:

[0018] Step 1, transesterification reaction stage: under normal pressure, the catalyst, small molecule polyol and methyl glycolate are all added into a reactor to carry out transesterification reaction of methyl glycolate and small molecule polyol;

[0019] Step 2, vacuum separation and purification stage: removing unreacted raw materials in the transesterification reaction stage through vacuum separation and purification to obtain a purified transesterification product;

[0020] Step 3, esterification reaction stage: under normal pressure, the catalyst, the purified transesterification product and the organic dicarboxylic acid are added to a reactor equipped with a distillation device to carry out an esterification reaction between the polyol and the organic dicarboxylic acid;

[0021] Step 4, the decompression and polycondensation stage: the pressure is reduced in stages from normal pressure, and a polycondensation reaction is carried out to further esterify and dehydrate the small molecule product obtained in the esterification reaction stage to achieve the growth of the molecular chain segment, remove by-products and excess reactants, and cool to obtain an oligomeric polyester polyol with a set molecular weight.

[0022] Furthermore, the small molecule polyol in step 1 is a linear or branched saturated fatty alcohol, the number of its carbon atoms is 2 to 25, and the hydroxyl functionality is ≥2.

[0023] Furthermore, the straight-chain saturated fatty alcohol is one or more of ethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol or triethylene glycol; the branched-chain saturated fatty alcohol is one or more of 1,2-propylene glycol, methylpropanediol, 1,3-butanediol, neopentyl glycol, 2-ethyl-hexanediol or trimethylolpropane.

[0024] Furthermore, the amount of catalyst used in step 1 is 50ppm to 1000ppm of the total mass of the reactants in the ester exchange reaction stage; the molar ratio of methyl glycolate to small molecule polyol is 1:1 to 2; the temperature of the ester exchange reaction is 140 to 170°C, and the time is 4hr to 12hr.

[0025] Furthermore, the vacuum separation and purification in step 2 is specifically as follows: purification is carried out by stepwise decompression from normal pressure to -0.095 MPa, the temperature of the decompression process is maintained at 110° C. to 115° C., and the vacuum separation time is 0.5 hr to 6 hr.

[0026] Furthermore, the organic dicarboxylic acid in step 3 is one or more of oxalic acid, malonic acid, succinic acid, maleic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, and terephthalic acid.

[0027] Furthermore, the amount of catalyst used in step 3 is 50ppm to 500ppm of the purified transesterification product; the molar ratio of the purified transesterification product to the organic dicarboxylic acid is 1.0 to 1.6:1; the esterification reaction temperature is 140°C to 200°C, and the reaction time is 3hr to 12hr.

[0028] Furthermore, in step 4, the pressure is reduced from normal pressure to -0.050 MPa to -0.095 MPa in stages, the temperature of the polycondensation reaction is 160° C. to 250° C., and the time is 2 hr to 12 hr.

[0029] Furthermore, the catalyst is an organic titanate, organic tin, or organic amine catalyst.

[0030] Furthermore, the catalyst is one of tetrabutyl titanate, tetraisopropyl titanate, dibutyltin oxide, and triethylamine.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] The methyl glycolate used in this invention has a unique hydroxyl and ester structure, making it the simplest alcohol-ester compound. The resulting oligomeric polyester polyol is a novel polyol structure, and its preparation method has not yet been reported. This polyester polyol has a higher ester group content and, when used in polyurethane synthesis, can impart stronger polarity and intermolecular hydrogen bonding, potentially improving the mechanical properties of the polyurethane. DETAILED DESCRIPTION

[0033] In order to further illustrate the technical solution of the present invention, the present invention is further described below through examples.

[0034] Example 1

[0035] A method for catalytically synthesizing oligomeric polyester polyols using methyl glycolate as a raw material comprises the following steps:

[0036] Step 1, transesterification reaction stage: In a 500 mL four-necked flask equipped with a stirring and heating system, a temperature measuring system, a constant pressure feeding tube, and a distillation column with a tower top reflux distributor, 90.08 g (1 mol) of methyl glycolate, 93.10 g (1.5 mol) of ethylene glycol, and 0.0427 g (233 ppm / wt. total mass of the reactants) of a catalyst (tetrabutyl titanate) were added all at once. The distillation column was opened to condense water at the top, the distillation column was preheated (the wall temperature was controlled at about 70°C), nitrogen was purged to displace the air in the reactor, stirring was started, and the reactor temperature was rapidly heated to 144°C. Methanol condensed and refluxed at the top of the distillation column. The reflux distributor was opened to remove the methanol generated by the transesterification reaction. The reaction was continued at normal pressure for 6 hours to obtain a crude transesterification product.

[0037] Step 2, vacuum separation and purification stage: use a rotary evaporator to remove residual methanol and unreacted methyl glycolate at 110°C for 1.5 hours under a reduced pressure of -0.095 MPa, cool and seal to obtain the purified transesterification reaction product, a small molecule diol (Di(MG / EG)OL).

[0038] Step 3, Esterification Reaction Stage: In another clean 500 mL four-necked flask equipped with a stirring system, heating system, temperature measurement system, and a distillation separation column with an overhead reflux distributor, add 211.99 g (1.19 mol) of the aforementioned small molecule diol (Di(MG / EG)OL), 120.37 g (0.82 mol) of adipic acid, and 0.0212 g (100 ppm / wt. of the starting small molecule diol) of tetrabutyl titanate catalyst. The synthesis of the polyester polyol using a vacuum melt polycondensation method consists of two stages: an atmospheric pressure esterification stage and a reduced pressure polycondensation stage. During the atmospheric pressure esterification stage, the reactor temperature is rapidly heated to 148°C. When condensation reflux appears at the top of the distillation column, the reflux distributor is opened to remove water generated by the esterification reaction. The reaction is continued at atmospheric pressure within the range of 150°C to 180°C for 6 hours.

[0039] Step 4, reduced pressure polyolation: During this reduced pressure polyolation stage, the reaction temperature is controlled at 180°C to 210°C, and the pressure is gradually reduced from atmospheric pressure to -0.05 MPa, -0.06 MPa, -0.07 MPa, -0.08 MPa, and -0.095 MPa. The reduced pressure polyolation reaction is continued for 4.5 hours to remove byproducts and excess low-molecule alcohol. Cooling is then performed to obtain the target product, oligomeric polyester polyol - P﹝AA / (Di(MG / EG)OL)﹞DL.

[0040] At room temperature, the product, P﹝AA / (Di(MG / EG)OL)﹞DL, is a light yellow liquid with a hydroxyl number of 109.83 mgKOH / g, an acid number of 0.02 mgKOH / g, an average molecular weight of 1021.39, a yield of 97.56%, and an ester content of 57.75% by weight. The product, P﹝AA / (Di(MG / EG)OL)﹞DL, was reacted with diphenylmethane-4,4'-diisocyanate (MDI) to prepare a prepolymer with a free NCO content of 8.5%. This prepolymer was then chain-extended with a small molecule diol (1,4-butanediol) to produce a polyurethane elastomer sample. Test performance results showed: Shore A hardness of 90, tensile strength of 40.1 MPa, elongation at break of 526%, tear strength of 112.4 kN / m, and impact resilience of 23%.

[0041] Example 2

[0042] A method for catalytically synthesizing oligomeric polyester polyols using methyl glycolate as a raw material comprises the following steps:

[0043] Step 1, transesterification reaction stage: In a 500 mL four-necked flask equipped with a stirring and heating system, a temperature measuring system, a constant pressure feeding tube, and a distillation column with a tower top reflux distributor, 90.08 g (1 mol) of methyl glycolate, 114.15 g (1.5 mol) of 1,3-propylene glycol, and 0.0448 g (219.5 ppm / wt. total mass of the reactants) of a catalyst (tetrabutyl titanate) were added at once. The distillation column was opened to condense water at the top, the distillation column was preheated (the wall temperature was controlled at about 70°C), nitrogen was purged to displace the air in the reactor, stirring was started, and the reactor temperature was rapidly heated to 147°C. Methanol condensed and refluxed at the top of the distillation column. The reflux distributor was opened to remove the methanol generated by the transesterification reaction. The reaction was continued at normal pressure for 6 hours to obtain a crude transesterification product.

[0044] Step 2, vacuum separation and purification stage: Residual methanol and unreacted methyl glycolate were removed using a rotary evaporator at 110° C. for 2 hours under a reduced pressure of −0.095 MPa. The mixture was cooled and sealed to obtain the purified transesterification reaction product, a small molecule diol (Di(MG / 1,3-PDO)OL).

[0045] Step 3, Esterification Reaction Stage: In another clean 500 mL four-necked flask equipped with a stirring system, heating system, temperature measurement system, and a distillation separation column with an overhead reflux distributor, add 265.21 g (1.38 mol) of the aforementioned small molecule diol (Di(MG / 1,3-PDO)OL), 141.76 g (0.97 mol) of adipic acid, and 0.0326 g (123 ppm / wt. of the starting small molecule diol) of tetrabutyl titanate catalyst. The synthesis of the polyester polyol using a vacuum melt polycondensation method consists of two stages: an atmospheric pressure esterification stage and a reduced pressure polycondensation stage. During the atmospheric pressure esterification stage, the reactor temperature is rapidly heated to 156°C. Reflux condensation appears at the top of the distillation column. The reflux distributor is then opened to remove water generated by the esterification reaction. The reaction is continued at atmospheric pressure within the range of 150°C to 180°C for 6 hours.

[0046] Step 4, reduced pressure polyolation: During this reduced pressure polyolation stage, the reaction temperature is controlled at 180°C to 210°C, and the pressure is gradually reduced from atmospheric pressure to -0.05 MPa, -0.06 MPa, -0.07 MPa, -0.08 MPa, and -0.095 MPa. The reduced pressure polyolation reaction is continued for 5 hours to remove byproducts and excess low-molecule alcohol. Cooling is then performed to obtain the target product, oligomeric polyester polyol - P﹝AA / (Di(MG / 1,3-PDO)OL)﹞DL.

[0047] At room temperature, the product, P﹝AA / (Di(MG / 1,3-PDO)OL)﹞DL, is a light yellow liquid with a hydroxyl number of 108.53 mgKOH / g, an acid number of 0.03 mgKOH / g, an average molecular weight of 1033.53, a yield of 97.15%, and an ester content of 54.03% by weight. The product, P﹝AA / (Di(MG / 1,3-PDO)OL)﹞DL, was reacted with diphenylmethane-4,4'-diisocyanate (MDI) to prepare a prepolymer with a free NCO content of 8.5%. This prepolymer was then chain-extended with a small diol (1,4-butanediol) to produce a polyurethane elastomer sample. Test performance results showed: Shore A hardness of 90, tensile strength of 42.3 MPa, elongation at break of 538%, tear strength of 126.8 kN / m, and impact resilience of 24%.

[0048] Example 3

[0049] A method for catalytically synthesizing oligomeric polyester polyols using methyl glycolate as a raw material comprises the following steps:

[0050] Step 1, transesterification reaction stage: In a 500 mL four-necked flask equipped with a stirring and heating system, a temperature measuring system, a constant pressure feeding tube, and a distillation column with a tower top reflux distributor, 90.08 g (1 mol) of methyl glycolate, 159.18 (1.5 mol) of diethylene glycol, and 0.0597 g (239.5 ppm / wt. total mass of reactants) of catalyst (tetraisopropyl titanate) were added at once. The distillation column was opened to condense water at the top, the distillation column was preheated (the wall temperature was controlled at about 70°C), nitrogen was purged to replace the air in the reactor, stirring was started, and the reactor temperature was rapidly heated to 151°C. Methanol condensed and refluxed at the top of the distillation column. The reflux distributor was opened to remove the methanol generated by the transesterification reaction. The reaction was continued at normal pressure for 6 hours to obtain a crude transesterification product.

[0051] Step 2, vacuum separation and purification stage: use a rotary evaporator to remove residual methanol and unreacted methyl glycolate at 110°C for 1 hour under a reduced pressure of -0.095 MPa, cool and seal to obtain the purified transesterification reaction product, a small molecule diol (Di(MG / DEG)OL).

[0052] Step 3, esterification reaction stage: In another clean 500 mL four-necked flask equipped with a stirring system, heating system, temperature measurement system, and a distillation separation column with an overhead reflux distributor, add 284.42 g (1.28 mol) of the aforementioned small molecule diol (Di(MG / DEG)OL), 135.91 g (0.93 mol) of adipic acid, and 0.0370 g (130 ppm / wt. of the starting small molecule diol) of tetraisopropyl titanate catalyst. The synthesis of the polyester polyol using a vacuum melt polycondensation method consists of two stages: an atmospheric pressure esterification stage and a reduced pressure polycondensation stage. During the atmospheric pressure esterification stage, the reactor temperature is rapidly heated to 150°C. When condensation reflux appears at the top of the distillation column, the reflux distributor is opened to remove water generated by the esterification reaction. The reaction is continued at atmospheric pressure within the range of 150°C to 180°C for 7 hours.

[0053] Step 4, reduced pressure polyol stage: During this reduced pressure polyol stage, the reaction temperature is controlled at 180°C to 210°C, and the pressure is gradually reduced from atmospheric pressure to -0.05 MPa, -0.06 MPa, -0.07 MPa, -0.08 MPa, and -0.095 MPa. The reduced pressure polyol reaction is continued for 4.5 hours to remove byproducts and excess low-molecule alcohol. Cooling is then performed to obtain the target product, oligomeric polyester polyol - P﹝AA / (Di(MG / DEG)OL)﹞DL.

[0054] At room temperature, the product, P﹝AA / (Di(MG / DEG)OL)﹞DL, is a light yellow liquid with a hydroxyl number of 73.83 mgKOH / g, an acid number of 0.03 mgKOH / g, an average molecular weight of 1519.09, a yield of 96.73%, and an ester content of 50.35% by weight. The product, P﹝AA / (Di(MG / DEG)OL)﹞DL, was reacted with diphenylmethane-4,4'-diisocyanate (MDI) to prepare a prepolymer with a free NCO content of 8.5%. This prepolymer was then chain-extended with a small diol (1,4-butanediol) to produce a polyurethane elastomer sample. Test performance results showed: Shore A hardness of 89, tensile strength of 37.8 MPa, elongation at break of 508%, tear strength of 105.4 kN / m, and impact resilience of 21%.

[0055] Example 4

[0056] A method for catalytically synthesizing oligomeric polyester polyols using methyl glycolate as a raw material comprises the following steps:

[0057] Step 1, transesterification reaction stage: In a 500mL four-necked flask equipped with a stirring and heating system, a temperature measuring system, a constant pressure feeding tube, and a distillation column with a tower top reflux distributor, 90.08g (1 mol) of methyl glycolate, 94.63 (1.05 mol) of 1,4-butanediol, and 0.0739g (400ppm / wt. total mass of the reactants) of a catalyst (tetrabutyl titanate) were added at once. The distillation column was opened to condense water at the top, the distillation column was preheated (the wall temperature was controlled at about 70°C), high-purity nitrogen was purged to displace the air in the reactor, stirring was started, and the reactor temperature was rapidly heated to 137°C. Methanol condensed and refluxed at the top of the distillation column. The reflux distributor was opened to remove the methanol generated by the transesterification reaction. The reaction was continued at normal pressure for 6 hours to obtain a crude transesterification product.

[0058] Step 2, vacuum separation and purification stage: Residual methanol and unreacted methyl glycolate were removed using a rotary evaporator at 110° C. for 1.5 hours under a reduced pressure of −0.095 MPa. The mixture was cooled and sealed to obtain the purified transesterification reaction product, a small molecule diol (Di(MG / 1,4-BDO)OL).

[0059] Step 3, Esterification Reaction Stage: In another clean 500 mL four-necked flask equipped with a stirring system, heating system, temperature measurement system, and a distillation separation column with an overhead reflux distributor, add 158.77 g (0.77 mol) of the aforementioned small molecule diol (Di(MG / 1,4-BDO)OL), 72.34 g (0.495 mol) of adipic acid, and 0.0318 g (200 ppm / wt. of the starting small molecule diol) of tetrabutyl titanate catalyst. The synthesis of the polyester polyol using a vacuum melt polycondensation method consists of two stages: an atmospheric pressure esterification stage and a reduced pressure polycondensation stage. During the atmospheric pressure esterification stage, the reactor temperature is rapidly heated to 149°C. Reflux condensation appears at the top of the distillation column. The reflux distributor is then opened to remove water generated by the esterification reaction. The reaction is continued at atmospheric pressure within the range of 150°C to 180°C for 7 hours.

[0060] Step 4, reduced pressure polyol stage: During this reduced pressure polyol stage, the reaction temperature is controlled at 180°C to 210°C, and the pressure is gradually reduced from atmospheric pressure to -0.05 MPa, -0.06 MPa, -0.07 MPa, -0.08 MPa, and -0.095 MPa. The reduced pressure polyol reaction is continued for 4.5 hours to remove byproducts and excess low-molecule alcohol. Cooling is then performed to obtain the target product, oligomeric polyester polyol - P (AA / (Di (MG / 1,4-BDO) OL)) DL.

[0061] At room temperature, the product, P﹝AA / (Di(MG / 1,4-BDO)OL)﹞DL, is a light yellow liquid with a hydroxyl number of 108.14 mgKOH / g, an acid number of 0.03 mgKOH / g, an average molecular weight of 1037.26, a yield of 96.81%, and an ester content of 51.07% by weight. The product, P﹝AA / (Di(MG / 1,4-BDO)OL)﹞DL, was reacted with diphenylmethane-4,4'-diisocyanate (MDI) to prepare a prepolymer with a free NCO content of 8.5%. This prepolymer was then chain-extended with a low-molecular-weight diol (1,4-butanediol) to produce a polyurethane elastomer sample. Test performance results showed: Shore A hardness of 90, tensile strength of 43.6 MPa, elongation at break of 556%, tear strength of 138.39 kN / m, and impact resilience of 23%.

[0062] Example 5

[0063] A method for catalytically synthesizing oligomeric polyester polyols using methyl glycolate as a raw material comprises the following steps:

[0064] Step 1, transesterification reaction stage: In a 500 mL four-necked flask equipped with a stirring and heating system, a temperature measuring system, a constant pressure feeding tube, and a distillation column with a tower top reflux distributor, 90.08 g (1 mol) of methyl glycolate, 94.63 (1.05 mol) of 1,4-butanediol, and 0.0434 g (235 ppm / wt. total mass of the reactants) of a catalyst (tetrabutyl titanate) were added at once. The distillation column was opened to condense water at the top, the distillation column was preheated (the wall temperature was controlled at about 70°C), high-purity nitrogen was purged to displace the air in the reactor, stirring was started, and the reactor temperature was rapidly heated to 140°C. Methanol condensed and refluxed at the top of the distillation column. The reflux distributor was opened to remove the methanol generated by the transesterification reaction. The reaction was continued at normal pressure for 7 hours to obtain a crude transesterification product.

[0065] Step 2, vacuum separation and purification stage: Residual methanol and unreacted methyl glycolate were removed using a rotary evaporator at 110° C. for 1.5 hours under a reduced pressure of −0.095 MPa. The mixture was cooled and sealed to obtain the purified transesterification reaction product, a small molecule diol (Di(MG / 1,4-BDO)OL).

[0066] Step 3, esterification reaction stage: In another clean 500 mL four-necked flask equipped with a stirring system, heating system, temperature measurement system, and a distillation separation column with an overhead reflux distributor, add 158.77 g (0.77 mol) of the aforementioned small molecule diol (Di(MG / 1,4-BDO)OL), 84.76 g (0.58 mol) of adipic acid, and 0.0238 g (150 ppm / wt. of the starting small molecule diol) of tetrabutyl titanate catalyst. The synthesis of the polyester polyol using a vacuum melt polycondensation method consists of two stages: an atmospheric pressure esterification stage and a reduced pressure polycondensation stage. During the atmospheric pressure esterification stage, the reactor temperature is rapidly heated to 167°C. Reflux condensation appears at the top of the distillation column. The reflux distributor is opened to remove water generated by the esterification reaction. The reaction is continued at atmospheric pressure within the range of 150°C to 180°C for 6 hours.

[0067] Step 4, reduced pressure polyolation: During this reduced pressure polyolation stage, the reaction temperature is controlled at 180°C to 210°C, and the pressure is gradually reduced from atmospheric pressure to -0.05 MPa, -0.06 MPa, -0.07 MPa, -0.08 MPa, and -0.095 MPa. The reduced pressure polyolation reaction is continued for 4 hours to remove byproducts and excess low-molecule alcohol. Cooling is then performed to obtain the target product, oligomeric polyester polyol - P﹝AA / (Di(MG / 1,4-BDO)OL)﹞DL.

[0068] At room temperature, the product, P﹝AA / (Di(MG / 1,4-BDO)OL)﹞DL, is a light yellow, viscous liquid with a hydroxyl number of 56.81 mgKOH / g, an acid number of 0.02 mgKOH / g, an average molecular weight of 1974.31, a yield of 96.29%, and an ester content of 55.02% by weight. The product, P﹝AA / (Di(MG / 1,4-BDO)OL)﹞DL, was reacted with diphenylmethane-4,4'-diisocyanate (MDI) to prepare a prepolymer with a free NCO content of 8.5%. This prepolymer was then chain-extended with a low-molecular-weight diol (1,4-butanediol) to produce a polyurethane elastomer sample. Test performance results showed: Shore A hardness of 91, tensile strength of 45.0 MPa, elongation at break of 561%, tear strength of 152.7 kN / m, and impact resilience of 25%.

[0069] Example 6

[0070] A method for catalytically synthesizing oligomeric polyester polyols using methyl glycolate as a raw material comprises the following steps:

[0071] Step 1, transesterification reaction stage: In a 500 mL four-necked flask equipped with a stirring and heating system, a temperature measuring system, a constant pressure feeding tube, and a distillation column with a tower top reflux distributor, 90.08 g (1 mol) of methyl glycolate, 94.63 (1.05 mol) of 1,4-butanediol, and 0.0434 g (235 ppm / wt. total mass of the reactants) of a catalyst (tetrabutyl titanate) were added all at once. The distillation column was opened to condense water at the top, the distillation column was preheated (the wall temperature was controlled at about 70°C), high-purity nitrogen was purged to displace the air in the reactor, stirring was started, and the reactor temperature was rapidly heated to 140°C. Methanol condensed and refluxed at the top of the distillation column. The reflux distributor was opened to remove the methanol generated by the transesterification reaction. The reaction was continued at normal pressure for 12 hours to obtain a crude transesterification product.

[0072] Step 2, vacuum separation and purification stage: Residual methanol and unreacted methyl glycolate were removed using a rotary evaporator at 110° C. for 1.5 hours under a reduced pressure of −0.095 MPa. The mixture was cooled and sealed to obtain the purified transesterification reaction product, a small molecule diol (Di(MG / 1,4-BDO)OL).

[0073] Step 3, esterification reaction stage: In another clean 500 mL four-necked flask equipped with a stirring system, heating system, temperature measurement system, and a distillation separation column with an overhead reflux distributor, add 158.77 g (0.77 mol) of the aforementioned small molecule diol (Di(MG / 1,4-BDO)OL), 84.76 g (0.58 mol) of adipic acid, and 0.0238 g (150 ppm / wt. of the starting small molecule diol) of tetrabutyl titanate catalyst. The synthesis of the polyester polyol using a vacuum melt polycondensation method consists of two stages: an atmospheric pressure esterification stage and a reduced pressure polycondensation stage. During the atmospheric pressure esterification stage, the reactor temperature is rapidly heated to 167°C. Reflux condensation appears at the top of the distillation column. The reflux distributor is opened to remove water generated by the esterification reaction. The reaction is continued at atmospheric pressure within the range of 150°C to 180°C for 6 hours.

[0074] Step 4, reduced pressure polyolation: During this reduced pressure polyolation stage, the reaction temperature is controlled at 180°C to 210°C, and the pressure is gradually reduced from atmospheric pressure to -0.05 MPa, -0.06 MPa, -0.07 MPa, -0.08 MPa, and -0.095 MPa. The reduced pressure polyolation reaction is continued for 4 hours to remove byproducts and excess low-molecule alcohol. Cooling is then performed to obtain the target product, oligomeric polyester polyol - P﹝AA / (Di(MG / 1,4-BDO)OL)﹞DL.

[0075] At room temperature, the product, P﹝AA / (Di(MG / 1,4-BDO)OL)﹞DL, is a light yellow, viscous liquid with a hydroxyl number of 56.92 mgKOH / g, an acid number of 0.02 mgKOH / g, an average molecular weight of 1970.65, a yield of 96.20%, and an ester content of 55.02% by weight. The product, P﹝AA / (Di(MG / 1,4-BDO)OL)﹞DL, was reacted with diphenylmethane-4,4'-diisocyanate (MDI) to prepare a prepolymer with a free NCO content of 8.5%. This prepolymer was then chain-extended with a low-molecular-weight diol (1,4-butanediol) to produce a polyurethane elastomer sample. Test performance results showed: Shore A hardness of 91, tensile strength of 44.8 MPa, elongation at break of 558%, tear strength of 152.1 kN / m, and impact resilience of 25%.

[0076] Example 7

[0077] A method for catalytically synthesizing oligomeric polyester polyols using methyl glycolate as a raw material comprises the following steps:

[0078] Step 1, transesterification reaction stage: In a 500 mL four-necked flask equipped with a stirring and heating system, a temperature measuring system, a constant pressure feeding tube, and a distillation column with a tower top reflux distributor, 90.08 g (1 mol) of methyl glycolate, 94.63 (1.05 mol) of 1,4-butanediol, and 0.0586 g (317 ppm / wt. total mass of the reactants) of a catalyst (tetrabutyl titanate) were added at once. The distillation column was opened to condense water at the top, the distillation column was preheated (the wall temperature was controlled at about 70°C), high-purity nitrogen was purged to displace the air in the reactor, stirring was started, and the reactor temperature was rapidly heated to 140°C. Methanol condensed and refluxed at the top of the distillation column. The reflux distributor was opened to remove the methanol generated by the transesterification reaction. The reaction was continued at normal pressure for 7 hours to obtain a crude transesterification product.

[0079] Step 2, vacuum separation and purification stage: Residual methanol and unreacted methyl glycolate were removed using a rotary evaporator at 110° C. for 1.5 hours under a reduced pressure of −0.095 MPa. The mixture was cooled and sealed to obtain the purified transesterification reaction product, a small molecule diol (Di(MG / 1,4-BDO)OL).

[0080] Step 3, Esterification Reaction Stage: In another clean 500 mL four-necked flask equipped with a stirring system, heating system, temperature measurement system, and a distillation separation column with an overhead reflux distributor, add 171.26 g (0.83 mol) of the aforementioned small molecule diol (Di(MG / 1,4-BDO)OL), 73.48 g (0.62 mol) of succinic acid, and 0.0257 g (150 ppm / wt. of the starting small molecule diol) of tetrabutyl titanate catalyst. The synthesis of the polyester polyol using a vacuum melt polycondensation method consists of two stages: an atmospheric pressure esterification stage and a reduced pressure polycondensation stage. During the atmospheric pressure esterification stage, the reactor temperature is rapidly heated to 161°C. Reflux condensation appears at the top of the distillation column. The reflux distributor is then opened to remove water generated by the esterification reaction. The reaction is continued at atmospheric pressure within a temperature range of 150°C to 180°C for 6 hours.

[0081] Step 4, reduced pressure polyol stage: During this reduced pressure polyol stage, the reaction temperature is controlled at 180°C to 210°C, and the pressure is gradually reduced from atmospheric pressure to -0.05 MPa, -0.06 MPa, -0.07 MPa, -0.08 MPa, and -0.095 MPa. The reduced pressure polyol reaction is continued for 4 hours to remove byproducts and excess low-molecule alcohol. Cooling is then performed to obtain the target product, oligomeric polyester polyol - P﹝SA / (Di(MG / 1,4-BDO)OL)﹞DL.

[0082] At room temperature, the product, P﹝SA / (Di(MG / 1,4-BDO)OL)﹞DL, is a light yellow, waxy solid with a hydroxyl number of 55.15 mgKOH / g, an acid number of 0.02 mgKOH / g, an average molecular weight of 2033.57, a yield of 96.18%, and an ester content of 58.19% by weight. The product, P﹝SA / (Di(MG / 1,4-BDO)OL)﹞DL, was reacted with diphenylmethane-4,4'-diisocyanate (MDI) to prepare a prepolymer with a free NCO content of 8.5%. This prepolymer was then chain-extended with a low-molecular-weight diol (1,4-butanediol) to produce a polyurethane elastomer sample. Test performance results showed: Shore A hardness of 91, tensile strength of 35.3 MPa, elongation at break of 385%, tear strength of 92.5 kN / m, and impact resilience of 19%.

[0083] Example 8

[0084] A method for catalytically synthesizing oligomeric polyester polyols using methyl glycolate as a raw material comprises the following steps:

[0085] Step 1, transesterification reaction stage: In a 500mL four-necked flask equipped with a stirring and heating system, a temperature measuring system, a constant pressure feeding tube, and a distillation column with a tower top reflux distributor, 90.08g (1mol) of methyl glycolate, 141.80g (1.2mol) of 1,6-hexanediol, and 0.0492g (212ppm / wt. total mass of reactants) of catalyst (tetrabutyl titanate) were added at one time. The distillation column was opened to condense water at the top, the distillation column was preheated (the wall temperature was controlled at about 70°C), high-purity nitrogen was purged to displace the air in the reactor, stirring was started, and the reactor temperature was rapidly heated to 144°C. Methanol condensed and refluxed at the top of the distillation column. The reflux distributor was opened to remove the methanol generated by the transesterification reaction. The reaction was continued at normal pressure for 6 hours to obtain a crude transesterification product.

[0086] Step 2, vacuum separation and purification stage: use a rotary evaporator to remove residual methanol and unreacted methyl glycolate at 110° C. for 1.5 hours under a reduced pressure of -0.095 MPa, cool and seal to obtain the purified transesterification reaction product, a small molecule diol (Di(MG / 1,6-HD)OL).

[0087] Step 3, esterification reaction stage: In another clean 500 mL four-necked flask equipped with a stirring system, heating system, temperature measurement system, and a distillation separation column with an overhead reflux distributor, add 302.19 g (1.29 mol) of the aforementioned small molecule diol (Di(MG / 1,6-HD)OL), 143.22 g (0.98 mol) of adipic acid, and 0.0544 g (180 ppm / wt. of the starting small molecule diol) of tetrabutyl titanate catalyst. The synthesis of the polyester polyol using a vacuum melt polycondensation method consists of two stages: an atmospheric pressure esterification stage and a reduced pressure polycondensation stage. During the atmospheric pressure esterification stage, the reactor temperature is rapidly heated to 159°C. When condensation reflux appears at the top of the distillation column, the reflux distributor is opened to remove water generated by the esterification reaction. The reaction is continued at atmospheric pressure within the range of 150°C to 180°C for 7 hours.

[0088] Step 4, reduced pressure polyolation: During this reduced pressure polyolation stage, the reaction temperature is controlled at 180°C to 210°C, and the pressure is gradually reduced from atmospheric pressure to -0.05 MPa, -0.06 MPa, -0.07 MPa, -0.08 MPa, and -0.095 MPa. The reduced pressure polyolation reaction is continued for 5.5 hours to remove byproducts and excess low-molecule alcohol. Cooling is then performed to obtain the target product, oligomeric polyester polyol - P﹝AA / (Di(MG / 1,6-HD)OL)﹞DL.

[0089] At room temperature, the product, P﹝AA / (Di(MG / 1,6-HD)OL)﹞DL, is a light yellow, waxy solid with a hydroxyl number of 55.48 mgKOH / g, an acid number of 0.03 mgKOH / g, an average molecular weight of 2021.26, a yield of 95.87%, and an ester content of 49.01% by weight. The product, P﹝AA / (Di(MG / 1,6-HD)OL)﹞DL, was reacted with diphenylmethane-4,4'-diisocyanate (MDI) to prepare a prepolymer with a free NCO percentage of 8.5%. This prepolymer was then chain-extended with a small molecule diol (1,4-butanediol) to produce a polyurethane elastomer sample. Test performance results showed: Shore A hardness of 92, tensile strength of 46.5 MPa, elongation at break of 580%, tear strength of 161.2 kN / m, and impact resilience of 27%.

Claims

1. A method for catalytically synthesizing oligomeric polyester polyols using methyl glycolate as a raw material, characterized in that: The following steps are involved: Step 1, transesterification reaction stage: under normal pressure, the catalyst, small molecule polyol and methyl glycolate are all added into a reactor to carry out transesterification reaction of methyl glycolate and small molecule polyol; Step 2, vacuum separation and purification stage: removing unreacted raw materials in the transesterification reaction stage through vacuum separation and purification to obtain a purified transesterification product; Step 3, esterification reaction stage: under normal pressure, the catalyst, the purified transesterification product and the organic dicarboxylic acid are added to a reactor equipped with a distillation device to carry out an esterification reaction between the polyol and the organic dicarboxylic acid; Step 4, the reduced pressure polycondensation stage: reducing the pressure in stages from normal pressure and carrying out polycondensation reaction to further esterify and dehydrate the small molecule product obtained in the esterification reaction stage, remove by-products and excess reactants, and cool down to obtain an oligomeric polyester polyol with a set molecular weight.

2. The method for synthesizing oligomeric polyester polyols using methyl glycolate as raw material according to claim 1, wherein: In step 1, the small molecule polyol is a linear or branched saturated fatty alcohol, the number of carbon atoms of which is 2 to 25 and the hydroxyl functionality is ≥2; The straight-chain saturated fatty alcohol is one or more of ethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol or triethylene glycol; the branched-chain saturated fatty alcohol is one or more of 1,2-propylene glycol, methylpropanediol, 1,3-butanediol, neopentyl glycol, 2-ethyl-hexanediol or trimethylolpropane.

3. A method for synthesizing novel oligomeric polyester polyols using methyl glycolate as raw material according to claim 2, characterized in that: The amount of catalyst used in step 1 is 50ppm~1000ppm of the total mass of the reactants in the ester exchange reaction stage; the molar ratio of methyl glycolate to small molecule polyol is 1:1~2; the temperature of the ester exchange reaction is 140~170℃, and the time is 4hr~12hr.

4. The method for synthesizing oligomeric polyester polyols using methyl glycolate as raw material according to claim 1, wherein: The vacuum separation and purification in step 2 is specifically as follows: purification is carried out by stepwise decompression from normal pressure to -0.095 MPa, the temperature of the decompression process is maintained at 110° C. to 115° C., and the vacuum separation time is 0.5 hr to 6 hr.

5. The method for synthesizing oligomeric polyester polyols using methyl glycolate as raw material according to claim 1, wherein: In step 3, the organic dicarboxylic acid is one or more of oxalic acid, malonic acid, succinic acid, maleic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, and terephthalic acid.

6. The method for synthesizing oligomeric polyester polyols using methyl glycolate as raw material according to claim 5, characterized in that: The amount of catalyst used in step 3 is 50ppm~500ppm of the purified transesterification product; the molar ratio of the purified transesterification product to the organic dicarboxylic acid is 1.0~1.6:1; the temperature of the esterification reaction is 140℃~200℃, and the time is 3hr~12hr.

7. The method for synthesizing oligomeric polyester polyols using methyl glycolate as raw material according to claim 1, characterized in that: In the step 4, the pressure is reduced from normal pressure to -0.050 MPa to -0.095 MPa in stages, the temperature of the polycondensation reaction is 160° C. to 250° C., and the time is 2 hr to 12 hr.

8. A method for synthesizing oligomeric polyester polyols using methyl glycolate as raw material according to claim 1, 3 or 6, characterized in that: The catalyst is an organic titanate, an organic tin or an organic amine catalyst.

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