A catalyst for modifying tdi with carbodiimide, a preparation method and applications thereof

Abstract

The present application provides a kind of carbodiimide modified TDI catalyst, preparation method and its application, carbodiimide modified TDI catalyst structure is as shown in formula 1:In formula 1, R is selected from C1-C5 alkyl, C6-C9 alkyl aryl, preferably C1-C3 alkyl, such as methyl, ethyl, propyl, phenyl, benzyl.The biggest advantage of the catalyst compared with conventional catalyst is that the selectivity of 2,4-TDI and 2,6-TDI is the same, the reduction of 2,6-TDI monomer in TDI curing agent raw material is realized, so that the preparation of low free (<0.4%), low viscosity and high tolerance TDI trimer curing agent is realized.

Description

Technical Field

[0001] This invention relates to a novel catalyst preparation method for carbodiimide-modified TDI, and also to the application of using the novel catalyst to modify TDI in the synthesis of low-free-TDI trimer curing agents. Background Technology

[0002] Toluene diisocyanate (TDI) is a major raw material for the preparation of polyurethane foams, elastomers, coatings, and adhesives. TDI trimer, as a curing agent, has advantages such as low volatility, high functionality, and excellent film properties. Under suitable temperature and catalyst conditions, TDI undergoes a trimerization reaction, generating trimers, pentamers, heptamers, and polymers with larger molecular weights, depending on the number of molecules involved in the reaction.

[0003] Free TDI monomers cause irreversible damage to the respiratory system of construction workers. Therefore, reducing the free TDI content in polyurethane curing agents has become a key research focus both domestically and internationally. The national standard GB1858-2009, "Limits of Hazardous Substances in Solvent-Based Wood Coatings for Interior Decoration and Renovation Materials," stipulates that the limit for free TDI after paint mixing should be ≤0.4%. This indicates that the free TDI content in the curing agent must be reduced to below 0.7% to meet the national standard.

[0004] Methods reported to date for reducing free monomer content include solvent extraction, thin-film evaporation, molecular sieve absorption, chemical methods, and supercritical fluid extraction. To improve the compatibility of the product with hydroxyl resins and ensure a uniform molecular weight distribution, an incomplete reaction method is generally adopted. This involves terminating the reaction at approximately 60% completion and using a thin-film evaporator to remove unreacted monomers. In recent years, thin-film evaporation technology has continuously improved, and equipment has been upgraded. Representative companies using this technology, such as Bayer, Dow, BASF, Wanhua, and Bogo, have achieved free TDI content in their curing agents down to ≤0.2%. However, the paint film prepared using trimers in this process dries very slowly, especially in northern winters, and its performance is inferior to that of trimers prepared using chemical methods.

[0005] Chemical processes achieve this by altering the formulation and increasing the degree of reaction. While ensuring low free monomer content, this directly leads to excessively high product viscosity, poor compatibility with hydroxyl resins, dark color, and process instability. Therefore, chemical processes, which achieve low free monomer content while maintaining extremely low viscosity for flowability and high tolerance to ensure compatibility with hydroxyl resins, still hold great promise in the field of curing agents.

[0006] Due to its low viscosity, low functionality, and high volatility, TDI's application in certain areas of polyurethane is limited. Based on the reactivity of isocyanates, various methods can be used to modify them, expanding the application range of TDI and improving the overall performance of downstream products.

[0007] Currently, common methods for modifying TDI and their main applications include: TDI-urethane modification, mainly used in HR foam, self-skinning foam, coatings, and adhesives; TDI-isocyanurate modification, mainly used in HR foam, coatings, and adhesives; TDI-urethane modification and TDI-polyamine condensation modification, used in HR foam; TDI-prepolymer modification, used in sealing materials and microporous foams; and modified TDI-polymerized MDI mixtures, etc. Currently, there are no TDI-carbodiimide modified products or applications in the curing agent field. The main reason is that existing catalysts modify TDI with low effective components, failing to selectively synthesize low molecular weight effective components, leading to problems with product curing and precipitation. Summary of the Invention

[0008] The foregoing has explained that the chemical process for preparing TDI trimer curing agents cannot simultaneously achieve low free concentration, low viscosity, and high tolerance, and there are currently no TDI-carbodiimide modified products available. Therefore, this invention first provides a novel catalyst preparation method for carbodiimide-modified TDI, and then applies the TDI modified using this novel catalyst to the chemical synthesis of TDI trimer curing agents with low free concentration, low viscosity, and high tolerance.

[0009] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0010] In a first aspect, the present invention provides a catalyst for TDI modified with carbodiimide, the structure of which is shown in Formula 1:

[0011]

[0012] In Formula 1, R is selected from C1-C5 alkyl and C6-C9 alkylaryl groups, preferably C1-C3 alkyl groups, such as methyl, ethyl, propyl, phenyl, and benzyl.

[0013] Secondly, the present invention provides a method for preparing the catalyst shown in Formula 1 above, comprising the following steps:

[0014] 1) Prepare intermediate A (Formula 3) by reacting the carboxyl-substituted benzenesulfonate ester shown in Formula 2 with an amide.

[0015] 2) Intermediate B, as shown in Formula 4, was prepared by reacting intermediate A (shown in Formula 3) and 1-chloromethyl-4-fluoro-1,4-diazabicyclo[2.2.2]octane di(tetrafluoroborate) salt as raw materials;

[0016] 3) The intermediate C described in Formula 5 was prepared by reacting N-chlorosuccinimide (NCS) with thiocyanate as a raw material;

[0017] 4) Using intermediate B prepared in step 2) and intermediate C prepared in step 3) as raw materials, and chiral dinitroxide ligand as catalyst, the reaction was carried out to prepare the catalyst shown in Formula 1.

[0018] The carboxyl-substituted benzenesulfonate ester of Formula 2, intermediate A of Formula 3, intermediate B of Formula 4, and intermediate C of Formula 5 have the following structures:

[0019]

[0020] In Equations 2 and 3, the definition of R is the same as that in Equation 1.

[0021] In this invention, the carboxylated benzene sulfonate in step 1) is selected from at least one of carboxylated methyl benzene sulfonate, carboxylated ethyl benzene sulfonate, carboxylated butyl benzene sulfonate, and carboxylated phenolic benzene sulfonate, preferably at least one of carboxylated methyl benzene sulfonate and carboxylated phenolic benzene sulfonate.

[0022] In this invention, the amide in step 1) is selected from 2-benzoylacetamide.

[0023] In this invention, the molar ratio of carboxyl-substituted benzenesulfonate to 2-benzoylacetamide in step 1) is 1:1-4:1, the reaction temperature is 60-100℃, the reaction time is 0.5-5h, and the solvent can be acetonitrile or dioxane. Preferably, the molar ratio of carboxyl-substituted benzenesulfonate to 2-benzoylacetamide is 2:1-3:1, the reaction temperature is 70-90℃, the reaction time is 1-3h, and the reaction solvent is dioxane.

[0024] In this invention, the 1-chloromethyl-4-fluoro-1,4-diazabicyclo[2.2.2]octane di(tetrafluoroborate) salt mentioned in step 2) is 1-chloromethyl-4-fluoro-1,4-diazobicyclo2.2.2octane ditetrafluoroborate (CAS140681-55-6).

[0025] In this invention, the molar ratio of intermediate A in step 2) to 1-chloromethyl-4-fluoro-1,4-diazabicyclo[2.2.2]octane di(tetrafluoroborate) salt is 1:0.5 to 1:4, for example 1:0.5, 1:1, 1:2, 1:3, 1:4, preferably 1:0.8 to 1:1.2.

[0026] In this invention, the reaction in step 2) further includes an optional solvent in the system. The solvent is selected from at least one of acetonitrile aqueous solution, N-methylformamide aqueous solution, and N-methylpyrrolidone aqueous solution. Preferably, the volume ratio of acetonitrile or N-methylformamide or N-methylpyrrolidone to water is 1:2 to 2:1; for example, 1:2, 1:1, 2:1.

[0027] In this invention, the amount of solvent used in step 2) is 150-250 ml / mol of intermediate A, for example, 150, 175, 200, 225, or 250 ml / mol of intermediate A.

[0028] In this invention, the reaction in step 2) is carried out at a temperature of 20-40°C, for example 20, 25, 30, 35, or 40°C, preferably 25-30°C, for a time of 2-8 hours, for example 2, 4, 6, or 8 hours, preferably 3-6 hours.

[0029] After the reaction described in step 2) is completed, the process also includes post-treatment steps such as extraction with an organic solvent such as ethyl acetate, static separation, and rotary evaporation to remove the extractant. These are all conventional operating procedures in the field, and there are no special requirements for them in this invention.

[0030] In this invention, the thiocyanate in step 3) is selected from at least one of potassium thiocyanate, sodium thiocyanate, and ammonium thiocyanate.

[0031] In this invention, the molar ratio of N-chlorosuccinimide to thiocyanate in step 3) is 1:1 to 1:4, for example 1:1, 1:2, 1:3, 1:4, preferably 1:2 to 1:3.

[0032] In this invention, the reaction in step 3) further includes an optional solvent, which is selected from at least one of N-methylformamide, N-methylpyrrolidone, and acetonitrile, preferably acetonitrile.

[0033] Preferably, the solvent dosage is 150-250 ml / mol N-chlorosuccinimide, for example 150, 175, 200, 225, or 250 ml / mol N-chlorosuccinimide.

[0034] In this invention, the reaction temperature in step 3) is 20-40°C, for example 20, 25, 30, 35, or 40°C, preferably 25-30°C, and the reaction time is 15-60 min, for example 15, 30, 45, or 60 min, preferably 30-45 min.

[0035] After the reaction is completed, post-processing steps such as filtration to remove salt and rotary evaporation to remove solvent are also included. These are all conventional operating methods in the field, and there are no special requirements for them in this invention.

[0036] In this invention, the molar ratio of intermediate B to intermediate C in step 4) is 2:1 to 1:4, for example 2:1, 1:1, 1:2, 1:3, 1:4, preferably 1:1 to 1:1.5.

[0037] In this invention, the chiral dinitroxide ligand in step 4) is selected from at least one of 2,3-bipyridine dinitroxide, 2,5-dimethylpyrazine dinitroxide, and phenolazine dinitroxide.

[0038] Preferably, the amount of the chiral bis(nitrogenoxy) ligand catalyst is 1 to 10% of the total mass of intermediate A and intermediate B, for example, 1, 3, 6, 9, 10%, preferably 3 to 7%.

[0039] In this invention, the reaction in step 4) may optionally include a solvent, wherein the solvent is selected from at least one of petroleum ether, dichloromethane, chloroform, and dichloroethane, preferably chloroform.

[0040] Preferably, the solvent dosage is 150-250 ml / mol (intermediate B + intermediate C), for example 150, 175, 200, 225, or 250 ml / mol (intermediate A + intermediate B).

[0041] In this invention, the reaction in step 4) is carried out at a temperature of 25-50°C, for example 20, 25, 30, 35, 40, 45, or 50°C, preferably 25-35°C, for a time of 0.5-8 hours, for example 0.5, 2, 4, 6, or 8 hours, preferably 1-3 hours.

[0042] After the reaction is completed, the process includes post-processing steps such as silica gel column chromatography, elution, and rotary evaporation to remove solvent. These are all conventional operating procedures in the field, and there are no special requirements for them in this invention. It is preferred to use 300-400 mesh silica gel column chromatography to separate the catalyst and the product, and to use n-hexane:ethyl acetate = 1:1 for elution.

[0043] Thirdly, the present invention provides a method for preparing a TDI trimer curing agent, the method comprising the following steps:

[0044] 1) Under nitrogen protection, a catalyst was added to the toluene diisocyanate monomer, and the mixture was stirred at a certain temperature for 1-4 hours to obtain carbodiimide-modified TDI.

[0045] 2) Under nitrogen protection, a polar solvent and a hydroxyl-containing trimerizing catalyst are added to the modified TDI and reacted at 50-60°C for 4-8 hours to obtain the modified TDI prepolymer; then a small molecule alcohol is added to the modified TDI prepolymer and kept at 50-60°C for 1-2 hours; finally, a polymerization inhibitor is added and kept at 50-60°C for another 1-2 hours, then the mixture is cooled and discharged to obtain the modified TDI trimer curing agent.

[0046] The toluene diisocyanate mentioned in step 1) is 2,4-toluene diisocyanate (2,4-TDI) or 2,6-toluene diisocyanate (2,6-TDI) or a mixture of the two, preferably TDI-80 (2,4-TDI / 2,6-TDI = 80 / 20);

[0047] The amount of modified catalyst used in step 1) is 0.05-1% of the TDI monomer mass, and the catalyst structure is as follows:

[0048] As shown in Equation 1:

[0049]

[0050] In step 1), the reaction temperature is 100-150℃ and the stirring speed is 100-300 r / min.

[0051] The polar solvent mentioned in step 2) is one or more of ethyl acetate, butyl acetate, and sec-butyl acetate, and the amount of the polar solvent added is 0.5 to 2 times the mass of the modified TDI.

[0052] The hydroxyl-containing trimerizing catalyst mentioned in step 2) is one or more of DMP-30, Mannich base, and trimethylhydroxypropyl ammonium salt, preferably DMP-30. The amount of the hydroxyl-containing trimerizing catalyst added is 0.05% to 0.5% of the total mass of the modified TDI and the polar solvent.

[0053] The small molecule alcohol mentioned in step 2) is one or more of ethylene glycol, glycerol, n-butanol, n-pentanol, n-decanol, n-dodecyl alcohol, and trimethylolpropane, and the amount added is 1 to 4% of the total mass of the modified TDI and the polar solvent.

[0054] The polymerization inhibitor mentioned in step 2) is one or more of phosphoric acid, benzoyl chloride, and oxalyl chloride, and the amount added is 0.1% to 1% of the total amount of hydroxyl-containing small molecule alcohol, modified TDI, and polar solvent.

[0055] Compared with the prior art, the present invention has the following advantages:

[0056] 1. This invention synthesizes a novel catalyst to catalyze the polymerization modification of TDI monomers. The biggest advantage of this catalyst over conventional catalysts is that it has the same selectivity for 2,4-TDI and 2,6-TDI, thereby reducing the amount of 2,6-TDI monomer in the TDI curing agent raw material and thus achieving the preparation of a low-free (<0.4%), low-viscosity and high-tolerance TDI trimer curing agent.

[0057] 2. This invention employs a chemical method to modify carbodiimide in a TDI system. The molecular weight of carbodiimide is controllable, with a degree of polymerization of 1–3, ensuring reactivity during trimer synthesis. Furthermore, even when the modified component content reaches 50%, no solid precipitation or deterioration occurs. This is something that conventional catalysts cannot achieve. Detailed Implementation

[0058] The sources of the chemical reagents used in the following examples are shown in the table below. Unless otherwise specified, all other raw materials and reagents were obtained through commercially available channels.

[0059]

[0060]

[0061] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0062] In the following examples, unless otherwise specified, all percentages (%) are by mass. The free monomer content was determined according to GB / T18446-2009, the percentage content of NCO was determined according to HG / T2409-1992, and the solid content was determined according to GB / 2793-1995.

[0063] A method for preparing carbodiimide-modified TDI and its application in the synthesis of low-free-TDI trimer curing agents includes the following steps:

[0064] 1. Catalyst preparation:

[0065] Preparation Example

[0066] Synthesis of catalyst intermediate B - Example 1:

[0067] In a 500 ml reactor equipped with a reflux condenser, 2 mol of methyl p-toluenesulfonate, 300 ml of 50% aqueous acetic acid solution, and 2.5 mol of KMnO4 were added sequentially. The mixture was refluxed for 1 h, cooled, and the solvent was evaporated by filtration. The solvent was dissolved in 200 ml of tetrahydrofuran and transferred to a 500 ml round-bottom flask. 2 mol of NH3·H2O was added, and the mixture was refluxed for 1 h. Then, 2 mol of benzoylacetic acid was added, and the mixture was refluxed for another 1.5 h. After cooling to room temperature, 200 ml of water was added, and the mixture was extracted with ethyl acetate. After standing and phase separation, the organic phase was removed, and the ethyl acetate extractant was removed by rotary evaporation at 50 °C and 25 mmHg to obtain intermediate A1.

[0068] 1 mol of intermediate A1 and 0.8 mol of 1-chloromethyl-4-fluoro-1,4-diazabicyclo[2.2.2]octane di(tetrafluoroborate) salt were dissolved in 200 ml of a mixture of acetonitrile and water (V:V = 1:1). The solution was added to a 500 ml reactor equipped with a thermometer and a reflux condenser. The reaction system temperature was controlled at 25 °C, and the mixture was stirred for 4 h. After the reaction was completed, the reactants were extracted with ethyl acetate. After standing and phase separation, the organic phase was removed, and the ethyl acetate extractant was removed by rotary evaporation at 50 °C and 25 mmHg to obtain intermediate B1. The reaction formula is as follows:

[0069]

[0070] 1H NMR(DMSO-d6,300MHz):3.85(s,3H),5.77(s,1H),7.55(dd,2H),7.68(d,1H),7.98(d,2H),8.00(d,2H)8.39(d,2H)11.69(s,1H).

[0071] Synthesis of catalyst intermediate B - Example 2:

[0072] In a 500 ml reactor equipped with a reflux condenser, 2 mol of phenyl p-toluenesulfonate, 300 ml of 50% aqueous acetic acid solution, and 2.5 mol of KMnO4 were added sequentially. The mixture was refluxed for 1 h, cooled, and the solvent was evaporated by filtration. The solvent was dissolved in 200 ml of tetrahydrofuran and transferred to a 500 ml round-bottom flask. 2 mol of NH3·H2O was added, and the mixture was refluxed for 1 h. Then, 2 mol of benzoylacetic acid was added, and the mixture was refluxed for another 1.5 h. After cooling to room temperature, 200 ml of water was added, and the mixture was extracted with ethyl acetate. After phase separation by standing, the organic phase was removed, and the ethyl acetate extractant was removed by rotary evaporation at 50 °C and 25 mmHg to obtain intermediate A2.

[0073] 1 mol of intermediate A2 and 1.2 mol of 1-chloromethyl-4-fluoro-1,4-diazabicyclo[2.2.2]octane di(tetrafluoroborate) salt were dissolved in 200 ml of a mixture of N-methylformamide and water (V:V = 1.5:1). The solution was added to a 500 ml reactor equipped with a thermometer and a reflux condenser. The reaction system temperature was controlled at 25 °C, and the mixture was stirred for 6 h. After the reaction was completed, the reactants were extracted with ethyl acetate. After standing and phase separation, the organic phase was removed, and the ethyl acetate extractant was removed by rotary evaporation at 50 °C and 25 mmHg to obtain intermediate A-2. The reaction formula is as follows:

[0074]

[0075] 1 H NMR(DMSO-d6,300MHz):5.79(s,1H),6.92(m,2H),7.02(m,1H),7.3(m,2H),7 .55(m,2H),7.68(m,1H),7.98(d,2H),8.0(d,2H),8.4(d,2H),11.68(s,1H).

[0076] Synthesis of catalyst intermediate C - Example 1:

[0077] 1 mol of NCS (N-chlorosuccinimide) and 2 mol of potassium thiocyanate were dissolved in 200 ml of acetonitrile solvent. The solution was added to a 500 ml reactor equipped with a thermometer and a reflux condenser. The reaction system temperature was controlled at 25 °C, and the mixture was stirred for 30 min. Excess salt was removed by filtration. The solvent and unreacted NCS were removed by rotary evaporation at 50 °C and 25 mmHg pressure to obtain intermediate C. The reaction formula is as follows:

[0078]

[0079] 1 H NMR (DMSO-d6, 300MHz): 2.64 (s, 4H).

[0080] Example 2: Synthesis of catalyst intermediate C:

[0081] 1 mol of NCS (N-chlorosuccinimide) and 3 mol of ammonium thiocyanate were dissolved in 250 ml of N-methylpyrrolidone solvent. The solution was added to a 500 ml reactor equipped with a thermometer and a reflux condenser. The reaction system temperature was controlled at 30 °C, and the mixture was stirred for 40 min. Excess salt was removed by filtration. The solvent and unreacted NCS were removed by rotary evaporation at 50 °C and 25 mmHg pressure to obtain intermediate B. The reaction formula is as follows:

[0082]

[0083] 1 H NMR (DMSO-d6, 300MHz): 2.64 (s, 4H).

[0084] Synthetic catalyst - Example 1:

[0085] 0.5 mol of intermediate B-1 (R group is methyl) and 0.5 mol of intermediate C were dissolved in 200 mL of chloroform solvent. 3% (by mass) of catalyst 2,3'-bipyridine-diazepine oxide (2,3'-bipyridine-diazepine oxide) of the total mass of intermediates B and C was added to a 500 mL reactor equipped with a thermometer and a reflux condenser. The reaction mixture was stirred at 25 °C for 2 h. The reaction solution was separated from the catalyst and product by 300-400 mesh silica gel column chromatography. Elution was performed using n-hexane:ethyl acetate = 1:1. The solvent was removed by rotary evaporation at 50 °C and 25 mmHg to obtain catalyst-1. The reaction formula is as follows:

[0086]

[0087] 1 H NMR (DMSO-d6, 300MHz): 3.85 (s, 3H), 7.55 (m, 2H), 7.68 (s, 1H), 7.98 (d, 2H), 8.00 (d, 2H), 8.39 (d, 2H), 11.69 (s, 1H).

[0088] Synthetic Catalyst - Example 2:

[0089] 0.5 mol of intermediate B-2 (R group is phenyl) and 0.4 mol of C were dissolved in 200 mL of chloroform solvent. 4% (by mass) of the catalyst 2,3'-bipyridine-diazepine oxide (2,3'-bipyridine-diazepine oxide) was added to a 500 mL reactor equipped with a thermometer and reflux condenser. The reaction mixture was stirred at 35 °C for 2 h. The reaction solution was separated from the catalyst and product by 300-400 mesh silica gel column chromatography. Elution was performed using n-hexane:ethyl acetate = 1:2. The solvent was removed by rotary evaporation at 50 °C and 25 mmHg to obtain catalyst-2. The reaction formula is as follows:

[0090]

[0091] 1 H NMR(DMSO-d6,300MHz):6.92(d,2H),7.02(m,1H),7.30(m,2H),7.55(m,2H),7.68(m,1H),7.98(d,2H),8.00(d,2H),8.40(d,2H),11.69(s,1H).

[0092] Example 1

[0093] Under nitrogen protection, 300g of TDI-80 was added to a 500ml four-necked flask equipped with a stirrer and a thermometer. The stirring speed was 200r / min. 1.5g of catalyst-1 was added, and the temperature was raised to 100℃. The reaction was maintained at this temperature for 2h to obtain modified carbodiimide-modified TDI.

[0094] Under nitrogen protection, 300g of modified TDI and 300g of butyl acetate were added to a 1000ml four-necked flask equipped with a stirrer and a thermometer. The temperature was raised to 50℃, and 0.3g of DMP-30 was added dropwise and the reaction was maintained at this temperature for 8 hours. Then, 6g of n-butanol was added, and the reaction was maintained at this temperature for another hour. Finally, 0.6g of benzoyl chloride was added to terminate the reaction, and the temperature was maintained for another hour. The mixture was then cooled and discharged to obtain the TDI trimer curing agent.

[0095] The physicochemical properties of the modified TDI and trimer curing agent obtained by the above preparation method are as follows:

[0096] Modified TDI: a colorless and transparent liquid with 90% TDI monomer content, 9.5% bicyclic CDI content, and 0.5% UTI content;

[0097] Curing agent: colorless and transparent liquid, solid content 50.5%, NCO=7.83, viscosity 356mPa·s, free TDI content 0.36%.

[0098] Example 2

[0099] Under nitrogen protection, 300g of TDI-80 was added to a 500ml four-necked flask equipped with a stirrer and a thermometer. The stirring speed was 200r / min. 3g of catalyst-1 was added, the temperature was raised to 110℃, and the reaction was maintained at this temperature for 1h to obtain modified carbodiimide-modified TDI.

[0100] Under nitrogen protection, 300g of modified TDI and 300g of ethyl acetate were added to a 1000ml four-necked flask equipped with a stirrer and thermometer. The temperature was raised to 55℃, and 0.6g of DMP-30 was added dropwise and the reaction was maintained at this temperature for 6 hours. Then, 24g of n-dodecyl alcohol was added, and the reaction was maintained at this temperature for another hour. Finally, 6g of benzoyl chloride was added to terminate the reaction, and the temperature was maintained for another hour. The mixture was then cooled and discharged to obtain the polyurethane curing agent.

[0101] The physicochemical properties of the modified TDI and trimer curing agent obtained by the above preparation method are as follows:

[0102] Modified TDI: a colorless and transparent liquid with 88% TDI monomer content, 11.2% bicyclic CDI content, and 0.8% UTI content;

[0103] Curing agent: colorless and transparent liquid, solid content 51%, NCO = 8.12, viscosity 342 mPa·s, free TDI content 0.26%.

[0104] Example 3

[0105] Under nitrogen protection, 300g of TDI-80 was added to a 500ml four-necked flask equipped with a stirrer and a thermometer. The stirring speed was 200r / min. 0.15g of catalyst-1 was added, the temperature was raised to 150℃, and the reaction was maintained at this temperature for 4h to obtain modified carbodiimide-modified TDI.

[0106] Under nitrogen protection, 300g of modified TDI and 300g of ethyl acetate were added to a 1000ml four-necked flask equipped with a stirrer and a thermometer. The temperature was raised to 60℃, and 3g of DMP-30 was added dropwise and the reaction was maintained at this temperature for 4 hours. Then, 12g of n-dodecyl alcohol was added, and the reaction was maintained at this temperature for another hour. The reaction was terminated by adding 3g of benzoyl chloride, and the temperature was maintained for another hour. The mixture was then cooled and discharged to obtain the polyurethane curing agent.

[0107] The physicochemical properties of the modified TDI and trimer curing agent obtained by the above preparation method are as follows:

[0108] Modified TDI: a colorless and transparent liquid with 85% TDI monomer content, 14.2% bicyclic CDI content, and 0.8% UTI content;

[0109] Curing agent: colorless and transparent liquid, solid content 50.5%, NCO=7.95, viscosity 361mPa·s, free TDI content 0.23%.

[0110] Example 4

[0111] Under nitrogen protection, 300g of TDI-80 was added to a 500ml four-necked flask equipped with a stirrer and a thermometer. The stirring speed was 200r / min. 0.2g of catalyst-2 was added, and the temperature was raised to 130℃. The reaction was maintained at this temperature for 4h to obtain modified carbodiimide-modified TDI.

[0112] Under nitrogen protection, 300g of modified TDI and 300g of butyl acetate were added to a 1000ml four-necked flask equipped with a stirrer and a thermometer. The temperature was raised to 60℃, and 3g of DMP-30 was added dropwise and the reaction was maintained at this temperature for 4 hours. Then, 12g of n-decyl alcohol was added, and the reaction was maintained at this temperature for another hour. Finally, 0.6g of benzoyl chloride was added to terminate the reaction, and the temperature was maintained for another hour. The mixture was then cooled and discharged to obtain the polyurethane curing agent.

[0113] The physicochemical properties of the modified TDI and trimer curing agent obtained by the above preparation method are as follows:

[0114] Modified TDI: a colorless and transparent liquid with 87.5% TDI monomer content, 12% bicyclic CDI content, and 0.5% UTI content;

[0115] Curing agent: colorless and transparent liquid, solid content 49.8%, NCO=8.05, viscosity 348mPa·s, free TDI content 0.18%.

[0116] Example 5

[0117] Under nitrogen protection, 300g of TDI-80 was added to a 500ml four-necked flask equipped with a stirrer and a thermometer. The stirring speed was 200r / min. 2g of catalyst-2 was added, the temperature was raised to 100℃, and the reaction was maintained at this temperature for 3h to obtain modified carbodiimide-modified TDI.

[0118] Under nitrogen protection, 300g of modified TDI and 300g of butyl acetate were added to a 1000ml four-necked flask equipped with a stirrer and a thermometer. The temperature was raised to 55℃, and 2.4g of DMP-30 was added dropwise and the reaction was maintained at this temperature for 6 hours. Then, 12g of n-butanol was added, and the reaction was maintained at this temperature for another hour. Finally, 0.6g of benzoyl chloride was added to terminate the reaction, and the temperature was maintained for another hour. The mixture was then cooled and discharged to obtain the polyurethane curing agent.

[0119] The physicochemical properties of the modified TDI and trimer curing agent obtained by the above preparation method are as follows:

[0120] Modified TDI: a colorless and transparent liquid with 86.5% TDI monomer content, 12% bicyclic CDI content, and 1.5% UTI content;

[0121] Curing agent: colorless and transparent liquid, solid content 51%, NCO=7.7, viscosity 330mPa·s, free TDI content 0.21%.

[0122] To illustrate the advantages of the self-made catalyst in this invention, the TDI polymer modified with conventional catalysts showed increased viscosity and even milky white fogging issues. The curing agent synthesized using this modified TDI as a raw material exhibited higher viscosity and free monomer content. Specific effects are as follows: Comparative Example 1

[0123] Under nitrogen protection, 300g of TDI-80 was added to a 500ml four-necked flask equipped with a stirrer and a thermometer. The stirring speed was 200r / min. 2g of triphenylphosphine was added, the temperature was raised to 100℃, and the reaction was maintained for 3h to obtain modified carbodiimide-modified TDI.

[0124] Under nitrogen protection, 300g of modified TDI and 300g of butyl acetate were added to a 1000ml four-necked flask equipped with a stirrer and a thermometer. The temperature was raised to 55℃, and 2.4g of DMP-30 was added dropwise and the reaction was maintained at this temperature for 6 hours. Then, 12g of n-butanol was added, and the reaction was maintained at this temperature for another hour. Finally, 0.6g of benzoyl chloride was added to terminate the reaction, and the temperature was maintained for another hour. The mixture was then cooled and discharged to obtain the polyurethane curing agent.

[0125] The physicochemical properties of the modified TDI and trimer curing agent obtained by the above preparation method are as follows:

[0126] Modified TDI: colorless and transparent liquid, with TDI monomer content of 80.5%, bicyclic CDI content of 1.5%, and UTI content of 18%; Curing agent: milky white liquid, with solid content of 51.2%, NCO=6.5, viscosity of 1330 mPa·s, and free TDI content of 0.87%.

[0127] Comparative Example 2

[0128] Under nitrogen protection, 300g of TDI-80 was added to a 500ml four-necked flask equipped with a stirrer and a thermometer. The stirring speed was 200r / min. 2g of triethyl phosphate was added, the temperature was raised to 100℃, and the reaction was maintained at this temperature for 3h to obtain modified carbodiimide-modified TDI.

[0129] Under nitrogen protection, 300g of modified TDI and 300g of butyl acetate were added to a 1000ml four-necked flask equipped with a stirrer and a thermometer. The temperature was raised to 55℃, and 2.4g of DMP-30 was added dropwise and the reaction was maintained at this temperature for 6 hours. Then, 12g of n-butanol was added, and the reaction was maintained at this temperature for another hour. Finally, 0.6g of benzoyl chloride was added to terminate the reaction, and the temperature was maintained for another hour. The mixture was then cooled and discharged to obtain the polyurethane curing agent.

[0130] The physicochemical properties of the modified TDI and trimer curing agent obtained by the above preparation method are as follows:

[0131] Modified TDI: Milky white, foggy liquid, with 75% TDI monomer content, 2% bicyclic CDI content, and 23% UTI content; Curing agent: Milky white liquid, with a solid content of 51.2%, NCO = 6.5, viscosity of 1850 mPa·s, and free TDI content of 1.2%.

Claims

1. A catalyst for carbodiimide-modified TDI, having the structure of Formula 1: In Formula 1, R is selected from C1-C5 alkyl, phenyl.

2. The catalyst for carbodiimide-modified TDI according to claim 1, wherein the C1-C5 alkyl is methyl, ethyl, or propyl.

3. The method of producing a catalyst according to claim 1 or 2, characterized by, comprising the following steps: 1) reacting a carboxyl-substituted benzene sulfonate ester represented by Formula 2 with an amide to prepare an intermediate A represented by Formula 3; 2) reacting the intermediate A represented by Formula 3 with 1-chloromethyl-4-fluoro-1,4-diazabicyclo[2.2.2]octane di(tetrafluoroborate) salt to prepare an intermediate B represented by Formula 4; 3) reacting N-chlorosuccinimide (NCS) with a thiocyanate salt to prepare an intermediate C represented by Formula 5; 4) reacting the intermediate B prepared in step 2) with the intermediate C prepared in step 3) using a chiral bisoxazoline ligand as a catalyst to prepare the catalyst represented by Formula 1, wherein the chiral bisoxazoline ligand is selected from at least one of 2,3-bipyridine dioxide, 2,5-dimethyl pyrazine dioxide, and phenazine dioxide; wherein the carboxyl-substituted benzene sulfonate ester represented by Formula 2, the intermediate A represented by Formula 3, the intermediate B represented by Formula 4, and the intermediate C represented by Formula 5 have the following structures: In Formulas 2 and 3, R has the same definition as R in Formula 1.

4. The production method according to claim 3, wherein In step 1), the carboxyl-substituted benzene sulfonate ester is selected from at least one of carboxyl-substituted benzene sulfonate methyl ester, carboxyl-substituted benzene sulfonate ethyl ester, carboxyl-substituted benzene sulfonate butyl ester, and carboxyl-substituted benzene sulfonate phenol ester; the amide is 2-benzoyl acetamide; the molar ratio of the carboxyl-substituted benzene sulfonate ester to 2-benzoyl acetamide is 1:1-4:1; the reaction temperature is 60-100°C; the reaction time is 0.5-5 h; and the solvent is acetonitrile or dioxane.

5. The production method according to claim 4, wherein The molar ratio of the carboxyl-substituted benzene sulfonate ester to 2-benzoyl acetamide is 2:1-3:1; the reaction temperature is 70-90°C; the reaction time is 1-3 h; and the reaction solvent is dioxane.

6. The production method according to any one of claims 3 to 5, wherein In step 2), the molar ratio of the intermediate A to 1-chloromethyl-4-fluoro-1,4-diazabicyclo[2.2.2]octane di(tetrafluoroborate) salt is 1:0.5-1:4; the reaction temperature is 20-40°C; and the reaction time is 2-8 h.

7. The production method according to claim 6, wherein In step 2), the molar ratio of the intermediate A to 1-chloromethyl-4-fluoro-1,4-diazabicyclo[2.2.2]octane di(tetrafluoroborate) salt is 1:0.8-1:1.2; the reaction temperature is 25-30°C; and the reaction time is 3-6 h.

8. The production method according to any one of claims 3 to 5, wherein In step 3), the thiocyanate salt is selected from at least one of potassium thiocyanate, sodium thiocyanate, and ammonium thiocyanate; the molar ratio of N-chlorosuccinimide to the thiocyanate salt is 1:1-1:4; the reaction temperature is 20-40°C; and the reaction time is 15-60 min.

9. The production method according to any one of claims 3 to 5, wherein The molar ratio of the intermediate B to the intermediate C in step 4) is 2:1-1:4; the amount of the chiral bis-nitrogen oxygen ligand catalyst is 1-10% of the total mass of the intermediate A and the intermediate B; the reaction temperature in step 4) is 25-50°C, and the reaction time is 0.5-8h.

10. A preparation method of a TDI trimer curing agent, the method comprising the following steps: 1) under nitrogen protection, a catalyst is added to a toluene diisocyanate monomer, and the mixture is stirred at a certain temperature for 1-4h to obtain a carbodiimide modified TDI; 2) under nitrogen protection, a polar solvent and a hydroxyl-containing trimerization catalyst are added to the modified TDI, and the mixture is incubated at 50-60°C for 4-8h to obtain a modified TDI prepolymer; then a small molecule alcohol is added to the modified TDI prepolymer, and the mixture is incubated at 50-60°C for 1-2h; finally, a polymerization inhibitor is added and the mixture is incubated for another 1-2h, and then the mixture is cooled and discharged to obtain a modified TDI trimer curing agent; the hydroxyl-containing trimerization catalyst is one or more of DMP-30, a Mannich base, and a trimethylhydroxypropyl ammonium salt; the small molecule alcohol is one or more of ethylene glycol, glycerol, n-butanol, n-pentanol, n-decanol, n-dodecanol, and trimethylolpropane; the catalyst in step 1) is the catalyst for the carbodiimide modified TDI as claimed in claim 1 or 2 or the catalyst for the carbodiimide modified TDI prepared by the preparation method as claimed in any one of claims 3-9. The toluene diisocyanate in step 1) is 2,4-toluene diisocyanate (2,4-TDI) or 2,6-toluene diisocyanate (2,6-TDI) or a mixture of the two; the amount of the modified catalyst in step 1) is 0.05-1% of the mass of the TDI monomer; the reaction temperature in step 1) is 100-150°C, and the stirring speed is 100-300r / min.

11. The production method according to claim 10, wherein The polar solvent in step 2) is one or more of ethyl acetate, butyl acetate, and sec-butyl acetate, and the addition amount of the polar solvent is 0.5-2 times the mass of the modified TDI; the addition amount of the hydroxyl-containing trimerization catalyst is 0.05%-0.5% of the total mass of the modified TDI and the polar solvent.

12. The production method according to claim 10 or 11, characterized by, The addition amount of the small molecule alcohol in step 2) is 1-4% of the total mass of the modified TDI and the polar solvent; the polymerization inhibitor in step 2) is one or more of phosphoric acid, benzoyl chloride, and oxalyl chloride, and the addition amount is 0.1-1% of the total amount of the hydroxyl-containing small molecule alcohol, the modified TDI, and the polar solvent.

13. The production method according to claim 10 or 11, wherein ​

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