A bio-based mannich base, its preparation method and application

Abstract

The application provides a bio-based Mannich base, a preparation method thereof, an application thereof, and a TDI curing agent prepared by using the bio-based Mannich base as a catalyst. The bio-based Mannich base is obtained by a Mannich reaction of natural phenol, dimethylamine and formaldehyde, wherein the natural phenol is one or more selected from the group consisting of sesamol, catechin, theaflavin, daidzein and procyanidin. The Mannich base catalyst prepared by using the natural phenol in the application improves steric hindrance, and the reaction selectivity of small molecule monomers can be improved through the steric hindrance effect. The content of free TDI monomers in the TDI curing agent can be reduced by adding the catalyst at one time, so that the free monomers in the prepared TDI curing agent are less than 0.5% advantageously.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of polyurethane curing agents, more particularly, to a bio-based Mannich base, a preparation method thereof and application thereof in preparing TDI curing agents, and a TDI curing agent prepared using the bio-based Mannich base as a catalyst. BACKGROUND

[0002] Polyurethane prepared using a polyisocyanate curing agent as one of the components has the advantages of high hardness, good toughness, strong chemical resistance and fast drying, and is widely used as a paint raw material and as a polyurethane elastomer and polyurethane foam. Toluene diisocyanate, as a curing agent, has the advantages of fast curing speed, high hydrolysis resistance, corrosion resistance and thermal stability compared to other curing agents. During the preparation of the polyisocyanate curing agent, a certain amount of isocyanate monomer remains. The national standard GB 1858-2009 “Limit of Harmful Substances in Solvent-based Wood Coatings for Indoor Decoration” stipulates that the limit of free toluene diisocyanate after the paint is prepared should be ≤0.4%, which puts higher requirements on the content of toluene diisocyanate in the curing agent. The commonly used methods for reducing the content of toluene diisocyanate in the curing agent include physical methods, chemical methods and extraction methods.

[0003] The most commonly used method in the physical method is the thin film evaporation method. The main equipment of the thin film evaporation method is a thin film evaporator and a high vacuum system. Under high temperature and negative pressure, the prepolymer rapidly passes through the tower plate in a thin film state, and the free isocyanate monomer is evaporated. CN200510101596 separates the free isocyanate in the polyurethane adduct by single-stage thin film evaporation, and the final product has a free TDI content of less than 0.5wt%. At present, the thin film evaporation technology has been relatively mature in the separation of free TDI in TDI-TMP adduct curing agents. However, the thin film evaporation technology has high energy consumption and high requirements for vacuum equipment, thereby increasing the production cost. In addition, due to the use of high temperature in the evaporation process, the product has a high color number.

[0004] The solvent extraction method mainly separates the free TDI according to the difference in solubility of TDI monomers and prepolymers in different solvents. CN02134225.3 removes the free TDI monomer by adding a high-boiling extraction agent using the extraction method, and the final product has a free TDI content of less than 0.5wt% and an extraction agent content of 1wt%. CN102659997A introduces a high-boiling ester solvent and adjusts the feed speed into the separation device to obtain a polyurethane curing agent with a residual free isocyanate monomer concentration of less than 0.5wt%. The solvent extraction method has low production efficiency due to the need for a large amount of solvent for multiple extractions, and the process is complicated. In addition, the extraction liquid needs to be treated again, and the production cost is high.

[0005] The chemical reaction method mainly uses a catalyst to make isocyanate self-polymerize to reduce the content of free TDI. The chemical synthesis method has the advantages of simple synthesis process, no additional separation operation, and low cost. However, the monomer content of the curing agent prepared by the chemical method is 0.5-1.0 wt%, and it is necessary to increase the reaction degree and change the formula to reduce the monomer content, which will lead to the increase of product color number, the decrease of NCO content, and the poor miscibility with hydroxyl resin. CN1470508A and CN103183808A use synthetic Mannich base catalysts, and need to add TDI-100 in the later stage to reduce the content of free monomers. The reaction process is complicated. CN105315433A uses alcohol modification to improve the compatibility of the product, uses a self-made Mannich base catalyst, needs to add the catalyst in multiple batches, and needs to add alcohol for modification after the reaction is terminated to reduce the monomer content to below 0.5%. In the comparative example, the traditional phenol and DMP-30 catalyst are used, alcohol is directly added for reaction in the catalytic reaction process, and the monomer content of the product is 1.32%. The raw materials of the catalysts synthesized in the above patents all come from fossil energy. Therefore, developing a high-efficiency and green catalyst for reducing monomers has become the main direction of the development of the chemical method technology. SUMMARY

[0006] In view of the technical problems existing in the prior art, the present application aims to provide a bio-based Mannich base, a preparation method and application thereof. The Mannich base as a catalyst can significantly reduce the content of free monomers in the preparation of TDI curing agent, and can control the monomer content in the curing agent to be below 0.5 wt%. The bio-based Mannich base catalyst is prepared by using natural phenolic compounds, and the prepared Mannich base catalyst is used. The catalyst is added at one time, alcohol is added for modification, and the compatibility of the product is improved.

[0007] According to a first aspect of the present application, a bio-based Mannich base is provided, which is obtained by Mannich reaction of natural phenol, dimethylamine and formaldehyde, wherein the natural phenol is one or more selected from the group consisting of sesamol, catechin, theaflavin, daidzein and procyanidin.

[0008] According to a second aspect of the present application, a method for preparing the bio-based Mannich base according to the present application is provided, which comprises the following steps:

[0009] 1) reacting the natural phenol, dimethylamine aqueous solution and formaldehyde aqueous solution in the presence of dilute hydrochloric acid catalyst at 80-100℃;

[0010] 2) after the reaction is completed, cooling and standing for layering, and then reducing pressure distillation of the organic phase to obtain the bio-based Mannich base.

[0011] Preferably, the molar ratio of natural phenol, dimethylamine and formaldehyde is 1:6-12:6-12.

[0012] Preferably, the concentration of the aqueous dimethylamine solution is 10% to 50%, preferably 20% to 40%.

[0013] Preferably, the concentration of the aqueous formaldehyde solution is 10% to 50%, preferably 20% to 40%.

[0014] Preferably, the concentration of the dilute hydrochloric acid catalyst is 0.1 to 0.8 mol / L, and the amount of the dilute hydrochloric acid catalyst is such that the HCl content in the reaction system is 100 to 500 ppm.

[0015] Preferably, the reaction time of step 1) is 8 to 10 hours.

[0016] According to a third aspect of the present application, there is provided the use of the bio-based Mannich base according to the present application as a catalyst in the preparation of a TDI curing agent.

[0017] According to a fourth aspect of the present application, there is provided a method for preparing a TDI curing agent, comprising the following steps:

[0018] a) mixing toluene diisocyanate and a solvent uniformly under an inert atmosphere, and then adding an alcohol to react;

[0019] b) adding the bio-based Mannich base catalyst according to the present application to the reactant obtained in step a) to perform a trimerization reaction;

[0020] c) adding a terminating agent to terminate the reaction when the content of NCO groups reaches the design requirement.

[0021] Preferably, the molar ratio of the NCO groups of toluene diisocyanate to the hydroxyl groups in the alcohol is 200 to 20:1.

[0022] Preferably, the amount of the bio-based Mannich base catalyst is 1000 to 5000 ppm based on TDI.

[0023] Preferably, the alcohol is a fatty alcohol having 1 to 22 carbon atoms, and more preferably is one or more selected from butanol, isobutanol, octanol, dodecanol, tetradecanol, hexadecanol and octadecanol.

[0024] Preferably, the toluene diisocyanate is 2,4-toluene diisocyanate and / or 2,6-toluene diisocyanate, and more preferably is a mixture of 80 wt% of 2,4-toluene diisocyanate and 20 wt% of 2,6-toluene diisocyanate.

[0025] Preferably, the solvent is one or more selected from toluene, acetone, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate and propylene glycol methyl ether acetate, and more preferably is ethyl acetate or butyl acetate.

[0026] Preferably, the solvent is used in an amount such that the mass concentration of the reactants in step a) is 20% to 80% by weight, preferably 40% to 60% by weight, and most preferably 50% by weight.

[0027] Preferably, the reaction temperature in step a) is 20 to 90°C.

[0028] Preferably, the reaction temperature in step b) is 20 to 90°C, and the reaction time is 10 to 30 hours.

[0029] Preferably, in step b), the bio-based Mannich base catalyst is added in the form of a solution, and further preferably, the concentration of the bio-based Mannich base in the solution is 10% to 30% by weight.

[0030] Preferably, the terminating agent is a protonic acid such as phosphoric acid, hydrochloric acid or sulfuric acid; an acylating agent such as benzoyl chloride; or an alkylating agent such as methyl-p-toluenesulfonate or di-n-butyl phosphate.

[0031] Preferably, the amount of the terminating agent added is 1 to 5 times the mass of the bio-based Mannich base catalyst.

[0032] Preferably, the reaction is terminated by adding the terminating agent when the content of NCO groups is 7% to 8.5%.

[0033] The content of NCO groups refers to the percentage content of isocyanate groups calculated based on the total mass of the TDI curing agent.

[0034] According to a fifth aspect of the present application, a TDI curing agent is provided, wherein the content of free diisocyanate monomers is less than 0.5% by weight, the platinum-cobalt color number thereof is less than 40 Hazen, and the viscosity thereof is less than 2000 cp.

[0035] Preferably, the TDI curing agent is prepared by the method for preparing a TDI curing agent according to the present application.

[0036] The TDI curing agent prepared in the present application is mainly applied in the field of polyurethane coatings or adhesives.

[0037] Compared with the Mannich base catalyst prepared from a chemically derived phenolic compound in the prior art, the Mannich base catalyst prepared from a natural phenolic compound in the present application has improved steric hindrance, which can improve the reaction selectivity of small molecule monomers through the steric hindrance effect. By adding the catalyst at one time, the content of free TDI monomers in the TDI curing agent can be reduced, so that the TDI curing agent prepared advantageously has a free monomer content of less than 0.5%. DETAILED DESCRIPTION

[0038] The following examples will further illustrate the application provided by the method of the present application, but the present application is not limited to the listed examples, and any other known changes within the scope of the claims of the present application should also be included, and the specific application of the present application is not limited to the application mentioned in the examples, and any modification and further development within the scope of the claims of the present application can be made by those skilled in the art.

[0039] Butanol, Aldrin reagent;

[0040] Dodecanol, Tianjin Guangfu Chemical;

[0041] Octanol, Aldrin reagent;

[0042] Myristyl alcohol, Tianjin Guangfu Chemical;

[0043] Toluene diisocyanate TDI-80, Wanhua Chemical;

[0044] Other raw materials and reagents can be purchased through commercial channels if no special instructions.

[0045] NCO content test according to standard GB / T 12009.4;

[0046] Dynamic viscosity was determined at 25℃ using a rotational viscometer (Brookfield DV-II);

[0047] Hazen color value was determined using a color value measuring device (BYK LCS IV);

[0048] Solid content was tested according to GB / T2793-1995;

[0049] Free TDI content was tested according to GB / T18446-2009;

[0050] Example 1

[0051] Preparation of Mannich base: 50g of sesame phenol was mixed with 300g of 33% mass fraction dimethylamine solution and 250g of 37% mass fraction formaldehyde solution, 5g of 0.5mol / L concentration hydrochloric acid solution was added, and the reaction was stopped after heating at 80℃ for 4h, and then cooled and settled to separate the layers. The organic phase was distilled under reduced pressure at 70℃ and 100Pa to obtain the Mannich base, which was diluted with butyl acetate to obtain a 20% Mannich base catalyst solution;

[0052] Preparation of TDI curing agent: 1000 g of TDI-80 and 1107 g of butyl acetate were added to a reaction kettle under nitrogen protection, stirred uniformly, then 107 g of dodecanol was added to the reaction kettle, 5.0 g of 20% butyl acetate catalyst solution of Mannich base was added to initiate the trimerization reaction after reaction for half an hour at 20°C, and 3.0 g of dibutyl phosphate was added to terminate the reaction when NCO% = 7.5% to obtain a TDI curing agent, and the indexes were as follows:

[0053] Solid content = 50.5%;

[0054] NCO% = 7.48%;

[0055] Viscosity = 195 cp;

[0056] Color number 15 Hazen;

[0057] Free monomer content 0.30%.

[0058] Example 2

[0059] Preparation of Mannich base: 100 g of catechin was mixed with 400 g of 33% mass fraction dimethylamine solution and 240 g of 37% mass fraction formaldehyde solution, 10 g of 0.5 mol / L concentrated hydrochloric acid solution was added, and the reaction was stopped after reaction for 6 h at 90°C. After cooling and standing, the organic phase was distilled under reduced pressure at 70°C and 100 Pa to obtain the Mannich base catalyst, which was diluted with xylene to 20% Mannich base catalyst solution;

[0060] Preparation of TDI curing agent: 1000 g of TDI-80 and 1021 g of butyl acetate were added to a reaction kettle under nitrogen protection, stirred uniformly, then 21 g of dodecanol was added to the reaction kettle, 10.0 g of 20% Mannich base catalyst solution diluted with xylene was added to initiate the trimerization reaction after reaction for half an hour at 40°C, and 15.0 g of dibutyl phosphate was added to terminate the reaction when NCO% = 7.7% to obtain a TDI curing agent, and the indexes were as follows:

[0061] Solid content = 51.1%;

[0062] NCO% = 7.71%;

[0063] Viscosity = 551 cp;

[0064] Color number 18 Hazen;

[0065] Free monomer content 0.25%.

[0066] Example 3

[0067] Preparation of Mannich base: 150 g of theaflavins was mixed with 350 g of 33% by mass dimethylamine solution and 210 g of 37% by mass formaldehyde solution, 8 g of 0.5 mol / L hydrochloric acid solution was added, and the reaction was stopped after 10 h of reaction at 100°C. After cooling and standing to separate the layers, the organic phase was distilled under reduced pressure at 70°C and 100 Pa to obtain the Mannich base catalyst. The Mannich base catalyst was diluted with DMF to obtain a 10% Mannich base catalyst solution;

[0068] Preparation of TDI curing agent: 1000 g of TDI-80 and 1014 g of butyl acetate were added to a reaction kettle under nitrogen protection, and 14 g of dodecanol was added to the reaction kettle. After stirring uniformly, the reaction was initiated by adding 18 g of 10% Mannich base catalyst solution diluted with DMF at 50°C for half an hour. When NCO% = 7.7%, 4.0 g of dibutyl phosphate was added to terminate the reaction to obtain the TDI curing agent, which had the following indexes:

[0069] Solid content = 50.2%;

[0070] NCO% = 7.81%;

[0071] Viscosity = 635 cp;

[0072] Color number 20 Hazen;

[0073] Free monomer content 0.23%.

[0074] Example 4

[0075] Preparation of Mannich base: 130 g of glycitein was mixed with 400 g of 33% by mass dimethylamine solution and 300 g of 37% by mass formaldehyde solution, 6 g of 0.5 mol / L hydrochloric acid solution was added, and the reaction was stopped after 10 h of reaction at 95°C. After cooling and standing to separate the layers, the organic phase was distilled under reduced pressure at 70°C and 100 Pa to obtain the Mannich base catalyst. The Mannich base catalyst was diluted with butyl acetate to obtain a 15% Mannich base catalyst solution;

[0076] Preparation of TDI curing agent: 1000 g of TDI-80 and 1017 g of ethyl acetate were added to a reaction kettle under nitrogen protection, and 17 g of n-butanol was added to the reaction kettle. After stirring uniformly, the reaction was initiated by adding 10 g of 15% Mannich base catalyst solution diluted with butyl acetate at 50°C for half an hour. When NCO% = 7.7%, 1.5 g of phosphoric acid was added to terminate the reaction to obtain the TDI curing agent, which had the following indexes:

[0077] Solid content = 51.1%;

[0078] NCO% = 7.69%;

[0079] Viscosity = 216 cp;

[0080] Color No. 22 Hazen;

[0081] Free monomer content 0.11%.

[0082] Example 5

[0083] Preparation of Mannich base: 110 g of procyanidins was mixed with 300 g of dimethylamine solution with a mass fraction of 33% and 180 g of formaldehyde solution with a mass fraction of 37%, 7 g of hydrochloric acid solution with a concentration of 0.5 mol / L was added, and the reaction was stopped after heating at 100°C for 8 h. After cooling and standing for layering, the organic phase was distilled under reduced pressure at 70°C and 100 Pa to obtain the Mannich base catalyst. Diluted with xylene to 20% Mannich base catalyst solution;

[0084] Preparation of TDI curing agent: 1000 g of TDI-80 and 1016 g of butyl acetate were added to the reaction kettle under nitrogen protection, stirred uniformly, then 16 g of octadecanol was added to the reaction kettle, and the trimerization reaction was initiated after adding 10 g of xylene diluted with 20% Mannich base catalyst solution at 90°C for half an hour. When NCO% = 7.8%, 4.5 g of dibutyl phosphate was added to terminate the reaction to obtain the TDI curing agent, and the indexes are as follows:

[0085] Solid content = 50.8%

[0086] NCO% = 7.82%

[0087] Viscosity = 1050 cp

[0088] Color No. 18 Hazen

[0089] Free monomer content 0.14%.

[0090] Example 6

[0091] Preparation of Mannich base: 100 g of daidzein was mixed with 360 g of dimethylamine solution with a mass fraction of 33% and 180 g of formaldehyde solution with a mass fraction of 37%, 8 g of hydrochloric acid solution with a concentration of 0.5 mol / L was added, and the reaction was stopped after heating at 100°C for 2 h. After cooling and standing for layering, the organic phase was distilled under reduced pressure at 70°C and 100 Pa to obtain the Mannich base catalyst. Diluted with butyl acetate to 10% Mannich base catalyst solution;

[0092] Preparation of TDI curing agent: 1000 g of TDI-80 and 1000 g of butyl acetate were added to the reaction kettle under nitrogen protection, stirred uniformly, and the trimerization reaction was initiated after adding 25 g of butyl acetate diluted with 10% Mannich base catalyst solution at 80°C for half an hour. When NCO% = 7.95%, 10 g of dibutyl phosphate was added to terminate the reaction to obtain the TDI curing agent, and the indexes are as follows:

[0093] Solid content = 51.3%;

[0094] NCO% = 7.94%;

[0095] Viscosity = 1650 cp;

[0096] Color number 15 Hazen;

[0097] Free monomer content 0.22%.

[0098] Comparative Example 1

[0099] Preparation of TDI curing agent: 1000 g of TDI-80 and 1107 g of butyl acetate were added to a reaction kettle under nitrogen protection, stirred uniformly, then 107 g of dodecanol was added to the reaction kettle, after reacting for half an hour at 50°C, 15 g of butyl acetate was added to dilute 15% Mannich base 2,4,6-tris(dimethylaminomethyl)phenol catalyst solution to initiate the trimerization reaction, when NCO% = 7.5%, 3.0 g of benzoyl chloride was added to terminate the reaction to obtain a TDI curing agent, and its indexes were as follows:

[0100] Solid content = 50.7%;

[0101] NCO% = 7.45%;

[0102] Viscosity = 356 cp;

[0103] Color number 46 Hazen;

[0104] Free monomer content 1.08%.

[0105] Comparing between the examples and the comparative examples, it can be seen that the catalyst prepared by using natural phenolic compounds in the application has improved steric hindrance compared with the catalyst prepared by using conventional chemical source phenolic compounds, and the reaction selectivity of small molecule monomers is improved through the steric hindrance effect, which is beneficial to reduce the content of free TDI monomers, so it is beneficial to prepare a TDI curing agent with free monomer content less than 0.5%.

Claims

1. A bio-based Mannich base obtained from a Mannich reaction of a natural phenol, dimethylamine and formaldehyde, wherein, The natural phenol is one or more selected from catechin, theaflavin, daidzein and procyanidin.

2. A method for preparing the bio-based Mannich base according to claim 1, comprising the following steps: 1) reacting the natural phenol, aqueous dimethylamine solution and aqueous formaldehyde solution in the presence of dilute hydrochloric acid catalyst at 80-100℃; 2) after the reaction is completed, cooling and standing to separate into layers, and distilling the organic phase under reduced pressure to obtain the bio-based Mannich base.

3. The method for preparing the bio-based Mannich base according to claim 2, wherein, the molar ratio of the natural phenol, dimethylamine and formaldehyde is 1:6-12:6-12; and / or, the concentration of the aqueous dimethylamine solution is 10%-50%; and / or, the concentration of the aqueous formaldehyde solution is 10%-50%; and / or, the concentration of the dilute hydrochloric acid catalyst is 0.1-0.8 mol / L, and the amount of the dilute hydrochloric acid catalyst is such that the HCl content in the reaction system is 100-500 ppm; and / or, the reaction time of step 1) is 8-10 hours.

4. The method for preparing the bio-based Mannich base according to claim 3, wherein, the concentration of the aqueous dimethylamine solution is 20%-40%; and / or, the concentration of the aqueous formaldehyde solution is 20%-40%.

5. Use of the bio-based Mannich base according to claim 1 as a catalyst in the preparation of TDI curing agent.

6. A method for preparing TDI curing agent, comprising the following steps: a) mixing toluene diisocyanate and a solvent homogeneously under an inert atmosphere, and then adding an alcohol to react, wherein, the alcohol is a fatty alcohol having 1 to 22 carbon atoms; b) trimerization reaction is carried out on the reactants obtained in step a) by adding the bio-based Mannich base according to claim 1 as a catalyst; c) when the content of NCO groups reaches the design requirement, a terminating agent is added to terminate the reaction.

7. The method for preparing TDI curing agent according to claim 6, wherein, the molar ratio of NCO groups of toluene diisocyanate to hydroxyl groups in the alcohol is 200-20:1; and / or, the amount of the bio-based Mannich base catalyst is 1000-5000 ppm based on TDI; and / or, the alcohol is one or more selected from butanol, isobutanol, octanol, dodecanol, tetradecanol, hexadecanol and octadecanol.

8. The method for preparing TDI curing agent according to claim 6, wherein, the toluene diisocyanate is 2,4-toluene diisocyanate and / or 2,6-toluene diisocyanate; and / or, the solvent is one or more selected from toluene, acetone, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate and propylene glycol methyl ether acetate; and / or, the amount of the solvent is such that the mass concentration of the reactants in step a) is 20% to 80% by weight; and / or, in step b), the bio-based Mannich base is added in the form of a solution.

9. The method for preparing TDI curing agent according to claim 8, wherein, the toluene diisocyanate is a mixture of 80 wt% 2,4-toluene diisocyanate and 20 wt% 2,6-toluene diisocyanate; and / or, the solvent is ethyl acetate or butyl acetate; and / or, the solvent is used in an amount such that the mass concentration of the reactants in step a) is 40% to 60% by weight; and / or, in step b), the bio-based Mannich base is added in the form of a solution, and the concentration of the bio-based Mannich base in the solution is 10wt% to 30wt%.

10. The method for preparing a TDI curing agent according to claim 8, wherein, the solvent is used in an amount such that the mass concentration of the reactants in step a) is 50% by weight.

11. The method for preparing a TDI curing agent according to any one of claims 6 to 10, wherein, the reaction temperature in step a) is 20 to 90°C; and / or, the reaction temperature in step b) is 20 to 90°C, and the reaction time is 10 to 30 hours; and / or, in step c), when the content of NCO groups is 7% to 8.5%, a terminating agent is added to terminate the reaction.

12. The method for preparing a TDI curing agent according to any one of claims 6 to 10, wherein, the terminating agent is a protic acid, an acylating agent, or an alkylating agent; and / or, the amount of the terminating agent added is 1 to 5 times the mass of the bio-based Mannich base catalyst.