Bio-based Mannich base as well as preparation method and application thereof

Abstract

The invention provides a bio-based Mannich base, a preparation method and 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 Mannich reaction of natural phenol, dimethylamine and formaldehyde, and the natural phenol is selected from one or more of sesamol, catechin, theaflavin, daidzein and procyanidine. The Mannich base catalyst prepared from natural phenol is used, the steric hindrance is improved, the reaction selectivity of micromolecular 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 a time, and therefore the content of the free monomers in the prepared TDI curing agent is advantageously lower than 0.5%.

Description

Technical Field

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

[0002] The polyurethane prepared with 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, as well as as a polyurethane elastomer and polyurethane foam. Toluene diisocyanate as a curing agent has fast curing speed, high hydrolysis resistance, corrosion resistance and thermal stability compared with other curing agents. There will be a certain amount of isocyanate monomer residue in the preparation process of polyisocyanate curing agent. The national standard GB1858-2009 "Limits of Harmful Substances in Solvent-based Wood Coatings for Interior Decoration and Renovation Materials" stipulates that the limit value of free toluene diisocyanate after painting should be ≤0.4%, which puts higher requirements on the limit of toluene diisocyanate content in curing agent. The commonly used methods to reduce the toluene diisocyanate content in curing agent are divided into physical method, chemical method and extraction method.

[0003] The most commonly used 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 is quickly passed 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 free TDI content in the final product is less than 0.5wt%. At present, the application of thin film evaporation technology in the separation of free TDI in TDI-TMP adduct curing agent has been relatively mature, but the thin film evaporation technology has high energy consumption and high requirements for vacuum equipment, thereby increasing production costs. In addition, due to the use of high temperature in the evaporation process, the product color number will also be higher.

[0004] The solvent extraction method is mainly based on the different polarities of TDI monomer and prepolymer, and thus the different solubility in different solvents to achieve the separation of free TDI. CN02134225.3 uses an extraction method to remove free TDI monomer by adding a high-boiling point extractant, and the free TDI content in the final product is less than 0.5wt%, and the extractant content is 1wt%. CN102659997A introduces a high-boiling point ester solvent and adjusts the feed rate 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 requires a large amount of solvent for multiple extractions, and the process is cumbersome, so the production efficiency is very low, and the extract needs to be reprocessed, 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 advantages of the chemical synthesis method are simple synthesis process, no need for additional separation operation, and low cost. However, the monomer content of the chemically prepared curing agent is 0.5-1.0wt%. To reduce the monomer content, it is necessary to increase the degree of reaction and change the formula, which will lead to an increase in product color number, a low NCO content, and poor miscibility with hydroxyl resins. CN1470508A and CN103183808A use synthetic Mannich base catalysts, and add alcohol for modification during the reaction. TDI-100 needs to be added later to reduce the content of free monomers, and the reaction process is cumbersome; CN105315433A uses alcohol modification to improve the compatibility of the product, and uses a homemade Mannich base catalyst, which requires multiple batches of catalysts to be added, and alcohol needs to be added for modification after the reaction is terminated to reduce the monomer to below 0.5%. In the comparative example, the DMP-30 catalyst made of traditional phenol is directly added during the catalytic reaction, and the product monomer content is 1.32%; the raw materials of the catalysts synthesized in the above patents all come from fossil energy. Therefore, the development of an efficient and green catalyst for reducing monomers has become the main direction of chemical technology development. Summary of the invention

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

[0007] According to a first aspect of the present invention, a bio-based Mannich base is provided, which is obtained by a Mannich reaction of natural phenol, dimethylamine and formaldehyde, wherein the natural phenol is one or more selected from sesamol, catechins, theaflavins, glycitein and proanthocyanidins.

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

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

[0010] 2) After the reaction is completed, the mixture is cooled and allowed to stand for stratification, and the organic phase is distilled under reduced pressure 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 dimethylamine aqueous solution is 10% to 50%, preferably 20% to 40%.

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

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

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

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

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

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

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

[0020] c) When the content of NCO groups reaches the design requirement, a terminator is added to terminate the reaction.

[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 bio-based Mannich base catalyst is used in an amount of 1000 to 5000 ppm based on TDI.

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

[0024] Preferably, the toluene diisocyanate is 2,4-toluene diisocyanate and / or 2,6-toluene diisocyanate, more preferably 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, more preferably ethyl acetate or butyl acetate.

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

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

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

[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 wt % to 30 wt %.

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

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

[0032] Preferably, when the content of NCO groups is 7% to 8.5%, a terminator is added to terminate the reaction.

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

[0034] According to a fifth aspect of the present invention, there is provided a TDI curing agent, wherein the free diisocyanate monomer content is less than 0.5 wt %, the platinum cobalt color number is less than 40 Hazen, and the viscosity is less than 2000 cp.

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

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

[0037] Compared with the Mannich base catalyst prepared from chemically derived phenolic compounds in the prior art, the Mannich base catalyst prepared from natural phenol in the present invention has improved steric hindrance, and the reaction selectivity of small molecular monomers can be improved through the steric hindrance effect. The free TDI monomer content in the TDI curing agent can be reduced by adding the catalyst once, so the free monomer content of the prepared TDI curing agent is advantageously less than 0.5%. DETAILED DESCRIPTION

[0038] The following examples will further illustrate the method provided by the present invention, but the present invention is not limited to the listed examples, and should also include any other known changes within the scope of the claims of the present invention. The specific application of the present invention is not limited to the application mentioned in the examples, and those familiar with the art can make any modifications and further development within the scope of the claims of the present invention.

[0039] Butanol, Aladdin reagent;

[0040] Dodecanol, Tianjin Guangfu Chemical Industry;

[0041] Octanol, Aladdin reagent;

[0042] Tetradecanol, Tianjin Guangfu Chemical;

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

[0044] Unless otherwise specified, other raw materials and reagents can be purchased through commercial channels.

[0045] NCO content test is in accordance with standard GB / T 12009.4;

[0046] The dynamic viscosity was measured at 25 °C using a rotor viscometer (Brookfield DV-II);

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

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

[0049] The free TDI content is tested according to GB / T18446-2009;

[0050] Example 1

[0051] Preparation of Mannich base: 50g of sesamol was mixed with 300g of 33% dimethylamine solution and 250g of 37% formaldehyde solution, and 5g of 0.5mol / L hydrochloric acid solution was added to react at 80°C for 4h, and then heating was stopped. After cooling and standing for stratification, the organic phase was distilled under reduced pressure at 70°C and 100Pa to obtain Mannich base, which was diluted with butyl acetate to obtain a 20% Mannich base catalyst solution;

[0052] Preparation of TDI curing agent: Under nitrogen protection, 1000g TDI-80 and 1107g butyl acetate were added to the reactor and stirred evenly. Then 107g dodecanol was added to the reactor. After reacting at 20°C for half an hour, 5.0g Mannich base 20% butyl acetate catalyst solution was added to initiate trimerization. When NCO% = 7.5%, 3.0g dibutyl phosphate was added to terminate the reaction to obtain TDI curing agent. Its indicators are as follows:

[0053] Solid content = 50.5%;

[0054] NCO% = 7.48%;

[0055] Viscosity = 195cp;

[0056] Color No. 15 Hazen;

[0057] The free monomer content is 0.30%.

[0058] Example 2

[0059] Preparation of Mannich base: 100g of catechins, 400g of 33% by mass dimethylamine solution and 240g of 37% by mass formaldehyde solution were mixed, 10g of 0.5mol / L hydrochloric acid solution was added, the mixture was reacted at 90°C for 6h, heating was stopped, the mixture was cooled and allowed to stand for stratification, and the organic phase was distilled under reduced pressure at 70°C and 100Pa to obtain the Mannich base catalyst, which was diluted with xylene to obtain a 20% Mannich base catalyst solution;

[0060] Preparation of TDI curing agent: Under nitrogen protection, 1000g TDI-80 and 1021g butyl acetate were added to the reactor and stirred evenly. Then 21g dodecanol was added to the reactor. After reacting at 40°C for half an hour, 10.0g xylene was added to dilute the 20% Mannich base catalyst solution to initiate trimerization. When NCO% = 7.7%, 15.0g dibutyl phosphate was added to terminate the reaction to obtain TDI curing agent. Its indicators are as follows:

[0061] Solid content = 51.1%;

[0062] NCO% = 7.71%;

[0063] Viscosity = 551cp;

[0064] Color No. 18 Hazen;

[0065] The free monomer content is 0.25%.

[0066] Example 3

[0067] Preparation of Mannich base: 150g of theaflavin is mixed with 350g of a 33% by mass dimethylamine solution and 210g of a 37% by mass formaldehyde solution, 8g of a 0.5mol / L hydrochloric acid solution is added, the mixture is reacted at 100°C for 10h, heating is stopped, the mixture is cooled and allowed to stand for stratification, and the organic phase is distilled under reduced pressure at 70°C and 100Pa to obtain the Mannich base catalyst, which is diluted with DMF to obtain a 10% Mannich base catalyst solution;

[0068] Preparation of TDI curing agent: Under nitrogen protection, 1000g TDI-80 and 1014g butyl acetate were added to the reactor and stirred evenly. Then 14g dodecanol was added to the reactor. After reacting at 50°C for half an hour, 18g DMF was added to dilute the 10% Mannich base catalyst solution to initiate trimerization. When NCO% = 7.7%, 4.0g dibutyl phosphate was added to terminate the reaction to obtain TDI curing agent. Its indicators are as follows:

[0069] Solid content = 50.2%;

[0070] NCO% = 7.81%;

[0071] Viscosity = 635cp;

[0072] Color No. 20 Hazen;

[0073] The free monomer content is 0.23%.

[0074] Example 4

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

[0076] Preparation of TDI curing agent: Under nitrogen protection, 1000g TDI-80 and 1017g ethyl acetate were added to the reactor and stirred evenly. Then 17g n-butanol was added to the reactor. After reacting at 50°C for half an hour, 10g butyl acetate was added to dilute the 15% Mannich base catalyst solution to initiate trimerization. When NCO% = 7.7%, 1.5g phosphoric acid was added to terminate the reaction to obtain TDI curing agent. Its indicators are as follows:

[0077] Solid content = 51.1%;

[0078] NCO% = 7.69%;

[0079] Viscosity = 216cp;

[0080] Color No. 22 Hazen;

[0081] The free monomer content is 0.11%.

[0082] Example 5

[0083] Preparation of Mannich base: 110g of proanthocyanidins, 300g of 33% dimethylamine solution and 180g of 37% formaldehyde solution were mixed, 7g of 0.5mol / L hydrochloric acid solution was added, and the mixture was reacted at 100°C for 8h, and then heating was stopped. After cooling and standing for stratification, the organic phase was distilled under reduced pressure at 70°C and 100Pa to obtain the Mannich base catalyst, which was diluted with xylene to obtain a 20% Mannich base catalyst solution;

[0084] Preparation of TDI curing agent: Under nitrogen protection, 1000g TDI-80 and 1016g butyl acetate were added to the reactor and stirred evenly. Then 16g octadecyl alcohol was added to the reactor. After reacting at 90°C for half an hour, 10g xylene was added to dilute to 20% Mannich base catalyst solution to initiate trimerization. When NCO% = 7.8%, 4.5g dibutyl phosphate was added to terminate the reaction to obtain TDI curing agent. Its indicators are as follows:

[0085] Solid content = 50.8%

[0086] NCO%=7.82%

[0087] Viscosity = 1050cp

[0088] Color No. 18Hazen

[0089] The free monomer content is 0.14%.

[0090] Example 6

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

[0092] Preparation of TDI curing agent: Under nitrogen protection, 1000g TDI-80 and 1000g butyl acetate were added to the reactor, stirred evenly, and reacted at 80°C for half an hour, and then 25g butyl acetate was added to dilute the 10% Mannich base catalyst solution to initiate trimerization. When NCO% = 7.95%, 10g dibutyl phosphate was added to terminate the reaction to obtain TDI curing agent, and its indicators are as follows:

[0093] Solid content = 51.3%;

[0094] NCO% = 7.94%;

[0095] Viscosity = 1650cp;

[0096] Color No. 15 Hazen;

[0097] The free monomer content is 0.22%.

[0098] Comparative Example 1

[0099] Preparation of TDI curing agent: Under nitrogen protection, 1000g TDI-80 and 1107g butyl acetate were added to the reactor and stirred evenly. Then 107g dodecanol was added to the reactor. After reacting at 50°C for half an hour, 15g butyl acetate was added to dilute 15% Mannich base 2,4,6-tris(dimethylaminomethyl)phenol catalyst solution to initiate trimerization. When NCO% = 7.5%, 3.0g benzoyl chloride was added to terminate the reaction to obtain TDI curing agent. Its indicators are as follows:

[0100] Solid content = 50.7%;

[0101] NCO% = 7.45%;

[0102] Viscosity = 356cp;

[0103] Color No. 46 Hazen;

[0104] The free monomer content is 1.08%.

[0105] It can be seen from the comparison between the examples and the comparative examples that the catalyst prepared by using natural phenolic compounds in the present invention has improved steric hindrance compared with the catalyst prepared by using phenolic compounds from conventional chemical sources, and the reaction selectivity of small molecule monomers is improved through the steric hindrance effect, which is beneficial to reduce the free TDI monomer content, so that the free monomer of the prepared TDI curing agent is lower than 0.5%.

Claims

1. A bio-based Mannich base 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, catechins, theaflavins, glycitein and proanthocyanidins.

2. A method for preparing the bio-based Mannich base according to claim 1, comprising the following steps: 1) reacting natural phenol, dimethylamine aqueous solution and formaldehyde aqueous solution at 80-100° C. in the presence of dilute hydrochloric acid catalyst; 2) After the reaction is completed, the mixture is cooled and allowed to stand for stratification, and the organic phase is distilled under reduced pressure to obtain the bio-based Mannich base.

3. The method for preparing a 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 dimethylamine aqueous solution is 10% to 50%, preferably 20% to 40%; and / or, the concentration of the formaldehyde aqueous solution is 10% to 50%, preferably 20% to 40%; and / or, 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; And / or, the reaction time of step 1) is 8 to 10 hours.

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

5. A method for preparing a TDI curing agent, comprising the steps of: a) in an inert atmosphere, mixing toluene diisocyanate and a solvent uniformly, and then adding alcohol to react; b) adding the bio-based Mannich base according to claim 1 as a catalyst to the reactant obtained in step a) to carry out a trimerization reaction; c) When the content of NCO groups reaches the design requirement, a terminator is added to terminate the reaction.

6. The method for preparing a TDI curing agent according to claim 5, wherein: The molar ratio of the NCO group of toluene diisocyanate to the hydroxyl group in the alcohol is 200 to 20:1; and / or, the bio-based Mannich base catalyst is used in an amount of 1000 to 5000 ppm based on TDI; And / or, the alcohol is a fatty alcohol having 1 to 22 carbon atoms, preferably one or more selected from butanol, isobutanol, octanol, dodecanol, tetradecanol, hexadecanol and octadecyl alcohol.

7. The method for preparing a TDI curing agent according to claim 5 or 6, wherein: Toluene diisocyanate is 2,4-toluene diisocyanate and / or 2,6-toluene diisocyanate, preferably a mixture of 80 wt % of 2,4-toluene diisocyanate and 20 wt % of 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, preferably ethyl acetate or butyl acetate; and / or, the amount of the solvent used is such that the mass concentration of the reactants in step a) is 20 wt % to 80 wt %, preferably 40 wt % to 60 wt %, most preferably 50 wt %; And / or, in step b), the bio-based Mannich base is added in the form of a solution, preferably, the concentration of the bio-based Mannich base in the solution is 10 wt % to 30 wt %.

8. The method for preparing a TDI curing agent according to any one of claims 5 to 7, wherein: The reaction temperature in step a) is 20-90° C.; And / or, the reaction temperature in step b) is 20-90° C., and the reaction time is 10-30 h; And / or, in step c), when the content of NCO groups is 7% to 8.5%, a terminator is added to terminate the reaction.

9. The method for preparing a TDI curing agent according to any one of claims 5 to 8, wherein: The terminator is a protonic acid, an acylating agent or an alkylating agent; And / or, the amount of the terminator added is 1 to 5 times the mass of the bio-based Mannich base catalyst.

10. A TDI curing agent, wherein The free diisocyanate monomer content is lower than 0.5 wt %, the platinum cobalt color number is lower than 40 Hazen, and the viscosity is lower than 2000 cp.