Method for preparing liquid polyurethane curing agent from chain extender residues

Abstract

The invention discloses a method for preparing a liquid polyurethane curing agent from chain extender residues, which comprises the following steps of: carrying out transesterification on excessive micromolecular diol or a mixture of diol and triol and p-aminobenzoic acid lower alkyl ester substances in the chain extender residues in low-viscosity low-molecular-weight polyether polyol; a monofunctional substance is converted into a product with the functionality of 2-3, and the environment-friendly liquid curing agent composition obtained after the reaction can be used for a bi-component solvent-free elastic polyurethane system independently or together with other chain extenders. According to the method, the chain extender residues are developed and recycled on the basis of analyzing the components of the chain extender residues, waste is turned into wealth, pollution to the environment caused by solid waste formed by the chain extender residues is avoided, the production cost of enterprises is reduced, and the requirements of green and clean production are met.

Description

Technical Field

[0001] The invention relates to a method for comprehensive utilization of chain extender residues in the field of fine chemicals, and in particular to a method for preparing a liquid polyurethane curing agent by utilizing residues containing ester groups and amino groups and application thereof. Background Art

[0002] 1,3-Propanediol bis(4-aminobenzoate) is an aromatic diamine with an ester bond, which is safe, low-toxic and has excellent curing properties. It is a grayish white to light brown solid at room temperature, with a melting point of 125-128°C. The aromatic diamine has a sufficient kettle life when used for curing polyurethane prepolymers. Polyurethane elastomers can be produced by hand pouring or machine pouring. The prepared polyurethane elastomer products have excellent mechanical properties as well as wear resistance, heat resistance, oil / solvent / humidity / ozone resistance and other properties.

[0003] The transesterification method is an important production process of 1,3-propylene glycol bis(4-aminobenzoate): p-aminobenzoic acid lower alkyl esters (such as ethyl ester, methyl ester, butyl ester) and 1,3-propylene glycol react under the action of an ester exchange catalyst and are obtained after recrystallization and purification. While obtaining a high-purity product through the recrystallization operation, a certain amount of recrystallized solid residue will also be produced. It is a concentrated mixture composed of incomplete transesterification byproducts (containing 1 amino group and 1 hydroxyl group in the molecule, which can react with isocyanate), 1,3-propylene glycol bis(4-aminobenzoate), unreacted p-aminobenzoic acid lower alkyl ester (only 1 amino group in the molecule can react with isocyanate, and the other end is a lower alkyl ester structure) and trace unknown impurities, and the composition is complex. After analysis and detection, it was found that the composition of different batches of recrystallized solid residues fluctuated within a certain range, and the content of p-aminobenzoic acid lower alkyl esters in the residue ranged from 15% to 35%.

[0004] In view of the above-mentioned recrystallized solid residue, the invention patent CN112029063B discloses a method for preparing a storage-stable liquid polyurethane curing agent composition by directly dissolving the solid residue with a mixture of a low-viscosity liquid polyether polyol and a small amount of triol. The method adds a small amount of triol when dissolving the residue, which can partially compensate for the adverse effects of lower alkyl p-aminobenzoate when used as a polyurethane curing agent. For the recrystallized solid residue with a high content of lower alkyl p-aminobenzoate, when the liquid curing agent composition prepared by the CN112029063B method is used to cure the prepolymer, the physical properties of the obtained elastomer are relatively low. The reason for this is that the presence of lower alkyl p-aminobenzoate plays a role in capping the prepolymer, and a high molecular weight polyurethane cannot be obtained, which reduces the performance of the elastomer.

[0005] In view of the defects of the above-mentioned prior art that it is not suitable for the situation where the content of lower alkyl p-aminobenzoate is high, the inventors have finally created the present invention which is truly practical after continuous research, design, repeated experiments and improvements. Summary of the invention

[0007] The main purpose of the present invention is to overcome the defects of the existing technology and provide a new method for preparing a liquid polyurethane curing agent from chain extender residue. The technical problem to be solved is to comprehensively develop the solid residue of the recrystallized chain extender containing ester groups and turn waste into treasure, thereby making full use of resources and finally obtaining a liquid curing agent composition that is easy to use and has good performance, which is very suitable for practical use.

[0008] Another object of the present invention is to provide a new method for preparing a liquid polyurethane curing agent from chain extender residue. The technical problem to be solved is to eliminate the adverse effects of lower alkyl p-aminobenzoate on the physical properties of polyurethane when used, thereby improving the mechanical properties of polyurethane products. The prepared liquid curing agent composition contains rigid and flexible chain segments, and gives the polyurethane elastomer good strength and flexibility, making it more suitable for practical use.

[0009] Another object of the present invention is to provide a new method for preparing liquid polyurethane curing agent from chain extender residue, and the technical problem to be solved is to enhance environmental protection, reduce enterprise costs, and thus be more suitable for practical use.

[0010] The purpose of the present invention and the technical problem solved are achieved by adopting the following technical scheme. According to the method for preparing a liquid polyurethane curing agent from a chain extender residue proposed by the present invention, a mixture of a recrystallized solid residue of a recovered aromatic diamine chain extender and a small molecule polyol and a low-viscosity, low-molecular-weight polyether polyol acting as an active diluent is subjected to an ester exchange reaction under the action of an ester exchange catalyst, and a lower alkyl para-aminobenzoate in the aromatic diamine recrystallized solid residue is converted into a product having a hydroxyl + amino functionality of not less than 2, and an environmentally friendly liquid curing agent composition is obtained, which can be used as a curing agent component of a solvent-free two-component polyurethane resin system.

[0011] Furthermore, the recrystallized solid residue is a monofunctional compound obtained by producing 1,3-propylene glycol bis(4-aminobenzoate) through an ester exchange reaction, such as a lower alkyl p-aminobenzoate and a trace amount of monofunctional impurities, with a content of 15% to 35% of the recrystallized solid residue.

[0012] Furthermore, the small molecule polyol is a low-cost small molecule alcohol containing at least two primary hydroxyl groups, such as ethylene glycol, diethylene glycol, triethylene glycol, 1,3-propylene glycol, 1,4-butylene glycol, polyethylene glycol PEG-200, trimethylolpropane and glycerol.

[0013] Furthermore, the molar ratio of the hydroxyl group of the small molecule polyol to the lower alkyl p-aminobenzoate is between 1.5 and 5:1, preferably between 2 and 4:1, the molar percentage of the diol in the small molecule polyol is in the range of 60% to 100%, preferably 80% to 100%, and the ester exchange catalyst used is tetraisopropyl titanate, tetrabutyl titanate or zinc acetate, and the amount used is 0 to 0.05% of the mass of the raw material.

[0014] Furthermore, the low-viscosity, low-molecular-weight liquid polyether polyol is selected from one or two of polyoxypropylene glycol, polyoxypropylene triol, polytetramethylene glycol PTMG-650, and polyoxyethylene glycol, preferably polyoxypropylene glycol, or a mixture of polyoxypropylene glycol and polyoxypropylene triol in a mass ratio of 100 to 80:(0 to 20), the relative molecular mass of the selected low-viscosity, low-molecular-weight liquid polyether polyol is in the range of 200 to 1000, preferably in the range of 300 to 700, and the mass fraction of the low-viscosity, low-molecular-weight liquid polyether polyol used in the environmentally friendly liquid curing agent composition is 25% to 70%, preferably 30% to 50%.

[0015] Further, the basic operation steps are:

[0016] (1) adding the recrystallized solid residue of 1,3-propylene glycol bis(4-aminobenzoate) into a reaction vessel, and then adding a small molecule polyol, a low-viscosity, low-molecular-weight liquid polyether polyol, and an auxiliary agent such as a catalyst in an amount of 0 to 0.05% by weight of the raw material, and heating to 90° C. to 110° C. under nitrogen protection to dissolve the recrystallized solid residue;

[0017] (2) conducting an ester exchange reaction at 130° C. to 150° C. for 2.5 to 4 hours under normal pressure and a controlled nitrogen flow;

[0018] (3) Raising the temperature to 140° C. to 170° C., and increasing the vacuum degree stepwise to a maximum vacuum degree of 5 to 10 kPa, and continuing the reaction for 2.5 to 4 hours;

[0019] (4) Maintain the vacuum state, stir and cool to 80°C, slowly return to normal pressure, then cool to about 50°C and discharge.

[0020] Furthermore, the environmentally friendly liquid curing agent composition is directly used as the curing agent component, i.e., the active hydrogen component, of a solvent-free two-component polyurethane resin system, and its application fields include polyurethane paving materials, polyurethane waterproof coatings, polyurethane sealants for construction, polyurethane potting glues, and polyurethane adhesives.

[0021] Compared with the prior art, the present invention has obvious advantages and beneficial effects. By means of the above technical solution, it has at least the following advantages:

[0022] (1) The present invention avoids the pollution to the environment caused by the incineration of solid waste formed by recrystallization of solid kettle residue;

[0023] (2) The liquid curing agent composition prepared by the present invention contains rigid and flexible segments, which can give the polyurethane elastomer good strength and flexibility;

[0024] (3) The present invention eliminates the adverse effects of lower alkyl p-aminobenzoate on the physical properties of polyurethane during use, thereby improving the mechanical properties of polyurethane products;

[0025] (3) The liquid curing agent composition prepared by the present invention realizes the maximum utilization of resources and reduces the production cost of the enterprise. The implementation of the patented method can achieve a win-win situation of environmental protection and reducing enterprise costs.

[0026] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the preferred embodiments of the present invention are described in detail as follows. DETAILED DESCRIPTION

[0029] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the following is a method for preparing a liquid polyurethane curing agent from a chain extender residue according to the present invention, in combination with the preferred embodiments, and its specific implementation method, method (manufacturing method, processing method), steps, characteristics and effects are described in detail as follows.

[0030] A method for preparing a liquid polyurethane curing agent from a chain extender residue in a preferred embodiment of the present invention is to perform an ester exchange reaction on a mixture of a recrystallized solid residue of a recovered aromatic diamine chain extender and a small molecule polyol and a low-viscosity, low-molecular-weight polyether polyol acting as an active diluent under the action of an ester exchange catalyst, converting the lower alkyl p-aminobenzoate in the aromatic diamine recrystallized solid residue into a product having a hydroxyl+amino functionality of not less than 2, and obtaining an environmentally friendly liquid curing agent composition, which can be used as a curing agent component of a solvent-free two-component polyurethane resin system. The adverse effects of the lower alkyl p-aminobenzoate on the physical properties of the polyurethane when used are eliminated, and the mechanical properties of the polyurethane product are improved.

[0031] The reaction formula of lower alkyl p-aminobenzoate and diol in the ideal situation is as follows:

[0032] 2NH2PhCOOR'+HO-R-OH→NH2PhCOO-R-OCOPhNH2+2R'OH

[0033] The reaction equation in the case of excess diol is as follows:

[0034] NH2PhCOOR'+HO-R-OH→NH2PhCOO-R-OH+R'OH

[0035] (HO-R-OH represents a small molecule diol, Ph represents a benzene ring or a nucleus containing a benzene ring byproduct, and R' represents -C2H5, -CH3 and H, etc.)

[0036] As can be seen from the above formula, the lower alkyl p-aminobenzoate undergoes an ester exchange reaction with a diol to transform into a difunctional product containing 2 amino groups, or 1 amino group + 1 hydroxyl group, which can be used as an active hydrogen component and used as a curing agent to react with a polyisocyanate component to obtain a polyurethane (urea).

[0037] The preferred technical solution is: for the recrystallized solid residue containing ester groups and monofunctional group substances produced in the process of preparing 1,3-propylene glycol bis(4-aminobenzoate) by the ester exchange method, the functional group refers to the group that can react with isocyanate. The present invention adds a small molecule polyol, whose hydroxyl group is a primary hydroxyl group, and a low-viscosity and low-molecular-weight polyether polyol mixture to the solid residue for ester exchange reaction. The small molecule polyol undergoes an ester exchange reaction with a low alkyl para-aminobenzoate compound or undergoes an esterification or ester exchange reaction with an unknown monofunctional impurity to obtain a product with a functionality of not less than 2, and the functionality of other compounds containing two functional groups in the recrystallized solid residue is not affected by the ester exchange reaction; the low-viscosity and low-molecular-weight polyether polyol can reduce the viscosity of the reaction system and improve the uniformity of mass transfer. The conventional low-viscosity and low-molecular-weight polyether polyol is a polyoxypropylene polyol, and the reaction activity of the secondary hydroxyl groups contained therein is lower than that of the primary hydroxyl groups. The small molecule polyols actually participating in the ester exchange reaction are still mainly primary hydroxyl small molecule polyols. Even if a small amount of polyether polyol participates in the ester exchange reaction, it does not affect the effects described in the present invention.

[0039] The recrystallized solid residue is a monofunctional compound obtained by producing 1,3-propylene glycol bis(4-aminobenzoate) through an ester exchange reaction, such as a lower alkyl p-aminobenzoate and a trace amount of monofunctional impurities, with a content of 15% to 35%.

[0040] The preferred technical solution is: the small molecule polyol is a low-cost small molecule alcohol containing at least 2 primary hydroxyl groups, such as ethylene glycol, diethylene glycol, triethylene glycol, 1,3-propylene glycol, 1,4-butylene glycol, polyethylene glycol PEG-200, trimethylolpropane and glycerol. A small amount of triol is added to the diol for transesterification reaction to obtain a product with an average functionality slightly greater than 2, which is conducive to appropriately shortening the curing time of the two-component polyurethane system and giving the polyurethane elastomer a certain degree of chemical crosslinking, thereby improving the strength of the elastomer. The molar percentage of diol in the small molecule polyol is controlled at 60% to 100%, preferably 80% to 100%, and the molar percentage of triol is 0 to 20%.

[0041] The preferred technical solution is: the molar ratio of the hydroxyl group of the small molecule polyol to the lower alkyl para-aminobenzoate in the residue is controlled at 1.5 to 5:1, preferably between 2 and 4:1. The excess hydroxyl group can promote the full ester exchange reaction. After the reaction is completed, the excess small molecule polyol is removed under high vacuum and high temperature conditions.

[0042] The preferred technical scheme is: the low-viscosity and low-molecular-weight liquid polyether polyol is selected from one or two of polyoxypropylene glycol, polyoxypropylene triol, polytetramethylene glycol PTMG-650, and polyoxyethylene glycol, preferably polyoxypropylene glycol, or a mixture of polyoxypropylene glycol and polyoxypropylene triol in a mass ratio of 100-80:(0-20), the relative molecular mass of the selected low-viscosity and low-molecular-weight liquid polyether polyol is in the range of 200-1000, preferably in the range of 300-700, and the mass fraction of the low-viscosity and low-molecular-weight liquid polyether polyol used in the environmentally friendly liquid curing agent composition is 25%-70%, preferably 30%-50%.

[0043] The preferred technical solution is: adding a trace amount of esterification / ester exchange reaction catalyst, such as tetraisopropyl titanate, tetra-n-butyl titanate, zinc acetate, etc., during the ester exchange process, and the amount of the ester exchange catalyst is 0-0.05% of the raw material mass.

[0044] The preferred technical solution is: the mixture of the recrystallized solid residue and the small molecule polyol and the low viscosity and low molecular weight liquid polyether polyol is subjected to transesterification reaction at 130°C to 170°C. The reaction temperature of the first stage is 130°C to 150°C, the reaction time is 2.5 to 4 hours, and the by-products of the transesterification reaction (such as methanol, ethanol, butanol) and water are taken out by nitrogen; the reaction temperature of the second stage is 140°C to 170°C, preferably 145°C to 165°C, and the vacuum degree is gradually increased to 10kPa (vacuum pressure gauge reading -0.091MPa) or higher vacuum degree within 2 to 3 hours, and the vacuum is kept for 0.5 to 1 hour and then cooled, and then restored to normal pressure and further cooled and discharged to obtain a product with hydroxyl + amino functionality not less than 2, and the small molecule alcohol evaporated during the reaction is collected.

[0045] The preferred technical solution is: a small amount of antioxidant such as 1076, 1010, etc. can be added during the reaction, and the added amount is 0-0.1% of the reaction raw materials. The addition of antioxidant can inhibit the darkening of the color of the ester exchange reaction system.

[0047] To achieve the above-mentioned purpose and other related purposes, the technical solution provided by the present invention is: the obtained environmentally friendly liquid curing agent composition can be used alone or together with other curing agents as a curing agent component (active hydrogen component) of a solvent-free two-component polyurethane resin system, and can be used for the production of polyurethane paving materials, polyurethane waterproof coatings, polyurethane sealants for construction, polyurethane potting glue, polyurethane adhesives, etc.

[0048] The basic operation steps of the present invention are:

[0049] (1) Add the recrystallized solid residue or hot molten liquid into a reaction vessel, then add a small molecule polyol, a low viscosity low molecular weight polyether polyol and a small amount of additives (such as a catalyst, etc.), and heat to 90-110° C. under nitrogen protection to dissolve the residue;

[0050] (2) conducting an ester exchange reaction at normal pressure, nitrogen bubbling, and a temperature of 130 to 150° C. for 2.5 to 4 hours;

[0051] (3) reacting for 2.5 to 4 hours at a temperature of 140 to 170° C. and increasing the vacuum degree stepwise to a maximum vacuum degree of 5 to 10 kPa;

[0052] (4) Maintaining the vacuum state, stirring and cooling to 80°C, then slowly returning to normal pressure and continuing to cool to about 50°C to discharge the material. The product is an environmentally friendly liquid curing agent composition.

[0053] The environmentally friendly liquid curing agent composition is a mixture containing aromatic diamine, liquid polyether polyol, aromatic alcohol amine and a small amount of other components with a functionality of not less than 2, and has the appearance of a yellow to amber viscous liquid.

[0054] When the above-mentioned environmentally friendly liquid curing agent composition is used alone or together with other curing agents as the curing agent component of a solvent-free two-component polyurethane resin system, its application fields include polyurethane paving materials, polyurethane waterproof coatings, polyurethane sealants for construction, polyurethane potting glue, polyurethane adhesives, etc.

[0055] The specific embodiments are as follows:

[0056] In order to facilitate understanding of the present invention, the following specific embodiments illustrate the features of the present invention. People familiar with the art can easily understand the various advantages of the present invention from the contents disclosed in this specification. However, these embodiments are only exemplary and do not constitute any limitation to the scope of the present invention. Synthesis of Liquid Polyurethane Curing Agent Composition

[0057] Embodiment 1:

[0058] The solid residue of recrystallization of 1,3-propylene glycol bis(4-aminobenzoate) is deduced to have a terminal ester content of 2.0 mmol / g based on the detection of the content of lower alkyl p-aminobenzoate, and the amount of the required small molecule polyol is calculated according to the ratio.

[0059] In a 2000mL four-necked bottle equipped with an esterification reaction kit (thorn-type fractionation column / thermometer / straight condenser / vacuum receiving tube / round connecting bottle), agitator, thermometer, and nitrogen inlet tube, 500g of the above solid residue was added, and 159g of diethylene glycol and 550g of polyoxypropylene glycol N-206 were added. Under nitrogen protection, the mixture was heated to dissolve evenly, and ester exchange and esterification reactions were carried out at 130°C to 150°C. The by-product alcohol etc. was removed by nitrogen flow, and the reaction was carried out at normal pressure for 3 hours. Then, the reaction was continued at 140-170° C. with step-wise reduced pressure, and the vacuum degree was increased every 0.5 hour for 2-3 hours until the vacuum degree was increased to 5 kPa. The reaction was continued for 0.5 hour. The vacuum degree was maintained and then the mixture was cooled to 80° C. and then restored to normal pressure. The mixture was further cooled to 50° C. to obtain 1099 g of a liquid polyurethane curing agent composition. The total equivalent weight (reactive groups were amino groups + hydroxyl groups) was measured to be 177. The viscosity of the yellow-brown viscous liquid at 25° C. was about 3150 mPa·s.

[0060] Embodiment 2:

[0061] A solid recrystallized residue of 1,3-propylene glycol bis(4-aminobenzoate) is detected to contain 34.7% of p-aminobenzoic acid lower alkyl ester with known chemical structure, and the terminal ester content is estimated to be 2.5 mmol / g. The amount of small molecule polyol required is calculated according to the ratio.

[0062] In a 1000 mL reaction bottle, 400 g of melted recrystallization residue, 62 g of ethylene glycol, 50 g of polyethylene glycol PEG-400, 5 g of glycerol and 124 g of polyoxypropylene glycol N-204 were added, and 0.1 g of tetraisopropyl titanate and 0.3 g of antioxidant 1076 were added. Nitrogen was passed through the bottle and reacted at 130-150° C. for 3 hours. Then, the vacuum degree was increased stepwise every 0.5 hour, and the reaction was continued at 145-165° C. under reduced pressure for 2.5 hours, until the reaction was carried out at a vacuum degree of 10 kPa for 0.5 hour, and then the temperature was cooled to 80° C. with stirring at a vacuum degree of 2 kPa, and the pressure was restored to normal to obtain 585 g of a liquid polyurethane curing agent composition. The total equivalent weight was measured to be about 166, and the viscosity of the yellow-brown viscous liquid at 25° C. was about 5500 mPa·s.

[0063] Embodiment 3:

[0064] In a 1000 mL reaction bottle, 400 g of a melted recrystallized residue having a terminal ester content of 1.2 mmol / g, 90 g of polyethylene oxide PEG-200, 43.5 g of diethylene glycol, 283 g of polyoxypropylene glycol N-204 and 31 g of polyoxypropylene triol N305 were added, and 0.1 g of zinc acetate was added. The mixture was reacted at 140-150° C. for 2.5 hours under nitrogen, and then the vacuum degree was increased stepwise within 2.5 hours to continue the reaction until the reaction was carried out at a vacuum degree of 5 kPa for 0.5 hours. The vacuum degree was maintained and then cooled to 80° C., then restored to normal pressure, and the temperature was continued to be lowered and the material was discharged to obtain about 795 g of a liquid polyurethane curing agent composition, with a total equivalent weight of about 165 and a product viscosity of about 3830 mPa·s.

[0065] Embodiment 4:

[0066] 500 g of solid residue with a low alkyl ester end group content of 2.0 mmol / g was added with 106.2 g of ethylene glycol, 17.5 g of propylene glycol and 225 g of polyoxypropylene glycol N-204. The reaction conditions were basically the same as those in Example 1 to obtain 740 g of a liquid polyurethane curing agent composition with a total equivalent (amino + hydroxyl) of 141. The yellow-brown viscous liquid had a viscosity of about 7100 mPa·s at 25°C.

[0067] Embodiment 5:

[0068] 500 g of solid residue with a lower alkyl ester end group content of 2.0 mmol / g was added with 55.3 g of 1,3-propylene glycol, 24.4 g of trimethylolpropane and 355 g of polytetrahydrofuran diol PTMG-650. The reaction conditions were basically the same as those in Example 1 to obtain 886 g of a liquid polyurethane curing agent composition with a total equivalent weight (amino group + hydroxyl group) of 159. The yellow-brown viscous liquid had a viscosity of about 6700 mPa·s at 25°C.

[0069] Embodiment 6:

[0070] 500g of solid residue with a low alkyl ester end group content of 2.0mmol / g was added with 147.5g of diethylene glycol, 9.8g of trimethylolpropane, 337g of polyoxypropylene diol N-204 and 18g of polyoxypropylene triol N-307. The reaction conditions were basically the same as those in Example 1 to obtain 897g of a liquid polyurethane curing agent composition with a total equivalent (amino + hydroxyl) of 145. The yellow-brown viscous liquid had a viscosity of about 5160mPa·s at 25°C.

[0071] Table 1 Synthesis of liquid polyurethane curing agent composition

[0072]

[0073] Application of liquid polyurethane curing agent composition

[0074] Embodiment 7:

[0075] Take 100g of TDI-PTMG polyurethane prepolymer with an NCO mass fraction of 5.7%, add the liquid curing agent composition obtained in Example 1 and 0.08g of the organic metal catalyst CUCAT-HS according to an isocyanate index of 1.1, mix evenly and degas, and then cure on a polytetrafluoroethylene template at 25°C. After 1 hour, there is no fluidity. After being placed at room temperature for one day, it is ripened at 100°C for 2 hours. After being placed for 2 days, the tensile strength is measured to be 4.87MPa and the elongation at break is 447%. The two-component polyurethane can be used as a polyurethane adhesive, etc.

[0076] Embodiment 8:

[0077] 50g of high-activity polyether 330N, 30g of polyether diol N-220, 10g of the liquid curing agent composition prepared in Example 2, 60g of nano-scale light calcium carbonate, 50g of plasticizer DPGDB (Wuhan Yikede ECOD-FLEX342), 0.6g of anti-settling agent FH-809, and 0.6g of organic metal catalyst CUCAT-HS were mixed uniformly to obtain component B. MDI-PPG prepolymer with an NCO mass fraction of 5.6% was used as component A.

[0078] The A / B components were mixed at an isocyanate index of 1.1 and cured according to the curing conditions of Example 5. The gel time at room temperature was 1.5 hours, the tensile strength of the elastomer was 3.38 MPa, and the elongation at break was 405%.

[0079] Embodiment 9:

[0080] Take 100g of TDI-PPG type polyurethane prepolymer with an NCO mass fraction of 5.2%, add the liquid curing agent composition obtained in Example 3 and 0.08g of organic metal catalyst K-Kat 604 (King Industries, USA) according to the isocyanate index of 1.1, and cure it on a polytetrafluoroethylene template at 25°C. After 1 hour, there is no fluidity. After being placed at room temperature for one day, it is placed in an oven at 50°C for 5 hours and then matured at 100°C for 2 hours. After being placed for 2 days, the tensile strength is measured to be 3.94MPa and the elongation at break is 315%.

[0081] Comparative Example 1:

[0082] 50g of 1,3-propylene glycol bis(4-aminobenzoate) recrystallized solid residue was heated and dissolved in 45g of polyoxypropylene glycol N-206 and 5g of glycerol, and vacuum dehydrated at 110℃~120℃ to obtain a compound liquid curing agent composition with a viscosity of about 6080mPa·s and a total equivalent weight of about 197. This curing agent composition is prepared according to the method introduced in CN112029063, wherein glycerol is a small molecule triol, which is blended with the monofunctional components in the residue so that the average functionality of the entire liquid curing agent composition is slightly greater than 2.

[0083] The compounded liquid curing agent composition was compared with the liquid curing agent composition obtained in Example 1. The prepolymer of Example 7 was used to prepare a polyurethane film with the same proportion, and the tensile strength was 2.74 MPa and the elongation at break was 298%.

[0084] Table 2 Application of liquid polyurethane curing agent

[0085]

[0086]

[0087] Under the same prepolymer conditions, Example 7 and Comparative Example 1 respectively adopt the liquid polyurethane curing agent composition prepared by the present invention and the curing agent prepared according to CN112029063 to synthesize polyurethane elastomers. It can be seen from the physical property test data that the elastomer obtained by curing the prepolymer with the liquid polyurethane curing agent prepared by the present invention has higher strength.

[0088] The polyurethane elastomer prepared by reacting the liquid polyurethane curing agent synthesized by the present invention with the prepolymer has good physical properties and can be used in the production of polyurethane paving materials, polyurethane waterproof coatings, polyurethane sealants for construction, polyurethane potting glue, polyurethane adhesives, etc.

[0089] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a liquid polyurethane curing agent from chain extender residue, characterized in that: The invention relates to a method for preparing an environmentally friendly liquid curing agent composition, wherein the solid residue of the recrystallized aromatic diamine chain extender recovered is subjected to an ester exchange reaction with a mixture of a small molecule polyol and a low-viscosity, low-molecular-weight polyether polyol acting as an active diluent, so as to convert the lower alkyl p-aminobenzoate in the solid residue of the recrystallized aromatic diamine into a product with a hydroxyl+amino functionality of not less than 2, and obtain the liquid curing agent composition. The liquid curing agent composition can be used as a curing agent component of a solvent-free two-component polyurethane resin system.

2. The method for preparing a liquid polyurethane curing agent from a chain extender residue according to claim 1, characterized in that: The recrystallized solid residue is a monofunctional compound obtained by producing 1,3-propylene glycol bis(4-aminobenzoate) through an ester exchange reaction, such as a lower alkyl p-aminobenzoate and a trace amount of monofunctional impurities, with a content of 15% to 35%.

3. The method for preparing a liquid polyurethane curing agent from a chain extender residue according to claim 1, characterized in that: The small molecule polyol is a low-cost small molecule alcohol containing at least two primary hydroxyl groups, such as ethylene glycol, diethylene glycol, triethylene glycol, 1,3-propylene glycol, 1,4-butylene glycol, polyethylene glycol PEG-200, trimethylolpropane and glycerol.

4. The method for preparing a liquid polyurethane curing agent from a chain extender residue according to claim 1, characterized in that: The molar ratio of the hydroxyl group of the small molecule polyol to the lower alkyl p-aminobenzoate is between 1.5 and 5:1, preferably between 2 and 4:1, the molar percentage of the diol in the small molecule polyol is in the range of 60% to 100%, preferably 80% to 100%, and the transesterification catalyst used is tetraisopropyl titanate, tetrabutyl titanate or zinc acetate, and the amount used is 0 to 0.05% of the mass of the raw material.

5. The method for preparing a liquid polyurethane curing agent from a chain extender residue according to claim 1, characterized in that: The low-viscosity and low-molecular-weight liquid polyether polyol is selected from one or two of polyoxypropylene diol, polyoxypropylene triol, polytetramethylene glycol PTMG-650, and polyoxyethylene diol, preferably polyoxypropylene diol, or a mixture of polyoxypropylene diol and polyoxypropylene triol in a mass ratio of 100-80:0-20. The relative molecular mass of the selected low-viscosity and low-molecular-weight liquid polyether polyol is in the range of 200-1000, preferably in the range of 300-700. The mass fraction of the low-viscosity and low-molecular-weight liquid polyether polyol used in the environmentally friendly liquid curing agent composition is 25%-70%, preferably 30%-50%.

6. A method for preparing a liquid polyurethane curing agent from a chain extender residue according to claims 1-5, characterized in that: The basic operation steps are: (1) adding the recrystallized solid residue of 1,3-propylene glycol bis(4-aminobenzoate) into a reaction vessel, and then adding a small molecule polyol, a low-viscosity, low-molecular-weight liquid polyether polyol, and an auxiliary agent such as a catalyst in an amount of 0 to 0.05% by weight of the raw material, and heating to 90° C. to 110° C. under nitrogen protection to dissolve the recrystallized solid residue; (2) conducting an ester exchange reaction at 130° C. to 150° C. for 2.5 to 4 hours under normal pressure and a controlled nitrogen flow; (3) Raising the temperature to 140° C. to 170° C., and increasing the vacuum degree stepwise to a maximum vacuum degree of 5 to 10 kPa, and continuing the reaction for 2.5 to 4 hours; (4) Maintain the vacuum state, stir and cool to 80°C, slowly return to normal pressure, then cool to about 50°C and discharge.

7. The method for preparing a liquid polyurethane curing agent from chain extender residue according to claim 6, characterized in that: The environmentally friendly liquid curing agent composition is directly used as the curing agent component, i.e., the active hydrogen component, of a solvent-free two-component polyurethane resin system, and its application fields include polyurethane paving materials, polyurethane waterproof coatings, polyurethane sealants for construction, polyurethane potting glues, and polyurethane adhesives.

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