Method for preparing water-resistant and fireproof modified polyurethane

Abstract

Disclosed is a method for preparing a water-resistant and fireproof modified polyurethane, belonging to the technical field of polyurethanes. The method comprises: using a polycaprolactone diol or polycarbonate diol as a polyester polyol; and performing a polymerization reaction with a diisocyanate compound such as isophorone diisocyanate, and then performing a hyperbranched crosslinking reaction with a polyhydroxyimide chain extender to obtain a modified polyurethane. A plurality of hydroxyl groups and an imide ring that are contained in the polyhydroxyimide chain extender both affect the water absorption, fireproofing, flame retardancy, and heat resistance of the polyurethane. The water absorption of the modified polyurethane is reduced, and the hydrolysis of the polyester polyurethane can be inhibited, thereby facilitating improving the water resistance. In addition, the thermal decomposition temperature of the modified polyurethane is increased, the peak value of the combustion heat release rate and the total heat release amount are reduced, and better heat resistance and flame retardant and fireproof performance are exhibited.

Description

A method for preparing water-resistant and fire-retardant modified polyurethane Technical Field

[0001] This invention belongs to the field of polyurethane technology, and in particular to a method for preparing water-resistant and fire-retardant modified polyurethane. Background Technology

[0002] Polyurethane is a high-performance polymer material, mainly divided into polyester-based polyurethane and polyether-based polyurethane. It possesses excellent elasticity, toughness, and mechanical strength, and is widely used in coatings, inks, foams, and fibers. However, ordinary polyurethane has poor heat resistance; it easily undergoes thermal decomposition at high temperatures, significantly affecting its mechanical properties. Simultaneously, polyurethane is flammable and has poor flame retardant properties, hindering its application in fire-resistant and refractory materials. Furthermore, polyester-based polyurethane contains a large number of ester groups, making it prone to hydrolysis upon water absorption, resulting in poor water resistance. Developing high-performance chain extenders is an effective method to improve the water resistance and fire resistance of polyurethane. The literature "Synthesis and Properties of Anionic Waterborne Polyurethane-Imine" reports the reaction of pyromellitic tetracarboxylic anhydride and ethylene glycol to obtain dihydroxypyromellitic imide monomer, which is used as a chain extender to improve the heat resistance and tensile properties of polyurethane. However, this literature does not address the problem of high water absorption and poor water resistance in polyurethane.

[0003] Summary of the Invention

[0004] In view of the shortcomings of the prior art, the present invention solves the problem of poor water resistance and flame retardant fireproof performance of polyurethane materials.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for preparing water-resistant and fire-retardant modified polyurethane, comprising the following steps:

[0006] Step S1: Add dry polyester polyol and diisocyanate compound to the reaction vessel, introduce nitrogen gas, and carry out the polymerization reaction to obtain polyurethane prepolymer.

[0007] Step S2: Mix the polyurethane prepolymer, polyhydroxyimide chain extender, and dibutyltin dilaurate. When the gel point is reached, quickly pour the mixture into a preheated mold, pressurize it in a flat vulcanizing machine, demold it, and then place it in a heating box for curing treatment to obtain water-resistant and fire-retardant modified polyurethane.

[0008] The reaction formula for polyhydroxyimide chain extenders is as follows:

[0009] Preferably, the polymerization reaction temperature is 60-80℃ and the reaction time is 2-4h.

[0010] Preferably, the molar ratio of polyester polyol, diisocyanate compound, and polyhydroxyimide chain extender is 1:(2-2.2):(0.5-0.6).

[0011] Preferably, the polyester polyol is polycaprolactone diol or polycarbonate diol; the diisocyanate compound is isophorone diisocyanate, toluene-2,4-diisocyanate or diphenylmethane-4,4'-diisocyanate.

[0012] Preferably, the pressure during pressurization is 10-15 MPa, the temperature is 110-125℃, and the time is 30-60 min.

[0013] Preferably, the aging process involves first placing the food at 100-120℃ for 18-24 hours, and then at 20-30℃ for 3-7 days.

[0014] Preferably, the preparation method of the polyhydroxyimide chain extender includes the following steps:

[0015] Step (1): Add glacial acetic acid, 4-hydroxyphthalic anhydride and 4-aminobenzoic acid in a molar ratio of 1:(0.9-1.1) to the reaction vessel, heat to 100-110℃, react for 3-4 hours, dilute with water, then add sodium hydroxide to adjust the pH of the solution to neutral, add dichloromethane for extraction, separate the organic phase, rotary evaporate, separate by silica gel column chromatography, and use a solution of petroleum ether and ethyl acetate as eluent to obtain the intermediate.

[0016] Step (2): Add acetonitrile, intermediate, 2,2'-[1,4-phenylenebis(oxymethylene)]bis(ethylene oxide) with a molar ratio of (2.2-2.6):1:(0.04-0.05), and tetrabutylammonium bromide catalyst to the reaction vessel. Heat to 80-85℃, reflux for 6-12 h, rotary evaporate, separate by silica gel column chromatography, and use petroleum ether and ethyl acetate solutions as eluents to obtain polyhydroxyimide chain extender.

[0017] This invention has the following technical effects: It utilizes polycaprolactone diol or polycarbonate diol as the polyester polyol; it undergoes a polymerization reaction with diisocyanate compounds such as isophorone diisocyanate, followed by a hyperbranching and crosslinking reaction with a polyhydroxyimide chain extender to obtain modified polyurethane. The multiple hydroxyl groups and imide rings contained in the polyhydroxyimide chain extender both affect the water absorption rate of the polyurethane. Containing four hydroxyl groups, it can undergo a hyperbranching and crosslinking reaction with the polyurethane prepolymer, which is beneficial for increasing the crosslinking density of the polyurethane molecular chains, forming a tight molecular chain crosslinking network, and inhibiting water molecules from entering the matrix. Furthermore, the polyhydroxyimide chain extender contains multiple imide rings, resulting in high structural rigidity and cohesive energy, and strong intermolecular forces, which can improve the interaction between polyurethane molecular chains, further enhancing the tightness between molecular chains and inhibiting water molecules from entering the matrix. This significantly reduces the water absorption rate of the modified polyurethane. The lower the water absorption rate, the more effectively the polyester-type polyurethane can be inhibited from undergoing hydrolysis, thus improving its water resistance.

[0018] The polyhydroxyimide chain extender of this invention contains multiple hydroxyl groups and imide rings, which affect the fire retardant and heat resistance properties of polyurethane. The polyhydroxyimide chain extender undergoes a crosslinking reaction with the polyurethane prepolymer to form a hyperbranched crosslinked network, restricting the movement of the polyurethane molecular chains. This results in higher energy requirements during the thermal decomposition of the polyurethane, thus increasing the thermal decomposition temperature of the modified polyurethane. Furthermore, the polyhydroxyimide chain extender contains high-temperature resistant and flame-retardant imide rings, which, when introduced into the polyurethane molecular backbone, further increase the thermal decomposition temperature, reduce the peak combustion heat release rate and total heat release, exhibiting better heat resistance and flame retardant properties. Detailed Implementation

[0019] To more clearly illustrate the present invention and to gain a clearer understanding of its technical features, objectives, and beneficial effects, the technical solution of the present invention will now be described in detail below, but this should not be construed as limiting the scope of the present invention.

[0020] Example 1

[0021] (1) Add 130 mL of glacial acetic acid, 30 mmol of 4-hydroxyphthalic anhydride, and 33 mmol of 4-aminobenzoic acid to a reaction vessel, heat to 100 °C, react for 4 h, dilute with water, then add sodium hydroxide to adjust the pH of the solution to neutral, extract with dichloromethane, separate the organic phase, rotary evaporate, separate by silica gel column chromatography, using a solution of petroleum ether and ethyl acetate as eluent, to obtain the intermediate. The preparation reaction formula is as follows:

[0022] (2) Add 140 mL of acetonitrile, 44 mmol of the intermediate, 20 mmol of 2,2'-[1,4-phenylenebis(oxymethylene)]bis(ethylene oxide), and 1 mmol of tetrabutylammonium bromide catalyst to the reaction vessel. Heat to 85 °C, reflux for 6 h, rotary evaporate, and separate by silica gel column chromatography, using petroleum ether and ethyl acetate solutions as eluents to obtain the polyhydroxyimide chain extender. The preparation reaction formula is as follows:

[0023] (3) Add 50 mmol of dry polycaprolactone diol 2000 and 106 mmol of isophorone diisocyanate to the reaction vessel, introduce nitrogen gas, heat to 60°C, and polymerize for 3 hours to obtain polyurethane prepolymer.

[0024] (4) The polyurethane prepolymer prepared above, 28 mmol of polyhydroxyimide chain extender and 0.36 mmol of dibutyltin dilaurate are stirred and mixed. When the gel point is reached, it is quickly poured into a preheated mold and subjected to pressure treatment at 120°C for 30 min under 15 MPa pressure in a flat vulcanizing machine. After demolding, it is placed in a heating box and cured at 110°C for 24 h, and then cured at 30°C for 3 days to obtain water-resistant and fire-retardant modified polyurethane.

[0025] Example 2

[0026] (1) Add 100 mL of glacial acetic acid, 30 mmol of 4-hydroxyphthalic anhydride and 27 mmol of 4-aminobenzoic acid to the reaction vessel, heat to 110 °C and react for 3 h. Add water to dilute, then add sodium hydroxide to adjust the pH of the solution to neutral, add dichloromethane to extract, separate the organic phase, rotary evaporate, separate by silica gel column chromatography, use petroleum ether and ethyl acetate solution as eluent to obtain the intermediate.

[0027] (2) Add 140 mL of acetonitrile, 52 mmol of intermediate, 20 mmol of 2,2'-[1,4-phenylenebis(oxymethylene)]bis(ethylene oxide) and 0.8 mmol of tetrabutylammonium bromide catalyst to the reaction vessel, heat to 80 °C, reflux for 12 h, rotary evaporate, separate by silica gel column chromatography, and use petroleum ether and ethyl acetate solution as eluent to obtain polyhydroxyimide chain extender.

[0028] (3) Add 50 mmol of dry polycaprolactone diol 2000 and 100 mmol of toluene-2,4-diisocyanate to the reaction vessel, introduce nitrogen gas, heat to 70°C, and polymerize for 4 hours to obtain polyurethane prepolymer.

[0029] (4) The polyurethane prepolymer prepared above, 25 mmol of polyhydroxyimide chain extender and 0.32 mmol of dibutyltin dilaurate are stirred and mixed. When the gel point is reached, it is quickly poured into a preheated mold and subjected to pressure treatment at 125°C for 30 min under 15 MPa pressure in a flat vulcanizing machine. After demolding, it is placed in a heating box and first placed at 100°C for 24 h to mature, and then at 20°C for 7 days to obtain water-resistant and fire-retardant modified polyurethane.

[0030] Example 3

[0031] (1) Prepare a polyhydroxyimide chain extender according to the method in Example 1.

[0032] (2) Add 50 mmol of dry polycarbonate diol 2000 and 110 mmol of isophorone diisocyanate to the reaction vessel, introduce nitrogen gas, heat to 60°C, and polymerize for 4 hours to obtain polyurethane prepolymer.

[0033] (3) The polyurethane prepolymer prepared above, 30 mmol of polyhydroxyimide chain extender and 0.38 mmol of dibutyltin dilaurate are stirred and mixed. When the gel point is reached, it is quickly poured into a preheated mold and subjected to pressure treatment at 125°C for 30 min under 10 MPa pressure in a flat vulcanizing machine. After demolding, it is placed in a heating box and first placed at 100°C for 24 h to mature, and then at 25°C for 7 days to obtain water-resistant and fire-retardant modified polyurethane.

[0034] Example 4

[0035] (1) Prepare a polyhydroxyimide chain extender according to the method in Example 1.

[0036] (2) Add 50 mmol of dry polycarbonate diol 2000 and 103 mmol of diphenylmethane-4,4'-diisocyanate to the reaction vessel, introduce nitrogen gas, heat to 80°C, and polymerize for 2 hours to obtain polyurethane prepolymer.

[0037] (3) The polyurethane prepolymer prepared above, 26 mmol of polyhydroxyimide chain extender and 0.38 mmol of dibutyltin dilaurate are stirred and mixed. When the gel point is reached, it is quickly poured into a preheated mold and subjected to pressure treatment at 110°C for 40 min under 15 MPa pressure in a flat vulcanizing machine. After demolding, it is placed in a heating box and cured at 110°C for 24 h, and then cured at 25°C for 7 days to obtain water-resistant and fire-retardant modified polyurethane.

[0038] Comparative Example 1

[0039] The difference between this comparative example and Example 1 is the use of triethanolamine. Replaces polyhydroxyimide chain extenders.

[0040] (1) Mix polyurethane prepolymer, 28 mmol polyhydroxyimide chain extender and 0.36 mmol dibutyltin dilaurate. When the gel point is reached, quickly pour it into a preheated mold. In a flat vulcanizing machine, pressurize at 120°C for 30 min under 15 MPa pressure. Demold and place in a heating box. First, cure at 110°C for 24 h, and then cure at 30°C for 3 days to obtain modified polyurethane.

[0041] Comparative Example 2

[0042] The difference between this comparative example and Example 1 is that dihydroxypyromellitic imide is used instead of polyhydroxyimide chain extender.

[0043] Dihydroxypyromellitic imide was prepared according to the method described in the journal *Applied Chemical Industry*, April 2019, Volume 48, Supplement 1, "Synthesis and Properties of Anionic Waterborne Polyurethane-Imidides". The structural formula is as follows:

[0044] (1) Mix polyurethane prepolymer, 28 mmol dihydroxybenzoimide and 0.36 mmol dibutyltin dilaurate. When the gel point is reached, quickly pour it into a preheated mold. In a flat vulcanizing machine, pressurize at 120°C for 30 min under 15 MPa pressure. Demold and place in a heating box. First, cure at 110°C for 24 h, and then cure at 30°C for 3 days to obtain modified polyurethane.

[0045] Prepare a 5cm×5cm×2cm sample of modified polyurethane and weigh it; then place it in distilled water and soak it in 25℃ for 48h. Take out the modified polyurethane, wipe off the residual moisture on the surface, weigh it, and calculate the water absorption rate Q according to the following formula.

[0046] Q = (m1 - m0) / m0 × 100%. Where m0 is the mass before water absorption, and m1 is the mass after water absorption.

[0047] The modified polyurethane was prepared into samples of 8cm×8cm×0.5cm, and its combustion performance was tested using a cone calorimeter, with the thermal radiation power controlled at 35kW / m². 2 .

[0048] The modified polyurethane was prepared into samples of 3cm×3cm×0.2cm. Thermogravimetric analysis was performed on the samples using a thermogravimetric analyzer under a nitrogen atmosphere at a temperature range of 25-700℃.

[0049] Table 1. Performance test of modified polyurethane.

[0050] In Table 1, PHRR is the peak rate of heat release during combustion, and THR is the total heat release. 5％ This is the temperature at which a 5% mass loss occurs. T max This is the maximum thermal decomposition temperature. Weight is the mass percentage remaining at 700℃.

[0051] As shown in Table 1, the modified polyurethane obtained by using polyhydroxyimide chain extenders to undergo hyperbranching and crosslinking reactions with polyurethane prepolymers in each embodiment has a water absorption rate of only 1.9-2.7%. Lower water absorption rates inhibit hydrolysis of polyester-type polyurethanes, thus improving water resistance. Polyhydroxyimide chain extenders contain four hydroxyl groups, which can undergo hyperbranching and crosslinking reactions with polyurethane prepolymers. This increases the crosslinking density of polyurethane molecular chains, forming a tight molecular chain crosslinking network that inhibits water molecules from entering the matrix. Furthermore, polyhydroxyimide chain extenders contain multiple imide rings, resulting in structural rigidity, high cohesive energy, and strong intermolecular forces. This enhances the interaction between polyurethane molecular chains, further increasing their tightness and inhibiting water molecules from entering the matrix, thereby significantly reducing the water absorption rate of the modified polyurethane. The multiple hydroxyl groups and imide rings in the polyhydroxyimide chain extender both affect the water absorption rate of the polyurethane.

[0052] The peak PHRR (heat release rate) of the modified polyurethane in each embodiment was only 476.2-532.8 kW / m³. 2 The total heat release (THR) is only 49.8-52.9 MJ / m³. 2 T 5％ Reaching 312.6-318.7℃, T max Reaching 406.9-410.2℃ with a mass residue of 11.1-12.6%, it exhibits excellent flame retardant and heat resistance properties. This is because the polyhydroxyimide chain extender undergoes a cross-linking reaction with the polyurethane prepolymer, forming a hyperbranched cross-linked network. This restricts the movement of the polyurethane molecular chains, requiring higher energy for thermal decomposition, thus increasing the thermal decomposition temperature of the modified polyurethane. Furthermore, the polyhydroxyimide chain extender contains high-temperature resistant and flame-retardant imide rings, which, when introduced into the polyurethane molecular backbone, further increase the thermal decomposition temperature, reduce the peak heat release rate and total heat release, resulting in better heat resistance and flame retardant properties. The multiple hydroxyl groups and imide rings in the polyhydroxyimide chain extender all influence the flame retardant and heat resistance properties of the polyurethane.

[0053] Comparative Example 1 used conventional triethanolamine as a chain extender. Triethanolamine contains three hydroxyl groups and can undergo hyperbranching and crosslinking reactions with the polyurethane prepolymer. The water absorption rate of the modified polyurethane after crosslinking was only 3.8%. However, it did not contain an imide ring, resulting in lower intermolecular forces and no significant improvement in the interaction between polyurethane molecular chains. This led to a higher water absorption rate than in Example 1. Furthermore, the modified polyurethane's main molecular chain did not contain imide, resulting in a lower thermal decomposition temperature than in Example 1, but a higher peak combustion heat release rate and total heat release. Consequently, its heat resistance and flame retardant properties were poor.

[0054] Comparative Example 2 used dihydroxyphenylimide as a chain extender. Containing two hydroxyl groups, it could not undergo hyperbranching and crosslinking with the polyurethane prepolymer, thus failing to significantly increase the crosslinking density of the polyurethane molecular chains and failing to form a tight molecular chain crosslinking network. This resulted in a higher water absorption rate for the modified polyurethane compared to Comparative Example 1 and Example 1. However, the modified polyurethane molecular backbone contained an imide ring, leading to a higher thermal decomposition temperature than Comparative Example 1, and lower peak combustion heat release rate and total heat release compared to Comparative Example 1.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A process for the preparation of a water-resistant fire-retardant modified polyurethane, characterized in that, The preparation method comprises the following steps: Step S1, adding dry polyester polyol, diisocyanate compound into a reaction container, passing nitrogen, and performing polymerization reaction to obtain polyurethane prepolymer; Step S2, stirring and mixing the polyurethane prepolymer, polyhydroxy imide chain extender and dibutyl tin dilaurate, pouring into a preheated mold, performing pressure treatment in a flat curing machine, demolding, and then placing in a heating box to perform curing treatment, thereby obtaining water-resistant and fire-resistant modified polyurethane; The structural formula of the polyhydroxy imide chain extender is shown as formula (I):

2. The process for the preparation of water-resistant flame-retardant modified polyurethane according to claim 1, characterized by the fact that, The polymerization reaction is performed at a temperature of 60-80℃ for 2-4h.

3. The method of preparing a water-resistant fireproof modified polyurethane according to claim 1, characterized in that, The molar ratio of the polyester polyol, diisocyanate compound and polyhydroxy imide chain extender is 1:(2-2.2):(0.5-0.6).

4. The process for the preparation of water-resistant flame-retardant modified polyurethane according to claim 3, characterized by the fact that, The polyester polyol is polycaprolactone diol or polycarbonate diol; the diisocyanate compound is isophorone diisocyanate, toluene-2,4-diisocyanate or diphenyl methane-4,4'-diisocyanate.

5. The method of preparing water-resistant fireproof modified polyurethane according to claim 1, characterized in that, The pressure treatment is performed at a pressure of 10-15MPa and a temperature of 110-125℃ for 30-60min.

6. The method of preparing water-resistant fireproof modified polyurethane according to claim 1, characterized by, The curing treatment is first placed at 100-120℃ for 18-24h, and then placed at 20-30℃ for 3-7 days.

7. The preparation method of the water-resistant and fire-retardant modified polyurethane according to claim 1, characterized in that, The preparation method of the polyhydroxy imide chain extender comprises the following steps: Step (1), adding glacial acetic acid, 4-hydroxy phthalic anhydride and 4-aminobenzoic acid into a reaction container, heating to 100-110℃, reacting for 3-4h, diluting with water, then adding sodium hydroxide to adjust the pH of the solution to neutral, extracting, and separating by silica gel column chromatography to obtain an intermediate with petroleum ether and ethyl acetate as eluent; Step (2), adding acetonitrile, the intermediate, 2,2'-[1,4-phenylene bis (oxymethylene)] bisoxirane and catalyst tetrabutylammonium bromide into a reaction container, performing rotary evaporation after reaction, and separating by silica gel column chromatography to obtain the polyhydroxy imide chain extender.

8. The preparation method of the water-resistant and fire-retardant modified polyurethane according to claim 1, characterized in that, The molar ratio of the 4-hydroxy phthalic anhydride and 4-aminobenzoic acid is 1:(0.9-1.1).

9. The preparation method of the water-resistant and fire-retardant modified polyurethane according to claim 1, characterized in that, In step (2), the molar ratio of the intermediate, 2,2'-[1,4-phenylene bis (oxymethylene)] bisoxirane and tetrabutylammonium bromide is (2.2-2.6):1:(0.04-0.05).

10. The method for preparing water-resistant and fire-retardant modified polyurethane according to claim 1, characterized in that, In step (2), the reaction is performed at a temperature of 80-85℃ for 6-12h.

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