A heat-resistant polyurethane composition for synthetic leather and its preparation method

Abstract

This invention relates to the field of polyurethane technology, specifically to a heat-resistant polyurethane composition for synthetic leather and its preparation method. The composition comprises poly(ricinoleic adipate) diol, polycarbonate diol, isocyanate, a heat-resistant chain extender, functionalized nano-kaolin, a catalyst, and an antioxidant; wherein the heat-resistant chain extender contains a triphenyl ring and a phosphoryl group structure, and the functionalized nano-kaolin is obtained by treating nano-kaolin with a phosphorus-silicon composite modifier. The preparation method mainly includes prepolymer synthesis, chain extension and functional filler dispersion, and degassing. This invention, through the rigid structure enhancement of the heat-resistant chain extender, the covalent anchoring of the functionalized kaolin, and the phosphorus-silicon synergistic flame-retardant mechanism, enables the obtained polyurethane composition to possess excellent heat resistance, high flame retardancy, good mechanical properties, and durability, making it particularly suitable for synthetic leather products with strict heat resistance requirements, such as automotive interiors and high-end furniture.

Description

Technical Field

[0001] This invention relates to the field of polyurethane technology, and in particular to a heat-resistant polyurethane composition for synthetic leather and its preparation method. Background Technology

[0002] Synthetic leather, widely used in footwear, furniture, and automotive interiors, faces increasingly stringent performance requirements, particularly in maintaining good mechanical stability, flame retardancy, and durability under high-temperature environments. Polyurethane materials, due to their excellent flexibility, abrasion resistance, and processability, have become one of the mainstream choices for synthetic leather production. However, traditional polyurethane compositions are prone to chain relaxation, thermal deformation, and oxidative degradation under high-temperature conditions, leading to decreased tensile strength and poor dimensional stability. Furthermore, their inherent flammability limits their application in scenarios with high safety requirements. In addition, ordinary polyurethane is susceptible to hydrolysis in high-heat or humid environments, causing molecular chain breakage and affecting its service life.

[0003] To improve the heat resistance of polyurethane, existing technologies typically employ methods such as adding inorganic fillers, using heat-resistant chain extenders, or introducing flame-retardant elements. For example, adding fillers such as nano-kaolin can improve the mechanical properties and thermal stability of the material to some extent. However, the interfacial bonding between unmodified kaolin and the polyurethane matrix is ​​weak, making it prone to debonding at high temperatures, leading to performance degradation. On the other hand, while conventional chain extenders (such as 1,4-butanediol) can lengthen molecular chains, their molecular structure lacks rigid groups, making it difficult to effectively increase the glass transition temperature of the hard segments and meet the requirements for long-term high-temperature use. Furthermore, single types of antioxidants or flame retardants often cannot comprehensively inhibit the oxidative aging and combustion behavior of polyurethane at high temperatures, leaving the material with shortcomings in both overall heat resistance and flame retardancy.

[0004] Although existing research has attempted to improve the heat resistance of polyurethane through composite modification or functionalization, most methods still suffer from insufficient synergistic effects, weak interfacial bonding, or complex preparation processes. For example, some modification methods focus only on physical blending, failing to achieve chemical bonding between the filler and the matrix, making them prone to interfacial failure under long-term thermal stress. Therefore, developing a polyurethane composition with high heat resistance, excellent flame retardancy, and good interfacial stability has become an urgent technical problem to be solved in the field of synthetic leather. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and to propose a heat-resistant polyurethane composition for synthetic leather and its preparation method.

[0006] To achieve the above objectives, the present invention provides a heat-resistant polyurethane composition for synthetic leather, comprising the following raw materials in parts by weight: polysorbate adipate diol: 15-25 parts; polycarbonate diol: 30-40 parts; isocyanate: 20-30 parts; heat-resistant chain extender: 5-10 parts; functionalized nano-kaolin: 3-7 parts; catalyst: 0.02-0.06 parts; antioxidant: 0.2-0.6 parts.

[0007] Preferably, the polysorbate adipate diol (Mn=1000, hydroxyl value 130 mgKOH / g) was purchased from Weiyi Trading Co., Ltd., Tongliao City, Inner Mongolia; and the polycarbonate diol (Mn=1000, hydroxyl value 140 mgKOH / g) was purchased from Qingdao Xinyutian Chemical Co., Ltd.

[0008] Preferably, the isocyanate refers to a mixture of dicyclohexylmethane diisocyanate and hexamethylene diisocyanate in a weight ratio of 4:1.

[0009] Preferably, the structure of the heat-resistant chain extender is as follows:

[0010] .

[0011] Preferably, the functionalized nano-kaolin is prepared by treating nano-kaolin with a phosphorus-silicon composite modifier; the structure of the phosphorus-silicon composite modifier is as follows:

[0012] .

[0013] Preferably, the catalyst is dibutyltin dilaurate.

[0014] Preferably, the antioxidant refers to a mixture of antioxidant 1010 and antioxidant 168 in a weight ratio of 1:1.

[0015] Preferably, the heat-resistant chain extender is prepared by the following method:

[0016] S101. Under nitrogen protection, 4-acetoxyphenol, (2,5-dichlorophenyl)phosphoric acid, and potassium carbonate were added to N,N-dimethylformamide, heated to 90-110℃, and reacted for 6-8 hours. After cooling to room temperature, deionized water was added, and a solid precipitated. The solid was collected by filtration, washed, dried, and recrystallized from an ethanol / water mixture to obtain (2,5-bis(4-acetoxyphenoxy)phenyl)phosphoric acid. The chemical reaction equation is as follows:

[0017] The product was characterized by 1H NMR. In this step, potassium carbonate acts as an acid-binding agent, first reacting with the phenolic hydroxyl group of 4-acetoxyphenol to deprotonate it and form a more nucleophilic phenoxy anion. This anion attacks the electron-deficient chlorinated carbon in the (2,5-dichlorophenyl) phosphate molecule with its lone pair electrons, undergoing a nucleophilic substitution reaction to construct a phosphate skeleton containing diacetoxyphenoxy groups.

[0018] S102. In a reaction vessel equipped with a reflux condenser, (2,5-bis(4-acetoxyphenoxy)phenyl)phosphoric acid was added to ethanol, followed by a 4 mol / L sodium hydroxide solution. The mixture was heated to 80-90°C and reacted for 2-4 hours. After cooling to room temperature, the ethanol was removed by rotary evaporation. The pH was then adjusted to 2-3 with 3 mol / L dilute hydrochloric acid, resulting in the precipitation of a large amount of solid. The solid was collected by filtration, washed, dried, and recrystallized in an ethanol / water mixture to obtain a heat-resistant chain extender. The chemical reaction equation is as follows:

[0019] The product was characterized by H NMR. In this step, the acetoxy group undergoes ester hydrolysis under alkaline conditions of sodium hydroxide, and the ester bond breaks to generate phenoxy anions and sodium acetate. The temperature of 80-90℃ can destroy the stability of the ester bond and increase the hydrolysis rate. Subsequently, acidification with dilute hydrochloric acid is used to protonate the phenoxy anions to obtain a heat-resistant chain extender containing free phenolic hydroxyl groups. The presence of phenolic hydroxyl groups provides active sites for the subsequent reaction with the -NCO of the polyurethane prepolymer.

[0020] Preferably, the molar ratio of 4-acetoxyphenol, (2,5-dichlorophenyl)phosphoric acid, and potassium carbonate in S101 is 1:1-1.3:1.5-3.

[0021] Preferably, in S101, the weight ratio of 4-acetoxyphenol, N,N-dimethylformamide and deionized water is 1:8-12:20-30.

[0022] Preferably, the volume ratio of ethanol to water in the ethanol / water mixed solution in S101 is 1:1.

[0023] Preferably, in S102, the weight ratio of (2,5-bis(4-acetoxyphenoxy)phenyl)phosphoric acid, ethanol, and sodium hydroxide solution with a concentration of 8 mol / L is 1:8-12:0.7-0.9.

[0024] Preferably, the volume ratio of ethanol to water in the ethanol / water mixed solution in S102 is 3:1.

[0025] Preferably, the preparation method of the functionalized nano-kaolin is as follows:

[0026] S201. Add 2-(triethoxysilyl)-N-[2-(triethoxysilyl)ethyl]ethylamine to ethanol, heat to 25-40℃, add epichlorohydrin dropwise over 20-40 min, react for 4-8 h, then heat to 40-60℃, add triethylamine, react for 1-3 h, cool to room temperature, filter, collect the filtrate, remove the solvent by rotary evaporation, and then perform silica gel column chromatography with gradient elution to obtain intermediate A; the chemical reaction equation is as follows:

[0027] The product was characterized by 1H NMR. In this step, the secondary amino nitrogen atom of 2-(triethoxysilyl)-N-[2-(triethoxysilyl)ethyl]ethylamine contains a lone pair of electrons, which acts as a nucleophile to attack the epoxy ring of epichlorohydrin (a three-membered ring with high strain and electron-deficient carbon atoms), resulting in a nucleophilic ring-opening reaction and generating an intermediate containing a hydroxyl group and a chloroethyl group. The subsequent addition of triethylamine (a weak base) promotes the hydrolysis of the ethoxy group in the silane molecule, generating a more reactive silanol group. Finally, intermediate A is separated and purified by gradient elution using silica gel column chromatography, taking advantage of the polarity difference of the different components.

[0028] S202. In a reaction vessel equipped with a reflux condenser, intermediate A is added to 1,4-dioxane, the temperature is raised to 80-110℃, then DOPO is added, the reaction is carried out for 6-12 hours, and after cooling to room temperature, the reaction solution is poured into diethyl ether to precipitate, the solid is collected, washed, and dried to obtain the phosphorus-silicon composite modifier; the chemical reaction equation is as follows:

[0029] The product was characterized by H NMR. In this step, the epoxy group of intermediate A undergoes an addition reaction with the PH bond of DOPO. Heating at 80-110℃ causes the PH bond of DOPO to cleave homogeneously, and the phosphorus atom forms a nucleophilic center, which attacks the electron-deficient carbon of the epoxy ring, resulting in a cycloaddition reaction to generate a POC covalent bond, introducing the phosphoranthroline ring into the molecule. After the reaction solution is poured into diethyl ether, the product contains silanol and phosphoryl groups (which are highly polar) and has extremely low solubility in diethyl ether (a nonpolar solvent), thus achieving precipitation separation and obtaining a high-purity phosphorus-silicon composite modifier.

[0030] S203. Add nano-kaolin to ethanol, ultrasonically disperse for 30-60 min, add phosphorus-silicon composite modifier, heat to 60-80℃ and stir for 3-4 h; collect the solid after filtration, wash, dry, and grind through a 300-mesh sieve to obtain functionalized nano-kaolin; the chemical reaction diagram is as follows:

[0031] In this step, a large number of Al-OH and Si-OH groups are exposed on the surface of the nano-kaolin. Under heating conditions of 60-80℃, the silanol groups in the phosphorus-silicon composite modifier molecule undergo a dehydration condensation reaction with the hydroxyl groups on the surface of kaolin. The hydroxyl groups are chemically anchored to the surface of kaolin through the process of "O-bond breaking → H2O removal → Si-O-Al / Si-O-Si covalent bond formation", rather than physical adsorption. This ultimately achieves the integrated structure of "kaolin-modifier", laying the foundation for subsequent bonding with the polyurethane matrix.

[0032] Preferably, in S201, the molar ratio of 2-(triethoxysilyl)-N-[2-(triethoxysilyl)ethyl]ethylamine, epichlorohydrin, and triethylamine is 1:1.1-1.4:1.5-2.5.

[0033] Preferably, in S201, 2-(triethoxysilyl)-N-[2-(triethoxysilyl)ethyl]ethylamine and ethanol are in a weight ratio of 1:8-12.

[0034] Preferably, in S201, gradient elution refers to the volume ratio of dichloromethane to methanol in the eluent of each step being 15:1, 10:1 to 8:1, respectively.

[0035] Preferably, in S202, the molar ratio of intermediate A to DOPO is 1:1.1-1.3.

[0036] Preferably, in S202, intermediate A, 1,4-dioxane and diethyl ether are in a weight ratio of 1:8-12:15-25.

[0037] Preferably, the nano-kaolin, ethanol and phosphorus silicon composite modifier in S203 are in a weight ratio of 1:8-12:0.2-0.3.

[0038] Furthermore, the present invention also provides a method for preparing a heat-resistant polyurethane composition for synthetic leather, comprising the following steps:

[0039] Step 1: In a dry reaction vessel, add polysorbate castor oil diol and polycarbonate diol, dehydrate at 100-120℃ and -0.095MPa vacuum for 1-2 hours, then cool to 70-80℃, add isocyanate and catalyst, and react for 2-3 hours to obtain a prepolymer with terminal isocyanate groups.

[0040] Step 2: Cool to 50-60℃, add N,N-dimethylformamide to the isocyanate-terminated prepolymer, stir for 10-20 min, then add heat-resistant chain extender and functionalized nano-kaolin, stir at 300-500 rpm for 2-3 h, then add antioxidant, continue stirring for 30-60 min, then place at 75-85℃ and -0.09 MPa for degassing for 20-25 min to obtain a heat-resistant polyurethane composition for synthetic leather; in this step, N,N-dimethylformamide (DMF) is added. This method utilizes the strong solubility of the material to reduce the viscosity of the prepolymer, providing an environment for the uniform dispersion of the heat-resistant chain extender and functionalized nano-kaolin. The phenolic hydroxyl groups of the heat-resistant chain extender react with the -NCO of the prepolymer to form a carbamate, extending the polyurethane molecular chain through the chain extension process of "-NCO+-OH→-NH-CO-O-", thereby improving the molecular weight and mechanical properties of the system. At the same time, the silanol hydroxyl groups remaining on the surface of the functionalized nano-kaolin further react with -NCO to form a covalent network of "polyurethane-kaolin", preventing the kaolin from debonding from the matrix at high temperatures.

[0041] Preferably, in step two, the prepolymer with terminal isocyanate groups and N,N-dimethylformamide are in a weight ratio of 1:2.5-3.2.

[0042] Preferably, the mechanism of action of the high-temperature resistant polyurethane composition for synthetic leather in this invention is as follows:

[0043] The heat-resistant chain extender in this invention is a crucial component for the system's high-temperature resistance. Structurally, the heat-resistant chain extender molecule contains a rigid polyphenyl ring structure and a phosphoryl group. The phenolic hydroxyl groups at both ends react with the -NCO of the terminal isocyanate group prepolymer, covalently bonding them through urethane bonds to embed the polyphenyl ring skeleton and phosphoryl group into the polyurethane hard segment structure. The rigidity of the polyphenyl ring significantly increases the glass transition temperature of the hard segment, inhibiting the thermal motion of the hard segment molecular chains at high temperatures and reducing performance degradation caused by chain segment relaxation. The phosphoryl group functions through a dual mechanism of "condensed phase catalytic char formation + gas phase flame retardancy." At high temperatures, the phosphoryl group catalyzes the cross-linking of polyurethane molecular chains into char, forming a dense carbonized layer that blocks heat transfer to the matrix. Simultaneously, it releases phosphorus-containing free radicals, capturing active free radicals participating in combustion in the gas phase and inhibiting the continued combustion reaction, thereby simultaneously improving the heat resistance and flame retardancy of the composition.

[0044] Functionalized nano-kaolin enhances the high-temperature stability and mechanical properties of the system through a dual effect of "covalent anchoring + physical barrier". During preparation, the silanol groups of the phosphorus-silicon composite modifier undergo dehydration condensation with the Al-OH and Si-OH on the surface of the nano-kaolin to form Si-O-Al / Si-O-Si covalent bonds, chemically anchoring the modifier to the kaolin surface. During the preparation of the polyurethane composition, the silanol groups remaining on the kaolin surface further react with the -NCO of the prepolymer to construct a covalent network of "polyurethane-kaolin". This covalent connection completely solves the problem of weak interfacial bonding between traditional unmodified kaolin and the polyurethane matrix, avoiding interfacial defects caused by kaolin debonding from the matrix at high temperatures. At the same time, the layered silicate structure of kaolin is uniformly dispersed in the matrix. At high temperatures, it can delay heat transfer and small molecule volatilization through physical barrier. Furthermore, the high-temperature resistance of the layered structure itself further supports the matrix structure, reducing thermal deformation at high temperatures and synergistically improving the heat resistance and mechanical retention of the composition.

[0045] The composite soft segment composed of polysorbate adipate diol and polycarbonate diol is key to balancing the heat resistance of the system with the flexibility required for synthetic leather. Both diols are low molecular weight diols with Mn=1000, and the soft segment chain formed by the reaction of their hydroxyl groups with isocyanates has a moderate length, which can avoid excessive creep at high temperatures due to excessively long chain segments. Among them, the carbonate bonds of polycarbonate diol have excellent hydrolysis resistance and thermal stability, which can reduce bond breakage under high temperature and humid heat environments. The castor oil fatty acid chains of polysorbate adipate diol give the soft segment a certain degree of flexibility, ensuring that the synthetic leather has bendability. After the two are combined, the soft segment will not cause the synthetic leather to become brittle due to excessive rigidity, nor will it reduce the dimensional stability at high temperatures due to excessive flexibility, thus establishing a balance between heat resistance and performance of the composition.

[0046] The phosphoryl group of the heat-resistant chain extender and the phosphorus and silicon elements of the phosphorus-silicon composite modifier in the composition form a "phosphorus-silicon synergistic" effect, further enhancing the high-temperature resistance and flame retardant properties. At high temperatures, during the process of phosphorus catalyzing char formation, silicon elements participate in the formation of a silicon-containing carbonized layer. Silicon atoms can combine with carbon atoms in the carbon layer to form Si-C bonds, improving the density and oxidation resistance of the carbon layer, preventing the carbon layer from being oxidized and decomposed at high temperatures, and extending the heat insulation and flame retardant effect of the carbon layer. At the same time, the high-temperature resistance of silicon elements can enhance the thermal stability of the matrix and reduce the thermal degradation rate of molecular chains at high temperatures. This synergistic effect of "phosphorus catalyzing char formation + silicon stabilizing the carbon layer" significantly increases the initial thermal decomposition temperature of the composition and maintains a high mechanical property retention rate under long-term high-temperature environments, meeting the requirements of synthetic leather for long-term heat resistance.

[0047] The combination of antioxidant 1010 and antioxidant 168 inhibits the thermal oxidative aging of polyurethane through a synergistic effect of "chain termination + hydroperoxide decomposition". At high temperatures, polyurethane molecular chains are prone to oxidation, generating hydroperoxides (ROOH), which then decompose to produce free radicals, triggering a chain oxidation reaction that leads to molecular chain breakage and performance degradation. Antioxidant 1010 (hindered phenol) acts as a chain terminator, providing hydrogen atoms to reactive free radicals (such as RO•, HO•), converting them into stable molecules and terminating the chain reaction. Antioxidant 168 (phosphite) decomposes hydroperoxides, converting them into inactive alcohols and ketones, reducing free radical generation at the source. The combination of these two antioxidants forms a complete antioxidant system at high temperatures, delaying the thermal oxidative degradation of polyurethane and ensuring that the composition maintains stable mechanical and heat resistance properties during long-term high-temperature use.

[0048] The beneficial effects of this invention are:

[0049] 1. This invention achieves molecular-level heat resistance enhancement through a heat-resistant chain extender with a specific structure. The three benzene ring conjugated structure contained therein can be embedded in the hard segment of polyurethane, and the π-π stacking effect enhances the intermolecular forces, significantly increasing the glass transition temperature of the hard segment and inhibiting chain segment relaxation at high temperatures. At the same time, the phosphoryl group of the chain extender forms a synergistic effect with the phosphorosilicate group of functionalized nano-kaolin. At high temperatures, the phosphoryl group catalyzes cross-linking to form carbon, and the silicon element constructs a silicon-containing carbonized layer. The dual effect blocks heat transfer and captures combustion free radicals, effectively solving the problems of rapid high-temperature strength decay and insufficient flame retardancy of traditional polyurethane, and meeting the long-term heat resistance requirements of automotive interiors, high-end furniture and other scenarios.

[0050] 2. In this invention, functionalized nano-kaolin is treated with a bissilane-phosphorus-silicon composite modifier. The surface hydroxyl groups form Si-O-Al / Si-O-Si covalent bonds with the silanol groups of the modifier, constructing a three-dimensional network of "kaolin-modifier-polyurethane." This completely overcomes the defects of traditional unmodified or monosilane-modified kaolin, such as weak interfacial bonding and easy debonding with the matrix. This covalent anchoring not only improves the efficiency of interfacial stress transfer and enhances tensile strength and abrasion resistance, but also reduces the volatilization of small molecules and thermal deformation at high temperatures through the physical barrier effect of the kaolin's layered structure, ensuring that the synthetic leather maintains structural integrity and mechanical stability during long-term use.

[0051] 3. The composite diol design of the soft segment in this invention achieves a balance between heat resistance and flexibility. The polycarbonate diol has high carbonate bond energy and excellent hydrolysis resistance, which can reduce bond breakage under high temperature and humid conditions. The ester bond of the polysorbate adipate diol imparts moderate flexibility to the soft segment, avoiding material embrittlement or heat deformation caused by a single soft segment. The soft segment chain length formed by the combination of the two is moderate, neither affecting the bending feel of synthetic leather due to excessive rigidity nor reducing high-temperature dimensional stability due to excessive flexibility, thus meeting the dual requirements of durability and comfort for synthetic leather.

[0052] 4. In this invention, the compound system of antioxidants 1010 and 168 forms a complete antioxidant chain: 1010 acts as a chain terminator to capture active free radicals, while 168 decomposes hydroperoxides to block the source of oxidation, effectively delaying the thermal oxidative degradation of polyurethane at high temperatures; simultaneously, the hydrophobic modification of functionalized kaolin and the hydrolysis-resistant bond type of the composite soft segments reduce water molecule penetration and hydrolysis reactions. This multi-layered protection allows the material to maintain a low degree of yellowing and a high mechanical retention rate even under long-term high-temperature and humid environments, significantly extending the service life of synthetic leather and reducing subsequent maintenance costs. Attached Figure Description

[0053] Figure 1 The 1H NMR spectrum of (2,5-bis(4-acetoxyphenoxy)phenyl)phosphoric acid prepared in Example 3 of this invention;

[0054] Figure 2 The H NMR spectrum of the heat-resistant chain extender prepared in Example 3 of this invention;

[0055] Figure 3 The H NMR spectrum of intermediate A prepared in Example 6 of this invention;

[0056] Figure 4 The 1H NMR spectrum of the phosphorus-silicon composite modifier prepared in Example 6 of this invention. Detailed Implementation

[0057] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0058] Preparation Example 1: The specific preparation method of the heat-resistant chain extender includes the following steps:

[0059] S1. Under nitrogen protection, 100g of 4-acetoxyphenol, 149.18g of (2,5-dichlorophenyl)phosphoric acid and 136.26g of potassium carbonate were added to 800g of N,N-dimethylformamide, heated to 90℃, reacted for 6h, cooled to room temperature, and then added to 2kg of deionized water. A solid precipitated out. The solid was collected by filtration, washed, dried, and recrystallized from an ethanol / water mixture (ethanol and water volume ratio of 1:1) to obtain (2,5-bis(4-acetoxyphenoxy)phenyl)phosphoric acid.

[0060] S2. In a reaction vessel equipped with a reflux condenser, 200g of (2,5-bis(4-acetoxyphenoxy)phenyl)phosphoric acid was added to 1.6kg of ethanol, along with 140g of a 4mol / L sodium hydroxide solution. The mixture was heated to 80℃ and reacted for 2 hours. After cooling to room temperature, the ethanol was removed by rotary evaporation. The pH was then adjusted to 2-3 with 3mol / L dilute hydrochloric acid, resulting in the precipitation of a large amount of solid. The solid was collected by filtration, washed, dried, and recrystallized in an ethanol / water mixture (ethanol to water volume ratio of 3:1) to obtain a heat-resistant chain extender.

[0061] Preparation Example 2: The specific preparation method of the heat-resistant chain extender includes the following steps:

[0062] S1. Under nitrogen protection, 100g of 4-acetoxyphenol, 171.56g of (2,5-dichlorophenyl)phosphoric acid and 199.84g of potassium carbonate were added to 1kg of N,N-dimethylformamide, heated to 100℃, reacted for 7h, cooled to room temperature, and then added to 2.5kg of deionized water. A solid precipitated out. The solid was collected by filtration, washed, dried, and recrystallized from an ethanol / water mixture (ethanol and water volume ratio of 1:1) to obtain (2,5-bis(4-acetoxyphenoxy)phenyl)phosphoric acid.

[0063] S2. In a reaction vessel equipped with a reflux condenser, 200g of (2,5-bis(4-acetoxyphenoxy)phenyl)phosphoric acid was added to 2kg of ethanol, along with 160g of a 4mol / L sodium hydroxide solution. The mixture was heated to 85℃ and reacted for 3 hours. After cooling to room temperature, the ethanol was removed by rotary evaporation. The pH was then adjusted to 2-3 with 3mol / L dilute hydrochloric acid, resulting in the precipitation of a large amount of solid. The solid was collected by filtration, washed, dried, and recrystallized in an ethanol / water mixture (ethanol to water volume ratio of 3:1) to obtain a heat-resistant chain extender.

[0064] Preparation Example 3: The specific preparation method of the heat-resistant chain extender includes the following steps:

[0065] S1. Under nitrogen protection, 100g of 4-acetoxyphenol, 193.94g of (2,5-dichlorophenyl)phosphoric acid and 272.51g of potassium carbonate were added to 1.2kg of N,N-dimethylformamide, heated to 110℃, reacted for 8h, cooled to room temperature, and then added to 3kg of deionized water. A solid precipitated out. The solid was collected by filtration, washed, dried, and recrystallized from an ethanol / water mixture (ethanol and water volume ratio of 1:1) to obtain (2,5-bis(4-acetoxyphenoxy)phenyl)phosphoric acid.

[0066] S2. In a reaction vessel equipped with a reflux condenser, 200g of (2,5-bis(4-acetoxyphenoxy)phenyl)phosphoric acid was added to 2.4kg of ethanol, along with 180g of a 4mol / L sodium hydroxide solution. The mixture was heated to 90℃ and reacted for 4 hours. After cooling to room temperature, the ethanol was removed by rotary evaporation. The pH was then adjusted to 2-3 with 3mol / L dilute hydrochloric acid, resulting in the precipitation of a large amount of solid. The solid was collected by filtration, washed, dried, and recrystallized in an ethanol / water mixture (ethanol to water volume ratio of 3:1) to obtain a heat-resistant chain extender.

[0067] Preparation Example 4: The specific preparation method of functionalized nano-kaolin includes the following steps:

[0068] S1. Add 10g of 2-(triethoxysilyl)-N-[2-(triethoxysilyl)ethyl]ethylamine to 80g of ethanol, heat to 25℃, add 2.56g of epichlorohydrin dropwise over 20min, react for 4h, then heat to 440℃, add 3.82g of triethylamine, react for 1h, cool to room temperature, filter, collect the filtrate, remove the solvent by rotary evaporation, and then perform silica gel column chromatography with gradient elution. The volume ratio of dichloromethane to methanol in the eluent changes from 15:1, 10:1 to 8:1 in each step to obtain intermediate A.

[0069] S2. In a reaction vessel equipped with a reflux condenser, 10g of intermediate A was added to 80g of 1,4-dioxane, the temperature was raised to 80℃, and then 8.33g of DOPO was added. The reaction was carried out for 6 hours. After cooling to room temperature, the reaction solution was poured into 150g of diethyl ether to precipitate. The solid was collected, washed, and dried to obtain the phosphorus-silicon composite modifier.

[0070] S3. Add 10g of nano-kaolin to 80g of ethanol, ultrasonically disperse for 30min, add 2g of phosphorus-silicon composite modifier, heat to 60℃ and stir for 3h; after filtration, collect the solid, wash, dry and grind through a 300-mesh sieve to obtain functionalized nano-kaolin.

[0071] Preparation Example 5: The specific preparation method of functionalized nano-kaolin includes the following steps:

[0072] S1. Add 10g of 2-(triethoxysilyl)-N-[2-(triethoxysilyl)ethyl]ethylamine to 100g of ethanol, heat to 30℃, add 2.91g of epichlorohydrin dropwise over 30min, react for 6h, then heat to 50℃, add 5.09g of triethylamine, react for 2h, cool to room temperature, filter, collect the filtrate, remove the solvent by rotary evaporation, and then perform silica gel column chromatography with gradient elution. The volume ratio of dichloromethane to methanol in the eluent changes from 15:1, 10:1 to 8:1 in each step to obtain intermediate A.

[0073] S2. In a reaction vessel equipped with a reflux condenser, 10g of intermediate A was added to 100g of 1,4-dioxane, the temperature was raised to 95℃, and then 9.09g of DOPO was added. The reaction was carried out for 8 hours. After cooling to room temperature, the reaction solution was poured into 200g of diethyl ether to precipitate. The solid was collected, washed, and dried to obtain the phosphorus-silicon composite modifier.

[0074] S3. Add 10g of nano-kaolin to 100g of ethanol, ultrasonically disperse for 45min, add 2.5g of phosphorus-silicon composite modifier, heat to 70℃ and stir for 3.5h; after filtration, collect the solid, wash, dry and grind through a 300-mesh sieve to obtain functionalized nano-kaolin.

[0075] Preparation Example 6: The specific preparation method of functionalized nano-kaolin includes the following steps:

[0076] S1. 10g of 2-(triethoxysilyl)-N-[2-(triethoxysilyl)ethyl]ethylamine was added to 120g of ethanol, heated to 40℃, and 3.26g of epichlorohydrin was added dropwise over 40min. The reaction was allowed to proceed for 8h, then the temperature was raised to 60℃, and 6.36g of triethylamine was added. The reaction was allowed to proceed for 3h, cooled to room temperature, filtered, and the filtrate was collected. The solvent was removed by rotary evaporation, and then silica gel column chromatography was performed. After gradient elution, the volume ratio of dichloromethane to methanol in the eluents changed from 15:1, 10:1 to 8:1, respectively, to obtain intermediate A.

[0077] S2. In a reaction vessel equipped with a reflux condenser, 10g of intermediate A was added to 120g of 1,4-dioxane, the temperature was raised to 110℃, and then 9.85g of DOPO was added. The reaction was carried out for 12h. After cooling to room temperature, the reaction solution was poured into 250g of diethyl ether to precipitate. The solid was collected, washed, and dried to obtain the phosphorus-silicon composite modifier.

[0078] S3. Add 10g of nano-kaolin to 120g of ethanol, ultrasonically disperse for 60min, add 3g of phosphorus-silicon composite modifier, heat to 80℃ and stir for 4h; after filtration, collect the solid, wash, dry and grind through a 300-mesh sieve to obtain functionalized nano-kaolin.

[0079] Comparative Preparation Example 1: The difference between Comparative Preparation Example 1 and Preparation Example 3 is that (2,5-dichlorophenyl)phosphoric acid is replaced with bis(2-chloroethyl)hydrophosphate, with the following chemical structural formula:

[0080] .

[0081] Comparative Preparation Example 2: The difference between Comparative Preparation Example 2 and Preparation Example 6 is that step S1 is omitted, intermediate A in step S2 is replaced with γ-glycidoxypropyltrimethoxysilane, and in step S3, ethanol is replaced with a mixed solution of ethanol and water in a volume ratio of 5:1, and ammonia is added to adjust the pH to 8-9.

[0082] Example 1: A specific preparation method of a heat-resistant polyurethane composition for synthetic leather, comprising the following steps:

[0083] Step 1: In a dry reaction vessel, add 150g of polyricinoleic adipate diol and 300g of polycarbonate diol, dehydrate at 100℃ and -0.095MPa vacuum for 1h, then cool to 70℃, add 200g of isocyanate (a mixture of dicyclohexylmethane diisocyanate and hexamethylene diisocyanate in a weight ratio of 4:1) and 0.2g of dibutyltin dilaurate, react for 2h to obtain a prepolymer with terminal isocyanate groups;

[0084] Step 2: Cool to 50°C, add 1.25 kg of N,N-dimethylformamide to 500 g of isocyanate-terminated prepolymer, stir for 10 min, then add 50 g of the heat-resistant chain extender prepared according to Preparation Example 1 and 30 g of the functionalized nano-kaolin prepared according to Preparation Example 4, stir at 300 rpm for 2 h, then add 2 g of antioxidant (a mixture of antioxidant 1010 and antioxidant 168 in a weight ratio of 1:1), continue stirring for 30 min, then place at 75°C and -0.09 MPa for degassing for 20 min to obtain a heat-resistant polyurethane composition for synthetic leather.

[0085] Example 2: A specific preparation method of a heat-resistant polyurethane composition for synthetic leather, comprising the following steps:

[0086] Step 1: In a dry reaction vessel, add 200g of polyricinoleic adipate diol and 350g of polycarbonate diol, dehydrate at 110℃ and -0.095MPa vacuum for 1.5h, then cool to 75℃, add 250g of isocyanate (a mixture of dicyclohexylmethane diisocyanate and hexamethylene diisocyanate in a weight ratio of 4:1) and 0.4g of dibutyltin dilaurate, react for 2.5h to obtain a prepolymer with terminal isocyanate groups;

[0087] Step 2: Cool to 55°C, add 1.425 kg of N,N-dimethylformamide to 500 g of isocyanate-terminated prepolymer, stir for 15 min, then add 70 g of the heat-resistant chain extender prepared according to Preparation Example 2 and 50 g of the functionalized nano-kaolin prepared according to Preparation Example 5, stir at 400 rpm for 2.5 h, then add 4 g of antioxidant (a mixture of antioxidant 1010 and antioxidant 168 in a weight ratio of 1:1), continue stirring for 45 min, and then place under conditions of 80°C and -0.09 MPa for degassing for 22 min to obtain a heat-resistant polyurethane composition for synthetic leather.

[0088] Example 3: A specific preparation method of a heat-resistant polyurethane composition for synthetic leather, comprising the following steps:

[0089] Step 1: In a dry reaction vessel, add 250g of polysorbate castor oil diol and 400g of polycarbonate diol, dehydrate at 120℃ and -0.095MPa vacuum for 2h, then cool to 80℃, add 300g of isocyanate (a mixture of dicyclohexylmethane diisocyanate and hexamethylene diisocyanate in a weight ratio of 4:1) and 0.6g of dibutyltin dilaurate, react for 3h to obtain a prepolymer with terminal isocyanate groups;

[0090] Step 2: Cool to 60°C, add 1.6 kg of N,N-dimethylformamide to 500 g of isocyanate-terminated prepolymer, stir for 20 min, then add 100 g of the heat-resistant chain extender prepared according to Preparation Example 3 and 70 g of the functionalized nano-kaolin prepared according to Preparation Example 6, stir at 500 rpm for 3 h, then add 6 g of antioxidant (a mixture of antioxidant 1010 and antioxidant 168 in a weight ratio of 1:1), continue stirring for 60 min, then place at 85°C and -0.09 MPa for degassing for 25 min to obtain a heat-resistant polyurethane composition for synthetic leather.

[0091] Comparative Example 1: The difference between Comparative Example 1 and Example 3 is that the heat-resistant chain extender prepared according to Preparation Example 3 is replaced with the heat-resistant chain extender prepared according to Comparative Preparation Example 1.

[0092] Comparative Example 2: The difference between Comparative Example 2 and Example 3 is that the heat-resistant chain extender prepared according to Preparation Example 3 is replaced with 1,4-butanediol.

[0093] Comparative Example 3: The difference between Comparative Example 3 and Example 3 is that the functionalized nano-kaolin prepared according to Preparation Example 6 is replaced with the functionalized nano-kaolin prepared according to Comparative Preparation Example 2.

[0094] Comparative Example 4: The difference between Comparative Example 4 and Example 3 is that the functionalized nano-kaolin prepared according to Preparation Example 6 is replaced with nano-kaolin.

[0095] Comparative Example 5: The difference between Comparative Example 5 and Example 3 is that 200g of polysorbate ricinoleate diol and 350g of polycarbonate diol were replaced with 650g of polysorbate ricinoleate diol.

[0096] Comparative Example 6: The difference between Comparative Example 6 and Example 2 is that 200g of polysorbate adipate diol and 350g of polycarbonate diol were replaced with 650g of polycarbonate diol.

[0097] Performance testing:

[0098] Preparation of uniform synthetic leather test samples:

[0099] Coating: Using a doctor blade coating process, the polyurethane compositions obtained in Examples 1-3 and Comparative Examples 1-6 were uniformly coated onto a polyester nonwoven fabric base (weight 120 g / m²). 2 On the surface, the wet film thickness is controlled to be 0.5 mm;

[0100] Coagulation: Immerse the coated base fabric in a 40°C deionized water coagulation bath and let it stand for 30 minutes to allow the polyurethane to solidify into a film.

[0101] Washing and drying: The solidified synthetic leather is washed three times with 40℃ deionized water (15 minutes each time to remove residual DMF), and then placed in a 120℃ hot air oven to dry for 20 minutes to obtain the dried synthetic leather product.

[0102] Post-treatment: The dried synthetic leather is calendered at a low temperature of 50℃ (pressure 0.3MPa, speed 2m / min) to ensure a smooth surface, and then set aside.

[0103] 1. Mechanical property testing: Referring to GB / T 3923.1-2013 "Textiles - Tensile properties of fabrics - Part 1: Determination of breaking strength and elongation at break (strip method)", the synthetic leather samples prepared using the heat-resistant polyurethane compositions of Examples 1-3 and Comparative Examples 1-6 were tested: Three standard strips (200mm × 50mm, gauge length 100mm) were cut from each synthetic leather sample in the warp and three in the weft directions; a universal testing machine was used, the tensile rate was set to 100mm / min, the two ends of the strips were fixed to the clamps, and the instrument was started until the strips broke. The maximum load at break and the elongation at break were recorded; the tensile strength at break and the elongation at break were calculated, and the average value of the warp and weft directions was taken as the final result. The experimental results are shown in Table 1.

[0104] 2. High-Temperature Heat Resistance Stability Test: Based on GB / T 13475-2009 "Methods for Determination of Thermal Resistivity and Thermal Conductivity of Building Components and Building Materials" and the characteristics of synthetic leather, the high-temperature stability of synthetic leather samples prepared using the heat-resistant polyurethane compositions of Examples 1-3 and Comparative Examples 1-6 was tested.

[0105] Tensile strength retention rate at 150℃: First, determine the initial tensile strength (σ1) of the synthetic leather according to the "Mechanical Property Test" method; then cut strips of the same specification, place them in a 150℃ constant temperature oven for 2 hours (without load), remove them and cool them to room temperature, then determine the tensile strength (σ2), and calculate the retention rate = σ2 / σ1 × 100%;

[0106] Heat shrinkage rate at 150℃: Cut a 100mm×100mm square strip from synthetic leather and mark the diagonal length (L1); place the strip in a 150℃ constant temperature oven for 2 hours, take it out and cool it down, measure the diagonal length (L2), and calculate the heat shrinkage rate = (L1-L2) / L1×100%; the experimental results are shown in Table 1.

[0107] 3. Flame retardant performance test: Referring to GB / T 2406.2-2009 (LOI) and UL 94-2013 (vertical burning), the flame retardant ability of synthetic leather samples prepared using the heat-resistant polyurethane compositions of Examples 1-3 and Comparative Examples 1-6 was tested.

[0108] Limiting Oxygen Index (LOI): Cut an 80mm×10mm×0.25mm sample and fix it vertically inside the combustion chamber of the oxygen index meter. Adjust the flow rate of the oxygen / nitrogen mixture (total flow rate 10L / min) and gradually increase it from a low oxygen concentration. Record the lowest oxygen concentration when the sample burns for 30s or the burning length reaches 50mm. This is the LOI value.

[0109] UL94 Vertical Flammability Rating: Cut a 127mm×12.7mm×0.25mm sample and suspend it vertically in a combustion chamber. Burn the bottom of the sample twice with a 20mm high Bunsen burner flame (10s each time, 10s interval). Record the flame burning time, flameless burning time, and whether the dripping material ignites the absorbent cotton. Determine the rating according to the standard (V-0 / V-1 / V-2 / no rating). The experimental results are shown in Table 1.

[0110] 4. Hydrolysis Resistance Test: Referring to GB / T 2951.51-2008 and considering the application scenarios of synthetic leather, the hydrolysis resistance of synthetic leather samples prepared using the heat-resistant polyurethane compositions of Examples 1-3 and Comparative Examples 1-6 was tested: 50mm×50mm×0.25mm strips were cut, the initial mass (m1) was accurately weighed, and the initial tensile strength at break (σ3) was measured. The strips were immersed in deionized water at 60℃, and the water was changed once a week for 30 days. After 30 days, the strips were removed, the surface moisture was dried, the mass (m2) was weighed, and the tensile strength at break (σ4) was measured. The mass loss rate = (m1-m2) / m1×100% and the tensile strength retention rate = σ4 / σ3×100% were calculated. The experimental results are shown in Table 1.

[0111] 5. Thermal oxidative aging performance test: Referring to GB / T 3512-2014, the long-term thermal stability of synthetic leather samples prepared using the heat-resistant polyurethane compositions of Examples 1-3 and Comparative Examples 1-6 was tested: 50mm×50mm×0.25mm strips were cut, and the initial yellowing index (YI1, measured by spectrophotometer using CIE LAB color system) and initial tensile strength at break (σ5) were determined. The strips were placed in a constant temperature oven at 150℃ (air was introduced at a flow rate of 20mL / min) for 200h of thermal aging. After aging, the strips were cooled to room temperature, and the yellowing index (YI2) and tensile strength at break (σ6) were determined. The change in yellowing index (ΔYI=YI2-YI1) and the tensile strength retention rate = σ6 / σ5×100% were calculated. The experimental results are shown in Table 1.

[0112] 6. Surface abrasion resistance test: Referring to GB / T 21196.2-2007, the surface durability of synthetic leather samples prepared using the heat-resistant polyurethane compositions of Examples 1-3 and Comparative Examples 1-6 was tested: synthetic leather strips with a diameter of 38 mm were cut and fixed on the sample stage of the Martindale abrasion tester; standard abrasive (wool cloth) was selected, the pressure was set to 9 kPa, the instrument was started to conduct the abrasion test, and the number of abrasion resistances when the strip first broke or exposed the substrate was recorded. The experimental results are shown in Table 1.

[0113] Table 1 Performance Test Results

[0114] Performance Analysis:

[0115] As can be seen from the performance test data in Table 1, the heat-resistant polyurethane composition for synthetic leather prepared by the present invention in the examples shows good performance in terms of mechanical strength, high temperature stability, flame retardancy, and hydrolysis resistance, which is better than the comparative examples. Among them, Example 3 has the best overall performance.

[0116] Example 3 exhibits excellent tensile strength and elongation at break. This may be because the heat-resistant chain extender contains a three-benzene-ring conjugated structure. The benzene rings form a strong π-π stacking effect through the overlap of π electron clouds, which significantly enhances the intermolecular forces of the hard segment molecules, providing rigid support for tensile strength. The composite diol in the soft segment, polycarbonate diol, has high carbonate bond energy and large steric hindrance, giving the soft segment a certain rigidity, while polysorbate adipate diol has good ester bond flexibility. Through the entanglement and interaction of molecular chain segments, the two ensure the creep of the chain segments under stress and avoid strength loss due to excessive flexibility. From the interface perspective, the Si atoms on the surface of the phosphorus-silicon composite modified kaolinite undergo dehydration condensation with the hydroxyl groups on the kaolinite surface through Si-O-Al and Si-O-Si bonds to form stable covalent bonds. At the same time, the hydroxyl groups in the modifier molecules can also react with the -NCO groups of the polyurethane prepolymer to construct a three-dimensional covalent network of "kaolinite-modifier-polyurethane", eliminating the traditional physical adsorption interface. The stress concentration defects on the surface allow external forces to be uniformly transmitted to the rigid kaolin particles and polyurethane molecular chains, significantly improving the interfacial bonding strength. In contrast, the chain extenders in Comparative Example 1 contain only two benzene rings, and the π-π stacking effect is weaker than that of three benzene rings, resulting in insufficient intermolecular forces in the hard segments and reduced tensile strength. Comparative Example 2 uses common aliphatic chain extenders such as 1,4-butanediol, which lacks the benzene ring conjugated structure, and the hard segments lack rigid support, resulting in a significant decrease in tensile strength. The monosilane modification in Comparative Example 3 reduces the Si-O covalent bond anchoring points on the kaolin surface, resulting in insufficient interfacial bonding strength and exacerbated stress concentration. The unmodified kaolin surface in Comparative Example 4 relies solely on van der Waals forces for physical adsorption, without Si-O covalent bond anchoring, making the interface prone to debonding. The single soft segments in Comparative Examples 5 and 6 disrupt the bond type complementarity of "carbonate bond rigidity - ester bond flexibility," or cause insufficient strength due to excessive flexibility (polysorbate adipate), or cause a sharp drop in elongation due to excessive rigidity (polycarbonate), both resulting in mechanical properties far lower than those in Example 3.

[0117] Example 3 demonstrates excellent high-temperature thermal stability, likely because the multi-benzene ring conjugated system of the chain extender gives the hard segment a high glass transition temperature (Tg). Even at 150°C, the hard segment molecular chains are still unlikely to undergo chain relaxation and intermolecular slippage, providing a structural basis for strength retention. From the perspective of the carbonization layer barrier, the phosphoryl group of the chain extender and the siloxane chain of the bissilane modifier preferentially undergo thermal degradation at high temperatures. The phosphoryl group releases PO· free radicals to catalyze the crosslinking of polyurethane molecular chains into carbon, while the siloxane chains form a SiO2 ceramic layer. The two work together to construct a "phosphorus-carbon-silicon-oxygen" composite carbon layer. This carbon layer, through the high stability of the Si-O bond, blocks heat transfer to the interior of the matrix, reducing the thermal motion amplitude of the soft segment chains. From the perspective of interfacial stress resistance, the covalently bonded Si-O-Al / Si-O-Si bonds can resist the expansion stress caused by the trace water absorption of kaolin at 150°C, avoiding a sudden drop in strength due to interfacial cracking, while also inhibiting the overall deformation of the hard segment caused by thermal shrinkage.

[0118] In the comparative examples: the chain extender benzene ring of Comparative Example 1 was reduced, the thermal resistance of hard segment conjugation was reduced, and the chain segment relaxation was intensified at 150°C. The strength retention rate and thermal shrinkage rate were both lower than those of Example 3. Comparative Example 2 had no benzene ring conjugation and phosphorus silicon groups, the hard segment Tg was low, the chain segment moved violently, and the thermal stability was greatly reduced. The hydrophilic hydroxyl groups on the surface of unmodified kaolin in Comparative Example 4 absorbed water at room temperature. At 150°C, due to the expansion of internal water evaporation, the internal stress generated destroyed the physical adsorption interface, resulting in a sharp drop in strength and a surge in shrinkage rate. The performance was far worse than that of Example 3.

[0119] Example 3 demonstrates excellent flame retardant performance, benefiting from a triple microscopic flame retardant mechanism of "phosphorus free radical quenching - silicon-oxygen carbon layer barrier - kaolin physical barrier". From the perspective of free radical quenching, the phosphoryl group in the chain extender undergoes thermal decomposition during combustion, releasing PO· free radicals. These free radicals can efficiently capture active free radicals such as H· and HO· in the combustion reaction, interrupting the chain combustion reaction. From the perspective of carbon layer barrier, the polybenzene rings of the chain extender provide a rigid carbon skeleton, which, together with the siloxane chains released by the bissilane modifier, forms a "phosphorus-carbon-silicon-oxygen" composite carbon layer. This carbon layer has a dense structure and is resistant to high temperatures, effectively blocking the diffusion of oxygen into the matrix and the release of combustible gases to the outside. From the perspective of physical barrier, nano-kaolin... During combustion, the layered silicate structure of the soil undergoes lamellar peeling, forming a physical barrier layer similar to "mica sheets," further enhancing the flame-retardant effect. In the comparative examples: the chain extender benzene rings in Comparative Example 1 are reduced, the carbon skeleton density is decreased, the integrity of the phosphorus-carbon-silicon-oxygen composite carbon layer is insufficient, and the flame-retardant efficiency decreases; Comparative Example 2 has no phosphorus-silicon groups, so it lacks both free radical quenching and carbon layer barrier, resulting in extremely poor flame-retardant performance; the unmodified kaolin in Comparative Example 4 has a hydrophilic surface, which easily leads to loose carbon layers during combustion, destroying the flame-retardant barrier, and its performance is significantly inferior to Example 3.

[0120] Example 3 exhibits excellent hydrolysis resistance, possibly because the carbonate bond energy of the polycarbonate diol in the composite soft segment is higher than that of the ester bond, and the electron-withdrawing effect of adjacent oxygen atoms reduces the positive charge of the carbonyl carbon, making it difficult for water molecules to attack, resulting in hydrolysis resistance far superior to that of the ester bond. From the perspective of interfacial hydrophobicity, the bissilane modification completely covers the hydrophilic Al-OH and Si-OH on the surface of kaolin with hydrophobic siloxane chains, increasing the water contact angle. At the same time, the Si-O covalent bond firmly anchors the kaolin in the matrix, preventing water molecules from penetrating to the interface and forming gaps. From the perspective of matrix hydrophobicity, the hydrophobicity of the multiple benzene rings in the hard segment reduces the overall water absorption rate of the polyurethane matrix, reducing the sites where hydrolysis reactions occur.

[0121] In the comparative examples: Comparative Example 5 uses a single polysorbate castor oil ester soft segment, and the ester bond is easily attacked and hydrolyzed by water molecules. The dissolution of small molecule products leads to mass loss and strength reduction. In Comparative Example 4, the unmodified kaolin surface hydrophilic hydroxyl groups absorb a large amount of water, and water molecules penetrate to the interface to trigger matrix hydrolysis. Its performance is far inferior to that of Example 3.

[0122] Example 3 demonstrates outstanding resistance to thermal oxidation, which is the result of the microscopic interaction of "antioxidant molecule synergy - conjugated chain electron cloud stabilization - covalent interface oxygen penetration barrier". From the perspective of antioxidant synergy, the main antioxidant 1010 (hindered phenol) captures ROO· free radicals by providing hydrogen atoms, while the auxiliary antioxidant 168 (phosphite) decomposes hydroperoxides into harmless alcohols and ketones. The two work synergistically to terminate the thermal oxidation chain reaction. From the perspective of molecular chain stability, the multi-benzene ring conjugated structure of the chain extender makes the electron cloud density distribution of the molecular chain uniform, making it less likely to generate chromophores such as carbonyl and peroxy groups and degradation sites due to oxidation. From the perspective of interfacial oxygen barrier, the covalently bonded Si-O-Al / Si-O-Si bonds form a dense interface, preventing oxygen from penetrating into the polyurethane matrix and reducing the oxidation rate of the molecular chain. In the comparative examples: Comparative Example 2 lacks antioxidant synergy and conjugated stabilizing structure, and the molecular chain is easily oxidized and degraded, resulting in severe yellowing and low mechanical retention. Comparative Example 4, with unmodified kaolin, absorbs water, accelerating the oxidation reaction, leading to a sharp increase in the yellowing index and a sharp drop in tensile strength retention, with performance worse than Example 3.

[0123] Example 3 exhibits excellent wear resistance primarily because the bissilane-modified kaolin is firmly anchored to the polyurethane surface by Si-O-Al / Si-O-Si covalent bonds. The rigid particles of kaolin significantly enhance surface hardness and reduce plastic deformation during friction. Simultaneously, the high bond energy of the covalent bonds effectively resists the shear stress generated by friction, preventing kaolin from detaching from the matrix and forming wear debris, thereby extending the surface wear life. In the comparative examples: Comparative Example 4, with its unmodified kaolin, relies solely on van der Waals forces for physical adsorption, resulting in weak interfacial bonding and easy detachment during friction, leading to a sharp decrease in wear resistance. Comparative Example 5 uses a single poly(adipate-castor oil) soft segment, which has low surface hardness and is easily scratched by abrasives, resulting in wear resistance far lower than that of Example 3.

[0124] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A heat-resistant polyurethane composition for synthetic leather, characterized by comprising: The polyricinoleic glycol has the following components: polyricinoleic glycol 15-25 parts, polycarbonate diol 30-40 parts, isocyanate 20-30 parts, heat-resistant chain extender 5-10 parts, functionalized nano kaolin 3-7 parts, catalyst 0.02-0.06 parts, and antioxidant 0.2-0.6 parts. The polyricinoleic glycol has an Mn of 1000 and a hydroxyl value of 130 mgKOH / g; the polycarbonate diol has an Mn of 1000 and a hydroxyl value of 140 mgKOH / g. The isocyanate is a mixture of dicyclohexylmethane diisocyanate and hexamethylene diisocyanate at a weight ratio of 4:

1. The heat-resistant chain extender has the following structure: ； The functionalized nano kaolin is obtained by treating nano kaolin with a phosphorus-silicon composite modifier; the phosphorus-silicon composite modifier has the following structure: ； The catalyst is dibutyltin dilaurate. The antioxidant is a mixture of antioxidant 1010 and antioxidant 168 at a weight ratio of 1:

1.

2. The heat-resistant polyurethane composition for synthetic leather according to claim 1, characterized by, The heat-resistant chain extender is prepared by the following method: S101. Under nitrogen protection, 4-acetyloxyphenol, (2,5-dichlorophenyl) phosphoric acid, and potassium carbonate are added to N,N-dimethylformamide, and the temperature is raised to 90-110°C, and the reaction is carried out for 6-8 hours. After cooling to room temperature, the mixture is added to deionized water, and a solid is precipitated. The solid is collected by suction filtration, washed, dried, and then recrystallized from an ethanol / water mixed solution to obtain (2,5-bis(4-acetyloxyphenoxy) phenyl) phosphoric acid. S102. In a reaction vessel equipped with a reflux condenser, (2,5-bis(4-acetyloxyphenoxy) phenyl) phosphoric acid is added to ethanol, and a 4 mol / L sodium hydroxide solution is added. The temperature is raised to 80-90°C, and the reaction is carried out for 2-4 hours. After cooling to room temperature, the ethanol is removed by rotary evaporation, and then a 3 mol / L dilute hydrochloric acid solution is used to adjust the pH to 2-3. A large amount of solid is precipitated, which is collected by suction filtration, washed, dried, and then recrystallized in an ethanol / water mixed solution to obtain the heat-resistant chain extender.

3. The heat-resistant polyurethane composition for synthetic leather according to claim 2, characterized by, In S101, the molar ratio of 4-acetyloxyphenol, (2,5-dichlorophenyl) phosphoric acid, and potassium carbonate is 1:1-1.3:1.5-3; the weight ratio of 4-acetyloxyphenol, N,N-dimethylformamide, and deionized water is 1:8-12:20-30; and the volume ratio of ethanol and water in the ethanol / water mixed solution is 1:

1.

4. The heat-resistant polyurethane composition for synthetic leather according to claim 2, characterized by, In S102, the weight ratio of (2,5-bis(4-acetyloxyphenoxy) phenyl) phosphoric acid, ethanol, and a 4 mol / L sodium hydroxide solution is 1:8-12:0.7-0.9; and the volume ratio of ethanol and water in the ethanol / water mixed solution is 3:

1.

5. The heat-resistant polyurethane composition for synthetic leather according to claim 1, characterized by, The functionalized nano kaolin is prepared by the following method: S201. 2-(triethoxysilyl)-N-[2-(triethoxysilyl)ethyl] ethylamine was added into ethanol, and the temperature was raised to 25-40℃, and epichlorohydrin was added dropwise, the dropwise time was 20-40 min, and the reaction was carried out for 4-8 h, then the temperature was raised to 40-60℃, and triethylamine was added, and the reaction was carried out for 1-3 h, and then the temperature was cooled to room temperature, and filtration was carried out, and the filtrate was collected, and the solvent was removed by rotary evaporation, and then silica gel column chromatography was used, and after gradient elution, intermediate A was obtained; S202. In a reaction vessel equipped with a condensation reflux device, intermediate A was added into 1,4-dioxane, and the temperature was raised to 80-110℃, and then DOPO was added, and the reaction was carried out for 6-12 h, and then the reaction solution was poured into diethyl ether to precipitate, and the solid was collected, washed and dried to obtain a phosphorus-silicon composite modifier; S203. Nano-kaolin was added into ethanol, and ultrasonic dispersion was carried out for 30-60 min, and the phosphorus-silicon composite modifier was added, and the temperature was raised to 60-80℃, and stirring was carried out for 3-4 h; after filtration, the solid was collected, washed and dried, and then ground through a 300 mesh sieve to obtain functionalized nano-kaolin.

6. The heat-resistant polyurethane composition for synthetic leather according to claim 5, characterized by, In S201, the molar ratio of 2-(triethoxysilyl)-N-[2-(triethoxysilyl)ethyl] ethylamine, epichlorohydrin and triethylamine was 1:1.1-1.4:1.5-2.5; the weight ratio of 2-(triethoxysilyl)-N-[2-(triethoxysilyl)ethyl] ethylamine and ethanol was 1:8-12; gradient elution means that the volume ratio of dichloromethane and methanol in each eluent was 15:1, 10:1 and 8:1 in turn.

7. The heat-resistant polyurethane composition for synthetic leather according to claim 5, characterized by, In S202, the molar ratio of intermediate A and DOPO was 1:1.1-1.3; the weight ratio of intermediate A, 1,4-dioxane and diethyl ether was 1:8-12:15-25.

8. The heat-resistant polyurethane composition for synthetic leather according to claim 5, characterized by, In S203, the weight ratio of nano-kaolin, ethanol and phosphorus-silicon composite modifier was 1:8-12:0.2-0.

3.

9. The method of producing a heat-resistant polyurethane composition for synthetic leather according to any one of claims 1 to 8, characterized by, It comprises the following steps: Step one, in a dry reaction vessel, polyricinolein glycol and polycarbonate diol were added, and dehydration was carried out at 100-120℃ under a vacuum degree of-0.095 MPa for 1-2 h, and then the temperature was lowered to 70-80℃, and isocyanate and catalyst were added, and the reaction was carried out for 2-3 h to obtain a pre-polymer with terminal isocyanate groups; Step two, the temperature was lowered to 50-60℃, and N,N-dimethylformamide was added into the pre-polymer with terminal isocyanate groups, and stirring was carried out for 10-20 min, and then heat-resistant chain extender and functionalized nano-kaolin were added, and stirring was carried out at 300-500 rpm for 2-3 h, and then antioxidant was added, and stirring was continued for 30-60 min, and then it was placed under the condition of 75-85℃ and-0.09 MPa for 20-25 min to remove bubbles, and a heat-resistant polyurethane composition for synthetic leather was obtained.

10. The method of producing a heat-resistant polyurethane composition for synthetic leather according to claim 9, characterized by, In step two, the weight ratio of the pre-polymer with terminal isocyanate groups and N,N-dimethylformamide was 1:2.5-3.2.

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