Solvent-resistant polyurethane composite and method of making same

Abstract

The application relates to the technical field of high polymer materials, and discloses a solvent-resistant polyurethane composite material and a preparation method thereof, which is prepared by the reaction of the following components: an isocyanate component, a polyhydric alcohol component and a functional chain extender component; the functional chain extender is a derivative of an ortho-amino aromatic carboxylic acid with a thermally unstable ester group protection, the protection group is decomposed under a heat treatment condition and in-situ releases a functional group which can be subjected to a cyclization reaction with a urea group on a polymer chain to form a heterocyclic crosslinking structure; the preparation method comprises the following steps: (a) reacting the isocyanate component, the polyhydric alcohol component and the functional chain extender to obtain a soluble and processable linear polyurethane precursor; and (b) performing high-temperature heat treatment on the precursor after shaping. Through the design of a latent functional group and a two-step process, the application solves the contradiction between the processability and the final performance of the crosslinking polyurethane, and the prepared material has excellent solvent resistance, thermal stability and good mechanical properties.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high polymer materials, in particular to a solvent-resistant polyurethane composite material and a preparation method thereof. BACKGROUND

[0002] Polyurethane is widely used in coatings, adhesives, elastomers and fibers and other fields due to its excellent mechanical properties and adjustable structure. However, the conventional linear thermoplastic polyurethane is mainly combined by secondary bonds such as hydrogen bonds between molecular chains, and the molecular chains are easily dissociated in strong polar solvents, resulting in serious swelling or even dissolution of the material, and the thermal stability is also relatively limited, which greatly limits its application in harsh environments such as chemical corrosion and high temperature.

[0003] To solve this problem, the method of introducing a chemical crosslinking network is usually used to improve the solvent resistance and thermal stability of polyurethane. However, there is an inherent contradiction in the existing chemical crosslinking method. If a conventional multifunctional crosslinking agent is directly introduced during polymerization, the viscosity of the reaction system will increase rapidly with the reaction, which is easy to cause irreversible gelation before the completion of polymerization, resulting in the loss of flowability and processability of the material, and the subsequent film coating, spinning or molding operation cannot be carried out. On the contrary, in order to ensure the processability, the conventional post-crosslinking reaction is often harsh in conditions and low in efficiency, and it is difficult to form a uniform and dense crosslinking network in a solid state, so the performance improvement effect of the final material is also limited. Therefore, it is a technical problem to be solved in the current field to develop a solvent-resistant polyurethane material which can maintain the excellent processability of the polyurethane precursor and form a high-density and high-stability chemical crosslinking network through a mild and controllable subsequent treatment, so as to prepare a solvent-resistant polyurethane material with excellent comprehensive performance. SUMMARY

[0004] The present application aims to solve the technical problem that the chemical solvent resistance of conventional polyurethane materials is difficult to balance with the processability and mechanical toughness in the prior art.

[0005] In a first aspect, the present application provides a solvent-resistant polyurethane composite material, which adopts the following technical solution:

[0006] A solvent-resistant polyurethane composite material is prepared by reacting the following raw material components by weight:

[0007] Isocyanate component: 100 parts;

[0008] Polyol component: 80-200 parts;

[0009] Functional chain extender component: 10-50 parts;

[0010] Wherein, to realize the technical effect of the application, the key lies in that the functional chain extender is a derivative of ortho-amino aromatic diamine with a thermally unstable protecting group, wherein the protecting group decomposes under specific thermal treatment conditions, thereby generating in situ a functional group capable of undergoing a highly efficient cyclization reaction with a urea group formed by the amino group on the polymer chain to form a heterocyclic crosslinking structure.

[0011] By adopting the technical scheme, the functional chain extender with the specific structure, i.e., the functional chain extender with the thermally unstable protecting group, is introduced into a synthesis system of polyurethane, so that latent reaction sites for subsequent chemical conversion are introduced into a polymer main chain while polyurethane segments are formed.

[0012] The protecting group is chemically inert during the polyurethane polymerization stage and does not participate in the reaction, ensuring that a linear, soluble and processable precursor can be stably prepared. During the subsequent thermal treatment stage, the protecting group decomposes under heat, generating a highly active functional group (such as a carboxyl group) in situ. The application arranges the functional group and a urea group that already exists in the polyurethane segment in the “ortho position” of an aromatic ring. The functional group then undergoes intramolecular or intermolecular dehydration condensation with the spatially adjacent urea group, forming a heterocycle with high chemical structural stability. It is generally believed by those skilled in the art that a reaction between an ester group and a urea group requires a strong base or other catalyst. However, one of the originalities of the application is that the “intramolecular catalysis” effect brought about by the “ortho position” design greatly reduces the energy barrier of the reaction, so that the cyclization reaction can occur efficiently under high-temperature solid-phase conditions without any additional catalyst. This process covalently connects the initial linear polymer chain through the newly generated heterocyclic structure, constructing a three-dimensional chemical crosslinking network.

[0013] Since the heterocyclic structure has better chemical stability and thermal stability than urethane bonds and urea bonds, the final composite material has anti-swelling and anti-dissolution ability to strong polar solvents and chlorinated hydrocarbons and the like without significantly losing the inherent mechanical toughness of polyurethane.

[0014] The functional chain extender described in the application is a derivative of ortho-amino aromatic carboxylic acid with a thermally unstable ester group protecting group.

[0015] By adopting the technical scheme, an ester group is used as a thermally unstable protecting group, and in particular, a tert-butyl ester group has a thermal decomposition temperature window (usually above 200°C) that is significantly different from the conventional processing and polymerization temperature of polyurethane (usually below 120°C). This ensures that the protecting group does not decompose prematurely during the first-stage polymerization and molding process, ensuring the stability of the process. At the same time, the thermal decomposition products of the ester group (such as olefins and carboxylic acids) react cleanly, and the by-products are easy to remove.

[0016] Preferably, the heterocyclic crosslinking structure is a quinazoline-dione heterocyclic structure.

[0017] By adopting the technical scheme, the quinazoline dione has a stable structure of a conjugated aromatic heterocyclic system, and its formation process is thermodynamically favorable. The quinazoline dione ring is used as a crosslinking node, which can provide excellent chemical inertness for the final composite network, thereby further improving the solvent resistance and heat resistance of the material.

[0018] Preferably, the functional chain extender is 3,3'-bis(tert-butoxycarbonyl)-4,4'-diaminodiphenyl methane. Its chemical structural formula is as shown below:

[0019]

[0020] By adopting the technical scheme, in the specific molecular structure, the tert-butoxycarbonyl group is used as a protective group, and the amino group is used as a group that reacts with isocyanate. The molecular conformation embodies the core design idea of the application, that is, the carboxyl group generated after deprotection is located at the ortho position of the urea group formed by the reaction of the amino group. This spatial layout promotes the intramolecular or intermolecular cyclization reaction, which is conducive to the efficient formation of a quinazoline dione crosslinking network.

[0021] Preferably, the 3,3'-bis(tert-butoxycarbonyl)-4,4'-diaminodiphenyl methane is prepared by the following steps:

[0022] (a) using 2-nitro-5-methylbenzoic acid and formaldehyde as raw materials, reacting in concentrated sulfuric acid at 95-105℃ to obtain 3,3'-dicarboxy-4,4'-dinitrodiphenyl methane;

[0023] (b) hydrogenating and reducing the product of step (a) in the presence of a Pd / C catalyst at a hydrogen pressure of 3.0-4.0 MPa and a temperature of 60-70℃ to obtain 3,3'-dicarboxy-4,4'-diaminodiphenyl methane;

[0024] (c) refluxing and esterifying the product of step (b) with tert-butyl alcohol under acid catalysis and azeotropic dehydration conditions to obtain the 3,3'-bis(tert-butoxycarbonyl)-4,4'-diaminodiphenyl methane.

[0025] Preferably, the raw material component further includes 0-20 parts by weight of a conventional chain extender component, and the conventional chain extender is selected from one or more of small molecule diols or small molecule diamines.

[0026] By adopting the technical scheme, the introduction of the conventional chain extender can be used to adjust the content, structure and regularity of the hard segment of the final material. By adjusting the types and amounts thereof, the mechanical properties and thermal properties of the composite material, such as modulus, hardness and glass transition temperature, can be fine-tuned, so as to realize the customization of the material performance within a certain range.

[0027] Preferably, the isocyanate component is selected from one or more of methylene diphenyl diisocyanate, toluene diisocyanate, isophorone diisocyanate or hexamethylene diisocyanate; and the polyol component is selected from one or more of polytetramethylene ether glycol, polypropylene glycol or polyester glycol.

[0028] By using the above technical solution, the isocyanate and polyol of different chemical structures can directly determine the basic structure of the hard segment and soft segment in the polyurethane precursor. For example, using aromatic isocyanate can build a hard segment with higher rigidity, while using aliphatic isocyanate can improve the weather resistance of the material. Selecting different types of polyol soft segment directly affects the flexibility, low temperature performance and affinity to specific chemicals of the material.

[0029] In a second aspect, the application provides a preparation method of a solvent-resistant polyurethane composite material, which uses the following technical solution:

[0030] A preparation method of a solvent-resistant polyurethane composite material, comprising the following steps:

[0031] (a) precursor preparation stage: reacting an isocyanate component with a polyol component to generate an isocyanate-terminated prepolymer; then performing a chain extension reaction on the prepolymer with the functional chain extender and optionally a conventional chain extender under conditions lower than the decomposition temperature of the protecting group, to obtain a linear polyurethane precursor that is soluble and fusible;

[0032] (b) heat treatment and curing stage: after the linear polyurethane precursor obtained in step (a) is formed, performing heat treatment under conditions higher than the decomposition temperature of the protecting group, so that the protecting group decomposes, and the ortho functional group synergistic effect designed in the application is used to trigger in-situ cyclization crosslinking reaction, forming a three-dimensional network structure.

[0033] By using the above technical solution, the preparation process of the material is divided into two independent and orthogonal stages.

[0034] In the first stage, all reactions are carried out under mild conditions, at which time the system is a linear polymer, has the flowability required for solution or melt processing, and is easy to be formed into a film, a fiber or a molded product.

[0035] In the second stage, an external energy (heat) is applied to trigger a pre-designed and programmed chemical transformation. This transformation occurs in series: first, the thermal decomposition of the protecting group, and then the efficient cyclization crosslinking between the newly generated functional group and the urea group driven by the ortho effect. This design, which separates the processability and the formation of the final performance in time and process conditions, solves the technical problem of the rapid viscosity increase and the narrow processing window of traditional crosslinked polyurethane in the polymerization process.

[0036] Preferably, in step (a), the temperature of the chain extension reaction is controlled at 0-30℃; in step (b), the temperature of the heat treatment is 200-300℃.

[0037] By adopting the above technical scheme, accurate temperature control is the key to realizing the separation of the two-stage reaction. The chain extension temperature of 0-30℃ ensures the efficient reaction of amino groups and isocyanate groups, while completely inhibiting the decomposition of heat-labile protecting groups such as tert-butyl ester. The heat treatment temperature of 200-300℃ can effectively provide the activation energy required for the decomposition of the protecting group and the subsequent cyclization and dehydration reaction, and is sufficient to activate the subsequent cyclization and dehydration reaction catalyzed by the ortho structure of the present application, ensuring that the network construction is completed within a reasonable time. These two non-overlapping temperature ranges form the basis of the operability of the present method.

[0038] Preferably, the heat treatment solidification in step (b) specifically includes solvent evaporation treatment at 80-120℃, followed by heating to 220-280℃ and constant temperature for deprotection and cyclization crosslinking reaction.

[0039] By adopting the above technical scheme, the programmed heat treatment process with step-by-step heating first removes the residual solvent in the precursor at a lower temperature (80-120℃), which can avoid defects (such as bubbles, pinholes) in the product caused by rapid evaporation of the solvent in the subsequent high-temperature curing stage. Subsequently, the temperature is raised to the reaction temperature zone (220-280℃), which can make the deprotection and cyclization reaction proceed smoothly in a uniform solid phase matrix, which is beneficial to the formation of a final material with uniform structure and consistent performance.

[0040] In summary, the present application includes at least one of the following beneficial technical effects:

[0041] 1. The present application has excellent chemical solvent resistance. By designing the "ortho" pre-arrangement of the reaction groups at the molecular level in the functional chain extender, efficient in-situ deprotection and cyclization reactions can be triggered without any additional catalyst during the subsequent heat treatment stage, forming a quinazoline-dione heterocyclic crosslinking structure with extremely stable chemical properties. A dense and regular three-dimensional chemical network is thus constructed. This network can effectively bind polyurethane molecular chains and resist the penetration and swelling of strong polar solvents (such as DMAc, NMP), thereby imparting structural stability and anti-dissolution ability to the material in chemical environments that traditional polyurethane cannot withstand.

[0042] 2.The application solves the contradiction between material processability and final high performance, and has high process controllability.The latent chemical design and two-stage preparation method adopted by the application, in the first stage of low-temperature polymerization, obtain a soluble and fusible linear polyurethane precursor, which has good fluidity and a wide processing window, and is convenient for forming by conventional methods such as solution casting, molding or spinning.In the second stage, the latent cyclization crosslinking reaction mediated by the ortho structure is triggered by programmed temperature rise.This design of clearly separating the process forming and performance solidification in process conditions overcomes the technical difficulties of traditional crosslinking systems, such as rapid viscosity rise in the polymerization process and difficult processing.

[0043] 3.The application can effectively maintain the inherent excellent mechanical toughness of polyurethane materials while improving solvent resistance.The crosslinking network of the application is built on the basis of the linear polyurethane polymer chain composed of flexible soft segments and rigid hard segments.The formation of crosslinking points does not destroy the basic segment structure that gives polyurethane elasticity and toughness, but reinforces it by moderate crosslinking.Therefore, the final material avoids the problem of increased brittleness often occurring in traditional high crosslinking density materials, and realizes good consideration of the two key performances of solvent resistance and mechanical toughness. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 The Fourier transform infrared spectrum of the functional chain extender 3,3'-bis(tert-butoxycarbonyl)-4,4'-diaminodiphenyl methane prepared in Preparation Example 1 of the application;

[0045] Figure 2 The nuclear magnetic resonance hydrogen spectrum of the functional chain extender 3,3'-bis(tert-butoxycarbonyl)-4,4'-diaminodiphenyl methane prepared in Preparation Example 1 of the application;

[0046] Figure 3 The Fourier transform infrared spectrum of the structural isomer 5,5'-bis(tert-butoxycarbonyl)-3,3'-diaminodiphenyl methane prepared in Preparation Example 4 of the application;

[0047] Figure 4 The nuclear magnetic resonance hydrogen spectrum of the structural isomer 5,5'-bis(tert-butoxycarbonyl)-3,3'-diaminodiphenyl methane prepared in Preparation Example 4 of the application;

[0048] Figure 5 The thermogravimetric analysis curve of Comparative Example CS2 of the application;

[0049] Figure 6 The Fourier transform infrared contrast spectrum of Comparative Example CS2 and Example S1 of the application. DETAILED DESCRIPTION

[0050] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with embodiments. It should be understood that the embodiments of the present application are only used for illustrating the present application, but not used for limiting the scope of the present application. Various modifications or changes made to the present application without departing from the spirit and essence of the present application shall fall into the protection scope of the present application.

[0051] The main raw materials and reagents used in the following examples and comparative examples are as follows, and the reagents not specifically described are commercially available analytical pure or higher grade products.

[0052] 4,4'-diphenyl methane diisocyanate (MDI): CAS No. 101-68-8; specification: 4,4'-isomer content ≥ 99.5%; NCO group content: 33.4%~33.6%.

[0053] Polytetrahydrofuran ether glycol (PTMEG): CAS No. 25190-06-1; linear polyether glycol, its repeating unit is (-O-CH2CH2CH2CH2-); specification: number average molecular weight (Mn) is 2000 g / mol; hydroxyl value: 54.0~58.0 mg KOH / g; moisture content ≤ 0.03 wt%.

[0054] Polypropylene glycol (PPG): CAS No. 25322-69-4; linear polyether glycol, its repeating unit is (-O-CH(CH3)-CH2-); specification: number average molecular weight (Mn) is 2000 g / mol; hydroxyl value: 54.5~57.5 mg KOH / g; moisture content ≤ 0.03 wt%.

[0055] p-toluene sulfonic acid (PTSA): CAS No. 104-15-4; analytical pure.

[0056] 4,4'-methylene bis(2-chloroaniline) (MOCA): CAS No. 101-14-4; specification: purity ≥ 99.0%; melting point: 108~110℃.

[0057] Functional chain extender: full name is 3,3'-di(tert-butoxycarbonyl)-4,4'-diamino diphenyl methane, abbreviated as DC-DDM-tBu, which is self-prepared, and its preparation method is shown in the following preparation example.

[0058] Its molecular formula is: 23 H 30 N2O4;

[0059] Its structural formula is as follows:

[0060] ;

[0061] The core structure of the molecule is 4,4'-diaminodiphenyl methane skeleton. On each benzene ring, the tert-butoxycarbonyl group (-C(=0)0-C(CH3)3) is at the ortho position of the amino group (-NH2). This ortho arrangement is the technical basis for realizing the subsequent thermal-induced cyclization crosslinking reaction of the application.

[0062] Preparation Examples 1-3: Preparation of functional chain extender DC-DDM-tBu

[0063] Preparation Example 1:

[0064] This preparation example provides a method for preparing the functional chain extender DC-DDM-tBu, the steps are as follows:

[0065] ;

[0066] (a) Synthesis of 3,3'-dicarboxy-4,4'-dinitrodiphenyl methane:

[0067] In a 500 mL three-necked flask equipped with mechanical stirring, reflux condenser and thermometer, 250 mL of concentrated sulfuric acid was added. Under stirring, 36.2 g (0.2 mol) of 2-nitro-5-methylbenzoic acid was added in portions, and after it was completely dissolved, 8.9 g (0.11 mol) of 37% aqueous formaldehyde solution was slowly added dropwise. After the addition was completed, the reaction system was heated to 100°C, and kept at this temperature for 6 hours. After the reaction was completed, the reaction mixture was cooled to room temperature, slowly poured into a beaker containing 1000 g of crushed ice, and a large amount of yellow solid was precipitated. Filtration, washing the filter cake with deionized water until neutral, and then drying in a vacuum oven at 80°C for 12 hours to obtain the yellow powder product 35.5 g.

[0068] (b) Synthesis of 3,3'-dicarboxy-4,4'-diaminodiphenyl methane:

[0069] The 3,3'-dicarboxy-4,4'-dinitrodiphenyl methane obtained in step (a) 30.0 g (about 0.083 mol) and 1.5 g of 10% Pd / C catalyst were added to a 500 mL high-pressure reaction kettle, and 250 mL of methanol was added as solvent. After replacing the air in the kettle with nitrogen three times, hydrogen was used to replace it three times. The hydrogen pressure was increased to 3.5 MPa, the stirring was started, and the reaction kettle was heated to 65°C. The hydrogenation reduction reaction was carried out under this condition until the pressure in the kettle no longer decreased. Stop heating, cool to room temperature, and slowly release the pressure in the kettle. The reaction liquid was filtered to remove the Pd / C catalyst, and the filtrate was concentrated to dryness under reduced pressure to obtain the off-white solid product 23.1 g.

[0070] (c) Synthesis of 3,3'-di(tert-butoxycarbonyl)-4,4'-diaminodiphenyl methane:

[0071] 20.0 g (approximately 0.07 mol) of 3,3'-dicarboxy-4,4'-diaminodiphenylmethane obtained in step (b), 0.7 g of p-toluenesulfonic acid, and 200 mL of tert-butanol were added to a 500 mL round-bottom flask equipped with a Dean-Stark water separator. The mixture was heated to reflux, and the water generated in the reaction was removed by azeotropic extraction through the water separator. After reacting for 24 hours, the mixture was cooled to room temperature. The reaction solution was concentrated under reduced pressure, and the residue was dissolved in 200 mL of ethyl acetate. The solution was washed successively with saturated sodium bicarbonate aqueous solution and saturated brine. The organic phase was dried over anhydrous magnesium sulfate, filtered, and the solvent was removed by evaporation under reduced pressure. The crude product was purified by silica gel column chromatography (eluent: petroleum ether / ethyl acetate = 3 / 1, v / v) to give 21.5 g of a white solid.

[0072] The final product obtained was a white crystalline powder with a melting point of 148–150 °C. (Reference) Figure 1 and Figure 2 Its chemical structure was determined by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance hydrogen spectroscopy (NMR). 1 Confirmed by H NMR analysis.

[0073] like Figure 1 As shown, the infrared spectrum (KBr pellet method) shows that at 3472 cm⁻¹... -1 and 3365 cm -1 The presence of a clear double peak of asymmetric and symmetric stretching vibrations of the NH bond at 1718 cm⁻¹ indicates the presence of a primary amine; -1 The strong and sharp absorption peak at this point is attributed to the stretching vibration of the C=O group in the tert-butyloxycarbonyl group.

[0074] like Figure 2 As shown, the 1H NMR spectrum (400 MHz, solvent CDCl3) shows: a singlet at chemical shift δ1.54 ppm, with an integrated area corresponding to 18 protons, belonging to two equivalent tert-butyl groups (-C(CH3)3); a singlet at δ3.88 ppm, with an integrated area corresponding to 2 protons, belonging to a methylene group (-CH2-) connecting two benzene rings; a broad singlet at δ4.25 ppm, with an integrated area corresponding to 4 protons, belonging to two primary amino groups (-NH2); and a set of multiplets in the aromatic region of δ6.80–7.55 ppm, with an integrated area corresponding to 6 protons, belonging to hydrogen atoms on the benzene ring.

[0075] Preparation Example 2:

[0076] (a) Synthesis of 3,3'-dicarboxy-4,4'-dinitrodiphenylmethane:

[0077] Except for controlling the reaction temperature at 95°C, the other feeding and operation steps are exactly the same as those in step (a) of preparation example 1.

[0078] (b) Synthesis of 3,3'-dicarboxy-4,4'-diaminodiphenylmethane:

[0079] Except that the hydrogen pressure was controlled at 3.0 MPa and the reaction temperature was controlled at 60°C, the rest of the raw materials and the operation steps were exactly the same as those in step (b) of Preparation Example 1.

[0080] (c) Synthesis of 3,3'-di(tert-butoxycarbonyl)-4,4'-diaminodiphenylmethane:

[0081] The product obtained in step (b) was subjected to exactly the same operation as that in step (c) of Preparation Example 1, to obtain a white solid product.

[0082] The final product obtained was a white crystalline powder having a melting point of 147-149°C. Its infrared spectrum and nuclear magnetic resonance hydrogen spectrum data were identical to those of the product obtained in Preparation Example 1.

[0083] Preparation Example 3:

[0084] (a) Synthesis of 3,3'-dicarboxy-4,4'-dinitrodiphenylmethane:

[0085] Except that the reaction temperature was controlled at 105°C, the rest of the raw materials and the operation steps were exactly the same as those in step (a) of Preparation Example 1.

[0086] (b) Synthesis of 3,3'-dicarboxy-4,4'-diaminodiphenylmethane:

[0087] Except that the hydrogen pressure was controlled at 4.0 MPa and the reaction temperature was controlled at 70°C, the rest of the raw materials and the operation steps were exactly the same as those in step (b) of Preparation Example 1.

[0088] (c) Synthesis of 3,3'-di(tert-butoxycarbonyl)-4,4'-diaminodiphenylmethane:

[0089] The product obtained in step (b) was subjected to exactly the same operation as that in step (c) of Preparation Example 1, to obtain a white solid product.

[0090] The final product obtained was a white crystalline powder having a melting point of 148-151°C. Its infrared spectrum and nuclear magnetic resonance hydrogen spectrum data were identical to those of the product obtained in Preparation Example 1.

[0091] Preparation Example 4: Preparation of a functional chain extender structural isomer, 5,5'-di(tert-butoxycarbonyl)-3,3'-diaminodiphenylmethane

[0092] In the early exploration stage of the present application, the following structural isomers were synthesized to study the effect of functional group position on the subsequent cyclization crosslinking reaction. In this isomer, the amino group and the ester group are in a meta relationship on the benzene ring. Experimental results show that this structure cannot achieve the technical problems to be solved by the present application, and its preparation method and performance data are as follows, which are only used for subsequent comparative experiments.

[0093] Chemical name: 5,5'-di(tert-butoxycarbonyl)-3,3'-diaminodiphenylmethane;

[0094] Molecular formula: C 23 H 30 N2O4;

[0095] The structural formula is as follows:

[0096] ;

[0097] The synthesis steps are as follows:

[0098] ;

[0099] (a) Synthesis of 5,5'-dicarboxy-3,3'-dinitrodiphenylmethane:

[0100] In a 500 mL three-necked flask equipped with mechanical stirring and a thermometer, 200 mL of concentrated sulfuric acid was added and cooled to 10°C. Under stirring, 33.4 g (0.2 mol) of 3-nitrobenzoic acid (CAS: 121-92-6) was slowly added. After complete dissolution, 8.9 g (0.11 mol) of 37% formaldehyde aqueous solution was slowly added dropwise, and the temperature was controlled not to exceed 20°C during the addition. After the addition was completed, it was restored to room temperature and the reaction was continued for 12 hours. The reaction mixture was slowly poured into 1000 g of crushed ice, and a milky white solid was precipitated. After filtration, it was washed with deionized water until neutral, and dried in a vacuum oven at 80°C to obtain the product 33.2 g.

[0101] (b) Synthesis of 5,5'-dicarboxy-3,3'-diaminodiphenylmethane:

[0102] The intermediate obtained in step (a) 30.0 g (about 0.087 mol) and 1.5 g of 10% Pd / C catalyst were added to a 500 mL high-pressure reaction kettle, and 250 mL of ethyl acetate was added as solvent. After replacing the air in the kettle with nitrogen three times, it was replaced with hydrogen three times. The hydrogen pressure was increased to 3.5 MPa, the stirring was started, and the reaction kettle was heated to 65°C for hydrogenation reduction reaction until the pressure in the kettle no longer decreased. After cooling to room temperature, the Pd / C catalyst was removed by filtration, and the filtrate was concentrated to dryness under reduced pressure to obtain the off-white solid product 23.8 g.

[0103] (c) Synthesis of 5,5'-bis(tert-butoxycarbonyl)-3,3'-diaminodiphenylmethane:

[0104] The product from step (b), 20.0 g (about 0.07 mol), 0.7 g p-toluenesulfonic acid and 200 mL tert-butanol were added to a 500 mL round bottom flask equipped with a Dean-Stark trap. The reaction was heated to reflux, azeotropically removed water, and reacted for 24 hours. After cooling, the reaction was concentrated under reduced pressure, dissolved in ethyl acetate, and washed with saturated aqueous sodium bicarbonate and saturated brine, successively. The organic phase was dried over anhydrous magnesium sulfate, filtered, and the solvent was removed under reduced pressure. The crude product was purified by column chromatography on silica gel to give 20.5 g of the product as a white solid.

[0105] The final product obtained was a white powder with a melting point of 162-164 °C. The chemical structure was confirmed by Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance spectroscopy (1H NMR) analysis. Figure 3 and Figure 4 The chemical structure was confirmed by Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance spectroscopy (1H NMR) analysis.

[0106] As shown in Figure 3 , the infrared spectrum (KBr pellet method) showed clear N-H bond asymmetric and symmetric stretching vibration doublet at 3480 cm -1 and 3370 cm -1 , indicating the presence of primary amino groups; a strong and sharp absorption peak at 1715 cm -1 was attributed to the stretching vibration of the ester group C=O in the tert-butyloxy carbonyl group.

[0107] As shown in Figure 4 , the proton nuclear magnetic resonance spectrum (400 MHz, solvent DMSO-d6) showed a single peak at chemical shift δ 1.52 ppm with an integral area corresponding to 18 protons, which was attributed to two equivalent tert-butyl groups (-C(CH3)3); a single peak at δ 3.85 ppm with an integral area corresponding to 2 protons, which was attributed to the methylene group (-CH2-) connecting the two benzene rings; a broad single peak at δ 5.30 ppm with an integral area corresponding to 4 protons, which was attributed to the two primary amino groups (-NH2); a group of multiple peaks in the aromatic region at δ 6.60-7.30 ppm with an integral area corresponding to 6 protons, which was attributed to the hydrogens on the benzene rings.

[0108] Examples 1-4: Preparation of solvent-resistant polyurethane composite

[0109] Example 1:

[0110] The present application provides a preparation method of a solvent-resistant polyurethane composite, comprising the following steps:

[0111] (a) Linear polyurethane precursor preparation:

[0112] In a 500 mL three-necked flask equipped with mechanical stirring, thermometer and nitrogen protection, 100 g of 4,4'-diphenylmethane diisocyanate (MDI) and 150 g of polytetramethylene ether glycol (PTMEG, Mn=2000) were added. The system was heated to 70°C under nitrogen protection and reacted for 2 hours to obtain an NCO-terminated prepolymer. The prepolymer was cooled to room temperature and diluted with 250 g of N,N-dimethylacetamide (DMAc).

[0113] In another beaker, 30 g of 3,3'-di(tert-butoxycarbonyl)-4,4'-diaminodiphenylmethane (DC-DDM-tBu) prepared by the method of Preparation Example 1 was dissolved in 100 g of DMAc to form a chain extender solution.

[0114] The chain extender solution was slowly added to the prepolymer solution under vigorous stirring and ice water bath cooling, and the temperature of the reaction system was controlled below 10°C during the whole addition process. After the addition was completed, the ice water bath was removed and the reaction was continued at 25°C for 4 hours to obtain a light yellow transparent and viscous linear polyurethane precursor solution with a solid content of about 40%.

[0115] (b) Thermal curing:

[0116] The precursor solution obtained in step (a) was uniformly cast on a clean horizontal glass plate, and a film thickness controller was used. The glass plate was placed in a forced air drying oven and subjected to thermal treatment according to the following program: first, constant temperature drying at 80°C for 12 hours to remove most of the DMAc solvent; then, the temperature program was raised to 250°C and held at 250°C for 2 hours for deprotection and cyclization crosslinking reaction. After the reaction was completed, the heating was turned off and the sample was naturally cooled to room temperature with the oven. Carefully peeling off the glass plate resulted in a light yellow, tough and transparent polyurethane composite film, denoted as S1.

[0117] Example 2:

[0118] The present embodiment provides a method for preparing a solvent-resistant polyurethane composite material. Except that the amount of functional chain extender DC-DDM-tBu is adjusted to 45 g, the types and amounts of all raw materials, the equipment used and all operation steps are exactly the same as in Example 1. Finally, a polyurethane composite film is obtained, denoted as S2.

[0119] Example 3:

[0120] The embodiment of the present application provides a kind of preparation method of solvent-resistant polyurethane composite material, wherein the amount of isocyanate component (MDI) is 100g, and the amount of functional chain extender (DC-DDM-tBu) is 30g.Polyol component uses 90g of polypropylene glycol (PPG, Mn=2000) instead of PTMEG.Except that the type and amount of polyol are different, the type and amount of all raw materials, the equipment used and all operation steps are exactly the same as in example 1.Finally, polyurethane composite material film is obtained, which is recorded as S3.

[0121] Example 4:

[0122] The embodiment of the present application provides a kind of preparation method of solvent-resistant polyurethane composite material, except that in the preparation of chain extender solution, 30g of DC-DDM-tBu is adjusted to the mixture of 20g of DC-DDM-tBu and 5g of 1,4-butanediol (BDO), and the type and amount of all raw materials, the equipment used and all operation steps are exactly the same as in example 1.Finally, polyurethane composite material film is obtained, which is recorded as S4.

[0123] Comparative examples 1-7:

[0124] Comparative example 1:

[0125] Compared with example 1, the difference is that: its chain extender does not use 30g of functional chain extender DC-DDM-tBu, but uses equal molar amount (18.8g) of conventional aromatic amine chain extender 4,4'-methylenebis(2-chloroaniline) (MOCA).The type and amount of all raw materials, the equipment used and all operation steps are the same.Finally, the film obtained is recorded as CS1.

[0126] Comparative example 2:

[0127] Compared with example 1, the difference is that: in the (b) heat treatment curing step, after the precursor solution is poured into film, only vacuum drying is carried out at 80℃ to constant weight, without subsequent high temperature heat treatment step at 250℃.The film obtained is recorded as CS2.

[0128] Comparative example 3:

[0129] Compared with example 1, this comparative example attempts to use conventional one-step method to prepare crosslinked polyurethane.The difference is that: all raw materials (100g MDI, 150g PTMEG, 30g DC-DDM-tBu, 350g DMAc) are added into reaction bottle at one time, and direct polymerization reaction is carried out at 70℃.It is observed that the reaction gels in a short time, and no processable solution can be obtained.Recorded as CS3.

[0130] Comparative example 4:

[0131] Comparative Example 2 is similar to Example 1 except that the chain extender is not DC-DDM-tBu but 10 g of 1,4-butanediol (BDO) is used for chain extension and 15 g of trimethylolpropane (TMP) is additionally added as a crosslinker. The remaining steps are the same. The final film is denoted as CS4.

[0132] Comparative Example 5:

[0133] Comparative Example 5 is similar to Example 1 except that the chain extender is not 30 g of functional chain extender DC-DDM-tBu but an equal molar amount (30 g) of its structural isomer 5,5'-bis(tert-butoxycarbonyl)-3,3'-diaminodiphenylmethane prepared by the method of Preparation Example 4. All other raw materials, equipment and operating steps are the same as in Example 1. The final film is denoted as CS5.

[0134] Comparative Example 6:

[0135] Comparative Example 6 is similar to Example 1 except that the amount of functional chain extender DC-DDM-tBu is reduced to 5 g (i.e. 5 parts relative to 100 g MDI). All other raw materials, equipment and operating steps are the same. The final film is denoted as CS6.

[0136] Comparative Example 7:

[0137] Comparative Example 7 is similar to Example 1 except that the amount of functional chain extender DC-DDM-tBu is increased to 70 g (i.e. 70 parts relative to 100 g MDI). All other raw materials, equipment and operating steps are the same. The final film is denoted as CS7.

[0138] To verify the comprehensive performance of the polyurethane material prepared according to the present application, the film samples prepared in Examples 1-4 and Comparative Examples 1-7 (denoted as S1-S4 and CS1-CS7, respectively) are subjected to the following performance tests.

[0139] 1) Mechanical property test:

[0140] Test standard: Refer to national standard GB / T 528-2009 "Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber".

[0141] Sample preparation: After all the prepared films (S1-S4, CS1, CS2, CS4-CS7) are placed in an environment of 25°C and 50% relative humidity for 24 hours, they are cut into standard test samples using dumbbell-shaped cutting knives (knife edge width 4 mm). At least 5 effective test samples are cut from each sample.

[0142] The test steps are as follows:

[0143] 1. Test using an electronic universal material testing machine.

[0144] 2. Clamp both ends of the dumbbell-shaped specimen in the upper and lower clamps of the testing machine, ensuring that the specimen is straight and moderately tight.

[0145] 3. Set the tensile rate of the testing machine to 200 mm / min.

[0146] 4. Start the testing machine and stretch the specimen until it breaks. The instrument automatically records and calculates the tensile strength and elongation at break of the specimen.

[0147] 5. Repeat the above process for all valid specimens of each sample, and take the arithmetic mean of the final results.

[0148] 2) Solvent resistance (swelling rate) and gel content test:

[0149] Test solvent: N,N-dimethylacetamide (DMAc).

[0150] The test steps are as follows:

[0151] 1. Accurately cut a square specimen of about 15 mm x 15 mm from each film sample.

[0152] 2. Dry the specimen in a vacuum oven at 80°C to a constant weight, and after cooling to room temperature in the desiccator, weigh its initial dry weight with a one-hundredth analytical balance, denoted as m0.

[0153] 3. Completely immerse the weighed specimen in a sealed glass bottle containing sufficient DMAc solvent, and stand for immersion at 25°C for 72 hours to allow it to swell fully.

[0154] 4. Take out the swollen specimen and quickly absorb the residual solvent on its surface with filter paper, and immediately weigh its swollen wet weight, denoted as m1. For samples that dissolve or disintegrate in the solvent, record their state.

[0155] 5. Place the specimen with the weighed wet weight again in a vacuum oven at 80°C to dry to a constant weight, and after cooling, weigh its final dry weight, denoted as m2.

[0156] 6. Calculate the swelling rate and gel content according to the following formula:

[0157] Swelling rate (%) = [(m1-m0) / m0] x 100%;

[0158] Gel content (%) = (m2 / m0) x 100%;

[0159] 3) Thermal stability test:

[0160] Test instrument: Thermogravimetric analyzer.

[0161] The test procedure is as follows:

[0162] 1. About 5-8 mg of sample was taken from each film sample and placed in an alumina crucible.

[0163] 2. The crucible was placed on the sample holder of the thermogravimetric analyzer.

[0164] 3. The test program was set: under the protection of high-purity nitrogen gas (gas flow rate: 50 mL / min), heated from room temperature (about 30°C) to 700°C at a heating rate of 10°C / min.

[0165] 4. The instrument automatically recorded the curve of the sample mass change with temperature. The temperature at which the sample lost 5% of its weight (T_d5) was read from the curve as an indicator of the thermal stability of the material.

[0166] The test results are summarized in Table 1:

[0167] Table 1: Performance test results of sample of examples and comparative examples:

[0168]

[0169] Based on the performance test data shown in Table 1, the following conclusions can be drawn:

[0170] The materials (S1-S4) prepared in Examples 1-4 of the present application all exhibit low swelling rate, high gel content and high thermal decomposition temperature. Specifically, the sample S1 of Example 1 has a swelling rate as low as 4.8% in DMAc solvent, a gel content of 98.6%, and a 5% thermal weight loss temperature of 363.1°C. The performance is attributed to the two-step process of the present application, which first utilizes the reaction of amino group with isocyanate group at low temperature to obtain a processable linear polyurethane precursor containing a tert-butyloxycarbonyl protecting group; then in the high-temperature heat treatment stage at 250°C, the tert-butyloxycarbonyl group undergoes thermal decomposition to generate in situ a highly reactive carboxyl group. Since the amino group and the tert-butyloxycarbonyl group in the molecular structure of the functional chain extender are in an ortho relationship on the benzene ring, the newly generated carboxyl group can undergo a highly efficient intramolecular cyclization dehydration reaction with the amino group that has been reacted on the adjacent segment, forming a quinazoline-dione heterocyclic structure that is stable in chemical and thermal properties. These heterocyclic structures form effective chemical crosslinking points between the polymer chains, thereby constructing a dense crosslinked network.

[0171] The results of the comparative examples demonstrate the necessity of the technical features in the technical solution of the present application. The sample CS2 of Comparative Example 2, after omitting the high-temperature heat treatment step at 250℃, is completely dissolved in DMAc, with a gel content of 0, and a thermal weight loss onset temperature of only 208.9℃, which indicates that high-temperature treatment is a necessary process condition for forming a solvent-resistant crosslinked network. The sample CS5 of Comparative Example 5 uses a structural isomer with amino and ester groups in a meta relationship as a chain extender, with a gel content of only 64.7% and a swelling rate of up to 86.4%, which confirms that the ortho arrangement of functional groups on the benzene ring is a key structural basis for efficient ring-opening crosslinking and excellent solvent resistance. The results of Comparative Examples 1 and 4 further show that, compared with conventional linear polyurethane (CS1, completely dissolved) and conventional trimethylolpropane crosslinked polyurethane (CS4, swelling rate of 28.5%), the solvent resistance obtained by forming a quinazoline-dione crosslinked network in the present application has been significantly improved. In addition, the instant gel phenomenon of Comparative Example 3 demonstrates the necessity of the two-step process used in the present application for obtaining a processable precursor. The results of Comparative Examples 6 and 7 show that there is an appropriate range for the amount of functional chain extender, too low (CS6) will result in insufficient crosslinking density and poor solvent resistance, and too high (CS7) will result in too high crosslinking density of the material, which manifests as too low elongation at break (33%) and brittle material.

[0172] In summary, the detailed data of the above examples and comparative examples collectively demonstrate that, by using a functional chain extender with amino and latent functional groups arranged in an ortho position and a specific two-step preparation process, the present application can form a high-stability quinazoline-dione chemical crosslinked network in the polymer matrix in situ through high-temperature treatment, while ensuring good processability of the precursor solution, thereby endowing the final composite material with excellent solvent resistance, thermal stability, and comprehensive mechanical properties.

[0173] Test Example 1:

[0174] To directly observe and confirm the chemical conversion process of the present application at the molecular level, FT-IR and TGA analyses were performed on key samples.

[0175] First step: quantitative confirmation of thermal deprotection reaction (TGA analysis)

[0176] To quantitatively verify the occurrence of thermal decomposition of the thermally unstable protecting group in the two-stage reaction of the present application, a linear precursor CS2 (its solid components are identical to those of Example 1) before heat treatment was subjected to thermogravimetric analysis (TGA). The theoretical weight loss rate of the linear polyurethane precursor (CS2) is calculated as follows:

[0177] 1) According to the formulation of Example 1, the total mass of the solid raw materials of the polymer is:

[0178] 100 g (MDI) + 150 g (PTMEG) + 30 g (functional chain extender) = 280 g;

[0179] 2) The weight fraction of the functional chain extender 3,3'-bis(tert-butoxycarbonyl)-4,4'-diaminodiphenylmethane in the final polymer solid (W_f) is:

[0180] W_f = 30 g / 280 g ≈ 10.71%;

[0181] 3) The theoretical weight loss rate of the functional chain extender monomer itself (W_loss_monomer) for removing two tert-butoxycarbonyl protecting groups in the form of isobutene is 24.69%.

[0182] 4) Therefore, the total theoretical weight loss rate of the entire linear polyurethane precursor (CS2) during thermal decomposition (W_loss_polymer) should be:

[0183] W_loss_polymer = W_f × W_loss_monomer = 10.71% × 24.69% ≈ 2.64%;

[0184] As shown in the TGA curve, Figure 5 a weight loss step occurred in the temperature range of 200°C to 300°C, indicating that the expected chemical decomposition reaction occurred in this temperature range. The weight loss rate of this step was measured to be 2.59%.

[0185] The experimentally measured weight loss rate (2.59%) is highly consistent with the theoretically calculated weight loss rate (2.64%) based on the formulation of Example 1. It is confirmed that the decomposition of the thermally unstable protecting group in the two-stage reaction mechanism of the present invention and the in-situ release of the active functional group indeed occur in the expected stoichiometric relationship.

[0186] Second step: confirmation of cyclization to form quinazoline dione structure (FT-IR analysis)

[0187] As shown in the FT-IR spectra before heat treatment (CS2, solid line) and after heat treatment (S1, dashed line), Figure 6 the occurrence of the reaction can be observed:

[0188] Complete disappearance of reactant characteristic peaks: The ester C=O peak at ~1720 cm -1 and the urea C=O peak at ~1650 cm -1 before heat treatment completely disappeared after heat treatment.

[0189] Clear generation of product characteristic peaks: At the same time, after heat treatment, at ~1770 cm -1 and ~1710 cm -1A pair of new, strong and sharp absorption doublet peaks appeared. This pair of characteristic doublet peaks is the signature signal of the two imide carbonyl groups in the specific heterocyclic structure of quinazoline dione.

[0190] The disappearance of the reactant characteristic peaks and the appearance of the product characteristic peaks confirm that the ester groups and urea groups pre-arranged on the polymer chain by the "ortho" design of the present application are indeed converted to the expected quinazoline dione crosslinking structure through a cyclization reaction at high temperature.

[0191] While embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, combinations, and alterations can be made to these embodiments without departing from the principles and spirit of the present application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A solvent resistant polyurethane composite, characterized in that, Prepared by reacting raw material components comprising the following parts by weight: Isocyanate component: 100 parts; Polyol component: 80-200 parts; Functional chain extender component: 10-50 parts; The functional chain extender is a derivative of ortho-amino aromatic carboxylic acid with a thermally unstable ester group protecting group; the functional chain extender is 3,3'-bis(tert-butoxycarbonyl)-4,4'-diaminodiphenylmethane; The preparation method of the solvent-resistant polyurethane composite comprises the following steps: 1) Precursor preparation stage: reacting the isocyanate component with the polyol component to form an isocyanate-terminated prepolymer; then, under conditions below the decomposition temperature of the protecting group, the prepolymer is subjected to chain extension reaction with the functional chain extender and conventional chain extender to obtain a soluble and meltable linear polyurethane precursor; 2) Heat treatment and curing stage: after the linear polyurethane precursor obtained in step 1) is formed, heat treatment is performed at a temperature higher than the decomposition temperature of the protecting group to decompose the protecting group and initiate in-situ cyclization crosslinking reaction to form a three-dimensional network structure.

2. The solvent resistant polyurethane composite of claim 1, wherein, The 3,3'-bis(tert-butoxycarbonyl)-4,4'-diaminodiphenylmethane is prepared by the following steps: (a) Using 2-nitro-5-methylbenzoic acid and formaldehyde as raw materials, reacting in concentrated sulfuric acid at 95-105°C to obtain 3,3'-dicarboxy-4,4'-dinitrodiphenylmethane; (b) Hydrogenation reduction of the product of step (a) in the presence of Pd / C catalyst at a hydrogen pressure of 3.0-4.0 MPa and a temperature of 60-70°C to obtain 3,3'-dicarboxy-4,4'-diaminodiphenylmethane; (c) Reflux esterification reaction of the product of step (b) with tert-butyl alcohol under acid catalysis and azeotropic water removal conditions to obtain the 3,3'-bis(tert-butoxycarbonyl)-4,4'-diaminodiphenylmethane.

3. The solvent resistant polyurethane composite of claim 1, wherein, The raw material components further include 0-20 parts by weight of a conventional chain extender component selected from one or more of small molecule diols or small molecule diamines.

4. The solvent resistant polyurethane composite of claim 1, wherein, The isocyanate component is selected from one or more of methylene diphenyl diisocyanate, toluene diisocyanate, isophorone diisocyanate or hexamethylene diisocyanate; the polyol component is selected from one or more of polytetrahydrofuran ether diol, polypropylene glycol or polyester diol.

5. The solvent resistant polyurethane composite of claim 1, wherein, In step 1), the temperature of the chain extension reaction is controlled at 0-30°C.

6. The solvent resistant polyurethane composite of claim 1, wherein, In step 2), the temperature of the heat treatment is 200-300°C.

7. The solvent resistant polyurethane composite of claim 1, wherein, The heat treatment and curing in step 2) specifically includes: (i) Solvent evaporation treatment at 80-120°C; (ii) Subsequently, the temperature is raised to 220-280°C, and the deprotection and cyclization crosslinking reaction is performed at a constant temperature.

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