High-toughness flame-retardant polyurethane containing phosphorus-containing triphenylene / cashew phenol-based chain extender, preparation method and application

Abstract

This invention relates to the field of polymer materials technology, and discloses a high-strength, tough, and flame-retardant polyurethane containing a phosphorus-containing phenanthrene / cainol-based chain extender, its preparation method, and its application. The core of this invention lies in introducing a cashew nut-based chain extender containing phosphorus-containing phenanthrene groups into a polyurethane system. The polyurethane material is prepared by reacting bio-based polyols, polyisocyanates, and the chain extender, which acts as a multifunctional crosslinking point in the material. This invention utilizes the inherent synergistic effect of the flexible cashew nut chain and the rigid phosphorus-containing phenanthrene groups in the chain extender molecule to achieve an organic combination of reinforcement, toughening, and flame-retardant functions at the molecular level, successfully solving the problem of the difficulty in simultaneously achieving mechanical strength, flexibility, and flame retardant properties in traditional polyurethane materials. The prepared material possesses both excellent mechanical properties and outstanding flame-retardant effects.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a high-strength, tough, flame-retardant polyurethane containing phosphorus-containing phenanthrene / cashew phenol chain extender, its preparation method, and its application. Background Technology

[0002] Polyurethane (PU) is a class of high-molecular polymers containing repeating urethane groups (-NHCOO-) in its main chain. Due to its excellent designability, abrasion resistance, and mechanical properties, it is widely used in coatings, adhesives, foams, elastomers, and other fields. With the increasing emphasis on environmental protection and sustainable development, bio-based polyurethanes made from renewable resources such as castor oil, soybean oil, and cashew nut shells have become a research hotspot. However, bio-based polyurethanes typically have two major performance limitations: firstly, their long aliphatic chain structure generally results in lower tensile strength and modulus compared to petroleum-based high-performance polyurethanes; secondly, polyurethanes themselves have a low limiting oxygen index, making them flammable materials and posing a fire hazard.

[0003] To improve flame retardancy, flame retardants are often added. Traditional additive flame retardants have problems such as toxicity, migration, or serious impairment of the material's mechanical properties. Reactive flame retardants, such as 9,10-dihydro-9-oxa-10-phosphaphenanthrene (DOPO) derivatives, can prevent migration through chemical bonding, but their rigid phosphaphenanthrene ring structure, while imparting flame retardancy, often leads to a significant decrease in the flexibility and elongation at break of polyurethane, making the material brittle. On the other hand, short-chain small-molecule chain extenders used to enhance mechanical strength further sacrifice the material's toughness and have no flame retardant function. Adding chain extenders and flame retardants separately can easily cause problems such as poor compatibility and phase separation.

[0004] Therefore, existing technologies lack an effective solution that can fundamentally reconcile the contradictions among the three aspects of polyurethane: reinforcement, toughening, and flame retardancy. Developing a multifunctional chain extender that integrates flexible segments, rigid flame-retardant groups, and reactive functional groups, and then preparing polyurethane materials with excellent comprehensive performance based on this, is a technical challenge that urgently needs to be overcome in this field. Summary of the Invention

[0005] The first technical problem to be solved by the present invention is to provide a high-strength and tough flame-retardant polyurethane containing phosphorus phenanthrene / cashew phenol-based chain extender, so as to solve the technical contradiction that bio-based polyurethanes in the prior art cannot simultaneously achieve high strength, high toughness and high flame retardancy, and that traditional modification methods have the technical contradiction of "strengthening makes it brittle and flame retardancy damages its properties".

[0006] The second technical problem to be solved by the present invention is to provide a method for preparing high-strength and tough flame-retardant polyurethane containing the above-mentioned phosphorus-containing phenanthrene / cashew phenol-based chain extender.

[0007] The third technical problem to be solved by the present invention is to provide the application of the above-mentioned high-strength and tough flame-retardant polyurethane containing phosphorus phenanthrene / cashew phenol-based chain extenders.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0009] A method for preparing a phosphenanthrene / cashew phenolic chain extender includes the following steps: (1) Dissolve cashew phenol and acid-binding agent in an organic solvent, add phosphorylation reagent to carry out the first reaction, and obtain tri-cashew phenol phosphate; (2) In a nitrogen atmosphere, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is heated and melted, and then the tricalycanthoxyphosphate obtained in step (1) is added to carry out a second reaction to obtain tricalycanthoxyphosphate containing phosphaphenanthrene groups. (3) The tri-coryl phosphate ester containing phosphorus phenanthrene group obtained in step (2) is subjected to photocatalytic reaction with a compound containing thiol and hydroxyl groups in the presence of a photoinitiator to obtain the product.

[0010] In some embodiments, in step (1), the acid-binding agent is any one of triethylamine, pyridine, or potassium carbonate; and / or, the organic solvent is any one or more of dichloromethane, tetrahydrofuran, toluene, or N,N-dimethylformamide; and / or, the phosphorylation reagent is any one or more of phosphorus oxychloride, phosphorus oxybromide, or phosphorus pentoxide; and / or, the molar ratio of cashew phenol, the acid-binding agent, and the phosphorylation reagent is 2.8~3.2:2.8~3.2:1, preferably 3:3:1; and / or, the first reaction is carried out at a temperature of 30~60℃ (preferably 40℃) for 4~8h, preferably 6h; and / or, the phosphorylation reagent is added dropwise to the reaction system at room temperature for a time controlled at 1~2h.

[0011] In some embodiments, in step (2), the heating and melting is carried out at a temperature of 140~160℃ (preferably 140℃) for 0.5~1h, preferably 30min; and / or, the molar ratio of the 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to the tricalycanthoxyphosphate is 1.2~1.5:1; and / or, the second reaction is carried out under a nitrogen atmosphere at a temperature of 160~180℃ (preferably 175℃) for 18~30h, preferably 24h.

[0012] In some embodiments, in step (3), the compound containing thiol and hydroxyl groups is any one or more of thioglycerol, mercaptoethanol, and 2,3-dimercapto-1-propanol; and / or, the photoinitiator is any one or more of 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexylphenyl ketone, or benzoin dimethyl ether; and / or, the molar ratio of the trisalicylic acid phosphate containing phenanthrene groups, the compound containing thiol and hydroxyl groups, and the photoinitiator is 1:3.0~5.0:0.005~0.03; and / or, the photocatalytic reaction has an ultraviolet wavelength of 320~400 nm and a light intensity of 10~100 mW / cm². 2 The temperature is 25~45℃, and the time is 24~48h.

[0013] The phosphenanthrene / cashew phenolic chain extender prepared by the above method is also within the scope of protection of this invention.

[0014] This invention also protects a high-strength, tough, flame-retardant polyurethane containing a phosphorus-containing phenanthrene / cashew phenol-based chain extender, comprising the following components in parts by weight: 100 parts of vegetable oil-based polyols; 40-150 parts of polyisocyanate; 5-20 parts of the aforementioned phosphenanthrene / cashew phenolic chain extender; Catalyst 0.1 to 5 parts.

[0015] In some embodiments, the vegetable oil-based polyol is hydroxylated epoxidized soybean oil or castor oil; and / or, the polyisocyanate is any one or more of hexamethylene diisocyanate, isophorone diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, or L-lysine diisocyanate; and / or, the catalyst is any one or more of stannous octoate, dibutyltin dilaurate, or bismuth neodecanoate.

[0016] In some embodiments, the hydroxylated epoxidized soybean oil is prepared by the following method: hydrochloric acid and acetone are mixed, epoxidized soybean oil is added under stirring, and the mixture is reacted at 35~45 °C for 1.5~3 h. After the reaction is completed, the reaction solution is post-treated to obtain the final product.

[0017] In some embodiments, the molar ratio of hydrochloric acid to epoxidized soybean oil is 3:1~2; and / or, the post-treatment specifically includes: first evaporating to remove acetone from the reaction solution, then extracting and washing with water until neutral, and finally evaporating to remove the solvent; and / or, the epoxidized soybean oil has an epoxy value of 5.0%~7.0% and a viscosity of 300~700 mPa·s; and / or, the hydroxylated epoxidized soybean oil has a hydroxyl value of 200~350 mg KOH / g, a viscosity of 1000~10000 mPa·s, and an epoxy value of 0.1%~0.5%.

[0018] In some embodiments, the epoxidized soybean oil is added dropwise to the reaction system, and the dropwise addition time is controlled at 1-2 hours.

[0019] In some embodiments, the castor oil has a hydroxyl value of 150-170 mg KOH / g.

[0020] The preparation method of the above-mentioned high-strength and tough flame-retardant polyurethane includes the following steps: a plant oil-based polyol, a polyisocyanate, the phosphenanthrene / cashew phenolic chain extender as described in claim 1, and a catalyst are polymerized in an organic solvent, and after the reaction is completed, the polyurethane is cured and molded to obtain the product.

[0021] In some embodiments, the organic solvent is dichloroethane or dimethylacetamide; and / or, the curing process involves first curing at 35-60°C for 4-24 hours, followed by curing at 70-80°C for 1-4 hours.

[0022] In some embodiments, when the vegetable oil-based polyol is hydroxylated epoxidized soybean oil, the polymerization reaction is a one-step process: the hydroxylated epoxidized soybean oil, the polyisocyanate, the phosphenanthrene / cashew phenolic chain extender and the catalyst are dissolved in an organic solvent, stirred at 30~40 °C for 4~6 h and then solidified.

[0023] In some embodiments, when the vegetable oil-based polyol is castor oil, the polymerization reaction is a prepolymerization method: the castor oil and the polyisocyanate are dissolved in an organic solvent and reacted at 70-90 °C for 1-2 h to obtain a prepolymer solution, then the phosphenanthrene / cashew phenolic chain extender is added and stirred for 0.5-1 h, and finally the catalyst is added, mixed evenly, and then solidified.

[0024] In some embodiments, the high-strength and tough flame-retardant polyurethane has a tensile strength of 3-50 MPa, an elongation at break of 250%-500%, a flaming burning time of 5-16 s, and a limiting oxygen index of 25% or higher.

[0025] In some embodiments, the high-strength and tough flame-retardant polyurethane containing phosphorus phenanthrene / cashew phenolic chain extender of the present invention is used to prepare polyurethane elastomers, polyurethane foams, polyurethane coatings or polyurethane adhesives; preferably, it is used to prepare high-performance polyurethane elastomers, flame-retardant polyurethane foams, long-lasting anti-corrosion coatings or structural adhesives.

[0026] In some embodiments, the method of application involves processing the polyurethane material into the desired article through casting, spraying, molding, or foaming processes. Preferably, when used as a coating, the reaction solution of the polyurethane material is directly applied to the surface of a substrate, and a coating is formed after curing.

[0027] Beneficial effects:

[0028] (1) The core of this invention lies in obtaining a polyurethane material with synergistic improvement in comprehensive performance, which is achieved by introducing a specific chain extender containing phosphorus-containing phenanthrene groups and cashew phenol groups as a key functional component. This material utilizes the synergistic effect of the rigid phosphorus-containing phenanthrene groups, flexible aliphatic long chains and active hydroxyl groups within the chain extender molecule to achieve significant reinforcement, toughening and flame retardancy simultaneously without sacrificing the inherent elasticity of the material, thereby directly solving the problems of insufficient strength and toughness and flammability of traditional materials.

[0029] (2) This invention provides a high-strength, tough, and flame-retardant polyurethane material with excellent comprehensive performance and its preparation method. This invention integrates strengthening, toughening, and flame-retardant functions in the material preparation stage by introducing a multifunctional chain extender with a specific molecular structure. The resulting polyurethane material (with only 5-10 wt% of this chain extender in the bio-based polyol added) exhibits tensile strength increased by more than 100% to over 40 MPa, elongation at break increased to over 390%, and it can pass the UL-94V-0 vertical burning test, fundamentally solving the technical contradiction of the difficulty in synergistically improving the strength, toughness, and flame retardancy of traditional polyurethane materials.

[0030] (3) The technical solution of the present invention has an inherent molecular synergistic effect and process simplicity. As a multifunctional component, the chain extender replaces the chain extender and flame retardant added separately in the traditional solution, avoiding problems such as poor compatibility, weak interface, and uneven performance that may be caused by physical blending. Its "rigid and flexible" molecular design allows it to play the roles of reinforcing nodes, toughening segments, and flame retardant units in the polyurethane network, achieving "multiple effects with one agent" and simplifying the formulation and process.

[0031] (4) The polyurethane material prepared by this invention has excellent mechanical properties, flame retardant properties, and good sustainability. Its main raw materials, including polyols and chain extender main chains, are derived from renewable resources such as cashew nut shell powder and vegetable oils. This material meets the stringent requirements for material strength and flame retardancy in high-end application fields such as transportation, electronics, and construction, while conforming to the trend of green environmental protection and sustainable development. Attached Figure Description

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0033] Figure 1 Infrared spectrum of trispinyl phosphate containing hydroxylated phosphorus-containing phenanthrene groups;

[0034] Figure 2 Scanning electron microscope (SEM) images of the liquid nitrogen brittle fracture sections of the polyurethane materials prepared in Comparative Example 1 and Example 2;

[0035] Figure 3 The strain-stress curves of the polyurethane materials prepared in Comparative Example 1 and Examples 1 and 2 are shown.

[0036] Figure 4 The strain-stress curves of the polyurethane materials prepared in Comparative Example 2 and Example 3 are shown.

[0037] Figure 5 Strain-stress curves of polyurethane materials prepared in Comparative Examples 1, 3, 4 and 1;

[0038] Figure 6 Dynamic thermomechanical analysis (DMA) curves of the polyurethane materials prepared in Comparative Example 1, Example 1, and Example 2;

[0039] Figure 7 Thermogravimetric analysis (TGA) curves of the polyurethane materials prepared in Comparative Example 1 and Example 2;

[0040] Figure 8 This is a comparison chart showing the vertical combustion test results of the polyurethane materials prepared in Comparative Example 1, Example 1, and Example 2. Detailed Implementation

[0041] The present invention will be further described in detail below with reference to specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0042] In this embodiment of the invention, the experimental methods described are conventional methods unless otherwise specified; the reagents described are commercially available unless otherwise specified.

[0043] The sources of the raw materials used in the embodiments of the present invention are as follows:

[0044]

[0045] The tough, flame-retardant polyurethane material provided by this invention is prepared by reacting bio-based polyol, polyisocyanate, and a cashew nut shell chain extender containing phosphorus-phenanthroline groups. The chain extender comprises 5-20 wt% of the bio-based polyol. The cashew nut shell chain extender containing phosphorus-phenanthroline groups has a structure of hydroxylated tricaenoic acid phosphate containing phosphorus-phenanthroline groups. This molecule possesses a flexible long-chain structure derived from cashew nut shells, a rigid flame-retardant group provided by 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), and terminal hydroxyl groups for participating in the polymerization reaction.

[0046] Example 1:

[0047] (1) Dissolve 0.3 mol cashew phenol and 0.3 mol triethylamine in 125 mL dichloromethane, and slowly add 0.1 mol phosphorus oxychloride dropwise over 1 h at room temperature. After the addition is complete, heat the mixture under reflux at 40 °C for 6 h. After the reaction is complete, cool and filter the mixture. Wash the filtrate three times with water and remove the solvent by rotary evaporation to obtain tricaenoic acid phosphate.

[0048] (2) 0.2 mol of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was heated to 140 °C under nitrogen protection to completely melt it and maintained at this temperature for 30 min. 0.15 mol of the tricalycanthoxyphosphate synthesized in step (1) was added and the temperature was raised to 175 °C under nitrogen protection for 24 h. After the reaction was completed, the crude product was dissolved in anhydrous ethanol (75 mL) and washed with 300 mL of deionized water in an oil bath at 100 °C for 30 min. The washing was repeated 4 times. Finally, the tricalycanthoxyphosphate containing the phosphaphenanthrene group was obtained by rotary evaporation.

[0049] (3) Take 0.1 mol of the tricalycanthoxyphenanthrene-containing tricalycanthoxyphosphate synthesized in step (2), 0.47 mol of thioglycerol, and 0.002 mol of 2,2-dimethoxy-2-phenylacetophenone, and irradiate them with a 365 nm ultraviolet lamp at 35 °C (irradiance approximately 6 mW / cm²). 2 The reaction was carried out for 36 hours. After the reaction was completed, dichloromethane (20 mL) was added to dissolve the contents, followed by the addition of ethanol-water (V). EtOH :V H2O A mixture of 1:3 to 1:5 (total volume 100 mL) was stirred at room temperature for 1.5 h, allowed to stand and separate into layers, and the lower water-alcohol phase was removed. The washing process was repeated four times. Finally, the organic phase was rotary evaporated to obtain hydroxylated tricalycanthoxyphosphate (chain extender) containing phosphorus-phenanthrene groups.

[0050] (4) Hydrochloric acid (0.15 mol) was mixed with acetone (60 ml), and then epoxidized soybean oil (0.1 mol) was added dropwise to the mixture over 1 h with stirring. After mixing, the flask was placed in an oil bath and stirred at about 40 °C for 2 h. After the reaction was completed, the acetone was evaporated to remove it, and an ethyl acetate-water (3:1) mixture was added to the reaction mixture to form two separate phases. The organic phase separated from the two layers was washed with plenty of water until the pH was neutral. The solvent was then evaporated to remove it, yielding a yellow viscous compound (hydroxylated epoxidized soybean oil). The hydroxyl value of the obtained hydroxylated epoxidized soybean oil was 300 mg KOH / g, the viscosity was 5600 mPa·s, and the epoxy value was 0.2%.

[0051] (5) Dissolve 1g of hydroxylated epoxidized soybean oil synthesized in step (4), 1.5g of L-lysine diisocyanate (L-LDI), and 0.05g of hydroxylated tricalycanthoxyphosphate containing phosphorus heterophenanthrene groups synthesized in step (3) in 4 mL of catalyst solution (5mg Sn(Oct)2 dissolved in 20 mL C2H4Cl2), and stir at 35 °C for 5 hours under nitrogen protection. Pour the resulting polyurethane solution into a polytetrafluoroethylene mold (10cm×10cm×0.2cm), and cure at 35 °C for 24 h and 80 °C for 1 h respectively to obtain a strong and tough flame-retardant polyurethane material.

[0052] Example 2:

[0053] (1) Dissolve 0.3 mol cashew phenol and 0.3 mol triethylamine in 125 mL dichloromethane, and slowly add 0.1 mol phosphorus oxychloride dropwise over 1 h at room temperature. After the addition is complete, heat the mixture under reflux at 40 °C for 6 h. After the reaction is complete, cool and filter the mixture. Wash the filtrate three times with water and remove the solvent by rotary evaporation to obtain tricaenoic acid phosphate.

[0054] (2) 0.2 mol DOPO was heated to 140 °C under nitrogen protection to completely melt it and maintained at this temperature for 30 min. 0.15 mol of the tricalycanthoxyphosphate synthesized in step (1) was added and the temperature was raised to 175 °C under nitrogen protection for 24 h. After the reaction was completed, the crude product was dissolved in anhydrous ethanol (75 mL) and washed with 300 mL of deionized water in a 100 °C oil bath for 30 min. The washing was repeated 4 times. Finally, the tricalycanthoxyphosphate containing phosphorus phenanthrene groups was obtained by rotary evaporation.

[0055] (3) Take 0.1 mol of the tricalycanthoxyphenanthrene-containing tricalycanthoxyphosphate synthesized in step (2), 0.47 mol of thioglycerol, and 0.002 mol of 2,2-dimethoxy-2-phenylacetophenone, and irradiate them with a 365 nm ultraviolet lamp at 35 °C (irradiance approximately 6 mW / cm²). 2 The reaction was carried out for 36 hours. After the reaction was completed, dichloromethane was added to dissolve the solution, and then ethanol-water (V) was added. EtOH :V H2O A mixture of 1:3 to 1:5 (total volume 100 mL) was stirred at room temperature for 1.5 h, allowed to stand and separate into layers, and the lower water-alcohol phase was removed. The washing process was repeated four times. Finally, the organic phase was rotary evaporated to obtain hydroxylated tricalycanthoxyphosphate containing phosphorus-containing phenanthrene groups.

[0056] (4) Hydrochloric acid (0.15 mol) was mixed with acetone (60 ml), and then epoxidized soybean oil (0.1 mol) was added dropwise to the mixture over 1 h with stirring. After mixing, the flask was placed in an oil bath and stirred at about 40 °C for 2 h. After the reaction was completed, the acetone was evaporated to remove it, and an ethyl acetate-water (3:1) mixture was added to the reaction mixture to form two separate phases. The organic phase separated from the two layers was washed with plenty of water until the pH was neutral. The solvent was then evaporated to remove it, yielding a yellow viscous compound (hydroxylated epoxidized soybean oil). The hydroxyl value of the obtained hydroxylated epoxidized soybean oil was 300 mg KOH / g, the viscosity was 5600 mPa·s, and the epoxy value was 0.2%.

[0057] (5) Dissolve 1g of hydroxylated epoxidized soybean oil, 1.5g of lysine diisocyanate (L-LDI), and 0.10g of the hydroxylated tricalycanthoxyphosphate synthesized in step (3) in 4mL of catalyst solution (5mg Sn(Oct)2 dissolved in 20mL C2H4Cl2), and stir at 35℃ for 5 hours under nitrogen protection. Pour the resulting polyurethane solution into a polytetrafluoroethylene mold (10cm×10cm×0.2cm), and cure at 35℃ for 24 h and 80℃ for 1 h respectively to obtain a strong and tough flame-retardant polyurethane material.

[0058] Example 3:

[0059] (1) Dissolve 0.3 mol cashew phenol and 0.3 mol triethylamine in 125 mL tetrahydrofuran, and slowly add 0.1 mol phosphorus oxychloride dropwise over 1 h at room temperature. After the addition is complete, heat the mixture under reflux at 60 °C for 7 h. After the reaction is complete, cool and filter the mixture. Wash the filtrate three times with water and remove the solvent by rotary evaporation to obtain tricaenoic acid phosphate.

[0060] (2) 0.2 mol DOPO was heated to 140 °C under nitrogen protection to completely melt it and maintained at this temperature for 30 min. 0.15 mol of the tricalycanthoxyphosphate synthesized in step (1) was added and the temperature was raised to 175 °C under nitrogen protection for 24 h. After the reaction was completed, the crude product was dissolved in anhydrous ethanol (75 mL) and washed with 300 mL of deionized water in a 100 °C oil bath for 30 min. The washing was repeated 4 times. Finally, the tricalycanthoxyphosphate containing phosphorus phenanthrene groups was obtained by rotary evaporation.

[0061] (3) Take 0.1 mol of the tricalycanthoxyphenanthrene-containing tricalycanthoxyphosphate synthesized in step (2), 0.35 mol of thioglycerol, and 0.002 mol of 1-hydroxycyclohexylphenyl ketone, and irradiate them with a 365 nm ultraviolet lamp at 40 °C (irradiance approximately 6 mW / cm²). 2The reaction was carried out for 24 hours. After the reaction was completed, dichloromethane was added to dissolve the solution, and then ethanol-water (V) was added. EtOH :V H2O A mixture of 1:3 to 1:5 (total volume 100 mL) was stirred at room temperature for 1.5 h, allowed to stand and separate into layers, and the lower water-alcohol phase was removed. The washing process was repeated four times. Finally, the organic phase was rotary evaporated to obtain hydroxylated tricalycanthoxyphosphate containing phosphorus-containing phenanthrene groups.

[0062] (4) Dissolve 1g castor oil (hydroxyl value 162 mg KOH / g, viscosity 840 mPa·s) and 0.42g isophorone diisocyanate in 4mL dimethylacetamide. Under nitrogen protection, react at 80 ℃ for 1.5h. Add 0.10g of hydroxylated tricalycanthoxyphosphate synthesized in step (3) containing phosphorus phenanthrene groups. Stir for 30min. Add 50 mg dibutyltin dilaurate. Stir evenly and pour into a polytetrafluoroethylene mold (10cm×10cm×0.2cm). Cure at 60 ℃ for 4h and 80 ℃ for 4h in sequence to obtain high-strength, tough, flame-retardant polyurethane material.

[0063] Comparative Example 1:

[0064] 1 g of hydroxylated epoxidized soybean oil and 1.5 g of L-lysine diisocyanate (L-LDI) were dissolved in 4 mL of catalyst solution (5 mg of Sn(Oct)2 dissolved in 20 mL of C2H4Cl2). The mixture was stirred at 35 °C for 5 hours under nitrogen protection. The resulting polyurethane solution was poured into a polytetrafluoroethylene mold and cured sequentially at 35 °C for 24 h and 80 °C for 1 h to obtain the polyurethane material.

[0065] Comparative Example 2:

[0066] 1g castor oil and 0.42g isophorone diisocyanate were dissolved in 4mL dimethylacetamide and reacted at 80℃ for 1.5h under nitrogen protection. 50mg dibutyltin dilaurate was added, and the mixture was stirred evenly and poured into a polytetrafluoroethylene mold. The mixture was then cured at 60℃ for 4h and 80℃ for 4h to obtain a polyurethane material.

[0067] Comparative Example 3:

[0068] 1 g of hydroxylated epoxidized soybean oil, 1.5 g of L-lysine diisocyanate (L LDI), and 0.05 g of 1,4-butanediol were dissolved in 4 mL of catalyst solution (5 mg of Sn(Oct)2 dissolved in 20 mL of C2H4Cl2). The mixture was stirred at 35 °C for 5 hours under nitrogen protection. The resulting polyurethane solution was poured into a polytetrafluoroethylene mold and cured sequentially at 35 °C for 24 h and 80 °C for 1 h to obtain the polyurethane material.

[0069] Comparative Example 4:

[0070] 1 g of hydroxylated epoxidized soybean oil and 1.5 g of L-lysine diisocyanate (L-LDI) were dissolved in 4 mL of catalyst solution (5 mg of Sn(Oct)2 dissolved in 20 mL of C2H4Cl2). The mixture was stirred at 35 °C for 5 hours under nitrogen protection. Then, 1 g of flame retardant resorcinol diphosphate was added and stirred for 30 min. The resulting polyurethane solution was poured into a polytetrafluoroethylene mold and cured sequentially at 35 °C for 24 h and 80 °C for 1 h to obtain the flame-retardant polyurethane material.

[0071] Example 4 Material Characterization and Performance Testing

[0072] 1. Fourier transform infrared spectroscopy characterization of chain extenders

[0073] Figure 1 The Fourier transform infrared (FTIR) spectra of the raw material, intermediate, and product of the chain extender in Example 1 are shown. Compared to the raw material cashew phenol, the intermediate tricainol phosphate exhibits a higher Fourier transform infrared (FTIR) spectrum at approximately 1457 cm⁻¹. -1 A distinct strong absorption peak appeared at 1051 cm⁻¹, which was attributed to the stretching vibration of the characteristic functional group P=O in phosphate esters, confirming the successful synthesis of tricalycanthoxyphosphate. Subsequently, in the spectrum of the tricalycanthoxyphosphate containing phosphorus heterophenanthrene groups obtained after the introduction of DOPO, a peak was observed at 1051 cm⁻¹. -1 Bending vibrational absorptions belonging to PO-Ph were observed nearby, indicating that the DOPO structure has been integrated into the molecular backbone. Finally, in the spectrum of the hydroxylated product, the 1020 cm⁻¹... -1 The appearance of a stretching vibration peak from the CO bond in the primary alcohol nearby confirms the successful introduction of the -CH2OH group from thioglycerol. The sequential appearance and regular changes of these characteristic peaks provide strong evidence for the successful synthesis of this chain extender.

[0074] 2. Scanning electron microscope image of the liquid nitrogen brittle fracture section of the polyurethane sample.

[0075] Figure 2 The liquid nitrogen brittle fracture sections of polyurethane samples prepared in Comparative Example 1 and Example 2, as observed by scanning electron microscopy, are shown. Due to the use of chain extenders, the fracture surface gradually evolved from a smooth and flat brittle fracture characteristic (Comparative Example 1) to a rough, wrinkled fracture with silver streaks and shear bands, and further developed into a significant dimple structure and filamentous plastic flow (Example 2). This indicates that the introduction of the chain extender in this invention effectively induced a ductile fracture mechanism. Through the synergistic effect of energy dissipation of the flexible cashew phenol long chain and physical crosslinking of the rigid phosphaphenanthrene groups, a balance between high strength and high toughness in polyurethane materials is achieved.

[0076] 3. Tensile property test

[0077] The mechanical properties of polyurethane strips were tested using a universal tensile testing machine at a tensile rate of 30 mm / min, according to GB / T 1040.

[0078] Figure 3 The stress-strain curves of the polyurethanes prepared in Comparative Example 1, Example 1, and Example 2 are presented. As shown in the figure, the epoxy soybean oil-based polyurethane with 5% of the chain extender of the present invention (Example 1) achieved a tensile strength of 43.26 MPa, which is approximately 132% higher than that of pure epoxy soybean oil-based polyurethane (Comparative Example 1); at the same time, the elongation at break also increased significantly from 302.68% to 391.74%. When the amount of chain extender added was increased to 10% (Example 2), the tensile strength of the material further increased to 48.22 MPa, and the elongation at break was comparable to that of the matrix. This indicates that the chain extender in the examples of the present invention can significantly improve the strength of polyurethane while basically maintaining or even improving the toughness of the material.

[0079] Figure 4 The stress-strain curves of the polyurethanes prepared in Comparative Example 2 and Example 3 are compared. The results show that, compared with pure castor oil-based polyurethane (Comparative Example 2), the tensile strength of the polyurethane with 10% chain extender added (Example 3) increased significantly from 1.91 MPa to 3.03 MPa; more importantly, its elongation at break increased significantly from 290% to 486%, fully demonstrating that the chain extender has a significant toughening effect while strengthening the polyurethane.

[0080] Figure 5 The stress-strain curves for Comparative Examples 1, 3, 4, and 1 are shown. Analysis reveals that pure epoxy soybean oil-based polyurethane (Comparative Example 1) exhibits low tensile strength and moderate elongation at break. Comparative Example 3, with the addition of the traditional small-molecule chain extender BDO, shows an increased yield strength of 31 MPa and a breaking strength of 28 MPa, but its elongation at break drops sharply to 144%, exhibiting a clear "reinforced but brittle" characteristic. Comparative Example 4, with the addition of the traditional flame retardant RDP, achieves flame retardancy, but its mechanical properties are severely degraded, with a tensile strength of only about 8.4 MPa and a significant decrease in elongation. In contrast, the polyurethane with 5% chain extender (Example 1) maintains a high elongation at break while achieving a tensile strength of 43.3 MPa, demonstrating significantly better overall mechanical properties than Comparative Examples 1, 3, and 4. The above results show that although traditional BDO chain extenders can improve strength to a certain extent, they sacrifice material toughness; while the chain extender of this invention achieves a balance between high strength and high toughness through the synergistic effect of flexible cashew phenol long chains and rigid phosphaphenanthrene groups, overcoming the defect of "imbalance between rigidity and flexibility" in traditional additives.

[0081] 4. Dynamic Thermomechanical Analysis (DMA) Test

[0082] The dynamic mechanical properties of polyurethane specimens were tested using a dynamic thermomechanical analyzer (model TA Q800) in tensile mode at a frequency of 1 Hz, a heating rate of 3 ℃ / min, and a temperature range of -80 ℃ to 120 ℃.

[0083] Figure 6 Dynamic thermomechanical analysis (DMA) curves of the polyurethanes prepared in Comparative Example 1, Example 1, and Example 2 are presented. As shown in the figure, in the glassy state and rubber plateau region, the storage modulus shows a trend of first decreasing and then increasing: the pure epoxy soybean oil-based polyurethane (Comparative Example 1) has the highest modulus due to its highly crystalline hard segments. At a 5% addition (Example 1), the modulus decreases, corresponding to the transformation of the hard segments from "closely crystalline" to "loosely ordered," while at a 10% addition (Example 2), the modulus rebounds, indicating the formation of a more rigid network structure. Meanwhile, the glass transition temperature of the soft segments continuously decreases with increasing chain extender content (53.16 ℃ → 47.11 ℃ → 46.25 ℃), and the tanδ peak gradually becomes sharper and the peak value gradually increases (0.611 → 0.639 → 0.767). This reflects that the chain extender promotes the ordered aggregation of hard segments and microphase separation, improving the purity of the soft segment phase and enhancing the uniformity of the motion environment, which is direct evidence of improved microphase separation.

[0084] 5. Thermogravimetric analysis (TGA) test

[0085] Figure 7The thermogravimetric analysis (TGA) curves of the polyurethanes prepared in Comparative Example 1 and Example 2 are presented. As shown in the figure, no significant weight loss was observed in either sample within the temperature range of 30-210℃, indicating that the materials are stable at normal operating temperatures and that the introduction of the chain extender did not affect their basic thermal behavior. Above 210℃, the samples exhibited phased weight loss: the 210-275℃ phase mainly corresponds to the breaking and depolymerization of urethane bonds in the hard segments; at 275℃, the pure epoxy soybean oil-based polyurethane (Comparative Example 1) retained 78.08%, while the polyurethane with 10% chain extender (Example 2) retained 80.08%. The 275-450℃ phase represents the random breaking and pyrolysis of CO and CC bonds in the soft segments, which is the main decomposition range of the material. In both phases, the residual mass of Example 2 was consistently higher than that of Comparative Example 1, indicating that the chain extender, through the synergistic effect of its rigid benzene ring promoting crosslinking and phosphorus group catalyzing char formation, effectively delayed the decomposition of both hard and soft segments and promoted the formation of a protective char layer. After 450 °C, the weight loss in Comparative Example 1 tended to plateau, while Example 2 continued to lose weight up to 475 °C, ultimately retaining 8.7%. This stage of weight loss is related to the deep carbonization and structural reorganization of the initially formed char layer: the chain extender promotes further dehydrogenation, cyclization, and aromatization of the generated char layer at higher temperatures, releasing small molecules while transforming into a denser and more stable structure, thereby improving the quality of the char layer. In addition, free radicals such as PO· generated by the high-temperature cracking of phosphorus-containing groups can enter the gas phase and capture active free radicals (such as H· and OH·) in the combustion chain reaction, indicating that the gas-phase flame retardant mechanism is activated at this time, forming a synergy with the condensed-phase flame retardancy to jointly improve the flame retardant performance of the material.

[0086] To evaluate and compare the long-term thermal stability of the two samples at constant temperature, based on the aforementioned thermogravimetric (TG) analysis data, the apparent thermal decomposition kinetic parameters of the samples were calculated using the method specified in the national standard GB / T 1544-2015. The Arrhenius equation was established, and its long-term isothermal thermal aging behavior at a specified temperature was then extrapolated and predicted. The activation energy of Comparative Example 1 was calculated to be 110409.96 J / mol, and the activation energy of Example 2 was 111342.64 J / mol. Using the Arrhenius equation, the reaction rate constant k1 of Comparative Example 1 at 240 °C was calculated to be 5.764044 min. -1 The reaction rate constant k2 in Example 2 is 4.632168 min. -1Finally, using first-order reaction kinetics, the time required for Comparative Example 1 to reach the same conversion rate (α=10%) was calculated to be 1.1 s, and for Example 2, it was 1.4 s; when α=30%, the time required for Comparative Example 1 was 3.7 s, and for Example 2, it was 4.6 s. The calculation results show that at 240 °C, the time required for Example 2 to reach the same conversion rate was approximately 20-30% longer than that for Comparative Example 1, which is consistent with its higher apparent activation energy, indicating superior thermal stability. To evaluate and compare the long-term thermal stability of the two samples at constant temperature, based on the above thermogravimetric (TG) analysis data, the apparent thermal decomposition kinetic parameters of the samples were calculated using the method specified in the national standard GB / T 1544-2015. The Arrhenius equation was established, and then extrapolated to predict their long-term isothermal thermal aging behavior at a specified temperature. The activation energy of Comparative Example 1 was calculated to be 110409.96 J / mol, and that of Example 2 was 111342.64 J / mol. Using the Arrhenius equation, the reaction rate constant k1 of Comparative Example 1 at a temperature of 240 °C was calculated to be 5.764044 min. -1 The reaction rate constant k2 in Example 2 is 4.632168 min. -1 Finally, using first-order reaction kinetics, the time required for Comparative Example 1 to reach the same conversion rate (α = 10%) was calculated to be 1.1 s, and for Example 2, it was 1.4 s; when α = 30%, the time required for Comparative Example 1 was 3.7 s, and for Example 2, it was 4.6 s. The calculation results show that at 240 °C, the time required for Example 2 to reach the same conversion rate was approximately 20-30% longer than that for Comparative Example 1, which is consistent with its higher apparent activation energy and indicates better thermal stability.

[0087] 6. Vertical Burning Test

[0088] Vertical burning (UL-94) test: The polyurethane prepared in the examples was subjected to vertical burning test according to GB / T 2408-2008 "Determination of flammability of plastics - Horizontal and vertical methods".

[0089] Figure 8 The table shows photographs of the vertical burning tests for Comparative Example 1, Example 1, and Example 2. Table 1 presents the results of the vertical burning tests for Comparative Example 1, Example 1, and Example 2. The table shows that pure epoxy soybean oil-based polyurethane (Comparative Example 1) continued to burn until exhausted after contact with the flame, failing to exhibit effective flame retardant properties. The flame retardancy of the material was significantly improved after the introduction of the chain extender. With increasing addition amount, the flaming burning time (t1, t2) after the sample left the flame source showed a significant shortening trend.

[0090] Table 1. Test results of the vertical combustion method

[0091]

[0092] 7. Limiting Oxygen Index Test

[0093] Limiting oxygen index (LOI) test: The limiting oxygen index of the polyurethane prepared in the examples was determined in accordance with GB / T 2406.2-2009 "Determination of flammability by oxygen index method for plastics - Part 2: Room temperature test".

[0094] Table 2 shows the limiting oxygen index (LOI) test results for Comparative Example 1, Example 1, and Example 2. The table shows that the LIO of the polyurethane material increased significantly from 18% in Comparative Example 1 to 31% in Example 2. In particular, the LOI value of Example 2 exceeded 30%, indicating that the material has reached an extremely high flame retardant level, which is well corroborated by its excellent V-0 rating in the vertical burning test.

[0095] Table 2 Limiting Oxygen Index Test Results

[0096]

[0097] The strengthening and flame-retardant mechanism of the polyurethane material described in this invention lies in the following: the cashew phenol-based chain extender containing phosphorus-containing phenanthrene groups reacts with isocyanate through multiple hydroxyl groups at its ends during polymerization, thus chemically bonding into the polyurethane network. The rigid DOPO groups in its molecule act as physical crosslinking points, enhancing the intermolecular forces and playing a role in both gas-phase and condensed-phase flame-retardant mechanisms during combustion. Its flexible cashew phenol long carbon chains (C15 unsaturated alkyl groups) act as flexible spacers, endowing the network chain segments with mobility and effectively dissipating stress, thereby synergistically achieving high strength, high toughness, and excellent flame retardancy in the material.

[0098] This invention provides a high-strength, tough, flame-retardant polyurethane containing a phosphorus-containing phenanthrene / cashew phenol-based chain extender, along with its preparation method and application. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A method for preparing a phosphenanthrene / cashew phenolic chain extender, characterized in that, Includes the following steps: (1) Dissolve cashew phenol and acid-binding agent in an organic solvent, add phosphorylation reagent to carry out the first reaction, and obtain tri-cashew phenol phosphate; (2) In a nitrogen atmosphere, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is heated and melted, and then the tricalycanthoxyphosphate obtained in step (1) is added to carry out a second reaction to obtain tricalycanthoxyphosphate containing phosphaphenanthrene groups. (3) The tri-coryl phosphate ester containing phosphorus phenanthrene group obtained in step (2) is subjected to photocatalytic reaction with a compound containing thiol and hydroxyl groups in the presence of a photoinitiator to obtain the product.

2. The preparation method according to claim 1, characterized in that, In step (1), the acid-binding agent is any one of triethylamine, pyridine, or potassium carbonate; and / or, the organic solvent is any one or more of dichloromethane, tetrahydrofuran, toluene, or N,N-dimethylformamide; and / or, the phosphorylation reagent is any one or more of phosphorus oxychloride, phosphorus oxybromide, or phosphorus pentoxide; and / or, the molar ratio of cashew phenol, the acid-binding agent, and the phosphorylation reagent is 2.8~3.2:2.8~3.2:1; and / or, the first reaction is carried out at a temperature of 30~60℃ for a time of 4~8h.

3. The preparation method according to claim 1, characterized in that, In step (2), the heating and melting are carried out at a temperature of 140~160℃ for 0.5~1h; and / or, the molar ratio of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to tricalycanthoxyphosphate is 1.2~1.5:1; and / or, the second reaction is carried out under a nitrogen atmosphere at a temperature of 160~180℃ for 18~30h.

4. The preparation method according to claim 1, characterized in that, In step (3), the compound containing thiol and hydroxyl groups is any one or more of thioglycerol, mercaptoethanol, and 2,3-dimercapto-1-propanol; and / or, the photoinitiator is any one or more of 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexylphenyl ketone, or benzoin dimethyl ether; and / or, the molar ratio of the trisalicylic acid phosphate containing phosphorus phenanthrene groups, the compound containing thiol and hydroxyl groups, and the photoinitiator is 1:3.0~5.0:0.005~0.03; and / or, the photocatalytic reaction has an ultraviolet wavelength of 320~400 nm and a light intensity of 10~100 mW / cm². 2 The temperature is 25~45℃, and the time is 24~48h.

5. The phosphenanthrene / cashew phenolic chain extender prepared by the preparation method according to any one of claims 1 to 4.

6. A high-strength, tough, flame-retardant polyurethane containing a phosphorus-containing phenanthrene / cashew phenol-based chain extender, characterized in that, It is made from the following components in parts by mass: 100 parts of vegetable oil-based polyols; 40-150 parts of polyisocyanate; 5-20 parts of the phosphenanthrene / cashew phenolic chain extender as described in claim 5; Catalyst 0.1~5 parts.

7. The high-strength, tough, flame-retardant polyurethane according to claim 6, characterized in that, The plant oil-based polyol is hydroxylated epoxidized soybean oil or castor oil; and / or, the polyisocyanate is any one or more of hexamethylene diisocyanate, isophorone diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, or L-lysine diisocyanate; and / or, the catalyst is any one or more of stannous octoate, dibutyltin dilaurate, or bismuth neodecanoate.

8. The high-strength, tough, flame-retardant polyurethane according to claim 7, characterized in that, The hydroxylated epoxidized soybean oil is prepared by the following method: hydrochloric acid and acetone are mixed, epoxidized soybean oil is added under stirring, and the mixture is reacted at 35~45 ℃ for 1.5~3 h. After the reaction is completed, the reaction solution is post-treated to obtain the final product.

9. The high-strength, tough, flame-retardant polyurethane according to claim 8, characterized in that, The molar ratio of hydrochloric acid to epoxidized soybean oil is 3:1~2; and / or the post-treatment specifically includes: first evaporating to remove acetone from the reaction solution, then extracting and washing with water until neutral, and finally evaporating to remove the solvent; and / or the epoxidized soybean oil has an epoxy value of 5.0%~7.0% and a viscosity of 300~700 mPa·s; and / or the hydroxylated epoxidized soybean oil has a hydroxyl value of 200~350 mg KOH / g, a viscosity of 1000~10000 mPa·s, and an epoxy value of 0.1%~0.5%.

10. The method for preparing the high-strength, tough, flame-retardant polyurethane according to claim 6, characterized in that, The process includes the following steps: polymerizing a vegetable oil-based polyol, a polyisocyanate, the phosphenanthrene / cashew phenolic chain extender as described in claim 1, and a catalyst in an organic solvent, followed by curing and molding after the reaction is complete to obtain the final product.

11. The preparation method according to claim 10, characterized in that, The organic solvent is dichloroethane or dimethylacetamide; and / or, the curing process involves first curing at 35-60 °C for 4-24 h, followed by curing at 70-80 °C for 1-4 h.

12. The preparation method according to claim 10, characterized in that, When the plant oil-based polyol is hydroxylated epoxidized soybean oil, the polymerization reaction is a one-step process: the hydroxylated epoxidized soybean oil, the polyisocyanate, the phosphenanthrene / cashew phenolic chain extender and the catalyst are dissolved in an organic solvent, stirred at 30~40 ℃ for 4~6 h and then solidified.

13. The preparation method according to claim 9, characterized in that, When the plant oil-based polyol is castor oil, the polymerization reaction is a prepolymerization method: the castor oil and the polyisocyanate are dissolved in an organic solvent and reacted at 70~90 °C for 1~2 h to obtain a prepolymer solution. Then, the phosphenanthrene / cashew phenolic chain extender is added and stirred for 0.5~1 h. Finally, a catalyst is added, mixed evenly, and then solidified.

14. The high-strength, tough, flame-retardant polyurethane containing phosphorus-containing phenanthrene / cashew phenol-based chain extender as described in claim 6, characterized in that, The high-strength and tough flame-retardant polyurethane has a tensile strength of 3~50MPa, an elongation at break of 250%~500%, a flaming burning time of 5~16s, and a limiting oxygen index of 25% or higher.

15. The use of the high-strength, tough, flame-retardant polyurethane containing phosphorus-containing phenanthrene / cashew phenolic chain extender as described in claim 6 in the preparation of polyurethane elastomers, polyurethane foams, polyurethane coatings, or polyurethane adhesives.

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