Preparation method of flame-retardant and aging-resistant high-transparency polyurethane

Abstract

The application discloses a kind of preparation methods of flame-retardant aging-resistant high-transparency polyurethane, the polyurethane is first with 2-amino-1,3-propanediol, 2-chloro-4,6-diphenyl-1,3,5-triazine, diphenyl phosphorochloridate and triphenylchlorosilane composite preparation DADT, then DADT is mixed with polyether polyol, isocyanate to obtain;The preparation method of the application is simple, the process is easy to control, the obtained polyurethane material limit oxygen index reaches 29.6%, meets commercial flame-retardant standard and reaches UL-94 V-0 flame-retardant grade;Material has excellent aging resistance, heat-oxygen tensile strength retention rate is 88.5%, heat-oxygen breaking elongation retention rate is 77.4%, and ultraviolet breaking elongation retention rate is 71.4%, can be applied to automobile ultraviolet protection diaphragm, flame-retardant filled foam, fire guide sign protection film and the like scene.

Description

Technical Field

[0001] This invention belongs to the field of polymer composite materials and relates to a method for preparing a flame-retardant, aging-resistant, and highly transparent polyurethane. Background Technology

[0002] Polymer materials, especially polyurethane (PU), are widely used in key sectors of the national economy such as construction, transportation, electronics, and home furnishings due to their excellent mechanical properties, processing adaptability, and design flexibility. However, the inherent chemical bonds in the polyurethane molecular structure (such as urethane bonds and ester / ether bonds) are susceptible to thermo-oxidative aging and ultraviolet aging during long-term use due to the effects of ultraviolet radiation, heat, oxygen, and moisture. This leads to yellowing, surface chalking, and a sharp decline in mechanical properties (especially toughness), severely shortening its service life. Furthermore, most polyurethanes are flammable materials, exhibiting high heat release rates during combustion, accompanied by molten droplets and dense smoke, posing significant safety hazards. Therefore, simultaneously endowing polyurethane with long-lasting anti-aging properties and inherent flame-retardant properties is crucial for its application in high-performance, long-life, and safe and reliable fields.

[0003] To address these challenges, existing technologies typically employ a physical blending solution of flame retardants and anti-aging agents. For flame retardancy, additive flame retardants based on elements such as phosphorus, nitrogen, and silicon, such as phosphonates, melamine derivatives, and organosilicon compounds, are widely used. For anti-aging, this relies on a combination of UV absorbers (such as benzotriazoles and triazines) and antioxidants (such as hindered phenols and phosphites). However, this discrete physical blending approach has several inherent drawbacks: First, different additives exhibit varying compatibility and dispersibility within the polymer matrix, leading to migration and precipitation (blooming) during long-term use or exposure to high temperatures and solvents, resulting in rapid functional degradation and potential contamination of contact surfaces, causing significant decreases in light transmittance and increases in haze. Second, there is a lack of synergistic effects between various small-molecule additives and between them and the matrix; some even exhibit antagonistic effects. For example, the acidic decomposition products of some flame retardants may catalyze and accelerate the hydrolytic aging of polyurethane, while some antioxidants may interfere with the formation of the intumescent flame-retardant carbon layer. Secondly, to achieve the required overall performance, a high total addition amount (typically >30%) is often necessary. This inevitably impairs the original mechanical properties of the matrix material (such as plasticization and embrittlement), processing fluidity, and severely affects optical transparency. Finally, the complex formulation system increases the difficulty of ingredient preparation in the production process, the cost of quality control, and batch instability.

[0004] In recent years, to overcome the drawbacks of physical blending, researchers have begun to explore the design of multifunctional integrated additives. For example, combining UV-absorbing groups with hindered phenolic structures into a single molecule, or synthesizing flame retardants containing both phosphorus and nitrogen. However, most designs still focus on the simple superposition of single-dimensional functions (such as anti-aging only or flame retardancy only), or while attempting to achieve both, their molecular structures fail to achieve deep synergy in the mechanism of action of different functional units, and often neglect the protection of key physical properties of materials (especially optical transparency). Specifically, existing designs often lack a systematic approach to the multi-stage, multi-phase requirements throughout the material's lifecycle, from "initial service aging protection" to "final fire safety flame retardancy." Furthermore, it is difficult to ensure molecular-level compatibility between additive molecules and the matrix while achieving high performance, thus avoiding light scattering problems caused by phase separation or aggregation. An ideal molecule should be able to efficiently and stably absorb ultraviolet light and capture free radicals during the aging stage, while simultaneously decomposing on demand and in an orderly manner during the combustion stage, exerting flame-retardant effects in both the gas and condensed phases, and promoting the formation of a robust and stable protective carbon layer. The realization of all these functions must be based on high compatibility with the matrix and without impairing the original appearance and optical properties of the material (especially transparent or light-colored products). Few existing technologies have reported the ability to precisely and synergistically control these complex processes through a single molecular structure.

[0005] Therefore, developing a novel intramolecular multifunctional integrated additive that can not only efficiently impart excellent UV resistance, heat and oxygen resistance, hydrolysis aging resistance, and high flame retardancy to polyurethane with low addition amounts, but also achieve intrinsic synergy and enhancement of different functional groups in the protective mechanism through its precise molecular structure design, while ensuring excellent compatibility with the polyurethane matrix, thereby maximizing the preservation of the original mechanical and optical properties of the material (such as high transparency and low haze) while imparting multiple functions, has become a technical bottleneck that urgently needs to be overcome in this field. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention aims to provide a method for preparing a flame-retardant, aging-resistant, and highly transparent polyurethane. The polyurethane is first prepared by compounding 2-amino-1,3-propanediol, 2-chloro-4,6-diphenyl-1,3,5-triazine, diphenylphosphine chloride, and triphenylchlorosilane to form DADT. Then, DADT is mixed with polyether polyol and isocyanate to obtain the final product. This invention offers a simple preparation method with easy process control. The resulting polyurethane material has a limiting oxygen index of 29.6%, meeting commercial flame-retardant standards and achieving a UL-94 V-0 flame-retardant rating. The material also exhibits excellent aging resistance, retaining 88.5% of its thermo-oxidative tensile strength, 77.4% of its thermo-oxidative elongation at break, and 71.4% of its UV elongation at break. It can be applied to automotive UV-protective films, flame-retardant filling foams, and protective films for fire hazard signs, among other applications.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a flame-retardant, aging-resistant, and highly transparent polyurethane, comprising the following steps in sequence:

[0009] S1. Preparation of triazine-phosphine ester-silane flame retardant and anti-aging agent

[0010] 2-Amino-1,3-propanediol was added to 100 mL of anhydrous tetrahydrofuran at -5 to 0 °C. 7 mL of triethylamine was then added, and the mixture was stirred until homogeneous. 2-Chloro-4,6-diphenyl-1,3,5-triazine was added dropwise, and the mixture was stirred for 2–3 h. Another 7 mL of triethylamine was added, and the mixture was stirred until homogeneous. Diphenylphosphine chloride was then added dropwise, and the mixture was stirred for 2–3 h. Another 7 mL of triethylamine was added, and the mixture was stirred until homogeneous. Triphenylchlorosilane was then added dropwise, and the reaction was heated to 50 °C and allowed to proceed for 5–6 h. After the reaction was complete, the reaction was quenched with deionized water. The mixture was extracted three times with a mixed solvent of ethyl acetate and deionized water at a volume ratio of 1:1.5, followed by two extractions with a saturated sodium chloride aqueous solution to separate the organic phase. 8 g of anhydrous sodium sulfate was added to the organic phase, and the mixture was distilled under reduced pressure to obtain a triazine-phosphine ester-silane flame retardant and anti-aging agent (DADT).

[0011] The structural formula of the triazine-phosphinic acid ester-silane flame retardant and anti-aging agent is:

[0012] ;

[0013] S2, Preparation of flame-retardant, aging-resistant, and highly transparent polyurethane

[0014] Polyether polyol and triazine-phosphines-silane flame retardant and anti-aging agent were added to a three-necked flask and heated to 120-130°C. The glass container was evacuated and filled with argon gas. The system was then cooled to 80-110°C. Isocyanate was added and stirred for 2 hours. The temperature was lowered to 55-60°C. A chain extender was added and stirred for 1-2 minutes to obtain a polymer emulsion. The emulsion was poured into a polytetrafluoroethylene mold and reacted and cured in an oven at 80°C for 48 hours to obtain a flame-retardant, aging-resistant, and highly transparent polyurethane.

[0015] As a limitation of the preparation method of the present invention, in step S1, the molar ratio between 2-amino-1,3-propanediol and 2-chloro-4,6-diphenyl-1,3,5-triazine, diphenylphosphine chloride, and triphenylchlorosilane is 1:1:1:1.

[0016] As another limitation of the preparation method of the present invention, in step S1, the rate of adding 2-chloro-4,6-diphenyl-1,3,5-triazine, diphenylphosphine chloride, and triphenylchlorosilane is 0.5~0.6 mL / min.

[0017] As a third limitation of the preparation method of the present invention, in step S2, the polyether polyol is polytetrahydrofuran diol with a weight-average molecular weight of 2000.

[0018] As a fourth limitation of the preparation method of the present invention, in step S2, the isocyanate is diphenylmethane diisocyanate or toluene diisocyanate.

[0019] As a fifth limitation of the preparation method of the present invention, in step S2, the chain extender is prepared by adding 0.45g of 1,4-butanediol to 2 mL of N,N-dimethylformamide and stirring until homogeneous.

[0020] As a sixth limitation of the preparation method of the present invention, in step S2, the molar ratio between the polyether polyol and the triazine-phosphines-silane flame retardant and anti-aging agent, isocyanate and chain extender is 15:(1~5):20:5.

[0021] In this invention, the molar ratio between polyether polyol and triazine-phosphines-silane flame retardant and anti-aging agent, isocyanate, and chain extender directly affects the crosslinking density, phase separation degree, flame retardant efficiency, and anti-aging performance of the material. If the molar ratio is less than this, i.e., the flame retardant and anti-aging agent or chain extender is relatively insufficient, or the isocyanate is relatively excessive, excessive rigid hard segments or urethane bonds will be formed. Simultaneously, the flame retardant network will be incomplete, resulting in excessively high material hardness, significantly reduced toughness, increased brittleness, and a tendency to crack under stress or thermal aging. Furthermore, due to uneven dispersion and insufficient concentration of flame retardant elements, the limiting oxygen index of the material decreases, and the flame retardant performance fails to meet standards. The reacted isocyanate groups can trigger subsequent degradation and accelerate material aging. If the molar ratio is greater than this, i.e., the flame retardant, anti-aging agent or chain extender is relatively excessive, or the isocyanate is relatively insufficient, it will destroy the inherent hard-segment-soft-segment microphase separation structure of polyurethane, leading to the introduction of too many rigid heterocycles or siloxane segments into the molecular chain, resulting in excessive cross-linking and loss of flexibility of the material, manifested as a simultaneous deterioration of tensile strength and elongation at break. Excessive additives may agglomerate, acting as stress weaknesses and causing early failure. Furthermore, excessive silane components may migrate to the surface, affecting the interlayer adhesion and surface properties of the material, and the durability of the anti-aging effect will actually decrease under long-term use.

[0022] The DADT obtained in step S1 of this invention, through its precise molecular structure design, achieves multi-level and synergistic anti-aging and flame-retardant effects from "surface defense" to "deep stability," while its molecular design ensures compatibility with the polyurethane matrix, enabling it to function at extremely low addition levels, thereby achieving a unity of functionality and optical transparency. Specifically: Primary defense (high-efficiency UV filtering and energy conversion): The anti-aging efficacy of DADT molecules lies in the synergistic effect between the 4,6-diphenyl-1,3,5-triazine structure and the triphenylsilane unit within the molecule. The triazine structure, as the UV absorption core, can efficiently capture high-energy UV light in the 280-380 nm range, while the adjacent triphenylsilane unit forms a stable energy transfer pathway through an extended conjugated system, allowing the absorbed light energy to be rapidly dispersed and converted into harmless heat, thus effectively preventing photodecomposition of the triazine structure itself due to energy accumulation. At the same time, the triphenylsilane, with its large spatial volume, further enhances the structural stability of the entire molecule, not only inhibiting its migration in the polyurethane matrix but also physically protecting the triazine active center and reducing the impact of the external environment. This integrated "absorption-transfer-dissipation-protection" intrinsic synergistic mechanism enables DADT molecules to persistently and efficiently inhibit UV-induced degradation reactions on the material surface, providing reliable long-term light-stable protection for polyurethane materials. Its extremely high UV absorption efficiency allows for sufficient protection even at very low addition levels, which is key to avoiding the impact on matrix transparency due to excessive addition. Secondary defense (free radical capture and chain reaction interruption): When free radicals are generated within the material due to trace amounts of thermo-oxidative action, DADT molecules exhibit a second layer of active protection. The nitrogen atom on the triazine ring and the P=O group in the diphenylphosphine ester structure can both serve as highly efficient free radical capture sites. These two sites form a dual-site synergistic capture network within the molecule, which can more efficiently quench alkyl free radicals (R·), alkoxy free radicals (RO·), and peroxy free radicals (ROO·) generated during the oxidative degradation of polyurethane, strongly interrupting the auto-oxidative chain reaction of material aging. This process continues within the polyurethane, providing in-depth protection. The intramolecular dual-site design improves the antioxidant efficiency of individual molecules, further reducing the need for high addition amounts and helping to maintain material uniformity and transparency.Three-tiered defense (physical barrier and microstructural stability): The introduction of triphenylsilyl groups not only improves the thermal stability and hydrophobicity of DADT, but also exerts a long-term stabilizing effect through the following mechanisms: Hydrophobic shielding: The silyl groups endow DADT with strong hydrophobicity, enabling it to effectively block the penetration and diffusion of water molecules and liquid media in the polyurethane matrix, significantly delaying the hydrolytic aging process of polyurethane (especially polyester type); Network anchoring and stiffening effect: DADT molecules are large and rigid, and their molecular structure has good compatibility with polyurethane chain segments. They can be uniformly dispersed in the matrix, acting as "micro-crosslinking points" and "physical entanglement centers" without causing macroscopic phase separation leading to turbidity. This effect can restrict the thermal movement of polyurethane molecular chain segments at the microscale, increase its glass transition temperature, and stabilize the amorphous region structure, thereby enhancing the overall dimensional stability of the material and its resistance to thermomechanical stress, slowing down physical aging, and maintaining optical uniformity.

[0023] Meanwhile, traditional flame retardant systems are often physically blended, with components easily separating, severely compromising material transparency. This invention integrates phosphorus, nitrogen, and silicon flame retardant elements into a single molecule through chemical bonds. This not only achieves seamless synergy across different stages and phases of combustion, but the single-molecule structure also ensures uniform dispersion within the matrix, avoiding light scattering caused by multiphase interfaces. Thus, while providing highly efficient flame retardancy, the matrix maintains high transparency. Specifically: Gas-phase flame retardancy (free radical quenching and dilution effect): When the material decomposes thermally, the diphenylphosphine ester portion of the DADT molecule preferentially decomposes, releasing phosphorus-containing free radicals (PO·, HPO·, etc.). These active substances can rapidly enter the gas-phase flame zone, efficiently capturing the H· and OH· free radicals necessary for combustion, chemically interrupting the combustion chain reaction. Simultaneously, the nitrogen, ammonia, and other non-combustible gases released by the thermal decomposition of the triazine structure dilute the concentration of combustibles and oxygen in the gas phase, producing a gas-phase physical-chemical synergistic flame retardancy with the phosphorus-containing free radicals, significantly reducing flame intensity. This intramolecular synergy results in extremely high gas-phase flame retardancy efficiency, reducing the total amount of additives required to achieve the desired flame retardancy rating. Condensed-phase flame retardancy (catalytic char formation and carbon layer reinforcement): Under thermal action, the DADT molecule itself decomposes and interacts with the polyurethane matrix, constructing a highly stable protective carbon layer in the condensed phase. The acidic substances such as phosphoric acid and polyphosphoric acid produced during decomposition catalyze the dehydration, crosslinking, and aromatization of the polyurethane matrix, significantly improving the char formation rate and carbon layer quality. Furthermore, the triazine structure, as a nitrogen-rich source, generates triazine ring fragments during decomposition, which serve as the carbon layer framework, promoting the formation of a dense and continuous expanded carbon layer. Most importantly, triphenylsilane can be converted into silica or silicate networks at high temperatures and undergo hybrid crosslinking with the phosphorus-nitrogen carbon layer, forming an "organic-inorganic hybrid ceramicized carbon layer." This carbon layer possesses extremely high thermal stability, oxidation resistance, and mechanical strength, effectively isolating heat transfer and preventing further decomposition of the internal substrate. The close intramolecular synergy of phosphorus, nitrogen, and silicon significantly reduces the additive concentration required to form an effective protective carbon layer.

[0024] It is worth noting that the anti-aging function of DADT in this invention directly enhances its flame-retardant function. Because DADT effectively delays the thermo-oxidative and UV aging of polyurethane during long-term use, maintaining the material's initial mechanical integrity and chemical stability, this results in a higher thermal decomposition temperature and a more controllable decomposition path for the polyurethane when exposed to an ignition source. This provides time and a material basis for the formation of a highly efficient flame-retardant carbon layer, achieving a synergistic effect of "anti-aging aiding flame retardancy." This synergistic effect means that the functions required to maintain long-term stability and the functions providing emergency fire safety mutually reinforce each other, allowing the achievement of comprehensive performance goals at a lower overall additive load. This is crucial for maintaining the original properties of polyurethane, such as transparency.

[0025] The above-mentioned technical solution of the present invention is a whole in which each step is closely related and mutually influential, and together they determine the morphological characteristics and performance of the product.

[0026] The above technical solution has the following advantages or beneficial effects:

[0027] 1. The DADT prepared by this invention solves the drawbacks of traditional physical blending additives, such as poor compatibility, easy migration, and insufficient long-term effect. Its integrated structure has good compatibility with the polyurethane matrix, which enables it to have good flame retardancy and aging resistance at low addition levels, and minimizes the negative impact on the original properties of the polyurethane matrix (such as transparency and mechanical properties).

[0028] 2. The DADT prepared by this invention can form a multi-dimensional, multi-level defense system from the surface to the substrate against various aging factors such as light, heat, oxygen, and water. During the combustion stage, it can construct a dynamic and continuous synergistic flame-retardant mechanism at the interface of the gas phase, condensed phase, and carbon layer. Each functional unit within the material molecule can respond to the target as needed, greatly improving the efficiency of action and effectively reducing the total amount added. There is a significant synergistic effect between its functions—the anti-aging effect indirectly improves the flame-retardant protection performance by maintaining the structural integrity of the substrate. At the same time, the introduction of elements such as phosphorus and silicon not only enhances the thermal stability and free radical capture ability of the molecular chain, but also strengthens the anti-aging effect in reverse. Ultimately, it achieves the same or even better comprehensive protection performance with a total amount added at a much lower level than traditional physical blending systems.

[0029] 3. The polyurethane material obtained by this invention has a limiting oxygen index of 29.6% and a UL-94 rating of V-0, exhibiting good flame retardant properties; it also has excellent anti-aging properties and can be used as a high-performance transparent film for resisting ultraviolet and heat-oxidative aging in fields such as automotive UV protection films and fire extinguisher sign protective films.

[0030] 4. The preparation method of this invention is simple, the process is easy to control, and it is suitable for large-scale industrial production.

[0031] This invention is applicable to the preparation of flame-retardant, aging-resistant, and highly transparent polyurethane.

[0032] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0033] Figure 1 Fourier transform infrared spectra of DADT, 2-amino-1,3-propanediol, 2-chloro-4,6-diphenyl-1,3,5-triazine, diphenylphosphine chloride, and triphenylchlorosilane prepared in step S1 of Example 5 of this invention.

[0034] Figure 2The infrared spectra of the polyurethane materials prepared in Examples 1-5 and Comparative Example 1 of this invention are shown below.

[0035] Figure 3 These are LOI test images of the polyurethane materials prepared in Examples 1-5 of this invention;

[0036] Figure 4 These are the LOI test images of the polyurethane materials prepared in Comparative Examples 1-5 of this invention;

[0037] Figure 5 These are UL-94 test images of the polyurethane materials prepared in Examples 1-5 of this invention;

[0038] Figure 6 These are UL-94 test images of the polyurethane materials prepared in Comparative Examples 1-5 of this invention;

[0039] Figure 7 The graphs show the LOI and UL-94 evaluation charts of the polyurethane materials prepared in Examples 1-5 and Comparative Examples 1-12 of this invention, where: the horizontal axis 1-5 represents Examples 1-5, and 6-17 represents Comparative Examples 1-12, respectively.

[0040] Figure 8 The images shown are scanning electron microscope (SEM) images of the carbon layers of polyurethane materials prepared in Example 5 and Comparative Example 1 after combustion. (a) is a 50 μm SEM image of the carbon layer of pure polyurethane prepared in Comparative Example 1 after combustion; (b) is a 5 μm SEM image of the carbon layer of pure polyurethane prepared in Comparative Example 1 after combustion; (c) is a 50 μm SEM image of the carbon layer of polyurethane material prepared in Example 5 after combustion; and (d) is a 5 μm SEM image of the carbon layer of polyurethane material prepared in Example 5 after combustion.

[0041] Figure 9 These are Raman characterization images of the carbon residue after combustion of the polyurethane materials prepared in Example 5 and Comparative Example 1 of the present invention.

[0042] Figure 10 The mechanical properties of the polyurethane materials prepared in Examples 1-5 and Comparative Examples 1-12 of the present invention are characterized by the following: the horizontal axis 1-5 represents Examples 1-5, and 6-17 represents Comparative Examples 1-12, respectively.

[0043] Figure 11 The above diagrams are characterization diagrams of the transparency properties of polyurethane materials prepared in Examples 1-5 and Comparative Examples 1-12 of the present invention, wherein: the horizontal axis 1-5 represents Examples 1-5 respectively, and 6-17 represent Comparative Examples 1-12 respectively.

[0044] Figure 12The graph shows the retention rate of tensile strength under thermo-oxidative aging after aging at 100°C for 10 days for polyurethane materials prepared in Examples 1-5 and Comparative Examples 1-12 of the present invention, where: the horizontal axis 1-5 represents Examples 1-5, and 6-17 represent Comparative Examples 1-12, respectively.

[0045] Figure 13 The graph shows the performance of the polyurethane materials prepared in Examples 1-5 and Comparative Examples 1-12 of the present invention after aging at 100°C for 10 days, representing the retention rate of elongation at break due to thermo-oxidative aging. In the graph, the horizontal axis 1-5 represents Examples 1-5, and 6-17 represents Comparative Examples 1-12.

[0046] Figure 14 The graph shows the thermo-oxidative aging yellowing index performance of the polyurethane materials prepared in Examples 1-5 and Comparative Examples 1-12 after aging at 100°C for 10 days. In the graph, the horizontal axis 1-5 represents Examples 1-5, and 6-17 represents Comparative Examples 1-12.

[0047] Figure 15 The polyurethane materials prepared in Examples 1-5 and Comparative Examples 1-12 of this invention are analyzed at 340 nm and 0.68 W / m. 2 The characterization graph of the retention rate of elongation at break after aging for 100 h under the condition of UV aging, where: the horizontal axis 1~5 represent Examples 1~5 respectively, and 6~17 represent Comparative Examples 1~12 respectively;

[0048] Figure 16 The polyurethane materials prepared in Examples 1-5 and Comparative Examples 1-12 of this invention are analyzed at 340 nm and 0.68 W / m. 2 Characterization of UV aging resistance color difference performance after aging for 100 h under the condition, where: the horizontal axis 1~5 represent Examples 1~5 respectively, and 6~17 represent Comparative Examples 1~12 respectively;

[0049] Figure 17 The polyurethane materials prepared in Examples 1-5 and Comparative Examples 1-12 of this invention are analyzed at 340 nm and 0.68 W / m. 2 Characterization of UV aging gloss retention rate after aging for 100 h under the specified conditions, where: the horizontal axis 1~5 represent Examples 1~5 respectively, and 6~17 represent Comparative Examples 1~12 respectively. Detailed Implementation

[0050] The following embodiments are merely some, not all, of the embodiments of the present invention. Therefore, the detailed descriptions of the embodiments provided below are not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0051] In this invention, unless otherwise specified, all equipment and raw materials are commercially available or commonly used in the industry. The methods described in the following embodiments are conventional methods in the art, unless otherwise specified.

[0052] Example 1

[0053] This embodiment prepares a flame-retardant, aging-resistant, and highly transparent polyurethane. The preparation process and steps are as follows:

[0054] S1. Preparation of triazine-phosphine ester-silane flame retardant and anti-aging agent

[0055] At -5°C, 1 mmol of 2-amino-1,3-propanediol was added to 100 mL of anhydrous tetrahydrofuran. 7 mL of triethylamine was then added, and the mixture was stirred thoroughly. 1 mmol of 2-chloro-4,6-diphenyl-1,3,5-triazine solution (prepared by dispersing 1 mmol of 2-chloro-4,6-diphenyl-1,3,5-triazine in 50 mL of tetrahydrofuran) was added dropwise at a rate of 0.5 mL / min. The mixture was stirred for 2 h, and then 7 mL of triethylamine was added. Next, 1 mmol of diphenylphosphine chloride solution (prepared by dispersing 1 mmol of diphenylphosphine chloride in 50 mL of tetrahydrofuran) was added dropwise at a rate of 0.5 mL / min, and the mixture was stirred for 2 h until the diphenylphosphine chloride reaction was complete. Then, 7 mL of triethylamine was added again, followed by the addition of 0.5 mL of triethylamine. 1 mmol of triphenylchlorosilane solution (prepared by dispersing 1 mmol of triphenylchlorosilane in 50 mL of tetrahydrofuran) was added dropwise at a rate of mL / min. The reaction system was heated to 50 °C and reacted for 5 h. After the reaction was complete, the reaction was quenched with deionized water. The organic phase was separated by extraction three times with a solution of 10 mL of ethyl acetate and 15 mL of deionized water, followed by extraction twice with saturated sodium chloride aqueous solution. 8 g of anhydrous sodium sulfate was added to the organic phase, and the mixture was distilled under reduced pressure to obtain the triazine-phosphines-silane flame retardant and anti-aging agent (DADT).

[0056] S2, Preparation of aging-resistant, highly transparent polyurethane

[0057] 15 mmol of polytetrahydrofuran diol (weight average molecular weight 2000) and 1 mmol of DADT were added to a three-necked flask and heated to 120°C. The glass container was evacuated and filled with argon gas. The system was cooled to 80°C, 20 mmol of diphenylmethane diisocyanate was added and stirred for 2 h. The temperature was then lowered to 55°C, and 5 mmol of 1,4-butanediol chain extender was added (the preparation method of 1,4-butanediol chain extender is: add 5 mmol of 1,4-butanediol to 2 mL of NN,dimethylformamide and stir evenly). The mixture was stirred for 1 min to obtain a polymer emulsion. This emulsion was poured into a polytetrafluoroethylene mold and reacted and cured in an oven at 80°C for 48 h to obtain a flame-retardant, aging-resistant, and highly transparent polyurethane.

[0058] Example 2

[0059] This embodiment prepares a flame-retardant, aging-resistant, and highly transparent polyurethane. The preparation process and steps are as follows:

[0060] S1. Preparation of triazine-phosphine ester-silane flame retardant and anti-aging agent

[0061] At -3°C, 1 mmol of 2-amino-1,3-propanediol was added to 100 mL of anhydrous tetrahydrofuran. 7 mL of triethylamine was then added, and the mixture was stirred thoroughly. 1 mmol of 2-chloro-4,6-diphenyl-1,3,5-triazine solution (prepared by dispersing 1 mmol of 2-chloro-4,6-diphenyl-1,3,5-triazine in 50 mL of tetrahydrofuran) was added dropwise at a rate of 0.55 mL / min. The mixture was stirred for 2.5 h, and then 7 mL of triethylamine was added. Following this, 1 mmol of diphenylphosphine chloride solution (prepared by dispersing 1 mmol of diphenylphosphine chloride in 50 mL of tetrahydrofuran) was added dropwise at a rate of 0.55 mL / min, and the mixture was stirred for 2.5 h until the diphenylphosphine chloride had completely reacted. Then, 7 mL of triethylamine was added, followed by the addition of 0.55 mL / min. 1 mmol of triphenylchlorosilane solution (prepared by dispersing 1 mmol of triphenylchlorosilane in 50 mL of tetrahydrofuran) was added dropwise at a rate of mL / min. The reaction system was heated to 50 °C and reacted for 5.5 h. After the reaction was complete, the reaction was quenched with deionized water. The organic phase was separated by three extractions with a solution of 10 mL of ethyl acetate and 15 mL of deionized water, followed by two extractions with saturated sodium chloride aqueous solution. 8 g of anhydrous sodium sulfate was added to the organic phase, and the mixture was distilled under reduced pressure to obtain the triazine-phosphines-silane flame retardant and anti-aging agent (DADT).

[0062] S2, Preparation of aging-resistant, highly transparent polyurethane

[0063] 15 mmol of polytetrahydrofuran glycol (weight average molecular weight 2000) and 2 mmol of DADT were added to a three-necked flask and heated to 125°C. The glass container was evacuated and filled with argon gas. The system was cooled to 100°C, 20 mmol of toluene diisocyanate was added and stirred for 2 h. The temperature was then lowered to 58°C, and 5 mmol of 1,4-butanediol chain extender was added (the preparation method of 1,4-butanediol chain extender is: 0.45 g of 1,4-butanediol is added to 2 mL of NN,dimethylformamide and stirred evenly). The mixture was stirred for 1.5 min to obtain a polymer emulsion, which was then poured into a polytetrafluoroethylene mold and reacted and cured in an oven at 80°C for 48 h to obtain a flame-retardant, aging-resistant, and highly transparent polyurethane.

[0064] Example 3

[0065] This embodiment prepares a flame-retardant, aging-resistant, and highly transparent polyurethane. The preparation process and steps are as follows:

[0066] S1. Preparation of triazine-phosphine ester-silane flame retardant and anti-aging agent

[0067] At -2°C, 1 mmol of 2-amino-1,3-propanediol was added to 100 mL of anhydrous tetrahydrofuran. 7 mL of triethylamine was then added, and the mixture was stirred thoroughly. 1 mmol of 2-chloro-4,6-diphenyl-1,3,5-triazine solution (prepared by dispersing 1 mmol of 2-chloro-4,6-diphenyl-1,3,5-triazine in 50 mL of tetrahydrofuran) was added dropwise at a rate of 0.6 mL / min. The mixture was stirred for 3 h, and then 7 mL of triethylamine was added. Next, 1 mmol of diphenylphosphine chloride solution (prepared by dispersing 1 mmol of diphenylphosphine chloride in 50 mL of tetrahydrofuran) was added dropwise at a rate of 0.6 mL / min, and the mixture was stirred for 3 h until the diphenylphosphine chloride reaction was complete. Then, 7 mL of triethylamine was added, followed by the addition of 0.6 mL of triethylamine. 1 mmol of triphenylchlorosilane solution (prepared by dispersing 1 mmol of triphenylchlorosilane in 50 mL of tetrahydrofuran) was added dropwise at a rate of mL / min. The reaction system was heated to 50 °C and reacted for 6 h. After the reaction was complete, the reaction was quenched with deionized water. The organic phase was separated by extraction three times with a solution of 10 mL of ethyl acetate and 15 mL of deionized water, followed by extraction twice with saturated sodium chloride aqueous solution. 8 g of anhydrous sodium sulfate was added to the organic phase, and the mixture was distilled under reduced pressure to obtain the triazine-phosphines-silane flame retardant and anti-aging agent (DADT).

[0068] S2, Preparation of aging-resistant, highly transparent polyurethane

[0069] 15 mmol of polytetrahydrofuran glycol (weight average molecular weight 2000) and 3 mmol of DADT were added to a three-necked flask and heated to 130°C. The glass container was evacuated and filled with argon gas. The system was cooled to 110°C, 20 mmol of toluene diisocyanate was added and stirred for 2 h. The temperature was then lowered to 60°C, and 5 mmol of 1,4-butanediol chain extender was added (the preparation method of 1,4-butanediol chain extender is: 0.45 g of 1,4-butanediol is added to 2 mL of NN,dimethylformamide and stirred evenly). The mixture was stirred for 2 min to obtain a polymer emulsion. This emulsion was poured into a polytetrafluoroethylene mold and reacted and cured in an oven at 80°C for 48 h to obtain a flame-retardant, aging-resistant, and highly transparent polyurethane.

[0070] Example 4

[0071] This embodiment prepares a flame-retardant, aging-resistant, and highly transparent polyurethane. The preparation process and steps are as follows:

[0072] S1. Preparation of triazine-phosphine ester-silane flame retardant and anti-aging agent

[0073] At 0 °C, 1 mmol of 2-amino-1,3-propanediol was added to 100 mL of anhydrous tetrahydrofuran. 7 mL of triethylamine was then added, and the mixture was stirred thoroughly. 1 mmol of 2-chloro-4,6-diphenyl-1,3,5-triazine solution (prepared by dispersing 1 mmol of 2-chloro-4,6-diphenyl-1,3,5-triazine in 50 mL of tetrahydrofuran) was added dropwise at a rate of 0.6 mL / min. The mixture was stirred for 2 h, and then 7 mL of triethylamine was added. Next, 1 mmol of diphenylphosphine chloride solution (prepared by dispersing 1 mmol of diphenylphosphine chloride in 50 mL of tetrahydrofuran) was added dropwise at a rate of 0.6 mL / min, and the mixture was stirred for 2 h until the diphenylphosphine chloride reaction was complete. Then, 7 mL of triethylamine was added again, followed by the addition of 0.6 mL of triethylamine. 1 mmol of triphenylchlorosilane solution (prepared by dispersing 1 mmol of triphenylchlorosilane in 50 mL of tetrahydrofuran) was added dropwise at a rate of mL / min. The reaction system was heated to 50 °C and reacted for 6 h. After the reaction was complete, the reaction was quenched with deionized water. The organic phase was separated by extraction three times with a solution of 10 mL of ethyl acetate and 15 mL of deionized water, followed by extraction twice with saturated sodium chloride aqueous solution. 8 g of anhydrous sodium sulfate was added to the organic phase, and the mixture was distilled under reduced pressure to obtain the triazine-phosphines-silane flame retardant and anti-aging agent (DADT).

[0074] S2, Preparation of aging-resistant, highly transparent polyurethane

[0075] 15 mmol of polytetrahydrofuran glycol (weight average molecular weight 2000) and 4 mmol of DADT were added to a three-necked flask and heated to 120°C. The glass container was evacuated and filled with argon gas. The system was cooled to 100°C, 20 mmol of diphenylmethane diisocyanate was added and stirred for 2 h. The temperature was then lowered to 60°C, and 5 mmol of 1,4-butanediol chain extender was added (the preparation method of 1,4-butanediol chain extender is: 0.45 g of 1,4-butanediol is added to 2 mL of NN,dimethylformamide and stirred evenly). The mixture was stirred for 1 min to obtain a polymer emulsion. This emulsion was poured into a polytetrafluoroethylene mold and reacted and cured in an oven at 80°C for 48 h to obtain a flame-retardant, aging-resistant, and highly transparent polyurethane.

[0076] Example 5

[0077] This embodiment prepares a flame-retardant, aging-resistant, and highly transparent polyurethane. The preparation process and steps are as follows:

[0078] S1. Preparation of triazine-phosphine ester-silane flame retardant and anti-aging agent

[0079] At -1 °C, 1 mmol of 2-amino-1,3-propanediol was added to 100 mL of anhydrous tetrahydrofuran. 7 mL of triethylamine was then added, and the mixture was stirred thoroughly. 2-chloro-4,6-diphenyl-1,3,5-triazine solution (prepared by dispersing 1 mmol of 2-chloro-4,6-diphenyl-1,3,5-triazine in 50 mL of tetrahydrofuran) was added dropwise at a rate of 0.5 mL / min. The mixture was stirred for 2 h, and then 7 mL of triethylamine was added. Next, diphenylphosphine chloride solution (prepared by dispersing 1 mmol of diphenylphosphine chloride in 50 mL of tetrahydrofuran) was added dropwise at a rate of 0.5 mL / min, and the mixture was stirred for 2 h until the diphenylphosphine chloride reaction was complete. Then, 7 mL of triethylamine was added again, followed by the addition of 0.5 mL of triethylamine. Triphenylchlorosilane solution (prepared by dispersing 1 mmol of triphenylchlorosilane in 50 mL of tetrahydrofuran) was added dropwise at a rate of mL / min. The reaction system was heated to 50 °C and reacted for 6 h. After the reaction was complete, the reaction was quenched with deionized water. The organic phase was separated by extraction three times with a solution of 10 mL ethyl acetate and 15 mL deionized water, followed by extraction twice with saturated sodium chloride aqueous solution. 8 g of anhydrous sodium sulfate was added to the organic phase, and the mixture was distilled under reduced pressure to obtain triazine-phosphines-silane flame retardant and anti-aging agent (DADT).

[0080] S2, Preparation of aging-resistant, highly transparent polyurethane

[0081] 15 mmol of polytetrahydrofuran glycol (weight average molecular weight 2000) and 5 mmol of DADT were added to a three-necked flask and heated to 120°C. The glass container was evacuated and filled with argon gas. The system was cooled to 80°C, 20 mmol of diphenylmethane diisocyanate was added and stirred for 2 h. The temperature was then lowered to 55°C, and 5 mmol of 1,4-butanediol chain extender was added (the preparation method of 1,4-butanediol chain extender is: 0.45 g of 1,4-butanediol is added to 2 mL of NN,dimethylformamide and stirred evenly). The mixture was stirred for 2 min to obtain a polymer emulsion. This emulsion was poured into a polytetrafluoroethylene mold and reacted and cured in an oven at 80°C for 48 h to obtain a flame-retardant, aging-resistant, and highly transparent polyurethane.

[0082] Comparative Example

[0083] To investigate the effects of different parameters or raw materials on the performance of the product during the preparation process of this invention, the following comparative experiments were conducted. Different polyurethane materials were prepared in the following comparative examples:

[0084] Comparative Example 1

[0085] This comparative example prepares a polyurethane material. The preparation process is similar to that of Example 5, except that DADT is not added in step 2.

[0086] Comparative Example 2

[0087] This comparative example prepares a polyurethane material. The preparation process is similar to that of Example 5, except that in step S2, 5 mmol DADT is replaced with 5 mmol 2-amino-1,3-propanediol.

[0088] Comparative Example 3

[0089] This comparative example prepares a polyurethane material. The preparation process is similar to that of Example 5, except that in step S2, 5 mmol DADT is replaced with 5 mmol 2-chloro-4,6-diphenyl-1,3,5-triazine.

[0090] Comparative Example 4

[0091] This comparative example prepares a polyurethane material. The preparation process is similar to that of Example 5, except that in step S2, 5 mmol DADT is replaced with 5 mmol diphenylphosphine chloride.

[0092] Comparative Example 5

[0093] This comparative example prepares a polyurethane material. The preparation process is similar to that of Example 5, except that in step S2, 5 mmol DADT is replaced with 5 mmol triphenylchlorosilane.

[0094] Comparative Example 6

[0095] This comparative example prepares a polyurethane material. The preparation process is similar to that of Example 5, except that in step S2, 5 mmol DADT is replaced with a mixture of 2.5 mmol 2-amino-1,3-propanediol and 2.5 mmol 2-chloro-4,6-diphenyl-1,3,5-triazine.

[0096] Comparative Example 7

[0097] This comparative example prepares a polyurethane material. The preparation process is similar to that of Example 5, except that in step S2, 5 mmol DADT is replaced with a mixture of 2.5 mmol 2-amino-1,3-propanediol and 2.5 mmol diphenylphosphine chloride.

[0098] Comparative Example 8

[0099] This comparative example prepares a polyurethane material. The preparation process is similar to that of Example 5, except that in step S2, 5 mmol DADT is replaced with a mixture of 2.5 mmol 2-amino-1,3-propanediol and 2.5 mmol triphenylchlorosilane.

[0100] Comparative Example 9

[0101] This comparative example prepares a polyurethane material. The preparation process is similar to that of Example 5, except that in step S2, 5 mmol DADT is replaced with a mixture of 2.5 mmol 2-chloro-4,6-diphenyl-1,3,5-triazine and 2.5 mmol diphenylphosphine chloride.

[0102] Comparative Example 10

[0103] This comparative example prepares a polyurethane material. The preparation process is similar to that of Example 5, except that in step S2, 5 mmol DADT is replaced with a mixture of 2.5 mmol 2-chloro-4,6-diphenyl-1,3,5-triazine and 2.5 mmol triphenylchlorosilane.

[0104] Comparative Example 11

[0105] This comparative example prepares a polyurethane material. The preparation process is similar to that of Example 5, except that in step S2, 5 mmol DADT is replaced with a mixture of 2.5 mmol diphenylphosphine chloride and 2.5 mmol triphenylchlorosilane.

[0106] Comparative Example 12

[0107] This comparative example prepares a polyurethane material. The preparation process is similar to that of Example 1, except that step S1 is omitted. Instead, 1 mmol of 2-amino-1,3-propanediol, 1 mmol of 2-chloro-4,6-diphenyl-1,3,5-triazine, 1 mmol of diphenylphosphine chloride, and 1 mmol of triphenylchlorosilane are directly added to the polyurethane matrix. That is, 1 mmol of DADT is replaced with a mixture consisting of 1 mmol of 2-amino-1,3-propanediol, 1 mmol of 2-chloro-4,6-diphenyl-1,3,5-triazine, 1 mmol of diphenylphosphine chloride, and 1 mmol of triphenylchlorosilane.

[0108] Performance testing

[0109] The polyurethane materials prepared in Examples 1-5 and Comparative Examples 1-12 of this invention were subjected to a series of performance tests, as detailed below:

[0110] like Figure 1 The Fourier transform infrared (FTIR) spectra of DADT prepared in step S1 of Example 5 of this invention, as well as 2-amino-1,3-propanediol, 2-chloro-4,6-diphenyl-1,3,5-triazine, diphenylphosphine chloride, and triphenylchlorosilane, are shown. From the FTIR spectrum of 2-amino-1,3-propanediol, it can be seen that: 3323 cm⁻¹ -1 The peak at 3180 cm⁻¹ is the -NH₂ stretching vibration peak. -1 The peak at this location is the -OH stretching vibration peak, 2970~2800 cm⁻¹. -1 The range is the CH stretching vibration peak, 1038 cm⁻¹. -1 The peak at 1600-1380 cm⁻¹ corresponds to the CO stretching vibration; 2-chloro-4,6-diphenyl-1,3,5-triazine shows a peak at 1600-1380 cm⁻¹. -1 The interval shows C=C and C=N triazine ring stretching vibration peaks, 843 cm⁻¹ -1 The peak at 1111 cm⁻¹ represents the C-Cl stretching vibration; diphenylphosphine chloride shows a peak at 1111 cm⁻¹. -1 The peak at 540 cm⁻¹ is the P=O stretching vibration peak. -1 The peak at 591 cm⁻¹ corresponds to the P-Cl stretching vibration; for triphenylchlorosilane, the peak is at 591 cm⁻¹. -1 A Si-Cl stretching vibration peak appears at [location missing]. In the Fourier transform infrared spectrum of the target product DADT, a peak can be observed at 1543 cm⁻¹. -1 POC stretching vibration peak, 1429 cm -1 CN stretching vibration peak and 695 cm -1The Si-C stretching vibration peak was observed. Comparison of the Fourier transform infrared spectra of the above reactants and DADT revealed that the -NH2 and -OH peaks in the raw material characteristic peaks completely disappeared, while new characteristic peaks such as POC, CN, and Si-C appeared. This confirms that the target product DADT has been successfully synthesized.

[0111] like Figure 2 The figures show the infrared spectra of the polyurethane materials prepared in Examples 1-5 and Comparative Example 1 of this invention. As can be seen from the figures, the synthesized DADT successfully entered the polyurethane matrix, with the sample showing a peak density at 2260 cm⁻¹. -1 The disappearance of the nearby -NCO absorption peak indicates that the -NCO group and the -OH group have reacted completely. The stretching vibration peaks of saturated CH2 in the molecular chain appear at 2942. -1 2888 -1 and 2855 cm -1 Nearby, under the influence of NH, the characteristic absorption peak of CO in polyurethane shifts slightly to a lower wavelength of 1719 cm⁻¹. -1 At the same location, compared with pure polyurethane (TPU), the characteristic peak of DADT in the polyurethanes prepared in Examples 1-5 of this invention is located at 1529 cm⁻¹. -1 (PO), 1419 cm -1 (CN), 1214 cm -1 (P=O), and 695 cm -1 (Si-C); of which 1214 cm -1 (P=O) and 695 cm -1 The characteristic peak at (Si-C) is the most prominent. The results show that DADT was successfully introduced into the polyurethane structure, and polyurethane elastomer materials with different DADT contents were successfully prepared.

[0112] like Figure 3 and Figure 4 The figures show the flame retardant properties of the polyurethane materials prepared in Examples 1-5 and Comparative Examples 1-5 of this invention, respectively. Figure 3 As can be seen, the combustion and dripping phenomena of the polyurethane elastomer material prepared by this invention are greatly improved, the mass loss of the polyurethane material is reduced, and the limiting oxygen index (LOI) increases from 17.8% to 29.6%. Figure 4It can be observed that the droplet phenomenon of pure polyurethane without flame retardant (Comparative Example 1) and polyurethane materials with added 2-amino-1,3-propanediol, 2-chloro-4,6-diphenyl-1,3,5-triazine, diphenylphosphine chloride and triphenylchlorosilane, respectively, is improved, and the oxygen indexes are 17.8%, 18.2%, 23.6%, 24.5% and 23.4%, respectively. However, the improvement effect is not as good as that of Examples 1 to 5 of the present invention. This is because: Comparative Example 2 only added 2-amino-1,3-propanediol, which, as a chain extender, can moderately increase the crosslinking density of the material and enhance the tendency to char, but the molecule itself does not contain flame-retardant active elements such as phosphorus, nitrogen, and silicon, and cannot provide effective flame retardancy in the gas phase or condensed phase, resulting in poor improvement effect; Comparative Example 3 only added 2-chloro-4,6-diphenyl-1,3,5-triazine, which, although containing nitrogen and able to capture free radicals and inhibit gas phase combustion to a certain extent, lacks the strong char-forming catalytic effect of phosphorus and the char-stabilizing function of silicon, resulting in limited flame retardant efficiency and insufficient thermal stability, thus leading to poor improvement effect. The improvement effect was poor because Comparative Example 4 only added diphenylphosphine chloride, which can decompose to generate phosphorus-containing free radicals during combustion, exerting a gas-phase flame retardant effect and promoting the dehydration and char formation of the material. However, its use alone lacks the free radical capture synergy of triazine structure and the char layer enhancement effect of silane. The flame retardant effect is singular and lacks persistence, resulting in a poor improvement effect. Comparative Example 5 only added triphenylchlorosilane, which can promote the formation of a silica-like protective char layer at high temperatures, improve the thermal stability of the material and inhibit dripping. However, it lacks the gas-phase flame retardant and free radical quenching ability of phosphorus and nitrogen elements, and the flame retardant synergy effect is missing, resulting in a poor improvement effect.

[0113] like Figure 5 and Figure 6 The figures show vertical combustion test diagrams of the polyurethane materials prepared in Examples 1-5 and Comparative Examples 1-5 of this invention. As can be seen from the figures, in the vertical combustion test, the polyurethane materials prepared in Examples 1-5 extinguished the flame immediately after leaving the fire source, and there was no dripping phenomenon. After being ignited a second time, the flame was still quickly extinguished. Its UL-94 flame retardant rating was improved from no rating to V-0 rating. Figure 6As can be seen from the results, Comparative Example 1, with its pure polyurethane without flame retardant, exhibited severe dripping during the vertical burning test. Comparative Example 2 showed significant burning with severe dripping, igniting the cotton wool on both ignitions, and the sample was almost completely burned, resulting in no UL-94 rating. Comparative Example 3 showed significant burning during the vertical burning test; although the first dripping failed to ignite the cotton wool, the second dripping ignited it, achieving a UL-94 rating of V-2. Comparative Example 4 showed rapid burning with a large amount of dripping during the vertical burning test; again, the cotton wool was not ignited on the first ignition, but was ignited on the second, resulting in a UL-94 rating of V-2. Comparative Example 5 showed significant burning during the vertical burning test; almost no dripping occurred on the first ignition, but the second dripping clearly ignited the cotton wool, leaving some residue on the sample, maintaining a UL-94 rating of V-2. Figure 5 This also shows that the introduction of DADT significantly improves the flame retardancy compared to pure polyurethane. The high-performance flame retardancy of polyurethane elastomers is mainly due to the excellent flame retardant effect of DADT.

[0114] like Figure 7The figure shows a comprehensive comparison of the Limiting Oxygen Index (LOI) and UL-94 rating of the polyurethanes prepared in the embodiments and comparative examples of this invention. This figure clearly demonstrates the flame-retardant performance of each group of samples. The LOI values ​​of Examples 1 to 5 show a regular gradient increase, at 26.2%, 26.9%, 27.8%, 28.9%, and 29.6%, respectively. More importantly, all five examples achieved the highest flame-retardant rating, V-0, in the UL-94 vertical burning test. This means that after two 10-second flame ignition tests, the flame duration was less than 10 seconds, and no molten droplets from the degreased cotton below were generated. This combination of data (high LOI value and V-0 rating) indicates that the material possesses excellent flame-retardant performance that meets stringent commercial standards. The root cause of DADT's outstanding flame-retardant effect lies in the "intrinsic intrinsic synergistic flame-retardant mechanism" achieved by its ingenious molecular structure. Comparative Example 1 (pure polyurethane) completely lacked flame retardant elements, and its LOI value (17.8%) reflected the intrinsic flammability of the polymer, burning violently with a large amount of molten droplets. Comparative Examples 2 to 5 demonstrated the limitations of a single flame retardant element: for example, Comparative Example 3, with only the addition of 2-chloro-4,6-diphenyl-1,3,5-triazine, achieved an LOI of 23.6%, reaching a V-2 rating. This was due to the gas-phase dilution from triazine decomposition and the small amount of free radical capture effect. However, due to the lack of strong catalytic char formation from phosphorus and the char layer stabilization effect from silicon, a sufficiently robust expanded char layer could not be formed, thus failing to suppress molten droplets and pass the more stringent V-0 test. Comparative Example 4, with only the addition of diphenylphosphine chloride, exhibited gas-phase flame retardancy and some charring properties, but lacked the synergistic effect of a nitrogen source, resulting in insufficient efficiency. Comparative Examples 6 to 11 achieved synergistic effects through physical mixing of two raw materials, but the data (LOI: 24.0%-26.1%, rating: V-2 for all) revealed the bottleneck of physical mixing. The LOI of Comparative Examples 6-11 ranged from 24.0% to 26.1%, but their UL-94 rating only reached V-2. Although the LOI of Comparative Example 9 also reached 26.1%, its UL-94 rating remained stuck at V-2, unable to break through. This series of comparative example data shows that, to achieve the V-0 level of high-efficiency flame retardancy achieved in this invention, pre-bonding phosphorus, nitrogen, and silicon elements through a specific chemical reaction to form a single DADT molecular structure is a necessary and irreplaceable step.

[0115] like Figure 8 The image shows the scanning electron microscope (SEM) characterization results of the carbon residue after combustion of the polyurethane materials prepared in Example 5 and Comparative Example 1 of this invention. Figure 8 (a) and Figure 8(b) The morphology of the char residue from Comparative Example 1 (pure polyurethane) at scales of 50 μm and 5 μm, respectively. It can be clearly observed that the char layer formed after combustion of pure polyurethane is extremely thin, loosely structured, and covered with numerous pores and intersecting cracks, exhibiting an overall fragile and discontinuous state. This type of defective char layer is unable to effectively cover and protect the underlying substrate. During combustion, it not only fails to insulate against heat transfer to the interior but also provides channels for the escape of combustible pyrolysis products and the penetration of oxygen, thus leading to continuous combustion and extremely poor flame retardant effect. In stark contrast, Figure 8 (c) and Figure 8 (d) The char residue from Example 5 exhibits a completely different microstructure. At the 50 μm scale, the char layer is continuous and intact, presenting a dense overall morphology; further magnification to 5 μm reveals a smooth and flat surface without obvious pores or cracks, exhibiting a solid and uniform structure. This dense and intact char layer acts like a robust ceramic barrier, effectively blocking the exchange of external heat with internal combustibles while inhibiting the formation of molten droplets, thus achieving highly efficient flame retardancy of the condensed phase. This morphological difference directly demonstrates the crucial role of DADT in promoting the formation of a high-quality protective char layer.

[0116] To further assess the quality of the carbon layers based on their graphitization degree, Raman spectroscopy analysis was performed on the combustion residues of Example 5 and Comparative Example 1. Figure 9 As shown. The D peak in the Raman spectrum (approximately 1350 cm⁻¹). -1 ) and G peak (approximately 1580 cm) -1 The two vibrations (ID / IG) correspond to the characteristic vibrations of disordered carbon and graphitized ordered carbon in carbon materials, respectively. Their intensity ratio is an important parameter for measuring the degree of graphitization and structural defect density of the carbon layer; a lower ID / IG value indicates a higher degree of graphitization, a more ordered structure, and greater stability. Analysis shows that the ID / IG value of the carbon residue in Comparative Example 1 is as high as 5.18, indicating a highly disordered carbon layer with numerous defects and poor thermal stability. In contrast, the ID / IG value of the carbon residue in Example 5 is significantly reduced to 2.71, quantitatively demonstrating that the introduction of DADT greatly improves the graphitization order of the carbon layer. A more ordered carbon layer exhibits better thermal stability, oxidation resistance, and mechanical strength, which is consistent with… Figure 8 The dense morphology observed in the samples corroborates each other, jointly elucidating the underlying mechanism by which DADT achieves efficient condensed phase flame retardancy by catalyzing the formation of a highly graphitized and structurally stable ceramic protective layer.

[0117] Figure 10 and Figure 11 The mechanical and optical properties of the polyurethane materials prepared in Examples 1-5 and Comparative Examples 1-12 of this invention are shown respectively. Figure 10As can be seen, the tensile strength of Examples 1-5 ranges from 27.62 to 28.31 MPa, showing almost no loss compared to pure polyurethane without any added functional components (Comparative Example 1, 28.28 MPa). Some examples even show a slight increase due to the minor reinforcing effect of DADT. However, Comparative Examples 2-5 exhibit a significant decrease in strength, ranging from 19.93 to 25.34 MPa, representing a loss of 10% to 30%. While the stress strength values ​​of Comparative Examples 6-11 (23.5-25.6 MPa) are slightly better than the worst single-component example, they are still significantly lower than the Example series. The stress strength of Comparative Example 12 is even lower, dropping to 18.5 MPa.

[0118] Figure 11 The transmittance data further corroborates the conclusions of the compatibility analysis. Transmittance is a sensitive indicator of the optical uniformity of a material; any microscopic or submicroscopic structural inhomogeneity that leads to light scattering will decrease it. As can be seen from the figure, the transmittance of Examples 1-5 is as high as 88.4% to 89.5%, not only not decreasing due to the addition of DADT, but even slightly exceeding the 87.6% of pure polyurethane. This indicates that DADT achieves optimal dispersion in the matrix, with the size of its dispersed phase much smaller than the wavelength of visible light, thus causing almost no Rayleigh or Mie scattering, allowing light to pass through almost unimpeded. In contrast, the transmittance of Comparative Examples 2-5 shows a significant decline, dropping to the range of 62.5% to 75.3%. This is because the size of the phase regions formed by the aggregation of these incompatible small molecules in the matrix falls within or is close to the wavelength range of visible light, resulting in strong scattering of light and causing the material to appear cloudy and hazy. Although the transmittance of Comparative Examples 6–11 (76.8%–83.2%) was somewhat higher than that of the single-component system, it was still significantly lower than that of the DADT system, which achieved molecular-level compatibility, due to the inherent light scattering interface of the multiphase system. The lowest transmittance of Comparative Example 12 was only 65.8%, which is an optical manifestation of its severe phase separation state.

[0119] Figures 12 to 17 The long-term durability of the material under harsh environments, i.e., its aging resistance, was evaluated. Thermo-oxidative aging test (…) Figures 12-14 The long-term use of the materials in a high-temperature, oxygen-rich environment was simulated and tested. After accelerated aging at 100°C for 10 days, Examples 1-5 exhibited excellent stability: tensile strength retention was as high as 82.2% to 88.5%, elongation at break retention was maintained at an excellent level of 75.2% to 77.4%, and the yellowing index, a measure of color stability, was controlled at an extremely low level of 2.81 to 3.63. In contrast, Comparative Example 1 had a strength retention of only 42.3%, an elongation retention of 53.2%, and a yellowing index as high as 8.95, indicating severe aging. The performance retention rates of other comparative examples were also significantly lower, with yellowing indices generally above 7. Ultraviolet aging test ( Figures 15-17 The ultraviolet (UV) irradiation conditions were simulated. After 100 hours of irradiation with 340 nm UV light, the elongation at break of Examples 1-5 retained 69.3% to 71.4%, with minimal color change (color difference ΔE of 3.82 to 4.25) and a surface gloss retention rate as high as 85.3% to 88.9%. In contrast, the comparative examples showed a comprehensive deterioration in all indicators. For example, the UV elongation retention rate of Comparative Example 1 was only 48.2%, the color difference ΔE was as high as 15.3, and the gloss retention rate was only 32.5%.

[0120] In summary, this invention, through groundbreaking molecular design, precisely integrates multiple previously separate functions, such as UV absorption, free radical capture, gas-phase flame retardancy, catalytic char formation, and char layer enhancement, into a single DADT molecular framework via stable chemical bonds. This integrated multifunctional molecular strategy brings significant technical advantages and solves the core dilemma of the long-standing contradiction between function and performance in the field of polymer material modification. Comparative Examples 1-12, in all key indicators such as flame retardancy, transparency, mechanical retention, and long-term aging resistance, consistently showed performance data significantly lower than that of Examples 1-5 using chemically bonded DADT. This indicates that the superior overall performance achieved by this invention stems from the unexpected and significant intramolecular synergistic effect triggered by the formation of the new chemical entity DADT through the specific chemical reaction described in this invention.

[0121] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A process for the preparation of a flame retardant, weatherable, high transparent polyurethane, characterized in that, Follow these steps in sequence: S1. Preparation of triazine-phosphine ester-silane flame retardant and anti-aging agent 2-Amino-1,3-propanediol was added to 100 mL of anhydrous tetrahydrofuran at -5 to 0 °C. 7 mL of triethylamine was then added, and the mixture was stirred until homogeneous. 2-Chloro-4,6-diphenyl-1,3,5-triazine was added dropwise, and the mixture was stirred for 2–3 h. Another 7 mL of triethylamine was added, and the mixture was stirred until homogeneous. Diphenylphosphinochloride was then added dropwise, and the mixture was stirred for 2–3 h. Another 7 mL of triethylamine was added, and the mixture was stirred until homogeneous. Triphenylchlorosilane was then added dropwise. The reaction system was heated to 50 °C and reacted for 5–6 h. After the reaction was complete, the reaction was quenched with deionized water. The mixture was extracted three times with a mixed solvent of ethyl acetate and deionized water at a volume ratio of 1:1.5, and then extracted twice with a saturated sodium chloride aqueous solution to separate the organic phase. 8 g of anhydrous sodium sulfate was added to the organic phase, and the mixture was distilled under reduced pressure to obtain a triazine-phosphinochloride-silane flame retardant and anti-aging agent. The structural formula of the triazine-phosphinic acid ester-silane flame retardant and anti-aging agent is: ； S2, Preparation of flame-retardant, aging-resistant, and highly transparent polyurethane Polyether polyol and triazine-phosphines-silane flame retardant and anti-aging agent were added to a three-necked flask and heated to 120-130°C. The glass container was evacuated and filled with argon gas. The system was cooled to 80-110°C, isocyanate was added and stirred for 2 h. The system temperature was then lowered to 55-60°C, chain extender was added and stirred for 1-2 min to obtain a polymer emulsion. This emulsion was poured into a polytetrafluoroethylene mold and reacted and cured in an 80°C oven for 48 h to obtain a flame-retardant, aging-resistant, and highly transparent polyurethane.

2. The preparation method of the flame-retardant and aging-resistant high-transparency polyurethane according to claim 1, characterized in that, In step S1, the molar ratio of 2-amino-1,3-propanediol to 2-chloro-4,6-diphenyl-1,3,5-triazine, diphenylphosphine chloride, and triphenylchlorosilane is 1:1:1:

1.

3. The preparation method of a flame-retardant, aging-resistant, and highly transparent polyurethane according to claim 1, characterized in that, In step S1, the rate of adding 2-chloro-4,6-diphenyl-1,3,5-triazine, diphenylphosphine chloride, and triphenylchlorosilane is 0.5~0.6 mL / min.

4. The preparation method of a flame-retardant, aging-resistant, and highly transparent polyurethane according to claim 1, characterized in that, In step S2, the polyether polyol is polytetrahydrofuran diol with a weight-average molecular weight of 2000.

5. The preparation method of a flame-retardant, aging-resistant, and highly transparent polyurethane according to claim 1, characterized in that, In step S2, the isocyanate is diphenylmethane diisocyanate or toluene diisocyanate.

6. The preparation method of a flame-retardant, aging-resistant, and highly transparent polyurethane according to claim 1, characterized in that, In step S2, the chain extender is prepared by adding 0.45g of 1,4-butanediol to 2 mL of N,N-dimethylformamide and stirring until homogeneous.

7. The preparation method of a flame-retardant, aging-resistant, and highly transparent polyurethane according to claim 1, characterized in that, In step S2, the molar ratio between the polyether polyol and the triazine-phosphines-silane flame retardant and anti-aging agent, isocyanate, and chain extender is 15:(1~5):20:5.

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