Flame retardant for thermoplastic resins, process for its preparation and use

Abstract

The application belongs to the field of organic polymer compounds, and particularly relates to a diphenyl phosphine oxide derivative flame retardant for thermoplastic resin and a preparation method and application thereof. Specifically disclosed is a diphenyl phosphine oxide derivative flame retardant structure for thermoplastic resin, which takes diphenyl phosphine oxide as a core unit, introduces amino thiazole and derivatives thereof and thiophene formaldehyde and derivatives thereof with high sulfur and nitrogen elements, synergizes three flame-retardant elements of phosphorus, nitrogen and sulfur in the molecular structure, improves gas phase activity and flame-retardant efficiency, has better flame-retardant effect compared to an existing physical compounding flame-retardant system, reduces the amount under the premise of the same flame-retardant performance, and is more conducive to maintaining the mechanical properties of the resin. The diphenyl phosphine oxide derivative flame retardant is mainly gas phase flame-retardant in the thermoplastic resin, and plays a flame-retardant effect through quenching of phosphorus oxygen and sulfur oxygen free radicals and dilution of sulfur oxygen and nitrogen-containing compounds.

Description

Technical Field

[0001] This invention belongs to the field of organic polymer compounds, specifically relating to diphenylphosphine oxide derivative flame retardants for thermoplastic resins, their preparation methods, and applications. Background Technology

[0002] Halogenated flame retardants were once widely used in flame-retardant polymer materials (such as plastics, rubber, coatings, and fabrics) in textiles, electronics, and transportation due to their high flame-retardant efficiency, low cost, and wide applicability. Compared to other types of flame retardants, halogenated flame retardants long held a dominant position. However, during combustion, halogenated flame retardants release toxic and harmful substances such as hydrogen halide gas and carcinogenic fumes. Furthermore, their persistent degradation and bioaccumulation violate the requirements of sustainable development, making global bans and restrictions inevitable.

[0003] Phosphorus-containing flame retardants, with their dual flame-retardant mechanisms of condensed phase charring and gas-phase free radical quenching, have become a core research and development direction for halogen-free flame-retardant systems. Through the physical compounding of different flame-retardant components, such as phosphorus-nitrogen, phosphorus-silicon, phosphorus-metal, and multi-phosphorus source compounds, a "1+1>2" flame-retardant effect can be achieved. However, the inherent properties of different flame-retardant components, such as polarity, particle size, and thermal stability, vary greatly, easily leading to uneven dispersion, poor compatibility, and interface defects. This results in problems such as decreased material mechanical properties, reduced migration resistance, and insufficient long-term stability. Furthermore, some components are prone to precipitation and decomposition during processing, affecting the material's appearance and service life, making it difficult to meet the stringent requirements of high-end applications for the comprehensive performance of flame-retardant materials.

[0004] Therefore, there is a need to develop new halogen-free flame retardants. Summary of the Invention

[0005] To address the technical problems existing in physically compounded flame-retardant systems, the present invention aims to provide a novel diphenylphosphine oxide derivative flame retardant for thermoplastic resins with good flame-retardant effect, its preparation method, and its application. Specifically, this is achieved through the following technical solution: Flame retardants for thermoplastic resins using diphenylphosphine oxide derivatives, including flame retardants with formula I structure: Formula I Wherein, R1 is a thiadiazole group and its derivative groups, and R2 is a thiophene group and its derivative groups.

[0006] Optionally, R1 is selected from one of formulas II (1) to (6). Formula II Where • indicates a connection site. For example, this is the location where R1 and N are connected by a single bond.

[0007] Optionally, R2 is selected from one of formulas III (7) to (10). Formula III Where • indicates a connection site. For example, this is the location where R2 is connected to C in the NCP bond via a single bond.

[0008] Optionally, the flame retardant of Formula I is prepared by reacting the intermediate product R1-N=C-R2 of the Schiff base reaction between aminothiadiazole and its derivatives and thiophene formaldehyde and its derivatives with DPO (diphenylphosphine oxide) via a nucleophilic addition reaction.

[0009] Optionally, the aminothiadiazole and its derivatives include one or more of the following: 2-amino-1,3,4-thiadiazole, 5-amino-1,2,3-thiadiazole, 5-amino-1,2,4-thiadiazole, 5-amino-4-phenyl-1,2,3-thiadiazole, 2-amino-5-mercapto-1,3,4-thiadiazole, and 2,5-diamino-1,3,4-thiadiazole.

[0010] Optionally, the thiophene formaldehyde and its derivatives include one or more of 2-thiophene formaldehyde, thiopheno[3,2-b]thiophene-2-formaldehyde, 3-methyl-2-thiophene formaldehyde, and 3-thiophene formaldehyde.

[0011] This application also provides a method for preparing the flame retardant described in any of the above technical solutions, comprising the following steps: S1: Aminothiadiazole and its derivatives, thiophene formaldehyde and its derivatives undergo Schiff base reaction, and intermediate products are obtained by one or more post-treatment methods such as separation, purification and drying as needed. S2: The intermediate product undergoes a nucleophilic addition reaction with DPO, and one or more post-treatment methods such as separation, purification, and drying are performed as needed to obtain the flame retardant described in Formula I; The intermediate product includes R1-N=C-R2. Those skilled in the art can understand, based on the mechanism of the Schiff base reaction, that R1-N=C-R2 is a way of expressing the product of the Schiff base reaction.

[0012] This application also provides a method for preparing the flame retardant described in any of the above technical solutions, comprising the following steps: Aminothiadiazole and its derivatives, thiophene formaldehyde and its derivatives undergo a Schiff base reaction to obtain an intermediate product. DPO is then directly added, undergoing a nucleophilic addition reaction with the intermediate product. Following separation, purification, or drying, or one or more post-treatment methods as needed, the flame retardant of Formula I is obtained. The intermediate product comprises R1-N=C-R2. This simplifies the preparation process and facilitates industrial production.

[0013] Optionally, the molar ratio of aminothiadiazole and its derivatives, thiophene formaldehyde and its derivatives and DPO is (1.0~1.5):1.0:1.0.

[0014] Optionally, the Schiff base reaction is carried out at a temperature of 70-90 °C for 6-8 h, and the nucleophilic addition reaction is carried out at a temperature of 70-90 °C for 12-18 h.

[0015] This application also provides the application of the flame retardant described in any of the above technical solutions as a non-reactive flame retardant for thermoplastic resins, wherein the thermoplastic resin includes one or more compositions of polyamides, polyesters, and polyolefins as the resin matrix.

[0016] Optionally, the composition may further include one or more of the following: reinforcing filler, antioxidant, lubricant, toughening agent, antistatic agent, laser marking agent, and colorant.

[0017] Optionally, the composition further includes a compound flame retardant, which includes one or more of nitrogen-based, phosphorus-based, boron-based, silicon-based, sulfur-based, and halogen flame retardants other than those of Formula I.

[0018] Optionally, the amount of the flame retardant of Formula I is 8 to 25 wt%.

[0019] Optionally, the composition comprises, by weight, the following components: 50-85 parts of thermoplastic resin; 10-40 parts of reinforcing filler; Formula I flame retardant: 8-25 parts.

[0020] Optionally, the composition comprises, by weight, the following components: 45-80 parts of polyamide / polyester resin; 10-35 parts of reinforcing filler; Formula I flame retardant 10-20 parts; The sum of all components is 100 parts by weight, and the composition has a 3.2mm vertical flammability rating of V-0.

[0021] Compared with the prior art, this application provides a novel flame retardant with a No. I structure, which has good flame retardant effect when applied to thermoplastic resins.

[0022] DPO (diphenylphosphine oxide) is a single-component organophosphorus flame retardant with high phosphorus content and good flame retardant effect. It exhibits high gas-phase activity, but due to its low melting point (approximately 56°C), it typically exists in a liquid / solid state, making it inconvenient to handle and limiting its use to epoxy resin flame retardancy. It cannot be used in thermoplastic resins for the following reasons: 1) In the thermoplastic resin processing environment, if the processing site temperature is high, or the frictional heat during the mixing process causes DPO to exist in a liquid state with a certain viscosity, it will cause particle agglomeration, resulting in uneven dispersion. It is also easy to bridge during the feeding process and is easy to remain on the mixing equipment, making cleaning difficult. 2) DPO is a secondary phosphine oxide. Its PH bond is highly reactive and readily reacts with oxygen in the air. For example, at 165°C, its oxidation products are corresponding phosphoric acid derivatives (phenylphosphine acid or its anhydrides) and diphenylphosphine, etc. The introduction of oxygen atoms macroscopically results in an increase in mass. Epoxy resins typically have curing temperatures below 100°C and generally do not undergo oxidation reactions. Therefore, in the prior art, DPO is only used as a flame retardant in epoxy resins. However, at the high processing temperatures of commonly used thermoplastic resins (polyamides are typically above 220°C, polyesters above 210°C, and polypropylene above 190°C), it may have already reacted and lost its original high flame retardant properties. Those skilled in the art can judge from common sense that it cannot be used in thermoplastic resin flame retardant systems. 3) DPO’s P=O is very easy to adsorb environmental moisture through hydrogen bonds or van der Waals forces. It will become damp when placed in the air under normal conditions. Even without considering thermal stability and processing decomposition, when used in thermoplastic resins, the parts will absorb water, which will promote the migration and precipitation of flame retardants, resulting in a decrease in flame retardant performance, unstable part dimensions or part deformation, and difficulty in subsequent assembly. For the reasons mentioned above, those skilled in the art may have technical biases and generally believe that DPO cannot be used in thermoplastic resin systems.

[0023] Compared to DPO, the flame retardant of Formula I of this invention has a higher melting point (up to 170~184℃), remains solid during processing, is easily dispersed, is less prone to oxidation during processing, and the processed parts are less susceptible to moisture and water absorption, exhibiting stable performance. It better meets the production and processing requirements of thermoplastic resins.

[0024] Formula I flame retardants enhance gas-phase activity and flame-retardant efficiency through the synergistic effect of phosphorus, nitrogen, and sulfur in their molecular structure, thus maintaining the mechanical properties of the resin. Simultaneously, the thiophene ring in the molecular structure is an electron-donating group, while the thiadiazole is an electron-withdrawing group. Their coexistence in a single molecule allows for a balanced electron cloud distribution throughout the molecule through electronic effects, reducing internal energy, improving structural stability, and enhancing the ability of the P=O double bond to bind water, thus imparting excellent resistance to hydrolysis and alcoholysis to the manufactured parts. Furthermore, the balanced electronic effect results in weaker acidity and lower corrosion to processing equipment compared to DOPO derivative flame retardants. Formula I flame retardants primarily exhibit gas-phase flame retardancy in thermoplastic resins, exerting their flame-retardant effect through the quenching of phosphorus-oxygen and sulfur-oxygen free radicals, as well as the dilution effect of sulfur-oxygen and nitrogen-containing compounds.

[0025] The flame retardant of Formula I described in this application, when applied to thermoplastic resins, exhibits superior flame retardant performance compared to existing physically compounded flame retardants. It requires a smaller dosage to achieve the same flame retardant effect, thus reducing the impact on the mechanical properties of the manufactured parts. For example, it can achieve a 3.2mm vertical flammability rating of V-0 in a composition with a dosage of 10-20 wt%, which is lower than the dosage required for conventional phosphorus-based flame retardant systems. Attached Figure Description

[0026] Figure 1 For the flame retardant of Example 1 1 H NMR spectrum; Figure 2 The FTIR spectrum of the flame retardant in Example 2 is shown below. Figure 3 For the flame retardant of Example 3 1 H NMR spectrum; Figure 4 For the flame retardant of Example 4 31 P NMR spectrum. Detailed Implementation

[0027] The specific implementation methods of this application are described in detail below through examples. However, the examples of this application are not intended to limit the technical solutions of this application. Any non-substantial changes, such as replacing common technical solutions in the field, using the technical solutions described in the examples of this application are within the protection scope of this application.

[0028] The raw materials used in the embodiments and comparative examples of this invention are as follows, but are not limited to these materials. Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this application can all be obtained commercially: DPO (diphenylphosphine oxide), CAS: 4559-70-0; 2-Amino-1,3,4-thiadiazole, CAS: 4005-51-0; 2-Thiophenecaraldehyde, CAS: 98-03-3; 5-Amino-1,2,3-thiadiazole, CAS: 4100-41-8; 3-Thiophenecaraldehyde, CAS: 498-62-4; 2,5-Diamino-1,3,4-thiadiazole, CAS: 2937-81-7; 3-Methyl-2-thiophenecarboxaldehyde, CAS: 5834-16-2; 2-Amino-5-mercapto-1,3,4-thiadiazole, CAS: 2349-67-9; Thiopheno[3,2-b]thiophene-2-carboxaldehyde, CAS: 31486-86-9; DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide), CAS: 35948-25-5; Ethanol, CAS: 64-17-5; PA6, Tianjin Changlu Haijing 2702BR; PBT, Zhejiang Changhong CH810; Short-cut fiberglass, China Jushi, ECS10-4.5-568H; Antioxidant 1098, commercially available.

[0029] The test methods and standards used in each comparative example and embodiment are as follows: Nuclear magnetic resonance (NMR) spectrometer, 400 MHz, ASTM E2977-15(2023); Fourier transform infrared spectroscopy (FT-IR) was performed using the potassium bromide pellet method, according to ASTM E1252-98 (2021). Differential scanning calorimetry (DSC): ISO 11357-3-2018; Thermogravimetric analysis (TG): ISO 11358-1:2014; The structure of the flame retardant additive was characterized by nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR), and its thermal properties were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TG). Flame retardancy rating: Injection-molded 3.2mm thick standard test strips, tested according to ASTM-D3801-26, which is equivalent to the ANSI / UL 94 20 mm (50W) vertical burning test (V-0, V-1, V-2); The limiting oxygen index was tested according to ASTM D2863-17 standard, and the sample size was 100mm × 6.5mm × 3.2mm.

[0030] The preparation method of the flame retardant of the Formula I diphenylphosphine derivative includes Method 1 and Method 2. It should be noted that the mechanism of Schiff base reaction and nucleophilic addition reaction is common knowledge. Those skilled in the art can obtain the flame retardant of Formula I by controlling the raw materials and reaction conditions according to the examples.

[0031] Method 1 includes the following steps: S1: Aminothiadiazole and its derivatives, thiophene formaldehyde and its derivatives undergo Schiff base reaction, and intermediate products are obtained by one or more post-treatment methods such as separation, purification and drying as needed. S2: The intermediate product undergoes a nucleophilic addition reaction with DPO, and one or more post-treatment methods such as separation, purification, and drying are performed as needed to obtain the flame retardant described in Formula I; The intermediate products include R1-N=C-R2.

[0032] Method 2: Includes the following steps: Aminothiadiazole and its derivatives, thiophene formaldehyde and its derivatives undergo a Schiff base reaction to obtain an intermediate product. DPO is then directly added, undergoing a nucleophilic addition reaction with the intermediate product. Following one or more post-treatment methods such as separation, purification, and drying, the flame retardant described in Formula I is obtained. The intermediate products include R1-N=C-R2.

[0033] The raw materials used to prepare the flame retardant of Formula 1 by the above methods are reasonably priced and easy to industrialize.

[0034] Examples 1-6 use Method 2 to prepare diphenylphosphine oxide derivative flame retardants of Formula I, and Example 7 uses Method 1 to prepare diphenylphosphine oxide derivative flame retardants of Formula I.

[0035] It should be noted that the separation, purification, and drying (if necessary) in Method 1 and Method 2 can be performed by those skilled in the art as needed. For example, purification can be achieved by washing with ethanol and deionized water multiple times. In all embodiments and comparative examples of this application, purification treatment was performed by washing with ethanol and deionized water three times. Example 1

[0036] 0.06 mol of 2-amino-1,3,4-thiadiazole, 0.05 mol of 2-thiophenecarboxaldehyde, and an appropriate amount of ethanol were added to the reaction vessel. Nitrogen gas was introduced to replace the air, and the temperature was then raised to 80 °C and maintained for 6 h. Subsequently, 0.05 mol of DPO was added, and the reaction was continued for 12 h. The product was then separated, purified, and dried to obtain flame retardant 1, a diphenylphosphine oxide derivative with formula I, in approximately 78% yield.

[0037] Thermal performance test results show that the flame retardant has a melting point of 176.2 ℃ and a decomposition start temperature of 287.6 ℃.

[0038] Compared to DPO, the flame retardant 1 prepared in Example 1 has a significantly increased melting point, remaining solid at room temperature. The frictional heat generated during processing and mixing is far below the melting point, which helps reduce unevenness and agglomeration during mixing, as well as bridging and residue issues during material feeding. The thermal decomposition temperature is also significantly increased, meeting the processing temperature requirements of thermoplastic resins such as polyamides, polyesters, and polyolefins.

[0039] The reaction equation is as follows:

[0040] Figure 1 The image shows flame retardant 1. 1The 1H NMR spectrum shows that 8.9 ppm represents the proton in the S-CH=N structure, 8.6 ppm represents the proton in the NH structure, 7.2 and 6.8 ppm represent hydrogen in the S-CH-CH-C structure, and 7.4 ppm represents the proton in the P-CH structure. This is consistent with the target flame retardant structural formula I, indicating that the flame retardant has been successfully synthesized. Example 2

[0041] 0.15 mol of 5-amino-1,2,3-thiadiazole, 0.1 mol of 3-thiophenecarboxaldehyde, and an appropriate amount of ethanol were added to the reaction vessel. Nitrogen gas was introduced to replace the air, and the temperature was then raised to 90 °C and maintained for 7 h. Subsequently, the temperature was set to 70 °C, and 0.1 mol of DPO was added. The reaction was continued for 18 h, and the product was separated, purified, and dried to obtain the diphenylphosphine oxide derivative flame retardant 2 with the structure of Formula I, with a yield of approximately 77%.

[0042] Thermal performance test results show that the flame retardant has a melting point of 170.4 ℃ and a decomposition start temperature of 270.9 ℃.

[0043] Figure 2 The image shows the FTIR spectrum of flame retardant 2. The wavelengths at 3091, 3058, and 1590 cm⁻¹ are also shown. -1 The peaks at 1437 cm⁻¹ correspond to the -N=CH, CH, and C=N bonds in the diazole ring, respectively. -1 The peak at 1095, 855, and 625-165 cm⁻¹ is attributed to the C=C structure of the thiophene ring, while the peaks at 1494, 1254, and 754 cm⁻¹ are caused by the CSC structure within the thiophene ring. Furthermore, the peaks at 1494, 1254, and 754 cm⁻¹ are also attributed to this structure. -1 The peaks at the specified locations correspond to phosphorus-related P-Ph, P=O, and PC bonds. Furthermore, the characteristic peaks corresponding to the PH bond in DPO and the C=N bond in the intermediate have all disappeared, indicating that the flame retardant has been successfully synthesized. Example 3

[0044] 0.2 mol of 2,5-diamino-1,3,4-thiadiazole, 0.15 mol of 3-methyl-2-thiophenecarboxaldehyde, and an appropriate amount of ethanol were added to the reaction vessel. Nitrogen gas was introduced to replace the air, and the temperature was then raised to 70 °C and maintained for 8 h. Subsequently, the temperature was set to 90 °C, and 0.15 mol of DPO was added. The reaction was continued for 14 h, and the product was separated, purified, and dried to obtain the diphenylphosphine oxide derivative flame retardant 3 with the structure of Formula I, with a yield of approximately 81%.

[0045] Thermal performance test results show that the flame retardant has a melting point of 173.2 ℃ and a decomposition start temperature of 281.4 ℃.

[0046] Figure 3 The image shows flame retardant 3.1 ¹H NMR spectrum. 8.9 ppm represents the proton in the S-CH=N structure, 8.7 ppm represents the proton in the NH structure, 7.4 ppm represents the proton in the P-CH structure, and 7.2 and 6.8 ppm represent hydrogen in the S-CH-CH-C structure. The remaining peaks are benzene rings and -CH-. This is consistent with the target flame retardant structural formula I, indicating that the flame retardant has been successfully synthesized. Example 4

[0047] 0.16 mol of 2-amino-5-mercapto-1,3,4-thiadiazole, 0.12 mol of thieno[3,2-b]thiophene-2-carboxaldehyde, and an appropriate amount of ethanol were added to a reaction vessel. Nitrogen gas was introduced to replace the air, and the temperature was then raised to 75°C and maintained for 7 h. Subsequently, 0.15 mol of DPO was added, and the reaction was continued for 17 h. The product was then separated, purified, and dried to obtain flame retardant 4, a diphenylphosphine oxide derivative with formula I, with a yield of approximately 79%.

[0048] Thermal performance test results show that the flame retardant has a melting point of 184.0 ℃ and a decomposition start temperature of 289.7 ℃.

[0049] Figure 4 The image shows flame retardant 4. 31 P NMR spectrum. The results showed that the target flame retardant had a peak at 29.5 ppm, corresponding to the PC bond, indicating that the flame retardant was successfully synthesized. Example 5

[0050] 0.05 mol of 2-amino-1,3,4-thiadiazole, 0.05 mol of 2-thiophenecarboxaldehyde, and an appropriate amount of ethanol were added to the reaction vessel. Nitrogen gas was introduced to replace the air, and the temperature was then raised to 80 °C and maintained for 6 h. Subsequently, 0.05 mol of DPO was added, and the reaction was continued for 12 h. The product was then separated, purified, and dried to obtain the diphenylphosphine oxide derivative flame retardant 5 with the structure of Formula I, with a yield of approximately 72%. Example 6

[0051] 0.05 mol of 2-amino-1,3,4-thiadiazole, 0.06 mol of 2-thiophenecarboxaldehyde, and an appropriate amount of ethanol were added to the reaction vessel. Nitrogen gas was introduced to replace the air, and the temperature was then raised to 80 °C and maintained for 6 h. Subsequently, 0.05 mol of DPO was added, and the reaction was continued for 12 h. The product was then separated, purified, and dried to obtain the diphenylphosphine oxide derivative flame retardant 6 with the formula I structure, with a yield of approximately 61%. Example 7

[0052] 0.06 mol of 2-amino-1,3,4-thiadiazole, 0.05 mol of 2-thiophenecarboxaldehyde, and an appropriate amount of ethanol were added to a reaction vessel. Nitrogen gas was introduced to replace the air, and the temperature was then raised to 80 °C and maintained for 6 h. After the reaction was completed, the intermediate product was obtained by separation, purification, and drying. The yield of the intermediate product was approximately 68%. The intermediate product was then dissolved in ethanol, and 0.05 mol of DPO was added. The reaction was continued for 12 h, and the product was separated, purified, and dried to obtain the diphenylphosphine oxide derivative flame retardant 7 with the formula I structure, with a yield of approximately 68%. Comparative Example 1

[0053] The following is the reaction equation for the flame retardant in Comparative Example 1. 0.06 mol of 2-amino-1,3,4-thiadiazole, 0.05 mol of 2-thiophenecarboxaldehyde, and an appropriate amount of ethanol were added to a reaction vessel. Nitrogen gas was introduced to replace the air, and the temperature was then raised to 80 °C and maintained for 6 h. Subsequently, 0.05 mol of DOPO was added, and the reaction continued for 12 h. The product was then separated, purified, and dried to obtain DOPO derivative flame retardant 8, with a yield of approximately 65%.

[0054] The reaction equation is as follows:

[0055] In the above embodiments and comparative examples: Compared with Example 5, the excess of aminothiadiazole and its derivatives in Example 1 yields a higher yield because the excess amino group can fully react with the aldehyde group in thiophene formaldehyde to form more C=N double bonds, which then react with the PH bond.

[0056] Compared with Example 6, Example 6 has an excess of aldehyde group. The aldehyde group will undergo an addition reaction with the PH bond during the nucleophilic addition process, which reduces the amount of intermediate product reacting with the PH bond. Therefore, the yield of flame retardant 6 will be reduced, and a lot of operations are required for purification, which will also lead to the loss of some products. Therefore, in order to obtain a higher yield, the amino compound needs to be in excess.

[0057] Examples 2, 3, and 4, through the selection of different aminothiadiazoles and their derivatives and thiophene formaldehyde and their derivatives, as well as different ratios with DPO, preparation conditions, and other parameters, combined with characterization, demonstrate that the DPO derivatives with the structure of Formula I were specifically synthesized as flame retardant 2, flame retardant 3, and flame retardant 4.

[0058] Compared to Example 7, Example 1 uses Method 2, resulting in a higher yield of flame retardant 1. Method 2's Schiff base reaction has a similar temperature to the nucleophilic addition reaction, allowing it to continue during the nucleophilic addition phase, thus achieving a higher yield. Furthermore, Method 2 reduces the separation, purification, and drying processes of intermediate products, specifically by reducing solvent dissolution and washing processes, decreasing the amount of washing solvent used, saving resources, and reducing energy consumption during the drying process.

[0059] Compared with Comparative Example 1, the yield of DPO derivative flame retardant 1 in Example 1 was higher than that of DOPO derivative flame retardant 8 because DPO has stronger PH bond activity and a more complete nucleophilic addition reaction.

[0060] Preparation of flame-retardant thermoplastic resins: Examples 8-11 and Comparative Example 2.

[0061] Table 1 shows the composition formulations and properties of the thermoplastic resins in Examples 8-11 and Comparative Example 2. Examples 8-11 used flame retardants 1, 2, 3, and 4 synthesized in Examples 1-4, respectively. Comparative Example 2 used flame retardant 8 synthesized in Comparative Example 1. The components of the compositions in Table 1 were weighed (by weight; 0.2 parts by weight of antioxidant 1098 were added to each example and comparative example composition, which is not shown in Table 1; those skilled in the art can choose whether to add antioxidant according to actual needs), mixed, melted, extruded, and granulated using a twin-screw extruder to prepare flame-retardant thermoplastic resins. The parameters such as the screw extruder temperature and speed, set according to the specific type of thermoplastic resin, are well known to those skilled in the art and will not be described further. Short-cut glass fiber was side-fed. Test strips were injection molded according to the testing standards.

[0062] The flame retardant properties of thermoplastic resins were characterized by flame retardant rating and limiting oxygen index. Test samples were immersed in deionized water and 50% ethylene glycol aqueous solution at 80℃ for 168h. The changes in flame retardant properties before and after immersion were used to evaluate the hydrolysis and alcoholysis resistance of the flame retardant.

[0063] Table 1 shows the composition and properties of the thermoplastic resins in Examples 8-11 and Comparative Example 2.

[0064] Table 1 shows the flame retardancy rating test data, where a is the sample before immersion, b is the sample after immersion in deionized water for 168 hours, and c is the sample after immersion in 50% ethylene glycol aqueous solution for 168 hours.

[0065] t in Table 1 1+2 This represents the sum of the combustion time after the first ignition and the combustion time after the second ignition.

[0066] The flame retardancy rating of the PBT material modified by DOPO derivative flame retardant 8 prepared in Comparative Example 1 was only V-1, with a limiting oxygen index of 28.4%. After soaking in water and ethylene glycol aqueous solution, the flame retardancy rating decreased to V-2, and the limiting oxygen index decreased significantly, indicating that the DOPO derivative has poor resistance to hydrolysis and alcoholysis in the flame retardancy performance of thermoplastic resins.

[0067] In Example 8, the DPO derivative-modified PBT material exhibited good flame retardant performance, with a limiting oxygen index of 30.2% and a flame retardant rating of V-0. After 168 hours of immersion treatment, its flame retardant properties did not significantly decrease, indicating good resistance to hydrolysis and alcoholysis in the thermoplastic resin. Compared to Comparative Example 1, it showed even better flame retardant performance and also demonstrated resistance to hydrolysis and alcoholysis.

[0068] The core raw material of the flame retardant of this invention, diphenylphosphine oxide, has a higher phosphorus content in its structure compared to DOPO, exhibiting higher reactivity and gas-phase flame retardant activity. Furthermore, DOPO contains hydrolyzable and alcoholyzable POC bonds, while diphenylphosphine oxide does not. DOPO has significantly stronger electron-withdrawing ability than diphenylphosphine oxide; stronger electron-withdrawing ability accelerates hydrolysis and alcoholysis. Therefore, flame retardants derived from diphenylphosphine oxide with the same structural framework exhibit better resistance to hydrolysis and alcoholysis. When the flame retardant is applied to thermoplastic resins, it demonstrates good resistance to hydrolysis and alcoholysis in improving the flame retardant properties of the thermoplastic resins.

[0069] DOPO exhibits stronger electron-withdrawing ability, more pronounced molecular polarization, and easier hydrogen dissociation, resulting in stronger acidity. Comparatively, under the same structural framework, DOPO derivatives are more acidic than diphenylphosphine oxide derivatives. The acidity of flame retardants can corrode processing equipment and molds, accelerate the aging and degradation of thermoplastic resins, and reduce the material's thermal stability, mechanical strength, and service life. For matrices containing ester or amide bonds, such as polyamides and polyesters, acidity can also promote bond hydrolysis, gradually reducing the material's overall resistance to hydrolysis, alcoholysis stability, and insulation properties over long-term use.

[0070] Compared with the DOPO derivative flame retardant of Comparative Example 1, the diphenylphosphine oxide derivative flame retardant in this application embodiment is more beneficial for the production and application of thermoplastic plastics such as polyamide and polyester.

[0071] In Examples 9-11, the thermoplastic resins modified with diphenylphosphine oxide derivative flame retardants all achieved excellent flame retardant performance, and the thermoplastic resins also showed good resistance to hydrolysis and alcoholysis.

[0072] It should be noted that the embodiments in this application are merely examples of specific implementation methods and are not intended to limit the scope of protection of this application. Those skilled in the art can replace the same or similar components according to actual needs, and all such replacements are within the scope of protection of this application.

Claims

1. A diphenylphosphine oxide derivative flame retardant for thermoplastic resins, characterized in that, Including flame retardants with Formula I structure: Formula I Among them, R1 is selected from one of formulas II (1) to (5), and R2 is selected from one of formulas III (7) to (10). Formula II Formula III Where • represents a connection site.

2. The method for preparing the flame retardant according to claim 1, characterized in that, Includes the following steps: S1: Aminothiadiazole and its derivatives, thiophene formaldehyde and its derivatives undergo Schiff base reaction, and intermediate products are obtained by one or more post-treatment methods such as separation, purification and drying as needed. S2: The intermediate product undergoes a nucleophilic addition reaction with diphenylphosphine oxide, and one or more post-treatment methods such as separation, purification, and drying are performed as needed to obtain the flame retardant described in Formula I; The intermediate product is R1-N=C-R2.

3. The method for preparing the flame retardant according to claim 1, characterized in that, Includes the following steps: Aminothiadiazole and its derivatives, thiophene formaldehyde and its derivatives undergo a Schiff base reaction to obtain an intermediate product. Diphenylphosphine oxide is then directly added, undergoing a nucleophilic addition reaction with the intermediate product. Following one or more post-treatment methods such as separation, purification, and drying, the flame retardant described in Formula I is obtained. The intermediate product is R1-N=C-R2.

4. The preparation method according to claim 2 or 3, characterized in that, The molar ratio of aminothiadiazole and its derivatives, thiophene formaldehyde and its derivatives and diphenylphosphine oxide is (1.0~1.5):1.0:1.

0.

5. The preparation method according to claim 2 or 3, characterized in that, The Schiff base reaction is carried out at a temperature of 70-90℃ for 6-8 h, and the nucleophilic addition reaction is carried out at a temperature of 70-90℃ for 12-18 h.

6. The application of the flame retardant according to claim 1, characterized in that, A non-reactive flame retardant used as a thermoplastic resin, wherein the thermoplastic resin is one or more of a composition with polyamide, polyester or polyolefin as the resin matrix.

7. The application according to claim 6, characterized in that, The composition further includes one or more of the following: reinforcing filler, antioxidant, lubricant, toughening agent, antistatic agent, laser marking agent, and colorant.

8. The application according to claim 6, characterized in that, The composition further includes a compound flame retardant, which includes one or more of nitrogen-based, phosphorus-based, boron-based, silicon-based, sulfur-based, and halogen flame retardants other than those of Formula I.

9. The application according to claim 6, characterized in that, The amount of flame retardant of Formula I is 8~25wt%.

10. The application according to claim 6, characterized in that, The composition comprises, by weight, the following components: 45-85 parts of thermoplastic resin; 10-40 parts of reinforcing filler; Formula I flame retardant: 8-25 parts; The sum of all components is 100 parts by weight.

11. The application according to claim 10, characterized in that, The composition comprises, by weight, the following components: 45-80 parts of polyamide and / or polyester resin; 10-35 parts of reinforcing filler; Formula I flame retardant 10-20 parts; The total weight of all components is 100 parts by weight, and the composition has a 3.2 mm vertical flammability rating of V-0.

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