An anti-yellowing lc grade dimethylthiophenyl diamine, its preparation method and application

Abstract

This invention discloses an anti-yellowing LC-grade dimethylthiotoluene diamine, its preparation method, and its applications, relating to the field of dimethylthiotoluene diamine chemical raw material technology. The method includes dimethylthiolation of diaminotoluene to obtain a crude product; partial acylation with trimesoyl chloride to introduce a steric barrier; and compounding with TEMPOL, antioxidants 1010 and 168 to construct a three-level synergistic antioxidant network, yielding an anti-yellowing intermediate; then introducing nano-boron nitride and octaphenyl cage-type silsesquioxane to construct an organic-inorganic hybrid heat-resistant network, obtaining an anti-yellowing and heat-resistant product; finally, using γ-cyclodextrin to encapsulate TEMPOL and phytic acid to chelate metal ions, achieving long-term antioxidant stability. The resulting product exhibits excellent anti-yellowing properties, heat resistance, and long-term stability during high-temperature service.

Description

Technical Field

[0001] This invention relates to the field of dimethylthiotoluene diamine chemical raw material technology, specifically to an anti-yellowing LC grade dimethylthiotoluene diamine, its preparation method, and its application. Background Technology

[0002] Dimethylthiotoluene diamine (DMTDA) is an important aromatic diamine curing agent used to replace the carcinogenic curing agent MOCA, and is widely used in the manufacture of cast polyurethane elastomers (CPUs). Existing technologies mainly focus on improving DMTDA synthesis catalysts and optimizing processes. For example, CN117304080A discloses a Lewis acid catalyst with Zn / Cu-supported chelating agent / polydopamine synergistic modification of mesoporous silica-alumina hollow nanospheres, used to improve the conversion rate and catalyst reusability of the DMTDA synthesis reaction. However, conventional DMTDA products still have two major drawbacks: first, the molecule contains a large number of free aromatic amine groups, making it sensitive to light and oxygen. During storage and processing, it is easily oxidized to form quinone chromophores, causing yellowing and severely affecting the appearance quality of downstream light-colored polyurethane products; second, its thermal stability is insufficient. In LC-grade (high-temperature liquid casting grade, typically requiring long-term thermal stability above 150℃) applications, it is prone to oxidation, desulfurization, and amine dehydrogenation degradation reactions, leading to deterioration of the mechanical properties of the cured product. Summary of the Invention

[0003] The purpose of this invention is to provide an anti-yellowing LC-grade dimethylthiotoluene diamine, its preparation method, and its application, so as to solve the technical problems mentioned in the background art.

[0004] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing anti-yellowing LC-grade dimethylthiotoluene diamine includes the following steps: 1) Diaminotoluene, xylene, zinc iodide and dimethyl disulfide were mixed and reacted. After the reaction was completed, the mixture was washed, dried and distilled under reduced pressure to obtain dimethylthiotoluene diamine. 2) The dimethylthiotoluene diamine obtained in step (1) is mixed with ethyl acetate, trimesoyl chloride, triethylamine, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxy radical, antioxidant 1010 and antioxidant 168 and reacted. After the reaction is completed, the mixture is filtered and distilled under reduced pressure to obtain the anti-yellowing dimethylthiotoluene diamine intermediate. 3) Mix and disperse nano boron nitride, toluene, and octaphenyl cage-type silsesquioxane, then add the anti-yellowing dimethyl thiotoluene diamine intermediate obtained in step (2) and mix and react. After the reaction is completed, distill under reduced pressure to obtain anti-yellowing and heat-resistant dimethyl thiotoluene diamine. 4) Mix phytic acid, triethylamine, γ-cyclodextrin, water and ethanol, then add the anti-yellowing heat-resistant dimethyl thiotoluene diamine obtained in step (3) and mix. Remove water and ethanol under reduced pressure to obtain the anti-yellowing LC grade heat-resistant dimethyl thiotoluene diamine.

[0005] The fundamental reason for the yellowing of dimethylthiotoluene diamine (DMTDA) lies in the auto-oxidation of the aromatic amine groups and thiomethyl groups in the molecule under the action of light and oxygen, gradually forming conjugated quinone imines, azo groups, and sulfur oxide chromophores, causing the product color to darken. This invention improves the anti-yellowing performance from two levels: steric protection and multi-level antioxidant blocking. Tristyroyl pyromellitic acid chloride selectively partially acylates with a very small amount of DMTDA aromatic amine at the ortho position under low temperature and ultra-low ratio conditions, constructing a molecular umbrella-like steric barrier around the vast majority of unreacted free amine groups, effectively blocking the attack of oxygen molecules and ultraviolet light on the aromatic amine. The 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPOL), with its NO· active site, rapidly captures the carbon-center alkyl radicals (R·) generated by thermal / photo-oxidative aging in the system at a near-diffusion controlled rate, thus controlling the chain growth reaction at the source. Head blocking; antioxidant 1010, as a hindered phenolic chain terminator, provides hydrogen atoms to peroxide radicals (ROO·) through phenolic hydroxyl groups to generate stable hydroperoxides (ROOH) and inert phenoxy radicals; antioxidant 168, as a phosphite-based auxiliary antioxidant, further decomposes ROOH into harmless alcohols; TEMPOL, 1010 and 168 form a three-level synergistic antioxidant network of R· capture + ROO· chain termination + ROOH decomposition, which, together with the steric barrier, constitutes four lines of defense, reducing the probability of chromophore formation from the source, so that DMTDA can maintain light color stability during long-term storage and high-temperature processing.

[0006] The failure of DMTDA under high-temperature operating conditions mainly manifests as increased molecular chain thermal vibration, homolytic cleavage of CS bonds, thermal oxidation of amine groups, and irreversible degradation caused by local hot spots. This invention addresses this issue by constructing a dual heat-resistant network of thermal conductivity and rigidity: nano-boron nitride possesses extremely high intrinsic thermal conductivity and a hexagonal layered graphene-like structure, uniformly dispersed within the DMTDA matrix to form highly efficient heat conduction channels, rapidly dissipating local hot spots to the whole, preventing heat accumulation on the molecular chains and thus avoiding degradation; octaphenyl cage-type silsesquioxane (OP-POSS) is a rigid nanocage-like molecule with a Si-O-Si inorganic cage as the core and eight phenyl groups as the shell. Its inorganic cage imparts excellent thermal decomposition stability to the material, while the phenyl shells... The boron nitride (BN) sheets are tightly bonded to the DMTDA layer through π-π stacking, while also being compatible with the aromatic rings of DMTDA. This prevents the BN sheets from agglomerating and anchors them firmly in the intermolecular spaces of DMTDA. Non-polar toluene is used as the dispersion medium throughout this step, and the temperature is controlled at 60–65°C to avoid the oxidation-induced effects of highly polar solvents and high temperatures on the aromatic amine system. Together, they form a heat-dissipating and ablation-resistant organic-inorganic hybrid protective layer, which significantly increases the initial decomposition temperature and high-temperature residual weight of DMTDA, thereby improving the heat resistance of DMTDA.

[0007] Preferably, in step 1), the molar ratio of diaminotoluene to dimethyl disulfide is 1:(2.0 to 2.2).

[0008] Preferably, in step 1), the reaction temperature is 105–110°C and the reaction time is 2–4 h.

[0009] Preferably, in step 2), the mass ratio of dimethylthiotoluene diamine to trimesoyl chloride is 100:(0.8-1.2).

[0010] Preferably, in step 2), the mass ratio of dimethylthiotoluene diamine to triethylamine is 100:(3.5-4.5).

[0011] Preferably, in step 3), the mass ratio of the nano-boron nitride to the octaphenyl cage-type silsesquioxane is 2.5:(1-2).

[0012] Preferably, in step 3), the reaction temperature is 60-65°C and the reaction time is 2-4 hours.

[0013] Preferably, in step 4), the mass ratio of phytic acid to γ-cyclodextrin is 2.5:(5-8).

[0014] The present invention found in experiments that dimethylthiotoluene diamine requires long-term stirring and dispersion at 60-65°C during the heat resistance modification process, and the final product will repeatedly undergo a thermal process of over 150°C during high-temperature casting. This continuous thermal environment will cause the core anti-yellowing component TEMPOL to undergo thermal deactivation processes such as α-H thermal migration, piperidine ring cracking, and migration and volatilization to the matrix surface. As a result, the anti-yellowing function will be reduced to varying degrees after heat resistance modification and in subsequent use, and the color index of the LC grade product will be difficult to stably meet the standard. To address this technical problem, this invention introduces γ-cyclodextrin and phytic acid in step 4: γ-cyclodextrin selectively encapsulates the tetramethylpiperidine hydrophobic segment of TEMPOL through its hydrophobic cavity, forming a host-guest inclusion complex (the polar NO· and 4-hydroxyl groups exposed at the cavity opening can still participate normally in free radical capture). By significantly restricting the translational / rotational degrees of freedom of the TEMPOL molecule, it inhibits its α-H thermal migration and ring cracking, thus reducing its volatilization loss and surface migration tendency during high-temperature processing, and significantly improving the thermal stability and migration resistance of TEMPOL; phytic acid is a natural polyhydroxy polyhydric acid... Phosphoric acid compounds, with their six phosphate groups, can strongly chelate with residual transition metal ions in the system, interrupting the catalytic decomposition pathway of nitroxide free radicals by metal ions. At the same time, their polyhydroxy structure can form a hydrogen bond network with DMTDA aromatic amines to further consolidate the anti-yellowing protective layer. Phytic acid is pre-neutralized to pH 5-6 with triethylamine before addition, which not only eliminates the risk of protonation of aromatic amines by its strong acidity, but also fully preserves the chelating ability of the phosphate groups. Both phytic acid and methyl methacrylate are stabilized by physical confinement and reinforced by chemical passivation, respectively, and the functions of TEMPOL are synergistically preserved through both spatial and electronic pathways, thereby achieving excellent anti-yellowing performance.

[0015] An anti-yellowing LC-grade dimethylthiotoluene diamine is prepared by the method described above.

[0016] Application of an anti-yellowing LC-grade dimethylthiotoluene diamine in polyurethane elastomer chain extenders or epoxy resin curing agents.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. By combining molecular umbrella-shaped steric hindrance shielding with a three-level synergistic antioxidant network of TEMPOL, antioxidant 1010, and antioxidant 168, the chromophore formation pathway is blocked at the source, enabling the product to maintain a stable light color during long-term storage and high-temperature processing.

[0018] 2. By utilizing the high thermal conductivity channels of nano-boron nitride and the rigid heat-resistant cage structure of octaphenyl cage-type silsesquioxane, an organic-inorganic hybrid dual network is constructed, which effectively disperses local hot spots and inhibits thermal degradation, significantly improving the product's initial decomposition temperature and high-temperature residual weight rate.

[0019] 3. γ-cyclodextrin is used to physically confine and encapsulate TEMPOL to inhibit its thermal deactivation and migration volatilization. At the same time, phytic acid is used to chelate metal ions and form hydrogen bond reinforcement networks. The core antioxidant components are protected from spatial and electronic pathways to ensure long-term anti-yellowing performance in subsequent high-temperature modification and casting use. Attached Figure Description

[0020] Figure 1 The thermogravimetric curve of dimethylthiotoluene diamine prepared in Example 4 of this invention is shown. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1 A method for preparing anti-yellowing LC-grade dimethylthiotoluene diamine includes the following steps: Step 1) In a 500 mL four-necked flask equipped with a mechanical stirrer, thermometer, reflux condenser, and nitrogen delivery tube, nitrogen gas was first purged for 30 min. 0.1 mol diaminotoluene was added, and the mixture was heated in an oil bath to 105 °C to melt. Then, 200 mL of anhydrous xylene was added and stirred to dissolve. 1.27 g of zinc iodide was added, and the temperature was raised to 110 °C. 0.215 mol dimethyl disulfide was added dropwise over 30 min through a constant pressure dropping funnel. After the addition was complete, the mixture was stirred at 400 r / min at 108 °C for 3 h. The mixture was cooled to below 30 °C, diluted with 200 mL of diethyl ether, and transferred to a separatory funnel. The mixture was washed three times with 100 mL of 0.5 mol / L dilute hydrochloric acid, and then washed with distilled water until neutral. The organic phase was dried with anhydrous sodium sulfate for 6 h, filtered, and then distilled under reduced pressure at 75 °C and -0.095 MPa to remove diethyl ether and xylene, yielding a pale yellow viscous liquid, namely dimethylthiotoluene diamine.

[0023] Step 2) Add 100g of dimethylthiotoluene diamine obtained in step (1) to a 1000mL four-necked flask equipped with a mechanical stirrer, thermometer, constant pressure dropping funnel and nitrogen delivery tube, then add 300g of anhydrous ethyl acetate and stir to dissolve. After purging with nitrogen for 30min, cool to 3℃. Separately, dissolve 1.1g of trimesoyl chloride in 50g of anhydrous ethyl acetate to prepare an acyl chloride solution, and slowly add it dropwise to the reaction flask at a rate of 2 drops per second over 30min. At the same time, add 4.3g of triethylamine as an acid-binding agent. After the addition is complete, remove the cold bath, and naturally heat to 25℃, stirring at 300r / min for 2h. Then add 0.8g of [acid-binding agent] at once. 4-Hydroxy-2,2,6,6-Tetramethylpiperidine-1-oxy radical was added and stirred at 25°C for 1 hour. Then, 0.6 g of antioxidant 1010 and 0.4 g of antioxidant 168 were added sequentially, and the mixture was heated to 40°C and stirred for 30 minutes until completely dispersed. The reaction solution was filtered through a 0.45 μm filter membrane while hot to remove triethylamine hydrochloride. The filtrate was transferred to a rotary evaporator and ethyl acetate was removed under reduced pressure at 40°C and -0.09 MPa to obtain a light yellow homogeneous liquid, which is the anti-yellowing dimethylthiotoluene diamine intermediate. It was sealed and stored under nitrogen protection.

[0024] Step 3) Add 2.5g of boron nitride nanoparticles with a particle size of 50-100nm to a 1000mL three-necked flask equipped with a mechanical stirrer and a thermometer, then add 500g of anhydrous toluene. Place the flask in a 500W ultrasonic water bath and use an ice-water bath to control the temperature at ≤30℃ for ultrasonic dispersion for 30min to form a milky white dispersion. Separately, dissolve 1.8g of octaphenylcage-type silsesquioxane in 100g of anhydrous toluene and stir at 200r / min for 40min in a 65℃ water bath until completely dissolved. While maintaining ultrasonic and ice-water bath conditions, slowly add the toluene solution of octaphenylcage-type silsesquioxane to the boron nitride nanoparticle dispersion dropwise over 15min. After the first drop was completed, sonication was continued for 15 minutes to obtain a BN@OP-POSS hybrid dispersion. 100g of the anti-yellowing dimethyl thiotoluene diamine intermediate obtained in step (2) was preheated and melted in a water bath at 70°C, and slowly poured into the above hybrid dispersion. The sonication device was removed, and the process was switched to oil bath heating. The temperature was raised to 63°C under nitrogen protection and stirred at 350r / min for 3h. After the reaction was completed, the mixture was transferred to a rotary evaporator and toluene was removed under reduced pressure at 75°C and -0.095MPa for 2h until no solvent was distilled off, resulting in a light yellow, semi-transparent, viscous liquid, i.e., anti-yellowing heat-resistant dimethyl thiotoluene diamine, which was then sealed and stored under nitrogen.

[0025] Step 4) Take 0.25g of phytic acid and add it to deionized water to prepare a 50wt% phytic acid aqueous solution. Add triethylamine dropwise under magnetic stirring to adjust the pH to 5-6. Take another 0.7g of γ-cyclodextrin and add it to a 250mL conical flask equipped with a magnetic stirrer. Add 10g of water / anhydrous ethanol mixed solvent (water:ethanol = 1:1w / w). Stir at 500r / min for 20min in a 40℃ water bath until completely dissolved. Combine the neutralized phytic acid solution with the γ-cyclodextrin solution and continue stirring at 40℃ for 10min to obtain a colorless and transparent homogeneous auxiliary agent solution. Transfer all the anti-yellowing and heat-resistant dimethylthiotoluene diamine obtained in step (3) into a 500mL double-layer reactor equipped with an anchor-type mechanical stirrer, thermometer and vacuum interface. Start the jacket circulation. The circulating water was heated to 50°C, and the vacuum pump was turned on to reduce the system pressure to -0.08 MPa. The auxiliary agent solution was slowly injected into the reactor in three batches, with each batch 10 minutes apart, through the needle valve. After injection, the mixture was stirred at 250 r / min for 1 hour at 50°C and -0.08 MPa, so that water and ethanol would evaporate under vacuum and be collected in a cold trap. After heating was stopped, the mixture was stirred under vacuum for another 30 minutes and cooled to room temperature. The product was then removed from the vacuum and a light yellow, uniform, viscous liquid was obtained, which is the anti-yellowing LC-grade heat-resistant dimethyl thiotoluene diamine product. It was then stored in a nitrogen-filled, light-proof, and sealed container.

[0026] Example 2 A method for preparing anti-yellowing LC-grade dimethylthiotoluene diamine includes the following steps: Step 1) In a 500 mL four-necked flask equipped with a mechanical stirrer, thermometer, reflux condenser, and nitrogen delivery tube, nitrogen gas was first purged for 30 min. 0.1 mol diaminotoluene was added, and the mixture was heated in an oil bath to 105 °C to melt. Then, 200 mL of anhydrous xylene was added and stirred to dissolve. 1.27 g of zinc iodide was added, and the temperature was raised to 110 °C. 0.205 mol dimethyl disulfide was added dropwise over 30 min through a constant pressure dropping funnel. After the addition was complete, the mixture was stirred at 400 r / min at 108 °C for 3 h. The mixture was cooled to below 30 °C, diluted with 200 mL of diethyl ether, and transferred to a separatory funnel. The mixture was washed three times with 100 mL of 0.5 mol / L dilute hydrochloric acid, and then washed with distilled water until neutral. The organic phase was dried with anhydrous sodium sulfate for 6 h, filtered, and then distilled under reduced pressure at 75 °C and -0.095 MPa to remove diethyl ether and xylene, yielding a pale yellow viscous liquid, namely dimethylthiotoluene diamine.

[0027] Step 2) Add 100g of dimethylthiotoluenediamine obtained in step (1) to a 1000mL four-necked flask equipped with a mechanical stirrer, thermometer, constant pressure dropping funnel and nitrogen delivery tube, then add 300g of anhydrous ethyl acetate and stir to dissolve. After purging with nitrogen for 30min, cool to 3℃. Separately, dissolve 0.9g of trimesoyl chloride in 50g of anhydrous ethyl acetate to prepare an acyl chloride solution, and slowly add it dropwise to the reaction flask at a rate of 2 drops per second over 30min. At the same time, add 3.8g of triethylamine as an acid-binding agent. After the addition is complete, remove the cold bath, allow the temperature to rise naturally to 25℃, and stir at 300r / min for 2h. Then add 0.8g of [acid-binding agent] all at once. 4-Hydroxy-2,2,6,6-Tetramethylpiperidine-1-oxy radical was added and stirred at 25°C for 1 hour. Then, 0.6 g of antioxidant 1010 and 0.4 g of antioxidant 168 were added sequentially, and the mixture was heated to 40°C and stirred for 30 minutes until completely dispersed. The reaction solution was filtered through a 0.45 μm filter membrane while hot to remove triethylamine hydrochloride. The filtrate was transferred to a rotary evaporator and ethyl acetate was removed under reduced pressure at 40°C and -0.09 MPa to obtain a light yellow homogeneous liquid, which is the anti-yellowing dimethylthiotoluene diamine intermediate. It was sealed and stored under nitrogen protection.

[0028] Step 3) Add 2.5g of boron nitride nanoparticles with a particle size of 50-100nm to a 1000mL three-necked flask equipped with a mechanical stirrer and a thermometer, then add 500g of anhydrous toluene. Place the flask in a 500W ultrasonic water bath and use an ice-water bath to control the temperature at ≤30℃ for ultrasonic dispersion for 30min to form a milky white dispersion. Separately, dissolve 1.2g of octaphenylcage-type silsesquioxane in 100g of anhydrous toluene and stir at 200r / min for 40min in a 65℃ water bath until completely dissolved. While maintaining ultrasonic and ice-water bath conditions, slowly add the toluene solution of octaphenylcage-type silsesquioxane to the boron nitride nanoparticle dispersion dropwise over 15min. After the first drop was completed, sonication was continued for 15 minutes to obtain a BN@OP-POSS hybrid dispersion. 100g of the anti-yellowing dimethyl thiotoluene diamine intermediate obtained in step (2) was preheated and melted in a water bath at 70°C, and slowly poured into the above hybrid dispersion. The sonication device was removed, and the process was switched to oil bath heating. The temperature was raised to 63°C under nitrogen protection and stirred at 350r / min for 3h. After the reaction was completed, the mixture was transferred to a rotary evaporator and toluene was removed under reduced pressure at 75°C and -0.095MPa for 2h until no solvent was distilled off, resulting in a light yellow, semi-transparent, viscous liquid, i.e., anti-yellowing heat-resistant dimethyl thiotoluene diamine, which was then sealed and stored under nitrogen.

[0029] Step 4) Take 0.25g of phytic acid and add it to deionized water to prepare a 50wt% phytic acid aqueous solution. Add triethylamine dropwise under magnetic stirring to adjust the pH to 5-6. Take another 0.6g of γ-cyclodextrin and add it to a 250mL conical flask equipped with a magnetic stirrer. Add 10g of water / anhydrous ethanol mixed solvent (water:ethanol = 1:1w / w). Stir at 500r / min for 20min in a 40℃ water bath until completely dissolved. Combine the neutralized phytic acid solution with the γ-cyclodextrin solution and continue stirring at 40℃ for 10min to obtain a colorless and transparent homogeneous auxiliary agent solution. Transfer all the anti-yellowing and heat-resistant dimethylthiotoluene diamine obtained in step (3) into a 500mL double-layer reactor equipped with an anchor-type mechanical stirrer, thermometer and vacuum interface. Start the jacket circulation. The circulating water was heated to 50°C, and the vacuum pump was turned on to reduce the system pressure to -0.08 MPa. The auxiliary agent solution was slowly injected into the reactor in three batches, with each batch 10 minutes apart, through the needle valve. After injection, the mixture was stirred at 250 r / min for 1 hour at 50°C and -0.08 MPa, so that water and ethanol would evaporate under vacuum and be collected in a cold trap. After heating was stopped, the mixture was stirred under vacuum for another 30 minutes and cooled to room temperature. The product was then removed from the vacuum and a light yellow, uniform, viscous liquid was obtained, which is the anti-yellowing LC-grade heat-resistant dimethyl thiotoluene diamine product. It was then stored in a nitrogen-filled, light-proof, and sealed container.

[0030] Example 3 A method for preparing anti-yellowing LC-grade dimethylthiotoluene diamine includes the following steps: Step 1) In a 500 mL four-necked flask equipped with a mechanical stirrer, thermometer, reflux condenser, and nitrogen delivery tube, nitrogen was first purged for 30 min. 0.1 mol of diaminotoluene was added, and the mixture was heated in an oil bath to 105 °C to melt. Then, 200 mL of anhydrous xylene was added and stirred to dissolve. 1.27 g of zinc iodide was added, and the temperature was raised to 110 °C. 0.210 mol of dimethyl disulfide was added dropwise over 30 min through a constant pressure dropping funnel. After the addition was complete, the mixture was stirred at 400 r / min at 108 °C for 3 h. The mixture was cooled to below 30 °C, diluted with 200 mL of diethyl ether, and transferred to a separatory funnel. The mixture was washed three times with 100 mL of 0.5 mol / L dilute hydrochloric acid, and then washed with distilled water until neutral. The organic phase was dried with anhydrous sodium sulfate for 6 h, filtered, and then distilled under reduced pressure at 75 °C and -0.095 MPa to remove diethyl ether and xylene, yielding a pale yellow viscous liquid, namely dimethylthiotoluene diamine.

[0031] Step 2) Add 100g of dimethylthiotoluene diamine obtained in step (1) to a 1000mL four-necked flask equipped with a mechanical stirrer, thermometer, constant pressure dropping funnel and nitrogen delivery tube, then add 300g of anhydrous ethyl acetate and stir to dissolve. After purging with nitrogen for 30min, cool to 3℃. Separately, dissolve 1.0g of trimesoyl chloride in 50g of anhydrous ethyl acetate to prepare an acyl chloride solution, and slowly add it dropwise to the reaction flask at a rate of 2 drops per second over 30min. At the same time, add 4.0g of triethylamine as an acid-binding agent. After the addition is complete, remove the cold bath, and naturally heat to 25℃, stirring at 300r / min for 2h. Then add 0.8g of [acid-binding agent] at once. 4-Hydroxy-2,2,6,6-Tetramethylpiperidine-1-oxy radical was added and stirred at 25°C for 1 hour. Then, 0.6 g of antioxidant 1010 and 0.4 g of antioxidant 168 were added sequentially, and the mixture was heated to 40°C and stirred for 30 minutes until completely dispersed. The reaction solution was filtered through a 0.45 μm filter membrane while hot to remove triethylamine hydrochloride. The filtrate was transferred to a rotary evaporator and ethyl acetate was removed under reduced pressure at 40°C and -0.09 MPa to obtain a light yellow homogeneous liquid, which is the anti-yellowing dimethylthiotoluene diamine intermediate. It was sealed and stored under nitrogen protection.

[0032] Step 3) Add 2.5g of boron nitride nanoparticles with a particle size of 50-100nm to a 1000mL three-necked flask equipped with a mechanical stirrer and a thermometer, then add 500g of anhydrous toluene. Place the flask in a 500W ultrasonic water bath and use an ice-water bath to control the temperature at ≤30℃ for ultrasonic dispersion for 30min to form a milky white dispersion. Separately, dissolve 1.5g of octaphenylcage-type silsesquioxane in 100g of anhydrous toluene and stir at 200r / min for 40min in a 65℃ water bath until completely dissolved. While maintaining ultrasonic and ice-water bath conditions, slowly add the toluene solution of octaphenylcage-type silsesquioxane to the boron nitride nanoparticle dispersion dropwise over 15min. After the first drop was completed, sonication was continued for 15 minutes to obtain a BN@OP-POSS hybrid dispersion. 100g of the anti-yellowing dimethyl thiotoluene diamine intermediate obtained in step (2) was preheated and melted in a water bath at 70°C, and slowly poured into the above hybrid dispersion. The sonication device was removed, and the process was switched to oil bath heating. The temperature was raised to 63°C under nitrogen protection and stirred at 350r / min for 3h. After the reaction was completed, the mixture was transferred to a rotary evaporator and toluene was removed under reduced pressure at 75°C and -0.095MPa for 2h until no solvent was distilled off, resulting in a light yellow, semi-transparent, viscous liquid, i.e., anti-yellowing heat-resistant dimethyl thiotoluene diamine, which was then sealed and stored under nitrogen.

[0033] Step 4) Take 0.25g of phytic acid and add it to deionized water to prepare a 50wt% phytic acid aqueous solution. Add triethylamine dropwise under magnetic stirring to adjust the pH to 5-6. Take another 0.65g of γ-cyclodextrin and add it to a 250mL conical flask equipped with a magnetic stirrer. Add 10g of water / anhydrous ethanol mixed solvent (water:ethanol = 1:1w / w). Stir at 500r / min for 20min in a 40℃ water bath until completely dissolved. Combine the neutralized phytic acid solution with the γ-cyclodextrin solution and continue stirring at 40℃ for 10min to obtain a colorless and transparent homogeneous auxiliary agent solution. Transfer all the anti-yellowing and heat-resistant dimethylthiotoluene diamine obtained in step (3) into a 500mL double-layer reactor equipped with an anchor-type mechanical stirrer, thermometer and vacuum interface. Start the jacket circulation. The circulating water was heated to 50°C, and the vacuum pump was turned on to reduce the system pressure to -0.08 MPa. The auxiliary agent solution was slowly injected into the reactor in three batches, with each batch 10 minutes apart, through the needle valve. After injection, the mixture was stirred at 250 r / min for 1 hour at 50°C and -0.08 MPa, so that water and ethanol would evaporate under vacuum and be collected in a cold trap. After heating was stopped, the mixture was stirred under vacuum for another 30 minutes and cooled to room temperature. The product was then removed from the vacuum and a light yellow, uniform, viscous liquid was obtained, which is the anti-yellowing LC-grade heat-resistant dimethyl thiotoluene diamine product. It was then stored in a nitrogen-filled, light-proof, and sealed container.

[0034] Example 4 A method for preparing anti-yellowing LC-grade dimethylthiotoluene diamine includes the following steps: Step 1) In a 500 mL four-necked flask equipped with a mechanical stirrer, thermometer, reflux condenser, and nitrogen delivery tube, nitrogen gas was first purged for 30 min. 0.1 mol of diaminotoluene was added, and the mixture was heated in an oil bath to 105 °C to melt. Then, 200 mL of anhydrous xylene was added and stirred to dissolve. 1.27 g of zinc iodide was added, and the temperature was raised to 110 °C. 0.22 mol of dimethyl disulfide was added dropwise over 30 min through a constant pressure dropping funnel. After the addition was complete, the mixture was stirred at 400 r / min at 110 °C for 4 h. The mixture was cooled to below 30 °C, diluted with 200 mL of diethyl ether, and transferred to a separatory funnel. The mixture was washed three times with 100 mL of 0.5 mol / L dilute hydrochloric acid, and then washed with distilled water until neutral. The organic phase was dried with anhydrous sodium sulfate for 6 h, filtered, and then distilled under reduced pressure at 75 °C and -0.095 MPa to remove diethyl ether and xylene, yielding a pale yellow viscous liquid, namely dimethylthiotoluene diamine.

[0035] Step 2) Add 100g of dimethylthiotoluene diamine obtained in step (1) to a 1000mL four-necked flask equipped with a mechanical stirrer, thermometer, constant pressure dropping funnel and nitrogen delivery tube, then add 300g of anhydrous ethyl acetate and stir to dissolve. After purging with nitrogen for 30min, cool to 3℃. Separately, dissolve 1.2g of trimesoyl chloride in 50g of anhydrous ethyl acetate to prepare an acyl chloride solution, and slowly add it dropwise to the reaction flask at a rate of 2 drops per second over 30min. At the same time, add 4.5g of triethylamine as an acid-binding agent. After the addition is complete, remove the cold bath, and naturally heat to 25℃, stirring at 300r / min for 2h. Then add 0.8g of [acid-binding agent] at once. 4-Hydroxy-2,2,6,6-Tetramethylpiperidine-1-oxy radical was added and stirred at 25°C for 1 hour. Then, 0.6 g of antioxidant 1010 and 0.4 g of antioxidant 168 were added sequentially, and the mixture was heated to 40°C and stirred for 30 minutes until completely dispersed. The reaction solution was filtered through a 0.45 μm filter membrane while hot to remove triethylamine hydrochloride. The filtrate was transferred to a rotary evaporator and ethyl acetate was removed under reduced pressure at 40°C and -0.09 MPa to obtain a light yellow homogeneous liquid, which is the anti-yellowing dimethylthiotoluene diamine intermediate. It was sealed and stored under nitrogen protection.

[0036] Step 3) Add 2.5g of boron nitride nanoparticles with a particle size of 50-100nm to a 1000mL three-necked flask equipped with a mechanical stirrer and a thermometer, then add 500g of anhydrous toluene. Place the flask in a 500W ultrasonic water bath and use an ice-water bath to control the temperature at ≤30℃ for ultrasonic dispersion for 30min to form a milky white dispersion. Separately, dissolve 2g of octaphenyl cage-type silsesquioxane in 100g of anhydrous toluene and stir at 200r / min for 40min in a 65℃ water bath until completely dissolved. While maintaining ultrasonic and ice-water bath conditions, slowly add the toluene solution of octaphenyl cage-type silsesquioxane to the boron nitride nanoparticle dispersion dropwise over 15min. After the droplet was added, sonication was continued for 15 minutes to obtain the BN@OP-POSS hybrid dispersion. 100g of the anti-yellowing dimethyl thiotoluene diamine intermediate obtained in step (2) was preheated and melted in a water bath at 70°C, and slowly poured into the above hybrid dispersion. The sonication device was removed, and the process was switched to oil bath heating. The temperature was raised to 65°C under nitrogen protection and stirred at 350r / min for 4h. After the reaction was completed, the mixture was transferred to a rotary evaporator and toluene was removed under reduced pressure at 75°C and -0.095MPa for 2h until no solvent was distilled off, resulting in a light yellow, semi-transparent, viscous liquid, i.e., anti-yellowing heat-resistant dimethyl thiotoluene diamine, which was then sealed and stored under nitrogen.

[0037] Step 4) Take 0.25g of phytic acid and add it to deionized water to prepare a 50wt% phytic acid aqueous solution. Add triethylamine dropwise under magnetic stirring to adjust the pH to 5-6. Take another 0.8g of γ-cyclodextrin and add it to a 250mL conical flask equipped with a magnetic stirrer. Add 10g of water / anhydrous ethanol mixed solvent (water:ethanol = 1:1w / w). Stir at 500r / min for 20min in a 40℃ water bath until completely dissolved. Combine the neutralized phytic acid solution with the γ-cyclodextrin solution and continue stirring at 40℃ for 10min to obtain a colorless and transparent homogeneous auxiliary agent solution. Transfer all the anti-yellowing and heat-resistant dimethylthiotoluene diamine obtained in step (3) into a 500mL double-layer reactor equipped with an anchor-type mechanical stirrer, thermometer and vacuum interface. Start the jacket circulation. The circulating water was heated to 50°C, and the vacuum pump was turned on to reduce the system pressure to -0.08 MPa. The auxiliary agent solution was slowly injected into the reactor in three batches, with each batch 10 minutes apart, through the needle valve. After injection, the mixture was stirred at 250 r / min for 1 hour at 50°C and -0.08 MPa, so that water and ethanol would evaporate under vacuum and be collected in a cold trap. After heating was stopped, the mixture was stirred under vacuum for another 30 minutes and cooled to room temperature. The product was then removed from the vacuum and a light yellow, uniform, viscous liquid was obtained, which is the anti-yellowing LC-grade heat-resistant dimethyl thiotoluene diamine product. It was then stored in a nitrogen-filled, light-proof, and sealed container.

[0038] like Figure 1 The graph shows the thermogravimetric curve of dimethylthiotoluene diamine prepared in Example 4 of this invention. It can be seen from the graph that the 5% thermogravimetric temperature is 295℃ and the residual weight at 600℃ is 20.6%.

[0039] Example 5 A method for preparing anti-yellowing LC-grade dimethylthiotoluene diamine includes the following steps: Step 1) In a 500 mL four-necked flask equipped with a mechanical stirrer, thermometer, reflux condenser, and nitrogen delivery tube, nitrogen gas was first purged for 30 min. 0.1 mol diaminotoluene was added, and the mixture was heated in an oil bath to 105 °C to melt. Then, 200 mL of anhydrous xylene was added and stirred to dissolve. 1.27 g of zinc iodide was added, and the temperature was raised to 110 °C. 0.2 mol dimethyl disulfide was added dropwise over 30 min through a constant pressure dropping funnel. After the addition was complete, the mixture was stirred at 400 r / min at 105 °C for 2 h. The mixture was cooled to below 30 °C, diluted with 200 mL of diethyl ether, and transferred to a separatory funnel. The mixture was washed three times with 100 mL of 0.5 mol / L dilute hydrochloric acid, and then washed with distilled water until neutral. The organic phase was dried with anhydrous sodium sulfate for 6 h, filtered, and then distilled under reduced pressure at 75 °C and -0.095 MPa to remove diethyl ether and xylene, yielding a pale yellow viscous liquid, namely dimethylthiotoluene diamine.

[0040] Step 2) Add 100g of dimethylthiotoluene diamine obtained in step (1) to a 1000mL four-necked flask equipped with a mechanical stirrer, thermometer, constant pressure dropping funnel and nitrogen delivery tube, then add 300g of anhydrous ethyl acetate and stir to dissolve. After purging with nitrogen for 30min, cool to 3℃. Separately, dissolve 0.8g of trimesoyl chloride in 50g of anhydrous ethyl acetate to prepare an acyl chloride solution, and slowly add it dropwise to the reaction flask at a rate of 2 drops per second over 30min. At the same time, add 3.5g of triethylamine as an acid-binding agent. After the addition is complete, remove the cold bath, and naturally heat to 25℃, stirring at 300r / min for 2h. Then add 0.8g of the solution all at once. 4-Hydroxy-2,2,6,6-Tetramethylpiperidine-1-oxy radical was added and stirred at 25°C for 1 hour. Then, 0.6 g of antioxidant 1010 and 0.4 g of antioxidant 168 were added sequentially, and the mixture was heated to 40°C and stirred for 30 minutes until completely dispersed. The reaction solution was filtered through a 0.45 μm filter membrane while hot to remove triethylamine hydrochloride. The filtrate was transferred to a rotary evaporator and ethyl acetate was removed under reduced pressure at 40°C and -0.09 MPa to obtain a light yellow homogeneous liquid, which is the anti-yellowing dimethylthiotoluene diamine intermediate. It was sealed and stored under nitrogen protection.

[0041] Step 3) Add 2.5g of boron nitride nanoparticles with a particle size of 50-100nm to a 1000mL three-necked flask equipped with a mechanical stirrer and a thermometer, then add 500g of anhydrous toluene. Place the flask in a 500W ultrasonic water bath and use an ice-water bath to control the temperature at ≤30℃ for ultrasonic dispersion for 30min to form a milky white dispersion. Separately, dissolve 1g of octaphenylcage-type silsesquioxane in 100g of anhydrous toluene and stir at 200r / min for 40min in a 65℃ water bath until completely dissolved. While maintaining ultrasonic and ice-water bath conditions, slowly add the toluene solution of octaphenylcage-type silsesquioxane to the boron nitride nanoparticle dispersion dropwise over 15min. After the droplet was added, sonication was continued for 15 minutes to obtain the BN@OP-POSS hybrid dispersion. 100g of the anti-yellowing dimethyl thiotoluene diamine intermediate obtained in step (2) was preheated and melted in a water bath at 70°C, and slowly poured into the above hybrid dispersion. The sonication device was removed, and the process was switched to oil bath heating. The temperature was raised to 60°C under nitrogen protection and stirred at 350r / min for 2h. After the reaction was completed, the mixture was transferred to a rotary evaporator and toluene was removed under reduced pressure at 75°C and -0.095MPa for 2h until no solvent was distilled off, resulting in a light yellow, semi-transparent, viscous liquid, i.e., anti-yellowing heat-resistant dimethyl thiotoluene diamine, which was then sealed and stored under nitrogen.

[0042] Step 4) Take 0.25g of phytic acid and add it to deionized water to prepare a 50wt% phytic acid aqueous solution. Add triethylamine dropwise under magnetic stirring to adjust the pH to 5-6. Take another 0.5g of γ-cyclodextrin and add it to a 250mL conical flask equipped with a magnetic stirrer. Add 10g of water / anhydrous ethanol mixed solvent (water:ethanol = 1:1w / w). Stir at 500r / min for 20min in a 40℃ water bath until completely dissolved. Combine the neutralized phytic acid solution with the γ-cyclodextrin solution and continue stirring at 40℃ for 10min to obtain a colorless and transparent homogeneous auxiliary agent solution. Transfer all the anti-yellowing and heat-resistant dimethylthiotoluene diamine obtained in step (3) into a 500mL double-layer reactor equipped with an anchor-type mechanical stirrer, thermometer and vacuum interface. Start the jacket circulation. The circulating water was heated to 50°C, and the vacuum pump was turned on to reduce the system pressure to -0.08 MPa. The auxiliary agent solution was slowly injected into the reactor in three batches, with each batch 10 minutes apart, through the needle valve. After injection, the mixture was stirred at 250 r / min for 1 hour at 50°C and -0.08 MPa, so that water and ethanol would evaporate under vacuum and be collected in a cold trap. After heating was stopped, the mixture was stirred under vacuum for another 30 minutes and cooled to room temperature. The product was then removed from the vacuum and a light yellow, uniform, viscous liquid was obtained, which is the anti-yellowing LC-grade heat-resistant dimethyl thiotoluene diamine product. It was then stored in a nitrogen-filled, light-proof, and sealed container.

[0043] Comparative Example 1: Compared with Example 4, the only difference is that step 2) of the anti-yellowing modification is omitted, that is, pyromellitic methyl chloride, triethylamine, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxy radical, antioxidant 1010 and antioxidant 168 are not added. The other raw materials, amounts and reaction conditions are exactly the same as those in Example 4.

[0044] Comparative Example 2: Compared with Example 4, the only difference is that the heat resistance modification in step 3) is omitted, that is, nano boron nitride, toluene and octaphenyl cage-type silsesquioxane are not added. The other raw materials, dosages and reaction conditions are exactly the same as those in Example 4.

[0045] Comparative Example 3: Compared with Example 4, the only difference is that the synergistic agent treatment in step 4) is omitted, that is, phytic acid, γ-cyclodextrin, water, ethanol and triethylamine are not added. The other raw materials, amounts and reaction conditions are exactly the same as in Example 4.

[0046] Comparative Example 4: Compared with Example 4, the only difference is that 0.8 g of γ-cyclodextrin was not added in step 4), while the other raw materials, amounts and reaction conditions were exactly the same as in Example 4.

[0047] Comparative Example 5: Compared with Example 4, the only difference is that 0.25g of phytic acid (50wt% aqueous solution) is not added in step 4), while the other raw materials, amounts and reaction conditions are exactly the same as in Example 4.

[0048] Comparative Example 6: Compared with Example 4, the only difference is that 0.8g of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxy radical was not added in step 2). All other raw materials, amounts and reaction conditions were exactly the same as in Example 4.

[0049] Comparative Example 7: Compared with Example 4, the only difference is that 0.6g of antioxidant 1010 and 0.4g of antioxidant 168 were not added in step 2). All other raw materials, amounts and reaction conditions were exactly the same as in Example 4.

[0050] Comparative Example 8: Compared with Example 4, the only difference is that 2.5g of nano boron nitride is not added in step 3), while the other raw materials, amounts and reaction conditions are exactly the same as in Example 4.

[0051] Comparative Example 9: Compared with Example 4, the only difference is that 2g of octaphenyl cage-type silsesquioxane was not added in step 3). All other raw materials, amounts and reaction conditions were exactly the same as in Example 4.

[0052] Performance testing: I. Product Purity (Main Content) Test The main content of each sample was determined by high performance liquid chromatography (HPLC). The instrument was an Agilent 1260 Infinity II, the column was an Agilent ZORBAX Eclipse XDB-C18 (4.6 mm × 250 mm, 5 μm), the mobile phase was acetonitrile / water (70:30 v / v), the flow rate was 1.0 mL / min, the column temperature was 30 °C, the detection wavelength was 254 nm, and the injection volume was 10 μL. 0.05 g of sample was accurately weighed and dissolved in 10 mL of chromatographic grade methanol, filtered through a 0.22 μm organic filter membrane, and then injected. The DMTDA main peak content (wt%) was calculated using the area normalization method.

[0053] II. Initial Colorimetric Aspect Ratio (APHA) Test The initial colorimetry of the samples was determined according to ASTM D1209 standard (platinum-cobalt colorimetric method). The sample to be tested was placed in a standard 50mL Nessler colorimetric tube with a liquid column height of 100mm. Under a standard D65 light source and a white diffuse background, the sample was visually compared with a series of platinum-cobalt standard colorimetric solutions (APHA5, 10, 15, 20, 25, 30, 40, 50, 60, 80, 100, 120), or the APHA value was directly read using a Lovibond PFXi-195 colorimeter. Each sample was measured in triplicate and the average value was taken.

[0054] III. Anti-yellowing performance (accelerated aging color change ΔAPHA test) The samples were subjected to accelerated thermo-oxidative aging tests in a 150℃ forced-air oven. 20g of sample was placed in a 40mm inner diameter glass petri dish with a liquid film thickness of approximately 5mm, and then placed in a forced-air oven (BPG-9070A) preheated to 150℃ for 100 hours of continuous exposure in air. Every 24 hours, the sample was removed, cooled to room temperature, and APHA was measured according to ASTM D1209. The difference between the final APHA value and the initial APHA value, ΔAPHA, was recorded (a smaller ΔAPHA value indicates better anti-yellowing performance).

[0055] IV. Heat resistance stability test (5% weight loss temperature T5% and residual weight percentage at 600℃) Thermogravimetric analysis (TGA 55) was used to determine the thermogravimetric behavior of the samples. 10.0 ± 0.5 mg of sample was accurately weighed and placed in a platinum crucible. Under a high-purity nitrogen atmosphere (flow rate 60 mL / min), the temperature was increased from room temperature to 600 °C at a rate of 10 °C / min, and the weight loss curve was recorded. The temperature T5% (reflecting the initial thermal decomposition temperature) corresponding to 5% weight loss and the residual weight R600 (reflecting high-temperature char stability) at 600 °C were read from the curve. Each sample was measured in duplicate.

[0056] V. Antioxidant component migration resistance (TEMPOL retention rate) test To evaluate the protective effect of γ-cyclodextrin and phytic acid as synergistic agents on TEMPOL, the relative retention rate of TEMPOL after aging at 150℃ for 100 h was determined by electron paramagnetic resonance spectroscopy (EPR, Bruker EMXnano). 10 mg of each sample before and after aging was dissolved in 1 mL of chloroform to prepare solutions. The characteristic triplet EPR spectra of TEMPOL were obtained by scanning at room temperature, a microwave frequency of 9.43 GHz, a microwave power of 2.0 mW, and a modulation amplitude of 1.0 G. The relative retention rate (%) of TEMPOL after aging was calculated based on the peak area before aging (100%).

[0057] Table 1: Performance test results of the examples and comparative examples ; The above data show that the main content of the anti-yellowing LC-grade DMTDA products obtained in Examples 1–5 is ≥99.5wt%, the initial color APHA is ≤30, the ΔAPHA after accelerated aging at 150℃×100h is ≤15, the 5% weight loss temperature T5% is ≥283℃, the residual weight rate at 600℃ is ≥16%, and the TEMPOL retention rate is ≥82%. Among them, Example 4 has the best overall performance. Comparative Example 1, due to the lack of anti-yellowing modification, has a ΔAPHA as high as 82, proving that molecular umbrella steric hindrance and the three-level antioxidant network are the core of anti-yellowing. Comparative Example 2, due to the lack of heat resistance modification, has a T5% reduced to 242℃ and an R600 of only 9.3%, proving that BN@OP- The POSS hybrid network is crucial for heat resistance. In Comparative Example 3, due to the lack of synergistic agents, the TEMPOL retention rate was only 41.6%, and the ΔAPHA increased to 42, proving that the synergistic protection of TEMPOL by γ-cyclodextrin and phytic acid is the key to achieving long-term anti-yellowing. Comparative Examples 4 and 5 further confirmed that γ-cyclodextrin (physical confinement) and phytic acid (chemical passivation) are indispensable. Comparative Examples 6 and 7 respectively verified the irreplaceable role of TEMPOL and antioxidant 1010 / 168 in the multi-level antioxidant network. Comparative Examples 8 and 9 respectively confirmed the necessity of nano-boron nitride (thermal conduction channel) and OP-POSS (rigid heat-resistant cage) in the heat-resistant network.

[0058] 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 essence and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing LC-grade dimethylthiotoluene diamine with anti-yellowing properties, characterized in that, Includes the following steps: 1) Diaminotoluene, xylene, zinc iodide and dimethyl disulfide were mixed and reacted. After the reaction was completed, the mixture was washed, dried and distilled under reduced pressure to obtain dimethylthiotoluene diamine. 2) The dimethylthiotoluene diamine obtained in step (1) is mixed with ethyl acetate, trimesoyl chloride, triethylamine, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxy free radical, antioxidant 1010 and antioxidant 168 and reacted. The mass ratio of dimethylthiotoluene diamine to trimesoyl chloride is 100:(0.8~1.2), and the mass ratio of dimethylthiotoluene diamine to triethylamine is 100:(3.5~4.5). After the reaction is completed, the mixture is filtered and distilled under reduced pressure to obtain the anti-yellowing dimethylthiotoluene diamine intermediate. 3) Mix and disperse nano boron nitride, toluene, and octaphenyl cage-type silsesquioxane, then add the anti-yellowing dimethyl thiotoluene diamine intermediate obtained in step (2) and mix and react. After the reaction is completed, distill under reduced pressure to obtain anti-yellowing and heat-resistant dimethyl thiotoluene diamine. 4) Mix phytic acid, triethylamine, γ-cyclodextrin, water and ethanol, then add the anti-yellowing heat-resistant dimethyl thiotoluene diamine obtained in step (3) and mix. Remove water and ethanol under reduced pressure to obtain the anti-yellowing LC grade heat-resistant dimethyl thiotoluene diamine.

2. The method for preparing an anti-yellowing LC-grade dimethylthiotoluene diamine according to claim 1, characterized in that, In step 1), the molar ratio of diaminotoluene to dimethyl disulfide is 1:(2.0 to 2.2).

3. The method for preparing an anti-yellowing LC-grade dimethylthiotoluene diamine according to claim 1, characterized in that, In step 1), the reaction temperature is 105–110°C and the reaction time is 2–4 h.

4. The method for preparing an anti-yellowing LC-grade dimethylthiotoluene diamine according to claim 1, characterized in that, In step 3), the mass ratio of the nano-boron nitride to the octaphenyl cage-type silsesquioxane is 2.5:(1-2).

5. The method for preparing an anti-yellowing LC-grade dimethylthiotoluene diamine according to claim 1, characterized in that, In step 3), the reaction temperature is 60-65℃ and the reaction time is 2-4h.

6. The method for preparing an anti-yellowing LC-grade dimethylthiotoluene diamine according to claim 1, characterized in that, In step 4), the mass ratio of phytic acid to γ-cyclodextrin is 2.5:(5-8).

7. A yellowing-resistant LC-grade dimethylthiotoluene diamine, characterized in that, It is prepared by the method described in any one of claims 1-6.

8. The application of the anti-yellowing LC grade dimethylthiotoluene diamine according to claim 7 in polyurethane elastomer chain extenders or epoxy resin curing agents.

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