Modified polyurethane optical material and preparation method thereof

Abstract

The invention relates to a modified polyurethane optical material and a preparation method thereof, and the optical material is prepared by polymerizing the following components: 25-40 parts by weight of an isocyanate compound; 15 to 30 parts by weight of a multi-mercapto thiol compound; 10 to 20 parts by weight of a cyclic sulfide monomer; 5-10 parts by weight of an acrylate monomer; 0.1 to 0.5 part by weight of a catalyst; the multi-sulfydryl thiol compound is a trisulfydryl thiol compound with a structure as shown in a formula (a). The hybrid modified polyurethane material is prepared by carrying out multi-component cross-linking curing polymerization on a multi-mercapto thiol compound, isocyanate, cyclic sulfide and acrylate. The material has the advantage of high impact resistance while maintaining the high refractive index optical performance of 1.64, is suitable for manufacturing optical components with high refractive index requirements, such as prisms, lenses, lenses and the like, and provides a wider material selection range for the application of high-end optical components. # imgabs0 #

Description

Technical Field

[0001] The invention belongs to the technical field of polyurethane optical materials, and in particular relates to modified polyurethane optical materials, preparation methods and applications in the field of optical components. Background Art

[0002] With the continuous advancement of science and technology and the improvement of people's living standards, the performance requirements for optical materials are getting higher and higher. In the optical field such as eyeglass lenses, traditional optical materials are gradually unable to meet modern needs in some aspects. There are some shortcomings in the common optical lens materials on the market. For example, the hardness of some materials is not high enough and they are easily scratched, which affects the service life and optical performance of the lenses. Some materials have poor impact resistance and are easily broken when impacted by external forces, posing a certain threat to the safety of users. In addition, the optical properties of traditional materials also have certain limitations, such as the refractive index is not high enough, the dispersion is large, etc., which affect the visual effect.

[0003] In order to solve these problems, researchers have been working hard to explore new optical materials. Polyurethane materials have attracted widespread attention in the field of optics because of their good mechanical properties, wear resistance, and chemical corrosion resistance. However, unmodified polyurethane materials still have room for improvement in optical and mechanical properties. In this context, the development of a modified polyurethane optical material is of great practical significance. This new material must not only have excellent optical properties, such as high refractive index and low dispersion, but also have good mechanical properties, such as strong impact resistance and high hardness, to meet the ever-evolving needs of the lens field.

[0004] The present invention is designed based on the above-mentioned problem, and aims to provide a new material with superior performance in the field of optical components. Summary of the invention

[0005] In view of the above problems of the prior art, the present invention provides a modified polyurethane optical material and a preparation method and application thereof. The present invention provides a novel trithiothiol thiol compound, which has good light transmittance and high refractive index. By subjecting the thiol compound to multi-element cross-linking curing polymerization with isocyanate, cyclic sulfide, acrylate, etc., the prepared hybrid modified polyurethane material has the advantages of strong impact resistance while maintaining the optical performance of a high refractive index of 1.64, and is suitable for making optical components with high requirements for refractive index, such as prisms, lenses and lenses, etc., providing a wider range of material selection for the application of high-end optical components.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A modified polyurethane optical material is prepared by polymerizing the following components:

[0008] Component A: isocyanate compound, 25-40 parts by weight;

[0009] Component B: polythiol mercaptan compound, 15 to 30 parts by weight;

[0010] Component C: cyclic sulfide monomer, 10 to 20 parts by weight;

[0011] Component D: acrylic acid ester monomer, 5 to 10 parts by weight;

[0012] Component E: catalyst, 0.1 to 0.5 parts by weight;

[0013] The polythiothiol compound is a trithiothiol compound having a structure shown in formula (a):

[0014]

[0015] The modified polyurethane optical material as described above, preferably, the isocyanate compound is a compound containing two or more isocyanate groups, selected from at least one of toluene diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, cyclohexane diisocyanate, tetramethylene diisocyanate, isophorone diisocyanate, xylene diisocyanate, 4,4'-diisocyanate dicyclohexylmethane, tetramethyl meta-xylyl diisocyanate, dithiodipropyl diisocyanate, dithiodiethyl diisocyanate, dihexyl thiodiisocyanate, dithiodipropyl diisocyanate, diethylene diisocyanate, trimethyl hexamethylene diisocyanate, lysine triisocyanate, o-tolidine diisocyanate, diphenyl ether diisocyanate and triphenylmethane triisocyanate.

[0016] In the modified polyurethane optical material as described above, preferably, the cyclic sulfide is selected from: 1,3,5-trithiopropylmercaptomethylbenzene, bis(B-thiopropylthio)methane, bis(B-thiopropyl)sulfide, bis(β-thiopropyl)disulfide, 1,2-bis(B-thiopropylthio)ethane, 1,3-bis(B-thiopropylthio)propane, 1,4-bis(B-thiopropylthio)butane and at least one of the following three thioether-type episulfide compounds:

[0017]

[0018] Wherein R and R1 are the same or different and are each H, CH3 or C6H5;

[0019]

[0020] Wherein R is H or CH3.

[0021] In the modified polyurethane optical material as described above, the acrylate monomer is a compound having a hydroxyl active hydrogen group or capable of self-polymerization or copolymerization with other monomers, preferably, at least one selected from methyl acrylate, ethyl acrylate, 2-methyl methacrylate, 2-ethyl methacrylate, hydroxymethyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, polyethylene glycol methacrylate, polyethylene glycol dimethacrylate, pentaerythritol tetraacrylate, ethoxylated nonylphenol acrylate, epoxy acrylate, bisphenol A epoxy acrylate and ethoxylated bisphenol A diacrylate.

[0022] In the modified polyurethane optical material as described above, preferably, the catalyst is selected from one of stannous octoate, dibutyltin dilaurate, dibutyltin dichloride, and dibutyltin oxide, preferably dibutyltin dilaurate and dibutyltin dichloride, more preferably dibutyltin dilaurate or dibutyltin dichloride.

[0023] The modified polyurethane optical material as described above, preferably, the components further include a colorant, a release agent and / or an ultraviolet absorber.

[0024] According to the needs of different refractive indices, the polythiothiol compound of the present application can adopt other compounds containing 3 or more thiol functional groups (-SH), preferably: 1,3,5-trimercaptomethylbenzenethiol, dimercaptomethyl-1,4-dithiacyclohexane, ethylene glycol bis(3-mercaptopropionate), 2-(2,2-bis(mercaptomethylthio)ethyl)-1,3-dithiacyclohexane, 4,6-bis(mercaptomethylthio)1,3-dithiacyclohexane, 4-mercaptomethyl-1,8-dimercapto-3,6-dithiaoctane, 5,7-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane and 4,8-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane, etc. At least one of the above.

[0025] On the other hand, the present invention provides a method for preparing the modified polyurethane optical material as described above, the method comprising the following steps:

[0026] I. Weigh each component according to the required ratio, add the polythiol mercaptan compound and the cyclic sulfide monomer to the isocyanate compound, stir to form a mixture, and stir to add the acrylate monomer to the mixture to obtain a prepolymer;

[0027] II. Add a catalyst to the prepolymer, heat to 40-60°C for prepolymerization for 80-120 minutes, remove bubbles in vacuo, and inject into a tempered mold; place the mold containing the prepolymer in a 50-85°C curing oven for curing for 5-8 hours, then heat to 75-100°C, continue to cool to room temperature and demold; keep the demolded optical resin substrate in a 80-110°C curing oven at a constant temperature for 2-5 hours to complete secondary curing, and obtain a modified polyurethane optical material.

[0028] In another aspect, the present invention provides a trithiothiol compound, the structure of which is shown in formula (a):

[0029]

[0030] In another aspect, the present invention provides a method for preparing the trithiothiol compound as described above, comprising the following steps: adding triallyl isocyanurate, thioacetic acid and ethanol in a weight ratio of (25-60): (30-70): (100-150) to a reaction container, adding an azo initiator with stirring, raising the reaction temperature to 50-70° C. and keeping the temperature for 5-9 hours after dissolution, and removing excess thioacetic acid by rotary evaporation to obtain a yellow viscous product; adding 30-38% hydrochloric acid and methanol to the product, and hydrolyzing at 50-65° C. for 9-12 hours. After the hydrolysis is completed, removing methanol, eluting, and rotary evaporation to obtain a colorless and transparent trithiothiol compound (a).

[0031] The specific reaction formula is as follows:

[0032]

[0033] In the preparation method as described above, preferably, the weight ratio of hydrochloric acid, methanol and ethanol is (0.5-1): (1-2): (1-2);

[0034] In the preparation method as described above, preferably, the azo initiator is selected from one of azobisisobutyronitrile, azobisisoheptanenitrile and dimethyl azobisisobutyrate, and the added amount thereof is 0.6-1.5 wt % of triallyl isocyanurate.

[0035] The beneficial effects of the present invention are:

[0036] (1) The modified polyurethane raw material monomer of the present invention adopts a novel trivalent thiol compound (Formula a), which has good light transmittance and a refractive index of 1.63, and the prepared modified polyurethane optical material has a refractive index of 1.64 to 1.67. The three thiol functional groups in the molecular structure of the novel trivalent thiol compound are more evenly and reasonably distributed, and the steric hindrance is small, so that it can contact with other reactants more fully in the chemical reaction, improve the reaction efficiency, and can react at a lower temperature or milder conditions, reducing the energy and time required for the reaction; in addition, the presence of the three thiol groups enables it to form a tighter and more stable cross-linked network structure when cross-linked with other compounds, thereby improving the mechanical properties and optical properties of the material. Its special structure helps to improve the refractive index of the material while maintaining good optical transparency, meeting the wide demand for medium and high refractive index and low dispersion materials in the optical field.

[0037] (2) The raw materials required for the thiol compound prepared by the present invention are abundant in domestic sources and are easily purchased. The synthesis process is controllable and practical, and the reaction conditions are mild. The prepared ternary thiol compound monomer has high purity and light color, which ensures the high transparency of the polyurethane material.

[0038] (3) Acrylate and cyclic sulfide are introduced into the raw monomer of the modified polyurethane of the present invention, and the traditional thiol-isocyanate (SH / NCO) binary curing system is improved. The double bond of acrylate is opened to react with the active group in the polyurethane to form a cross-linked and interpenetrating network structure. This structure can absorb and disperse the stress applied from the outside. When the material is subjected to external force, the stress can be transmitted and dispersed through the two polymer networks, reducing stress concentration, making the material less likely to crack and break, and improving toughness and impact resistance. The sulfur atoms in the episulfide compound have a large relative mass and a high electron cloud density, and they themselves have a high molar refractive index. When the episulfide compound is polymerized with the monomer, the polarization degree of the polymer molecule can be increased, and the molecular chain can be made more regular, thereby increasing the refractive index of the polymer. Give full play to the advantages of the thiol-isocyanate-cyclic sulfide-acrylate multi-hybrid polymerization system. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is the infrared spectrum of the trithiothiol compound prepared in Example 1.

[0040] Figure 2 This is the HNMR nuclear magnetic resonance hydrogen spectrum of the trithiothiol compound prepared in Example 1. DETAILED DESCRIPTION

[0041] The present invention is further described below by means of specific examples, but this is not intended to limit the protection scope of the present invention.

[0042] Example 1: Preparation of trithiolthiol compound (a) and modified polyurethane optical material

[0043] (I) Preparation of trithiolthiol compound (a)

[0044] 950 g of triallyl isocyanurate and 1050 g of thioacetic acid are added to a reaction container containing 2000 ml of ethanol, and 10.5 g of azobisisobutyronitrile is added with stirring. After dissolution, the reaction temperature is raised to 65° C. and kept warm for 7.5 hours. The remaining thioacetic acid is removed by rotary evaporation to produce a yellow viscous liquid product. 960 ml of hydrochloric acid (36%) and 1800 ml of methanol are added to the yellow viscous product, and hydrolyzed at 60° C. for 10 hours. After elution and rotary evaporation, 1240 g of trithiothiol compound monomer (a) is obtained, with a refractive index of 1.632 and a yield of 76.2%.

[0045] Infrared spectrum FT-IR test: The product prepared in step (i) was subjected to Fourier transform infrared spectrum FT-IR) test. Figure 1 The middle curve analysis shows that at 3078 -1 The absorption peak at 2590 cm is the characteristic absorption peak of residual allyl group. -1 The absorption peak of 1703 cm is the characteristic peak of thiol. -1 cm and 1485 -1 The absorption peaks at cm are C=O and CN on the isocyanurate ring.

[0046] H NMR nuclear magnetic resonance hydrogen spectrum analysis: Figure 2 As shown, δ=1.30 is mercapto hydrogen (-SH), δ=1.99, 2.53, 3.99 correspond to the methylene (-CH2-) hydrogen in the N-connected mercaptopropyl group, and δ=5.20-5.88 corresponds to the residual allylic hydrogen.

[0047] (II) Preparation of tetracyclic sulfur compound monomer (II)

[0048]

[0049] Add 900 g of 1,3-diphenylacetone and 1680 g of anhydrous ethanol to a reaction vessel, stir evenly, and then introduce hydrogen sulfide and hydrogen chloride dry gas for 6 hours. The reaction temperature is controlled at 2°C. After 10 hours, the precipitate is vacuum dried to obtain a thiol intermediate.

[0050] Take 360 ​​g of the thiol intermediate prepared in the above step and add it to 1080 ethanol. After dissolving, add 820 g of ferric chloride and 650 g of water and stir repeatedly. The temperature is controlled at 5°C and react for 4.5 hours. The collected precipitate is recrystallized with n-hexane and dried in vacuo to obtain 186 g of tetracyclic sulfur compound (II) with a yield of 51.5%.

[0051] (III) Preparation of modified polyurethane optical materials

[0052] (1) 210 g of the trithiothiol compound (a) prepared in Example 1 and 165 g of the tetracyclic sulfide compound monomer (II) were added to 320 g of diphenylmethane diisocyanate by stirring, and then 70 g of hydroxymethyl methacrylate was added by stirring to obtain a prepolymer.

[0053] (2) Add 3.2 g of catalyst to the prepolymer, heat to 45°C for prepolymerization for 90 min, remove bubbles by vacuum, and inject into the tempered mold by injection gun; place the mold containing the prepolymer in a 60°C curing oven for curing for 6 h, then heat to 90°C, continue to stand for 3.5 h, and finally cool to room temperature for demolding; keep the demolded optical resin substrate in a 95°C curing oven for 3 hours to complete secondary curing, thereby obtaining a modified polyurethane optical material.

[0054] Example 2: Preparation of modified polyurethane optical material

[0055] (1) 160 g of the trithiothiol compound (a) prepared in Example 1 and 175 g of the tetracyclic sulfide compound monomer (II) were added to 320 g of diphenylmethane diisocyanate by stirring, and then 70 g of hydroxymethyl methacrylate was added by stirring to obtain a prepolymer.

[0056] (2) Add 3.2 g of catalyst to the prepolymer, heat to 45°C for prepolymerization for 90 min, remove bubbles by vacuum, and inject into the tempered mold by injection gun; place the mold containing the prepolymer in a 60°C curing oven for curing for 6 h, then heat to 90°C, continue to stand for 3.5 h, and finally cool to room temperature for demolding; keep the demolded optical resin substrate in a 95°C curing oven for 3 hours to complete secondary curing, thereby obtaining a modified polyurethane optical material.

[0057] Example 3: Preparation of modified polyurethane optical material

[0058] (1) 260 g of the trithiothiol compound (a) prepared in Example 1 and 125 g of the tetracyclic sulfide compound monomer (II) were added to 320 g of toluene diisocyanate by stirring, and then 70 g of hydroxymethyl methacrylate was added by stirring to obtain a prepolymer.

[0059] (2) Add 3.2 g of catalyst to the prepolymer, heat to 45°C for prepolymerization for 90 min, remove bubbles by vacuum, and inject into the tempered mold by injection gun; place the mold containing the prepolymer in a 60°C curing oven for curing for 6 h, then heat to 90°C, continue to stand for 3.5 h, and finally cool to room temperature for demolding; keep the demolded optical resin substrate in a 95°C curing oven for 3 hours to complete secondary curing, thereby obtaining a modified polyurethane optical material.

[0060] Example 4: Preparation of modified polyurethane optical material

[0061] (1) 185 g of the trithiothiol compound (a) prepared in Example 1 and 150 g of the tetracyclic sulfide compound monomer (II) were stirred and added to 320 g of m-xylylene diisocyanate, and then 70 g of hydroxymethyl methacrylate was stirred and added to obtain a prepolymer.

[0062] (2) Add 3.2 g of catalyst to the prepolymer, heat to 45°C for prepolymerization for 90 min, remove bubbles by vacuum, and inject into the tempered mold by injection gun; place the mold containing the prepolymer in a 60°C curing oven for curing for 6 h, then heat to 90°C, continue to stand for 3.5 h, and finally cool to room temperature for demolding; keep the demolded optical resin substrate in a 95°C curing oven for 3 hours to complete secondary curing, thereby obtaining a modified polyurethane optical material.

[0063] Example 5: Preparation of modified polyurethane optical material

[0064] (1) 230 g of the trithiothiol compound (a) prepared in Example 1 and 135 g of the tetracyclic sulfide compound monomer (II) were added to 320 g of m-xylylene diisocyanate by stirring, and then 70 g of hydroxymethyl methacrylate was added by stirring to obtain a prepolymer.

[0065] (2) Add 3.2 g of catalyst to the prepolymer, heat to 45°C for prepolymerization for 90 min, remove bubbles by vacuum, and inject into the tempered mold by injection gun; place the mold containing the prepolymer in a 60°C curing oven for curing for 6 h, then heat to 90°C, continue to stand for 3.5 h, and finally cool to room temperature for demolding; keep the demolded optical resin substrate in a 95°C curing oven for 3 hours to complete secondary curing, thereby obtaining a modified polyurethane optical material.

[0066] Comparative Examples 1-5:

[0067] Comparative Examples 1-5 respectively adopt the preparation conditions corresponding to Example 1, except that some components are replaced or reduced. The specific formulation conditions are detailed in Table 1. The commercially available mercaptan is a Japanese brand product.

[0068] Table 1 Comparison of comparative samples prepared under different formulation conditions

[0069]

[0070] Example 6: Testing of optical properties and impact strength of polyurethane optical materials

[0071] The optical properties of the polyurethane optical materials prepared in Examples 1-5 and Comparative Examples 1-5 were tested respectively.

[0072] Light transmittance is one of the most important properties of optical materials, which is expressed by transmittance. The test was performed using the UV-8000 UV-visible photometer from Shanghai Yuanxi Instrument Co., Ltd. The test method was: directly place the sample on the UV-visible photometer to measure the transmittance.

[0073] The refractive index was measured using the WZS1 Abbe refractometer produced by Shanghai Optical Instruments and Equipment Co., Ltd. The measuring method was as follows: the polyurethane optical material samples prepared in Examples 1-5 were placed on the prism of the Abbe refractometer to measure the refractive index.

[0074] The impact strength is the highest steel ball mass without cracks on the substrate surface. For example, if a 90g steel ball impacts three times and the material has no cracks, and a 100g steel ball impacts and cracks appear, then the impact strength of this material is 90g. Test method: Fix a substrate with a central thickness of 1.95mm and a certain curvature on the bottom of the instrument with the convex surface facing up, select steel balls of different masses (70, 80g, 90g, 100g), and let them fall vertically and freely from a height of 1.30m to the center of the substrate material surface in turn. Each steel ball of each mass is tested three times. The test results are shown in Table 2.

[0075] Table 2 Performance of substrate samples prepared under different formulation conditions

[0076]

[0077] The following conclusions can be drawn from the performance comparison in Table 2:

[0078] 1. The data of Comparative Example 1 show that in the absence of trivalent thiol (a), the refractive index of the polymerized material is low;

[0079] 2. The data of Comparative Example 2 show that in the absence of acrylate, the impact resistance of the material is low;

[0080] 3. The data of Comparative Example 3 show that in the absence of tetracyclic sulfur compounds, the refractive index of the polymerized material is low;

[0081] 4. The data of Comparative Example 4 show that in the absence of acrylate, the impact resistance of the material is low, and the imported mercaptan is expensive, resulting in high raw material costs;

[0082] 5. The data of Comparative Example 5 show that in the absence of acrylate and tetracyclic sulfur (II), the impact resistance of the material is low. At the same time, the imported mercaptan is expensive, resulting in high raw material costs.

[0083] Conclusion: The products prepared in the examples, while meeting the requirements of medium and high refractive index optical properties and mechanical properties, control product costs by increasing the amount of high-cost materials and reducing the amount of low-cost materials. At the same time, restrictions on the purchase of imported raw materials are effectively avoided.

Claims

1. A modified polyurethane optical material, characterized in that: It is polymerized from the following components: Component A: isocyanate compound, 25-40 parts by weight; Component B: polythiol mercaptan compound, 15 to 30 parts by weight; Component C: cyclic sulfide monomer, 10 to 20 parts by weight; Component D: acrylic acid ester monomer, 5 to 10 parts by weight; Component E: catalyst, 0.1 to 0.5 parts by weight; The polythiothiol compound is a trithiothiol compound having a structure shown in formula (a):

2. The modified polyurethane optical material according to claim 1, characterized in that: The isocyanate compound is a compound containing two or more isocyanate groups, and is selected from at least one of toluene diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, cyclohexane diisocyanate, tetramethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, 4,4'-diisocyanate dicyclohexylmethane, tetramethyl meta-xylylene diisocyanate, dithiodipropyl diisocyanate, dithiodiethyl diisocyanate, dihexyl thiodiisocyanate, dithiodipropyl diisocyanate, diethylene diisocyanate, trimethyl hexamethylene diisocyanate, lysine triisocyanate, o-tolidine diisocyanate, diphenyl ether diisocyanate and triphenylmethane triisocyanate.

3. The modified polyurethane optical material according to claim 1, characterized in that: The cyclic sulfide is selected from: 1,3,5-trithiopropylmercaptomethylbenzene, bis(B-thiopropylthio)methane, bis(B-thiopropyl)sulfide, bis(β-thiopropyl)disulfide, 1,2-bis(B-thiopropylthio)ethane, 1,3-bis(B-thiopropylthio)propane, 1,4-bis(B-thiopropylthio)butane and at least one of the following three thioether-type episulfide compounds: Wherein R and R1 are the same or different and are each H, CH3 or C6H5; Wherein R is H or CH3.

4. The modified polyurethane optical material according to claim 1, characterized in that: The acrylic acid ester monomer is selected from at least one of methyl acrylate, ethyl acrylate, methyl 2-methacrylate, ethyl 2-methacrylate, hydroxymethyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, polyethylene glycol methacrylate, polyethylene glycol dimethacrylate, pentaerythritol tetraacrylate, ethoxylated nonylphenol acrylate, epoxy acrylate, bisphenol A epoxy acrylate and ethoxylated bisphenol A diacrylate.

5. The modified polyurethane optical material according to claim 1, characterized in that: The catalyst is selected from one of stannous octoate, dibutyltin dilaurate, dibutyltin dichloride and dibutyltin oxide, preferably dibutyltin dilaurate and dibutyltin dichloride.

6. The modified polyurethane optical material according to any one of claims 1 to 5, characterized in that: The components may also include a toner, a release agent and / or an ultraviolet absorber.

7. The method for preparing a modified polyurethane optical material according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: I. Weigh each component according to the required ratio, add the polythiol mercaptan compound and the cyclic sulfide monomer to the isocyanate compound, stir to form a mixture, and stir to add the acrylate monomer to the mixture to obtain a prepolymer; II. Add a catalyst to the prepolymer, heat to 40-60°C for prepolymerization for 80-120 minutes, remove bubbles in vacuo, and inject into a tempered mold; place the mold containing the prepolymer in a 50-85°C curing oven for curing for 5-8 hours, then heat to 75-100°C, continue to cool to room temperature and demold; keep the demolded optical resin substrate in a 80-110°C curing oven at a constant temperature for 2-5 hours to complete secondary curing, and obtain a modified polyurethane optical material.

8. A trithiothiol mercaptan compound, characterized in that Its structure is shown in formula (a):

9. The method for preparing the trithiothiol compound according to claim 8, characterized in that: The method comprises the following steps: adding triallyl isocyanurate, thioacetic acid and ethanol into a reaction container in a weight ratio of (25-60): (30-70): (100-150), adding an azo initiator with stirring, raising the reaction temperature to 50-70°C and keeping the temperature for 5-9 hours after dissolution, and removing excess thioacetic acid by rotary evaporation to obtain a yellow viscous product; adding hydrochloric acid and methanol with a concentration of 30-38% to the product, and hydrolyzing at 50-65°C for 9-12 hours. After the hydrolysis is completed, removing the methanol, eluting, and rotary evaporation to obtain a colorless and transparent trithiolthiol compound (a).

10. The preparation method according to claim 9, characterized in that: The weight ratio of hydrochloric acid, methanol and ethanol is (0.5-1):(1-2):(1-2); The azo initiator is selected from one of azobisisobutyronitrile, azobisisoheptanenitrile and dimethyl azobisisobutyrate, and the added amount thereof is 0.6-1.5 wt % of triallyl isocyanurate.

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