Preparation method of pentaerythritol tetramercaptocarboxylate composition

Abstract

The present invention belongs to the technical field of synthesizing and preparing organic polymer optical materials, and specifically relates to a method for preparing a pentaerythritol tetramercaptocarboxylate composition. The method comprises the following two steps: first, an addition reaction of thiourea with acrylic acid under photocatalysis to generate mercaptopropionic acid in situ; and second, a lipase-catalyzed esterification reaction of mercaptopropionic acid with pentaerythritol to obtain colorless, transparent, high-purity pentaerythritol tetramercaptocarboxylate. Simultaneously, a polymerizable modified polyurethane optical material containing the pentaerythritol tetramercaptocarboxylate is prepared, characterized by low cost, high light transmittance, and adjustable refractive index.

Description

Technical Field

[0001] The invention belongs to the technical field of synthesis and preparation of organic polymer optical materials, and particularly relates to a preparation method of a pentaerythritol tetramercaptocarboxylate composition. Background Art

[0002] Pentaerythritol tetramercaptocarboxylate, an important class of multifunctional organosulfides, possesses a highly symmetrical tetramercapto structure. As a tetrafunctional thiol (-SH) compound, it plays a key role in optical materials, photocurable coatings, 3D printing resins, and medical polymer networks. Compared to traditional dithiols, the cross-linked networks constructed with pentaerythritol exhibit higher cross-link density and mechanical strength while maintaining excellent optical transparency.

[0003] Existing technologies for preparing pentaerythritol tetramercaptocarboxylate primarily rely on acid-catalyzed esterification, a process that suffers from poor selectivity, numerous byproducts, and complex post-processing. Strong acids such as concentrated sulfuric acid and p-toluenesulfonic acid are typically used during the reaction, which are highly corrosive to equipment and pose a threat to operator safety and environmental protection. Reaction temperatures range from 80°C to 120°C, which easily trigger oxidative coupling of thiol groups to form disulfide bonds. Reaction times range from 6 to 20 hours, and the carboxylic acid readily dehydrates to form anhydrides, severely impacting product purity. From an application perspective, the high market price of mercaptopropionic acid, the raw material required for the reaction, increases production costs. Furthermore, the optical materials industry places high demands on monomer purity, and trace impurities can affect the optical properties of the material. Existing synthesis methods struggle to simultaneously meet the multiple requirements of high purity, high yield, affordability, and environmental friendliness.

[0004] In response to the bottleneck of existing technology, the patent of this invention adopts a one-pot method, through enzyme-photosynergistic catalysis, to assist in accelerating the free radical esterification reaction, replacing the use of strong acid, significantly improving the efficiency, economy and safety of the reaction; low-temperature step-by-step control, precisely regulating the degree of substitution, shortening the reaction time, and reducing high-temperature side reactions; introducing a green post-treatment process, simplifying the purification steps, while recycling and reusing lipase and organic solvents, reducing production costs. Summary of the Invention

[0005] The present invention provides a method for preparing a pentaerythritol tetramercaptocarboxylate composition. The method comprises two steps: first, a photocatalytic addition reaction of thiourea with acrylic acid to generate mercaptopropionic acid in situ; and second, a photoenzymatic esterification reaction of mercaptopropionic acid with pentaerythritol to obtain colorless, transparent, high-purity pentaerythritol tetramercaptocarboxylate. The present invention also provides a polymerizable modified urethane optical material containing pentaerythritol tetramercaptocarboxylate. This material exhibits low cost, high light transmittance, and adjustable refractive index.

[0006] The object of the present invention is achieved through the following technical solutions:

[0007] The present invention provides a method for preparing pentaerythritol tetramercaptocarboxylate, which comprises the following steps:

[0008] (1) Addition reaction: Dissolve thiourea in a solvent, add acrylic acid, mix well, heat to 25-35°C, and irradiate with an intensity of 5-25 mW / cm 2 Irradiation was performed with a 450nm wavelength blue LED array. The mixed liquid circulated in an annular tank. The light source was 2-3cm away from the liquid surface in the annular tank. Under nitrogen protection, HCl / NaOH was added dropwise to adjust the pH of the reaction solution to 6-7. Irradiation was continued for 60-120 minutes.

[0009] (2) Esterification reaction: add pentaerythritol and lipase to the reaction solution in step (1), mix well and heat to 35-45°C, control the light intensity to 5-15 mW / cm 2 , the mixed liquid continues to circulate in the annular groove, controlling the water activity at α w =0.2~0.5, detect the peak value of mercaptopropionic acid by HPLC every hour, continue irradiation for 3~6 hours, filter and elute the organic phase, and evaporate the solvent under reduced pressure to obtain colorless and transparent pentaerythritol tetramercaptocarboxylate.

[0010] Furthermore, the weight ratio of pentaerythritol, thiourea, acrylic acid and solvent is (1-2): (2-5): (2-5): (15-50).

[0011] Furthermore, the lipase is selected from Candida antarctica lipase B, and the amount of lipase used is 2-6% wt% of the amount of pentaerythritol used.

[0012] Furthermore, the solvent is selected from at least one of dioxane, tert-butanol, butane nitrile and water.

[0013] The preparation method of the pentaerythritol tetramercaptocarboxylate specifically comprises the following two stages:

[0014] Photocatalytic addition stage: Thiourea generates isothiocyanate (HN=C=S) under photocatalysis. Its sulfur atom acts as a strong nucleophile and undergoes Michael addition reaction with the β-carbon of acrylic acid to generate mercaptopropionic acid in situ. During the reaction, the excessive decomposition of thiourea is suppressed by controlling the pH value and light intensity. The specific reaction formula is as follows:

[0015] .

[0016] Enzymatic esterification stage: Light and enzymes synergistically catalyze the esterification reaction between mercaptopropionic acid and pentaerythritol. First, the serine hydroxyl group in the lipase attacks the carboxyl carbon of mercaptopropionic acid, forming an acyl-enzyme intermediate. Second, the hydroxyl group of pentaerythritol attacks the acyl-enzyme intermediate, forming an ester bond and releasing free enzyme. The specific reaction formula is as follows:

[0017] .

[0018] The present invention also provides pentaerythritol tetramercaptocarboxylate prepared by the preparation method.

[0019] The present invention also provides a use of the pentaerythritol tetramercaptocarboxylate in the preparation of a polymerizable modified polyurethane optical material containing the pentaerythritol tetramercaptocarboxylate. The polymerizable modified polyurethane optical material containing the pentaerythritol tetramercaptocarboxylate comprises the following components:

[0020] Component A: isocyanate, 25-45 parts by weight;

[0021] Component B: pentaerythritol tetramercaptocarboxylate, 20-45 parts by weight;

[0022] Component C: acrylic acid ester monomer, 5 to 10 parts by weight;

[0023] The isocyanate is selected from at least one of diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, diphenyl ether diisocyanate, toluene diisocyanate, diethylene diisocyanate, cyclohexane diisocyanate, hexamethylene diisocyanate, diethyl disulfide diisocyanate, tetramethylene diisocyanate, dihexyl thiodiisocyanate, dipropyl thiodiisocyanate, dipropyl disulfide diisocyanate, isophorone diisocyanate, trimethylhexamethylene diisocyanate, xylylene diisocyanate, and o-tolidine diisocyanate.

[0024] The present invention also provides a method for preparing the polymerizable modified polyurethane optical material containing pentaerythritol tetramercaptocarboxylate, which specifically comprises the following steps:

[0025] (1) adding the pentaerythritol tetramercaptocarboxylate and acrylic acid ester monomers into a reactor containing isocyanate, stirring at 50-120 rpm for 30-40 minutes, then adding a catalyst, and continuing to stir to form a prepolymer;

[0026] (2) The prepolymer is vacuum-debubbled and injected into a tempered mold. The tempered mold containing the prepolymer is placed in a curing oven, heated to 30-50°C for curing for 1-3 hours, then heated to 55-75°C for curing for 2-5 hours. The prepolymer is naturally cooled to room temperature and then demolded and sampled to obtain the polymerizable modified polyurethane optical material containing pentaerythritol tetramercaptocarboxylate.

[0027] Furthermore, the isocyanate is selected from at least one of diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, diphenyl ether diisocyanate, toluene diisocyanate, diethylene diisocyanate, cyclohexane diisocyanate, hexamethylene diisocyanate, diethyl diisocyanate, tetramethylene diisocyanate, dihexyl thiodiisocyanate, dipropyl thiodiisocyanate, dipropyl diisocyanate, triphenylmethane triisocyanate, isophorone diisocyanate, trimethylhexamethylene diisocyanate, m-xylylenediisocyanate, xylylenediisocyanate, o-tolidine diisocyanate, lysine triisocyanate and isothiocyanate.

[0028] Furthermore, the acrylic acid ester monomer is selected from at least one of methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, hydroxymethyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, polyethylene glycol dimethacrylate, pentaerythritol tetraacrylate, polyethylene glycol methacrylate, ethoxylated nonylphenol acrylate, epoxy acrylate, bisphenol A epoxy acrylate and ethoxylated bisphenol A diacrylate.

[0029] Furthermore, the catalyst is selected from any one of stannous octoate, dibutyltin dilaurate, dibutyltin dichloride and dibutyltin oxide, and the amount of the catalyst is 0.1 to 0.9 wt% of the isocyanate.

[0030] The present invention realizes the thiocyanate anion (SCN) through photocatalysis - ) non-alkaline generation: Visible light (450 nm) excites photosensitizers (such as Ru(bpy)3 2+ ) to an excited state, oxidizing thiourea to generate a radical cation, which deprotonates and breaks the SC bond to form an isothiocyanate radical (N=C=S), which is then reduced by a single electron to generate SCN - , the whole process does not require alkaline conditions and can be operated at neutral pH. In the light-enzyme synergistic catalysis, SCN - After photoinduced homolysis, it is split into cyanide radicals (-CN) and sulfhydryl radicals. The sulfhydryl radicals recombine to form sulfhydryl (-SH). At the same time, -CN captures hydrogen atoms to form HCN. Due to the high volatility of HCN, it is carried out of the system by inert gas, thus achieving efficient conversion of sulfhydryl.

[0031] The beneficial effects of the present invention are:

[0032] The present invention produces significant beneficial effects through the triple innovation of replacing mercaptopropionic acid with thiourea and acrylic acid, light-driven reaction, and precise enzyme catalysis. Specifically:

[0033] (1) The present invention reduces the production cost from RMB 22,000 per ton to RMB 14,000 per ton, a cost reduction of 36.3%, and the product has significant market competitiveness.

[0034] (2) The entire reaction conditions of the present invention are mild and energy consumption is low, which avoids side reactions caused by high temperature and strong acid, conforms to the green manufacturing concept, and meets the EU REACH regulations.

[0035] (3) The traditional acid-catalyzed esterification method has low product purity. The new process in the present invention avoids the risks of dimerization and oxidation, and the product purity reaches 99.5%, meeting the demand for high-end products. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0037] Figure 1 This is an infrared spectrum FT-IR graph of pentaerythritol tetramercaptocarboxylate prepared in Example 1 of the present invention;

[0038] Figure 2 This is the hydrogen nuclear magnetic resonance spectrum of pentaerythritol tetramercaptocarboxylate prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0039] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0040] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0041] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0042] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0043] As used herein, the terms "comprising," "including," "having," and "containing" are open-ended, meaning inclusive but not limited to. The raw materials used in this invention include thiourea purchased from Jiangsu Anbang Electrochemical Co., Ltd., acrylic acid purchased from Shandong Xinshunli Chemical Technology Co., Ltd., pentaerythritol purchased from Jiangsu Ruiyang Chemical Co., Ltd., and CALB immobilized enzyme purchased from Shangke Biopharmaceutical (Shanghai) Co., Ltd.

[0044] The specific reaction scheme of pentaerythritol tetramercaptocarboxylate in the present invention is shown in the following formula I:

[0045]

[0046] Formula I

[0047] The specific preparation method comprises the following steps:

[0048] (1) Addition reaction: Dissolve thiourea in a solvent, add acrylic acid, mix well, heat to 25-35°C, and irradiate with an intensity of 5-25 mW / cm 2 The mixed liquid circulates in the annular tank under irradiation by a blue LED array with a wavelength of 450nm. The light source is 2-3cm away from the liquid surface in the annular tank. Under N2 protection, HCI / NaOH is added dropwise to adjust the pH of the reaction liquid to 6-7. Irradiation is continued for 60-120 minutes.

[0049] (2) Esterification reaction: Add pentaerythritol and lipase to the reaction solution of step (1), mix well, and then heat to 35~45℃. Control the light intensity in the range of 5~15mW / cm 2 , the mixed liquid continues to circulate in the annular groove, controlling the water activity at α w=0.2~0.5, detect the peak value of mercaptopropionic acid by HPLC every hour, continue irradiation for 3~6 hours, filter and elute the organic phase, and evaporate the solvent under reduced pressure to obtain colorless and transparent pentaerythritol tetramercaptocarboxylate.

[0050] The weight ratio of the pentaerythritol, thiourea, acrylic acid and solvent is (1-2): (2-5): (2-5): (5-10).

[0051] The lipase is selected from Candida antarctica lipase B (CALB immobilized enzyme), and the amount of lipase used is 2-6% by weight of the amount of pentaerythritol used.

[0052] The solvent is selected from at least one of dioxane, tert-butanol, butane nitrile and water, preferably a mixed solution of dioxane, tert-butanol and water; the weight ratio of dioxane, tert-butanol and water is (10-20): (2-5): (1-2).

[0053] The specific steps of preparing a polymerizable modified polyurethane optical material containing pentaerythritol tetramercaptocarboxylate using pentaerythritol tetramercaptocarboxylate in the present invention are as follows:

[0054] (1) Add pentaerythritol tetramercaptocarboxylate and acrylic ester monomers into a reactor containing isocyanate, stir at 50-120 rpm for 30-40 minutes, then add the catalyst and continue stirring to form a prepolymer.

[0055] (2) The prepolymer is vacuum-debubbled and injected into a tempered mold. The tempered mold containing the prepolymer is placed in a curing oven, heated to 30-50°C for curing for 1-3 hours, then heated to 55-75°C for curing for 2-5 hours. After cooling naturally to room temperature, the prepolymer is demoulded and sampled to obtain a modified polyurethane optical material.

[0056] Among them, the above-mentioned isocyanate and composition are selected from at least one of diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, diphenyl ether diisocyanate, toluene diisocyanate, diethylene diisocyanate, cyclohexane diisocyanate, hexamethylene diisocyanate (HDI), diethyl diisocyanate, tetramethylene diisocyanate, thiodihexyl diisocyanate, thiodipropyl diisocyanate, dithiodipropyl diisocyanate, triphenylmethane triisocyanate, isophorone diisocyanate, trimethylhexamethylene diisocyanate, meta-xylylenediisocyanate (XDI), xylylenediisocyanate, o-tolidine diisocyanate, lysine triisocyanate and isothiocyanate (described in Patent Publication No.: CN202411227016).

[0057] The above-mentioned acrylic acid ester monomer is selected from at least one of methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, hydroxymethyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, polyethylene glycol dimethacrylate, pentaerythritol tetraacrylate, polyethylene glycol methacrylate, ethoxylated nonylphenol acrylate, epoxy acrylate, bisphenol A epoxy acrylate and ethoxylated bisphenol A diacrylate.

[0058] The catalyst is selected from one of stannous octoate, dibutyltin dilaurate, dibutyltin dichloride and dibutyltin oxide, and the amount of the catalyst is 0.1 to 0.9 wt% of the isocyanate.

[0059] The polymerizable modified polyurethane optical material finally obtained comprises the following components:

[0060] Component A: isocyanate, 25-45 parts by weight;

[0061] Component B: 20 ​​to 45 parts by weight of pentaerythritol tetramercaptocarboxylate of formula I;

[0062] Component C: acrylic acid ester monomer, 5 to 10 parts by weight.

[0063] The present invention will be further described below by way of examples.

[0064] Example 1 Preparation of pentaerythritol tetramercaptocarboxylate

[0065] I. Addition reaction: 500g of thiourea was dissolved in a mixed solvent consisting of 2550g of dioxane, 500g of tert-butyl alcohol and 200g of water, and then 420g of acrylic acid was added. After mixing well, the temperature was heated to 30°C and the irradiation intensity was 20mW / cm 2 The mixed liquid circulates in the annular tank under irradiation by a blue LED array with a wavelength of 450nm. The light source is 2cm away from the liquid surface in the annular tank, and the pH value is controlled at 6.5 under N2 protection. The irradiation lasts for 60 minutes.

[0066] II. Esterification reaction: 180 g of pentaerythritol and 6.5 g of CALB immobilized enzyme were added to the reaction solution in step I above, mixed well, and then heated to 40 ° C. The light intensity was controlled at 10 mW / cm 2 The mixed liquid continues to circulate in the annular groove, and the water activity is controlled at α by molecular sieve adsorption and dehydration. w = 0.3, and irradiation was continued for 4.5 hours. Irradiation was stopped when the peak area of ​​mercaptopropionic acid detected by HPLC dropped to 1% of the initial value. The organic phase was filtered and eluted, and the solvent was evaporated under reduced pressure to obtain 512 g of colorless, transparent pentaerythritol tetramercaptocarboxylate. Yield: 80.1%.

[0067] Infrared spectrum FT-IR test: The product prepared in Example 1 was subjected to Fourier transform infrared spectrum FT-IR) test, and the results are as follows Figure 1 As shown, 2568cm -1 The absorption peak at 1735 cm is the characteristic peak of thiol. -1 The absorption peak at is the characteristic peak of ester carbonyl (C=O), indicating that the esterification is successful.

[0068] 1H-NMR analysis: The product prepared in Example 1 was subjected to 1H-NMR analysis. Figure 2 As shown, the compound has a singlet at δ=4.25ppm (s, 8H, 4×-CH2-O) which is a methylene group connected to the oxygen atom; a triplet at δ=2.86ppm (t, 8H, 4×-CH2-SH) which is a methylene group connected to the thiol group; a triplet at δ=2.63ppm (t, 8H, 4×-CH2-COO) which is a methylene group connected to carbon and oxygen; and a broad singlet at 1.57~1.59ppm (br s, 4H, 4×-SH) which is a -SH peak.

[0069] Example 2 Preparation of Pentaerythritol Tetramercaptocarboxylate

[0070] I. Addition reaction: 500g of thiourea was dissolved in a mixed solvent consisting of 2550g of dioxane, 500g of tert-butyl alcohol and 200g of water, and then 350g of acrylic acid was added. After mixing well, the temperature was heated to 30°C and the irradiation intensity was 20mW / cm 2 The mixed liquid circulates in the annular tank under irradiation by a blue LED array with a wavelength of 450nm. The light source is 2cm away from the liquid surface in the annular tank, and the pH value is controlled at 6.5 under N2 protection. The irradiation lasts for 50 minutes.

[0071] II. Esterification reaction: 180 g of pentaerythritol and 7.5 g of CALB immobilized enzyme were added to the reaction solution in step I above, mixed well, and then heated to 40 ° C. The light intensity was controlled at 10 mW / cm 2 The mixed liquid continues to circulate in the annular groove, and the water activity is controlled at α by molecular sieve adsorption and dehydration. w = 0.3, and irradiation was continued for 4.2 hours. Irradiation was stopped when the peak area of ​​mercaptopropionic acid detected by HPLC dropped to 1% of the initial value. The organic phase was filtered and eluted, and the solvent was evaporated under reduced pressure to obtain 472 g of colorless, transparent pentaerythritol tetramercaptocarboxylate. Yield: 80.1%.

[0072] Example 3 Preparation of Pentaerythritol Tetramercaptocarboxylate

[0073] I. Addition reaction: 500g of thiourea was dissolved in a mixed solvent consisting of 3000g of dioxane and 500g of water, and then 400g of acrylic acid was added. After mixing well, the temperature was heated to 30°C and the irradiation intensity was 20mW / cm 2 The mixed liquid circulates in the annular tank under irradiation by a blue LED array with a wavelength of 450nm. The light source is 2cm away from the liquid surface in the annular tank, and the pH value is controlled at 6.5 under N2 protection. The irradiation lasts for 60 minutes.

[0074] II. Esterification reaction: 180 g of pentaerythritol and 8.5 g of CALB immobilized enzyme were added to the reaction solution in step I above, mixed well, and then heated to 40 ° C. The light intensity was controlled at 10 mW / cm 2 The mixed liquid continues to circulate in the annular groove, and the water activity is controlled at α by molecular sieve adsorption and dehydration. w = 0.3, and irradiation was continued for 4.2 hours. Irradiation was stopped when the peak area of ​​mercaptopropionic acid detected by HPLC decreased to 0.9% of the initial value. The organic phase was filtered and eluted, and the solvent was evaporated under reduced pressure to obtain 511 g of colorless, transparent pentaerythritol tetramercaptocarboxylate. Yield: 80.2%.

[0075] Application Example 1 Preparation of modified polyurethane optical material containing pentaerythritol tetramercaptocarboxylate

[0076] 170 g of pentaerythritol tetramercaptocarboxylate prepared in Example 1 and 30 g of epoxy acrylate were added to a reactor containing 175 g of diphenylmethane diisocyanate, stirred at 80 rpm for 35 minutes, 0.8 g of dibutyltin dilaurate was added, and stirring was continued to form a prepolymer; the prepolymer was vacuum-debubbled and injected into a tempered mold, the tempered mold containing the prepolymer was placed in a curing oven, heated to 40° C. and cured for 2.5 hours, heated to 65° C. and maintained for curing for 3 hours, cooled to room temperature, and demolded and sampled to obtain a modified polyurethane optical material.

[0077] Application Example 2 Preparation of Modified Polyurethane Optical Material Containing Pentaerythritol Tetramercaptocarboxylate

[0078] 170 g of pentaerythritol tetramercaptocarboxylate prepared in Example 2 and 40 g of hydroxymethyl methacrylate were added to a reactor containing 165 g of m-phenylenedimethyl isocyanate, stirred at 80 rpm for 35 minutes, 0.85 g of dibutyltin dilaurate was added, and stirring was continued to form a prepolymer; the prepolymer was vacuum-debubbled and injected into a tempered mold, the tempered mold containing the prepolymer was placed in a curing oven, the temperature was raised to 40° C. for curing for 2.5 hours, the temperature was raised to 65° C. for curing for 3 hours, and the modified polyurethane optical material was obtained after demolding and sampling after cooling to room temperature.

[0079] Application Example 3 Preparation of Modified Polyurethane Optical Material Containing Pentaerythritol Tetramercaptocarboxylate

[0080] 170 g of pentaerythritol tetramercaptocarboxylate prepared in Example 3 and 30 g of bisphenol A epoxy acrylate were added to a reactor containing 70 g of isothiocyanate and 125 g of diphenylmethane diisocyanate, respectively, and stirred at 80 rpm for 35 minutes. 0.9 g of dibutyltin dilaurate was added and stirred evenly to form a prepolymer. The prepolymer was vacuum-debubbled and injected into a tempered mold. The tempered mold containing the prepolymer was placed in a curing oven, heated to 40° C. for curing for 2.5 hours, heated to 65° C. for curing for 3 hours, and then cooled to room temperature and demolded and sampled to obtain a modified polyurethane optical material.

[0081] Application Example 4: Comparison of economic efficiency under different preparation process conditions

[0082] A comparison of the economic performance of the new photoenzyme-catalyzed esterification process with the traditional acid-catalyzed esterification process revealed that the production cost of the new process dropped from 22,000 RMB per ton to 14,000 RMB, a 36.3% reduction. This product demonstrates significant market competitiveness. See Table 1 for details.

[0083]

[0084] Test Example 1: Purity Test of Pentaerythritol Tetramercaptocarboxylate Compound

[0085] The pentaerythritol tetramercaptocarboxylate prepared in Examples 1-3 was tested for purity using an Agilent 1260 Infinity II high-performance liquid chromatograph (HPLC). The purity was determined by integrating the peak areas and calibrating against a standard peak. Purity = (PETMP peak area / total peak area) × 100%. The test results are detailed in Table 2.

[0086]

[0087] Test Example 2: Optical Performance Test Experiment

[0088] The pentaerythritol tetramercaptocarboxylate compounds prepared in Examples 1-3 and the modified polyurethane optical material prepared in Application Example 1 were tested for optical properties. Transmittance was measured using a UV-8000 UV-visible photometer from Shanghai Yuanxi Instrument Co., Ltd. The test method was to directly apply the compound monomer to the prism of the UV-visible photometer and measure the transmittance. Refractive index was measured using a WYV-S digital V-prism refractometer from Shanghai Yidian Physical Optical Instruments Co., Ltd. The test method was to directly apply the monomer to the prism and measure the refractive index. The optical properties of polymers were tested by simply placing the test material in the test position. The yellowness index (YI) was calculated from the spectrophotometer reading using the formula: YI = (1.28X - 1.06Z) × 100 ÷ Y. The test results are shown in Table 3.

[0089]

[0090] Conclusion: The pentaerythritol tetramercaptocarboxylate compound prepared by the present invention has a transmittance of 90.2%, a refractive index of 1.52, and a yellowness index of 0.88; the transmittance of the prepared polymer optical material is 90.4%, and the refractive index can be adjusted in the range of 1.56-1.62.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should all be covered by the scope of the claims of the present invention.

Claims

1. A method for preparing pentaerythritol tetramercaptocarboxylate, characterized in that: The method comprises the following steps: (1) Addition reaction: Dissolve thiourea in a solvent, add acrylic acid, mix well, heat to 25-35°C, and irradiate with an intensity of 5-25 mW / cm 2 Irradiation was performed with a 450nm wavelength blue LED array. The mixed liquid circulated in an annular tank. The light source was 2-3cm away from the liquid surface in the annular tank. Under nitrogen protection, HCl / NaOH was added dropwise to adjust the pH of the reaction solution to 6-7. Irradiation was continued for 60-120 minutes. (2) Esterification reaction: add pentaerythritol and lipase to the reaction solution in step (1), mix well and heat to 35-45°C, control the light intensity to 5-15 mW / cm 2 , the mixed liquid continues to circulate in the annular groove, controlling the water activity at α w = 0.2~0.5, detect the peak value of mercaptopropionic acid by HPLC every hour, continue irradiation for 3~6 hours, filter and elute the organic phase, and evaporate the solvent under reduced pressure to obtain colorless and transparent pentaerythritol tetramercaptocarboxylate; The lipase is selected from Candida antarctica lipase B.

2. The method for preparing pentaerythritol tetramercaptocarboxylate according to claim 1, wherein The weight ratio of pentaerythritol, thiourea, acrylic acid and solvent is (1-2): (2-5): (2-5): (15-50).

3. The method for preparing pentaerythritol tetramercaptocarboxylate according to claim 1, wherein The amount of lipase used is 2-6 wt% of the amount of pentaerythritol used.

4. The method for preparing pentaerythritol tetramercaptocarboxylate according to claim 1, wherein The solvent is selected from at least one of dioxane, tert-butyl alcohol, butane nitrile and water.

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