Free radical polymerization inhibitor as well as preparation method and application thereof

Abstract

The invention provides a free radical polymerization inhibitor, a preparation method and application thereof, and a composition containing hydroxyethyl methylacrylate. The radical polymerization inhibitor has a boiling point of 350 DEG C or more. When the free radical polymerization inhibitor is applied to the extraction, rectification and separation process of hydroxyethyl methylacrylate, the content of hydroxyethyl methylacrylate products brought to the tower top is extremely low, and adverse effects on the color number and downstream application of the hydroxyethyl methylacrylate products are avoided. The free radical polymerization inhibitor is selected from one or more of the following structures: # imgabs0 #

Description

Technical Field

[0001] The invention relates to the field of chemical synthesis, and in particular to a free radical polymerization inhibitor, a preparation method and use thereof, and a composition containing hydroxyethyl methacrylate. Background Art

[0002] Hydroxyethyl methacrylate, referred to as HEMA, is a special ester monomer of methacrylate. Low-purity products (purity <99%) are mainly used in thermosetting coatings and adhesives. The high-end application field of hydroxyethyl methacrylate is the contact lens field, which has higher requirements for the purity of hydroxyethyl methacrylate, above 99.6%. It has strict requirements for the impurity ethylene glycol dimethacrylate, the content of which is less than 0.1wt%. It is necessary to purify and prepare the hydroxyethyl methacrylate separation liquid by optimizing the separation process.

[0003] At present, there are many methods for preparing hydroxyethyl methacrylate, and most reports focus on reaction synthesis. There are few studies on separation process, and no relevant reports on separation process research of high-purity hydroxyethyl methacrylate have been found.

[0004] The normal pressure boiling point of hydroxyethyl methacrylate is 225°C, which is polar. The normal pressure boiling point of ethylene glycol dimethacrylate is 243°C, which is not much different from the boiling point of hydroxyethyl methacrylate product. Moreover, it is a non-polar compound and can be easily evaporated into the hydroxyethyl methacrylate product, affecting the purity of the hydroxyethyl methacrylate product.

[0005] How to prepare high-purity hydroxyethyl methacrylate products and reduce the content of ethylene glycol dimethacrylate impurities in the products is an urgent problem to be solved.

[0006] In the separation process of hydroxyethyl methacrylate, the materials involved are all easily polymerizable monomers, and the process is at high temperature. In the separation process, an inhibitor needs to be added to prevent the materials from polymerizing in the tower. 2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide free radical (referred to as 701) has a good inhibitory effect, but its boiling point is low, at 270°C. It is easy to evaporate into the hydroxyethyl methacrylate product during the separation process, affecting the product color and downstream applications. In this regard, it is necessary to develop a high-boiling point free radical inhibitor.

[0007] The inventors of the present invention have developed a silicon-modified negative nitroxide free radical inhibitor after long-term research. The inhibitor has a boiling point higher than 350°C and is applied to the separation process of hydroxyethyl methacrylate to reduce the content of the inhibitor in hydroxyethyl methacrylate as much as possible, thereby preparing high-quality hydroxyethyl methacrylate products, which can be applied to the field of contact lenses. Summary of the invention

[0008] The purpose of the present invention is to provide a silicon-modified free radical polymerization inhibitor, a preparation method and use thereof, and a composition containing hydroxyethyl methacrylate. The present invention modifies 2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide free radical polymerization inhibitor by 1,3,5-trichloro-1,3,5-trimethyl-1,3,5-trisilacyclohexane to increase the boiling point of the polymerization inhibitor to above 350°C, and applies it to the separation process of high-purity hydroxyethyl methacrylate. The purity of the obtained hydroxyethyl methacrylate is greater than 99.9%, and it can be applied to the high-end field of contact lenses.

[0009] According to a first aspect of the present invention, there is provided a free radical inhibitor, which is one or more selected from the following structures:

[0010]

[0011] Preferably, the boiling point of the free radical inhibitor is above 350°C.

[0012] It should be noted that, in the present invention, the free radical inhibitor can be any one of the above three structures, or a mixture of any two or three of them in any proportion. For example, relative to 100wt% of the free radical inhibitor, R-Si-

[701] 3 The content of may be 0wt%, 10wt% or more, 20wt% or more, 30wt% or more, 40wt% or more, 50wt% or more, 60wt% or more, or 70wt% or more.

[0013] According to a second aspect of the present invention, there is provided a method for preparing the free radical inhibitor according to the present invention, comprising the following steps:

[0014] (1) 2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide free radical reacts with metallic sodium in an organic solvent to generate a mixed solution containing 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy sodium salt;

[0015] (2) reacting the mixed solution containing 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy sodium salt obtained in step (1) with 1,3,5-trichloro-1,3,5-trimethyl-1,3,5-trisilacyclohexane in the presence of a quaternary ammonium salt catalyst to generate a reaction solution containing an inhibitor.

[0016] Preferably, in step (1), the molar ratio of 2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide free radical to metallic sodium is 1:(1.00-1.05).

[0017] Preferably, in step (1), the reaction temperature is 0 to 25°C.

[0018] Preferably, in step (1), the reaction pressure is 0.09-0.1 MPaA.

[0019] Preferably, in step (1), the reaction time is 3 to 4 hours.

[0020] Preferably, in step (1), the organic solvent is at least one selected from cyclohexane, n-hexane and n-heptane.

[0021] Preferably, in step (1), the molar ratio of 2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide free radical to the organic solvent is 1:(10-15).

[0022] Preferably, in step (2), the molar ratio of 1,3,5-trichloro-1,3,5-trimethyl-1,3,5-trisilacyclohexane to 2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide radical is 1:(3.0-3.05).

[0023] Preferably, in step (2), the reaction temperature is 80-90°C.

[0024] Preferably, in step (2), the reaction pressure is 0.2-0.3 MPaG.

[0025] Preferably, in step (2), the reaction time is 2 to 3 hours.

[0026] Preferably, in step (2), the quaternary ammonium salt catalyst is at least one selected from tetramethylammonium bromide, tetramethylammonium chloride, trimethylbenzylammonium chloride, triethylbenzylammonium chloride, hexadecyltrimethylbenzylammonium chloride and hexadecyltriethylbenzylammonium chloride.

[0027] Preferably, in step (2), the amount of the quaternary ammonium salt catalyst is 0.19 wt % to 1.0 wt % based on the total amount of the reaction solution.

[0028] Preferably, the method for preparing a free radical inhibitor according to the present invention further comprises the following steps:

[0029] (3) filtering, washing with water and distilling the reaction solution containing the free radical inhibitor obtained in step (2) to obtain the free radical inhibitor in solid form.

[0030] Preferably, in step (3), the filtration temperature is 20-30°C.

[0031] Preferably, in step (3), the filtration pressure is 0.1-0.3 MPaG.

[0032] Preferably, in step (3), the water washing temperature is 20 to 30° C., and the number of water washings is 3 to 5 times.

[0033] Preferably, in step (3), the distillation temperature is 50-60° C., and the distillation pressure is 50-60 kPaA.

[0034] According to a third aspect of the present invention, there is provided a use of the free radical inhibitor according to the present invention in the purification of hydroxyethyl methacrylate.

[0035] According to a fourth aspect of the present invention, there is provided a method for refining hydroxyethyl methacrylate, comprising the following steps:

[0036] a) adding the free radical inhibitor according to the present invention to crude hydroxyethyl methacrylate to obtain a crude hydroxyethyl methacrylate mixture, and preparing a hydroxyethyl methacrylate solution of the free radical inhibitor using the free radical inhibitor according to the present invention and hydroxyethyl methacrylate;

[0037] b) feeding the crude hydroxyethyl methacrylate mixture to a tray position near the bottom of the extractive distillation tower, feeding the hydroxyethyl methacrylate solution of the free radical inhibitor to a tray position near the top, and feeding the extractant to a tray below the tray to which the hydroxyethyl methacrylate solution of the free radical inhibitor is fed, performing extractive distillation in the extractive distillation tower, and obtaining a top liquid from the top of the tower is hydroxyethyl methacrylate with a purity of more than 99.90wt%.

[0038] In a specific embodiment, the crude hydroxyethyl methacrylate comprises: based on the total weight of the crude hydroxyethyl methacrylate, 40 wt% to 50 wt% of hydroxyethyl methacrylate; 40 wt% to 50 wt% of diethylene glycol methacrylate and 2 wt% to 3 wt% of ethylene glycol dimethacrylate.

[0039] In a specific embodiment, the content of the free radical inhibitor in the crude hydroxyethyl methacrylate containing the free radical inhibitor is 0.1 wt % to 0.2 wt %.

[0040] In a specific embodiment, the concentration of the hydroxyethyl methacrylate solution of the free radical inhibitor is 0.5 wt % to 2 wt %.

[0041] In a specific embodiment, the number of theoretical plates of the distillation tower for extractive distillation is 10-15.

[0042] In a specific embodiment, the extractive distillation adopts a continuous feeding method, and the feeding position of the crude hydroxyethyl methacrylate mixture is 7 to 12 theoretical plates.

[0043] In a specific embodiment, the extractant is at least one selected from dioctyl sebacate, dibutyl sebacate, dibutyl sebacate, dioctyl azelate and dibutyl suberate.

[0044] In a specific embodiment, the mass ratio of the extractant to the crude hydroxyethyl methacrylate mixture is (1-2):1.

[0045] In a specific embodiment, the extractant feeding position is at 2 to 3 theoretical plates.

[0046] In a specific embodiment, the feeding position of the hydroxyethyl methacrylate solution of the free radical inhibitor is 1 to 2 theoretical plates.

[0047] In a specific embodiment, the top pressure of the extractive distillation tower is 100-300 PaA, and the top temperature is 60-75°C.

[0048] The purity of the prepared hydroxyethyl methacrylate reaches more than 99.9wt%, the content of ethylene glycol dimethacrylate is less than 0.03wt%, the content of diethylene glycol methacrylate is less than 0.01wt%, the content of silicon-modified free radical inhibitor is less than 10ppm, the content of extractant is less than 20ppm, and the color number is less than 10 (Pt-Co).

[0049] According to a fifth aspect of the present invention, a hydroxyethyl methacrylate composition is provided, wherein the purity of hydroxyethyl methacrylate is above 99.9 wt %, the content of free radical inhibitor is less than 10 ppm, and the color number is less than 10 (Pt-Co).

[0050] Preferably, in the hydroxyethyl methacrylate composition, the content of ethylene glycol dimethacrylate is less than 0.03 wt %.

[0051] Preferably, in the hydroxyethyl methacrylate composition, the content of diethylene glycol methacrylate is less than 0.01 wt %.

[0052] Preferably, in the hydroxyethyl methacrylate composition, the content of extractant is less than 20 ppm.

[0053] The beneficial effects of the present invention are:

[0054] 1. The present invention prepares a silicon-modified free radical inhibitor, whose boiling point is significantly increased to above 350°C. The silicon-modified free radical inhibitor is used in the extraction and distillation separation process of hydroxyethyl methacrylate, and the content of hydroxyethyl methacrylate in the product brought to the top of the tower is extremely small, which will not have an adverse effect on its color number and downstream applications;

[0055] 2. The present invention develops a method for separating high-purity hydroxyethyl methacrylate, which adopts an extractive distillation process and a high-boiling-point extractant, the boiling point of which is higher than 310° C., which is significantly higher than the boiling point of hydroxyethyl methacrylate (225° C.). The content of hydroxyethyl methacrylate in the product carried to the top of the tower as an extractant during the separation process is extremely small and will not affect downstream applications.

[0056] 3. The silicon-modified free radical inhibitor prepared by the present invention is used in the extraction and distillation separation process of hydroxyethyl methacrylate to obtain a high-purity hydroxyethyl methacrylate product with a purity greater than 99.9%, which meets the index requirements of the contact lens application field. The entire separation process is a continuous operation, no waste water or waste alkali solution is generated, and it is environmentally friendly and can be used for large-scale continuous production of high-purity hydroxyethyl methacrylate. DETAILED DESCRIPTION

[0057] The present invention is further described below by way of examples, which are not limited to the following examples. The present invention extends to any new features or any new combination disclosed in the specification, and any new method or process steps or any new combination disclosed.

[0058] 1. Sources of main raw materials in the examples:

[0059] Hydroxyethyl methacrylate to be separated liquid, Wanhua Chemical Group Co., Ltd., industrial grade;

[0060] 2,2,6,6-Tetramethyl-4-hydroxypiperidinyl nitroxide free radical, Sinopharm Chemical Reagent Co., Ltd., analytical grade;

[0061] Sodium metal was purchased from Beijing Inokai Technology Co., Ltd., analytical grade;

[0062] 1,3,5-Trichloro-1,3,5-trimethyl-1,3,5-trisilacyclohexane, Shanghai Tangui New Material Technology Co., Ltd., analytical grade;

[0063] n-Hexane, analytical grade, Beijing Inokai Technology Co., Ltd.;

[0064] Cyclohexane was purchased from Beijing Inokai Technology Co., Ltd., analytical grade;

[0065] Tetramethylammonium chloride, Kent Catalytic Materials Co., Ltd., analytical grade;

[0066] Benzyltrimethylammonium chloride, Jiangsu Bisheng Chemical Co., Ltd., analytical grade;

[0067] Dioctyl sebacate, Shandong Xinheng Chemical Co., Ltd., analytical grade;

[0068] Dibutyl sebacate, Beijing Inokai Technology Co., Ltd., analytical grade;

[0069] Dibutyl suberate, Shaanxi Didu New Materials Co., Ltd., analytical grade;

[0070] 2. Product analysis method in the embodiment:

[0071] Gas chromatography was used to analyze the components and contents of the reaction solution and products using the correction factor method. Instrument manufacturer and model: Shimadzu 1020-plus;

[0072] Liquid chromatography was used to analyze the content of 2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide free radicals. Instrument manufacturer and model: Agilent 1290 Infinity II;

[0073] The boiling point of the inhibitor was determined by a thermogravimetric analyzer (TGA), instrument manufacturer and model: METTLER (Switzerland) TGA / DSC1;

[0074] Use nuclear magnetic resonance (NMR) to determine the structure of the high temperature inhibitor. Instrument manufacturer and model:

[0075] Bruker AVANCE III 400M.

[0076] Example 1 (Preparation of Inhibitor)

[0077] A method for preparing a silicon-modified free radical inhibitor, comprising the following steps:

[0078] (1) adding 172 g (1 mol) of 2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide free radical to a 2 L jacketed kettle, then adding 860 g (10 mol) of n-hexane solvent to the jacketed kettle, stirring and dissolving a mixed solution of 2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide free radical and n-hexane, and cooling the mixed solution to 10° C. by a jacketed refrigerant, and slowly adding 23 g (1 mol) of metallic sodium at 0.09 MPaA. After the addition is completed, continuing the reaction for 3 h to obtain a mixed solution containing 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy sodium salt;

[0079] (2) adding 92.5 g (0.33 mol) of 1,3,5-trichloro-1,3,5-trimethyl-1,3,5-trisilacyclohexane to the mixed solution containing 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy sodium salt obtained in step (1), and then adding 2.249 g of tetramethylammonium chloride, heating to 80° C. with stirring, and then continuing the reaction at a pressure of 0.2 MPaG for 2 h to obtain a reaction solution containing a free radical inhibitor;

[0080] (3) The temperature of the reaction solution obtained in step (2) was lowered to 20° C., and then filtered at 0.1 MPaG, and the by-product sodium chloride generated therein was filtered to obtain a clarified organic phase, and then the organic phase was washed with water three times, and the amount of water used each time was equal to the mass of the oil phase to be washed with water. After the oil phase after washing was distilled to remove the solvent therein, a solid sample of silicon-modified nitroxide free radical inhibitor was obtained in the bottom of the tower, which was R-Si-

[701] , R-Si-

[701] 2 and R-Si-

[701] 3 The boiling point of the mixture is 389°C.

[0081] Among them, the hydrogen spectrum of R-Si-

[701] is: 1 HNMR(500MHz, CDCl3)δ3.23(1H),1.67(2H),1.42(2H),1.4(6H),1.14(12H),0.42(6H),0.21(3H).

[0082] R-Si-

[701] 2 Proton spectrum: 1 HNMR(500MHz, CDCl3)δ3.23(2H),1.67(4H),1.42(4H),1.4(6H),1.14(24H),0.42(3H),0.21(6H)

[0083] R-Si-

[701] 3 Proton spectrum: 1 HNMR(500MHz, CDCl3)δ3.23(3H),1.67(6H),1.42(6H),1.4(6H),1.14(36H),0.21(9H)

[0084] The composition of the obtained inhibitor is shown in Table 1.

[0085] Example 2 (Preparation of Inhibitor)

[0086] A method for preparing a silicon-modified nitroxide free radical inhibitor, comprising the following steps:

[0087] (1) adding 172 g (1 mol) of 2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide free radical into a 2 L jacketed kettle, then adding 860 g (10 mol) of solvent cyclohexane into the jacketed kettle, stirring and dissolving a mixed solution of 2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide free radical and cyclohexane, and cooling the mixed solution to 25° C. by a jacketed refrigerant, and slowly adding 23 g (1 mol) of metallic sodium at 0.09 MPaA. After the addition is completed, continuing the reaction for 4 h to obtain a mixed solution containing 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy sodium salt;

[0088] (2) adding 92.5 g (0.33 mol) of 1,3,5-trichloro-1,3,5-trimethyl-1,3,5-trisilacyclohexane to the mixed solution containing 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy sodium salt obtained in step (1), and then adding 2.249 g (0.021 mol) of tetramethylammonium chloride, heating to 90° C. with stirring, and then continuing the reaction for 3 h to obtain a reaction solution containing an inhibitor;

[0089] (3) The temperature of the reaction solution obtained in step (2) was lowered to 20° C., and then filtered at 0.1 MPaG, and the by-product sodium chloride was filtered to obtain a clarified organic phase, and then the organic phase was washed with water three times, and the amount of water used each time was equal to the mass of the oil phase to be washed. After the oil phase after washing was distilled to remove the solvent therein, the silicon-modified free radical inhibitor sample was obtained in the bottom of the tower, which was R-Si-

[701] , R-Si-

[701] 2 and R-Si-

[701] 3 The boiling point of the mixture is 401°C.

[0090] The composition of the obtained inhibitor is shown in Table 1.

[0091] Example 3 (Preparation of Inhibitor)

[0092] A method for preparing a silicon-modified nitroxide free radical inhibitor, comprising the following steps:

[0093] (1) adding 172 g (1 mol) of 2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide free radical to a 2 L jacketed kettle, then adding 860 g (10 mol) of n-heptane solvent to the jacketed kettle, stirring and dissolving a mixed solution of 2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide free radical and n-heptane, and cooling the mixed solution to 10° C. by a jacketed refrigerant, and slowly adding 23 g (1 mol) of metallic sodium at 0.09 MPaA. After the addition is completed, continuing the reaction for 3 h to obtain a mixed solution containing 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy sodium salt;

[0094] (2) adding 92.5 g (0.33 mol) of 1,3,5-trichloro-1,3,5-trimethyl-1,3,5-trisilacyclohexane to the mixed solution containing 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy sodium salt obtained in step (1), and then adding 2.249 g (0.021 mol) of tetramethylammonium chloride, heating to 85° C. with stirring, and then continuing the reaction for 2 h to obtain a reaction solution containing an inhibitor;

[0095] (3) The temperature of the reaction solution obtained in step (2) was lowered to 20° C., and then filtered at 0.1 MPaG, and the by-product sodium chloride was filtered to obtain a clarified organic phase, and then the organic phase was washed with water three times, and the amount of water used each time was equal to the mass of the oil phase to be washed. After the oil phase after washing was distilled to remove the solvent therein, the silicon-modified free radical inhibitor sample was obtained in the bottom of the tower, which was R-Si-

[701] , R-Si-

[701] 2 and R-Si-

[701] 3 The boiling point of the mixture is 413°C.

[0096] The composition of the obtained inhibitor is shown in Table 1.

[0097] Table 1 Composition results of the inhibitors prepared in Examples 1 to 3

[0098] R-Si-

[701] <![CDATA[R-Si-

[701] 2 ]]> <![CDATA[R-Si-

[701] 3 ]]> Example 1 2.10wt% 22.40wt% 75.50wt% Example 2 1.90wt% 19.30wt% 78.80wt% Example 3 3.20wt% 20.40wt% 76.40wt%

[0099] Example 4 (HEMA separation)

[0100] Hydroxyethyl methacrylate is purified by the following steps:

[0101] 1) adding 10 g of the silicon-modified nitroxide free radical inhibitor sample prepared in Example 1 to 10000 g of crude hydroxyethyl methacrylate, stirring and dissolving to obtain a crude hydroxyethyl methacrylate mixture, wherein the crude hydroxyethyl methacrylate comprises: 48 wt % of hydroxyethyl methacrylate, 49 wt % of diethylene glycol methacrylate and 3 wt % of ethylene glycol dimethacrylate;

[0102] 2) using HEMA product to prepare a silicon-modified free radical inhibitor solution (prepared in Example 1), wherein the content of the silicon-modified nitroxide free radical inhibitor is 1 wt %;

[0103] 3) using an extractive distillation tower to purify hydroxyethyl methacrylate, the extractive distillation tower has 10 theoretical plates, the feeding position of the silicon-modified free radical inhibitor solution obtained in step 2) is the first plate, the feeding rate is 4 g / h, the feeding position of the extractant dioctyl sebacate is the third plate, the feeding rate is 200 g / h, the feeding position of the crude hydroxyethyl methacrylate mixture is the seventh plate, the feeding rate is 200 g / h, the tower top pressure is 100 PaA, the tower top temperature is 60°C, the purity of hydroxyethyl methacrylate in the obtained tower top liquid is 99.97wt%, ethylene glycol dimethacrylate is 0.02wt%, diethylene glycol methacrylate is 89ppm, the content of dioctyl sebacate is 11ppm, the silicon-modified free radical inhibitor is 5ppm, and the color number is 5 (Pt-Co).

[0104] Example 5 (HEMA separation)

[0105] Hydroxyethyl methacrylate is purified by the following steps:

[0106] 1) adding 10 g of the silicon-modified nitroxide free radical inhibitor sample prepared in Example 2 to 10000 g of crude hydroxyethyl methacrylate, stirring and dissolving to obtain a crude hydroxyethyl methacrylate mixture, wherein the crude hydroxyethyl methacrylate raw material comprises: 47 wt % of hydroxyethyl methacrylate, 50 wt % of diethylene glycol methacrylate, and 3 wt % of ethylene glycol dimethacrylate;

[0107] 2) using HEMA product to prepare a silicon-modified free radical inhibitor solution (prepared in Example 2), wherein the content of the silicon-modified nitroxide free radical inhibitor is 1 wt %;

[0108] 3) using an extractive distillation tower to purify a high-purity hydroxyethyl methacrylate product, the extractive distillation tower has 10 theoretical plates, the feeding position of the silicon-modified free radical inhibitor solution is the first plate, the feed rate is 4 g / h, the feeding position of the extractant dibutyl sebacate is the third plate, the feed rate is 400 g / h, the feeding position of the hydroxyethyl methacrylate crude mixture is the seventh plate, the feed rate is 200 g / h, the tower top pressure is 300 PaA, the tower top temperature is 75°C, the purity of hydroxyethyl methacrylate in the obtained tower top liquid is 99.97wt%, ethylene glycol dimethacrylate is 0.02wt%, diethylene glycol methacrylate is 73ppm, the content of dibutyl sebacate is 13ppm, the silicon-modified free radical inhibitor is 6ppm, and the color number is 6 (Pt-Co).

[0109] Example 6 (HEMA separation)

[0110] Hydroxyethyl methacrylate is purified by the following steps:

[0111] 1) adding 10 g of the silicon-modified nitroxide free radical inhibitor sample prepared in Example 3 to 10000 g of crude hydroxyethyl methacrylate, and stirring to dissolve the crude hydroxyethyl methacrylate mixture, wherein the crude hydroxyethyl methacrylate raw material comprises: 49 wt % of hydroxyethyl methacrylate, 49 wt % of diethylene glycol methacrylate, and 2 wt % of ethylene glycol dimethacrylate;

[0112] 2) using HEMA product to prepare a silicon-modified free radical inhibitor solution (prepared in Example 3), wherein the content of the silicon-modified nitroxide free radical inhibitor is 1 wt %;

[0113] 3) using an extractive distillation tower to purify hydroxyethyl methacrylate, the extractive distillation tower has 15 theoretical plates, the feeding position of the silicon-modified free radical inhibitor solution is the second plate, the feeding rate is 6 g / h, the feeding position of the extractant dibutyl sebacate is the fourth plate, the feeding rate is 400 g / h, the feeding position of the crude hydroxyethyl methacrylate mixture is the 12th plate, the feeding rate is 200 g / h, the tower top pressure is 100 PaA, the tower top temperature is 60° C., the purity of hydroxyethyl methacrylate in the obtained tower top liquid is 99.98wt%, ethylene glycol dimethacrylate is 0.01wt%, diethylene glycol methacrylate is 55ppm, the content of dibutyl sebacate is 10ppm, the silicon-modified free radical inhibitor is 5ppm, and the color number is 5 (Pt-Co);

[0114] Comparative Example 1

[0115] Different from Example 6, 2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide free radical (701) is used to replace the silicon-modified free radical inhibitor in the refined hydroxyethyl methacrylate, and the steps are as follows:

[0116] 1) adding 10 g of 2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide (701) sample to 10000 g of crude hydroxyethyl methacrylate, stirring and dissolving to obtain a crude hydroxyethyl methacrylate mixture, wherein the crude hydroxyethyl methacrylate raw material comprises: 48 wt % of hydroxyethyl methacrylate, 49 wt % of diethylene glycol methacrylate and 3 wt % of ethylene glycol dimethacrylate;

[0117] 2) using HEMA product to prepare 2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide free radical (701) solution, the content of 701 is 1wt%;

[0118] 3) using an extractive distillation tower to purify a high-purity hydroxyethyl methacrylate product, the extractive distillation tower has 15 theoretical plates, the 2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide (701) solution is fed to the second plate at a feed rate of 6 g / h, the extractant dibutyl sebacate is fed to the fourth plate at a feed rate of 400 g / h, the hydroxyethyl methacrylate crude mixture is fed to the 12th plate at a feed rate of 200 g / h, and the tower top pressure is 1.5 100PaA, tower top temperature 60 ° C, the purity of hydroxyethyl methacrylate in the obtained tower top liquid is 99.98wt%, ethylene glycol dimethacrylate is 0.01wt%, diethylene glycol methacrylate is 55ppm, dibutyl sebacate content is 10ppm, 2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide free radical (701) is 48ppm, and the color number is 29 (Pt-Co), which cannot meet the high-purity HEMA index requirements in the contact lens field.

Claims

1. A free radical inhibitor, which is one or more selected from the following structures: Preferably, the boiling point of the free radical inhibitor is above 350°C.

2. A method for preparing the free radical inhibitor according to claim 1, comprising the following steps: (1) 2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide free radical reacts with metallic sodium in an organic solvent to generate a mixed solution containing 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy sodium salt; (2) reacting the mixed solution containing 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy sodium salt obtained in step (1) with 1,3,5-trichloro-1,3,5-trimethyl-1,3,5-trisilacyclohexane in the presence of a quaternary ammonium salt catalyst to generate a reaction solution containing an inhibitor.

3. The method for preparing a free radical inhibitor according to claim 2, in, In step (1), the molar ratio of 2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide free radical to metallic sodium is 1:(1.00-1.05); and / or In step (1), the reaction temperature is 0 to 25°C; and / or In step (1), the reaction pressure is 0.09 to 0.1 MPaA; and / or In step (1), the reaction time is 3 to 4 hours; and / or In step (1), the organic solvent is at least one selected from cyclohexane, n-hexane and n-heptane; and / or In step (1), the molar ratio of 2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide free radical to the organic solvent is 1:(10-15).

4. The method for preparing a free radical inhibitor according to claim 2 or 3, in, In step (2), the molar ratio of 1,3,5-trichloro-1,3,5-trimethyl-1,3,5-trisilacyclohexane to 2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide radical is 1:(3.0-3.05); and / or In step (2), the reaction temperature is 80-90°C; and / or In step (2), the reaction pressure is 0.2-0.3 MPaG; and / or In step (2), the reaction time is 2 to 3 hours; and / or In step (2), the quaternary ammonium salt catalyst is at least one selected from tetramethylammonium bromide, tetramethylammonium chloride, trimethylbenzylammonium chloride, triethylbenzylammonium chloride, hexadecyltrimethylbenzylammonium chloride and hexadecyltriethylbenzylammonium chloride; and / or In step (2), the amount of the quaternary ammonium salt catalyst is 0.19 wt% to 1.0 wt% based on the total amount of the reaction solution.

5. The method for preparing a free radical inhibitor according to any one of claims 2 to 4, further comprising the steps of: (3) filtering, washing with water and distilling the reaction solution containing the free radical inhibitor obtained in step (2) to obtain the free radical inhibitor in solid form.

6. The method for preparing a free radical inhibitor according to claim 5, in, In step (3), the filtration temperature is 20 to 30°C; and / or In step (3), the filtration pressure is 0.1-0.3 MPaG; and / or In step (3), the water washing temperature is 20 to 30° C. and the number of water washings is 3 to 5 times; and / or In step (3), the distillation temperature is 50-60°C and the distillation pressure is 50-60 kPaA.

7. A method for refining hydroxyethyl methacrylate, comprising the steps of: a) adding the free radical inhibitor according to claim 1 to crude hydroxyethyl methacrylate to obtain a crude hydroxyethyl methacrylate mixture, and preparing a hydroxyethyl methacrylate solution of the free radical inhibitor using the free radical inhibitor according to claim 1 and hydroxyethyl methacrylate; b) feeding the crude hydroxyethyl methacrylate mixture to a tray position near the bottom of the extractive distillation tower, feeding the hydroxyethyl methacrylate solution of the free radical inhibitor to a tray position near the top, and feeding the extractant to a tray below the tray to which the hydroxyethyl methacrylate solution of the free radical inhibitor is fed, performing extractive distillation in the extractive distillation tower, and obtaining a top liquid from the top of the tower is hydroxyethyl methacrylate with a purity of more than 99.90wt%.

8. The method for refining hydroxyethyl methacrylate according to claim 8, in, The crude hydroxyethyl methacrylate comprises: based on the total weight of the crude hydroxyethyl methacrylate, 40 wt% to 50 wt% of hydroxyethyl methacrylate; 40 wt% to 50 wt% of diethylene glycol methacrylate and 2 wt% to 3 wt% of ethylene glycol dimethacrylate; and / or The content of the free radical inhibitor in the crude hydroxyethyl methacrylate containing the free radical inhibitor is 0.1wt% to 0.2wt%; and / or The concentration of the hydroxyethyl methacrylate solution of the free radical inhibitor is 0.5wt% to 2wt%; and / or The number of theoretical plates of the distillation tower for extractive distillation is 10 to 15; and / or The extractive distillation adopts a continuous feeding method, and the feeding position of the crude hydroxyethyl methacrylate mixture is 7 to 12 theoretical plates; and / or The extractant is at least one selected from dioctyl sebacate, dibutyl sebacate, dibutyl sebacate, dioctyl azelate and dibutyl suberate; and / or The mass ratio of the extractant to the crude hydroxyethyl methacrylate mixture is (1-2):1; and / or The extractant feed position is 2 to 3 theoretical plates; and / or The feeding position of the hydroxyethyl methacrylate solution of the free radical inhibitor is 1 to 2 theoretical plates; and / or The top pressure of the extractive distillation tower is 100-300 PaA, and the top temperature is 60-75°C.

9. A hydroxyethyl methacrylate composition, in, The purity of hydroxyethyl methacrylate is above 99.9 wt %, and the content of free radical inhibitor is lower than 10 ppm.

10. The hydroxyethyl methacrylate composition according to claim 9, in, The color number of the hydroxyethyl methacrylate composition is less than 10 (Pt-Co); and / or In the hydroxyethyl methacrylate composition, the content of ethylene glycol dimethacrylate is less than 0.03 wt %; and / or In the hydroxyethyl methacrylate composition, the content of diethylene glycol methacrylate is less than 0.01 wt %.

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