Radical polymerization inhibitor, method for its preparation and use

Abstract

The present invention provides a free radical polymerization inhibitor, its preparation method and use, and a composition comprising hydroxyethyl methacrylate. The free radical polymerization inhibitor has a boiling point of 350°C or higher. The free radical polymerization inhibitor is applied in the extractive distillation separation process of hydroxyethyl methacrylate, and the content of the free radical polymerization inhibitor in the hydroxyethyl methacrylate product taken to the top of the column is very small, which does not adversely affect the color number and downstream application. The free radical polymerization inhibitor is selected from one or more of the following structures:

Description

Technical Field

[0001] This invention relates to the field of chemical synthesis, specifically to a free radical polymerization inhibitor, its preparation method and uses, and a composition containing hydroxyethyl methacrylate. Background Technology

[0002] Hydroxyethyl methacrylate, abbreviated 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 of hydroxyethyl methacrylate is in the contact lens industry, which has higher purity requirements, above 99.6%. There are strict requirements for the impurity ethylene glycol dimethacrylate, with a content of less than 0.1 wt%. It is necessary to purify the hydroxyethyl methacrylate solution to be separated by optimizing the separation process.

[0003] Currently, there are many methods for preparing hydroxyethyl methacrylate, and most reports focus on reaction synthesis, with little research on separation processes. No reports have been found on the separation process of high-purity hydroxyethyl methacrylate.

[0004] Hydroxyethyl methacrylate has a normal boiling point of 225℃ and is polar. Ethylene glycol dimethacrylate has a normal boiling point of 243℃, which is not much different from that of hydroxyethyl methacrylate. Moreover, it is a non-polar compound and can easily be 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 operation is carried out at high temperatures. Therefore, a polymerization inhibitor is needed to prevent polymerization within the separation tower. 2,2,6,6-Tetramethyl-4-hydroxypiperidine nitroxide radical (referred to as 701) has a good polymerization inhibitory effect, but its low boiling point of 270℃ makes it easily evaporated into the hydroxyethyl methacrylate product during separation, affecting the product's color and downstream applications. Therefore, a high-boiling-point radical polymerization inhibitor needs to be developed.

[0007] The inventors of this invention have developed a silicon-modified negative nitrogen oxide free radical polymerization inhibitor with a boiling point above 350°C through long-term research. This inhibitor is applied to the separation process of hydroxyethyl methacrylate to minimize the content of the polymerization inhibitor in hydroxyethyl methacrylate, thereby preparing high-quality hydroxyethyl methacrylate products that can be used in the field of contact lenses. Summary of the Invention

[0008] The purpose of this invention is to provide a silicon-modified free radical polymerization inhibitor, its preparation method and uses, and a composition containing hydroxyethyl methacrylate. This invention modifies a 2,2,6,6-tetramethyl-4-hydroxypiperidine nitroxide free radical polymerization inhibitor with 1,3,5-trichloro-1,3,5-trimethyl-1,3,5-trisilycyclohexane, raising the boiling point of the inhibitor above 350°C. When applied to the separation process of high-purity hydroxyethyl methacrylate, the obtained hydroxyethyl methacrylate has a purity >99.9%, making it suitable for high-end applications in contact lenses.

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

[0010]

[0011] Preferably, the free radical polymerization inhibitor has a boiling point of 350°C or higher.

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

[701] 3 can be 0 wt%, 10 wt% or more, 20 wt% or more, 30 wt% or more, 40 wt% or more, 50 wt% or more, 60 wt% or more, or 70 wt% or more.

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

[0014] (1) 2,2,6,6-Tetramethyl-4-hydroxypiperidine nitric oxide radical reacts with metallic sodium in an organic solvent to generate a mixture containing sodium salt of 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineoxy.

[0015] (2) The mixture containing sodium 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineoxy obtained in step (1) is reacted with 1,3,5-trichloro-1,3,5-trimethyl-1,3,5-trisilylonhexane under quaternary ammonium salt catalyst conditions to generate a reaction solution containing a polymerization inhibitor.

[0016] Preferably, in step (1), the molar ratio of 2,2,6,6-tetramethyl-4-hydroxypiperidine nitroxide radical to sodium metal 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 to 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-hydroxypiperidine nitroxide radical to 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-trisilycyclohexane to 2,2,6,6-tetramethyl-4-hydroxypiperidine nitroxide radical is 1:(3.0 to 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 to 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 polymerization inhibitor according to the present invention further includes the following steps:

[0029] (3) The reaction solution containing the free radical polymerization inhibitor obtained in step (2) is filtered, washed with water and distilled to obtain the free radical polymerization 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 to 0.3 MPaG.

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

[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 invention, there is provided the use of the free radical polymerization inhibitor according to the invention in the refining of hydroxyethyl methacrylate.

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

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

[0037] b) The crude hydroxyethyl methacrylate mixture is fed into an extractive distillation column at a plate near the bottom, a hydroxyethyl methacrylate solution containing the free radical polymerization inhibitor is fed into a plate near the top, and an extractant is fed into a plate below the plate containing the hydroxyethyl methacrylate solution containing the free radical polymerization inhibitor. Extractive distillation is carried out in the extractive distillation column, and the overhead liquid obtained from the top of the column is hydroxyethyl methacrylate with a purity of 99.90 wt% or higher.

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

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

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

[0041] In one specific implementation, the theoretical number of plates in the extractive distillation column is 10 to 15.

[0042] In one specific implementation, the extractive distillation adopts a continuous feeding method, with the crude hydroxyethyl methacrylate mixture fed at the 7th to 12th theoretical plates.

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

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

[0045] In one specific implementation, the extractant feed location is at 2 to 3 theoretical plates.

[0046] In one specific implementation, the hydroxyethyl methacrylate solution of the free radical polymerization inhibitor is fed at the location of 1 to 2 theoretical plates.

[0047] In one specific implementation, the pressure at the top of the extractive distillation column is 100–300 PaA, and the temperature at the top of the column is 60–75°C.

[0048] The obtained hydroxyethyl methacrylate has a purity of over 99.9 wt%, ethylene glycol dimethacrylate content is less than 0.03 wt%, diethylene glycol methacrylate content is less than 0.01 wt%, silicon-modified free radical polymerization inhibitor content is less than 10 ppm, extractant content is less than 20 ppm, and 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 hydroxyethyl methacrylate has a purity of 99.9 wt% or more, the content of free radical polymerization 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, the extractant content in the hydroxyethyl methacrylate composition is less than 20 ppm.

[0053] The beneficial effects of this invention are as follows:

[0054] 1. This invention prepares a silicon-modified free radical polymerization inhibitor with a significantly increased boiling point, exceeding 350℃. When the silicon-modified free radical polymerization inhibitor is applied to the extractive distillation separation process of hydroxyethyl methacrylate, the content of hydroxyethyl methacrylate product carried to the top of the column is extremely low, and it will not have an adverse effect on its color number and downstream applications.

[0055] 2. This invention develops a high-purity hydroxyethyl methacrylate separation method, which adopts an extractive distillation process and uses a high-boiling-point extractant with a boiling point higher than 310℃, which is significantly higher than the boiling point of hydroxyethyl methacrylate (225℃). During the separation process, the content of hydroxyethyl methacrylate product carried to the top of the column as an extractant is extremely small and will not affect downstream applications.

[0056] 3. The silicon-modified free radical polymerization inhibitor prepared in this invention is applied to the extractive distillation separation process of hydroxyethyl methacrylate to obtain a high-purity hydroxyethyl methacrylate product with a purity greater than 99.9%, which meets the requirements of the contact lens application field. The entire separation process is a continuous operation with no wastewater or waste alkali generated, which is environmentally friendly and can be used for the large-scale continuous production of high-purity hydroxyethyl methacrylate. Detailed Implementation

[0057] The present invention will be further illustrated below by way of embodiments, but the present invention is not limited to the embodiments described below. The present invention extends to any new feature or any new combination disclosed in the specification, as well as any new method or process step or any new combination disclosed.

[0058] I. Sources of main raw materials in the embodiments:

[0059] The separation solution of hydroxyethyl methacrylate, Wanhua Chemical Group Co., Ltd., industrial grade;

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

[0061] Sodium metal, Beijing Innocare Technology Co., Ltd., analytical grade;

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

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

[0064] Cyclohexane, Beijing Innocare 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 octanedioate, Shaanxi Didu New Materials Co., Ltd., analytical grade;

[0070] II. Product Analysis Methods in the Examples:

[0071] Gas chromatography is used to analyze the components and content of reaction solutions 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-hydroxypiperidine nitric oxide radicals. Instrument manufacturer and model: Agilent 1290 Infinity II.

[0073] The boiling point of the polymerization inhibitor was determined using a thermogravimetric analyzer (TGA). Instrument manufacturer and model: METTLER (Switzerland) TGA / DSC1.

[0074] Determining the structure of high-temperature polymerization inhibitors using nuclear magnetic resonance (NMR), instrument manufacturer and model:

[0075] Bruker Avance III 400M.

[0076] Example 1 (Preparation of polymerization inhibitor)

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

[0078] (1) 172 g (1 mol) of 2,2,6,6-tetramethyl-4-hydroxypiperidine nitroxide radical was added to a 2 L jacketed vessel, and then 860 g (10 mol) of hexane was added to the jacketed vessel. The mixture of 2,2,6,6-tetramethyl-4-hydroxypiperidine nitroxide radical and hexane was stirred and dissolved. At the same time, the temperature of the mixture was cooled to 10 °C by the jacket coolant. 23 g (1 mol) of metallic sodium was slowly added at 0.09 MPaA. After the addition was completed, the reaction was continued for 3 h to obtain a mixture containing sodium salt of 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineoxy.

[0079] (2) Add 92.5 g (0.33 mol) of 1,3,5-trichloro-1,3,5-trimethyl-1,3,5-trisilylonhexane to the mixture containing sodium 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinoxy sodium salt obtained in step (1), then add 2.249 g of tetramethylammonium chloride, heat to 80 °C with stirring, and then continue to react for 2 h under a pressure of 0.2 MPaG to obtain a reaction solution containing a free radical polymerization inhibitor;

[0080] (3) The temperature of the reaction solution obtained in step (2) is reduced to 20°C, and then filtered at 0.1 MPaG. The byproduct sodium chloride generated therein is filtered to obtain a clear organic phase. Then the organic phase is washed with water 3 times, and the amount of water used each time is equal to the mass of the oil phase to be washed. After the oil phase is washed with water, the solvent in it is removed by distillation, and a solid sample of silicon-modified nitrogen oxide free radical polymerization inhibitor is obtained in the tower bottom. It is a mixture of R-Si-

[701] , R-Si-

[701] 2 and R-Si-

[701] 3 with a boiling point of 389°C.

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

[701] is as follows: 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] The proton spectrum of R-Si-

[701] 2: 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] The proton spectrum of R-Si-

[701] 3: 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 polymerization inhibitor is shown in Table 1.

[0085] Example 2 (Preparation of polymerization inhibitor)

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

[0087] (1) 172g (1mol) of 2,2,6,6-tetramethyl-4-hydroxypiperidine nitroxide radical was added to a 2L jacketed vessel, and then 860g (10mol) of cyclohexane was added to the jacketed vessel. The mixture of 2,2,6,6-tetramethyl-4-hydroxypiperidine nitroxide radical and cyclohexane was stirred and dissolved. At the same time, the temperature of the mixture was cooled to 25°C by the jacket coolant. 23g (1mol) of metallic sodium was slowly added at 0.09MPaA. After the addition was completed, the reaction was continued for 4h to obtain a mixture containing sodium salt of 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineoxy.

[0088] (2) Add 92.5 g (0.33 mol) of 1,3,5-trichloro-1,3,5-trimethyl-1,3,5-trisilylonhexane to the mixture containing 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinoxy sodium salt obtained in step (1), then add 2.249 g (0.021 mol) of tetramethylammonium chloride, heat to 90 °C with stirring, and then continue to react for 3 h to obtain a reaction solution containing a polymerization inhibitor;

[0089] (3) The temperature of the reaction solution obtained in step (2) is reduced to 20°C, and then filtered at 0.1 MPaG. The generated byproduct sodium chloride is filtered to obtain a clear organic phase. This organic phase is then washed with water three times, with the amount of water used each time being equal to the mass of the oil phase to be washed. After the oil phase is washed, the solvent is removed by distillation, and a silicon-modified free radical polymerization inhibitor sample is obtained in the bottom of the tower. It is a mixture of R-Si-

[701] , R-Si-

[701] 2 and R-Si-

[701] 3 with a boiling point of 401°C.

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

[0091] Example 3 (Preparation of polymerization inhibitor)

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

[0093] (1) 172 g (1 mol) of 2,2,6,6-tetramethyl-4-hydroxypiperidine nitroxide radical was added to a 2 L jacketed vessel, and then 860 g (10 mol) of n-heptane solvent was added to the jacketed vessel. The mixture of 2,2,6,6-tetramethyl-4-hydroxypiperidine nitroxide radical and n-heptane was stirred and dissolved. At the same time, the temperature of the mixture was cooled to 10 °C by the jacket coolant. 23 g (1 mol) of metallic sodium was slowly added at 0.09 MPaA. After the addition was completed, the reaction was continued for 3 h to obtain a mixture containing sodium salt of 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineoxy.

[0094] (2) Add 92.5 g (0.33 mol) of 1,3,5-trichloro-1,3,5-trimethyl-1,3,5-trisilylonhexane to the mixture containing 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinoxy sodium salt obtained in step (1), then add 2.249 g (0.021 mol) of tetramethylammonium chloride, heat to 85 °C with stirring, and then continue to react for 2 h to obtain a reaction solution containing the polymerization inhibitor;

[0095] (3) The temperature of the reaction solution obtained in step (2) is reduced to 20°C, and then filtered at 0.1 MPaG. The by-product sodium chloride generated therein is filtered to obtain a clear organic phase. Then the organic phase is washed with water 3 times, and the amount of water used each time is equal to the mass of the oil phase to be washed. After the oil phase is washed with water, the solvent in it is removed by distillation, and the silicon-modified free radical polymerization inhibitor sample is obtained in the tower bottom. It is a mixture of R-Si-

[701] , R-Si-

[701] 2 and R-Si-

[701] 3 with a boiling point of 413°C.

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

[0097] Table 1. Composition results of the polymerization 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% 78.80 wt% Example 3 3.20wt% 20.40wt% 76.40 wt%

[0099] Example 4 (HEMA separation)

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

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

[0102] 2) A solution of silicon-modified free radical polymerization inhibitor (prepared in Example 1) was prepared using HEMA products, with the content of silicon-modified nitroxide free radical polymerization inhibitor being 1 wt%.

[0103] 3) Hydroxyethyl methacrylate was purified using an extractive distillation column with 10 theoretical plates. The silicon-modified free radical polymerization inhibitor solution obtained in step 2) was fed onto plate 1 at a flow rate of 4 g / h. The extractant dioctyl sebacate was fed onto plate 3 at a flow rate of 200 g / h. The crude hydroxyethyl methacrylate mixture was fed onto plate 7 at a flow rate of 200 g / h. The column top pressure was 100 PaA, and the column top temperature was 60°C. The purity of the hydroxyethyl methacrylate in the resulting overhead liquid was 99.97 wt%, ethylene glycol dimethacrylate was 0.02 wt%, diethylene glycol methacrylate was 89 ppm, dioctyl sebacate was 11 ppm, silicon-modified free radical polymerization inhibitor was 5 ppm, and the color number was 5 (Pt-Co).

[0104] Example 5 (HEMA separation)

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

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

[0107] 2) A solution of silicon-modified free radical polymerization inhibitor (prepared in Example 2) was prepared using HEMA products, with the content of silicon-modified nitroxide free radical polymerization inhibitor being 1 wt%.

[0108] 3) High-purity hydroxyethyl methacrylate was refined using an extractive distillation column. The extractive distillation column had 10 theoretical plates. The silicon-modified free radical polymerization inhibitor solution was fed onto plate 1 at a flow rate of 4 g / h. The extractant, dibutyl sebacate, was fed onto plate 3 at a flow rate of 400 g / h. The crude hydroxyethyl methacrylate mixture was fed onto plate 7 at a flow rate of 200 g / h. The column top pressure was 300 PaA, and the column top temperature was 75℃. The resulting overhead liquid contained 99.97 wt% hydroxyethyl methacrylate, 0.02 wt% ethylene glycol dimethacrylate, 73 ppm diethylene glycol methacrylate, 13 ppm dibutyl sebacate, 6 ppm silicon-modified free radical polymerization inhibitor, and a color number of 6 (Pt-Co).

[0109] Example 6 (HEMA separation)

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

[0111] 1) Add 10g of the silicon-modified nitroxide radical inhibitor sample prepared in Example 3 to 10000g of crude hydroxyethyl methacrylate, and stir to dissolve the crude hydroxyethyl methacrylate mixture. The crude hydroxyethyl methacrylate raw material contains: 49wt% hydroxyethyl methacrylate, 49wt% diethylene glycol methacrylate, and 2wt% ethylene glycol dimethacrylate.

[0112] 2) A solution of silicon-modified free radical polymerization inhibitor (prepared in Example 3) was prepared using HEMA products, with the content of silicon-modified nitroxide free radical polymerization inhibitor being 1 wt%.

[0113] 3) Hydroxyethyl methacrylate was purified using an extractive distillation column. The extractive distillation column had 15 theoretical plates. The silicon-modified free radical polymerization inhibitor solution was fed onto the 2nd plate at a flow rate of 6 g / h. The extractant, dibutyl sebacate, was fed onto the 4th plate at a flow rate of 400 g / h. The crude hydroxyethyl methacrylate mixture was fed onto the 12th plate at a flow rate of 200 g / h. The top pressure was 100 PaA, and the top temperature was 60℃. The resulting overhead liquid contained 99.98 wt% hydroxyethyl methacrylate, 0.01 wt% ethylene glycol dimethacrylate, 55 ppm diethylene glycol methacrylate, 10 ppm dibutyl sebacate, 5 ppm silicon-modified free radical polymerization inhibitor, and a color number of 5 (Pt-Co).

[0114] Comparative Example 1

[0115] Unlike Example 6, 2,2,6,6-tetramethyl-4-hydroxypiperidine nitroxide radical (701) was used instead of the silicon-modified free radical polymerization inhibitor in the purification of hydroxyethyl methacrylate, as follows:

[0116] 1) Add 10g of 2,2,6,6-tetramethyl-4-hydroxypiperidine nitroxide radical (701) sample to 10000g of crude hydroxyethyl methacrylate, stir and dissolve to obtain a mixture of crude hydroxyethyl methacrylate, wherein the raw material crude hydroxyethyl methacrylate contains: 48wt% hydroxyethyl methacrylate, 49wt% diethylene glycol methacrylate and 3wt% ethylene glycol dimethacrylate;

[0117] 2) Prepare a solution of 2,2,6,6-tetramethyl-4-hydroxypiperidine nitroxide radical (701) using HEMA products, with a 701 content of 1 wt%.

[0118] 3) High-purity hydroxyethyl methacrylate was refined using an extractive distillation column. The extractive distillation column had 15 theoretical plates. The 2,2,6,6-tetramethyl-4-hydroxypiperidine nitric oxide radical (701) solution was fed onto the 2nd plate at a flow rate of 6 g / h. The extractant, dibutyl sebacate, was fed onto the 4th plate at a flow rate of 400 g / h. The crude hydroxyethyl methacrylate mixture was fed onto the 12th plate at a flow rate of 200 g / h. The top pressure of the column was... At 100 PaA and a top temperature of 60℃, the purity of hydroxyethyl methacrylate in the resulting overhead liquid was 99.98 wt%, ethylene glycol dimethacrylate was 0.01 wt%, diethylene glycol methacrylate was 55 ppm, dibutyl sebacate was 10 ppm, and 2,2,6,6-tetramethyl-4-hydroxypiperidine nitroxide radical (701) was 48 ppm. The color number was 29 (Pt-Co), which does not meet the high-purity HEMA requirements for contact lenses.

Claims

1. A free radical polymerization inhibitor, which is selected from one or more of the following structures:

2. The free radical polymerization inhibitor according to claim 1, wherein, The free radical polymerization inhibitor has a boiling point of 350°C or higher.

3. A method for preparing the free radical polymerization inhibitor according to claim 1 or 2, comprising the following steps: (1) 2,2,6,6-Tetramethyl-4-hydroxypiperidine nitric oxide radical reacts with metallic sodium in an organic solvent to generate a mixture containing sodium salt of 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineoxy. (2) The mixture containing sodium 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineoxy obtained in step (1) is reacted with 1,3,5-trichloro-1,3,5-trimethyl-1,3,5-trisilylonhexane under quaternary ammonium salt catalyst conditions to generate a reaction solution containing a polymerization inhibitor.

4. The method for preparing a free radical polymerization inhibitor according to claim 3, wherein, In step (1), the molar ratio of 2,2,6,6-tetramethyl-4-hydroxypiperidine nitroxide radical to metallic sodium is 1:(1.00–1.05); and / or In step (1), the reaction temperature is 0–25 °C; and / or In step (1), the reaction pressure is 0.09–0.1 MPaA; and / or In step (1), the reaction time is 3–4 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-hydroxypiperidine nitric oxide radical to organic solvent is 1:(10-15).

5. The method for preparing a free radical polymerization inhibitor according to claim 3 or 4, wherein, In step (2), the molar ratio of 1,3,5-trichloro-1,3,5-trimethyl-1,3,5-trisilycyclohexane to 2,2,6,6-tetramethyl-4-hydroxypiperidine 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 2–3 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.

6. The method for preparing a free radical polymerization inhibitor according to claim 3 or 4, further comprising the following steps: (3) The reaction solution containing the free radical polymerization inhibitor obtained in step (2) is filtered, washed with water and distilled to obtain the free radical polymerization inhibitor in solid form.

7. The method for preparing a free radical polymerization inhibitor according to claim 6, wherein, In step (3), the filtration temperature is 20–30°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 20–30°C, and the number of water washing cycles is 3–5; and / or In step (3), the distillation temperature is 50-60℃ and the distillation pressure is 50-60 kPaA.

8. A method for purifying hydroxyethyl methacrylate, comprising the following steps: a) Add the free radical polymerization inhibitor according to claim 1 to crude hydroxyethyl methacrylate to obtain a mixture of crude hydroxyethyl methacrylate, and a hydroxyethyl methacrylate solution for preparing the free radical polymerization inhibitor using the free radical polymerization inhibitor according to claim 1 and hydroxyethyl methacrylate. b) The crude hydroxyethyl methacrylate mixture is fed into an extractive distillation column at a plate near the bottom, a hydroxyethyl methacrylate solution containing the free radical polymerization inhibitor is fed into a plate near the top, and an extractant is fed into a plate below the plate containing the hydroxyethyl methacrylate solution containing the free radical polymerization inhibitor. Extractive distillation is carried out in the extractive distillation column, and the overhead liquid obtained from the top of the column is hydroxyethyl methacrylate with a purity of 99.90 wt% or higher.

9. The method for refining hydroxyethyl methacrylate according to claim 8, wherein, The crude hydroxyethyl methacrylate comprises: 40 wt% to 50 wt% hydroxyethyl methacrylate based on the total weight of the crude hydroxyethyl methacrylate; 40 wt% to 50 wt% diethylene glycol methacrylate and 2 wt% to 3 wt% ethylene glycol dimethacrylate; and / or The crude hydroxyethyl methacrylate containing a free radical polymerization inhibitor contains 0.1 wt% to 0.2 wt% of the free radical polymerization inhibitor; and / or The concentration of the hydroxyethyl methacrylate solution of the free radical polymerization inhibitor is 0.5 wt% to 2 wt%; and / or The theoretical plate number of the distillation column for extractive distillation is 10–15; and / or Extractive distillation employs a continuous feed method, with the crude hydroxyethyl methacrylate mixture fed into the 7th to 12th theoretical plates; and / or The extractant is at least one selected from dioctyl sebacate, dibutyl sebacate, dioctyl azelate, and dibutyl octanoate; and / or The mass ratio of the extractant to crude hydroxyethyl methacrylate is (1–2):1; and / or The extractant feed point is at 2-3 theoretical plates; and / or The hydroxyethyl methacrylate solution of the free radical polymerization inhibitor is fed into the reactor at the location of 1-2 theoretical plates; and / or The pressure at the top of the extractive distillation column is 100–300 PaA, and the temperature at the top is 60–75℃.

10. A hydroxyethyl methacrylate composition, wherein, The hydroxyethyl methacrylate has a purity of 99.9 wt% or higher, and the hydroxyethyl methacrylate composition contains less than 10 ppm of the free radical polymerization inhibitor according to claim 1.

11. The hydroxyethyl methacrylate composition according to claim 10, wherein, The color number of the hydroxyethyl methacrylate composition is less than 10; 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%.

Images