A method for producing optical grade polymethyl methacrylate

Abstract

The present invention belongs to the technical field of polar olefin polymerization, and specifically relates to a method for producing optical-grade polymethyl methacrylate. The present invention utilizes a rare earth metal compound containing a large sterically hindered ligand as a catalyst to efficiently and highly selectively obtain polymethyl methacrylate at room temperature. The polymerization solvent is selected from toluene and chlorobenzene; the molar ratio of the monomer to the catalyst is between 100 and 10,000. In the obtained polymethyl methacrylate, the product stereoselectivity and syndiotactic selectivity content are between 40% and 90%, the product molecular weight is between 60,000 and 120,000, and the molecular weight distribution is between 1.4 and 1.7. After purification of the obtained polymethyl methacrylate, the transmittance can reach 93%, and in some wavelength ranges, the transmittance can reach 94%.

Description

Technical Field

[0001] The invention belongs to the technical field of polar olefin polymerization, and particularly relates to a method for preparing optical-grade polymethyl methacrylate. Background Art

[0002] In recent years, the integration of polymer science and organometallic chemistry has achieved remarkable success. Some progress has also been made in the polymerization of polar monomers (such as methyl methacrylate) using electron-deficient, highly active metallocenes and related single-site metal catalysts. Fifty years ago, conventional Ziegler-Natta type catalysts including TiCl4 / AlR3 and Cp2TiCl2 / AlEt3 had been used for the specific polymerization of methyl methacrylate (MMA), although the active species, polymerization mechanism and degree of polymerization control were not clear. In 1972, Ballard and Van Lienden reported the polymerization of MMA in toluene by coordinating anions using metal tetrabenzyl complexes such as Zr(CH2Ph)4. In 1988, Farnham and Hertler reported in a US patent the polymerization of discrete chloro-metallocene enol esters, Cp2MCl[OC(OMe)=CMe2] (Cp is η 5 [The text then abruptly shifts topics.] [The text then abruptly shifts topics.] [The text then abruptly shifts topics.] [The text then abruptly shifts topics.] [The text then abruptly shifts topics.] [The text then abruptly shifts topics.] [The text then abruptly shifts topics.] [The text then abruptly shifts topics.] [The text then abruptly shifts topics.] [The text then abruptly shifts topics.] [The text then abruptly shifts topics.] [The text then abruptly shifts topics.] [The text then abruptly shifts topics.] [The text then abruptly shifts topics.] [The text then abruptly shifts topics.] [The text then abruptly shifts topics.] [The text then abruptly shifts topics.] [The text then abruptly shifts topics.] [The text then abruptly shifts topics.] [The text then abruptly shifts topics.] [The text then abruptly shifts topics.] [The text then abruptly shifts topics.]

[0003] Optical-grade PMMA, a polymer with extremely high molecular regularity and purity, differs from standard-grade PMMA in its higher light transmittance. Standard optical-grade PMMA has a transmittance of 92%, while the highest-grade optical-grade PMMA currently boasts a transmittance of 96%. Optical-grade PMMA also exhibits improved electrical insulation, chemical and solvent resistance, and heat and cold resistance. After post-processing, it can be used in high-end devices such as liquid crystal light guide film, LED lamps, optical fiber materials, and optical products. With the rapid development of markets such as LCDs, LED displays, and automobiles, demand for high-grade optical-grade PMMA is also rapidly increasing. The current state of research on optical-grade PMMA reveals that the core challenge lies in the development of efficient and highly selective catalytic systems. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for producing optical-grade polymethyl methacrylate (PMMA) with high efficiency and high selectivity.

[0005] The present invention first provides a catalyst for producing optical-grade polymethyl methacrylate. The catalyst is a single-component rare earth complex (containing a rare earth metal compound with a large steric ligand), and its structure is shown in Formula 1 below:

[0006]

[0007] Wherein, the ligand R group can be a hydrocarbon group ((CH2) n(n＝2～6) ), dibenzylamino ((C6H5CH2)2N), aryl (such as phenyl, substituted phenyl, etc.), rare earth metal (Ln) is scandium (Sc), yttrium (Y) and all lanthanide elements (such as lanthanum (La), neodymium (Nd), samarium (Sm), lutetium (Lu), etc.).

[0008] Preferably, the rare earth metal is Lu or Sc; and the ligand substituent is R=(C6H5CH2)2N or R=p-OMe-Ph.

[0009] The present invention provides a method for producing optical-grade polymethyl methacrylate, using the above-mentioned single-component rare earth complex as a catalyst, and the specific steps of production are as follows:

[0010] (1) Drying monomers and solvents:

[0011] Methyl methacrylate was mixed with CaH2 at room temperature, stirred for 16-24 hours, evaporated under reduced pressure, and degassed three times to remove oxygen; then stored at low temperature (-35°C) under anhydrous and oxygen-free conditions; after the solvent was purified, it was soaked in sodium tablets and placed in a glove box for later use;

[0012] (2) Solution polymerization of methyl methacrylate:

[0013] At room temperature, in an anhydrous and oxygen-free environment (in a glove box), take 0.01-10 mmol of the catalyst, place it in an eggplant-shaped flask, add 1-1000 mL of solvent to dissolve it, then weigh 0.2-1000 g of methyl methacrylate and add it to the flask; react for 1-12 hours; then inject 1-20 mL of ethanol containing a small amount of concentrated hydrochloric acid into the system to quench the reaction; after 5-20 minutes, slowly add 5-5000 mL of ethanol until the solid is completely precipitated; the resulting solid is placed in a vacuum drying oven and dried at 40-70°C to constant weight;

[0014] (3) Purification of polymethyl methacrylate:

[0015] After constant weight, 2-20 g of polymethyl methacrylate is dissolved in 5-50 mL of THF, and then 20-200 mL of ethanol is added to precipitate it. This process is repeated several times, and the mixture is dried in a vacuum drying oven to constant weight.

[0016] The polymerization solvent is selected from toluene and chlorobenzene.

[0017] Polymethyl methacrylate transmittance test:

[0018] Weigh 2-10g of purified polymethyl methacrylate, add 5-50ml of THF, and stir to dissolve. Place in an ultrasonic cleaner and sonicate for 10-30 minutes to remove any bubbles. Then, pour the solution into a grooved glass container and place in a fume hood for 2-4 days to air dry. Cut the appropriate shape and place it in a cuvette. Before the transmittance test, place two sets of blank cuvettes for a blank test. Then, place the PMMA sample film in the cuvette for the transmittance test.

[0019] The molecular weight of the polymers was determined by gel permeation chromatography (GPC, Waters 410 1515_2707_2414 system). The meso-, isotactic-, and atactic-stereoselectivities of the polymers were calculated from nuclear magnetic resonance spectroscopy.

[0020] Results showed that the product's stereoselectivity and syndiotactic selectivity ranged from 40% to 90%, with a molecular weight between 60,000 and 120,000, and a molecular weight distribution between 1.4 and 1.7. After purification, the resulting polymethyl methacrylate achieved a transmittance of 93%, with a transmittance of 94% at certain wavelengths.

[0021] Furthermore, the present invention screens out a catalyst with high polymethyl methacrylate yield and optimal light transmittance from catalysts of various structures of single-component rare earth complexes by controlling the reaction time and the molar ratio of monomer to catalyst.

[0022] The results show that when the rare earth metal is Lu or Sc and the ligand substituent is R = (C6H5CH2)2N or R = p-OMe-Ph, the prepared polymethyl methacrylate has the highest yield and the best transmittance, as shown in Table 1 below:

[0023] Table 1, yield, stereostructure information and activity results of polymethyl methacrylate obtained using different catalysts:

[0024]

[0025] in:

[0026] 1-Sc catalyst, the R group on the ligand is phenyl and the central metal is Sc;

[0027] 2-Sc catalyst, the R group on the ligand is p-methoxyphenyl, and the central metal is Sc;

[0028] 3-Lu catalyst, the R group on the ligand is dibenzylamino and the central metal is Lu;

[0029] 3-Sc catalyst, the R group on the ligand is dibenzylamino, and the central metal is Sc.

[0030] As can be seen from Table 1, the catalysts with the highest catalytic activity and better polymethyl methacrylate stereomicrostructure are 1-Sc, 2-Sc, 3-Lu, and 3-Sc.

[0031] This invention utilizes rare earth metal compounds containing sterically hindered ligands as catalysts for the efficient and highly selective production of optical-grade PMMA. Using only a single catalyst precursor, without the need for additional co-catalysts, the process efficiently and selectively produces polymethyl methacrylate at room temperature. After purification, optical-grade PMMA can be obtained. In the laboratory, 100 grams of optical-grade PMMA can be produced, demonstrating promising application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the GPC spectrum of the product described in Example 1.

[0033] Figure 2 The UV-visible spectra of the products obtained after different times of purification of the product described in Example 1 are shown.

[0034] Figure 3 This is the GPC spectrum of the product described in Example 2.

[0035] Figure 4 This is the GPC spectrum of the product described in Example 3. DETAILED DESCRIPTION

[0036] The present invention is further described below through specific examples.

[0037] Example 1: Weigh 0.0078g (0.01mmol) of complex 2-Sc into a 25mL reaction tube, dissolve it in 2mL of toluene, and then weigh 0.200g (2.0mmol) of methyl methacrylate and add it. Stir and react for 12 hours. After the reaction is complete, slowly add ethanol dropwise with stirring until the solid is completely precipitated. Pour off the liquid and the resulting polymethyl methacrylate is a white solid. Dry in a vacuum drying oven at 60°C to constant weight to obtain a net yield of approximately 200mg of the blend with a conversion rate of approximately 100%. After dissolving the blend using gel chromatography and testing, a single peak is obtained with a molecular weight of 85,000 and a molecular weight distribution of 1.74. Analysis by hydrogen nuclear magnetic resonance spectroscopy shows that the content of syndiotactic components is 81.0%. After purification six times, the sample has a transmittance of more than 93%, and some bands reach 94%.

[0038] Example 2, weigh 0.0084g (0.01mmol) of complex 3-Lu in a 25mL reaction tube, dissolve it with 2mL of toluene, then weigh 0.200g (2.0mmol) of methyl methacrylate and add it thereto, and start stirring. React for 12 hours. After the reaction is complete, slowly add ethanol dropwise with stirring until the solid is completely precipitated. Pour off the liquid, and the obtained polymethyl methacrylate is a white solid. Dry to constant weight in a vacuum drying oven at 60°C, and the net yield of the blend is about 200mg, and the conversion rate is about 100%. After dissolving the blend using gel chromatography, a single peak can be obtained, and its molecular weight is: 103,000, and the molecular weight distribution is: 1.42. Using nuclear magnetic resonance hydrogen spectrum analysis, the content of the syndiotactic component is 80.0%.

[0039] Example 3: Weigh 0.0160g (0.02mmol) of complex 3-Sc into a 25mL schelank bottle, dissolve it with 6mL of toluene, and place it in -78 degree ice ethanol. After 15 minutes, add 2.000g (20.0mmol) of methyl methacrylate and start stirring. React for 12 hours. After the reaction is completed, slowly add ethanol dropwise with stirring until the solid is completely precipitated. Pour off the liquid and the obtained polymethyl methacrylate is a white solid. Dry to constant weight in a vacuum drying oven at 60°C to obtain a net yield of about 2g of the blend and a conversion rate of about 100%. After dissolving the blend using gel chromatography, a single peak is obtained with a molecular weight of 644,000 and a molecular weight distribution of 1.27. Analysis by hydrogen nuclear magnetic resonance spectroscopy shows that the content of the syndiotactic component is 71.0%.

Claims

1. A method for producing optical grade polymethyl methacrylate, characterized in that: A single-component rare earth complex is used as a catalyst. The structure of the single-component rare earth complex is shown in the following formula 1: ； Wherein, in the single-component rare earth complex, the rare earth metal Ln is Lu or Sc; the ligand substituent is R=(C6H5CH2)2N or R= p -OMe-Ph; The specific steps of manufacturing are as follows: (1) Drying monomers and solvents: Mix methyl methacrylate with CaH2 at room temperature, stir for 16-24 hours, evaporate under reduced pressure, and degas three times to remove oxygen; then store at low temperature under anhydrous and oxygen-free conditions; after the solvent is purified, soak it in sodium tablets and store in a glove box for later use; (2) Solution polymerization of methyl methacrylate: At room temperature, in an anhydrous and oxygen-free environment, take 0.01-10 mmol of the catalyst, place it in an eggplant-shaped flask, add 1-1000 mL of solvent to dissolve it, then weigh 0.2-1000 g of methyl methacrylate and add it to the flask; react for 1-12 hours; then inject 1-20 mL of ethanol containing a small amount of concentrated hydrochloric acid into the system to quench the reaction; after 5-20 minutes, slowly add 5-5000 mL of ethanol until the solid is completely precipitated; the resulting solid is placed in a vacuum drying oven and dried at 40-70°C to constant weight; (3) Purification of polymethyl methacrylate: After constant weight, 2-20 g of polymethyl methacrylate is dissolved in 5-50 mL of THF, and then 20-200 mL of ethanol is added to precipitate it. This process is repeated several times, and the mixture is dried in a vacuum drying oven to constant weight.

2. The manufacturing method according to claim 1, characterized in that The single-component rare earth complex is one of the following: The R group on the ligand is p-methoxyphenyl and the central metal is Sc; it is denoted as 2-Sc catalyst; The R group on the ligand is dibenzylamino and the central metal is Sc; it is denoted as 3-Sc catalyst; The R group on the ligand is dibenzylamino and the central metal is Lu; it is denoted as 3-Lu catalyst.

3. The manufacturing method according to claim 1, characterized in that The solvent is selected from toluene and chlorobenzene.

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