Alkoxy amine and application thereof in induction of NMP (N-Methyl Pyrrolidone) polymerization

Abstract

The invention discloses alkoxy amine and application of the alkoxy amine in induction of NMP (N-Methyl Pyrrolidone) polymerization of methacrylate monomers and styrene monomers. The alkoxy amine is a novel compound which is synthesized by taking benzaldehyde and isopropylamine as raw materials through three-step reaction of Schiff base reduction, oxidizing agent oxidation and free radical coupling. The obtained alkoxyamine can be used as a monomolecular initiator to effectively regulate and control controllable polymerization of methacrylate and styrene monomers under anaerobic or aerobic conditions, and the peak pattern of a gel chromatography outflow curve is symmetrical and has no obvious tailing phenomenon, so that the alkoxyamine can expand the range of nitroxide free radical polymerization regulation and control monomers, and the preparation method is simple and easy to implement. The method has a good application prospect in the aspect of synthesis of functional polymer materials.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of polymer materials, and particularly relates to an alkoxyamine and its application in the nitroxide-mediated radical polymerization (NMP) of methacrylate and styrene monomers. Background Art

[0002] Reversible-deactivation radical polymerization (RDRP) plays an important role in the preparation of functional polymers with well-defined structures, controllable molecular weights, and narrow molecular weight distributions. Widely used RDRP methods include nitroxide-mediated radical polymerization (NMP), atom transfer radical polymerization (ATRP), and reversible addition-fragmentation chain transfer radical polymerization (RAFT). NMP is the earliest invented RDRP method. Compared with ATRP and RAFT, NMP-mediated polymerization does not introduce metal ions, special odors, and colors, so it has more advantages in industrialization. However, in the early stage, due to the relatively high polymerization temperature and fewer applicable monomers, the development of NMP was limited.

[0003] In recent years, with the in-depth research, the polymerization temperature of NMP has been significantly decreased, and the monomer types have been extended from styrene-based to acrylate-based. However, the NMP-mediated polymerization of methacrylates is still relatively difficult. This is because when NMP regulates the polymerization of methacrylates, disproportionation reactions are likely to occur, resulting in the failure of the regulated polymerization, and its conversion rate is low, and the molecular weight distribution of the prepared polymer ( M w / M n ) is relatively wide. To solve the NMP polymerization problem of methacrylates, Ballard et al. (Ballard N., Aguirre M., Simula A., Agirre A., Leiza J. R., Asua J. M., van Es S., ACS Macro Letters , 2016, 5 (9), 1019-1022) first reported the synthesis of 3-(((2-cyanopropan-2-yl)oxy)-(cyclohexyl)amino)-2,2-dimethyl-3-phenylpropanenitrile (Dispolreg 007) nitroxide-stable radical. By the electron-withdrawing effect of the cyano group, the electron cloud density of the oxygen atom is reduced, realizing the regulated polymerization of methacrylate and styrene monomers. However, the molecular weight distribution of the NMP polymerization of methacrylates based on Dispolreg 007 is relatively wide, and there is an obvious tailing phenomenon. Therefore, the performance of its regulated polymerization needs to be improved; in addition, a large amount of toxic benzyl bromide is required in the synthesis of Dispolreg 007. At the same time, in order to avoid side reactions, the amount of cyclohexylamine used is 3.5 times that of benzyl bromide, and the safety and atom economy of its synthesis process are relatively poor. Summary of the Invention

[0004] The object of the present invention is to provide a novel alkoxyamine to solve the problems of wide molecular weight distribution and poor controllability existing in the regulation of methacrylate polymerization by existing alkoxyamines, expand the range of NMP polymerization regulating monomers, and its synthesis method is simple, the raw materials are low-toxic and easily available, and the atom economy is good.

[0005] To achieve the above object, the present invention adopts the following technical solutions: One object of the present invention is to protect an alkoxyamine, specifically 3-(((2-cyanopropan-2-yl)oxy)(isopropyl)amino)-2,2-dimethyl-3-phenylpropanenitrile, and its chemical structural formula is .

[0006] Another object of the present invention is to protect a preparation method of the alkoxyamine, which includes the following steps: 1) Mix benzaldehyde and isopropylamine evenly in methanol, and reflux in an oil bath at 40-70 °C for 4-24 h. After the reaction is completed, cool to room temperature, then add a reducing agent in batches, stir for 2 h, and monitor the complete reaction of the raw materials by thin-layer chromatography. Then, rotary evaporate to remove the solvent. The obtained crude product is dissolved in ethyl acetate, washed with saturated brine, dried over anhydrous magnesium sulfate, and then rotary evaporated to remove the solvent to obtain a pale yellow viscous liquid product; 2) Dissolve the liquid product prepared in step 1) and sodium bicarbonate in a mixed solvent of acetone and water. Add an oxidizing agent in batches under ice bath conditions, stir for 2-8 h, then filter. The filtrate is washed with saturated brine, and the upper organic phase is collected. After drying over anhydrous magnesium sulfate, rotary evaporate to remove the solvent to obtain a pale yellow viscous liquid, which is separated and purified by a chromatography column to obtain a liquid compound; 3) Mix the liquid compound prepared in step 2) and AIBN evenly in a solvent, then react at 92 °C for 6 h. After the reaction is completed, rotary evaporate to remove the solvent. The obtained crude product is separated and purified by a chromatography column to obtain a pale yellow viscous liquid compound.

[0007] Further, the molar ratio of benzaldehyde, isopropylamine, and sodium borohydride used in step 1) is 1:1:(1.3-2.0).

[0008] Further, the reducing agent in step 1) is one or more of sodium borohydride, sodium cyanoborohydride, lithium aluminum hydride, and sodium borohydride acetate, preferably sodium borohydride.

[0009] Further, the volume ratio of acetone to water in the mixed solvent in step 2) is 1:1.

[0010] Further, the oxidant described in step 2) is one or more of potassium peroxymonosulfate compound (Oxone), hydrogen peroxide, m-chloroperbenzoic acid, and sodium periodate, preferably Oxone.

[0011] Further, the mass ratio of the liquid product, sodium bicarbonate, and the oxidant used in step 2) is 1:2:(3 - 4).

[0012] Further, the mass ratio of the liquid compound and AIBN used in step 3) is 1:(1.3 - 2.0).

[0013] Further, the solvent described in step 3) is toluene.

[0014] Further, when performing column chromatography separation and purification in steps 2) and 3), a mixed solution of petroleum ether / ethyl acetate with a volume ratio of 7:1 is used as the eluent.

[0015] The third object of the present invention is to protect the application of the alkoxyamine in inducing NMP polymerization, which includes NMP polymerization of methacrylic acid monomers or styrene monomers under anaerobic conditions and NMP polymerization of methacrylic acid monomers under aerobic conditions.

[0016] Further, the application method specifically includes the following steps: 1) Using the alkoxyamine as a unimolecular initiator, adding it and MMA to toluene and mixing evenly, and then reacting at 90 °C for 4 - 6 h under anaerobic or non-oxygen-removing conditions to obtain poly(methyl methacrylate) (PMMA); 2) Using the obtained PMMA as a macroinitiator, and using MMA, EMA, or St as monomers, reacting at 90 °C for 4 - 6 h to obtain the corresponding block copolymer.

[0017] Furthermore, the molar ratio of MMA and the alkoxyamine used in step 1) is 50 - 200.

[0018] The process of single-molecule alkoxyamine-regulated reversible deactivation radical polymerization is simple, the prepared polymers have a light color and a small odor, and do not contain metal ion impurities. However, the design and synthesis of alkoxyamines that can regulate the polymerization of methacrylate monomers is a challenging task. In the present invention, benzaldehyde and isopropylamine are used as raw materials to prepare a novel alkoxyamine through three simple reactions. First, a Schiff base is formed by the "one-pot" condensation of benzaldehyde and isopropylamine, and the Schiff base is reduced with a reducing agent to form an amine. Then, the obtained amine is oxidized by an oxidant to form an N-oxide intermediate. Finally, a 1,3-di-tert-butyl radical addition reaction is carried out between the radical generated by the decomposition of AIBN at a relatively high temperature and the obtained N-oxide intermediate to form the alkoxyamine. The synthetic route has low toxicity of raw materials, is cheap and easily available, and has atom economy. Moreover, the isopropyl group connected to the N atom in the obtained alkoxyamine has a large steric hindrance, and the alkoxy group is more likely to break, which can solve the problems of tailing and wide molecular weight distribution existing in the current regulation of MMA polymerization.

[0019] The remarkable advantages of the present invention are as follows: The present invention provides a novel alkoxyamine, which can be used as a single-molecule initiator to regulate the polymerization behavior of methacrylic or styrenic monomers. The molecular weight distribution of its product is narrow, the peak shape is symmetric, and there is no obvious tailing phenomenon, showing the characteristics of controlled radical polymerization. At the same time, the obtained novel alkoxyamine can also realize the NMP polymerization of MMA under low temperature and aerobic conditions. Therefore, the present invention solves the long-standing problem that it is difficult to regulate the polymerization of methacrylate monomers by NMP, enriches the types of alkoxyamines used in NMP polymerization and the range of regulable monomers, and has broad application prospects. Description of the Drawings

[0020] Figure 1 It is a schematic flow chart for preparing the alkoxyamine in Example 1.

[0021] Figure 2 It is the 1H-NMR spectrum of PMMA prepared with CPDMN as the initiator (this figure shows the signals caused by terminal unsaturation).

[0022] Figure 3 It is the molecular weight distribution of MMA (A), St (B), and EMA (C) before and after chain extension by PMMA ([MMA] / [CPDMN]=100) initiated by CPDMN, and the 1H-NMR spectra of the obtained PMMA-b-PMMA (D), PMMA-b-PSt (E), and PMMA-b-PDMA (F).

[0023] Figure 4 It is the optical photos of MMA polymerization under anaerobic (A) and aerobic (B) conditions in Example 5, and the GPC spectrum of the polymerized PMMA (C). Detailed Embodiments

[0024] To make the content of the present invention more understandable, the technical solutions of the present invention will be further described below in conjunction with specific embodiments. However, the present invention is not limited thereto.

[0025] In the examples, the theoretical molecular weight is calculated by the following formula: M n,th = [M] 0 / [I] 0 × M w Monomer ×α + M w Initiator , where α is the monomer conversion rate, [M] 0 and [I] 0 are the initial concentrations of the monomer and CPDMN, respectively.

[0026] Example 1 Preparation of Alkoxyamine 1) Add 5.0 g (47 mmol) of benzaldehyde, 2.78 g (47 mmol) of isopropylamine, and 60 mL of methanol to a 250 mL three-necked flask. Add a magnetic stir bar and reflux in an oil bath at 65 °C for 8 h. After the reaction is completed, cool to room temperature. Add 2.83 g (75 mmol) of sodium borohydride to the solution in batches. Stir for 2 h and monitor the complete reaction of the raw materials by thin layer chromatography. Then remove the solvent with a rotary evaporator. Dissolve the crude product in ethyl acetate, wash with saturated brine, dry with anhydrous magnesium sulfate, and remove the solvent by rotary evaporation to obtain 6.56 g of a pale yellow viscous liquid product (Compound 1), with a yield of 95.0%. 1 H NMR (Chloroform-d) δ: 7.60 - 7.14 (m, 5H), 3.86 - 3.68 (m, 2H), 2.92 - 2.76 (m, 1H), 1.14 - 1.06 (m, 6H); 13 C NMR (Chloroform-d) δ: 140.75, 129.22, 128.38 (d, J = 28.0 Hz), 126.95, 51.71, 48.14, 22.98.

[0027] 2) Dissolve 6.56 g of Compound 1 and 13.12 g of sodium bicarbonate in a mixed solvent of 22 mL of acetone and water (1:1, v / v). Add 24.1 g of potassium peroxymonosulfate compound (Oxone) to the reaction system in portions under ice bath conditions. After stirring for 2 h, filter the mixture. Wash the filtrate with saturated brine, collect the upper organic phase, dry it over anhydrous magnesium sulfate, and then remove the solvent by rotary evaporation to obtain a pale yellow viscous liquid. Then, separate and purify it through a chromatography column ( V 石油醚 : V 乙酸乙酯 = 7:1) to obtain 4.82 g of a pale yellow liquid (Compound 2), with a yield of 67.2%. 1 ¹H NMR (Chloroform-d) δ: 8.27 - 8.17 (m, 2H), 7.42 - 7.30 (m, 4H), 4.17 (hept, J = 6.5 Hz, 1H), 1.46 (d, J = 6.5 Hz, 6H); 13 ¹³C NMR(Chloroform-d) δ: 132.17, 130.79, 130.26, 128.62 (d, J = 11.1 Hz), 67.87, 20.96.

[0028] 3) Add 4.82 g of Compound 2, 7.76 g of azobisisobutyronitrile (AIBN), and 50 mL of toluene to a 100 mL single-necked flask in sequence. React at 92 °C for 6 h, remove the solvent by rotary evaporation to obtain a crude product, and then separate and purify it through a chromatography column ( V 石油醚 : V 乙酸乙酯 = 7:1) to obtain 4.7 g of a pale yellow viscous liquid (Compound 3), named CPDMN, with a yield of 61.1%. 1 ¹H NMR(Chloroform-d) δ: 7.61 - 7.57 (m, 2H), 7.31 - 7.28 (m, 3H), 4.27 - 4.16 (m, 1H), 3.49 - 3.40 (m, 1H), 1.64 - 1.55 (m, 6H), 1.34 - 0.87 (m, 12H); 13 ¹³C NMR (Chloroform-d) δ: 137.29, 128.45, 128.15 (d, J = 8.1 Hz), 125.21, 122.73, 122.45, 75.88, 69.70, 54.89, 52.94, 34.38, 28.75, 25.21, 20.70.

[0029] Example 2 NMP Polymerization of Monomers Initiated by CPDMN Methyl methacrylate (MMA, 5 g, 50 mmol), CPDMN prepared in Example 1 (0.15 g, 0.5 mmol), and toluene (5 g) were added to a Schlenk tube. The tube was evacuated and filled with nitrogen three times in an ice bath to remove oxygen. Then, the reaction was carried out at 90 °C for 4 h. After the reaction, it was cooled with ice water. Then, the polymer solution was precipitated in an ice methanol solution, and then filtered and dried under vacuum to obtain the polymer. The conversion was calculated by the weighing method, and samples were taken for 1 1H NMR testing and GPC testing.

[0030] The GPC test of PMMA showed that Mn = 8500 g·mol -1 , M w / M n = 1.40. As Figure 2 The 1H NMR spectrum showed that there was no characteristic signal peak of vinyl groups generated by disproportionation between δ = 5.2 and 6.8, indicating that in the polymerization system initiated by CPDMN, the hydrogen transfer disproportionation reaction phenomenon that easily occurs in the NMP-regulated MMA polymerization reported in the literature did not occur.

[0031] Example 3 Synthesis of Block Copolymers To further verify the end-group activity of the polymer, MMA, St, and EMA were chain-extended using the PMMA prepared in Example 2 as a macroinitiator. The specific operations are as follows: Synthesis of PMMA- b -PMMA: The obtained macroinitiator PMMA ( M n = 6300 g·mol -1 , M w / M n = 1.25, 0.8 g) was dissolved in toluene (1.44 g), 0.64 g MMA and a magnetic stir bar were added. The solution was evacuated and filled with nitrogen three times in an ice bath to remove oxygen, and then the reaction was carried out at 90 °C for 5 h. After the reaction, the polymer solution was precipitated in an ice methanol solution, and then filtered and dried under vacuum to obtain the polymer.

[0032] Synthesis of PMMA- b -PSt: 1.15 g of styrene (St) was used to replace 0.64 g of MMA, and PMMA- b -PSt was prepared.

[0033] Synthesis of PMMA- b-Synthesis of PEMA: Replace 0.64 g of MMA used with 1.76 g of ethyl methacrylate (EMA) to prepare PMMA- b -PEMA.

[0034] As can be seen from Figure 3 , when MMA, St, and EMA are used as monomers respectively, after PMMA is used to initiate chain extension, their molecular weights increase from 6300 g·mol -1 to 9000, 13500, and 9100 g·mol -1 (A - C) respectively, indicating that the alkoxyamine at the end group of the macromolecular initiator has good retention, and it has good re-initiation regulation performance for a variety of methacrylate monomers and styrene. At the same time, from the b 1H-NMR spectrum (D) of the obtained PMMA- 1 -PMMA block copolymer, the absorption peaks of the protons of the MMA repeating unit at 0.8 ppm to 2.0 ppm and the absorption peak of the methoxy protons at 3.6 ppm can be observed; in the b 1H-NMR spectrum (E) of the PMMA- 1 -PSt block copolymer, the characteristic signal of the phenyl protons of styrene appears at 6.4 - 7.1 ppm; in the b 1H-NMR spectrum (F) of the PMMA- 1 -PEMA block copolymer, the proton peak representing the methoxy group (-OCH3) in the PMMA block is at 3.60 ppm, the signal at 4.04 ppm is the proton peak of the methylene group (-OCH2-) connected to the ester group, and the signal at 1.25 ppm corresponds to the proton peak of the side-chain terminal methyl group (-CH3) in the PEMA block. The results once again prove the formation of the block copolymer.

[0035] Example 4: Controlled Polymerization of MMA by CPDMA under Aerobic Conditions Due to its simple process and easy industrialization, RDRP polymerization under aerobic conditions has received extensive attention. Therefore, the possibility of controlled polymerization of MMA by CPDMN under non-deoxygenated conditions was explored. The specific operation was to add methyl methacrylate (MMA, 5 g, 50 mmol), CPDMN prepared in Example 1 (0.15 g, 0.5 mmol), and toluene (5 g) into a schlenk tube, then react at 90 °C for 4 h. After the reaction, it was cooled with ice water, and then the polymer solution was precipitated in an ice methanol solution, and then obtained the polymer through filtration and vacuum drying. The conversion was calculated by the gravimetric method, and samples were taken for 1 1H NMR test and GPC test. At the same time, the sample prepared under anaerobic conditions was used as a control.

[0036] From Figure 4It can be seen that the MMA polymerized under anaerobic conditions gives a colorless transparent solution (A), while the MMA polymerized under non-deoxygenated conditions gives a light yellow viscous liquid (B). Under anaerobic conditions, the conversion rate of MMA is 84.1%; under aerobic conditions, the conversion rate of MMA reaches 91.3%. At the same time, it can be seen from the GPC spectra (C) of PMMA under aerobic and anaerobic conditions that the polymerization rate is faster under non-deoxygenated conditions, but the dispersity is wider ( M w / M n = 1.48). There is no obvious inhibition phenomenon in the polymerization without deoxygenation, and the reaction rate is faster; only the solution changes from colorless to light yellow, which may be caused by oxidation during the polymerization process. Under aerobic conditions, the reason for the regulation of MMA polymerization by CPDMN may be that CPDMN generates nitrogen-oxygen stable free radicals and growing free radicals when heated. In the presence of a small amount of oxygen, the growing free radicals preferentially generate alkyl peroxy radicals, and then react with alkoxyamine to generate new diisobutyronitrile peroxides. The new alkoxy free radicals generated by the thermal decomposition, and the binding ability of the alkoxy free radicals to CPDMN is weak, so the polymerization rate is faster and the molecular weight distribution is wider.

[0037] In summary, the present invention proposes a new type of alkoxyamine CPDMN. When the temperature is 90 °C and the reaction time is 4 h, the conversion rate of the regulated MMA polymerization is 85.4%, and the molecular weight of the obtained PMMA is 8500, M w / M n is 1.40; and the molecular weight distribution is narrow, the peak shape is symmetrical, there is no obvious tailing phenomenon, and it has the characteristics of controlled radical polymerization. The nuclear magnetic resonance hydrogen spectrum shows that no disproportionation reaction induced by nitrogen oxides occurs during the polymerization process. The results of initiating MMA, St, and EMA with the PMMA macromolecular chain initiator prove that the alkoxyamine end group is well retained and the target block copolymer can be synthesized. The possibility of regulating the polymerization of MMA by CPDMN under aerobic conditions was explored. The results show that compared with the polymerization under anaerobic conditions, the polymerization rate is faster and the obtained molecular weight is close to the theoretical value, which proves that CPDMA can achieve the regulated polymerization of MMA under non-deoxygenated conditions. The synthesis of the alkoxyamine CPDMN solves the long-standing problem that NMP is difficult to regulate the polymerization of methacrylate monomers, realizes the NMP polymerization of MMA under lower temperature and aerobic conditions, enriches the types of alkoxyamines used in NMP polymerization and the range of monomers that can be regulated, and has broad application prospects.

[0038] The above are only the preferred embodiments of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope covered by the present invention.

Claims

1. An alkoxyamine, characterized in that, The alkoxyamine is specifically 3-(((2-cyanopropan-2-yl)oxy)(isopropyl)amino)-2,2-dimethyl-3-phenylpropanenitrile, and its chemical structural formula is .

2. The alkoxyamine according to claim 1, wherein Its preparation includes the following steps: 1) Mix benzaldehyde and isopropylamine evenly in methanol, and react in an oil bath at 40 - 70 °C for 4 - 24 h. After the reaction is completed, cool to room temperature. Then add the reducing agent in batches. After stirring until the raw materials react completely, rotary evaporate to remove the solvent. The obtained crude product is dissolved in ethyl acetate, washed with saturated brine, dried with anhydrous magnesium sulfate, and then rotary evaporated to remove the solvent to obtain a liquid product; 2) Dissolve the liquid product obtained in step 1) and sodium bicarbonate in a mixed solvent of acetone and water. Add the oxidizing agent in batches under ice bath conditions, stir for 2 - 8 h, then filter. The filtrate is washed with saturated brine, and the upper organic phase is collected. After drying with anhydrous magnesium sulfate, rotary evaporate to remove the solvent. The obtained product is separated and purified by a chromatography column to obtain a liquid compound; 3) Mix the liquid compound obtained in step 2) and AIBN evenly in a solvent, and then react at 92 °C for 6 h. After the reaction is completed, rotary evaporate to remove the solvent. The obtained crude product is separated and purified by a chromatography column to obtain the target product.

3. The alkoxyamine according to claim 2, wherein, In step 1), the molar ratio of benzaldehyde, isopropylamine, and sodium borohydride used is 1:1:(1.3 - 2.0).

4. The alkoxyamine according to claim 2, characterized in that, The reducing agent in step 1) is one or more of sodium borohydride, sodium cyanoborohydride, lithium aluminum hydride, and sodium cyanoborohydride.

5. The alkoxyamine according to claim 2, wherein In the mixed solvent in step 2), the volume ratio of acetone to water is 1:

1.

6. The alkoxyamine according to claim 2, wherein The oxidizing agent in step 2) is one or more of Oxone, hydrogen peroxide, m-chloroperoxybenzoic acid, and sodium periodate.

7. The alkoxyamine according to claim 2, wherein In step 2), the mass ratio of the liquid product, sodium bicarbonate, and the oxidizing agent used is 1:2:(3 - 4).

8. The alkoxyamine according to claim 2, characterized in that, In step 3), the mass ratio of the liquid compound to AIBN used is 1:(1.3 - 2.0).

9. The alkoxyamine according to claim 2, wherein, The solvent in step 3) is toluene.

10. Use of an alkoxyamine as described in the claims in the NMP polymerization of methacrylic acid or styrene monomers under anaerobic / aerobic conditions.

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