High-steric-hindrance pyridine tertiary amine oxide and application thereof in synthesis of low-PDI polymerization product

Abstract

The invention discloses a high-steric-hindrance pyridine tertiary amine oxide and application thereof in synthesis of low-PDI polymerization products, secondary amine and aryl halide are subjected to catalytic oxidation and then refined and separated to obtain the tertiary amine oxide, and the tertiary amine oxide can be used for active free radical polymerization in a solvent system and can be used for preparing high-PDI polymerization products. And effective regulation and control of the polymerization process are realized through binding-dissociation balance with the growth chain segment in the polymerization process. The initiation system of the high-steric-hindrance piperidyl tertiary amine oxide is more applicable to a vinyl acetate polymerization system, the Mw of a polymerization product is distributed in a range of 8000-50000, and the corresponding PDI (Poly Diisocyanate) range is 1.20-1.36.

Description

Technical Field

[0001] The present invention belongs to the technical field of living radical polymerization, and particularly relates to the aryl capping, oxidation of secondary amine compounds, and the application of the obtained products as regulators in controlled / living radical polymerization. Background Art

[0002] In the actual production process of general free radical polymerization, the obtained polymer products have a relatively wide molecular weight distribution, and the mechanical strength, heat resistance and other properties of polymer products with different molecular weights vary significantly in the application scenarios. Relevant researchers (Surf.Sci.2004,570(1-2):1-12; J.Polym.Res.2014,21:1-9; J.Am.Chem.Soc.2006,128(23):7622-7629.) systematically summarized the defects in the traditional free radical polymerization process due to the kinetic characteristics of "slow initiation, fast propagation, and rapid termination", resulting in irreversible termination of free radical chains, broad molecular weight distribution (PDI>2), and difficulty in precisely controlling the degree of polymerization.

[0003] Regarding nitroxide-mediated radical polymerization (NMP), there have been some reports on the structure of nitroxide stable radicals (Macromolecules 31.9(1998):2883-2888; J.Am.Chem.Soc.122.25(2000):5929-5939; US20130059964A1; US20170015762A1; US20230192962A1; CN115380054A). They are all based on the reaction products of secondary amine structures and peroxides, which can be precisely controlled during polymerization. However, the secondary amine precursors of such structures often require complex synthesis steps and are not common chemical raw materials. Some secondary amine oxides such as 2,2,6,6-tetramethylpiperidine oxide have been developed on a large scale and are commercially available, but the yields in the synthesis process are generally low, the synthesis cost is high, and generally a high temperature above 120°C is required to maintain its reaction activity during its application, consuming a large amount of energy, and the side reactions brought about by high temperature cannot be controlled.

[0004] Some researchers have used the reaction products of secondary amine structures and peroxides for precise control during polymerization. However, the synthesis steps of the secondary amine precursors of such structures are complex, the raw material sources are not common substances on the market, and the yields in the synthesis process are generally low, the synthesis cost is high. Generally, a high temperature above 120°C is required to maintain its reaction activity during its application, consuming a large amount of energy, and the side reactions brought about by high temperature cannot be controlled.

[0005] The regulation of the existing amine oxides on the polymerized free radical chain segments is that the oxygen atoms in the oxide carry partial positive charges, act on the free radical long chains obtained by polymerization through single electron transfer, and then combine with them. The regulation of the molecular weight distribution is achieved through the dynamic equilibrium of binding-dissociation, as shown below:

[0006]

[0007] The dynamic equilibrium of the polyether amine oxide binding with the free radical chain segments. However, such structures are of a single category, and most of them use long-chain amine polyethoxy ethers as the oxidation precursors, which can only be applied to the emulsion polymerization system, and the reaction scenarios are relatively single. Summary of the Invention

[0008] Object of the Invention: Aiming at the defects and technical problems existing in the background technology, the present invention provides a high steric hindrance pyridine tertiary amine oxide and its application in the synthesis of low-PDI polymerization products. The initiation system of the oxidation product of the high steric hindrance tertiary amine compound is applicable to solution polymerization occurring in common solvents such as toluene, xylene, butyl acetate, DMSO, DMF, etc., and the PDI range of the polymerization product is 1.20 - 1.36.

[0009] Technical Solution: To achieve the above object of the invention, the present invention adopts the following technical solution: A high steric hindrance pyridine tertiary amine oxide has the following molecular structural formula,

[0010]

[0011] In structural formula (I), R is mono- to deca-substituted, and the substituents are each independently selected from a hydrogen atom, C 1-4 alkyl, benzyl, ester group, phenyl; Ar is selected from indenyl, fluorenyl or dimethylfluorenyl, naphthyl, substituted phenyl, phenanthryl; there is at least 1 substituent on the substituted phenyl, and the substituents are independently selected from an ester group, alkyl, alkoxy.

[0012] The present invention also provides a synthesis method of the above high steric hindrance pyridine tertiary amine oxide, including the following steps:

[0013] S1, Synthesis of the tertiary amine precursor: In a reaction vessel, add a solvent, a secondary amine, and a halogenated hydrocarbon. After fully dissolving and mixing evenly, continue to add a basic catalyst, and raise the temperature to 60 - 150 °C for reaction for 4 - 48 h to obtain a crude tertiary amine product; the halogenated hydrocarbon is a halogenated aromatic hydrocarbon or a halogenated cycloalkane;

[0014] S2, Refinement of the tertiary amine: Column chromatography separate the crude tertiary amine product with a petroleum ether / ethyl acetate eluent with a volume ratio of 50:1 - 1:1 to obtain a pure tertiary amine product;

[0015] S3, Synthesis of tertiary amine oxide: Add the pure tertiary amine product and an organic solvent into a container, heat up to 40 - 150 °C to fully dissolve them; then dropwise add hydrogen peroxide into it, react for 3 - 72 h to obtain a tertiary amine oxide solution;

[0016] S4, After removing the solvent from the tertiary amine oxide solution by vacuum distillation, tertiary amine oxide is obtained.

[0017] Further, in step S1, the molar ratio of the halogenated hydrocarbon to the secondary amine is 0.5 - 3:1.

[0018] Further, the secondary amine is selected from 2 - methylpiperidine, 3 - methylpiperidine, 4 - methylpiperidine, 2 - ethylpiperidine, 3 - ethylpiperidine, 4 - ethylpiperidine, 2 - n - propylpiperidine, 3 - n - propylpiperidine, 4 - n - propylpiperidine, 2 - isopropylpiperidine, 3 - isopropylpiperidine, 4 - isopropylpiperidine, 2 - n - butylpiperidine, 3 - n - butylpiperidine, 4 - n - butylpiperidine, 3 - isobutylpiperidine, 4 - isobutylpiperidine, 3 - (tert - butyl)piperidine, 4 - (3 - methylbutyl)piperidine, 2 - tert - butylpiperidine, 4 - (tert - butyl)piperidine, 4 - (sec - butyl)piperidine, 2,4,6 - trimethylpiperidine, 3,3,4 - trimethylpiperidine, 3,3,5 - trimethylpiperidine, 2,2,6,6 - tetramethylpiperidine, 3,3,5,5 - tetramethylpiperidine, 2,2,4,6 - tetramethylpiperidine, 2 - benzylpiperidine, 3 - benzylpiperidine, 4 - benzylpiperidine, methyl 2 - piperidinecarboxylate, methyl 3 - piperidinecarboxylate, methyl 4 - piperidinecarboxylate, ethyl 2 - piperidinecarboxylate, ethyl 3 - piperidinecarboxylate, ethyl 4 - piperidinecarboxylate, dimethyl piperidine - 2,5 - dicarboxylate, dimethyl piperidine - 2,6 - dicarboxylate, dimethyl piperidine - 3,5 - dicarboxylate, 2 - phenylpiperidine, 3 - phenylpiperidine, 4 - phenylpiperidine.

[0019] Further, the halogenated aromatic hydrocarbon is selected from 2 - bromoindene, 1 - bromo - 9H - fluorene, 2 - bromofluorene, 3 - bromo - 9H - fluorene, 4 - bromo - 9H - fluorene, 9,9 - dimethyl - 2 - bromofluorene, 3 - bromo - 9,9 - dimethylfluorene, 4 - bromo - 9,9 - dimethylfluorene, 1 - bromonaphthalene, 2 - bromonaphthalene, ethyl 2 - bromobenzoate, tert - butyl 2 - bromobenzoate, dimethyl 2 - bromoisophthalate, 1 - bromo - 4 - tert - butyl - 2 - ethylbenzene, 2,6 - di - tert - butylbromobenzene, 1 - bromo - 2,6 - dimethoxybenzene, 1 - bromo - 2,4,6 - trimethoxybenzene, 3 - bromophenanthrene, 9 - bromophenanthrene.

[0020] Further, the basic catalyst is selected from sodium bicarbonate, potassium bicarbonate, sodium carbonate, potassium carbonate, cesium carbonate, sodium hydroxide, potassium hydroxide, calcium hydroxide, cesium hydroxide, sodium methoxide, potassium methoxide, sodium ethoxide, potassium ethoxide, sodium isopropoxide, trimethylamine, triethylamine, ethylenediamine, diethylamine, tert-butylamine, piperidine, pyridine, 4-dimethylaminopyridine, sodium tert-butoxide, potassium tert-butoxide, lithium diisopropylamide, n-butyllithium, tritylsodium.

[0021] Further, the organic solvent is selected from benzene, toluene, ethylbenzene, xylene, dichloromethane, chloroform, carbon tetrachloride, dichloroethane, methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, acetone, butanone, cyclohexanone, ether, tetrahydrofuran, ethylene glycol dimethyl ether, ethyl acetate, butyl acetate, dimethyl carbonate, diethyl carbonate, N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, hexamethylphosphoric triamide, sulfolane.

[0022] Further, the molar ratio of the addition amount of the halogenated hydrocarbon to the addition amount of the secondary amine is 1-1.5:1, the molar ratio of the basic catalyst to the secondary amine is 1.2-1.8:1, and the molar ratio of hydrogen peroxide to the pure tertiary amine product is 8-20:1.

[0023] Further, the reaction temperature in step S1 is 80±10°C and the reaction time is 8±1 h; the reaction temperature in step S3 is 85±5°C and the reaction temperature is 8±1 h.

[0024] The present invention also provides an application of the above-mentioned high steric hindrance pyridine tertiary amine oxide in a radical polymerization reaction to obtain a polymerization product with a lower PDI.

[0025] The present invention also provides a method for synthesizing a low-PDI polymerization product, which is characterized in that in a reaction vessel, after adding a polymerization monomer, an azo initiator and an appropriate amount of solvent, add 0.1-3% of the high steric hindrance pyridine tertiary amine oxide according to any one of claims 1-9 in terms of the molar ratio relative to the polymerization monomer. After sealing and freeze-thaw degassing several times, heat the system to 60-140°C. After reacting for 3-12 hours, immediately place it in liquid nitrogen to terminate the reaction, and rotary evaporate to remove the solvent and the remaining monomer to obtain a low-PDI polymerization product.

[0026] Further, the polymerization monomer is selected from vinyl acetate and its derivatives, vinylpyrrolidone and its derivatives.

[0027] Further, the azo initiator is azobisisobutyronitrile, azobisisoheptonitrile, dimethyl azobisisobutyrate, azobisisobutamidine hydrochloride, azobisisobutimidazoline hydrochloride, azoisopentanenitrile, azoisobutyronitrile carboxamide. Beneficial effects: Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The steric hindrance in the molecular structure of the pyridine tertiary amine of the present invention is greater, and its oxidation product has a better regulation and stabilization effect on chain growth free radicals, and can effectively adjust the molecular weight during the polymerization process. Especially for the polymerization monomers of vinyl acetate and vinyl pyrrolidone, it has an excellent PDI value.

[0029] (2) When this tertiary amine oxide is used as a regulator in solution polymerization, it exhibits the characteristics of living polymerization, and the resulting polymer has a narrow molecular weight distribution.

[0030] (3) A high steric hindrance pyridine tertiary amine oxide regulator with a small molecular weight was developed, and on the basis of the previous tertiary amine oxide surfactants, the application scenario was broadened to the solution polymerization system. And this type of tertiary amine oxide has a small molecular weight and moderate polarity, can be dissolved in a variety of organic solvents, and has a certain universality.

[0031] (4) The temperature required to maintain the reaction activity of the tertiary amine oxide is lower, 80 - 90 °C is sufficient, and the energy consumption is less. Description of the Drawings

[0032] Figure 1 It is the molecular structural formula of the tertiary amine oxide described in the present invention. Detailed Embodiments

[0033] The following further clarifies the present invention in conjunction with the drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. After reading the present invention, various equivalent forms of modification by those skilled in the art fall within the scope defined by the appended claims of this application.

[0034] Example 1

[0035]

[0036] Synthesis of tertiary amine compound a1: Add 141 mg of 2,2,6,6 - tetramethylpiperidine, 10 mL of DMF, and 234 mg of 2 - bromoindene into a round - bottom flask in sequence. After stirring evenly to ensure that all components are completely dissolved, add 106 mg of sodium carbonate, stir evenly to dissolve, heat up to 80 °C, react for 8 hours, filter to obtain the filtrate, and obtain the crude product after rotary evaporation. Column chromatography purification is carried out with an eluent ratio of petroleum ether / ethyl acetate of 10:1 to obtain the pure product.

[0037] Synthesis of tertiary amine oxide b1: Add 255 mg of tertiary amine compound a1 and 20 mL of ethanol into the flask, then heat up to 60 °C to fully dissolve the two. Slowly dropwise add 1.1 mL of 30% hydrogen peroxide, raise the temperature to 85 °C, and heat under reflux for 7 hours. After evaporating the solvent, the oxide b1 is obtained.

[0038] Example 2

[0039]

[0040] Synthesis of tertiary amine compound a2: Add 141 mg of 2,2,6,6-tetramethylpiperidine, 10 mL of DMF, and 260 mg of 3-bromo-9H-fluorene into a round-bottom flask in sequence. After stirring evenly to ensure complete dissolution of each component, add 106 mg of sodium carbonate. After stirring evenly and dissolving, heat up to 80 °C. After reacting for 9 hours, filter to obtain the filtrate. After rotary evaporation, the crude product is obtained, and column chromatography purification is carried out with an eluent ratio of petroleum ether / ethyl acetate of 13:1 to obtain the pure product.

[0041] Synthesis of tertiary amine oxide b2: Add 305 mg of tertiary amine compound a2 and 20 mL of ethanol into a flask, then heat up to 60 °C to fully dissolve the two. Slowly add 1.1 mL of 30% hydrogen peroxide dropwise, raise the temperature to 85 °C, and heat under reflux for 7 hours. After evaporating the solvent, the oxide b2 is obtained.

[0042] Example 3

[0043]

[0044] Synthesis of tertiary amine compound a3: Add 141 mg of 2,2,6,6-tetramethylpiperidine, 10 mL of DMF, and 285 mg of 3-bromo-9,9-dimethylfluorene into a round-bottom flask in sequence. After stirring evenly to ensure complete dissolution of each component, add 106 mg of sodium carbonate. After stirring evenly and dissolving, heat up to 80 °C. After reacting for 9 hours, filter to obtain the filtrate. After rotary evaporation, the crude product is obtained, and column chromatography purification is carried out with an eluent ratio of petroleum ether / ethyl acetate of 15:1 to obtain the pure product.

[0045] Synthesis of tertiary amine oxide b3: Add 333 mg of tertiary amine compound a3 and 20 mL of ethanol into a flask, then heat up to 60 °C to fully dissolve the two. Slowly add 1.1 mL of 30% hydrogen peroxide dropwise, raise the temperature to 85 °C, and heat under reflux for 7 hours. After evaporating the solvent, the oxide is obtained.

[0046] Example 4

[0047]

[0048] Synthesis of tertiary amine compound a4: Add 141 mg of 2,2,6,6-tetramethylpiperidine, 10 mL of DMF, and 228 mg of 1-bromonaphthalene into a round-bottom flask in sequence. After stirring evenly to ensure complete dissolution of each component, add 106 mg of sodium carbonate. After stirring evenly and dissolving, heat up to 80 °C. After reacting for 9 hours, filter to obtain the filtrate. After rotary evaporation, the crude product is obtained, and column chromatography purification is carried out with an eluent ratio of petroleum ether / ethyl acetate of 8:1 to obtain the pure product.

[0049] Synthesis of tertiary amine oxide b4: Add 267 mg of tertiary amine compound a4 and 20 mL of ethanol into a flask, then heat up to 60 °C to fully dissolve the two. Slowly add 1.1 mL of 30% hydrogen peroxide drop by drop, raise the temperature to 85 °C, and reflux for 7 hours. After evaporating the solvent, the oxide is obtained.

[0050] Example 5

[0051]

[0052] Synthesis of tertiary amine compound a5: Add 141 mg of 2,2,6,6-tetramethylpiperidine, 10 mL of DMF, and 300 mg of dimethyl 2-bromoisophthalate into a round-bottom flask in sequence. After stirring evenly to ensure complete dissolution of each component, add 106 mg of sodium carbonate. After stirring evenly and dissolving, heat up to 80 °C, react for 9 hours, filter to obtain the filtrate, and obtain the crude product after rotary evaporation. Purify by column chromatography with a petroleum ether / ethyl acetate eluent ratio of 6:1 to obtain the pure product.

[0053] Synthesis of tertiary amine oxide b5: Add 333 mg of tertiary amine compound a5 and 20 mL of ethanol into a flask, then heat up to 60 °C to fully dissolve the two. Slowly add 1.1 mL of 30% hydrogen peroxide drop by drop, raise the temperature to 85 °C, and reflux for 7 hours. After evaporating the solvent, the oxide is obtained.

[0054] Example 6

[0055]

[0056] Synthesis of tertiary amine compound a6: Add 141 mg of 2,2,6,6-tetramethylpiperidine, 10 mL of DMF, and 296 mg of 2,6-di-tert-butylbromobenzene into a round-bottom flask in sequence. After stirring evenly to ensure complete dissolution of each component, add 106 mg of sodium carbonate. After stirring evenly and dissolving, heat up to 80 °C, react for 9 hours, filter to obtain the filtrate, and obtain the crude product after rotary evaporation. Purify by column chromatography with a petroleum ether / ethyl acetate eluent ratio of 6:1 to obtain the pure product.

[0057] Synthesis of tertiary amine oxide b6: Add 333 mg of tertiary amine compound a6 and 20 mL of ethanol into a flask, then heat up to 60 °C to fully dissolve the two. Slowly add 1.1 mL of 30% hydrogen peroxide drop by drop, raise the temperature to 85 °C, and reflux for 7 hours. After evaporating the solvent, the oxide is obtained.

[0058] Example 7

[0059]

[0060] Synthesis of tertiary amine compound a7: Add 141 mg of 2,2,6,6-tetramethylpiperidine, 10 mL of DMF, and 272 mg of 1-bromo-2,4,6-trimethoxybenzene into a round-bottom flask in sequence. After stirring evenly to ensure complete dissolution of each component, add 106 mg of sodium carbonate. After stirring evenly to dissolve, heat up to 80 °C. After reacting for 9 hours, filter to obtain the filtrate. After rotary evaporation, the crude product is obtained, and column chromatography purification is carried out with a petroleum ether / ethyl acetate eluent ratio of 5:1 to obtain the pure product.

[0061] Synthesis of tertiary amine oxide b7: Add 307 mg of tertiary amine compound a7 and 20 mL of ethanol into a flask, then heat up to 60 °C to fully dissolve the two. Slowly add 1.1 mL of 30% hydrogen peroxide dropwise, raise the temperature to 85 °C, and heat under reflux for 7 hours. After evaporating the solvent, the oxide is obtained.

[0062] Example 8

[0063]

[0064] Synthesis of tertiary amine compound a8: Add 141 mg of 2,2,6,6-tetramethylpiperidine, 10 mL of DMF, and 349 mg of 9-bromophenanthrene into a round-bottom flask in sequence. After stirring evenly to ensure complete dissolution of each component, add 106 mg of sodium carbonate. After stirring evenly to dissolve, heat up to 80 °C. After reacting for 9 hours, filter to obtain the filtrate. After rotary evaporation, the crude product is obtained, and column chromatography purification is carried out with a petroleum ether / ethyl acetate eluent ratio of 9:1 to obtain the pure product.

[0065] Synthesis of tertiary amine oxide b8: Add 307 mg of tertiary amine compound a8 and 20 mL of ethanol into a flask, then heat up to 60 °C to fully dissolve the two. Slowly add 1.1 mL of 30% hydrogen peroxide dropwise, raise the temperature to 85 °C, and heat under reflux for 7 hours. After evaporating the solvent, the oxide is obtained.

[0066] Example 9

[0067]

[0068] Synthesis of tertiary amine compound a9: Add 175 mg of 2-benzylpiperidine, 10 mL of DMF, and 213 mg of 2-bromoindene into a round-bottom flask in sequence. After stirring evenly to ensure complete dissolution of each component, add 106 mg of sodium carbonate. After stirring evenly to dissolve, heat up to 80 °C. After reacting for 9 hours, filter to obtain the filtrate. After rotary evaporation, the crude product is obtained, and column chromatography purification is carried out with a petroleum ether / ethyl acetate eluent ratio of 13:1 to obtain the pure product.

[0069] Synthesis of tertiary amine oxide b9: Add 289 mg of tertiary amine compound a9 and 20 mL of ethanol into a flask, then heat up to 60 °C to fully dissolve the two. Slowly add 1.1 mL of 30% hydrogen peroxide dropwise, raise the temperature to 85 °C, and reflux for 7 hours. After evaporating the solvent, the oxide is obtained.

[0070] Example 10

[0071]

[0072] Synthesis of tertiary amine compound a10: Add 175 mg of 2-benzylpiperidine, 10 mL of DMF, and 270 mg of 3-bromo-9H-fluorene into a round-bottom flask in sequence. After stirring evenly to ensure complete dissolution of each component, add 106 mg of sodium carbonate. After stirring evenly and dissolving, heat up to 80 °C and react for 9 hours. Then filter to obtain the filtrate. After rotary evaporation, the crude product is obtained, and column chromatography purification is carried out with a petroleum ether / ethyl acetate eluent ratio of 11:1 to obtain the pure product.

[0073] Synthesis of tertiary amine oxide b10: Add 339 mg of tertiary amine compound a10 and 20 mL of ethanol into a flask, then heat up to 60 °C to fully dissolve the two. Slowly add 1.1 mL of 30% hydrogen peroxide dropwise, raise the temperature to 85 °C, and reflux for 7 hours. After evaporating the solvent, the oxide is obtained.

[0074] Example 11

[0075]

[0076] Synthesis of tertiary amine compound a11: Add 175 mg of 2-benzylpiperidine, 10 mL of DMF, and 285 mg of 3-bromo-9,9-dimethylfluorene into a round-bottom flask in sequence. After stirring evenly to ensure complete dissolution of each component, add 106 mg of sodium carbonate. After stirring evenly and dissolving, heat up to 80 °C and react for 9 hours. Then filter to obtain the filtrate. After rotary evaporation, the crude product is obtained, and column chromatography purification is carried out with a petroleum ether / ethyl acetate eluent ratio of 12:1 to obtain the pure product.

[0077] Synthesis of tertiary amine oxide b11: Add 368 mg of tertiary amine compound a11 and 20 mL of ethanol into a flask, then heat up to 60 °C to fully dissolve the two. Slowly add 1.1 mL of 30% hydrogen peroxide dropwise, raise the temperature to 85 °C, and reflux for 7 hours. After evaporating the solvent, the oxide is obtained.

[0078] Example 12

[0079]

[0080] Synthesis of tertiary amine compound a12: Add 175 mg of 2-benzylpiperidine, 10 mL of DMF, and 228 mg of 1-bromonaphthalene into a round-bottom flask in sequence. After stirring evenly to ensure complete dissolution of each component, add 106 mg of sodium carbonate. After stirring evenly and dissolving, heat up to 80 °C. After reacting for 9 hours, filter to obtain the filtrate. After rotary evaporation, the crude product is obtained, and column chromatography purification is carried out with a petroleum ether / ethyl acetate eluent ratio of 10:1 to obtain the pure product.

[0081] Synthesis of tertiary amine oxide b12: Add 301 mg of tertiary amine compound a12 and 20 mL of ethanol into a flask, then heat up to 60 °C to fully dissolve the two. Slowly dropwise add 1.1 mL of 30% hydrogen peroxide, raise the temperature to 85 °C, and heat under reflux for 7 hours. After evaporating the solvent, the oxide is obtained.

[0082] Example 13

[0083]

[0084] Synthesis of tertiary amine compound a13: Add 175 mg of 2-benzylpiperidine, 10 mL of DMF, and 301 mg of dimethyl 2-bromoisophthalate into a round-bottom flask in sequence. After stirring evenly to ensure complete dissolution of each component, add 106 mg of sodium carbonate. After stirring evenly and dissolving, heat up to 80 °C. After reacting for 9 hours, filter to obtain the filtrate. After rotary evaporation, the crude product is obtained, and column chromatography purification is carried out with a petroleum ether / ethyl acetate eluent ratio of 10:1 to obtain the pure product.

[0085] Synthesis of tertiary amine oxide b13: Add 367 mg of tertiary amine compound a13 and 20 mL of ethanol into a flask, then heat up to 60 °C to fully dissolve the two. Slowly dropwise add 1.1 mL of 30% hydrogen peroxide, raise the temperature to 85 °C, and heat under reflux for 7 hours. After evaporating the solvent, the oxide is obtained.

[0086] Example 14

[0087]

[0088] Synthesis of tertiary amine compound a14: Add 175 mg of 2-benzylpiperidine, 10 mL of DMF, and 300 mg of 1,3-di-tert-butyl-2-bromobenzene into a round-bottom flask in sequence. After stirring evenly to ensure complete dissolution of each component, add 106 mg of sodium carbonate. After stirring evenly and dissolving, heat up to 80 °C. After reacting for 9 hours, filter to obtain the filtrate. After rotary evaporation, the crude product is obtained, and column chromatography purification is carried out with a petroleum ether / ethyl acetate eluent ratio of 17:1 to obtain the pure product.

[0089] Synthesis of tertiary amine oxide b14: Add 363 mg of tertiary amine compound a14 and 20 mL of ethanol into a flask, then heat up to 60 °C to fully dissolve the two. Slowly and evenly add 1.1 mL of 30% hydrogen peroxide, raise the temperature to 85 °C, and reflux for 7 hours. After evaporating the solvent, the oxide is obtained.

[0090] Example 15

[0091]

[0092] Synthesis of tertiary amine compound a15: Add 175 mg of 2-benzylpiperidine, 10 mL of DMF, and 271 mg of 2-bromo-1,3,5-trimethoxybenzene into a round-bottom flask in sequence. After stirring evenly to ensure complete dissolution of each component, add 106 mg of sodium carbonate, stir evenly until dissolved, heat up to 80 °C, react for 9 hours, filter to obtain the filtrate, and obtain the crude product after rotary evaporation. Purify by column chromatography with a petroleum ether / ethyl acetate eluent ratio of 9:1 to obtain the pure product.

[0093] Synthesis of tertiary amine oxide b15: Add 341 mg of tertiary amine compound a15 and 20 mL of ethanol into a flask, then heat up to 60 °C to fully dissolve the two. Slowly and evenly add 1.1 mL of 30% hydrogen peroxide, raise the temperature to 85 °C, and reflux for 7 hours. After evaporating the solvent, the oxide is obtained.

[0094] Example 16

[0095]

[0096] Synthesis of tertiary amine compound a16: Add 175 mg of 2-benzylpiperidine, 10 mL of DMF, and 283 mg of 9-bromophenanthrene into a round-bottom flask in sequence. After stirring evenly to ensure complete dissolution of each component, add 106 mg of sodium carbonate, stir evenly until dissolved, heat up to 80 °C, react for 9 hours, filter to obtain the filtrate, and obtain the crude product after rotary evaporation. Purify by column chromatography with a petroleum ether / ethyl acetate eluent ratio of 9:1 to obtain the pure product.

[0097] Synthesis of tertiary amine oxide b16: Add 317 mg of tertiary amine compound a16 and 20 mL of ethanol into a flask, then heat up to 60 °C to fully dissolve the two. Slowly and evenly add 1.1 mL of 30% hydrogen peroxide, raise the temperature to 85 °C, and reflux for 7 hours. After evaporating the solvent, the oxide is obtained.

[0098] Example 17

[0099]

[0100] Synthesis of tertiary amine compound a17: 201 mg of dimethyl piperidine-2,5-dicarboxylate, 10 mL of DMF, and 213 mg of 2-bromoindene were successively added to a round-bottom flask. After stirring evenly to ensure complete dissolution of each component, 106 mg of sodium carbonate was added. After stirring evenly and dissolving, the temperature was raised to 80 °C. After reacting for 9 hours, the filtrate was obtained by filtration. After rotary evaporation, the crude product was obtained, and column chromatography purification was carried out with a petroleum ether / ethyl acetate eluent ratio of 10:1 to obtain the pure product.

[0101] Synthesis of tertiary amine oxide b17: 315 mg of tertiary amine compound a17 and 20 mL of ethanol were added to a flask, and then the temperature was raised to 60 °C to fully dissolve the two. 1.1 mL of 30% hydrogen peroxide was added dropwise at a constant speed, the temperature was raised to 85 °C, and reflux was carried out for 7 hours. After evaporating the solvent, the oxide was obtained.

[0102] Example 18

[0103]

[0104] Synthesis of tertiary amine compound a18: 201 mg of dimethyl piperidine-2,5-dicarboxylate, 10 mL of DMF, and 270 mg of 3-bromo-9H-fluorene were successively added to a round-bottom flask. After stirring evenly to ensure complete dissolution of each component, 106 mg of sodium carbonate was added. After stirring evenly and dissolving, the temperature was raised to 80 °C. After reacting for 9 hours, the filtrate was obtained by filtration. After rotary evaporation, the crude product was obtained, and column chromatography purification was carried out with a petroleum ether / ethyl acetate eluent ratio of 13:1 to obtain the pure product.

[0105] Synthesis of tertiary amine oxide b18: 365 mg of tertiary amine compound a18 and 20 mL of ethanol were added to a flask, and then the temperature was raised to 60 °C to fully dissolve the two. 1.1 mL of 30% hydrogen peroxide was added dropwise at a constant speed, the temperature was raised to 85 °C, and reflux was carried out for 7 hours. After evaporating the solvent, the oxide was obtained.

[0106] Example 19

[0107]

[0108] Synthesis of tertiary amine compound a19: 201 mg of dimethyl piperidine-2,5-dicarboxylate, 10 mL of DMF, and 285 mg of 3-bromo-9,9-dimethylfluorene were successively added to a round-bottom flask. After stirring evenly to ensure complete dissolution of each component, 106 mg of sodium carbonate was added. After stirring evenly and dissolving, the temperature was raised to 80 °C. After reacting for 9 hours, the filtrate was obtained by filtration. After rotary evaporation, the crude product was obtained, and column chromatography purification was carried out with a petroleum ether / ethyl acetate eluent ratio of 15:1 to obtain the pure product.

[0109] Synthesis of tertiary amine oxide b19: Add 393 mg of tertiary amine compound a19 and 20 mL of ethanol into a flask, then heat up to 60 °C to fully dissolve the two. Slowly add 1.1 mL of 30% hydrogen peroxide dropwise, raise the temperature to 85 °C, and reflux for 7 hours. After evaporating the solvent, the oxide is obtained.

[0110] Example 20

[0111]

[0112] Synthesis of tertiary amine compound a20: Add 201 mg of dimethyl piperidine-2,5-dicarboxylate, 10 mL of DMF, and 228 mg of 1-bromonaphthalene into a round-bottom flask in sequence. After stirring evenly to ensure complete dissolution of each component, add 106 mg of sodium carbonate. After stirring evenly and dissolving, heat up to 80 °C and react for 9 hours. Then filter to obtain the filtrate, and after rotary evaporation, the crude product is obtained. Column chromatography purification is carried out with an eluent ratio of petroleum ether / ethyl acetate of 13:1 to obtain the pure product.

[0113] Synthesis of tertiary amine oxide b20: Add 327 mg of tertiary amine compound a20 and 20 mL of ethanol into a flask, then heat up to 60 °C to fully dissolve the two. Slowly add 1.1 mL of 30% hydrogen peroxide dropwise, raise the temperature to 85 °C, and reflux for 7 hours. After evaporating the solvent, the oxide is obtained.

[0114] Example 21

[0115]

[0116] Synthesis of tertiary amine compound a21: Add 201 mg of dimethyl piperidine-2,5-dicarboxylate, 10 mL of DMF, and 301 mg of dimethyl 2-bromoisophthalate into a round-bottom flask in sequence. After stirring evenly to ensure complete dissolution of each component, add 106 mg of sodium carbonate. After stirring evenly and dissolving, heat up to 80 °C and react for 9 hours. Then filter to obtain the filtrate, and after rotary evaporation, the crude product is obtained. Column chromatography purification is carried out with an eluent ratio of petroleum ether / ethyl acetate of 10:1 to obtain the pure product.

[0117] Synthesis of tertiary amine oxide b21: Add 393 mg of tertiary amine compound a21 and 20 mL of ethanol into a flask, then heat up to 60 °C to fully dissolve the two. Slowly add 1.1 mL of 30% hydrogen peroxide dropwise, raise the temperature to 85 °C, and reflux for 7 hours. After evaporating the solvent, the oxide is obtained.

[0118] Example 22

[0119]

[0120] Synthesis of tertiary amine compound a22: 201 mg of dimethyl piperidine-2,5-dicarboxylate, 10 mL of DMF, and 300 mg of 1,3-di-tert-butyl-2-bromobenzene were successively added to a round-bottom flask. After stirring evenly to ensure complete dissolution of each component, 106 mg of sodium carbonate was added. After stirring evenly and dissolving, the temperature was raised to 80 °C. After reacting for 9 hours, the filtrate was obtained by filtration. After rotary evaporation, the crude product was obtained, and column chromatography purification was carried out with a petroleum ether / ethyl acetate eluent ratio of 19:1 to obtain the pure product.

[0121] Synthesis of tertiary amine oxide b22: 389 mg of tertiary amine compound a22 and 20 mL of ethanol were added to a flask, and then the temperature was raised to 60 °C to fully dissolve the two. 1.1 mL of 30% hydrogen peroxide was added dropwise at a constant speed, the temperature was raised to 85 °C, and the mixture was heated under reflux for 7 hours. After evaporating the solvent, the oxide was obtained.

[0122] Example 23

[0123]

[0124] Synthesis of tertiary amine compound a23: 201 mg of dimethyl piperidine-2,5-dicarboxylate, 10 mL of DMF, and 271 mg of 2-bromo-1,3,5-trimethoxybenzene were successively added to a round-bottom flask. After stirring evenly to ensure complete dissolution of each component, 106 mg of sodium carbonate was added. After stirring evenly and dissolving, the temperature was raised to 80 °C. After reacting for 9 hours, the filtrate was obtained by filtration. After rotary evaporation, the crude product was obtained, and column chromatography purification was carried out with a petroleum ether / ethyl acetate eluent ratio of 9:1 to obtain the pure product.

[0125] Synthesis of tertiary amine oxide b23: 367 mg of tertiary amine compound a23 and 20 mL of ethanol were added to a flask, and then the temperature was raised to 60 °C to fully dissolve the two. 1.1 mL of 30% hydrogen peroxide was added dropwise at a constant speed, the temperature was raised to 85 °C, and the mixture was heated under reflux for 7 hours. After evaporating the solvent, the oxide was obtained.

[0126] Example 24

[0127]

[0128] Synthesis of tertiary amine compound a24: 201 mg of dimethyl piperidine-2,5-dicarboxylate, 10 mL of DMF, and 283 mg of 9-bromophenanthrene were successively added to a round-bottom flask. After stirring evenly to ensure complete dissolution of each component, 106 mg of sodium carbonate was added. After stirring evenly and dissolving, the temperature was raised to 80 °C. After reacting for 9 hours, the filtrate was obtained by filtration. After rotary evaporation, the crude product was obtained, and column chromatography purification was carried out with a petroleum ether / ethyl acetate eluent ratio of 9:1 to obtain the pure product.

[0129] Synthesis of tertiary amine oxide b24: Add 377 mg of tertiary amine compound a24 and 20 mL of ethanol into a flask, then heat up to 60 °C to fully dissolve the two. Slowly add 1.1 mL of 30% hydrogen peroxide drop by drop, raise the temperature to 85 °C, and reflux for 7 hours. After evaporating the solvent, the oxide is obtained.

[0130] Example 25

[0131]

[0132] Synthesis of tertiary amine compound a25: Add 161 mg of 2-phenylpiperidine, 10 mL of DMF, and 213 mg of 2-bromoindene into a round-bottom flask in sequence. After stirring evenly to ensure complete dissolution of each component, add 106 mg of sodium carbonate. After stirring evenly and dissolving, heat up to 80 °C and react for 9 hours. Then filter to obtain the filtrate, and after rotary evaporation, the crude product is obtained. Column chromatography purification is carried out with an eluent ratio of petroleum ether / ethyl acetate of 10:1 to obtain the pure product.

[0133] Synthesis of tertiary amine oxide b25: Add 275 mg of tertiary amine compound a25 and 20 mL of ethanol into a flask, then heat up to 60 °C to fully dissolve the two. Slowly add 1.1 mL of 30% hydrogen peroxide drop by drop, raise the temperature to 85 °C, and reflux for 7 hours. After evaporating the solvent, the oxide is obtained.

[0134] Example 26

[0135]

[0136] Synthesis of tertiary amine compound a26: Add 161 mg of 2-phenylpiperidine, 10 mL of DMF, and 270 mg of 3-bromo-9H-fluorene into a round-bottom flask in sequence. After stirring evenly to ensure complete dissolution of each component, add 106 mg of sodium carbonate. After stirring evenly and dissolving, heat up to 80 °C and react for 9 hours. Then filter to obtain the filtrate, and after rotary evaporation, the crude product is obtained. Column chromatography purification is carried out with an eluent ratio of petroleum ether / ethyl acetate of 13:1 to obtain the pure product.

[0137] Synthesis of tertiary amine oxide b26: Add 325 mg of tertiary amine compound a26 and 20 mL of ethanol into a flask, then heat up to 60 °C to fully dissolve the two. Slowly add 1.1 mL of 30% hydrogen peroxide drop by drop, raise the temperature to 85 °C, and reflux for 7 hours. After evaporating the solvent, the oxide is obtained.

[0138] Example 27

[0139]

[0140] Synthesis of tertiary amine compound a27: Add 161 mg of 2-phenylpiperidine, 10 mL of DMF, and 285 mg of 3-bromo-9,9-dimethylfluorene into a round-bottom flask in sequence. After stirring evenly to ensure complete dissolution of each component, add 106 mg of sodium carbonate. After stirring evenly to dissolve, heat up to 80 °C. After reacting for 9 hours, filter to obtain the filtrate. After rotary evaporation, the crude product is obtained, and column chromatography purification is carried out with an eluent ratio of petroleum ether / ethyl acetate of 15:1 to obtain the pure product.

[0141] Synthesis of tertiary amine oxide b27: Add 353 mg of tertiary amine compound a27 and 20 mL of ethanol into a flask, then heat up to 60 °C to fully dissolve the two. Slowly add 1.1 mL of 30% hydrogen peroxide dropwise, raise the temperature to 85 °C, and heat under reflux for 7 hours. After evaporating the solvent, the oxide is obtained.

[0142] Example 28

[0143]

[0144] Synthesis of tertiary amine compound a28: Add 161 mg of 2-phenylpiperidine, 10 mL of DMF, and 228 mg of 1-bromonaphthalene into a round-bottom flask in sequence. After stirring evenly to ensure complete dissolution of each component, add 106 mg of sodium carbonate. After stirring evenly to dissolve, heat up to 80 °C. After reacting for 9 hours, filter to obtain the filtrate. After rotary evaporation, the crude product is obtained, and column chromatography purification is carried out with an eluent ratio of petroleum ether / ethyl acetate of 13:1 to obtain the pure product.

[0145] Synthesis of tertiary amine oxide b28: Add 287 mg of tertiary amine compound a28 and 20 mL of ethanol into a flask, then heat up to 60 °C to fully dissolve the two. Slowly add 1.1 mL of 30% hydrogen peroxide dropwise, raise the temperature to 85 °C, and heat under reflux for 7 hours. After evaporating the solvent, the oxide is obtained.

[0146] Example 29

[0147]

[0148] Synthesis of tertiary amine compound a29: Add 161 mg of 2-phenylpiperidine, 10 mL of DMF, and 301 mg of dimethyl 2-bromoisophthalate into a round-bottom flask in sequence. After stirring evenly to ensure complete dissolution of each component, add 106 mg of sodium carbonate. After stirring evenly to dissolve, heat up to 80 °C. After reacting for 9 hours, filter to obtain the filtrate. After rotary evaporation, the crude product is obtained, and column chromatography purification is carried out with an eluent ratio of petroleum ether / ethyl acetate of 10:1 to obtain the pure product.

[0149] Synthesis of tertiary amine oxide b29: Add 353 mg of tertiary amine compound a29 and 20 mL of ethanol into a flask, then heat up to 60 °C to fully dissolve the two. Slowly add 1.1 mL of 30% hydrogen peroxide drop by drop, raise the temperature to 85 °C, and reflux for 7 hours. After evaporating the solvent, the oxide is obtained.

[0150] Example 30

[0151]

[0152] Synthesis of tertiary amine compound a30: Add 161 mg of 2-phenylpiperidine, 10 mL of DMF, and 297 mg of 1,3-di-tert-butyl-2-bromobenzene into a round-bottom flask in sequence. After stirring evenly to ensure complete dissolution of each component, add 106 mg of sodium carbonate. After stirring evenly and dissolving, heat up to 80 °C and react for 9 hours. Then filter to obtain the filtrate, and after rotary evaporation, the crude product is obtained. Column chromatography purification is carried out with an eluent ratio of petroleum ether / ethyl acetate of 14:1 to obtain the pure product.

[0153] Synthesis of tertiary amine oxide b30: Add 349 mg of tertiary amine compound a30 and 20 mL of ethanol into a flask, then heat up to 60 °C to fully dissolve the two. Slowly add 1.1 mL of 30% hydrogen peroxide drop by drop, raise the temperature to 85 °C, and reflux for 7 hours. After evaporating the solvent, the oxide is obtained.

[0154] Example 31

[0155]

[0156] Synthesis of tertiary amine compound a31: Add 161 mg of 2-phenylpiperidine, 10 mL of DMF, and 271 mg of 2-bromo-1,3,5-trimethoxybenzene into a round-bottom flask in sequence. After stirring evenly to ensure complete dissolution of each component, add 106 mg of sodium carbonate. After stirring evenly and dissolving, heat up to 80 °C and react for 9 hours. Then filter to obtain the filtrate, and after rotary evaporation, the crude product is obtained. Column chromatography purification is carried out with an eluent ratio of petroleum ether / ethyl acetate of 9:1 to obtain the pure product.

[0157] Synthesis of tertiary amine oxide b31: Add 327 mg of tertiary amine compound a31 and 20 mL of ethanol into a flask, then heat up to 60 °C to fully dissolve the two. Slowly add 1.1 mL of 30% hydrogen peroxide drop by drop, raise the temperature to 85 °C, and reflux for 7 hours. After evaporating the solvent, the oxide is obtained.

[0158] Example 32

[0159]

[0160] Synthesis of tertiary amine compound a32: 161 mg of 2-phenylpiperidine, 10 mL of DMF, and 283 mg of 9-bromophenanthrene were successively added to a round-bottom flask. After stirring evenly to ensure complete dissolution of each component, 106 mg of sodium carbonate was added. After stirring evenly to dissolve, the temperature was raised to 80 °C. After reacting for 9 hours, the filtrate was obtained by filtration. After rotary evaporation, the crude product was obtained and purified by column chromatography with a petroleum ether / ethyl acetate eluent ratio of 9:1 to obtain the pure product.

[0161] Synthesis of tertiary amine oxide b32: 337 mg of tertiary amine compound a32 and 20 mL of ethanol were added to a flask, and then the temperature was raised to 60 °C to dissolve the two components fully. 1.1 mL of 30% hydrogen peroxide was added dropwise at a constant rate, and the temperature was raised to 85 °C, and heated under reflux for 7 hours. After evaporating the solvent, the oxide was obtained.

[0162] Comparative Example 1

[0163] Synthesis of tertiary amine oxide c1: 155 mg of 1,2,2,6,6,-pentamethylpiperidine and 20 mL of toluene were added to a flask, and then the temperature was raised to 70 °C to dissolve the two components fully. 2.5 mL of 30% hydrogen peroxide was added dropwise at a constant rate, and the temperature was raised to 90 °C and reacted for 6 hours. After evaporating the solvent, the oxide c1 was obtained, and its structure is shown in the following formula.

[0164]

[0165] Comparative Example 2

[0166] Synthesis of tertiary amine oxide c2: 145 mg of 3-(4-morpholino)-1-propanol and 20 mL of xylene were added to a flask, and then the temperature was raised to 75 °C to dissolve the two components fully. 2.5 mL of 30% hydrogen peroxide was added dropwise at a constant rate, and the temperature was raised to 100 °C and reacted for 8 hours. After evaporating the solvent, the oxide c2 was obtained, and its structure is shown in the following formula.

[0167]

[0168] Application test

[0169] To systematically explore the effects of different tertiary amine oxide regulators in various monomer copolymerization systems, we applied all the even-numbered tertiary amine oxide regulators in the examples and the two molecular weight regulators in the comparative examples to the polymerization reactions of different monomers, compared their performances in specific polymerization reactions, and systematically discussed the effects of the addition of different tertiary amine oxides on the final monomer conversion rate and weight-average molecular weight M w 、number-average molecular weight M n 、PDI and other indicators.

[0170] In the following table, unless otherwise specified, the reaction conditions and feedstocks are as follows:

[0171] 1 mol of tertiary amine oxide, 246 mg of azobisisobutyronitrile, 0.4 mol of a specific monomer, and 40 mL of toluene were successively added to a 100 mL Schlenk tube. After sealing, it was degassed by freezing and thawing with liquid nitrogen three times. After returning to room temperature, it was placed at a specific temperature for a specific reaction time. The reaction was terminated by freezing with liquid nitrogen. The solvent and unreacted monomers were removed by rotary evaporation under reduced pressure, and then placed in a vacuum oven to dry to a constant weight. The conversion rate, weight-average molecular weight, number-average molecular weight, and PDI were measured and calculated.

[0172] Table 1

[0173]

[0174]

[0175] Note: “—” in the table indicates that the polymerization reaction is difficult to occur under this condition.

[0176] It can be seen from the results in Table 1 that after adding the oxides of different high steric hindrance piperidine tertiary amine derivatives to the vinyl acetate reaction system, the molecular weight distribution can reach a maximum of 1.36 and a minimum of 1.20. Among them, tertiary amine oxide b30 corresponds to the lowest PDI of 1.20, which proves that the strategy of preparing a molecular weight regulator based on the oxidation of high steric hindrance piperidine tertiary amine derivatives is feasible, and the regulators of this structure can indeed effectively regulate the free radical polymerization process. Subsequently, the performance of tertiary amine oxide b30 in the polymerization of styrene, methyl methacrylate, and acrylonitrile monomers was discussed. The PDI obtained under the same reaction conditions was slightly higher, indicating that the piperidine-based tertiary amine oxide represented by b30 is more suitable in the vinyl acetate polymerization system, which may be related to the compatibility between the tertiary amine oxide and the monomer structure at the structural level.

[0177] To explore the performance of the structures obtained by oxidizing common tertiary amines in the same polymerization system, c1 and c2 were added. The PDI values obtained were both above 2.0, which were relatively close to the PDI of the blank group without adding tertiary amine oxide. Therefore, it is impossible to effectively regulate the polymerization process by oxidizing the existing tertiary amine structures. The effects of reaction temperature and reaction time were discussed, and it was found that the polymerization of vinyl acetate could not occur at 50 °C in this system. When the reaction time was extended to 12 h, both the PDI and M w both increased. The tertiary amine oxide of the present invention can accurately regulate the degree of polymerization in the vinyl acetate polymerization reaction, and the PDI range of the degree of polymerization is between 1.20 and 1.36.

[0178] The above embodiments are only illustrative of the principles and effects of the present application, and are not intended to limit the present application. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed in the present application should still be covered by the claims of the present application.

Claims

1. A high steric hindrance pyridine tertiary amine oxide, having the following molecular structural formula, (I) ， In the structural formula (I), R is mono- to deca-substituted, and the substituents are each independently selected from a hydrogen atom, a C 1-4 alkyl group, a benzyl group, an ester group, and a phenyl group; Ar is selected from an indenyl group, a fluorenyl group, a dimethylfluorenyl group, a naphthyl group, a substituted phenyl group, and a phenanthryl group; there is at least one substituent on the substituted phenyl group, and the substituents are independently selected from an ester group, an alkyl group, and an alkoxy group.

2. A method for synthesizing the high steric hindrance pyridine tertiary amine oxide according to claim 1, comprising the following steps: S1, Synthesis of the tertiary amine precursor: In a reaction vessel, a solvent, a secondary amine, and a halogenated hydrocarbon are added, and after fully dissolving and mixing evenly, an alkaline catalyst is further added, and the temperature is raised to 60 - 150 °C for reaction for 4 - 48 h to obtain a crude tertiary amine product; the halogenated hydrocarbon is a halogenated aromatic hydrocarbon or a halogenated cycloalkane; S2, Purification of the tertiary amine: The crude tertiary amine product is separated by column chromatography with a petroleum ether / ethyl acetate eluent with a volume ratio of 50:1 - 1:1 to obtain a pure tertiary amine product; S3, Synthesis of the tertiary amine oxide: The pure tertiary amine product and an organic solvent are added to a container, and the temperature is raised to 40 - 150 °C to fully dissolve it; then hydrogen peroxide is dropped into it, and the reaction is carried out for 3 - 72 h to obtain a tertiary amine oxide solution; S4, The tertiary amine oxide solution is obtained by removing the solvent through vacuum distillation to obtain the tertiary amine oxide.

3. The synthesis method of the high steric hindrance pyridine tertiary amine oxide according to claim 2, wherein In step S1, the molar ratio of the halogenated hydrocarbon to the secondary amine is 0.5 - 3:

1.

4. The synthesis method of the high steric hindrance pyridine tertiary amine oxide according to claim 2, wherein The secondary amine is selected from 2 - methylpiperidine, 3 - methylpiperidine, 4 - methylpiperidine, 2 - ethylpiperidine, 3 - ethylpiperidine, 4 - ethylpiperidine, 2 - n - propylpiperidine, 3 - n - propylpiperidine, 4 - n - propylpiperidine, 2 - isopropylpiperidine, 3 - isopropylpiperidine, 4 - isopropylpiperidine, 2 - n - butylpiperidine, 3 - n - butylpiperidine, 4 - n - butylpiperidine, 3 - isobutylpiperidine, 4 - isobutylpiperidine, 3 - (tert - butyl)piperidine, 4 - (3 - methylbutyl)piperidine, 2 - tert - butylpiperidine, 4 - (tert - butyl)piperidine, 4 - (sec - butyl)piperidine, 2,4,6 - trimethylpiperidine, 3,3,4 - trimethylpiperidine, 3,3,5 - trimethylpiperidine, 2,2,6,6 - tetramethylpiperidine, 3,3,5,5 - tetramethylpiperidine, 2,2,4,6 - tetramethylpiperidine, 2 - benzylpiperidine, 3 - benzylpiperidine, 4 - benzylpiperidine, methyl 2 - piperidinecarboxylate, methyl 3 - piperidinecarboxylate, methyl 4 - piperidinecarboxylate, ethyl 2 - piperidinecarboxylate, ethyl 3 - piperidinecarboxylate, ethyl 4 - piperidinecarboxylate, dimethyl piperidine - 2,5 - dicarboxylate, dimethyl piperidine - 2,6 - dicarboxylate, dimethyl piperidine - 3,5 - dicarboxylate, 2 - phenylpiperidine, 3 - phenylpiperidine, 4 - phenylpiperidine.

5. The synthesis method of the high steric hindrance pyridine tertiary amine oxide according to claim 2, wherein The halogenated aromatic hydrocarbon is selected from 2 - bromoindene, 1 - bromo - 9H - fluorene, 2 - bromofluorene, 3 - bromo - 9H - fluorene, 4 - bromo - 9H - fluorene, 9,9 - dimethyl - 2 - bromofluorene, 3 - bromo - 9,9 - dimethylfluorene, 4 - bromo - 9,9 - dimethylfluorene, 1 - bromonaphthalene, 2 - bromonaphthalene, ethyl 2 - bromobenzoate, tert - butyl 2 - bromobenzoate, dimethyl 2 - bromoisophthalate, 1 - bromo - 4 - tert - butyl - 2 - ethylbenzene, 2,6 - di - tert - butylbromobenzene, 1 - bromo - 2,6 - dimethoxybenzene, 1 - bromo - 2,4,6 - trimethoxybenzene, 3 - bromophenanthrene, 9 - bromophenanthrene.

6. The synthesis method of the high steric hindrance pyridine tertiary amine oxide according to claim 2, wherein, The basic catalyst is selected from sodium bicarbonate, potassium bicarbonate, sodium carbonate, potassium carbonate, cesium carbonate, sodium hydroxide, potassium hydroxide, calcium hydroxide, cesium hydroxide, sodium methoxide, potassium methoxide, sodium ethoxide, potassium ethoxide, sodium isopropoxide, trimethylamine, triethylamine, ethylenediamine, diethylamine, tert-butylamine, piperidine, pyridine, 4-dimethylaminopyridine, sodium tert-butoxide, potassium tert-butoxide, lithium diisopropylamide, n-butyllithium, tritylsodium.

7. The synthesis method of the high steric hindrance pyridine tertiary amine oxide according to claim 2, wherein The organic solvent is selected from benzene, toluene, ethylbenzene, xylene, dichloromethane, chloroform, carbon tetrachloride, dichloroethane, methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, acetone, butanone, cyclohexanone, diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, ethyl acetate, butyl acetate, dimethyl carbonate, diethyl carbonate, N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, hexamethylphosphoric triamide, sulfolane.

8. The synthesis method of the high steric hindrance pyridine tertiary amine oxide according to claim 2, wherein The molar ratio of the addition amount of the halogenated hydrocarbon to the addition amount of the secondary amine is 1-1.5:1, the molar ratio of the basic catalyst to the secondary amine is 1.2-1.8:1, and the molar ratio of hydrogen peroxide to the pure tertiary amine product is 8-20:

1.

9. The synthesis method of the high steric hindrance pyridine tertiary amine oxide according to claim 9, characterized in that, The reaction temperature in step S1 is 80±10°C, and the reaction time is 8±1 h; the reaction temperature in step S3 is 85±5°C, and the reaction temperature is 8±1 h.

10. Use of the high steric hindrance pyridine tertiary amine oxide according to any one of claims 1-9 in a radical polymerization reaction to obtain a polymerization product with a lower PDI.

11. A method for synthesizing a polymer product with a low PDI, characterized in that, In a reaction vessel, after adding a polymerization monomer, an azo initiator and an appropriate amount of solvent, add the high steric hindrance pyridine tertiary amine oxide according to any one of claims 1-9 in a molar ratio of 0.1-3% relative to the polymerization monomer. After sealing and freeze-thaw degassing several times, heat the system to 60-140°C. After reacting for 3-12 hours, immediately place it in liquid nitrogen to terminate the reaction, and rotary evaporate to remove the solvent and the remaining monomer to obtain a low PDI polymerization product.

12. The method for synthesizing a low PDI polymer product according to claim 12, characterized in that, The polymerization monomer is selected from vinyl acetate and its derivatives, vinyl pyrrolidone and its derivatives.

13. The method for synthesizing a low PDI polymerization product according to claim 12, characterized in that, The azo initiator is azobisisobutyronitrile, azobisisoheptonitrile, dimethyl azobisisobutyrate, azobis(isobutyramidine) dihydrochloride, azobis(2-methylpropionamidine) dihydrochloride, azobisisopentanenitrile, azoisobutyronitrile carboxamide.

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