Method for producing nitroxide, and curable composition

Abstract

Provided are: a method for producing a nitroxide having excellent safety without using a peroxide such as hydrogen peroxide; and a curable composition having excellent curing temperature, curing speed and wettability.　A nitroxide is generated without using a peroxide by simultaneously irradiating a reactive compound with atmospheric-pressure, low-temperature plasma and ultrasonic waves, and a curable composition having excellent curing temperature, curing rate, and wettability can be obtained by constituting the curable composition using the reactive compound containing the nitroxide.

Description

Method for producing nitroxides and curable compositions

[0001] This invention relates to a method for producing nitroxide and a curable composition. More specifically, it relates to a method for producing nitroxide that can be obtained with excellent safety without using peroxides, and a curable composition containing nitroxide.

[0002] Traditionally, radicals have been recognized as highly reactive and unstable intermediates. However, stable radicals with kinetic and thermodynamic stability are known through stabilization via electronic effects (delocalization of unpaired electrons in radicals) and steric effects (inhibition of various reactions or suppression of dimerization due to steric hindrance near the radical center).

[0003] Among stable radicals, nitroxides are widely used in various industries due to their versatility. Examples of nitroxides include 2,2,6,6-tetramethylpiperidine 1-oxyl (hereinafter referred to as "TEMPO") and 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (hereinafter referred to as "TEMPO"). Various methods exist for producing nitroxides, but in all cases, nitroxide formation is achieved by reacting a nitroxide precursor such as an amine with a peroxide, such as hydrogen peroxide. For example, Patent Document 1 describes that (meth)acrylic acid nitroxide polymers can be safely and inexpensively obtained by reacting an imine polymer with hydrogen peroxide in an amide solvent in the presence of a tungstic acid catalyst and phosphonic acids, while reducing the amount of hydrogen peroxide used in nitration.

[0004] On the other hand, it is known that by bonding nitroxides such as TEMPO and TEMPOL to the side chains of polymers including acrylic, epoxy, urethane, etc., functions such as weather resistance, flame retardancy, and redox ability can be imparted to the polymers. For example, Patent Document 2 describes that a curable composition containing an isocyanate group-containing compound having a nitroxide free radical is excellent in weather resistance. Patent Document 3 describes that a curable composition containing a room-temperature curable resin that reacts with an active hydrogen-containing compound and crosslinks and cures and a compound having a nitroxide free radical with a number average molecular weight of 2,000 or more is excellent in workability, anti-pollution property, weather resistance, and rubber physical properties.

[0005] Japanese Patent Application Laid-Open No. 2013-87256, Japanese Patent Application Laid-Open No. 2015-140383, Japanese Patent Application Laid-Open No. 2017-31399

[0006] However, in the invention described in Patent Document 1, the amount of hydrogen peroxide used cannot be made zero even when using a tungstic acid catalyst. Further, in the inventions described in Patent Document 2 and Patent Document 3, since a curable composition is synthesized using nitroxide as a starting material, the manufacturing method of nitroxide itself is not described, and the curing temperature, curing rate, and wettability in the curable composition are also not described. Therefore, a highly safe method for producing nitroxide and a curable composition excellent in curing temperature, curing rate, and wettability have been demanded.

[0007] The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for producing nitroxide with excellent safety that does not use peroxides including hydrogen peroxide, and further, an object thereof is to provide a curable composition excellent in curing temperature, curing rate, and wettability.

[0008] The present invention provides a method for producing nitroxide that solves the above problems, characterized by simultaneously irradiating a reactive compound with atmospheric pressure low-temperature plasma and ultrasound. Furthermore, the curable composition according to the present invention, which solves the above problems, is characterized by containing nitroxide produced by the nitroxide production method according to the present invention. The reactive compound can be selected from compounds having one or more vinyl groups or vinylidene groups in its molecule. The reactive compound preferably has a vapor pressure of 0.001 to 50 Pa at room temperature. The discharge gas of the atmospheric pressure low-temperature plasma is preferably nitrogen or a nitrogen-containing mixed gas. The frequency of the ultrasound is preferably 28 to 120 kHz.

[0009] According to the present invention, by simultaneously irradiating a reactive compound with atmospheric pressure low-temperature plasma and ultrasound, a nitroxide is generated without using a peroxide. Furthermore, by constructing a curable composition with the stable radical-containing reactive compound, a curable composition with excellent curing temperature, curing speed, and wettability can be obtained.

[0010] This is a diagram illustrating the main components of an example of a manufacturing apparatus used in the nitroxide manufacturing method according to the present invention. This is a graph of an electron spin resonance spectrum showing an example of a nitroxide produced by the nitroxide manufacturing method according to the present invention.

[0011] Embodiments of the present invention will be described in detail below. In the following example, a nitroxide is generated by simultaneously irradiating a reactive compound with atmospheric pressure low-temperature plasma and ultrasound, and a curable composition is obtained from the stable radical-containing reactive compound. It should be noted that the embodiments shown herein are just one aspect of the configuration of the present invention, and the present invention is not limited to these configurations.

[0012] [Reactive Compounds] As reactive compounds, compounds having one or more vinyl or vinylidene groups, which are reactive functional groups, in their molecule are preferred, such as vinyl compounds and vinylidene compounds. The composition of the reactive compound may be single or a mixture, but it is preferred to be in a liquid state at room temperature. The vapor pressure of the reactive compound is preferably 100 Pa or less at room temperature, and particularly preferably in the range of 0.001 to 50 Pa. The molecular weight is preferably 100 or more, and particularly preferably in the range of 120 to 25,000.

[0013] Reactive compounds having one vinyl group or vinylidene group in their molecule include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-propyl acrylate, n-propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, sec-butyl acrylate, sec-butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, n-pentyl acrylate, n-pentyl methacrylate, and Isopentyl acrylate, isopentyl methacrylate, sec-pentyl acrylate, sec-pentyl methacrylate, neopentyl acrylate, neopentyl methacrylate, cyclopentyl acrylate, cyclopentyl methacrylate, n-hexyl acrylate, n-hexyl methacrylate, isohexyl acrylate, isohexyl methacrylate, sec-hexyl acrylate, sec-hexyl methacrylate, tert-hexyl acrylate, tert-hexyl methacrylate, neohexyl acrylate, neohexyl methacrylate, acrylic acid Cyclohexyl, cyclohexyl methacrylate, n-heptyl acrylate, n-heptyl methacrylate, isoheptyl acrylate, isoheptyl methacrylate, sec-heptyl acrylate, sec-heptyl methacrylate, cycloheptyl acrylate, cycloheptyl methacrylate, n-octyl acrylate, n-octyl methacrylate, isooctyl acrylate, isooctyl methacrylate, sec-octyl acrylate, sec-octyl methacrylate, cyclooctyl acrylate, cyclooctyl methacrylate, n-nonyl acrylate, methacrylate n-nonyl acrylate, isononyl acrylate, isononyl methacrylate, sec-nonyl acrylate, sec-nonyl methacrylate, n-decyl acrylate, n-decyl methacrylate, isodecyl acrylate, isodecyl methacrylate, sec-decyl acrylate, sec-decyl methacrylate, cyclodecyl acrylate, cyclodecyl methacrylate, undecyl acrylate, undecyl methacrylate, dodecyl acrylate, dodecyl methacrylate, cyclododecyl acrylate, cyclododecyl methacrylate, tridecyl acrylate, tridecyl methacrylate,Tetradecyl acrylate, tetradecyl methacrylate, pentadecyl acrylate, pentadecyl methacrylate, hexadecyl acrylate, hexadecyl methacrylate, heptadecyl acrylate, heptadecyl methacrylate, octadecyl acrylate, octadecyl methacrylate, nonadecyl acrylate, nonadecyl methacrylate, eicosyl acrylate, eicosyl methacrylate, phenyl acrylate, phenyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, methacrylate 2-Hydroxypropyl Acrylate, 3-Hydroxypropyl Acrylate, 3-Hydroxypropyl Methacrylate, 2-Hydroxybutyl Acrylate, 2-Hydroxybutyl Methacrylate, 3-Hydroxybutyl Acrylate, 3-Hydroxybutyl Methacrylate, 4-Hydroxybutyl Acrylate, 4-Hydroxybutyl Methacrylate, 6-Hydroxyhexyl Acrylate, 6-Hydroxyhexyl Methacrylate, 2-Methoxyethyl Acrylate, 2-Methoxyethyl Methacrylate, 3-Hydroxypropyl Acrylate, 3-Hydroxypropyl Methacrylate , acrylamide, methacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-isopropylacrylamide, N-isopropylmethacrylamide, 2-aminoethyl acrylate, 2-aminoethyl methacrylate, 2-(dimethylamino)ethyl acrylate, 2-(dimethylamino)ethyl methacrylate, 2-(diethylamino)ethyl acrylate, 2-(diethylamino)ethyl methacrylate, tetrahydrofurfuryl acrylate, tetrahydrofuryl methacrylate, vinyltrimethoxysilane, vinyltriethoxysilane, p - Styryltrimethoxysilane, 3-acryloxypropylmethyldimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 2,2,2-trifluoroethyl acrylate, 2,2,2-trifluoroethyl methacrylate, 2-(perfluorobutyl)ethyl acrylate, 2-(perfluorobutyl)ethyl methacrylate, (perfluorocyclohexyl)methyl acrylate,Examples include methyl perfluorocyclohexyl methacrylate, glycidyl acrylate, and glycidyl methacrylate.

[0014] Reactive compounds having two vinyl groups or vinylidene groups in their molecule include ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol dimethacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, tetraethylene glycol diacrylate, tetraethylene glycol dimethacrylate, dipropylene glycol diacrylate, dipropylene glycol dimethacrylate, tripropylene glycol diacrylate, tripropylene glycol dimethacrylate, 1,3-butylene glycol diacrylate, 1,3-butylene glycol dimethacrylate, allyl acrylate, and allyl methacrylate.

[0015] Examples of reactive compounds having three vinyl or vinylidene groups in their molecule include trimethylolpropane triacrylate and trimethylolpropane trimethacrylate.

[0016] <Nitroxide Production Apparatus> The nitroxide production apparatus comprises a plasma irradiation device 1 that irradiates the reactive compound with plasma, and an ultrasonic irradiation device 2 that irradiates the reactive compound with ultrasound.

[0017] [Plasma] As the plasma, it is preferable to use atmospheric pressure plasma (plasma that is stably generated in normal atmospheric pressure without depressurization), and it is particularly preferable to use, for example, a non-equilibrium plasma jet or atmospheric pressure low-temperature plasma produced by AC pulse discharge (see, for example, Japanese Patent Application Publication No. 2020-140794).

[0018] A plasma irradiation device is a device that irradiates a reactive compound with plasma at atmospheric pressure or a pressure approximately equal to atmospheric pressure. The example shown here includes an electrode pair consisting of a first electrode 4 and a second electrode (ground electrode) 5 connected to a power supply, and a gas flow generator 3 that supplies discharge gas to the space (gas flow path) provided between the electrode pair to generate a gas flow toward the reactive compound.

[0019] The first electrode 4 and the second electrode 5 are arranged opposite each other via a slit 7 of uniform width that serves as a gas flow path. For example, by adopting a configuration in which a dielectric layer 6 is placed between the electrode pair, as shown in Figure 1, the discharge current can be reduced and the plasma temperature can be lowered. The first electrode 4 and the second electrode 5 can be made of conductive materials such as tungsten, molybdenum, aluminum, copper, carbon, or stainless steel. The dielectric layer 6 can be made of a material with a relative permittivity of about 2.0 to 10.0 that is resistant to plasma. For example, dielectric materials such as silicone resin (silicone rubber), polyethylene resin, polyester resin, nylon resin, natural rubber, neoprene, glass, or ceramics can be used.

[0020] [Discharge Gas] For plasma generation, nitrogen, argon, or helium, or a mixed gas containing any of these, can be used as the discharge gas. The nitrogen concentration in the discharge gas is preferably 80 vol% or more, and particularly preferably 99 vol% or more. The discharge gas pressure is preferably 1.0 MPa or less, and particularly preferably 0.1 to 0.3 MPa, considering the vapor pressure of the reactive compound. The gas flow rate is preferably 50 liters / min or less, and particularly preferably 10 liters / min or less, considering the vapor pressure of the reactive compound. The gas flow generator 3 is one that has the ability to create the above conditions and environment in a sealed reaction chamber.

[0021] [Ultrasound] The ultrasonic frequency is preferably in the range of 28 to 1000 kHz, and particularly preferably in the range of 28 to 120 kHz. The ultrasonic irradiation device 2 consists of an oscillation means 8 and a processing tank 9 that receives ultrasonic vibrations generated by the oscillation means 8. The oscillation means 8 is equipped with a transducer 10 that vibrates when a voltage is applied, and is a means for transmitting the vibrations of the transducer 10 to the processing tank 9. The processing tank 9 transmits the vibrations to a vibrating medium (liquid) stored inside, and the vibrating medium transmits the vibrations to the object to be processed immersed in the processing tank 9. The reactive compound to be processed is a liquid or gel-like fluid at room temperature, so it is placed in a plasma-resistant processing container 11 with an open top and is positioned in the processing tank 9 facing the outlet of the slit 7, which is the gas flow path for the discharge gas.

[0022] [Operation of the Nitroxide Production Apparatus] The plasma irradiation device 1 of the nitroxide production apparatus generates plasma by applying a voltage of several kilovolts to tens of kilovolts between a pair of electrodes facing each other via a dielectric layer 6 and a slit 7. The gas flow generator 3 supplies discharge gas into the generated plasma and injects the plasma-like gas toward the reactive compound. This remote plasma method has the advantage that, since voltage is not directly applied to the reactive compound, it does not cause electrical damage to the reactive compound and the heat (plasma temperature) can be kept low. The plasma temperature is preferably 100°C or less, and particularly preferably 0 to 100°C, considering the vapor pressure of the reactive compound. The plasma irradiation distance is preferably 100 mm or less, and particularly preferably 60 mm or less.

[0023] The ultrasonic irradiation device 2 of the nitroxide production apparatus operates almost simultaneously with the plasma irradiation device 1, and generates ultrasonic waves by applying an electrical signal to the transducer 10, causing the transducer 10 to vibrate. The transducer 10 transmits ultrasonic waves to the reactive compound in the processing container 11 via the processing tank 9, the liquid (water) in the processing tank 9, and the processing container 11. In this way, irradiating the reactive compound with ultrasonic waves provides a stirring effect on the reactive compound in the processing container 11, as well as sonochemical effects depending on the selection of the frequency band. By adjusting the frequency within the preferred range described above, the cavitation effect on the reactive compound can be adjusted according to the desired function.

[0024] [Curable Composition] The curable composition is composed of a stable radical-containing reactive compound obtained by irradiating the reactive compound with atmospheric pressure low-temperature plasma and ultrasound. The concentration of the stable radical-containing reactive compound in the curable composition is preferably 5% by mass or more, and particularly preferably 20% by mass or more. The composition of the curable composition may be a single compound or a mixture.

[0025] In addition to the components mentioned above, the curable composition of the present invention may contain monomers, oligomers, polymers, various solvents, polymerization initiators, polymerization inhibitors, curing accelerators, gelling agents, dispersants, surfactants, fillers, plasticizers, adhesion promoters, tackifiers, property modifiers, dehydrating agents, UV absorbers, antioxidants, flame retardants, colorants, friction inhibitors, and the like.

[0026] [Uses of the curable composition] Depending on the components it contains, the curable composition can be used in adhesives, sealants, paints, coatings, batteries, spin labels, inks, and the like.

[0027] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0028] Manufacturing Example 1 [Production of Stable Radical-Containing Reactive Compound A] 10 g of 2-hydroxyethyl methacrylate (hereinafter referred to as "HEMA"), a reactive compound, was placed in a beaker. While maintaining the HEMA temperature at 60°C, the HEMA was simultaneously irradiated for 15 minutes with atmospheric pressure low-temperature plasma (discharge gas: nitrogen, discharge gas pressure: 0.28 MPa, discharge gas flow rate: 8 liters / min, discharge voltage: 8.5 kV, irradiation distance: 55 mm) and ultrasound at a frequency of 40 kHz to obtain stable radical-containing reactive compound A. The radicals generated by the simultaneous irradiation of atmospheric pressure low-temperature plasma and ultrasound were confirmed to be nitroxides from the electron spin resonance (ESR) results of stable radical-containing reactive compound A. Figure 2 shows the ESR spectrum of stable radical-containing reactive compound A.

[0029] Manufacturing Example 2 [Production of Stable Radical-Containing Reactive Compound B] 10 g of 4-hydroxybutyl acrylate (hereinafter referred to as "4-HBA"), a reactive compound, was placed in a beaker. While maintaining the temperature of the 4-HBA at 60°C, the 4-HBA was simultaneously irradiated for 15 minutes with atmospheric pressure low-temperature plasma (using nitrogen as the discharge gas, a discharge gas pressure of 0.28 MPa, a discharge gas flow rate of 8 liters / minute, a discharge voltage of 8.5 kV, and an irradiation distance of 55 mm) and ultrasound at a frequency of 40 kHz to obtain stable radical-containing reactive compound B. The radicals generated by the simultaneous irradiation of atmospheric pressure low-temperature plasma and ultrasound were confirmed to be nitroxides from the ESR results of stable radical-containing reactive compound B.

[0030] Manufacturing Example 3 [Production of Stable Radical-Containing Reactive Compound C] 10 g of 2-hydroxypropyl methacrylate (hereinafter referred to as "HPMA"), a reactive compound, was placed in a beaker. While maintaining the temperature of HPMA at 60°C, the HPMA was simultaneously irradiated for 15 minutes with atmospheric pressure low-temperature plasma (discharge gas: nitrogen, discharge gas pressure: 0.28 MPa, discharge gas flow rate: 8 liters / min, discharge voltage: 8.5 kV, irradiation distance: 55 mm) and ultrasound at a frequency of 40 kHz to obtain stable radical-containing reactive compound C. The radicals generated by the simultaneous irradiation of atmospheric pressure low-temperature plasma and ultrasound were confirmed to be nitroxides from the ESR results of stable radical-containing reactive compound C.

[0031] Manufacturing Example 4 [Production of Stable Radical-Containing Reactive Compound D] 10 g of tripylene glycol diacrylate (hereinafter referred to as "TPGDA"), a reactive compound, was placed in a beaker. While maintaining the temperature of TPGDA at 60°C, the TPGDA was simultaneously irradiated for 15 minutes with atmospheric pressure low-temperature plasma (discharge gas: nitrogen, discharge gas pressure: 0.28 MPa, discharge gas flow rate: 8 liters / min, discharge voltage: 8.5 kV, irradiation distance: 55 mm) and ultrasound at a frequency of 40 kHz to obtain stable radical-containing reactive compound D. The radicals generated by the simultaneous irradiation of atmospheric pressure low-temperature plasma and ultrasound were confirmed to be nitroxides from the ESR results of stable radical-containing reactive compound D.

[0032] Manufacturing Example 5 [Production of Stable Radical-Containing Reactive Compound E] 10 g of trimethylolpropane triacrylate (3), a reactive compound, was placed in a beaker. While maintaining the temperature of the PTMPTA at 60°C, the PTMPTA was simultaneously irradiated for 15 minutes with atmospheric pressure low-temperature plasma (using nitrogen as the discharge gas, a discharge gas pressure of 0.28 MPa, a discharge gas flow rate of 8 liters / min, a discharge voltage of 8.5 kV, and an irradiation distance of 55 mm) and ultrasound at a frequency of 40 kHz to obtain stable radical-containing reactive compound E. The radicals generated by the simultaneous irradiation of atmospheric pressure low-temperature plasma and ultrasound were confirmed to be nitroxides from the ESR results of stable radical-containing reactive compound E.

[0033] Examples 1-7 [Preparation of Curable Compositions] The stable radical-containing reactive compounds obtained in the above production examples were mixed according to the formulations shown in Table 1 to obtain curable compositions. The curing temperature of the obtained curable compositions was evaluated by the following method. The results are shown in Table 1.

[0034] [Evaluation of curing temperature] 1 g of the prepared curable composition was placed in a high-pressure reaction vessel made of polytetrafluoroethylene under a nitrogen atmosphere, and a thermal polymerization reaction was carried out in an electric furnace at 25 to 200°C for 100 minutes. The degree of curing of the obtained thermal polymerization product was checked according to the evaluation criteria below, and the curing temperature was evaluated. The results are shown in Table 1. (Evaluation criteria) ◎: Cured uniformly and changed to a solid. ○: Partially gelled. ×: No change from liquid.

[0035]

[0036] Comparative Examples 1-7 [Preparation of Comparative Compositions] Comparative compositions were prepared by mixing reactive compounds that had not been irradiated with atmospheric pressure low-temperature plasma and ultrasound, according to the formulations shown in Table 2.

[0037] [Evaluation of curing temperature] The curing temperature was evaluated using the same method as in Examples 1 to 7. The results are shown in Table 2.

[0038]

[0039] Tables 1 and 2 show that the curable compositions of the examples had lower curing temperatures and superior curability in the thermal polymerization reaction compared to the comparative examples.

[0040] Examples 8-9 [Preparation of Curable Compositions] The stable radical-containing reactive compounds obtained in the above production examples were mixed with the photopolymerization initiator 1-hydroxycyclohexylphenyl ketone (hereinafter referred to as "HCPK") in the formulations shown in Table 3 to obtain curable compositions. The curing rate of the obtained curable compositions was evaluated by the following method. The results are shown in Table 3.

[0041] [Evaluation of curing speed] 1.5 g of the prepared curable composition was placed in a glass bottle and irradiated with 365 nm light from a UV lamp for 50 to 350 seconds under a nitrogen atmosphere to carry out the photopolymerization reaction. The results are shown in Table 3. The degree of curing of the obtained photopolymerized product was checked according to the evaluation criteria below, and the curing speed was evaluated. The results are shown in Table 3. (Evaluation criteria) ○: Partially gelled. ×: No change from liquid.

[0042]

[0043] Comparative Examples 8 to 10 [Production of Comparative Compositions] The comparative compositions were each mixed using reactive compounds not irradiated with atmospheric pressure low-temperature plasma and ultrasonic waves so as to have the formulations shown in Table 4.

[0044] [Evaluation of Curing Rate] The evaluation of the curing rate was carried out in the same manner as in Examples 8 to 10. The results are shown in Table 4.

[0045]

[0046] From Tables 3 and 4, it was found that the curable compositions of the examples are superior in the curing rate in the photopolymerization reaction to the comparative examples.

[0047] Examples 11 to 13 [Production of Curable Composition] The stable radical-containing reactive compound obtained in the above production example was prepared according to the formulations in Table 5, and the wettability was evaluated by the following method. The results are shown in Table 5.

[0048] [Evaluation of Wettability] The produced curable composition was dropped onto a substrate made of polytetrafluoroethylene using a contact angle measuring device, and the contact angle at room temperature was measured. The results are shown in Table 5.

[0049]

[0050] Comparative Examples 11 to 13 [Production of Comparative Compositions] The comparative compositions were prepared using reactive compounds not irradiated with atmospheric pressure low-temperature plasma and ultrasonic waves so as to have the formulations shown in Table 6.

[0051] [Evaluation of Wettability] The evaluation of the wettability was carried out in the same manner as in Examples 11 to 13. The results are shown in Table 6.

[0052]

[0053] From Tables 5 and 6, it was found that the curable compositions of the examples have a smaller contact angle and are superior in wettability to the comparative examples.

[0054] 1 Plasma irradiation device, 2 Ultrasonic irradiation device, 3 Gas flow generation device, 4 First electrode, 5 Second electrode, 6 Dielectric layer, 7 Slit, 8 Oscillation means, 9 Treatment tank, 10 Vibrator, 11 Treatment container

Claims

1. A method for producing nitroxides by simultaneously irradiating a reactive compound with atmospheric pressure low-temperature plasma and ultrasound.

2. The method for producing a nitroxide according to claim 1, characterized in that the reactive compound is a compound having one or more vinyl groups or vinylidene groups in its molecule.

3. The method for producing a nitroxide according to claim 1, characterized in that the reactive compound has a vapor pressure of 0.001 to 50 Pa at room temperature.

4. The method for producing nitroxide according to claim 1, characterized in that the discharge gas of the atmospheric pressure low-temperature plasma is nitrogen or a nitrogen-containing mixed gas.

5. The method for producing nitroxide according to claim 1, characterized in that the frequency of the ultrasonic waves is 28 to 120 kHz.

6. A curable composition containing a nitroxide produced by the nitroxide production method described in claim 1, claim 2, claim 3, claim 4, or claim 5.

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