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Patent Issued for Method for Producing Polymer Nanocomposite, and Flame-Retardant Polymer Nanocomposite Formed by the Production Method

June 17, 2014



By a News Reporter-Staff News Editor at Life Science Weekly -- Kyushu University, National University Corporation (Fukuoka, JP) has been issued patent number 8742044, according to news reporting originating out of Alexandria, Virginia, by NewsRx editors (see also Kyushu University, National University Corporation).

The patent's inventors are Takahara, Atsushi (Fukuoka, JP); Otsuka, Hideyuki (Fukuoka, JP); Kobayashi, Motoyasu (Fukuoka, JP); Yukutake, Hideaki (Saitama, JP); Kamimoto, Tetsuo (Saitama, JP).

This patent was filed on November 18, 2009 and was published online on June 3, 2014.

From the background information supplied by the inventors, news correspondents obtained the following quote: "Synthetic polymers (also referred to hereinafter as 'resins'), such as styrene resins, epoxy resins, silicone resins, polyurethane resins, phenolic resins, urea resins, polycarbonate resins, polyester resins, polyethylene resins, polypropylene resins, polyamide resins, polyimide resins, polyvinyl alcohol resins, styrene-butadiene-styrene resins, acrylonitrile-styrene resins, ethylene propylene rubber, acrylonitrile-butadiene-styrene resins, vinylidene chloride-acrylonitrile resins, vinylidene chloride-vinyl chloride resins, and ethylene-vinyl acetate resins, have already found use in various applications. Materials having the properties of inorganic compounds, such as high strength, high elastic modulus, heat resistance, and electric properties, while retaining the properties of polymers, such as flexibility, low specific gravity, and formability, are under active development as means for improving the various properties of resins, such as mechanical properties, heat resistance, and flame-retardant properties. So-called polymer nanocomposites--i.e., composite materials employing inorganic particles wherein at least one of the three dimensions thereof is in the nanoscale range--are receiving attention as such means for improving the resin properties, replacing conventional resins reinforced with fiberglass, talc, etc.

"Examples of such conventionally-used inorganic compounds include clay minerals, such as layered inorganic compounds. Clay minerals, however, have poor dispersibility to polymers. To tackle this problem, Patent Document 1, for example, proposes a method of displacing alkali metal ions contained in a layered inorganic compound with organic onium ions and making the compound organic, to facilitate the dispersion of the compound into polymers and improve the polymers' mechanical properties.

"The method of Patent Document 1, however, is still not at a satisfactory level, and there still have been demands for methods of producing polymer nanocomposites capable of improving both mechanical properties and heat resistance of the polymer matrix at the same time.

"Against this backdrop, studies are being conducted on a technique of starting radical polymerization in a monomer from the interlayer surface of a layered inorganic compound (called 'surface-initiated radical polymerization') to cause interlayer exfoliation and improve the dispersibility of the layered inorganic compound to resins. Non-Patent Documents 1 to 3 disclose methods of synthesizing polystyrene nanocomposites using montmorillonite modified with organic ammonium salts having the ability of initiating living free radical polymerization. The disclosed nanocomposites, however, have drawbacks in that the organic ammonium salts have poor heat resistance and that it takes a long time for the polymerization.

"The same goes for azo-based polymerization initiators: all known methods for immobilizing azo-based polymerization initiators onto the interlayer surface of layered inorganic compounds also involve introduction of an onium salt, such as an ammonium salt, into the azo-based polymerization initiator's molecule and immobilization thereof by utilizing electrostatic effects, thus giving rise to the above-described drawbacks regarding heat resistance etc. In addition, because the molecular weight distribution is not controlled as contrasted with living free radical polymerization initiators (Non-Patent Documents 1 and 2), the molecular weight distribution tends to become broad. Controlled molecular weight distribution intimately relates to the exfoliation and dispersion of layered inorganic compounds: a narrow molecular weight distribution means that the polymer will grow uniformly from the interlayer surface, which will contribute to the exfoliation and dispersion of the layered inorganic compound. In other words, a narrow molecular weight distribution benefits the exfoliation and dispersion of layered inorganic compounds, whereas polymers with a broad molecular weight distribution without controlled polymer growth tend to result in incomplete exfoliation and dispersion of layered inorganic compounds."

Supplementing the background information on this patent, NewsRx reporters also obtained the inventors' summary information for this patent: "Technical Problem

"An object of the present invention is to provide a method capable of producing, in a short time, a polymer nanocomposite in which the dispersibility of layered inorganic compounds to synthetic polymers--especially radically-polymerized polymers--is favorable and that has high molecular weight components and a narrow molecular weight distribution, by carrying out surface-initiated radical polymerization in a monomer from the interlayer surface, and also provide a method capable of producing a polymer nanocomposite in which the polymer has excellent heat resistance (thermal decomposition temperature) and flame-retardant properties.

"Solution to Problem

"In view of the above, Inventors have made diligent research to arrive at the present invention. That is, in this invention, the interlayer space of a layered inorganic compound is expanded using an organic onium salt, and then, a specific polymerization initiator is immobilized on the interlayer surface of the layered inorganic compound via a covalent bond. In this way, the organic onium salt used for the interlayer expansion can be removed from the system. Further, in the present invention, surface-initiated radical polymerization is carried out in a monomer from the specific polymerization initiator immobilized on the interlayer surface via the covalent bond, which allows polymerization to be achieved in a short time. Furthermore, Inventors have found that polymer nanocomposites made by the present production method have high molecular weight components and a narrow molecular weight distribution, exhibit improved dispersibility of the layered inorganic compound into the polymer, and can also improve the heat resistance and flame-retardant properties of the polymer matrix.

"A first aspect of the invention is a method for producing a polymer nanocomposite, including: after expanding an interlayer space of a layered inorganic compound using an organic onium salt, immobilizing a radical polymerization initiator having a group represented by general formula (1) shown below on an interlayer surface of the layered inorganic compound via a covalent bond; and carrying out surface-initiated radical polymerization in a monomer from the immobilized radical polymerization initiator:

"##STR00002## wherein, R.sup.1 represents a C.sub.1-25 alkylene group, a C.sub.2-25 alkenylene group, a C.sub.5-8 cycloalkylene group, or a C.sub.6-12 arylene group, each of which being optionally substituted by a C.sub.1-18 alkyl group, a phenyl group, or a cyano group and being optionally interrupted by an oxygen atom, a carbonyl group, an ester group, a phenylene group, an amide group, or an imino group, the substitution and the interruption being optionally combined with each other; and X.sup.1 to X.sup.3 each independently represent a halogen atom, a hydroxy group, a methyl group, an ethyl group, a methyloxy group, or an ethyloxy group.

"A second aspect of the invention is a polymer nanocomposite production method according to the first aspect of the invention, wherein, in the radical polymerization initiator having the group represented by the general formula (1), at least one of X.sup.1 to X.sup.3 in the formula is a chlorine atom.

"A third aspect of the invention is a polymer nanocomposite production method according to the first or second aspect of the invention, wherein, in the radical polymerization initiator having the group represented by the general formula (1), R.sup.1 in the formula is a C.sub.1-25 alkylene group or a C.sub.2-25 alkenylene group optionally interrupted by an oxygen atom or an ester group and optionally substituted by a phenyl group.

"A fourth aspect of the invention is a polymer nanocomposite production method according to any one of the first to third aspects of the invention, wherein a layered polysilicate selected from a group consisting of magadiite, kenyaite, makatite, kanemite, and ilerite is used as the layered inorganic compound.

"A fifth aspect of the invention is a polymer nanocomposite production method according to any one of the first to fourth aspects of the invention, wherein the radical polymerization initiator having the group represented by the general formula (1) and a silane compound represented by general formula (2) shown below are used in combination as compounds to be immobilized on the interlayer surface of the layered inorganic compound via covalent bonds:

"##STR00003## wherein, R.sup.2 represents a C.sub.1-25 alkyl group, a C.sub.2-25 alkenyl group, a C.sub.5-8 cycloalkyl group, or a C.sub.6-12 aryl group, each of which being optionally substituted by a C.sub.1-18 alkyl group, a phenyl group, or a cyano group and being optionally interrupted by an oxygen atom, a carbonyl group, an ester group, a phenylene group, an amide group, or an imino group, the substitution and the interruption being optionally combined with each other; and X.sup.1 to X.sup.3 each represent the same groups as X.sup.1 to X.sup.3 in the general formula (1).

"A sixth aspect of the invention is a polymer nanocomposite production method according to the fifth aspect of the invention, wherein, in the silane compound represented by the general formula (2), at least one of X.sup.1 to X.sup.3 in the formula is a chlorine atom.

"A seventh aspect of the invention is a polymer nanocomposite production method according to any one of the first to sixth aspects of the invention, wherein a nitroxide-based or azo-based polymerization initiator is used as the radical polymerization initiator having the group represented by the general formula (1).

"An eighth aspect of the invention is a polymer nanocomposite production method according to the seventh aspect of the invention, wherein a tetramethylpiperidine oxide-based compound represented by general formula (3) shown below is used as the nitroxide-based polymerization initiator:

"##STR00004## wherein, Y.sup.1 represents the group represented by the general formula (1); and R.sup.3 represents a hydrogen atom, an oxygen atom, a hydroxy group, a C.sub.1-8 straight-chain or branched alkyl group, a C.sub.1-8 alkoxy group, or a C.sub.5-8 cycloalkyl group, the alkyl group or the alkoxy group being optionally interrupted by an oxygen atom, a sulfur atom, a carbonyl group, an ester group, an amide group, or an imino group, the substitution and the interruption being optionally combined with each other.

"A ninth aspect of the invention is a polymer nanocomposite production method according to the eighth aspect of the invention, wherein, in the tetramethylpiperidine oxide-based compound represented by the general formula (3), R.sup.3 in the formula is a hydrogen atom, an oxygen atom, or a C.sub.1-8 alkoxy group.

"A tenth aspect of the invention is a polymer nanocomposite production method according to the seventh aspect of the invention, wherein an azo-based compound represented by general formula (4) shown below is used as the azo-based polymerization initiator:

"##STR00005## wherein, Y.sup.1 represents the group represented by the general formula (1); Y.sup.2 represents the group represented by the general formula (1) or a methyl group; and R.sup.4 to R.sup.7 each independently represent a methyl group or a nitrile group.

"An eleventh aspect of the invention is a polymer nanocomposite production method according to the tenth aspect of the invention, further including: adding, to the monomer, at least one of a nitroxide-based compound, an alkoxyamine-based compound, or an iodine-based compound as a molecular weight adjuster when performing the surface-initiated radical polymerization reaction from the azo-based compound represented by the general formula (4) immobilized on the interlayer surface of the layered inorganic compound.

"A twelfth aspect of the invention is a polymer nanocomposite production method according to any one of the first to eleventh aspects of the invention, wherein an organic ammonium salt, an organic pyridinium salt, an organic imidazolium salt, an organic phosphonium salt, or an organic sulfonium salt is used as the organic onium salt.

"A thirteenth aspect of the invention is a polymer nanocomposite made by the polymer nanocomposite production method according to any one of the first to twelfth aspects of the invention.

"A fourteenth aspect of the invention is a polymer nanocomposite according to the thirteenth aspect of the invention, characterized by being used as a flame-retardant material.

"Advantageous Effects of Invention

"The production method of the invention can improve the dispersibility of layered inorganic compounds into synthetic polymers, especially radically-polymerized polymers, can also improve the heat resistance (thermal decomposition temperature) and flame-retardant properties of such polymers, and can also produce polymer nanocomposites having high molecular weight components and a narrow molecular weight distribution in a short polymerization time."

For the URL and additional information on this patent, see: Takahara, Atsushi; Otsuka, Hideyuki; Kobayashi, Motoyasu; Yukutake, Hideaki; Kamimoto, Tetsuo. Method for Producing Polymer Nanocomposite, and Flame-Retardant Polymer Nanocomposite Formed by the Production Method. U.S. Patent Number 8742044, filed November 18, 2009, and published online on June 3, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8742044.PN.&OS=PN/8742044RS=PN/8742044

Keywords for this news article include: Anions, Styrenes, Chlorides, Chalcogens, Acrylonitrile, Nanocomposite, Nanotechnology, Flame Retardants, Hydrochloric Acid, Benzene Derivatives, Emerging Technologies, Kyushu University National University Corporation.

Our reports deliver fact-based news of research and discoveries from around the world. Copyright 2014, NewsRx LLC


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Source: Life Science Weekly


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