Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1999-04-05
2001-06-26
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S243000, C526S126000, C501S141000, C501S145000, C501S148000, C428S327000, C428S407000, C428S500000, C428S403000, C428S405000
Reexamination Certificate
active
06252020
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a method for preparing polymer composites. More particularly, it relates to a method for preparing a nanocomposite comprising a vinyl polymer matrix having dispersed therein layered silicate particles.
2. Description of the Related Arts
Nanocomposites are a new class of materials which exhibit ultrafine phase dimensions, typically in the range 1-100 nm. Experimental work on these materials has generally shown that virtually all types and classes of nanocomposites lead to new and improved properties when compared to their micro- and macrocomposite counterparts.
A specific category of polymer nanocomposites has been described as a composite material comprising a polymer matrix containing a polyamide having uniformly dispersed therein layers of silicate. This polyamide composite was reported to exhibit enhanced stiffness, strength, and heat resistance. The improvements in properties observed with these nanocomposites are significant when compared (on an equal weight basis of particulate filler) to those conventionally prepared composites.
In J. Mater. Sci.,31(13), 3589-3596, 1996, a method is disclosed for making polystyrene nanocomposites wherein montmorillonite which has been surface modified with vinylbenzyltrimethylammonium is mixed with styrene monomer and a suitable organic solvent and then polymerization is effected in the presence of the organic solvent. The interlayer spacing of the montmorillonite contained in the resulting composite is expanded to 1.72-2.45 nm (from 0.96 nm).
Similarly, in Japanese Laid Open Patent Application No. 63-215,775, a layered clay material is surface modified by a vinyl-containing ammonium salt by an ion exchange mechanism and then mixed with an organic solvent and a vinyl monomer, followed by polymerization. As further background for the preparation of vinyl polymer nanocomposite, attention is directed to Japanese Laid Open Patent Application No. 08-151,449.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a method for preparing a vinyl polymer nanocomposite in which layered silicate particles are uniformly dispersed within the polymeric matrix.
The present method for nanocomposite preparation involves dispersion of a layered clay material which has been surface modified with a surfactant and optionally a silane coupling agent in a vinyl monomer, followed by bulk polymerization and suspension polymerization.
The method according to the invention includes the sequential steps of: (a) modifying a clay material comprising layered silicate particles by ion exchange with a surfactant to form an organically modified clay; (b) optionally, functionalizing the organically modified clay by treatment with an organofunctional silane; (c) dispersing the silane-treated clay in a vinyl monomer and bulk polymerizing the monomer in the presence of a catalyst; and (d) adding a liquid suspension to the above mixture to effect suspension polymerization when the conversion rate of the polymerization is about 10% to 50%, thereby forming a composite having the particles uniformly dispersed in a vinyl polymer matrix.
In the present invention, organically modified clays, hereinafter referred to as “organoclays”, are used as the mineral component of the composite. In general, organoclays represent the reaction product of a layered clay with a higher alkyl containing ammonium compound (often a quaternary). The clay materials used in the invention are layered clay minerals having exchangeable cations between the layers which can be reacted with a surfactant to form the organoclay products and can be intercalated by reactive organo silanes via an insertion mechanism. Illustrative of such layered clay materials are montmorillonite, mica, talc, and the like.
At the outset, a cation-type ammonium surfactant is used to surface modify the layered clay material. Illustrative of such surfactants are pyridinium salts and quaternary ammonium salts that have at least one alkyl group containing at least 12 carbon atoms, such as cetylpyridinium chloride, cetyltrimethyl-ammonium chloride, and the like.
In step (b), the organoclay is functionalized by organofunctional silanes which preferably have a functional group selected from one or more members of the group consisting of vinyl, epoxy, and acrylic groups. Illustrative of such silane coupling agents are vinyltriethoxysilane, 3-methacryloxypropyl-trimethoxysilane, 3-glycidyloxypropyltrimethoxysilane, and the like.
In step (c), the functionalized organoclay is dispersed in a vinyl monomer, followed by bulk polymerization. The polymerization may be effected at a temperature ranging from 50° C. to 100° C. Preferably the clay material is present in an amount of 0.05% to 30% by weight based on the weight of the vinyl monomer. In the case where the clay amount is greater than 30%, the resulting composite has inferior processability, while in the case where the clay amount is less than 0.05%, no strengthening action to the composite is observed. Illustrative examples of vinyl monomers include styrene monomers, acrylonitrile monomers, and acrylic monomers. Illustrative examples of catalysts for polymerization of vinyl monomers include organo peroxides such as benzoyl peroxide (BPO) and lauroyl peroxide (LPO), and diazo compounds such as azobisisobutyronitrile (AIBN).
In step (d), a liquid suspension is added to the reaction mixture of step (c) when the conversion rate of the bulk polymerization is about 10% to 50% so as to effect suspension polymerization. The liquid suspension is preferably an aqueous suspension of polyvinyl alcohol or inorganic salts such as magnesium carbonate.
According to a feature of the invention, an intercalated material is first prepared by surface modifying a layered silicate with an alkyl ammonium salt and optionally an organofuntional silane. The layered silicate suitable for used herein has a cation-exchange capacity ranging from 50 to 200 meq/100 g. The X-ray diffraction analysis of the intercalated silicates shows a interlayer spacing (d
001
) of more than 17 Å.
According to another feature of the invention, a polymer nanocomposites having uniformly dispersed layered silicate is obtained by dispersing the intercalated silicate in a vinyl monomer and then proceeding bulk polymerization and suspension polymerization sequentially. The X-ray diffraction analysis of the intercalated silicates contained in the nanocomposite shows a interlayer spacing (d
001
) of more than 31 Å.
The polymer nanocomposites of the invention may be a styrene-based composite comprising polystyrene (PS), styrene-acrylonitrile (SAN), high impact polystyrene (HIPS), or acrylonitrile-butadiene-styrene (ABS); or an acrylic-based composite comprising, for example, polymethyl methacrylate.
Other objects, features, and advantages of the present invention will become apparent from the following detailed description which makes reference to the accompanying drawings.
REFERENCES:
patent: 3696172 (1972-10-01), Kaiho et al.
patent: 4618528 (1986-10-01), Sacks et al.
patent: 5073447 (1991-12-01), Mizuno et al.
patent: WO 97/00910 (1997-01-01), None
Kuo Wen-Faa
Lee Mao-Song
Liao Chien-Shiun
Choi Ling-Siu
Darby & Darby
Industrial Technology Research Institute
Wu David W.
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