Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-10-24
2002-08-13
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S529000, C524S533000, C524S555000, C524S556000, C524S558000, C524S559000, C524S560000
Reexamination Certificate
active
06433061
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is directed to a rheology-modifying copolymer composition utilizing a hydrophobic chain transfer agent which provides increased viscosity in electrolyte-containing environments.
2. Description of the Prior Art
Polymeric rheology modifiers provide various rheological properties to aqueous systems, including thickening and viscosity. For example, various such aqueous compositions may provide improved stability, pigment suspension and application properties. Various rheological modified compositions for cosmetics and personal care items provide smoothness and silkiness, while in pharmaceutical applications, the compositions can provide suspension of insoluble materials or controlled release of pharmaceutical actives, or bioadhesive properties.
Carboxyl-containing polymers of vinyl or vinylidene monomers containing at least one terminal CH
2
═C< for use as rheology modifiers are well-known. Such polymers can be homopolymers of unsaturated polymerizable carboxylic acids, such as acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid, and the like. The polymers may also be copolymers of the aforesaid acids or anhydride monomers with (meth)acrylate esters, (meth)acrylamides, olefins, maleic anhydrides, vinyl esters, vinyl ethers, and styrenics, or copolymers with other vinyl or vinylidene monomers. Copolymers of these acids are often crosslinked with small amounts of crosslinking agents. Such polymers have been disclosed in U.S. Pat. Nos. 2,798,053, 3,915,921, 3,940,351, 4,062,817, 4,066,583, 4,267,103, 5,349,030, and 5,373,044.
These rheology-modifying polymers, however, are frequently pH dependent, are hydrolytically unstable, require their use in large amounts to effectively increase viscosity, or are sensitive to ionic components of the formulation. Additionally, these polymers are efficient only in aqueous systems having no electrolyte, such as sodium chloride.
Naturally occurring substances are also known for use as rheology modifiers in aqueous systems. Natural rheology modifiers include casein, alginates, gum tragacanth, and modified cellulose, including methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose and carbomethoxy cellulose. These products, however, vary in their thickening efficiency, generally provide poor flow and leveling properties, and are subject to microbial attack, thereby requiring the presence of antimicrobial agents.
The use of “associative” thickeners as rheology modifiers in aqueous systems is also known in the art. An associative thickener refers to a water-soluble or water-swellable polymer having chemically attached groups capable of hydrophobic associations similar to those of conventional surfactants. These hydrophobic associations promote water insolubility and include such chemical groups as alkyl and aralkyl groups containing from about 4 to about 30 carbon atoms, or complex hydrophobic comonomers. Such associative thickeners have been disclosed in U.S. Pat. No. 4,384,096 which describes associative polymers made via emulsion polymerization known as Hydrophobically-Modified Alkali-Soluble Emulsion Polymers (HASE). These polymers include both complex hydrophobes and conventional hydrophobes. However, while small amounts (0.01 to 5% by weight of monomer) of mercaptan-containing chain transfer agents have been disclosed for use in the polymerization of the HASE polymers, their use is not recommended as the mercaptan-containing chain transfer agent reduces the molecular weight of the polymer and, therefore, the polymer's thickening efficiency.
SUMMARY OF THE INVENTION
There has now been found a rheology-modifying copolymer composition desirably formed by dispersion or precipitation polymerization which, when introduced into an aqueous electrolyte-containing environment, will increase the viscosity of the solution. The polymeric rheology modifier is generally derived from one or more carboxylic acid monomers and hydrophobic monomers, with the incorporation of a hydrophobic mercaptan, a thioester or amino acid containing chain transfer agent into the copolymer composition, and a crosslinking agent. Optionally, a steric stabilizer can be included in the copolymer composition of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A monomeric component of the present invention utilized to form the polymeric rheology modifier is one or more monounsaturated carboxylic acid monomers having a total of from about 3 to about 12 carbon atoms. The monomer can be monocarboxylic or polycarboxylic. More specifically, the carboxylic monomers are the olefinically-unsaturated carboxylic acids containing at least one activated carbon-to-carbon olefinic double bond, and at least one carboxyl group; that is, an acid or function readily converted to an acid containing an olefinic double bond either in the alpha-beta position with respect to a carboxyl group, C═C—COOH; or as part of a terminal methylene grouping, CH
2
═C<. Olefinically-unsaturated acids of this class include acrylic acids typified by acrylic acid itself, methacrylic acid, ethacrylic acid, alpha- cyano acrylic acid, beta methylacrylic acid (crotonic acid), alpha-phenyl acrylic acid, beta-acryloxy propionic acid, cinnamic acid, p-chloro cinnamic acid, 1-carboxy4-phenyl butadiene-1,3, 3-acrylamido-3-methylbutanoic acid, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, aconitic acid, maleic acid, fumaric acid, and tricarboxy ethylene. As used herein, the term “carboxylic acid” includes the polycarboxylic acids and those acid anhydrides, such as maleic anhydride, wherein the anhydride group is formed by the elimination of one molecule of water from two carboxyl groups located on the same carboxylic acid molecule. Maleic anhydride and other acid anhydrides useful herein have the general structure
wherein R and R′, independently, is hydrogen, halogen, or cyanogens, (C═N) or a hydrocarbon having a total of from 1 to 18 carbon atoms, such as alkyl, aryl, alkaryl, aralkyl, and cycloalkyl groups such as methyl, ethyl, propyl, octyl, decyl, phenyl, tolyl, xylyl, benzyl, cyclohexyl, and the like.
The preferred carboxylic monomers are the monoolefinic acrylic acids having the general structure
wherein R
2
is a substituent such as hydrogen, halogen, and the cyanogens (C═N) groups, monovalent alkyl radicals, monovalent aryl radicals, monovalent aralkyl radicals, monovalent alkaryl radicals and the monovalent cycloaliphatic radicals having a total of from 1 to 4 carbon atoms. Of this class, acrylic and methacrylic acid are most preferred.
The amounts of such carboxylic acid monomers is generally from about 60% to 98% by weight, and preferably from about 80% to about 95% by weight based upon the total weight of the unsaturated acid monomers and the hydrophobic monomers.
Another monomeric component is a hydrophobic comonomer, these generally being esters of acids, and include the various (meth)acrylates or (meth)acrylamides of the formula:
with R
3
=H or methyl; X=O or NH; and R
4
containing an alkyl, an amide such as an acrylamide and the like, or an alkoxy derivative or an cyano derivative thereof, having from about 2 to about 30 carbon atoms with 6 to about 30 carbon atoms being desirable and 12 to about 30 carbon atoms being preferred. The alkyl structure can contain primary, secondary, or tertiary carbon configurations. Examples of such acrylates include methyl acrylate, ethyl acrylate, propyl acrylate, n-pentyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-methyl-pentyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, n-decyl acrylate, n-dodecyl acrylate, n-hexadecyl acrylate, n-octadecyl acrylate, behenyl acrylate, and the like; and also alkoxy derivatives thereof, such as methoxymethyl acrylate, methoxyethyl acrylate, ethoxyethyl acrylate, butoxyethyl acrylate, ethoxypropyl acrylate, and the like; and cyano derivatives thereof, such as &agr;,&bgr;-cyanoethyl acrylate, &agr;, &bgr; and &dgr;-cyanopropyl acrylate, cyanobutyl
Marchant Nancy
Yu Simon
Asinovsky Olga
Dunlap Thoburn T.
Hudak & Shunk Co. L.P.A.
Kolkowski Brian M.
Noveon IP Holdings Corp.
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