FIELD OF THE INVENTION

This invention relates generally to copolymers that are useful in oral care formulations. The oral care formulations contain copolymer particles bearing phosphorus acid groups.

BACKGROUND

Oral care compositions contain a variety of additives that provide a wide array of benefits to the composition. Toothpastes, for example, contain additives that offer protection from acid dissolution of tooth enamel. Bacteria thrive on sugar and produce high acid levels in oral settings that can erode tooth enamel, leading to the formation of dental caries. Currently, fluoride containing compositions are widely used to protect against acid erosion of tooth enamel and to prevent the formation of dental caries. Conventional fluoride containing compositions, however, lack the efficacy to provide long term enamel protection, for example, lasting 8 to 12 hours after deposition.

Improved enamel protection of teeth by increased deposition of fluoride has been addressed in the art. For example, U.S. Patent Application Publication No. US 2014/0134116 discloses block copolymers which are effective in binding to the surface of hard tissue which includes hydroxyapatite and enamel. However, the prior art does not disclose an oral care composition according to the present invention which gives superior fluoride deposition and adhesion properties to prevent erosion of calcium on teeth.

Accordingly, there is a need to develop new oral care compositions including fluoride that are biologically acceptable, readily applied, and can coat and protect tooth enamel against acid erosion.

STATEMENT OF INVENTION

One aspect of the invention provides an oral care composition comprising (a) 0.001 to 50 weight % copolymer particles dispersed in an aqueous medium, based on the weight of the composition, wherein the copolymer particles comprise polymerized units derived from (i) 0.1 to 20 weight % of phosphorus acid monomers, and (ii) 80 to 99.9 weight % of comonomers, and (b) an orally acceptable carrier.

In another aspect, the invention provides a method for protecting tooth enamel from acid erosion comprising applying to the tooth enamel an oral care composition comprising (a) 0.001 to 50 weight % copolymer particles dispersed in an aqueous medium, based on the weight of the composition, wherein the copolymer particles comprise polymerized units derived from (i) 0.1 to 20 weight % of phosphorus acid monomers, and (ii) 80 to 99.9 weight % of comonomers, and (b) an orally acceptable carrier.

DETAILED DESCRIPTION

The inventors have now surprisingly found copolymer particles comprising polymerized units derived from phosphorus acid monomers provide superior fluoride deposition and adhesion properties to prevent erosion of calcium on teeth, while also being biologically acceptable and readily applicable. Accordingly, the present invention provides in one aspect an oral care composition comprising copolymer particles dispersed in an aqueous medium comprising polymerized units of phosphorus acid monomers and comonomers, and an orally acceptable carrier. In the present invention, "oral care compositions" is intended to refer to compositions suitable for preventing or treating a disease or condition of the oral cavity, including, for example dentifrices, toothpastes, tooth gels, dental creams, mouthwashes, mouth rinses, chewing gums, denture adhesives, or portable dosage articles including, for example, a lozenge, a mint, bead, wafer, liquid formulated for oral application in a small portable nebulizer (spray bottle), liquid formulated for oral application in a small portable drop -generating bottle, or a soft pliable tablet ("chewie"). Preferably, the oral care composition is orally acceptable. "Orally acceptable" refers to ingredients typically used in oral care compositions, and is intended to underscore that materials that are toxic when present in the amount typically found in oral care compositions are not contemplated as part of the invention. The compositions of the invention may be

manufactured by processes well known in the art, for example, by means of conventional mixing, dissolving, granulating, emulsifying, encapsulating, entrapping or lyophilizing processes.

As used herein, the term "polymer" refers to a polymeric compound prepared by polymerizing monomers, whether of the same or a different type. The generic term "polymer" includes the terms "homopolymer," "copolymer," and "terpolymer." As used herein, the term "polymerized units derived from" refers to polymer molecules that are synthesized according to polymerization techniques wherein a product polymer contains "polymerized units derived from" the constituent monomers which are the starting materials for the polymerization reactions.

As used herein, the term "(meth)acrylate" refers to either acrylate or methacrylate, and the term "(meth)acrylic" refers to either acrylic or methacrylic.

As used herein, the term "phosphorus acid group" refers to a phosphorus oxo acid having a POH moiety in which the hydrogen atom is ionizable. Also included in the term "phosphorus acid group" are salts of the phosphorus oxo acid. In its salt or basic form, the phosphorus acid group has a cation such as a metal ion or an ammonium ion replacing at least one acid proton. Examples of phosphorus acid groups include groups formed from phosphinic acid, phosphonic acid, phosphoric acid, pyrophosphinic acid, pyrophosphoric acid, partial esters thereof, and salts thereof.

As used herein, the terms "glass transition temperature" or "T _g " refers to the temperature at or above which a glassy polymer will undergo segmental motion of the polymer chain. Glass transition temperatures of a polymer can be estimated by the Fox equation {Bulletin of the American Physical Society, 1 (3) Page 123 (1956)) as follows:

l/T _g = wi/r _g (i) + w ₂ IT _gi 2)

For a copolymer, w _\ and w ₂ refer to the weight fraction of the two comonomers, and r _g(1) and r _g(2) refer to the glass transition temperatures of the two corresponding homopolymers made from the monomers. For polymers containing three or more monomers, additional terms are added (νν _η /¾ι))· The ¾ of a polymer can also be calculated by using appropriate values for the glass transition temperatures of homopolymers, which may be found, for example, in "Polymer Handbook," edited by J. Brandrup and E.H. Immergut, Interscience Publishers. The T _g of a polymer can also be measured by various techniques, including, for example, differential scanning calorimetry ("DSC"). The values of T _g reported herein are measured by DSC.

The oral care compositions of the present invention also contain copolymer particles bearing phosphorus acid groups pendant to a polymer backbone. The copolymer particles are dispersed in an aqueous medium, and are insoluble in the aqueous medium. The copolymer particles are addition polymers, which comprise polymerized units derived from (i) ethylenically unsaturated monomers having a phosphorus acid groups, referred to herein as "phosphorus acid monomers," and (ii) ethylenically unsaturated monomers, referred to herein as "comonomers."

The phosphorus acid monomers contain at least one ethylenic unsaturation and a phosphorus acid group. The phosphorus acid monomer may be in the acid form or as a salt of the phosphorus acid group. Suitable phosphorus acid monomers include, for example:

O

R- -OH RO- o— -OH

R' and OR' OR"

wherein R is an organic group containing an acryloxy, methacryloxy, or a vinyl group; and R' and R" are independently selected from H and a second organic group. The second organic group maybe saturated or unsaturated. Suitable phosphorus acid monomers include, for example, dihydrogen phosphate-functional monomers, e.g., dihydrogen phosphate esters of an alcohol in which the alcohol also contains a polymerizable vinyl or olefinic group (e.g., allyl phosphate, mono- or diphosphate of bis(hydroxyl-methyl)fumarate or itaconate), and derivatives of (meth)acrylic acid esters, e.g., phosphates of hydroxyalkyl (meth)acrylates (e.g., 2- hydroxyethyl (meth)acrylate and 3-hydroxypropyl (meth)acrylates). Other suitable phosphorus acid monomers include, for example phosphonate functional monomers, e.g., vinyl phosphonic acid, allyl phosphonic acid, a-phosphonostyrene, and 2-methylacrylamido-2- methylpropanephosphonic acid. Further suitable phosphorus functional monomers include, for example, 1,2-ethylenically unsaturated (hydroxy )phosphinylalkyl (meth)acrylate monomers, e.g., (hydroxy)phosphinylmethyl methacrylate. In certain preferred embodiments, the phosphorus acid monomers comprise dihydrogen phosphate monomers, e.g., 2-phosphoethyl (meth)acrylate, 2-phosphopropyl (meth)acrylate, 3-phosphopropyl (meth)acrylate, and 3-phospho-2- hydroxypropyl (meth)acrylate. In certain embodiments, the inventive copolymers comprise polymerized units of phosphorus acid monomers in an amount of at least 0.1 weight %, preferably at least 0.5 weight %, and more preferably at least 1 weight %, by weight of the copolymer. In certain embodiments, the inventive copolymer comprise polymerized units of phosphorus acid monomers in an amount of no more than 20 weight %, preferably no more than 10 weight %, and more preferably no more than 6 weight %.

The comonomers are ethylenically unsaturated monomers which are not phosphorus acid monomers and are copolymerizable with an ethylenically unsaturated phosphorus acid monomer. Suitable comonomers include, for example, styrene, butadiene, a-methyl styrene, vinyl toluene, vinyl naphthalene, ethylene, propylene, vinyl acetate, vinyl versatate, vinyl chloride, vinylidene chloride, acrylonitrile, methacrylonitrile, (meth)acrylamide, various Ci-C ₄ o alkyl esters of (meth)acrylic acid (e.g., methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, 2- ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, n-octyl (meth)acrylate, n-decyl

(meth)acrylate, n-dodecyl (meth)acrylate, tetradecyl (meth)acrylate, lauryl (meth)acrylate, oleyl (meth)acrylate, palmityl (meth)acrylate, and stearyl (meth)acrylate)), and other (meth)acrylates (e.g., isobornyl (meth)acrylate, benzyl (meth)acrylate, phenyl (meth)acrylate, 2-bromoethyl (meth)acrylate, 2-phenylethyl (meth)acrylate, and 1-naphthyl (meth)acrylate)), alkoxyalkyl (meth)acrylates, e.g., ethoxyethyl (meth)acrylate, mono-, di-, trialkyl esters of ethylenically unsaturated di- and tricarboxylic acids and anhydrides (e.g., ethyl maleate, dimethyl fumarate, trimethyl aconitate, and ethyl methyl itaconate), and carboxylic acid containing monomers, e.g., (meth)acrylic acid, itaconic acid, fumaric acid, and maleic acid. In certain embodiments, the inventive copolymers comprise polymerized units of comonomers in an amount of at least 80 weight %, preferably at least 90 weight %, and more preferably at least 94 weight %, by weight of the copolymer. In certain embodiments, the inventive copolymer comprise polymerized units of comonomers in an amount of no more than 99.9 weight %, preferably no more than 99.5 weight %, and more preferably no more than 99 weight %.

In certain embodiments, the polymer may be a crosslinked polymer, wherein a crosslinker, such as a monomer having two or more non-conjugated ethylenically unsaturated groups, is included with the copolymer components during polymerization. Suitable crosslinker monomers include, for example, di- or tri-allyl ethers and di- or tri-(meth)acrylyl esters of diols or polyols (e.g., trimethylolpropane diallyl ether, ethylene glycol dimethacrylate), di- or tri-allyl esters of di- or tri-acids, allyl (meth)acrylate, divinyl sulfone, triallyl phosphate, divinylaromatics (e.g., divinylbenzene). In certain embodiments, the inventive copolymers comprise polymerized units of crosslinker monomers in an amount of no more than 5 weight %, preferably no more than 3 weight %, more preferably no more than 2 weight %, and even more preferably no more than 1 weight %, by weight of the copolymer.

Polymer molecular weights can be measured by standard methods such as, for example, size exclusion chromatography. In certain embodiments, the copolymer particles of the present invention have a weight average molecular weight (M _w ) of 5,000,000 or less, 3,000,000 or less, 2,000,000 or less, or 1,000,000 or less, as measured by gel permeation chromatography. In certain embodiments, the copolymer particles have a M _w of 5,000 or more, preferably 50,000 or more, and more preferably 100,000 or more, as measured by gel permeation chromatography. Copolymer particles suitable for use in the inventive oral care compositions including a two stage copolymer have T _g values in the range of from 50°C to 150°C, preferably from 65°C to 100°C, and more preferably from 80°C to 90°C. Copolymer particles suitable for use in the inventive oral care compositions including a three stage copolymer have T _g values in the range of from -5°C to 50°C, preferably from 5°C to 35°C, and more preferably from 10°C to 25°C. In certain embodiments, the inventive copolymer particles have an average diameter in a range of from 10 nm to 20 microns, preferably from 20 nm to 1 micron, and more preferably from 50 nm to 500 nm. The diameters of the copolymer particles may be characterized by distributions such as unimodal or multimodal, including bimodal. The average diameter of the copolymer particles may be determined by a light scattering technique.

In certain embodiments, the inventive oral care composition includes copolymer particles in an amount of from 0.001 to 50 weight %, preferably from 0.01 to 20 weight %, and more preferably from 0.1 to 10 weight, by weight of the composition.

Suitable polymerization techniques for preparing the copolymer particles contained in the inventive oral care compositions include, for example, emulsion polymerization, as disclosed in U.S. Patent No. 6,710,161. Aqueous emulsion polymerization processes typically are conducted in an aqueous reaction mixture, which contains at least one monomer and various synthesis adjuvants, such as the free radical sources, buffers, and reductants in an aqueous reaction medium. In certain embodiments, a chain transfer agent may be used to limit molecular weight. The aqueous reaction medium is the continuous fluid phase of the aqueous reaction mixture and optionally contains one or more water miscible solvents, based on the weight of the aqueous reaction medium. Suitable water miscible solvents include, for example, methanol, ethanol, propanol, acetone, ethylene glycol ethyl ethers, propylene glycol propyl ethers, and diacetone alcohol. In certain embodiments, the aqueous reaction medium contains more than 90 weight % water, preferably more than 95 weight % water, and more preferably more than 98 weight % water, based on the weight of the aqueous reaction medium.

The polymerization process may be conducted as a batch, semicontinuous, or continuous process. In certain embodiments, the polymer is formed in a two stage reaction. In certain embodiments, the first stage comprises polymerizing 1 to 10 weight % of phosphorus acid monomers, 99 to 80 weight % comonomers, and 0 to 5 weight % of crosslinker, based on the total weight of monomers polymerized in the first stage. In certain embodiments, the second stage comprises polymerizing 95 to 100 weight % comonomers, and 0 to 5 weight % of crosslinker, based on the total weight of monomers polymerized in the second stage. In certain embodiments, the phosphorus acid monomers comprise a phosphoethyl methacrylate. In certain embodiments, the comonomers comprise at least one of butyl acrylate, methyl methacrylate, and methacrylic acid. In certain embodiments, the crosslinker comprises allyl methacrylate. In certain embodiments, the total ratio of monomers polymerized in stage 1 and stage 2 ranges from 97:3 to 3:97, preferably from 20:80 to 80:20, more preferably from 25:75 to 75:25, and even more preferably from 30:70 to 70:30.

The inventive oral care compositions contain the copolymer particles dispersed in an aqueous medium. The aqueous medium may contain cosolvents, e.g., water miscible cosolvents. Suitable water miscible cosolvents include, for example, methanol, ethanol, propanol, acetone, ethylene glycol ethyl ethers, propylene glycol propyl ethers, and diacetone alcohol; and water immiscible solvents such as propyl acetate, butyl acetate, methyl isoamyl ketone, amyl acetate, diisobutyl ketone, xylene, toluene, butanol, and mineral spirits. The pH of the oral care composition may be in the range of 3 to 11. In certain embodiments of the present invention, the inventive oral care composition comprise one or more fluoride salts or fluoride ion sources (i.e., fluoride salts which may be soluble). Suitable fluoride ion sources include, for example, stannous fluoride, sodium fluoride, potassium fluoride, potassium monofluorophosphate, sodium monofluorophosphate, ammonium monofluorophosphate, sodium fluorosilicate, ammonium fluorosilicate, amine fluoride such as olaflur (N'-ociadecySirimethykmdiamine-N,N,'-tris(2-ethanol)-dihydro fluoride), ammonium fluoride, and combinations thereof. Preferably, the fluoride ion source includes stannous fluoride, sodium fluoride, amine fluorides, sodium monofluorophosphate, as well as mixtures thereof. In certain embodiments, the oral care composition of the invention may also contain a source of fluoride ions or fluorine-providing ingredient in amounts sufficient to supply 50 to 5000 ppm fluoride ion, preferably from 100 to 1000 ppm fluoride ion, and more preferably from 200 to 500 ppm fluoride ion. The amount of fluoride ion source effective for achieving the desired property provided by such components can be readily determined by one skilled in the art. In certain embodiments, the fluoride ion source is present in a range of from 0.001 to 10 weight %, preferably of from 0.003 to 5 weight %, and more preferably of from 0.01 to 1 weight %.

Oral care compositions of the invention also include an orally acceptable carrier. Such material is typically characterized as a carrier or diluent that are safe for use and do not negate the activity and properties of the active agent(s) in the composition. Suitable orally acceptable carriers include, for example, water (such as deionized or distilled water) and various solvents that may contain a humectant including, for example, glycerin, sorbitol, xylitol, and the like. In some embodiments, the composition contains from about 99.99 to about 50 percent by weight of the orally acceptable carrier, based on the total weight of the composition.

The oral care compositions of the invention may also include other ingredients known in the art of oral care compositions and which are operably for the prevention of treatment of a condition or a disorder of hard or soft tissue of the oral cavity, the prevention or treatment of a physiological disorder or condition, or which provide a cosmetic benefit. Such other ingredients include, for example, anti-plaque agents, whitening agents, cleaning agents, flavoring agents, sweetening agents (e.g., sorbitol, sucralose, sodium saccharin, and xylitol), adhesion agents, surfactants, foam modulators, abrasives, pH modifying agents, humectants, mouth feel agents, colorants, abrasives (e.g., aluminum hydroxide, calcium carbonate, dicalcium phosphate, and silicas), remineralizers, hydroxyapatite, phosphates (e.g., calcium phosphate), tartar control (anti- calculus) agents, saliva stimulating agents, anti- sensitivity agents, antioxidants, nutrients, viscosity modifiers, diluents, opacifiers, breath freshening agents, zinc salts, antibacterial agents (e.g., phenol, thymol, eugenol, eucalyptol, and menthol), and combinations thereof. The amount of optional ingredients effective for achieving the desired property provided by such ingredients can be readily determined by one skilled in the art.

As noted above, oral care compositions of the present invention are highly effective at aiding the deposition and adhesion of fluoride on teeth enamel, and also to bind to hard tissue including hydroxyapatite and enamel, thereby preventing of the erosion of calcium on teeth. Accordingly, the oral care compositions of the present invention are effective to protect the hard tissue from loss of calcium by at least 5 percent after exposure of the hydroxyapatite to the polymers for 0.1-10 minutes and subsequent exposure of the polymer coated hydroxyapatite to a 0.3-1% citric acid solution, such as for 15 minutes at 37°C, as compared to hydroxyapatite which is not bound to the copolymer particles. In certain embodiments, the inventive copolymer particles are effective to protect the hard tissue from loss of calcium by at least 10 percent, preferably at least 15 percent, preferably at least 20 percent, preferably at least 25 percent, preferably at least 30 percent, preferably at least 35 percent, preferably at least 40 percent, preferably at least 45 percent, preferably at least 50 percent, preferably at least 55 percent, and even more preferably at least 60 percent.

In another aspect, the present invention provides that the oral care compositions may be used in a method for protecting tooth enamel from acid erosion comprising applying to the tooth enamel an oral care composition comprising (a) 0.001 to 50 weight % copolymer particles dispersed in an aqueous medium, based on the weight of the composition, wherein the copolymer particles comprise polymerized units derived from (i) 0.1 to 20 weight % of phosphorus acid monomers, and (ii) 80 to 99.9 weight % of comonomers, and (b) a dermatologically acceptable carrier. In certain embodiments, the phosphorous acid monomers comprise phosphoethyl methacrylate, and the comonomers comprise at least one of butyl acrylate, methyl methacrylate, and methacrylic acid.

In practicing the methods of the invention, the oral care compositions are generally administered via a toothpaste, mouthwash, strips, and gel containing trays which include the copolymer particles described herein. Regular applications of the inventive compositions are effective for providing a protective layer on tooth enamel at a first time of application, and thereafter. A person of ordinary skill in the art can readily determine the frequency with which the compositions should be applied. The frequency may depend, for example, on the level of exposure to foods that result in high acid levels that an individual is likely to encounter in a given day and/or the sensitivity of the individual to such high acid levels. By way of non-limiting example, administration on a frequency of at least once per day may be desirable.

Some embodiments of the invention will now be described in detail in the following Examples.

EXAMPLES

Example 1

Preparation of Exemplary and Comparative Copolymer Particles

Exemplary copolymer particles in accordance with the present invention contain the components recited in Table 1.

Table 1. Exemplary Copolymer Particles

Stage 2 (56.5%): 45 BA / 42.2 MMA / 1 MAA / 2.9 PEM / 8.9 AAEM Stage 3 (3%): 20 BA / 74 MMA / 6 MAA

G Stage 1 (40.5%): 52 BA / 47.6 MMA / 0.4 MAA

Stage 2 (56.5%): 50 BA / 37.18 MMA / 1 MAA / 2.92 PEM / 8.9 AAEM Stage 3 (3%): 20 BA / 74 MMA / 6 MAA

H Stage 1 (40.5%): 61.5 BA / 38.1 MMA / 0.4 MAA

Stage 2 (65.5%): 61.1 BA / 26.18 MMA / 1 MAA / 8.8 AAEM / 2.92 PEM Stage 3 (3%): 20 BA / 74 MMA / 6 MAA

I Stage 1 (40.5%): 66 BA / 32.6 MMA / 0.4 MAA

Stage 2 (56.5%): 66 BA / 21.28 MMA / 1 MAA / 8.8 AAEM / 2.92 PEM Stage 3 (3%): 20 BA / 74 MMA / 6 MAA

* = Comparative

BA = butyl acrylate

MMA = methyl methacrylate

MAA = methacrylic acid

PEM = phosphoethyl methacrylate

ALMA = allyl methacrylate

AAEM = acetoacetoxyethyl methacrylate

Two Stage Polymer Polymerization Procedure

For polymer B, a Stage 1 monomer emulsion was prepared by mixing 65.5 g DI water, 16.5 g (30% active) anionic surfactant-A (surfactant having an average composition of lauryl- (ethylene oxide) ₄ sodium sulfate; 30 wt % solids), 27.14 g BA, 202.36 g MMA, 0.50 g MAA, and 16.2 g PEM. A Stage 2 monomer emulsion was then prepared by mixing 136 g DI water, 15.4 g (30% active) anionic surfactant A, 64.5 g BA, 392.2 g MMA, and 0.95 g MAA. A 3 liter reactor, four-necked round bottom flask equipped with a paddle stirrer, a thermocouple, nitrogen inlet, and reflux condenser was assembled. To the flask was added 1,170 g DI water and 16.5 g (30% active) anionic surfactant A, and stirring was started. The contents of the flask were heated to 84°C. under a nitrogen atmosphere. A solution of 1.4 g NaPS in 13 g DI water was added. The stage 1 monomer emulsion was fed into the reactor over 40 minutes. A solution of 0.71 g NaPS in 43 g DI water was fed separately to the flask for 40 minutes. After the addition of Stage 1 monomer emulsion the container was rinsed with a small portion of DI water and added into the flask. The NaPS co-feed was stopped and the reaction held at 87 °C for 10 minutes. The Stage 2 monomer emulsion was fed into the flask over 65 minutes. The NaPS co-feed was restarted and fed for 65 minutes. Furthermore, a separate solution containing 5.3 g of ammonium hydroxide (28% solution), 20 g of water was fed over 65 minutes. After the addition of Stage 2 monomer emulsion the container was rinsed with a small portion of DI water and fed into the flask. The contents of the flask were maintained at 84-86°C for 5 minutes. The batch was then cooled to 65°C. A redox pair of hydrogen peroxide aqueous solution and iso-ascorbic acid solution was fed into the kettle separately. The batch was cooled to room temperature.

Polymers A and C-E were prepared substantially as described above, with the appropriate changes in monomer amounts as recited in Table 1.

Three Stage Polymer Polymerization Procedure

For polymer F, a first monomer emulsion was prepared by mixing 160.0 deionized water, 38.1 g DISPONIL FES 32 surfactant (available from BASF; 30% active), 323.6 g BA, 396.2 g MMA, and 2.9 g MAA. A second monomer emulsion was then prepared by mixing 272.1 g deionized water, 37.5 g DISPONIL FES 993 surfactant (available from BASF; 30% active), 29.8 g PEM, 452.7 g BA, 422.4 g MMA, 74.5 g AAEM, and 9.9 g MAA. A third monomer mixture was prepared by mixing 43.8 g deionized water, 10.5 g BA, 38.0 g MMA, and 4.3 g MAA.

Deionized water (1106.3 g) and DISPONIL FES 32 surfactant (2.3 g, 30% active) were added to a 5-L, four-necked round-bottom flask equipped with a paddle stirrer, a thermometer, nitrogen inlet, and a reflux condenser. The contents of the flask were heated to 85°C under a N ₂ atmosphere, and stirring was initiated. A portion of the first monomer emulsion (110.4 g) was added to the flask followed by a rinse of DI water (5.0 g). A solution of sodium persulfate (5.4 g) dissolved in deionized water (33.9 g), followed by a rinse of deionized water (6.7 g) was subsequently added to the reactor. After stirring for 10 min, the remainder of the first monomer emulsion was added over 45 minutes followed by a DI water rinse (27.0 g). An initiator solution of sodium persulfate (0.58 g) dissolved in DI water (31.7 g) was added separately added over 45 min. Stirring was continued at 85°C for 15 min.

The second monomer emulsion and an initiator solution containing sodium persulfate (0.99 g) dissolved in DI water (52.8 g) were added linearly and separately to the vessel over 75 min. The temperature was maintained at 85°C. The second monomer emulsion vessel was rinsed to the reactor with deionized water (27 g).

When all additions were complete, the flask was cooled to 65 °C. The third monomer mix was added to the kettle as quickly as possible. Subsequently, a solution of sodium persulfate (0.047 g) and i-butyl hydroperoxide (0.39, 70%) dissolved in DI water (2.6 g) was added to the flask followed by a solution of copper nitrate (0.05g, 42% active), VERSENE (CAS# 6381-92-6) (0.01 g, 1% active; available from The Dow Chemical Company), and isoascorbic acid (0.29 g) dissolved in DI water (14.5 g). After 10 minutes, solutions of i-butyl hydroperoxide (0.58 g, 70%) in deionized water (14.2 g) and isoascorbic acid (0.44 g) in deionized water (14.2 g) were separately added to the flask over 15 min to reduce residual monomer as the reactor continued to cool. The polymer was then neutralized to pH 9.0 with an ammonium hydroxide solution (43.0 g, 30%). Block additive CAPSTONE FS-61 (9.6 g; available from DuPont) followed by a rinse of DI water (10.1 g) and a solution of sodium bisulfite anhydrous (0.4 g) dissolved in DI water (28.0 g) were subsequently added. PROXEL BZ (10.1 g, 24% active; available from Arch Chemicals, Inc.), and ROCEVIA BT 2S (19% active; available from The Dow Chemical Company) were finally added.

Polymers G-I were prepared substantially as described above, with the appropriate changes in monomer amounts as recited in Table 1.

Example 2

Characterization of Exemplary and Comparative Copolymer Particles

Copolymer particles as prepared in Examples 1 and 2 above were evaluated for pH, % solids, and particle size, as show in Table 3.

Table 3. Characterization of Copolymer Particles

F 18 4.8 45.5 107

G 10 4.9 45.6 108

H 5 4.9 45.5 107

I -2 4.9 45.5 109

The r _g was measured by DSC using a TA Instruments Q2000 DSC. The particle size for Samples A-E was measured using a Matex CHDF 2000, and for samples F-I using a Malvern BI

90.

Example 3

Anti-Erosion Study of Copolymer Particles in Presence of Fluoride

The anti-erosion properties of the inventive oral care compositions in the presence of fluoride were evaluated.

Preparation of 250 ppm Sodium Fluoride Solution: A 1% citric acid solution was prepared by dissolving, in a 1L glass beaker with stir bar, anhydrous citric acid (9g) in 900. OmL of DI H ₂ 0. The solution was stirred until all solids completely dissolved. While stirring, diluted NaOH (0.1M) was added dropwise until pH = 3.2. A 250 ppm sodium fluoride solution was prepared by charging a 150 mL glass jar with 24.9mg (0.593mmol) of sodium fluoride and lOOmL of DI H ₂ 0. The solution was stirred for 5min or until all the solids have completely dissolved.

Preparation of Polymer and Fluoride Suspension Treatments: Polymer and fluoride suspensions were prepared on the day the treatments were conducted. An equivalent amount of polymer was added (based on weight % of NaF) to a 20 mL vial with 4mL of NaF (250ppm) solution. The solution was stirred and was added dropwise with either diluted HC1 or NaOH until the desired pH was reached (pH = 4.1 or pH = 9). The polymer-fluoride suspensions were stirred at 37°C for at least 1 hour.

Experimental Procedures: Twenty sintered hydroxyapatite discs and 50 mL DI water was added to a 100 mL clear glass jar. The jar was placed in a sonicator for 15 min. After 15min, the discs were washed with DI water 3 times (50 mL of DI water each time). The discs were dried in the oven (45°C) for 1 hour. Once the discs were dried, the back sides of each disc were coated with a clear nail varnish. Once the varnish has completely dried, each disc was placed in a labeled, clean, dry 20 mL vial. The discs were now ready for the pre-conditioning step.

Preconditioning step: Each 20mL vial with disc was added with 4mL of 1% citric acid solution and was stirred at 37°C for 15min. After 15min, each discs in vials were rinsed with DI water (5 times, 20mL each time). The discs were dried in the oven (45°C) for lh. At this time, the discs are now ready for the initial acid treatment. Initial acid treatment: Each 20mL vial with disc was added with 4mL of 1% citric acid solution and was stirred at 37°C for 15min. After 15min, the solution from each vials were transferred to a labeled 20mL vials for analytical testing. Each disc in vials were rinsed with 4mL DI water and the rinsed solution was added to the newly labeled vials for analytical testing. (Note: Each vials for analytical, contained 8mL of solution.) The vials with discs were added with 5mL of PBS pH = 7 and rinsed with DI water (5 times, 20 mL each time). The discs were air dry for lh. If necessary, pat the dry nail side of the disc. At this point, treatment solutions were prepared (see above for preparation). After preparation of each treatment, each discs were treated accordingly to the planned experiments. Each disc was treated with the appropriate polymer-fluoride suspension for 2 minutes. After treatment, the discs were rinsed thoroughly with DI water (5 times, 20 mL each time). After thorough rinsing, pat the dry nail side of the disc. At this point the discs are now ready for the final acid treatment.

Final acid treatment: Each 20mL vial with disc was added with 4 mL of 1% citric acid solution and was stirred at 37°C for 15 min. After 15min, the solution from each vials were transferred to a labeled 20 mL vials for analytical testing. Each disc in vials was rinsed with 4 mL DI water and the rinsed solution were added to the newly labeled vials for analytical testing. (Note: Each vials for analytical testing, contained 8mL of solution.)

Samples from each of the vials was diluted 1: 100 using DI water to a volume of 50 mL and evaluated using an Agilent 7500 ICP-MS. Samples were monitored for ⁴⁴ Ca and ⁴⁵ Sc with integration times of 0.30 seconds per point and rinse times of 60 seconds (random samples were spiked with 0.2 ppm of Ca in solution). The reagent blank contained 0.5 mL of citric acid, 2 mLs of 0.1 ppm Sc, and 47.5 mL of DI water. The results of the anti-erosion study are shown below in Table 4.

Table 4. Anti-Erosion Properties of Inventive Oral Care Formulations

NaF + Polymer A 9 25 30 120.0 -20.0 (comparative)

NaF + Polymer B 9 33 26 78.8 21.2

NaF + Polymer F 9 55 42 76.4 23.6

NaF + Polymer G 9 26 20 76.9 23.1

Calcium level = ([Ca] treat / [Ca] _ref ) x 100 %

% Protection = (([Ca]i _nitia i - [Ca] _finaL ) / [Ca]i _nitia i) x 100

The results demonstrate that exemplary oral care compositions prepared in accordance with the present invention provide significant protection against anti-erosion as compared against comparative compositions.