The present invention is a polymer latex that includes polymer particles having a core portion and a shell portion. The core portion contains polymerized hydrophobic ethylenically unsaturated monomers with a water solubility less than 1% at room temperature. The shell portion contains polymerized monomers defined by formula (I) ##STR1## wherein X is O or NH, or NCH.sub.3, R.sub.1 and R.sub.2 are H, CH.sub.3, C.sub.2 H.sub.5, C.sub.3 H.sub.7, or C.sub.4 H.sub.9, R.sub.3 and R.sub.4 are H or CH.sub.3, n1 and n2 are integers, n1 is from 1 to 4, n2 is from 1 to 20. The polymer particles having a size of less than 50 nm.

FIELD OF THE INVENTION
 The present invention describes small polymer particles that are useful in
 silver halide applications. More specifically, the present invention is
 concerned with polymer particles having a size less than 50 nm and have
 minimum interaction with gelatin.
 BACKGROUND OF THE INVENTION
 Polymer latex has been used extensively for silver halide photographic
 products. For example, polymer latexes have been employed in several
 applications in which physical property modification was advantageous or
 essential. Properties that can be affected include dimensional stability,
 flexibility, drying rate, cracking, abrasion resistance, and differential
 swelling. The maintenance of dimensional stability is especially important
 in graphic arts products, microfilm, X-ray products, and other
 applications with a premium on resolution. Incorporation of a hydrophobic,
 nonswelling phase proportionately reduces swelling as a function or
 relative humidity and thus the drying will be also improved. Low glass
 transition (Tg) latexes and gelatin grafted latex have been used for the
 reduction of pressure sensitivity or undesirable fog of the photographic
 products. Polymer latexes are especially useful as the carrier of the
 photographically useful compounds. The photographically useful compounds
 include image couplers, developers, masking couplers, antifoggants,
 brightners, lubricants, latent image stabilizers, sensitizers, filter
 dyes, UV absorbers, oxidized developer scavengers, hardeners, stabilizers,
 antioxidants, bleach accelerators, and coupler solvents. This process is
 often called "loading". There are two major processes for the loading of
 photographically useful compounds into polymer latexes. In the first
 process, the photographically useful compounds, coupler solvents, such as
 o-dibutylphthalate, and a low boiling water-miscible organic solvents,
 such as tetrahydrofuran, acetone, or methanol are mixed to form a
 homogeneous solution. This solution was then added slowly to the polymer
 latex with vigorous stiring to force the loading of photographically
 compounds into polymer latex. The low boiling organic solvents is removed
 by evaporation after the loading is completed, with the result that the
 hydrophobic compounds becomes imbedded in the latex particles. The first
 process is described in U.S. Pat. Nos. 4,203,716, 4,304,769, and U.S. Pat.
 No. 4,368,258. In the second loading process the photographically useful
 compounds, such as couplers, and optional high-boiling solvents, such as
 o-dibutylphthalate, are combined at a temperature sufficient to prepare a
 liquid solution of the oil compounds. This oil solution is then combined
 with an aqueous solution containing gelatin and surfactants to form
 pre-mix. Polymer latex is either included in the aqueous solution before
 the oil phase is added, or is added to the oil-gelatin premix. The mixture
 is then passed through a high shear device, such as homogenizer, colloid
 mill, or microfluidizer, to force the loading of the photographically
 useful compounds into the polymer latex. The second loading process is
 described in U.S. Pat. No. 5,594,047, EP 0 727 703 and EP 0 727 703. The
 second process is preferred since low boiling organic solvents are not
 required.
 The particle size of the polymer latexes used in the photographic products
 are usually under 100 nm or preferably under 50 nm. Larger particle size
 polymer latexes tend to scatter light and reduce the film clarity of the
 photographic products. Large particle size latex also reduce the loading
 efficiency and reduce the photographic performance of the photographically
 useful compounds. However, gelatin solution containing small particle size
 latexes or dispersions tend to have very high melt viscosities. The cause
 of the high melt viscosity of small particle size latexes or dispersion is
 due to adsorption of gelatin onto the surface of these particles and thus
 the apparent hydrodynamic volume of the particles increase dramatically.
 The schematic explanation of this phenomena was shown column 4 lines 3-4
 of U.S. Pat. No. 5,135,844. High melt viscosity not only cause
 manufacturing difficulties and reduced the coating speed but also caused
 coating defects, such as coating unevenness and coating streaking. This is
 especially true when the particle size of the hydrophobic latex is less
 than 50 nm.
 There are few addenda known in the prior art for the reduction of high melt
 viscosity of small particle size latex or dispersions. U.S. Pat. Nos.
 3,409,435, U.S. Pat. No. 5,135,844, and U.S. Pat. No. 5,300,418 describe
 the use of oligomeric surfactants for the reduction of high melt
 viscosity. Three types of surfactants which are effective to reduce the
 high melt viscosity are mentioned. The first type is a surfactant composed
 of a 6 to 22 carbon atom hydrophobic tail with one or more attached
 hydrophilic chains of at least 8 oxyethylene and/or glycidyl ether groups
 that may or may not be terminated with a negative charge such as a sulfate
 group. The second type are block oligomeric surfactants composed of
 hydrophobic polyoxypropylene blocks(A) and hydrophilic polyoxyethylene
 blocks(B) joined in the manner of A-B-A, B-A-B, A-B, or with a connecting
 moiety between them. The third addenda type are sugar surfactants,
 composed of between one to three 6 to 22 carbon atom hydrophilic tails
 with one or more attached hydrophilic mono or oligosaccharidic chains that
 may or may not be terminated by a negatively charged group such as a
 sulfate group. However, such prior art materials that containing a large
 number of polyalkylene oxide groups produce adverse photographic
 (sensitometric) effects in some photographic products. These oligomeric
 surfactants tend to migrate from layer to layer or be adsorbed to the
 silver halide grain which fogs the emulsion. Sugar surfactants do not have
 the adverse photographic effects but they tend to reduce the surface
 tension of the layer and create coating problems, such as repellency. EP 0
 695 968 discloses the use of a-cyclodextran for the reduction of melt
 viscosity. However, .alpha.-cyclodextran is expensive and fairly large
 amounts are needed to be effective. Another way of reducing high melt
 viscosities is by dilution with water. However, such a procedure leads to
 increased water load in the drier, and reduced the drying time.
 Therefore, there is a need for the alternative ways to reduce the high melt
 viscosity when small particle size polymer latexes are used in
 photographic systems.
 SUMMARY OF THE INVENTION
 The present invention is a polymer latex that includes polymer particles
 having a core portion and a shell portion. The core portion contains
 polymerized hydrophobic ethylenically unsaturated monomers with a water
 solubility less than 1% at room temperature. The shell potion contains
 polymerized monomers defined by formula (I)
 ##STR2##
 wherein X is O or NH, or NCH.sub.3,
 R.sub.1 and R.sub.2 are H, CH.sub.3, C.sub.2 H., C.sub.3 H.sub.7, or
 C.sub.4 H.sub.9,
 R.sub.3 and R.sub.4 are H, CH.sub.3,
 n1 and n2 are integers, n1 is from 1 to 4, n2 is from 1 to 20
 DETAILED DESCRIPTION OF THE INVENTION
 This invention relates to the preparation and composition of extra fine
 particle size polymer latexes for the use in the AgX photographic
 materials. The average particle size of the polymer latexes is less than
 50 nm. The polymer latexes of this invention have the core-shell
 morphology. The composition of the core is derived from monomers with low
 water solubilities (less than 1% in water at 25.degree. C.). The class of
 monomers with low water solubility include alkyl acrylate, alkyl
 methacrylate, alkyl acrylamide, alkyl methacrylamide, styrene,
 acrylonitrile, butadiene, and ethylene. Two or more hydrophobic monomers
 can be copolymerized to from the core. The composition of shell is derived
 from monomers with high water solubilities (higher than 1% in water at
 25.degree. C.) and with poly(ethylene oxide) or poly(propylene oxide)
 repeating units, such as methoxyethyl (meth)acrylate, as
 methoxyethoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate,
 ethoxyethoxyethyl (meth)acrylate, hydroxyethyl (meth)acrylate,
 poly(ethylyne oxide) (meth)acrylate, methoxy poly(ethylene oxide)
 (meth)acrylate, and ethoxy poly(ethylene oxide) (meth)acrylate.
 We have developed a method preparing ultrafine small particle size polymer
 latexes which have much lower melt viscosity than the regular polymer
 latexes with same particle size. This is accomplished by the combination
 of two stage seeded polymerization and the incorporation of special
 functional monomers on the surface of the preformed seed particles, This
 invention does not require the addition of oligomeric surfactants as
 described in the prior art, therefore, the drawbacks of prior art can be
 avoided. The functional monomers incorporated in the second stage as shell
 materials are covalently bonded to the polymer particles and therefore
 would not migrate through layers and cause adverse sensitometric effects.
 The two stage seeded polymerization process is not new and is fully
 described in the "Emulsion Polymerization and Emulsion Polymers,
 P.A.Lovell and M.S.El-Aasser ed., Wiley, NY(1997) pp. 294-323. However,
 ultrafine polymer latexes (less than 50 nm in diameter) with the
 composition of this invention which have very low gelatin-particle
 interaction is new.
 The first stage is the preparation of ultrafine small particle size core
 particles. The composition of the core is mainly the hydrophobic monomers
 such that their homopolymer or copolymer have with water solubility less
 than 0.1% at room temperature. Examples of the hydrophobic monomers
 include ethylene, propylene, 1-butene, styrenic monomers (such as styrene,
 vinyl toluene, alpha-methyl styrene), and mono-ethylenic vinyl esters
 (such as vinyl acetate, vinyl pivalate, vinyl propionate, vinyl laurate),
 alkyl acrylate or methacrylate (such as methyl acrylate, isopropy
 acrylate, isopropyl methacrylate, ethyl acrylate, ethyl methacrylate,
 n-butyl acrylate, n-butyl methacrylate, methyl methacrylate, n-butyl
 methacrylate, benzyl acrylate, 2-ethylhexyl acrylate, cyclohexyl
 methacrylate, tetrafiirfryl acrylate, tetrafiiryl methacrylate diethyl
 maleate, diethyl itaconate), ethylenic unsaturated monocarboxlic acid
 amides (such as isopropylacrylamide, n-butylacrylamide, n-hexylacrylamide,
 t-butylacrylamide, n-butylmethacrylamide, n-hexylmethacrylamide, and
 dimethylacrylamide), acrylonitrile), methacrylonitrile, and dienes (such
 as butadiene, isoprene). Most preferred hydrophobic monomers include
 methylmethacrylate, ethylmethacrylate, n-butylacrylate,
 n-butylmethacrylate, 2-ethylhexylacrylate, isopropylacrylate,
 isopropylmethacrylate, and styrene. Two or more hydrophobic monomers can
 be copolymerized to form the core. The total weight percent of the
 hydrophobic monomers is from 50 to 95%, and preferably from 70 to 90%
 based on the total amount of core-shell polymer compositions.
 The second stage is the formation of shell around the surface of the core
 particles. In order to minimize the interaction of the gelatin with the
 hydrophobic core particles, we have discovered that monomers defined in
 formula (I) are especially effective.
 ##STR3##
 Where X is O or NH, or NCH.sub.3.
 R.sub.1 and R.sub.2 are H, CH.sub.3, C.sub.2 H.sub.5, C.sub.3 H.sub.7, or
 C.sub.4 H.sub.9.
 R.sub.3 and R.sub.4 are H , CH.sub.2 or --CHCH.sub.3,
 n1 and n2 are integers, n1 is from 1 to 4, n2 is from 1 to 20
 Examples of the monomers as defined in formula (I) are shown in the Table
 1.
 TABLE 1
 ##STR4##
 ##STR5##
 ##STR6##
 ##STR7##
 ##STR8##
 ##STR9##
 ##STR10##
 ##STR11##
 ##STR12##
 ##STR13##
 ##STR14##
 ##STR15##
 ##STR16##
 ##STR17##
 ##STR18##
 ##STR19##
 ##STR20##
 ##STR21##
 ##STR22##
 ##STR23##
 ##STR24##
 ##STR25##
 ##STR26##
 ##STR27##
 ##STR28##
 ##STR29##
 ##STR30##
 ##STR31##
 ##STR32##
 Two or more of the hydrophilic commonomers can be copolymerized together.
 The total weight percent of the hydrophilic comonomers is from 2 to 30
 percent, and preferably from 5 to 20 percent based on the total amount of
 coreshell polymer compositions.
 In addition to the hydrophobic and hydrophilic monomers described above,
 water-soluble ionogenic monomers containing carboxylic acid, sulfonic
 acid, sulfuric acid, and phosphoric acid functional groups may be used to
 modify the physical properties of polymer latex such as particle size and
 latex stability. Examples of these ionogenic monomers are vinyl
 sulfonate(H.sup.+, Na, or K.sup.+ salt), 2-sulfoethylmethacrylate(H.sup.+,
 Na, or K.sup.+ salt), 3-sulfopropyl-methacrylate(H.sup.+, Na, or K.sup.+
 salt), sodium styrene sulfonate, potassium styrene sulfonate,
 2-acryloamido-2-methyl-1-propanesulfonic acid(H.sup.+, Na, or K.sup.+
 salt), vinyl phosphoric acid, acrylic and methacrylic acid. Surface-active
 ionogenic monomers, such as examples in U.S. Pat. No. 4,340,664, can also
 be used to modify the physical properties of polymer latex. The preferred
 water soluble ionogenic monomer for use in the process is the
 2-acryloamido-2-methyl-1-propanesulfonic acid as this material provides a
 stable polymer latex dispersion. Ionogenic monomers can be used with
 hydrophobic monomers to form the core or used with hydrophilic monomers
 defined in formula (I) to form the shell.
 A buffering agent can also be used to control the pH of the polymerization
 medium. Examples of buffering agents include sodium bicarbonate, sodium
 carbonate, potassium phosphate, potassium hydrogen phosphate, potassium
 hydrogen phthalate, sodium acetate, sodium succinate, and Borax.
 These polymer latexes are prepared by the emulsion polymerization method.
 Emulsion polymerizations are well known in the art and are described in:
 (1) F. A. Bovey, Emulsion Polymerization, Interscience Publishers Inc.,
 New York, 1955; (2) C. Schildknecht and I. Skeist, Polymerization Process,
 pp. 143-197, Wiley-Interscience Publication, NY, 1977; (3) R. Fitch,
 Polymer Colloid II, Plenum Press, NY, 1980; and (4) P. A. Lovell, M. S.
 El-Aasser, Emulsion Polymerization and Emulsion Polymers, Wiley, NY, 1997.
 .alpha.-olefin sulfonate. The amount of surfactant used to stabilize the
 polymer latex is between 0.1 and 20% and, preferably, between 2 to 10%
 based on the total weight of monomers. A large number of surface-active
 compounds are suitable as emulsifying agents, such as soaps,
 alkylsulfonate and sulfates, cationic compounds, amphoteric compounds,
 nonionic surfactants, and high molecular weight protective colloids. A
 complete list of surfactants can be found in McCutcheon's Emulsifiers &
 Detergents, MC Publishing Co., Glen Rock, NJ, USA. Examples are sodium
 N-methyl-Noleoyltaurate, .alpha.-olefin sulfonate, sodium dodecylbenzene
 sulfonate, sodium dodecyl sulfate, sodium or ammonimn salt of sulfated
 nonylphenoxypoly (ethyleneoxy) ethanol, sodium alkylnaphthalene sulfonate,
 ethoxylated alkylphenols, monM-1 thanolamine dodecyldiphenyloxide
 disulfonate, derivatives of sulfosuccinate,
 poly(ethyleneoxy-b-propyleneoxy), sodium salt of alkylaryl polyether
 sulfonate, poly(saccharides), sucrose and glucose esters and derivatives.
 Preferred surfactants are sodium dodecyl sulfate, sodium
 N-methyl-N-oleoyltaurate, and .alpha.-olefin sulfonate. .alpha.-olefin
 sulfonate is especially efficient to prepare the ultrafine particle size
 latex of this invention.
 The free-radical polymerization of solid monomer is initiated by the
 addition to the monomer molecule of a free radical that has been formed
 either by thermal decomposition, by the oxidation-reduction reaction, or
 by physical action such as by UV light or other high energy radiation,
 ultrasonic waves, etc. A more complete list of initiating agents is given
 in F. A. Bovey, Emulsion Polymerization, Interscience Publishers, Inc.,
 New York, (1955), p. 59-93. Watersoluble initiators are preferred and can
 be added to the solid dispersion, to the polymerization vessel, or both.
 Examples are the salt of persulfate (sodium, potassium, and ammonium),
 hydrogen peroxide, 4,4-azobis(4-cyanovaleric acid),
 2,2'-azobis(2-methyl-N-(2-hydroxyethyl)propionamide),
 2,2'-azobis(2-methyl-N-(1,1-bis(hydroxymethyl)ethyl) propionamide,
 2,2'-azobis(N,N'-dimethyleneisobutyramide) dihydrochloride, hydrogen
 peroxide-Fe.sup.+, persulfate-metabisulfite, persulfate-bisulfite,
 persulfate-sodium formaldehyde sulfoxylate, talkyl hydroperoxide, sodium
 formaldehyde sulfoxylate, etc. Examples of oil-soluble initiators include
 azobis(isobutyronitrile), dimethyl 2,2'-azobis-isobutyrate, alkyl
 hydroperoxide, etc. The amount of catalyst is usually from 0.01 to 5% by
 weight, preferably 0.1 to 3.0% by weight of the total monomers. The
 preferred free radical polymerization initiator is sodium persulfate as
 this material gives a high yield of the polymer latex and rapid
 polymerization.
 The formation of core-shell latexes with the composition of this invention
 is carried out by the seeded polymerization method. The hydrophobic
 monomers of this invention were polymerized by batch or semicontinous
 process first to form the seed. The hydrophilic monomers of this invention
 was then fed to the preformed seed polymer particles semicontinously to
 form the shell structure.
 Preferred polymers of this invention are shown in Table 2.
 TABLE 2
 Polymer I.D. Core (wt %) Shell(wt %)
 P-1 Ema(85) M-1(10)
 NaAMPS(4.5) NaAMPS(0.5)
 P-2 Ema(85) M-2(10)
 NaAMPS(4.5) NaAMPS(0.5)
 P-3 Ema(85) M-20(10)
 NaAMPS(4.5) NaAMPS(0.5)
 P-4 Ema(85) M-20(15)
 NaAMPS(4.5) NaAMPS(0.5)
 P-5 Ema(75) M-4(10)
 NaAMPS(4) Ema(10)
 NaAMPS(1)
 P-6 Ema(75) M-28(10)
 NaAMPS(4) Ema(10)
 NaAMPS(1)
 P-7 Ema(75) M-27(10)
 NaAMPS(4) Ema(10)
 NaAMPS(1)
 P-8 Ema(75) M-23(10)
 NaAMPS(4) Ema(10)
 NaAMPS(1)
 P-9 Ema(75) M-24(10)
 NaAMPS(4) Ema(10)
 NaAMPS(1)
 P-10 Ema(80) M-1(15)
 NaAMPS(4.5) NaAMPS(0.5)
 P-11 Ema(80) M-2(15)
 NaAMPS(4.5) NaAMPS(0.5)
 P-12 Ema(80) M-20(15)
 NaAMPS(4.5) NaAMPS(0.5)
 P-13 Ema(85) M-1(14.5)
 NaAMPS(0.5)
 P-14 Ema(85) M-2(14.5)
 NaAMPS(0.5)
 P-15 Ema(85) M-20(10)
 NaAMPS(0.5)
 P-13 Ema:Aa(80:5) M-1(14.5)
 NaAMPS(0.5)
 P-14 Ema:Aa(80:5) M-2(14.5)
 NaAMPS(0.5)
 P-15 Ema:Aa(80:5) M-20(14.5)
 NaAMPS(0.5)
 P-16 Ema:Aa(80:5) M-3(14.5)
 NaAMPS(0.5)
 P-17 Mma(85) M-1(10)
 NaAMPS(4.5) NaAMPS(0.5)
 P-18 Mma(85) M-2(10)
 NaAMPS(4.5) NaAMPS(0.5)
 P-19 Mma(85) M-20(10)
 NaAMPS(4.5) NaAMPS(0.5)
 P-20 Mma(80) M-20(15)
 NaAMPS(4.5) NaAMPS(0.5)
 P-21 Mma(85) M-4(10)
 NaAMPS(4.5) NaAMPS(0.5)
 P-22 Mma(85) M-28(10)
 NaAMPS(4.5) NaAMPS(0.5)
 P-23 Bma(85) M-1(10)
 NaAMPS(4.5) NaAMPS(0.5)
 P-24 Bma(85) M-2(10)
 NaAMPS(4.5) NaAMPS(0.5)
 P-25 Bma(85) M-20(10)
 NaAMPS(4.5) NaAMPS(0.5)
 P-26 Bma(80) M-20(15)
 NaAMPS(4.5) NaAMPS(0.5)
 P-27 Bma(85) M-4(10)
 NaAMPS(4.5) NaAMPS(0.5)
 P-28 Bma(85) M-28(10)
 NaAMPS(4.5) NaAMPS(0.5)
 P-29 Ba(85) M-1(10)
 NaAMPS(4.5) NaAMPS(0.5)
 P-30 Ba(85) M-2(10)
 NaAMPS(4.5) NaAMPS(0.5)
 P-31 Ba(85) M-20(10)
 NaAMPS(4.5) NaAMPS(0.5)
 P-32 Ba(85) M-20(15)
 NaAMPS(4.5) NaAMPS(0.5)
 P-33 Ba(85) M-4(10)
 NaAMPS(4.5) NaAMPS(0.5)
 P-34 Ba(85) M-28(10)
 NaAMPS(4.5) NaAMPS(0.5)
 Ema: Ethyl methacrylate
 Mma: Methyl methacrylate
 NaAMPS: 2-acryloamido-2-methyl-1-propanesulfonic acid, sodium salt
 Bma: n-Butyl methacrylate
 Ba: n-Butyl acrylate
 Aa: Acrylic acid
 The core-shell latexes of this invention are particularly useful for the
 loading of photographically useful compounds. Examples of the
 photographically useful compounds which can be loaded into polymer latexes
 of this invention include couplers (yellow, cyan, and magenta), masking
 couplers, inhibitor-releasing couplers, bleach accelerator-releasing
 couplers, white couplers, dye-releasing couplers, WV absorbers,
 photostabilizers, filter dyes, high-boiling organic solvents, reducing
 agents(including oxidized developer scavengers and nucleators),
 developers, development inhibitors and moderators, optical brighteners,
 and lubricants, etc. Examples of the photographically useful compounds are
 listed in EP 0 727 704, p-4 to p-21.
 The typical procedure for the preparation of core-shell latex of this
 invention are demonstrated by the following examples.

EXAMPLE 1
 Preparation of P-1 core-shell latex
 First stage-preparation core latex
 200 ml deionized water and 3.75 g of Rhodacal A-246L (.alpha.-olefin
 sulfonate, 40 percent solid) were charged to a 500 ml 3-neck round flask
 equipped with a condenser, mechanical stirrer, and nitrogen inlet. The
 flask was immersed in an 80.degree. C. constant temperature bath and
 purged with nitrogen for 30 mins. A monomer emulsion comprising 95 g of
 ethylmethacrylate, 10 g of 2-acryloamido2-methyl-1-propanesulfonic
 acid(sodium salt,50%), 3.75 g of Rhodacal A-246L (.alpha.-olefin
 sulfonate, 40% solid), 10 g of 10% sodium persulfate, and 200 ml of
 deionized water was fed to the reactor over 2.25 hours. The latex was
 further polymerized for 30 mins after the monomer addition was finished.
 Second stage- preparation of shell latex
 A second monomer emulsion comprising 11.1 g of 2-ethoxyethylacrylate, 1.17
 g of 2-acryloamido-2-methyl-1-propanesulfonic acid (sodium salt, 50%), 1.1
 g of 10% sodium persulfate, 0.83 g of Rhodacal A-246L (.alpha.-olefin
 sulfonate, 40% solid), and 20 g deionized water was fed to the preformed
 latex from stage one over 10 mins and further polymerized for one hour.
 The latex was then cooled to room temperature and filtered. The % solid of
 the core-shell latex was 20.5% and the Z-average particle size was 43.8
 nm.
 EXAMPLE 2
 Preparation of P-2 core-shell latex
 The preparation and composition of the ethylmethacrylate core latex was
 same as in example 1. The second stage monomer feed was composed of 11.1 g
 of 2-methoxyethylacrylate, 1.17 g of 2-acryloamido-2-methyl-1
 propanesulfonic acid (sodium salt, 50%), 1.1 g of 10% sodium persulfate,
 0.83 g of Rhodacal A-246L(.alpha.-olefin sulfonate, 40% solid), and 20 g
 D.I. water. The percent solids of the core-shell latex was 20.1% and the
 Z-average particle size was 40.9 nm.
 EXAMPLE 3
 Preparation of P-3 core-shell latex
 The preparation and composition of the ethylmethacrylate core latex was
 same as in example 1. The second stage monomer feed was composed of 11.1 g
 of 2-ethoxyethoxyethylacrylate, 1.17 g of
 2-acryloamido-2-methyl-1-propanesulfonic acid (sodium salt, 50%), 1.1 g of
 10% sodium persulfate, 0.83 g of Rhodacal A-246L (.alpha.-olefin
 sulfonate, 40% solid), and 20 g deionized water. The percent solid of the
 core-shell latex was 20.0% and the Z-average particle size was 42.5 nm.
 EXAMPLE 4
 Preparation of P-4 core-shell latex
 The preparation and composition of the ethyhnethacrylate core latex was
 same as example 1. The second stage monomer feed was composed of 17.8 g of
 2-ethoxyethoxyethylacrylate, 1.87 g of
 2-acryloamido-2-methyl-1-propanesulfonic acid (sodium salt, 50%), 1.87 g
 of 10% sodium persulfate, 1.33 g of Rhodacal A-246L (.alpha.-olefin
 sulfonate, 40% solid), and 30 g deionized. water. The % solid of the
 core-shell latex was 20.8% and the Z-average particle size was 46.2 nm.
 EXAMPLE 5
 Preparation of P-5 core-shell latex
 The preparation of the ethylmethacrylate core latex was same as in example
 1 except 83.9 g of ethylmethacrylate and 8.84 g of
 2-acryloamido-2-methyl-1-propanesulfonic acid (sodium salt) was used. The
 second stage monomer feed was composed of 11.1 g of ethylmethacrylate,
 11.1 g of 2-hydroxyethylmethacrylate, 2.34 g of
 2-acryloamido-2-methyl-1-propanesulfonic acid (sodium salt, 50%), 2.2 g of
 10% sodium persulfate, 1.66 g of Rhodacal A246L (.alpha.-olefin sulfonate,
 40 percent solid), and 40 g deionized water. The % solid of the core-shell
 latex was 19.6% and the Z-average particle size was 44.6 nm.
 EXAMPLE 6
 Preparation of P-6 core-shell latex
 The preparation of the ethylmethacrylate core latex was the same as example
 5. The second stage monomer feed was composed of 11.1 g of
 ethylmethacrylate, 11.1 g of Sartomer SR-604 (polypropylene glycol
 methacrylate, MW. 405), 2.34 g of 2-acryloamido-2-methyl-1-propanesulfonic
 acid (sodium salt, 50%), 2.2 g of 10% sodium persulfate, 1.66 g of
 Rhodacal A246L (.alpha.-olefin sulfonate, 40% solid), and 40 g D.I. water.
 The % solid of the core-shell latex was 19.4% and the Z-average particle
 size was 42.6 nm.
 EXAMPLE 7
 Preparation of P-7 core-shell latex
 The preparation of the ethylmethacrylate core latex was the same as example
 5. The second stage monomer feed was composed of 1.1 g of
 ethylmethacrylate, 11.1 g of methoxypolyoxyethylene methacrylate
 (Polyscience catalogue number 16663), 2.34 g of
 2-acryloamido-2-methyl-1-propanesulfonic acid (sodium salt, 50%), 2.2 g of
 10% sodium persulfate, 1.66 g of Rhodacal A246L (.alpha.-olefin sulfonate,
 40% solid), and 40 g deionized water. The % solid of the core-shell latex
 was 19.1% and the Z-average particle size was 40.8 nm.
 EXAMPLE 8
 Preparation of P-8 core-shell latex
 The preparation of the ethylmethacrylate core latex was the same as example
 5. The second stage monomer feed was composed of 11.1 g of
 ethylmethacrylate, 11.1 g of polyethyleneoxide methacrylate
 (Monomer&Polymer, Dajac, catalogue #8926), 2.34 g of
 2-acryloamido-2-methyl-1-propanesulfonic acid (sodium salt, 50%), 2.2 g of
 10% sodium persulfate, 1.66 g of Rhodacal A-246L (.alpha.-olefin
 sulfonate, 40% solid), and 40 g deionized water. The % solid of the
 core-shell latex was 19.2% and the Z-average particle size was 41.2 nm.
 EXAMPLE 9
 Preparation of P-9 core-shell latex
 The preparation of the ethylmethacrylate core latex was the same as example
 5. The second stage monomer feed was composed of 11.1 g of
 ethylmethacrylate, 11.1 g of polyethyleneoxide methacrylate (HEMA-20 by
 Alcolac), 2.34 of 2-acryloamido-2-methyl-1-propanesulfonic acid sodium
 salt, 50%), 2.2 g of 10% sodium persulfate, 1.66 g of Rhodacal A-246L
 (.alpha.-olefin sulfonate, 40% solid), and 40 g deionized water. The %
 solid of the core-shell latex was 19.1% and the Z-average particle size
 was 45 nm.
 The preparation of small particle size latexes which do not have the
 core-shell structures as described in this invention are described below
 as comparison examples.
 Comparison Example 1
 Preparation of Ema/NaAMPS(95/5) non core-shell latex
 200 ml deionized water and 3.75 g of Rhodacal A-246L (.alpha.-olefin
 sulfonate, 40% solid) were charged to a 500 ml 3-neck round bottom flask
 equipped with a condenser, mechanical stirrer, and nitrogen inlet. The
 flask was immersed in an 80.degree. C. constant temperature bath and
 purged with nitrogen for 30 mins. A monomer emulsion comprising 95 g of
 ethylmethacrylate, 10 g of 2-acryloamido-2-methyl-1-propanesulfonic acid
 (sodium salt), 3.75 g of Rhodacal A-246L (.alpha.-olefin sulfonate, 40%
 solid), 10 g of 10% sodium persulfate, and 200 ml of deionized water was
 fed to the reactor over 2.25 hours. The latex was further polymerized for
 30 mins after the monomer addition was finished. The latex was cooled and
 filtered. The % solid of the core-shell latex was 20% and the Z-average
 particle size was 40.0 nm.
 Comparison Example 2
 Preparation of Ema/Aa/NaAMPS(85/10/5) core-shell latex
 The preparation and composition of the ethylmethacrylate core latex was
 same as in example 5. The second stage monomer feed was composed of 11.1 g
 of ethylmethacrylate, 11.1 g of acrylic acid, 2.34 g of
 2-acryloamido-2-methyl-1-propanesulfonic acid(sodium salt, 50%), 2.2 g of
 10% sodium persulfate, 1.66 g of Rhodacal A-246L (.alpha.-olefin
 sulfonate, 40% solid), and 40 g deionized water. The % solid of the
 core-shell latex was 20.1% and the Z-ave particle size was 43 nm.
 Comparison Example 3
 Preparation of Ema/Maa/NaAMPS(85/10/5) coreshell latex
 The preparation and composition of the ethylmethacrylate core latex was
 same as in example 5. The second stage monomer feed was composed of 11.1 g
 of ethylmethacrylate, 11.1 g of methacrylic acid, 2.34 g of
 2-acryloamido2-methyl-1-propanesulfonic acid (sodium salt, 50%), 2.2 g of
 10% sodium persulfate, 1.66 g of Rhodacal A-246L (.alpha.-olefin
 sulfonate, 40% solid), and 40 g deionized water. The % solid of the
 core-shell latex was 19.9% and the Z-average particle size was 43.2 nm.
 Comparison Example 4
 Preparation of Ba/NaAMPS(95/5) non core-shell latex
 The preparation of Ba/NaAMPS(95/5) non core-shell latex was same as in
 comparison example 1 except that 95 g of n-butyl acrylate was used. The
 particle size was 44 nm and the % solid of the core-shell latex was 19.8%.
 Comparison Example 5
 Preparation of Bma/NaAMPS(95/5) non core-shell latex
 The preparation of Bma/NaAMPS(95/5) non core-shell latex was same as in
 comparison example 1 except that 95 g of n-butyl methacrylate was used.
 The particle size was 55 nm and the % solid of the core-shell latex was
 19.9%.
 Comparison Example 6
 Preparation of non Core-Shell Ema/M2/NaAMPS(85/10/5)latex
 The composition is the same as invention example 2 except that all monomers
 were fed together to the reactor over three hours. The resulting non
 core-shell latex had a particle size of 65 nm, which is much larger than
 the corresponding core-shell latex prepared by the seeded polymerization
 of this invention.
 Comparison Example 7
 Preparation of non Core-Shell Ema/M-28/NaAMPS(85/10/5)latex
 The composition is the same as invention example 7 except that all monomers
 were fed together to the reactor over three hours. The resulting non
 core-shell latex had a particle size of 80 nm, which is much larger than
 the corresponding core-shell latex prepared by the seeded polymerization
 of this invention.
 The advantages of the latexes of this invention will become more apparent
 by the following two viscosity experiments.
 Viscosity of Gelatin Solution Containing Ultrafine Particle Size Latexes
 Viscosity measurement were made on a solution containing 5.32% gelatin and
 8% latex to simulate the photographic dispersion. The viscosity was
 measured at 45.degree. C. by using a Brookfield HBTDV-IICP200 Digital
 Viscomer. Table 3 shows the viscosity values of a series ultrafine latexes
 of this invention and comparative examples.
 TABLE 3
 Particle
 Viscosity cps @
 Polymer ID Composition Wt Ratio Core-shell Size (nm) 75
 sec-1 Remark
 Comparison Ema:NaAMPS 95/5 No 40
 41.80 Comparison
 1
 Comparison Ema:Aa:NaAMPS 85/10/5 No 43
 44.50 Comparison
 2
 Comparison Ema:Maa:NaAMPS 85/10/5 Yes 43 41.8
 Comparison
 3
 Comparison Ba:NaAMPS 95/5 No 44 123
 Comparison
 4
 Comparison Bma:NaAMPS 95/5 No 55 63
 Comparison
 5
 Comparison Ema:M-2:NaAMPS 85/10/5 No 65 36
 Comparison
 6
 Comparison Ema:M-28:NaAMPS 85/10/5 No 80 38
 Comparison
 7
 P-2 Ema:M-2:NaAMPS 85/10/5 Yes 41
 31.40 Invention
 P-3 Ema:M-20:NaAMPS 85/10/5 Yes 43
 31.40 Invention
 P-4 Ema:M-20:NaAMPS 80/15/5 Yes 46
 23.50 Invention
 P-5 Ema:M-4:NaAMPS 85/10/5 Yes 45
 23.50 Invention
 P-6 Ema:M-28:NaAMPS 85/10/5 Yes 43 28.8
 Invention
 P-7 Ema:M-27:NaAMPS 85/10/5 Yes 41
 18.30 Invention
 P-8 Ema:M-23:NaAMPS 85/10/5 Yes 41 23.5
 Invention
 P-9 Ema:M-24:NaAMPS 85/10/5 Yes 45 26.2
 Invention
 Ema: Ethyl methacrylate
 Mma: Methyl methacrylate
 NaAMPS: 2-acryloamido-2-methyl-1-propanesulfonic acid, sodium salt
 Bma: n-Butyl methacrylate
 Ba: n-Butyl acrylate
 Aa: Acrylic acid
 Maa: Methacrylic acid
 It is clear from Table 3 that polymer latexes of this invention have much
 lower melt viscosities than the comparative examples of similar particle
 sizes (comparison example 1, 2, 3) without the functional monomers of this
 invention. Also, comparison example 6 and 7, which have the same
 composition as invention example P-2 and P-7, have much larger particle
 size and higher viscosity. This table also demonstrates that other
 hydrophilic monomers, such as acrylic acid and methacrylic acids
 (comparison examples 2 and 3) are not as effective to reduce the melt
 viscosity as the functional monomers defined in formula (1).
 Viscosity of Gelatin Solution Containing Ultrafine Particle Size Latexes
 Loaded with Oxidized Developer Scavenger
 Selected latexes were chosen for the loading of Dox scavenger (Table 4) to
 the study the effect of comonomers on the reactivity of Dox scavengers and
 their melt viscosity. The dispersion was composed of 5.32% Dox scavenger,
 2.26% dibutyl phthalate, 5.32% of latexes, and 8.0% of gelatin. Dox
 scavenger and dibutyl phthalate were mixed and heated at 110-120.degree.
 C. until a homogeneous solution was obtained. An aqueous solution
 containing gelatin and latex was added to form a pre-mix. The premix was
 then passed through a microfluidizer in a constant temperature bath at
 70.degree. C., and with pressure of 7200 psi for three cycles. This
 process is described in U.S. Pat. No. 5,594,047.
 In order to effectively evaluate magenta crosstalk (i. e., magenta dye
 density from a blue separation exposure) as a function of Dox scavengers
 reactivity, a simplified multilayer coating format (Table 4) was
 developed. Dox scavengers from various dispersions were coated at 6 and 12
 mg/sq.fi. Coatings were then exposed and processed through standard RA4
 process. Crosstalk was determined by the ratio of Dmax(Green) to
 Dmax(Blue), where high crosstalk is ndicative of low Dox scavengers
 reactivity. The dispersion viscosity at 7.5 and 75 sec.sup.-1 and the
 reactivity of the loaded Dox scavenger dispersion were tabulated in Table
 5.
 TABLE 4
 SOC Gel 100 mg/ft.2
 Alk-XC 0.86 mg/ft.2
 FT-248 0.35 mg/ft.2
 BVSME 1.8% total gel
 Magenta Magenta Coupler 1 27 mg/ft.2
 coupler Alk-XC 1 mg/ft.2
 Gel 120 mg/ft.2
 IL Dox Scavenger 6, 12 mg/ft.2
 Alk-XC 1 mg/ft.2
 Gel 70 mg/ft.2
 Yellow Yellow Coupler 1 45 mg/ft.2
 coupler/AgX AgX 24 mg/ft.2
 Gel 146 mg/ft.2
 Q2171 (DOX-4012) 0.13 mg/ft.2
 ##STR33##
 Coating format for the investigation of Dox scavengers reactivity.

##STR34##
 TABLE 5
 Particle Viscosity
 Viscosity
 Size (nm) cps @ 7.5 cps @
 75 Crosstalk @
 Polymer ID Composition Wt Ratio of latex sec-1
 sec-1 12 mg/ft2 Remarks
 Comparison Ema:NaAMPS 95/5 40 1260 510
 0.287 Comparison
 1
 Comparison Ema:Aa:NaAMPS 85/10/5 43 1650 645
 0.296 Comparison
 2
 Comparison Ema:Maa:NaAMPS 85/10/5 43 1340 600
 0.263 Comparison
 3
 P-2 Ema:M-2:NaAMPS 85/10/5 41 705 356
 0.276 Invention
 P-5 Ema:M-4:NaAMPS 85/10/5 45 735 382
 0.318 Invention
 P-6 Ema:M-28:NaAMPS 85/10/5 43 680 358
 0.286 Invention
 The advantages of the polymer latexes of this invention is very clear from
 Table 5 that the dispersion comprising Dox scavenger loaded in the latexes
 of this invention have good scavenging activities but their melt
 viscosities are much lower than the comparative polymer latexes of similar
 particle sizes.
 The invention has been described in detail with particular reference to
 certain preferred embodiments thereof, but it will be understood that
 variations and modifications can be effected within the spirit and scope
 of the invention.