WO2018087710A1

WO2018087710A1 - Method of making core-shell particles by osmotic swelling

Info

Publication number: WO2018087710A1
Application number: PCT/IB2017/057049
Authority: WO
Inventors: Martin LOPEZ MARTINEZ; Raymundo MASCORRO DE LA FUENTE
Original assignee: Centro De Investigacion En Polimeros S.A. De C.V.
Priority date: 2016-11-11
Filing date: 2017-11-10
Publication date: 2018-05-17
Also published as: MX2019005460A

Abstract

An aqueous dispersion of polymeric particles, the particles comprising (a) a core polymer prepared from at least one hydrophilic ethylenically unsaturated monomer; (b) at least one first shell polymer at least partially encapsulating the core polymer, the first shell polymer prepared from a mixture of reactants comprising (b)(i) at least one hydrophilic ethylenically unsaturated monomer and (b)(ii) at least one aromatic monomer having a hydrophilic surfactant group and an ethylenically unsaturated group reactive with the hydrophilic ethylenically unsaturated monomer (b)(i); (c) at least one second shell polymer at least partially encapsulating the first shell polymer, the second shell polymer prepared from a mixture of reactants comprising (c)(i) at least one aromatic monomer having an ethylenically unsaturated group and (c)(ii) an aromatic monomer having a hydrophilic surfactant group and an ethylenically unsaturated group reactive with the aromatic monomer (c)(i); and (d) an optional third shell polymer at least partially encapsulating the second shell polymer, the third shell polymer prepared from at least one polymerizable aromatic monomer, wherein the polymeric particle defines a void.

Description

METHOD OF MAKING CORE-SHELL PARTICLES BY OSMOTIC SWELLING

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 62/420,999 filed November 11, 2016, the disclosure of which is hereby incorporated in its entirety by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to polymeric particles having a core-shell structure, processes for producing the particles, and their use in coating compositions.

BACKGROUND OF THE INVENTION

[0003] Hollow particles having a core-shell structure defining an internal void have been developed as scattering components in coating compositions. Such particles may replace at least a portion of titanium dioxide that is conventionally used as a white pigment in paints and other coating compositions.

SUMMARY OF THE INVENTION

[0004] The present invention includes an aqueous dispersion of polymeric particles, the particles comprising: (a) a core polymer prepared from at least one hydrophilic ethylenically unsaturated monomer; (b) at least one first shell polymer at least partially encapsulating the core polymer, the first shell polymer prepared from a mixture of reactants comprising (b)(i) at least one hydrophilic ethylenically unsaturated monomer and (b)(ii) at least one aromatic monomer having a hydrophilic surfactant group and an ethylenically unsaturated group reactive with the hydrophilic ethylenically unsaturated monomer (b)(i); (c) at least one second shell polymer at least partially encapsulating the first shell polymer, the second shell polymer prepared from a mixture of reactants comprising (c)(i) at least one aromatic monomer having an ethylenically unsaturated group and (c)(ii) an aromatic monomer having a hydrophilic surfactant group and an ethylenically unsaturated group reactive with the aromatic monomer (c)(i); and (d) an optional third shell polymer at least partially encapsulating the second shell polymer, the third shell polymer prepared from at least one polymerizable aromatic monomer, wherein the polymeric particle defines a void.

[0005] Also included in the present invention is a method of producing polymeric particles comprising: (a) forming an aqueous dispersion of a core polymer by polymerizing at least one hydrophilic ethylenically unsaturated monomer; (b) forming at least one first shell polymer at least partially encapsulating the core polymer by polymerizing onto the core polymer at least one hydrophilic ethylenically unsaturated monomer (i) and at least one aromatic monomer (ii) having a hydrophilic surfactant group and an ethylenically unsaturated group reactive with the hydrophilic ethylenically unsaturated monomer (i); (c) forming at least one second shell polymer at least partially encapsulating the first shell polymer by polymerizing onto the first shell polymer at least one aromatic monomer (iii) having an ethylenically unsaturated group and an aromatic monomer (iv) having a hydrophilic surfactant group and an ethylenically unsaturated group reactive with the aromatic monomer (iii); (d) optionally forming a third shell polymer at least partially encapsulating the second shell polymer by polymerizing onto the second shell polymer at least one aromatic monomer; and (e) adding a swelling agent to the aqueous dispersion during or after polymerization of the second or third shell polymer in steps (c) or (d).

[0006] The present invention further includes a method of producing core-shell polymeric particles in a multi-stage emulsion polymerization process comprising: (a) producing core polymeric particles and a plurality of polymeric shells at least partially encapsulating the core polymeric particles, wherein the core polymeric particles are prepared from at least one hydrophilic ethylenically unsaturated monomer and at least one of the polymeric shells are produced from a mixture of reactants comprising (i) at least one hydrophilic ethylenically unsaturated monomer and (ii) an ionic ethylenically unsaturated surfactant molecule; and (b) forming an outer shell polymer at least partially encapsulating the particles from step (a) by polymerizing thereon an ethylenically unsaturated monomer in the presence of a swelling agent to swell the core polymeric particles.

DESCRIPTION OF THE INVENTION

[0007] For purposes of the following detailed description, it is to be understood that the invention may assume various alternative variations and step sequences, except where expressly specified to the contrary. Moreover, other than in any operating examples, or where otherwise indicated, all numbers expressing, for example, quantities of ingredients used in the specification and claims are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0008] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard variation found in their respective testing measurements.

[0009] Also, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of "1 to 10" is intended to include all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10.

[0010] In this application, the use of the singular includes the plural and plural encompasses singular, unless specifically stated otherwise. In addition, in this application, the use of "or" means "and/or" unless specifically stated otherwise, even though "and/or" may be explicitly used in certain instances. Further, in this application, the use of "a" or "an" means "at least one" unless specifically stated otherwise. For example, "a" polymer shell, "a" polymerizable ethylenically unsaturated hydrophilic monomer, and the like refer to one or more of any of these items.

[0011] As used herein, the term "non-aqueous" refers to a liquid medium comprising less than 50 weight (wt.) % water, based on the total weight of the liquid medium. In accordance with the present invention, such non-aqueous liquid mediums can comprise less than 40 wt. % water, or less than 30 wt. % water, or less than 20 wt. % water, or less than 10 wt. % water, or less than 5 wt. % water, based on the total weight of the liquid medium. The solvents that make up 50 wt. % or more of the liquid medium include organic solvents. Non-limiting examples of suitable organic solvents include polar organic solvents (e.g., protic organic solvents such as glycols, glycol ether alcohols, alcohols; and ketones, glycol diethers, esters, and diesters). Other non-limiting examples of organic solvents include aromatic and aliphatic hydrocarbons.

[0012] Further, the term "polymer" refers to oligomers and homopolymers (e.g., prepared from a single monomer species), copolymers (e.g., prepared from at least two monomer species), polymers prepared with more than two, such as three or more, monomer species, and graft polymers. The term "resin" is used interchangeably with "polymer." [0013] As used herein, "(meth)acrylate" and like terms refer both to the acrylate and the corresponding methacrylate. The term "(meth)acryloyl" and like terms refer both to the acryloyl and the corresponding methacryloyl. Also, "(meth)acrylamide" and like terms refer both to the acrylamide and the corresponding methacrylamide. Herein, the term "silane" refers to a compound derived from S1H4 by substituting organic groups for at least some of the hydrogen atoms, and the term "alkoxy" refers to an -O-alkyl group. Further, an "alkoxysilane" refers to a silane compound with at least one alkoxy group bonded to a silicon atom.

[0014] As used herein, a "hydrocarbon" refers to a group formed from hydrogen and carbon atoms. The hydrocarbon can include a linear, branched, and/or cyclic hydrocarbon group.

[0015] The term "alkyl" as used herein refers to a linear, branched, and/or cyclic monovalent hydrocarbon radical. The alkyl group may include, but is not limited to, a linear or branched Cl- C30 monovalent hydrocarbon radical, or a linear or branched C1-C20 monovalent hydrocarbon radical, or a linear or branched C1-C10 monovalent hydrocarbon radical. The alkyl group may also include, but is not limited to, a cyclic C3-C19 monovalent hydrocarbon radical, or a cyclic C3-C12 monovalent hydrocarbon radical, or a cyclic C5-C7 monovalent hydrocarbon radical.

[0016] Further, the term "alkylene" refers to a linear, branched, and/or cyclic divalent hydrocarbon radical. The alkylene group may include, but is not limited to, a linear or branched C1-C30 divalent hydrocarbon radical, or linear or branched C1-C20 divalent hydrocarbon radical, or linear or branched CI -CIO divalent hydrocarbon radical. The alkylene group may also include, but is not limited to, a cyclic C3-C19 divalent hydrocarbon radical, or a cyclic C3-C12 divalent hydrocarbon radical, or a cyclic C5-C7 divalent hydrocarbon radical.

[0017] The alkyl and alkylene groups, as well as any of the other groups described herein, can also include substituted groups thereof. As used herein, "substituted" and "substituted group" means a group, such as an alkyl group or alkylene group for example, in which at least one hydrogen thereof has been optionally replaced or substituted with a group that is other than hydrogen, such as, but not limited to, halo groups (e.g., F, CI, I, and Br), hydroxyl groups, ether groups, thiol groups, thio ether groups, carboxylic acid groups, carboxylic acid ester groups, phosphoric acid groups, phosphoric acid ester groups, sulfonic acid groups, sulfonic acid ester groups, nitro groups, cyano groups, hydrocarbyl groups, and amine groups.

[0018] The polymeric particles of the present invention are provided in an aqueous dispersion, where the aqueous dispersion includes (a) a core polymer prepared from at least one hydrophilic ethylenically unsaturated monomer; (b) at least one first shell polymer at least partially encapsulating the core polymer, the first shell polymer prepared from a mixture of reactants comprising (b)(i) at least one hydrophilic ethylenically unsaturated monomer and (b)(ii) at least one aromatic monomer having a hydrophilic surfactant group and an ethylenically unsaturated group reactive with the hydrophilic ethylenically unsaturated monomer (b)(i); (c) at least one second shell polymer at least partially encapsulating the first shell polymer, the second shell polymer prepared from a mixture of reactants comprising (c)(i) at least one aromatic monomer having an ethylenically unsaturated group and (c)(ii) an aromatic monomer having a hydrophilic surfactant group and an ethylenically unsaturated group reactive with the aromatic monomer (c)(i); and (d) an optional third shell polymer at least partially encapsulating the second shell polymer, the third shell polymer prepared from at least one polymerizable aromatic monomer, wherein the polymeric particle defines a void.

[0019] As used herein, "ethylenically unsaturated" refers to a group having at least one carbon- carbon double bond. The phrase "polymerizable ethylenically unsaturated" refers to an ethylenically unsaturated group that participates in chemical reactions.

[0020] The term "hydrophilic" refers to a property of a compound or a group having an affinity for water and aqueous solutions or aqueous dispersions.

[0021] By "core polymer" it is meant from 5 to 100 percent by weight, based on the weight of the core polymer, of at least one hydrophilic ethylenically unsaturated monomer and up to 98 percent by weight, based on the weight of the core polymer, of at least one nonionic ethylenically unsaturated monomer. By "seed" or "seed emulsion" it is meant a dispersion of particles of core polymers.

[0022] Suitable hydrophilic ethylenically unsaturated monomers useful for producing the core polymer (a) include ethylenically unsaturated monomers containing acid-functionality such as monomers containing at least one carboxylic acid group including acrylic acid, methacrylic acid, acryloxypropionic acid, (meth)acryloxypropionic acid, itaconic acid, aconitic acid, maleic acid or anhydride, fumaric acid, crotonic acid, monomethyl maleate, monomethyl fumarate, monomethyl itaconate and the like.

[0023] The copolymer may be produced from at least one hydrophilic ethylenically unsaturated monomer that is susceptible to swelling, as described below, by water or aqueous solutions. The monomers used to produce the copolymer may further include other monomers, such as nonionic ethylenically unsaturated monomers.

[0024] Suitable nonionic ethylenically unsaturated monomers for producing the core polymer include ethylene, vinyl acetate, vinyl chloride, vinylidene chloride, (meth)acrylonitrile, (meth)acrylamide, (Ci-C2o)alkyl or (C3-C2o)alkenyl esters of (meth)acrylic acid, such as methyl(meth)acrylate, ethyl(meth)acrylate, butyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, hydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate, 1,3-propane diol di(meth)acrylate, 1,4-butane diol di(meth)acrylate, 1,6-hexane diol di(meth)acrylate, ethylene glycol di(meth)acrylate, benzyl(meth)acrylate, lauryl (meth)acrylate, oleyl(meth)acrylate, palmityl(meth)acrylate, stearyl(meth)acrylate and the like.

[0025] The core polymer may be produced in a single polymerization process or in a multi-stage polymerization process. The core polymer, whether obtained by a single stage process or a process involving several stages, may have an average particle size (diameter) of from 50 nm to 1.0 micron, such as from 100 nm to 300 nm, in an unswollen condition.

[0026] The polymeric particles include at least one first shell polymer (b) at least partially encapsulating the core polymer. The first shell polymer (b) is prepared from a mixture of reactants comprising (b)(i) at least one hydrophilic ethylenically unsaturated monomer and (b)(ii) at least one aromatic monomer having a hydrophilic surfactant group and an ethylenically unsaturated group reactive with the hydrophilic ethylenically unsaturated monomer (b)(i). The at least one hydrophilic ethylenically unsaturated monomer (b)(i) may be the same as used to prepare the core polymer (a). The at least one aromatic monomer having a hydrophilic surfactant group and an ethylenically unsaturated group that is reactive with the hydrophilic ethylenically unsaturated monomer of the at least one first shell polymer may include a phenyl group, such as an alkyl phenyl ether group or a styrenated phenyl ether group. Suitable aromatic monomers having a hydrophilic surfactant group for use in the at least one first shell polymer include the HITENOL® BC series (BC-10, BC-1025, BC-20, BC-2020 or BC-30) or the HITENOL® AR series (AR-10, AR-20, AR-1025, AR-2020) available from Montello, Inc. of Japan. The

HITENOL® BC series include polyoxyethylene alkylphenylether ammonium sulfates having the structure of chemical formula I,

I where n is 10-30, such as 10, 20, or 30, and X is C9H19. The HITENOL® AR series include polyoxyethylene styrenated phenylether ammonium sulfates having the structure of chemical formula I, where n is 10-30, such as 10, 20, or 30, and X is

where m is 1 or 2.

[0027] It is believed that upon reaction of the ethylenically unsaturated portion of the aromatic monomer (such as the ethylene portion of the afore-described HITENOL® monomers) with other ethylenically unsaturated monomers in the first shell, the aromatic monomer having a hydrophilic surfactant group within the first shell polymer provides hydrophilic properties to the first shell polymer via the ionic (polyoxyethylene ether ammonium sulfate) group. Other suitable aromatic monomers having a hydrophilic surfactant group for use in the at least one first shell polymer include the NOIGEN® RN series (available from Montello, Inc. of Japan) having a polyoxyethylene alkyl phenyl ether structure such as NOIGEN® RN-10, NOIGEN® RN-20, NOIGEN® RN-30, NOIGEN® RN-40 and NOIGEN® RN-5065 having a structure similar to chemical formula I except a hydrogen in place of the ammonium sulfate group. [0028] The monomers used to produce the at least one first shell polymer (b) may further include other monomers, such as nonionic ethylenically unsaturated monomers. The nonionic ethylenically unsaturated monomers may be the same as those used to prepare the core polymer (a).

[0029] The first shell polymer is at least partially encapsulated by at least one second shell polymer (c). The second shell polymer (c) may be prepared from a mixture of reactants including (c)(i) at least one aromatic monomer having an ethylenically unsaturated group and (c)(ii) an aromatic monomer having a hydrophilic surfactant group and an ethylenically unsaturated group reactive with the aromatic monomer having an ethylenically unsaturated group. Suitable aromatic monomers (c)(i) having an ethylenically unsaturated group include styrene, a-methyl styrene, p- methyl styrene, t-butyl styrene, vinyl toluene and the like. The aromatic monomer (c)(ii) having a hydrophilic surfactant and an ethylenically unsaturated group reactive with the aromatic monomer of the at least one second shell polymer may be the same aromatic monomer (b)(ii) used to prepare the first shell polymer, such as those of the HITENOL® BC series described above. It is believed that upon reaction of the aromatic monomer (c)(i) with ethylenic saturation with the ethylenically unsaturated portion of the aromatic monomer (c)(ii) provides hydrophilic properties to the second shell polymer via the ionic (polyoxyethylene ether ammonium sulfate) group. In this manner, both the first polymer shell and the second polymer shell exhibit hydrophilic properties, thereby creating "hydrophilic channels" in both shells which aid in swelling of the polymeric particle via a base as described below. In addition, stability of the second shell polymer is achieved via conjugation of the aromatic groups originating from both of monomers (c)(i) and (c)(ii).

[0030] The monomers used to produce the at least one second shell polymer (c) may further include other monomers, such as at least one hydrophilic ethylenically unsaturated monomer. The hydrophilic ethylenically unsaturated monomer may be the same as used to prepare the core polymer (a).

[0031] The second shell polymer (c) may be at least partially encapsulated by an optional third shell polymer (d), where the third shell polymer (d) is prepared from at least one polymerizable aromatic monomer. Suitable aromatic monomers are those that may be used to prepare the at least one second shell polymer. [0032] In each of the at least one first shell polymer and at least one second shell polymer, the aromatic monomer (b)(ii) and (c)(ii) having a hydrophilic surfactant group and an ethylenically unsaturated group reactive with a monomer having ethylenically unsaturated group (b)(i) and (c)(i) may be present in an amount of at least 2 wt. %, at least 5 wt. %, at least 10 wt. %, or at least 15 wt. % based on the total weight of the first and/or second shell polymer. The aromatic monomer (b)(ii) and (c)(ii) may be present in the respective first shell polymer and second shell polymer in an amount of 98 wt. % or less, 95 wt. % or less, 90 wt. % or less, 85 wt. % or less based on the total weight of the respective first and second shell polymers.

[0033] The core polymer, the at least one first polymer shell, the at least one second shell polymer, and the at least one third shell polymer may each be made in a single stage or step of the sequential polymerization or may be made by a plurality of steps in sequence following the polymerization. As used herein, the term "sequentially emulsion polymerized" or "sequentially emulsion produced" refers to polymers (including homopolymers and copolymers) that are prepared in an aqueous medium by an emulsion polymerization process in the presence of the dispersed polymer particles of a previously formed emulsion polymer such that the previously formed emulsion polymers are increased in size by deposition thereon of emulsion polymerized product of one or more successive monomer charges introduced into the medium containing the dispersed particles of the preformed emulsion polymer.

[0034] The core polymer may be produced in a single stage polymerization reactor in a multistage process. The monomers used to produce the core polymer may be mixed together with surfactant and water and charged to a reactor vessel and a remaining portion retained. Upon initiating reaction in the reactor vessel, such as by increasing temperature and/or adding an initiator, an emulsion of the core polymer monomers may be later fed to the reactor vessel. One or more of the monomers used to produce the core polymer may be excluded from the mixture charged to the reactor vessel and is added only as a component of the later added emulsion or of an earlier added emulsion.

[0035] The first, second, and third shell polymers may be produced sequentially in a similar manner. For example, the core polymer is dispersed into a reactor with a mixture of the monomer used to prepare the second polymer, wherein a portion of the mixture is retained as an emulsion that is charged to the reactor vessel after polymerization of the monomers of the first shell polymer. Likewise, one or more of the monomers used to produce the first, second, and/or third shell polymers may be excluded from the mixture of monomers charged to the reactor vessel and is added only as a component of a later added emulsion or of an earlier added emulsion.

[0036] A water-soluble free radical initiator may be utilized in the aqueous emulsion polymerization. Suitable water-soluble free radical initiators include hydrogen peroxide; tert-butyl peroxide; alkali metal persulfates such as sodium, potassium and lithium persulfate; and ammonium persulfate. The amount of initiator is preferably from 0.01 to 5 percent by weight, based on the total amount of monomer. The temperature may be in the range of about 10°C to 100°C. In the case of the persulfate systems, the temperature is preferably in the range of 60°C to 90°C. The type and amount of initiator may be the same or different in the various stages of the multi-stage polymerization.

[0037] The polymeric particles of the present invention are prepared by sequential emulsion polymerization, which, as noted above, includes charging the monomers that form the at least one first shell into an aqueous dispersion of the core polymer. In each of the at least one first shell polymer, and at least one second shell polymer, one of the monomers includes the aromatic monomer having a hydrophilic surfactant group and an ethylenically unsaturated group. By including this reactive surfactant in the polymer shells, it is believed that the polymer shells then include a hydrophilic moiety that allows for subsequent swelling of the first and second shells.

[0038] The optional third polymer shell including an aromatic monomer is polymerized in the presence of a swelling agent. Suitable swelling agents include volatile bases such as ammonia, ammonium hydroxide, and volatile lower aliphatic amines, such as morpholine, trimethylamine, and triethylamine, and the like; and fixed or permanent bases such as potassium hydroxide, lithium hydroxide, zinc ammonium complex, copper ammonium complex, silver ammonium complex, strontium hydroxide, barium hydroxide and the like. While the base is typically provided in an aqueous solution, solvents, such as, for example, ethanol, hexanol and octanol, may be added to aid in fixed or permanent base penetration.

[0039] Suitable contrast ratio of a coating composition containing the polymeric particles of the present invention has been found when the polymerization of the third polymer shell is conducted simultaneously (not sequentially) with swelling of the first and second polymer shells by adding the swelling agent during polymerization of the third polymer shell. The presence of the aromatic monomer having hydrophilic surfactant group (the anionic ethylenically unsaturated moiety) allows for efficient transfer of the swelling agent into the first and second polymer shells. [0040] When the swollen particle is dried (water and/or swelling agent are removed from the central region of the swollen particle), the core polymer may shrink and a void develops, the extent of which depends upon the resistance of the outermost (e.g. third) shell to return to its previous size. One method of controlling the change in the size of the third polymer shell is to include a crosslinking agent during polymerization thereof. Polymerization of the monomer in the optional third polymer shell may be conducted in the presence of a crosslinker. Suitable crosslinkers include vinyl acrylate, vinyl methacrylate, vinyl itaconate, divinyl adipate, butanediol divinyl ether, trimethylolpropane trivinyl ether, allyl acrylate, allyl methacrylate, pentaerythritol triallyl ether, triallylsucrose, pentaallylsucrose, pentaallylsaccharose, methylenebis(meth)acrylamide, divinylethyleneurea, divinylpropyleneurea, divinylbenzene, divinyldioxane, triallylcyanurate, tetraallylsilane, tetravinylsilane, and bis- or polyacryloylsiloxanes.

[0041] Other useful crosslinkers are compounds having two or more ethylenically unsaturated groups, such as diacrylates or dimethacrylates of at least dihydric saturated alcohols.

[0042] The voided particles that are produced according to the present invention are particularly useful in coating compositions, such as aqueous based coating compositions including paint. The polymeric particles produced according to the present invention and including a void impart improved gloss, brightness, and opacity to the coating compositions to which they are included.

[0043] The following examples are presented to demonstrate the general principles of the present invention. The invention should not be considered as limited to the specific examples presented. All parts and percentages in the examples are by weight unless otherwise indicated. Contrast ratio (%) was determined by dispersing the particles in a latex at 15 parts by weight (85 wt. % latex and 15 wt.% particles or 85: 15) and drawing the dispersion down as a film onto an opacity chart and determining the reflectance of the drawdown film over a black surface as compared to an identical film over a white surface, where the contrast ratio is calculated as the percentage of the reflectance of the dispersion over the white substrate relative to the reflectance of the dispersion over the black substrate. As reported herein, particle size was measured via DSL (Dynamic Light Scattering) with a NICOMP® 380 from Particle Sizing System (PSS- NICOMP®). Contrast ratio was determined as follows:

a) Sample preparation:

a.l. To 85.0 grams of vinyl acrylic emulsion were added 15.0 grams of opaque polymer and mixed. a.2. The mixture was stirred for at least 5 minutes or until a homogeneous sample was achieved.

b) Opaque polymer emulsion mix application:

Using a 5 mils drawdown bar film applicator, the sample was applied over a test chart and allowed to dry for 24 hours at room ambient conditions.

c) Application measurement:

Using a Minolta (model CM-3700A) spectrophotometer (observer 10°, illuminant D65 and opacity index) three measurements were made in different places of the sample; the average value was reported.

EXAMPLES

Examples 1-7: Core Polymer

EXAMPLE 1

[0044] A seed emulsion was prepared as follows. A 2-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 1077 grams, EMULTEN™ 430 (sodium dodecylbenzene sulfonate, 32%, available from Tenso Quimicos, S.A. de C.V., Monterrey, MX), 0.8 grams, methyl methacrylate, 51 grams, butyl acrylate, 4.7 grams, and methacrylic acid, 0.51 grams were added to the reactor and heated to 80°C. A monomer emulsion was prepared by mixing 94 grams of deionized water, 9.7 grams of EMULTEN™ 430 (sodium dodecylbenzene sulfonate, 32%), 29 grams of butyl acrylate, 317.9 grams of methyl methacrylate, 17.3 grams of 1,4-butanediol dimethacrylate, and 231.2 grams of methacrylic acid. With the reactor internal temperature at 78°C, a mixture of 2.56 grams of sodium persulfate in 12.5 grams of deionized water was added to the reactor. The reaction temperature was raised to 82°C, and the reaction mixture was stirred for 20 minutes at 82°C. The monomer emulsion and a mixture of 0.77 grams of sodium persulfate in 100.0 grams of deionized water were then fed to the reactor over a four hour period at 82°C. After completion of the monomer and initiator feed the reaction mixture was held at 82°C for one hour, cooled to 25°C, and filtered to remove any grit. The filtered emulsion had a pH of 2.6, 33.6% solids content, and an average particle size of 237 nm. EXAMPLE 2

[0045] A seed emulsion was prepared as follows. A 2-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 1080 grams, and DISPONIL® FES 993 (30%), available from BASF Corporation (Florham Park, NJ) 0.4 grams, were added to the reactor and heated to 80°C. A monomer emulsion was prepared by mixing 96.4 grams of deionized water, 10.0 grams of DISPONIL® FES 993 (30%), 33.8 grams of butyl acrylate, 370 grams of methyl methacrylate, 17.7 grams of 1 ,4-butanediol dimethacrylate, and 240 grams of methacrylic acid. From the monomer emulsion, 15.3 grams were removed and set aside. With the reactor internal temperature at 78°C, the monomer emulsion previously removed from the initial monomer emulsion, followed by a mixture of 1.8 grams of sodium persulfate in 12.8 grams of deionized water, was added to the reactor. The reaction temperature was raised to 82°C, and the reaction mixture was stirred for 20 minutes at 82°C. The remaining monomer emulsion and a mixture of 1.8 grams of sodium persulfate in 100.0 grams of deionized water were then fed to the reactor over a three and a half hour period at 82°C. After completion of the monomer and initiator feed, the reaction mixture was held at 82°C for one hour, cooled to 25°C, and filtered to remove any grit. The filtered emulsion had a pH of 2.6, 33.7% solids content and an average particle size of 190 nm.

EXAMPLE 3

A seed emulsion was prepared as follows. A 2-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 1077 grams, and ABEX® EP 110 (32%), available from Solvay USA Inc. (Princeton, NJ), 0.4 grams, were added to the reactor and heated to 80°C. A monomer emulsion was prepared by mixing 96.1 grams of deionized water, 10 grams of ABEX® EP 110 (32%), 32.3 grams of butyl acrylate, 353 grams of methyl methacrylate, 9.9 grams of 1 ,4-butanediol dimethacrylate, and 264 grams of methacrylic acid. From the monomer emulsion, 18.2 grams were removed and set aside. With the reactor internal temperature at 78°C, the monomer emulsion previously removed from the initial monomer emulsion, followed by a mixture of 1.8 grams of sodium persulfate in 13 grams of deionized water, was added to the reactor. The reaction temperature was raised to 82°C, and the reaction mixture was stirred for 20 minutes at 82°C. The remaining monomer emulsion and a mixture of 1.8 grams of sodium persulfate in 100.0 grams of deionized water were then fed to the reactor over a three and a half hour period at 82°C. After the completion of the monomer and initiator feed, the reaction mixture was held at 82°C for one hour, cooled to 25 °C, and filtered to remove any grit. The filtered emulsion had a pH of 2.5, 33.5% solids content and an average particle size of 194 nm.

EXAMPLE 4

[0046] A seed emulsion was prepared as follows. A 2-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 1080 grams, and ABEX® EP 110 (32%), 0.5 grams, were added to the reactor and heated to 80°C. A monomer emulsion was prepared by mixing 96.5 grams of deionized water, 6.5 grams of ABEX® EP 110 (32%), 33.8 grams of butyl acrylate, 377.7 grams of methyl methacrylate, 9.9 grams of 1 ,4-butanediol dimethacrylate, and 240 grams of methacrylic acid. From the monomer emulsion, 15.5 grams were removed and set aside. With the reactor internal temperature at 78°C, the monomer emulsion previously removed from the initial monomer emulsion, followed by a mixture of 1.8 grams of sodium persulfate in 12.8 grams of deionized water was added to the reactor. The reaction temperature was raised to 82°C, and the reaction mixture was stirred for 20 minutes at 82°C. The remaining monomer emulsion and a mixture of 1.8 grams of sodium persulfate in 100.0 grams of deionized water were then fed to the reactor over a three and a half hour period at 82°C. After the completion of the monomer and initiator feed, the reaction mixture was held at 82°C for one hour, cooled to 25°C, and filtered to remove any grit. The filtered emulsion had a pH of 2.3, 33.5% solids content, and an average particle size of 211 nm.

EXAMPLE 5

[0047] A seed emulsion was prepared as follows. A 2-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 1078 grams, and ABEX® EP 110 (32%), 1.6 grams, were added to the reactor and heated to 80°C. A monomer emulsion was prepared by mixing 96.3 grams of deionized water, 9.9 grams of ABEX® EP 110 (32%), 36.3 grams of butyl acrylate, 380 grams of methyl methacrylate, 6.6 grams of 1,4- butanediol dimethacrylate, and 238 grams of methacrylic acid. From the monomer emulsion, 20.9 grams were removed and set aside. With the reactor internal temperature at 78°C, the monomer emulsion previously removed from the initial monomer emulsion was added to the reactor, followed by a mixture of 1.8 grams of sodium persulfate in 12.8 grams of deionized water. The reaction temperature was raised to 82°C, and the reaction mixture was stirred for 20 minutes at 82°C. The remaining monomer emulsion and a mixture of 1.8 grams of sodium persulfate in 100.0 grams of deionized water were then fed to the reactor over a three and a half hour period at 82°C. After the completion of the monomer and initiator feed the reaction mixture was held at 82 °C for one hour, cooled to 25°C, and filtered to remove any grit. The filtered emulsion had a pH of 2.5, 33.8% solids content, and an average particle size of 148 nm.

EXAMPLE 6

[0048] A seed emulsion was prepared as follows. A 2-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 1078 grams, and ABEX® EP 110 (32%), 0.8 grams, were added to the reactor and heated to 80°C. A monomer emulsion was prepared by mixing 96.3 grams of deionized water, 9.9 grams of ABEX® EP 110 (32%), 36.3 grams of butyl acrylate, 380 grams of methyl methacrylate, 6.6 grams of 1,4- butanediol dimethacrylate, and 238 grams of methacrylic acid. From the monomer emulsion, 20.9 grams were removed and set aside. With the reactor internal temperature at 78°C, the monomer emulsion previously removed from the initial monomer emulsion was added to the reactor, followed by a mixture of 1.8 grams of sodium persulfate in 12.8 grams of deionized water. The reaction temperature was raised to 82°C, and the reaction mixture was stirred for 20 minutes at 82°C. The remaining monomer emulsion and a mixture of 1.8 grams of sodium persulfate in 100.0 grams of deionized water were then fed to the reactor over a three and a half hour period at 82°C. After the completion of the monomer and initiator feed, the reaction mixture was held at 82°C for one hour, cooled to 25°C, and filtered to remove any grit. The filtered emulsion had a pH of 2.7, 34% solids content, and an average particle size of 183 nm.

EXAMPLE 7

[0049] A seed emulsion was prepared as follows. A 2-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 1077.0 grams, and ABEX® EP 110 (32%), 0.75 grams, were added to the reactor and heated to 80°C. A monomer emulsion was prepared by mixing 96.1 grams of deionized water, 9.9 grams of ABEX® EP 110 (32%), 36.3 grams of butyl acrylate, 379.2 grams of methyl methacrylate, and 6.6 grams of 1 ,4-butanediol dimethacrylate. From the monomer emulsion, 19.1 grams were removed and set aside. To the remaining monomer emulsion was added 237.4 grams of methacrylic acid. With the reactor internal temperature at 78°C, the monomer emulsion previously removed from the initial monomer emulsion was added to the reactor, followed by a mixture of 1.8 grams of sodium persulfate in 12.8 grams of deionized water. The reaction temperature was raised to 82°C and the reaction mixture was stirred for 20 minutes at 82°C. The remaining monomer emulsion and a mixture of 1.8 grams of sodium persulfate in 99.8 grams of deionized water were then fed to the reactor over a three and a half hour period at 82 °C. After the completion of the monomer and initiator feed the reaction mixture was held at 82°C for one hour, cooled to 25°C, and filtered to remove any grit. The filtered emulsion had a pH of 2.7, 33.1% solids content, and an average particle size of 182 nm.

Examples 8-43: Multi-stage Hollow Particles

EXAMPLE 8

[0050] A 2-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 473 grams, and DOWFAX™ 2A1 (45%), available from Dow Chemical Company (Midland, MI), 0.7 grams, were added to the reactor and heated to 80°C. 102 Grams of the seed emulsion prepared in Example 1 were added to the heated reaction mixture. They were immediately followed by 0.8 grams of ammonium persulfate in 6 grams of deionized water. A first monomer emulsion was prepared by mixing 45 grams of deionized water, 0.6 grams of DOWFAX™ 2A1 (45%), 2.3 grams of butyl acrylate, 15 grams of methyl methacrylate, and 0.4 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.6 grams of ammonium persulfate in 23 grams of deionized water were then fed to the reactor over a 30 minute period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 74 grams of deionized water, 9.5 grams of DOWFAX™ 2A1 (45%), and 303 grams of styrene. The second monomer emulsion and a mixture of 0.5 grams of ammonium persulfate in 25 grams of deionized water were then fed to the reactor over a 90 minute period at 80°C. Upon completion of the addition, 12 grams of UCAR FILMER™ IBT, available from the DOW Chemical Company (Midland, MI) were added to the reactor. A third monomer emulsion was prepared by mixing 86 grams of deionized water, 5 grams of DOWFAX™ 2A1 , 169 grams of styrene, and 19 grams of ammonium hydroxide. The third monomer and a mixture of 0.5 grams of ammonium persulfate in 27 grams of deionized water were co-fed to the reactor over a 90 minute period at 80°C. The reaction mixture was held for four hours at 80°C and then cooled to room temperature and filtered to remove any formed grit. The final latex had a solids content of 36.07%, a pH of 9.96, and a particle size of 618 nm. Dry density was 0.68 g/mL. The contrast ratio of this polymer, determined in an 85: 15 mixture with a vinyl-acrylic latex, was 68%.

EXAMPLE 9

[0051] A 2-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 631 grams, and RHODACAL® DSB (45%), available from Solvay USA Inc. (Princeton, NJ), 1.0 grams, were added to the reactor and heated to 80°C. 136 Grams of the seed emulsion prepared in Example 2 were added to the heated reaction mixture. This was immediately followed by 1 gram of ammonium persulfate in 8 grams of deionized water. A first monomer emulsion was prepared by mixing 60 grams of deionized water, 0.8 grams of RHODACAL® DSB (45%), 3 grams of butyl acrylate, 20 grams of methyl methacrylate, and 0.5 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.8 grams of ammonium persulfate in 31 grams of deionized water were then fed to the reactor over a 30 minute period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 99 grams of deionized water, 13 grams of RHODACAL® DSB (45%), and 405 grams of styrene. The second monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 33 grams of deionized water were then fed to the reactor over a 90 minute period at 80°C. Upon completion of the addition, 16 grams of UCAR FILMER™ IBT were added to the reactor. A third monomer emulsion was prepared by mixing 114 grams of deionized water, 7 grams of RHODACAL® DSB, 225 grams of styrene, and 25 grams of ammonium hydroxide. The third monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 35 grams of deionized water were co-fed to the reactor over a 90 minute period at 80°C. The reaction mixture was held for four hours at 80°C and then cooled to room temperature and filtered to remove any formed grit. The final latex had a solids content of 36.1%, a pH of 9.74, and a particle size of 565 nm. Dry density was 0.67 g/mL. The contrast ratio of this polymer, determined in an 85: 15 mixture with a vinyl-acrylic latex, was 67%.

EXAMPLE 10

[0052] A 5-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 1576 grams, and RHODACAL® DSB (45%), 2.4 grams, were added to the reactor and heated to 80°C. 338 Grams of the seed emulsion prepared in Example 3 were added to the heated reaction mixture. They were immediately followed by 2.7 gram of ammonium persulfate in 19 grams of deionized water. A first monomer emulsion was prepared by mixing 150 grams of deionized water, 1.9 grams of RHODACAL® DSB (45%), 7.7 grams of butyl acrylate, 48.7 grams of methyl methacrylate, and 1.15 grams of methacrylic acid. The first monomer emulsion and a mixture of 1.9 grams of ammonium persulfate in 77 grams of deionized water were then fed to the reactor over a 30 minute period at 80°C. Upon completion of addition, a second monomer emulsion was prepared by mixing 247 grams of deionized water, 31.78 grams of RHODACAL® DSB (45%), and 1011 grams of styrene. The second monomer emulsion and a mixture of 1.7 grams of ammonium persulfate in 82 grams of deionized water were then fed to the reactor over a 90 minute period at 80°C. Upon completion of the addition, 38 grams of UCAR FILMER™ IBT were added to the reactor. A third monomer emulsion was prepared by mixing 285 grams of deionized water, 17.0 grams of RHODACAL® DSB, 562 grams of styrene, and 62.8 grams of ammonium hydroxide. The third emulsion and a mixture of 1.7 grams of ammonium persulfate in 88 grams of deionized water were co-fed to the reactor over a 90 minute period at 80°C. The reaction mixture was held for four hours at 80°C and then cooled to room temperature and filtered to remove any formed grit. The final latex had a solids content of 36.6%, a pH of 9.9, and a particle size of 600 nm. Dry density was 0.68 g/mL. The contrast ratio of this polymer, determined in an 85: 15 mixture with a vinyl-acrylic latex, was 70%.

EXAMPLE 11

[0053] A 2-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 794.7 grams, and HITENOL® BC 1025 (25%), 1.5 grams, were added to the reactor and heated to 80°C. 123 Grams of the seed emulsion prepared in Example 4 were added to the heated reaction mixture. They were immediately followed by 1 gram of ammonium persulfate in 7 grams of deionized water. A first monomer emulsion was prepared by mixing 20 grams of deionized water, 1.3 grams of HITENOL® BC-1025, 2.79 grams of butyl acrylate, 17.7 grams of methyl methacrylate, and 0.4 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 28 grams of deionized water were then fed to the reactor over a 30 minute period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 90 grams of deionized water, 20.8 grams of HITENOL® BC-1025, and 367.5 grams of styrene. The second monomer emulsion and a mixture of 0.61 grams of ammonium persulfate in 30 grams of deionized water were then fed to the reactor over a 90 minute period at 80°C. Upon completion of the addition, 14 grams of UCAR FILMER™ IBT were added to the reactor. A third monomer emulsion was prepared by mixing 103.6 grams of deionized water, 6.4 grams of RHODACAL® DSB, 204.2 grams of styrene, and 26.4 grams of ammonium hydroxide. The third emulsion and a mixture of 0.6 grams of ammonium persulfate in 32 grams of deionized water were co-fed to the reactor over a 90 minute period at 80°C. The reaction mixture was held for four hours at 80°C and then cooled to room temperature and filtered to remove any formed grit. The final latex had a solids content of 33.2%, a pH of 10.1, and a particle size of 620 nm. Dry density was 0.65 g/mL. The contrast ratio of this polymer, determined in an 85: 15 mixture with a vinyl-acrylic latex, was 72%.

EXAMPLE 12

[0054] A 2-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 873 grams, and HITENOL® BC-1025 (25%), 1.6 grams, were added to the reactor and heated to 80°C. 129 Grams of the seed emulsion prepared in Example 3 were added to the heated reaction mixture. They were immediately followed by 1 gram of ammonium persulfate in 7 grams of deionized water. A first monomer emulsion was prepared by mixing 21 grams of deionized water, 1.3 grams of HITENOL® BC-1025, 2.9 grams of butyl acrylate, 19 grams of methyl methacrylate, and 0.5 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 29 grams of deionized water were then fed to the reactor over a 30 minute period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 142 grams of deionized water, 21.7 grams of HITENOL® BC-1025, and 517 grams of styrene. The second monomer emulsion and a mixture of 0.61 grams of ammonium persulfate in 31 grams of deionized water were then fed to the reactor over a 90 minute period at 80°C. Upon completion of the addition, 14 grams of UCAR FILMER™ IBT were added to the reactor. A third monomer emulsion was prepared by mixing 12 grams of deionized water, 3.4 grams of RHODACAL® DSB, 65 grams of styrene, and 26 grams of ammonium hydroxide. The third emulsion and a mixture of 0.6 grams of ammonium persulfate in 34 grams of deionized water were co-fed to the reactor over a 90 minute period at 80°C. The reaction mixture was held for four hours at 80°C and then cooled to room temperature and filtered to remove any formed grit. The final latex had a solids content of 33.5%, a pH of 9.6, and a particle size of 596 nm. Dry density was 0.69 g/mL. The contrast ratio of this polymer, determined in an 85: 15 mixture with a vinyl-acrylic latex, was 68%.

EXAMPLE 13

[0055] A 2-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 794 grams, and HITENOL® BC-1025 (25%), 1.5 grams, were added to the reactor and heated to 80°C. 123 Grams of the seed emulsion prepared in Example 5 were added to the heated reaction mixture. They were immediately followed by 1 gram of ammonium persulfate in 7 grams of deionized water. A first monomer emulsion was prepared by mixing 20 grams of deionized water, 1.3 grams of HITENOL® BC-1025, 2.8 grams of butyl acrylate, 18 grams of methyl methacrylate, and 0.4 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 28 grams of deionized water were then fed to the reactor over a 30 minute period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 90 grams of deionized water, 20.8 grams of HITENOL® BC-1025, and 368 grams of styrene. The second monomer emulsion and a mixture of 0.61 grams of ammonium persulfate in 30 grams of deionized water were then fed to the reactor over a 90 minute period at 80°C. Upon completion of the addition, 14 grams of UCAR FILMER™ IBT were added to the reactor. A third monomer emulsion was prepared by mixing 104 grams of deionized water, 6.4 grams of RHODACAL® DSB, 204 grams of styrene, and 26 grams of ammonium hydroxide. The third emulsion and a mixture of 0.61 grams of ammonium persulfate in 32 grams of deionized water were co-fed to the reactor over a 90 minute period at 80°C. The reaction mixture was held for four hours at 80°C and then cooled to room temperature and filtered to remove any formed grit. The final latex had a solids content of 33.2%, a pH of 9.9, and a particle size of 362 nm. Dry density was 0.69 g/mL. The contrast ratio of this polymer, determined in an 85: 15 mixture with a vinyl-acrylic latex, was 71%.

EXAMPLE 14

[0056] A 2-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 794 grams, and HITENOL® BC-1025 (25%), 1.5 grams, were added to the reactor and heated to 80°C. 123 Grams of the seed emulsion prepared in Example 6 were added to the heated reaction mixture. They were immediately followed by 1 gram of ammonium persulfate in 7 grams of deionized water. A first monomer emulsion was prepared by mixing 20 grams of deionized water, 1.3 grams of HITENOL® BC-1025, 2.8 grams of butyl acrylate, 18 grams of methyl methacrylate, and 0.4 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 28 grams of deionized water were then fed to the reactor over a 30 minute period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 90 grams of deionized water, 20.8 grams of HITENOL® BC-1025, and 368 grams of styrene. The second monomer emulsion and a mixture of 0.61 grams of ammonium persulfate in 30 grams of deionized water were then fed to the reactor over a 90 minute period at 80°C. Upon completion of the addition, 14 grams of UCAR FILMER™ IBT were added to the reactor. A third monomer emulsion was prepared by mixing 104 grams of deionized water, 6.4 grams of RHODACAL® DSB, 204 grams of styrene, and 26 grams of ammonium hydroxide. The third emulsion and a mixture of 0.61 grams of ammonium persulfate in 32 grams of deionized water were co-fed to the reactor over a 90 minute period at 80°C. The reaction mixture was held for four hours at 80°C and then cooled to room temperature and filtered to remove any formed grit. The final latex had a solids content of 33.4%, a pH of 9.9, and a particle size of 516 nm. Dry density was 0.69 g/mL. The contrast ratio of this polymer, determined in an 85: 15 mixture with a vinyl-acrylic latex, was 76%.

EXAMPLE 15

[0057] A 2-liter, four necked reactor was equipped with paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 794 grams, and HITENOL® BC-1025 (25%), 1.1 grams, were added to the reactor and heated to 80°C. To the heated reaction mixture was added 123 grams of the seed emulsion prepared in Example 6. This was immediately followed by 1 gram of ammonium persulfate in 7 grams of deionized water. A first monomer emulsion was prepared by mixing 20 grams of deionized water, 1.3 grams of HITENOL® BC-1025, 2.8 grams of butyl acrylate, 18 grams of methyl methacrylate, and 0.4 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 28 grams of deionized water were then fed to the reactor over a 30 minute period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 90 grams of deionized water, 15.8 grams of HITENOL® BC-1025, and 368 grams of styrene. The second monomer emulsion and a mixture of 0.61 grams of ammonium persulfate in 30 grams of deionized water were then fed to the reactor over a 90 minute period at 80°C. 0.1 Grams of HYDROSULFITE® AWC (available from Henkel Corporation (Amber, PA), in 7 grams of deionized water were added to the reactor. The reaction mixture was held for 15 minutes at 80°C. A third monomer emulsion was prepared by mixing 104 grams of deionized water, 6.4 grams of RHODACAL® DSB, and 204 grams of styrene. The third emulsion was added over a 30 minute period at 80°C. The reaction mixture was held for 10 minutes at 80°C. After holding, 22 grams of ammonium hydroxide were added to the reactor. The reaction mixture was held for 15 minutes at 80°C. After the 15 minute hold, a mixture of 0.62 grams ammonium persulfate dissolved in 32 grams of deionized water were added to the reactor. The reaction mixture was held for four hours at 80°C, then cooled to room temperature and filtered to remove any grit formed. The final latex had a solids content of 33.20%, a pH of 9.9, and a particle size of 505 nm. Dry density was 0.69 g/mL. The contrast ratio of this polymer was determined to be 77.87%.

EXAMPLE 16

[0058] A 2-liter, four necked reactor was equipped with paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 794 grams, and HITENOL® BC-1025 (25%), 1.5 grams, were added to the reactor and heated to 80°C. To the heated reaction mixture was added 123 grams of the seed emulsion prepared in Example 6. This was immediately followed by 1 gram of ammonium persulfate in 7 grams of deionized water. A first monomer emulsion was prepared by mixing 20 grams of deionized water, 1.3 grams of HITENOL® BC-1025, 2.8 grams of butyl acrylate, 18 grams of methyl methacrylate, and 0.4 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 28 grams of deionized water were then fed to the reactor over a 30 minutes period at 80°C. Upon completion of the addition a second monomer emulsion was prepared by mixing 90 grams of deionized water, 20.8 grams of HITENOL® BC-1025, and 368 grams of styrene. The second monomer emulsion was fed to the reactor over a 90 minute period at 80°C. A third monomer emulsion was prepared by mixing 104 grams of deionized water, 6.4 grams of RHODACAL® DSB, and 204 grams of styrene. The third emulsion was added over a thirty minute period at 80°C. The reaction mixture was held 10 minutes at 80°C. After the 10 minute hold, 26.4 grams of ammonium hydroxide were added to the reactor. The reaction mixture was held for 15 minutes at 80°C. After the 15 minute hold, a mixture of 0.62 grams of ammonium persulfate dissolved in 32 grams of deionized water was added to the reactor. The reaction mixture was held for four hours at 80°C, then cooled to room temperature and filtered to remove any grit formed. The final latex had a solids content of 33.13%, a pH of 9.9, and a particle size of 456 nm. Dry density was 0.69 g/mL. The contrast ratio of this polymer was determined to be 78.85%.

EXAMPLE 17

[0059] A 2-liter, four necked reactor was equipped with paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 748 grams, and HITENOL® BC-1025 (25%), 1.61 grams, were added to the reactor and heated to 80°C. To the heated reaction mixture was added 153.5 grams of the seed emulsion prepared in Example 6. This was immediately followed by 1 gram of ammonium persulfate in 10 grams of deionized water. A first monomer emulsion was prepared by mixing 24 grams of deionized water, 1.3 grams of HITENOL® BC-1025, 3.5 grams of butyl acrylate, 22 grams of methyl methacrylate, and 0.5 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 31 grams of deionized water were then fed to the reactor over a 30 minute period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 180 grams of deionized water, 20.9 grams of HITENOL® BC-1025, and 462 grams of styrene. The second monomer emulsion and a mixture of 0.62 grams of ammonium persulfate in 30 grams of deionized water were then fed to the reactor over a 90 minute period at 80°C. 0.2 Grams of HYDROSULFITE® AWC in 10 grams of deionized water were added to the reactor. The reaction mixture was held for 15 minutes at 80°C. A third monomer emulsion was prepared by mixing 35 grams of deionized water 5.3 grams of RHODACAL® DSB, and 102 grams of styrene. The third emulsion was added over a 30 minute period at 80°C. The reaction mixture was held for 10 minutes at 80°C. After the 10 minute hold, 25 grams of ammonium hydroxide were added to the reactor. The reaction mixture was held for 15 minutes at 80°C. After the 15 minutes hold, a mixture of 0.62 grams of ammonium persulfate dissolved in 32 grams of deionized water was added to the reactor. The reaction mixture was held for four hours at 80°C, then cooled to room temperature and filtered to remove any grit formed. The final latex had a solids content of 33.35%, a pH of 9.8, and a particle size of 430 nm. Dry density was 0.67 g/mL. The contrast ratio of this polymer was determined to be 74.64%. EXAMPLE 18

[0060] A 2-liter, four necked reactor was equipped with paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 742 grams, and HITENOL® BC-1025 (25%), 1.6 grams, were added to the reactor and heated to 80°C. To the heated reaction mixture was added 151 grams of the seed emulsion prepared in Example 6. This was immediately followed by 1 gram of ammonium persulfate in 10 grams of deionized water. A first monomer emulsion was prepared by mixing 24.4 grams of deionized water, 1.3 grams of HITENOL® BC-1025, 3.4 grams of butyl acrylate, 21.8 grams of methyl methacrylate, and 0.5 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 30 grams of deionized water were then fed to the reactor over a 30 minute period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 176 grams of deionized water, 20.6 grams of HITENOL® BC-1025, and 455 grams of styrene. The second monomer emulsion was fed to the reactor over a 90 minute period at 80°C. A third monomer emulsion was prepared by mixing 35 grams of deionized water, 5.2 grams of RHODACAL® DSB, and 101 grams of styrene. The third emulsion was added over a 30 minute period at 80°C. The reaction mixture was held for 10 minutes at 80°C. After the 10 minute hold, 25.1 grams of ammonium hydroxide were added to the reactor. The reaction mixture was held for 15 minutes at 80°C. After the 15 minute hold, a mixture of 0.6 grams of ammonium persulfate dissolved in 33 grams of deionized water was added to the reactor. The reaction mixture was held for four hours at 80°C, then cooled to room temperature and filtered to remove any grit formed. The final latex had a solids content of 33.23%, a pH of 9.8, and a particle size of 513 nm. Dry density was 0.69 g/mL. The contrast ratio of this polymer was determined to be 77.61%.

EXAMPLE 19

[0061] A 2-liter, four necked reactor was equipped with paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 791 grams, and HITENOL® BC-1025 (25%), 1.5 grams, were added to the reactor and heated to 80°C. To the heated reaction mixture was added 122 grams of the seed emulsion prepared in Example 6. This was immediately followed by 1 gram of ammonium persulfate in 7 grams of deionized water. A first monomer emulsion was prepared by mixing 20 grams of deionized water, 1.3 grams of HITENOL® BC-1025, 2.8 grams of butyl acrylate, 18 grams of methyl methacrylate, and 0.4 grams of methacrylic acid. The first monomer solution and a mixture of 0.7 grams of ammonium persulfate in 28 grams of deionized water were then fed to the reactor over a 30 minute period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 96 grams of deionized water, 20.1 grams of HITENOL® BC-1025, and 364 grams of styrene. The second monomer emulsion and a mixture of 0.60 grams of ammonium persulfate in 30 grams of deionized water were then fed to the reactor over a 90 minute period at 80°C. 13.9 Grams of HALTANOL™ (solvent available from Monument Chemical, Indianapolis, IN) were added to the reactor. A third monomer emulsion was prepared by mixing 102 grams of deionized water, 6.4 grams of RHODACAL® DSB, 202 grams of styrene, and 7.25 grams of sodium hydroxide (10 wt. % solution). The third monomer emulsion and a mixture of 0.61 grams of ammonium persulfate in 31 grams of deionized water were then fed to the reactor over a 90 minute period at 86°C. Fifteen minutes after finishing the addition, the reaction system coagulated, and no material was recovered for latex characterization.

EXAMPLE 20

[0062] A 2-liter, four necked reactor was equipped with paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 791 grams, and HITENOL® BC-1025 (25%), 1.5 grams, were added to the reactor and heated to 80°C. To the heated reaction mixture was added 122 grams of the seed emulsion prepared in Example 6. This was immediately followed by 1 gram of ammonium persulfate in 7 grams of deionized water. A first monomer emulsion was prepared by mixing 20 grams of deionized water, 1.3 grams of HITENOL® BC-1025, 2.8 grams of butyl acrylate, 18 grams of methyl methacrylate, and 0.4 grams of methacrylic acid. The first monomer solution and a mixture of 0.7 grams of ammonium persulfate in 28 grams of deionized water were then fed to the reactor over a 30 minute period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 96 grams of deionized water, 20.1 grams of HITENOL® BC-1025, and 364 grams of styrene. The second monomer emulsion and a mixture of 0.60 grams of ammonium persulfate in 30 grams of deionized water were then fed to the reactor over a 90 minute period at 80°C. 13.9 Grams of HALTANOL™ were added to the reactor. A third monomer emulsion was prepared by mixing 102 grams of deionized water, 6.4 grams of RHODACAL® DSB, 202 grams of styrene, 18.6 of ammonium hydroxide, and 5.25 grams of sodium hydroxide. The third monomer emulsion and a mixture of 0.61 grams of ammonium persulfate in 31 grams of deionized water were then fed to the reactor over a 90 minute period at 86°C. The reaction mixture was held for four hours at 86°C, then cooled to room temperature and filtered to remove any grit formed. The final latex had a solids content of 33.19%, a pH of 10.1, and a particle size of 522 nm. Dry density was 0.68 g/mL. The contrast ratio of this polymer was determined to be 75.39%.

EXAMPLE 21

[0063] A 2-liter, four necked reactor was equipped with paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 791 grams, and HITENOL® BC-1025 (25%), 1.5 grams, were added to the reactor and heated to 80°C. To the heated reaction mixture was added 122 grams of the seed emulsion prepared in Example 6. This was immediately followed by 1 gram of ammonium persulfate in 7 grams of deionized water. A first monomer emulsion was prepared by mixing 20 grams of deionized water, 1.2 grams of HITENOL® BC-1025, 2.8 grams of butyl acrylate, 17.5 grams of methyl methacrylate, and 0.4 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 28 grams of deionized water were then fed to the reactor over a 30 minute period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 96 grams of deionized water, 20.5 grams of HITENOL® BC-1025, and 363 grams of styrene. The second monomer emulsion and a mixture of 0.60 grams of ammonium persulfate in 30 grams of deionized water were then fed to the reactor over a 90 minute period at 80°C. 13.8 grams of HALTANOL™ were added to the reactor. A third monomer emulsion was prepared by mixing 102 grams of deionized water, 6.4 grams of RHODACAL® DSB, 202 grams of styrene, 18.6 of ammonium hydroxide, and 10.3 grams of sodium hydroxide. The third monomer emulsion and a mixture of 0.61 grams of ammonium persulfate in 31 grams of deionized water were then fed to the reactor over a 90 minute period at 86°C. The reaction mixture was held for four hours at 86°C, then cooled to room temperature and filtered to remove any grit formed. The final latex had a solids content of 33.27%, a pH of 10.7, and a particle size of 468 nm. Dry density was 0.69 g/mL. The contrast ratio of this polymer was determined to be 75.11%.

EXAMPLE 22

[0064] A 2-liter, four necked reactor was equipped with paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 631 grams, and RHODACAL® DSB (45%), 1.0 gram, were added to the reactor and heated to 80°C. To the heated reaction mixture was added 136 grams of the seed emulsion prepared in Example 6. This was immediately followed by 1 gram of ammonium persulfate in 8 grams of deionized water. A first monomer emulsion was prepared by mixing 60 grams of deionized water, 0.8 grams of RHODACAL® DSB (45%), 3 grams of butyl acrylate, 20 grams of methyl methacrylate, and 0.5 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.8 grams of ammonium persulfate in 31 grams of deionized water were then fed to the reactor over a 30 minute period at 80°C, followed by a second monomer emulsion was prepared by mixing 99 grams of deionized water, 13 grams of RHODACAL® DSB (45%), and 405 grams of styrene. The second monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 33 grams of deionized water were then fed to the reactor over a 90 minute period at 80°C. Upon completion of the addition 16 grams of UCAR FILMER™ IBT were added to the reactor. A third monomer emulsion was prepared by mixing 114 grams of deionized water, 7 grams of RHODACAL® DSB, 225 grams of styrene, and 25 grams of ammonium hydroxide. The third monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 35 grams of deionized water were co-fed to the reactor over a 90 minute period at 80°C. The reaction mixture was held for four hours at 80°C and then cooled to room temperature and filtered to remove any grit formed. The final latex had a solids content of 36.1%, a pH of 9.74, and a particle size of 565 nm. Dry density was 0.67 g/mL. The contrast ratio of this polymer was determined to be 67.2%.

EXAMPLE 23

[0065] A 2-liter, four necked reactor was equipped with paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 628 grams, and DISPONIL® FES 993, 1.4 grams, were added to the reactor and heated to 80°C. To the heated reaction mixture was added 135 grams of the seed emulsion prepared in Example 6. This was immediately followed by 1.1 grams of ammonium persulfate in 8 grams of deionized water. A first monomer emulsion was prepared by mixing 60 grams of deionized water, 1.1 grams of DISPONIL® FES 993, 3 grams of butyl acrylate, 19 grams of methyl methacrylate, and 0.5 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.8 grams of ammonium persulfate in 31 grams of deionized water were then fed to the reactor over a 30 minute period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 99 grams of deionized water, 18 grams of DISPONIL® FES 993, and 403 grams of styrene. The second monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 33 grams of deionized water were then fed to the reactor over a 90 minute period at 80°C This was immediately followed by 15 grams of UCAR FILMER™ IBT were added to the reactor. A third monomer emulsion was prepared by mixing 114 grams of deionized water, 10.6 grams of DISPONIL® FES 993, 224 grams of styrene, and 25 grams of ammonium hydroxide. The third monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 35 grams of deionized water were co-fed to the reactor over a 90 minute hour period at 80°C. The reaction mixture was held for four hours at 80°C and then cooled to room temperature and filtered to remove any grit formed. The final latex had a solids content of 36.4%, a pH of 9.9, and a particle size of 650 nm. Dry density was 0.68 g/mL. The contrast ratio of this polymer was determined to be 64.0%.

EXAMPLE 24

[0066] A 2-liter, four necked reactor was equipped with paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 628 grams, and AEROSOL® A- 102, 1.4 grams, were added to the reactor and heated to 80°C. To the heated reaction mixture was added 135 grams of the seed emulsion prepared in Example 6. This was immediately followed by 1.1 grams of ammonium persulfate in 8 grams of deionized water. A first monomer emulsion was prepared by mixing 60 grams of deionized water, 1.1 grams of AEROSOL® A- 102 (emulsifier, available from Cytec Solvay Group, Woodland Park, NJ), 3 grams of butyl acrylate, 19 grams of methyl methacrylate, and 0.5 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.8 grams of ammonium persulfate in 31 grams of deionized water were then fed to the reactor over a 30 minute period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 98 grams of deionized water, 18 grams of AEROSOL® A- 102, and 403 grams of styrene. The second monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 33 grams of deionized water were then fed to the reactor over a 90 minute period at 80°C. Upon completion of the second monomer emulsion, 15 grams of UCAR FILMER™ IBT were added to the reactor. A third monomer emulsion was prepared by mixing 114 grams of deionized water, 10.2 grams of AEROSOL® A- 102, 224 grams of styrene, and 25 grams of ammonium hydroxide. The third monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 35 grams of deionized water were co-fed to the reactor over a 90 minute period at 80°C. The reaction mixture was held for four hours at 80°C and then cooled to room temperature and filtered to remove any grit formed. The final latex had a solids content of 35.9%, a pH of 9.8, and a particle size of 628 nm. Dry density was 0.69 g/mL. The contrast ratio of this polymer was determined to be 55.0%.

EXAMPLE 25

[0067] A 2-liter, four necked reactor was equipped with paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 628 grams, and RHODAFAC® RS-610/A25 (emulsifier, available from Cytec Solvay Group, Woodland Park, NJ), 1.7 grams, were added to the reactor and heated to 80°C. To the heated reaction mixture was added 135 grams of the seed emulsion prepared in Example 6. This was immediately followed by 1.1 grams of ammonium persulfate in 8 grams of deionized water. A first monomer emulsion was prepared by mixing 60 grams of deionized water, 1.4 grams of RHODAFAC® RS-610/A25 3 grams of butyl acrylate, 19 grams of methyl methacrylate, and 0.5 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.8 grams of ammonium persulfate in 31 grams of deionized water were then fed to the reactor over a 30 minute period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 98 grams of deionized water, 22.8 grams of RHODAFAC® RS- 610/A25, and 403 grams of styrene. The second monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 33 grams of deionized water were then fed to the reactor over a 90 minute period at 80°C. Upon completion of the addition, 15 grams of UCAR FILMER™ IBT were added to the reactor. A third monomer emulsion was prepared by mixing 114 grams of deionized water, 12.6 grams of RHODAFAC® RS-610/A25, 224 grams of styrene, and 25 grams of ammonium hydroxide. The third monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 35 grams of deionized water were co-fed to the reactor over a 90 minute period at 80°C. The reaction mixture was held for four hours at 80°C and then cooled to room temperature and filtered to remove any grit formed. The final latex had a solids content of 36.2%, a pH of 10.0, and a particle size of 631 nm. Dry density was 0.68 g/mL. The contrast ratio of this polymer was determined to be 70.0%

EXAMPLE 26

[0068] A 2-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 790.2 grams, and HITENOL® BC-1025 (25%), 1.5 grams, were added to the reactor and heated to 80°C. 122 Grams of the seed emulsion prepared in Example 7 were added to the heated reaction mixture. They were immediately followed by 1 gram of ammonium persulfate in 7.0 grams of deionized water. A first monomer emulsion was prepared by mixing 19.8 grams of deionized water, 1.3 grams of HITENOL® BC-1025, 2.8 grams of butyl acrylate, 17.6 grams of methyl methacrylate, and 0.4 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 27.8 grams of deionized water were then fed to the reactor over a 30 minute period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 93.8 grams of deionized water, 20.7 grams of HITENOL® BC-1025, 365.4 grams of styrene, and 3.7 grams of methacrylic acid. The second monomer emulsion and a mixture of 0.6 grams of ammonium persulfate in 29.6 grams of deionized water were then fed to the reactor over a 90 minute period at 80°C. Upon completion of the addition, 13.9 grams of UCAR FILMER™ IBT were added to the reactor. A third monomer emulsion was prepared by mixing 103 grams of deionized water, 6.4 grams of RHODACAL® DSB, 203.0 grams of styrene, and 23.4 grams of ammonium hydroxide. The third emulsion and a mixture of 0.6 grams of ammonium persulfate in 32.0 grams of deionized water were co-fed to the reactor over a 90 minute period at 80°C. The reaction mixture was held for four hours at 80°C and then cooled to room temperature and filtered to remove any formed grit. The final latex had a solids content of 33.8%, a pH of 9.7, and a particle size of 543 nm. Dry density was 0.69 g/mL. The contrast ratio of this polymer, determined in an 85: 15 mixture with a vinyl-acrylic latex, was 78.8%.

EXAMPLE 27

[0069] A 2-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 790.3 grams, and HITENOL® BC-1025 (25%), 1.5 grams, were added to the reactor and heated to 80°C. 121.6 Grams of the seed emulsion prepared in Example 7 were added to the heated reaction mixture, immediately followed by 1 gram of ammonium persulfate in 6.9 grams of deionized water. A first monomer emulsion was prepared by mixing 19.6 grams of deionized water, 1.2 grams of HITENOL® BC-1025, 2.8 grams of butyl acrylate, 17.5 grams of methyl methacrylate, and 0.4 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 27.6 grams of deionized water were then fed to the reactor over a 30 minute period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 96.1 grams of deionized water, 20.6 grams of HITENOL® BC-1025, 363.4 grams of styrene, and 7.4 grams of methacrylic acid. The second monomer emulsion and a mixture of 0.6 grams of ammonium persulfate in 29.5 grams of deionized water were then fed to the reactor over a 90 minute period at 80°C. Upon completion of the addition, 13.8 grams of UCAR FILMER™ IBT were added to the reactor. A third monomer emulsion was prepared by mixing 102.5 grams of deionized water, 6.4 grams of RHODACAL® DSB, 202.0 grams of styrene, and 24.8 grams of ammonium hydroxide. The third emulsion and a mixture of 0.6 grams of ammonium persulfate in 31.8 grams of deionized water were co-fed to the reactor over a 90 minute period at 80°C. The reaction mixture was held for four hours at 80 °C and then cooled to room temperature and filtered to remove any formed grit. The final latex had a solids content of 33.1%, a pH of 9.6, and a particle size of 498 nm. Dry density was 0.70 g/mL. The contrast ratio of this polymer, determined in an 85: 15 mixture with a vinyl-acrylic latex, is 79.07%.

EXAMPLE 28

[0070] A 2-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 790.3 grams, and HITENOL® AR-1025 (25%), 1.5 grams, were added to the reactor and heated to 80°C. 121.6 Grams of the seed emulsion prepared in Example 7 were added to the heated reaction mixture, immediately followed by 1 gram of ammonium persulfate in 6.9 grams of deionized water. A first monomer emulsion was prepared by mixing 19.6 grams of deionized water, 1.2 grams of HITENOL® AR-1025, 2.8 grams of butyl acrylate, 17.5 grams of methyl methacrylate, and 0.4 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 27.6 grams of deionized water were then fed to the reactor over a 30 minute period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 96.1 grams of deionized water, 20.6 grams of HITENOL® AR-1025, 363.4 grams of styrene, and 7.4 grams of methacrylic acid. The second monomer emulsion and a mixture of 0.6 grams of ammonium persulfate in 29.5 grams of deionized water were then fed to the reactor over a 90 minute period at 80°C. Upon completion of the addition, 13.8 grams of UCAR FILMER™ IBT were added to the reactor. A third monomer emulsion was prepared by mixing 102.5 grams of deionized water, 6.4 grams of RHODACAL® DSB, 202.0 grams of styrene, and 24.8 grams of ammonium hydroxide. The third emulsion and a mixture of 0.6 grams of ammonium persulfate in 31.8 grams of deionized water were co-fed to the reactor over a 90 minute period at 80°C. The reaction mixture was held for four hours at 80°C and then cooled to room temperature and filtered to remove any formed grit. The final latex had a solids content of 33.5%, a pH of 9.8, and a particle size of 537 nm. Dry density was 0.71 g/mL. The contrast ratio of this polymer, determined in an 85: 15 mixture with a vinyl-acrylic latex, was 78.70%.

EXAMPLE 29

[0071] A 2-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 790.2 grams, and HITENOL® BC-1025 (25%), 1.5 grams, were added to the reactor and heated to 80°C. 121.6 Grams of the seed prepared in Example 7 were added to the heated reaction mixture, immediately followed by 1 gram of ammonium persulfate in 6.9 grams of deionized water. A first monomer emulsion was prepared by mixing 19.6 grams of deionized water, 1.2 grams of HITENOL® BC-1025, 2.8 grams of butyl acrylate, 17.5 grams of methyl methacrylate, and 0.4 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 27.6 grams of deionized water were then fed to the reactor over a 30 minute period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 96.1 grams of deionized water, 20.6 grams of HITENOL® BC-1025, 359.6 grams of styrene, and 11.1 grams of methacrylic acid. The second monomer emulsion and a mixture of 0.6 grams of ammonium persulfate in 29.5 grams of deionized water were then fed to the reactor over a 90 minute period at 80°C. Upon completion of the addition, 13.8 grams of UCAR FILMER™ IBT were added to the reactor. A third monomer emulsion was prepared by mixing 102.5 grams of deionized water, 6.4 grams of RHODACAL® DSB, 202.0 grams of styrene, and 32.6 grams of ammonium hydroxide. The third emulsion and a mixture of 0.6 grams of ammonium persulfate in 31.8 grams of deionized water were co-fed to the reactor over a 90 minute period at 80°C. The reaction mixture was held for four hours at 80°C and then cooled to room temperature and filtered to remove any formed grit. The final latex had a solids content of 32.6%, a pH of 10.0, and a particle size of 473 nm. Dry density was 0.68 g/mL. The contrast ratio of this polymer, determined in an 85: 15 mixture with a vinyl-acrylic latex, was 78.3%.

EXAMPLE 30

[0072] A 2-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 790.3 grams, and HITENOL® BC-1025 (25%), 1.5 grams, were added to the reactor and heated to 80°C. 121.6 Grams of the seed prepared in Example 7 were added to the heated reaction mixture. They were immediately followed by 1 gram of ammonium persulfate in 6.9 grams of deionized water. A first monomer emulsion was prepared by mixing 19.6 grams of deionized water, 1.2 grams of HITENOL® BC-1025, 2.8 grams of butyl acrylate, 17.5 grams of methyl methacrylate, and 0.4 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 27.6 grams of deionized water were then fed to the reactor over a 30 minute period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 96.1 grams of deionized water, 20.6 grams of HITENOL® BC-1025, 356.0 grams of styrene, and 14.8 grams of methacrylic acid. The second monomer emulsion and a mixture of 0.6 grams of ammonium persulfate in 29.5 grams of deionized water were then fed to the reactor over a 90 minute period at 80°C. Upon completion of the addition, 13.8 grams of UCAR FILMER™ IBT were added to the reactor. A third monomer emulsion was prepared by mixing 102.5 grams of deionized water, 6.4 grams of RHODACAL® DSB, 201.9 grams of styrene, and 37.3 grams of ammonium hydroxide. The third emulsion and a mixture of 0.6 grams of ammonium persulfate in 31.8 grams of deionized water were co-fed to the reactor over a 90 minute period at 80°C. The reaction mixture was held for four hours at 80°C and then cooled to room temperature and filtered to remove any formed grit. The final latex had a solids content of 32.4%, a pH of 10.1, and a particle size of 475 nm. Dry density was 0.69 g/mL. The contrast ratio of this polymer, determined in an 85: 15 mixture with a vinyl-acrylic latex, was 76.4%.

EXAMPLE 31

[0073] A 2-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 790.3 grams, and HITENOL® BC-1025 (25%), 1.5 grams, were added to the reactor and heated to 80°C. 121.6 Grams of the seed emulsion prepared in Example 7 were added to the heated reaction mixture. They were immediately followed by 1 gram of ammonium persulfate in 6.9 grams of deionized water. A first monomer emulsion was prepared by mixing 19.6 grams of deionized water, 1.2 grams of HITENOL® BC- 1025, 2.8 grams of butyl acrylate, 17.5 grams of methyl methacrylate, and 0.4 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 27.6 grams of deionized water were then fed to the reactor over a 30 minutes period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 96.1 grams of deionized water, 20.6 grams of HITENOL® BC-1025, and 356.0 grams of styrene. From the second monomer emulsion, 360 grams were removed and set aside (i). To the remaining monomer emulsion were added 7.4 grams of methacrylic acid (ii). The second monomer emulsion (ii) was added to the reactor at a rate of 5.4 grams/minute, simultaneously a mixture of 0.6 grams of ammonium persulfate in 29.5 grams of deionized water was fed to the reactor at a rate of 20 grams/hour at 80°C. Upon completion of the addition, the second monomer emulsion (i) was added to the reactor at a rate of 5.4 grams/minute. Upon completion of the addition, 13.8 grams of UCAR FILMER™ IBT were added to the reactor. A third monomer emulsion was prepared by mixing 102.5 grams of deionized water, 6.4 grams of RHODACAL® DSB, 202.0 grams of styrene, and 27.9 grams of ammonium hydroxide. The third emulsion and a mixture of 0.6 grams of ammonium persulfate in 31.8 grams of deionized water were co-fed to the reactor over a 90 minute period at 80°C. The reaction mixture was held for four hours at 80°C and then cooled to room temperature and filtered to remove any formed grit. The final latex had a solids content of 32.8%, a pH of 10.2, and a particle size of 504 nm. Dry density was 0.68 g/mL. The contrast ratio of this polymer, determined in an 85: 15 mixture with a vinyl-acrylic latex, was 79.3%.

EXAMPLE 32

[0074] A 2-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 790.3 grams, and HITENOL® BC-1025 (25%), 1.5 grams, were added to the reactor and heated to 80°C. 121.6 Grams of the seed emulsion prepared in Example 7 were added to the heated reaction mixture. They were immediately followed by 1 gram of ammonium persulfate in 6.9 grams of deionized water. A first monomer emulsion was prepared by mixing 19.6 grams of deionized water, 1.2 grams of HITENOL® BC- 1025, 2.8 grams of butyl acrylate, 17.5 grams of methyl methacrylate, and 0.4 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 27.6 grams of deionized water were then fed to the reactor over a 30 minutes period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 96.1 grams of deionized water, 20.6 grams of HITENOL® BC-1025, and 363.4 grams of styrene. From the second monomer emulsion, 240 grams were removed and set aside (i). To the remaining monomer emulsion were added 7.4 grams of methacrylic acid (ii). The second monomer emulsion (ii) was added to the reactor at a rate of 5.4 grams/minute, simultaneously a mixture of 0.6 grams of ammonium persulfate in 29.5 grams of deionized water was fed to the reactor at a rate of 20 grams/hour at 80°C. Upon completion of the addition, the second monomer emulsion (i) was added to the reactor at a rate of 5.4 grams/minute. Upon completion of the addition, 13.8 grams of UCAR FILMER™ IBT were added to the reactor. A third monomer emulsion was prepared by mixing 102.5 grams of deionized water, 6.4 grams of RHODACAL® DSB, 202.0 grams of styrene, and 27.9 grams of ammonium hydroxide. The third emulsion and a mixture of 0.6 grams of ammonium persulfate in 31.8 grams of deionized water were co-fed to the reactor over a 90 minute period at 80°C. The reaction mixture was held for four hours at 80°C and then cooled to room temperature and filtered to remove any formed grit. The final latex had a solids content of 32.8%, a pH of 10.3, and a particle size of 456 nm. Dry density was 0.69 g/mL. The contrast ratio of this polymer, determined in an 85: 15 mixture with a vinyl-acrylic latex, was 79.2%.

EXAMPLE 33

[0075] A 2-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 790.3 grams, and HITENOL® AR-1025 (25%), 1.5 grams, were added to the reactor and heated to 80°C. 121.6 Grams of the seed emulsion prepared in Example 7 were added to the heated reaction mixture. They were immediately followed by 1 gram of ammonium persulfate in 6.9 grams of deionized water. A first monomer emulsion was prepared by mixing 19.6 grams of deionized water, 1.2 grams of HITENOL® AR- 1025, 2.8 grams of butyl acrylate, 17.5 grams of methyl methacrylate, and 0.4 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 27.6 grams of deionized water were then fed to the reactor over a 30 minutes period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 96.1 grams of deionized water, 20.6 grams of HITENOL® AR-1025, and 363.4 grams of styrene. From the second monomer emulsion, 240 grams were removed and set aside (i). To the remaining monomer emulsion were added 7.4 grams of methacrylic acid (ii). The second monomer emulsion (ii) was added to the reactor at a rate of 5.4 grams/minute, simultaneously a mixture of 0.6 grams of ammonium persulfate in 29.5 grams of deionized water was fed to the reactor at a rate of 20 grams/hour at 80°C. Upon completion of the addition, the second monomer emulsion (i) was added to the reactor at a rate of 5.4 grams/minute. Upon completion of the addition, 13.8 grams of UCAR FILMER™ IBT were added to the reactor. A third monomer emulsion was prepared by mixing 102.5 grams of deionized water, 6.4 grams of RHODACAL® DSB, 202.0 grams of styrene, and 27.9 grams of ammonium hydroxide. The third emulsion and a mixture of 0.6 grams of ammonium persulfate in 31.8 grams of deionized water were co-fed to the reactor over a 90 minute period at 80°C. The reaction mixture was held for four hours at 80°C and then cooled to room temperature and filtered to remove any formed grit. The final latex had a solids content of 32.8%, a pH of 10.3, and a particle size of 531 nm. Dry density was 0.68 g/mL. The contrast ratio of this polymer, determined in an 85: 15 mixture with a vinyl-acrylic latex, was 79.19%.

EXAMPLE 34

[0076] A 2-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 790.3 grams, and HITENOL® BC-1025 (25%), 1.5 grams, were added to the reactor and heated to 80°C. 121.6 Grams of the seed emulsion prepared in Example 7 were added to the heated reaction mixture. They were immediately followed by 1 gram of ammonium persulfate in 6.9 grams of deionized water. A first monomer emulsion was prepared by mixing 19.6 grams of deionized water, 1.2 grams of HITENOL® BC- 1025, 2.8 grams of butyl acrylate, 17.5 grams of methyl methacrylate, and 0.4 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 27.6 grams of deionized water were then fed to the reactor over a 30 minutes period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 96.1 grams of deionized water, 20.6 grams of HITENOL® BC-1025, and 363.4 grams of styrene. From the second monomer emulsion 120 grams were removed and set aside (i). To the remaining monomer emulsion were added 7.4 grams of methacrylic acid (ii). The second monomer emulsion (ii) was added to the reactor at a rate of 5.4 grams/minute, simultaneously a mixture of 0.6 grams of ammonium persulfate in 29.5 grams of deionized water was fed to the reactor at a rate of 20 grams/hour at 80°C. Upon completion of the addition, the second monomer emulsion (i) was added to the reactor at a rate of 5.4 grams/minute. Upon completion of the addition, 13.8 grams of UCAR FILMER™ IBT were added to the reactor. A third monomer emulsion was prepared by mixing 102.5 grams of deionized water, 6.4 grams of RHODACAL® DSB, 202.0 grams of styrene, 5.65 grams of divinylbenzene and 27.9 grams of ammonium hydroxide. The third emulsion and a mixture of 0.6 grams of ammonium persulfate in 31.8 grams of deionized water were co-fed to the reactor over a 90 minute period at 80°C. The reaction mixture was held for four hours at 80°C and then cooled to room temperature and filtered to remove any formed grit. The final latex had a solids content of 33.0%, a pH of 10.2, and a particle size of 484 nm. Dry density was 0.67 g/mL. The contrast ratio of this polymer, determined in an 85: 15 mixture with a vinyl-acrylic latex, was 79.8%.

EXAMPLE 35

[0077] A 2-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 790.3 grams, and HITENOL® BC-1025 (25%), 1.5 grams, were added to the reactor and heated to 80°C. 121.6 Grams of the seed emulsion prepared in Example 7 were added to the heated reaction mixture. They were immediately followed by 1 gram of ammonium persulfate in 6.9 grams of deionized water. A first monomer emulsion was prepared by mixing 19.6 grams of deionized water, 1.2 grams of HITENOL® BC- 1025, 2.8 grams of butyl acrylate, 17.5 grams of methyl methacrylate, and 0.4 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 27.6 grams of deionized water were then fed to the reactor over a 30 minute period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 96.1 grams of deionized water, 20.6 grams of HITENOL® BC-1025, and 363.4 grams of styrene. From the second monomer emulsion 120 grams were removed and set aside (i). To the remaining monomer emulsion were added 7.4 grams of methacrylic acid (ii). The second monomer emulsion (ii) was added to the reactor at a rate of 5.4 grams/minute, simultaneously a mixture of 0.6 grams of ammonium persulfate in 29.5 grams of deionized water was fed to the reactor at a rate of 20 grams/hour at 80°C. Upon completion of the addition, the second monomer emulsion (i) was added to the reactor at a rate of 5.4 grams/minute. Upon completion of the addition, 13.8 grams of UCAR FILMER™ IBT were added to the reactor. A third monomer emulsion was prepared by mixing 102.5 grams of deionized water, 6.4 grams of RHODACAL® DSB, 202.0 grams of styrene, 22.6 grams of divinylbenzene and 22.9 grams of ammonium hydroxide. The third emulsion and a mixture of 0.6 grams of ammonium persulfate in 31.8 grams of deionized water were co-fed to the reactor over a 90 minute period at 80°C. The reaction mixture was held for four hours at 80°C and then cooled to room temperature and filtered to remove any formed grit. The final latex had a solids content of 33.6%, a pH of 9.9, and a particle size of 527 nm. Dry density was 0.71 g/mL. The contrast ratio of this polymer, determined in an 85: 15 mixture with a vinyl-acrylic latex, was 76.6%.

EXAMPLE 36 [0078] A 2-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 828.7 grams, and HITENOL® BC-1025 (25%), 1.5 grams, were added to the reactor and heated to 80°C. 117.4 Grams of the seed emulsion prepared in Example 7 were added to the heated reaction mixture. They were immediately followed by 1 gram of ammonium persulfate in 6.7 grams of deionized water. A first monomer emulsion was prepared by mixing 19.0 grams of deionized water, 1.2 grams of HITENOL® BC- 1025, 2.7 grams of butyl acrylate, 16.9 grams of methyl methacrylate, and 0.4 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 26.7 grams of deionized water were then fed to the reactor over a 30 minutes period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 92.8 grams of deionized water, 19.9 grams of HITENOL® BC-1025, and 350.9 grams of styrene. From the second monomer emulsion 116 grams were removed and set aside (i). To the remaining monomer emulsion were added 7.2 grams of methacrylic acid (ii). The second monomer emulsion (ii) was added to the reactor at a rate of 5.2 grams/minute, simultaneously a mixture of 0.6 grams of ammonium persulfate in 28.5 grams of deionized water was co-fed to the reactor at a rate of 19.4 grams/hour at 80°C. Upon completion of the addition, the second monomer emulsion (i) was added to the reactor at a rate of 5.2 grams/minute. Upon completion of the addition, 13.3 grams of UCAR FILMER™ IBT were added to the reactor. A third monomer emulsion was prepared by mixing 99.0 grams of deionized water, 6.1grams of RHODACAL® DSB, 195.0 grams of styrene, 32.8 grams of divinylbenzene and 22.2 grams of ammonium hydroxide. The third emulsion and a mixture of 0.6 grams of ammonium persulfate in 30.7 grams of deionized water were co-fed to the reactor over a 90 minute period at 80°C. The reaction mixture was held for four hours at 80°C and then cooled to room temperature and filtered to remove any formed grit. The final latex had a solids content of 32.6%, a pH of 9.7, and a particle size of 533 nm. Dry density was 0.69 g/mL. The contrast ratio of this polymer, determined in an 85: 15 mixture with a vinyl-acrylic latex, was 75.7%.

EXAMPLE 37

[0079] A 2-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 837.0 grams, and HITENOL® BC-1025 (25%), 1.5 grams, were added to the reactor and heated to 80°C. 115.0 Grams of the seed emulsion prepared in Example 7 were added to the heated reaction mixture. They were immediately followed by 0.9 grams of ammonium persulfate in 6.5 grams of deionized water. A first monomer emulsion was prepared by mixing 18.6 grams of deionized water, 1.2 grams of HITENOL® BC- 1025, 2.6 grams of butyl acrylate, 16.6 grams of methyl methacrylate, and 0.4 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.6 grams of ammonium persulfate in 26.1 grams of deionized water were then fed to the reactor over a 30 minutes period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 90.9 grams of deionized water, 19.4 grams of HITENOL® BC-1025, and 343.6 grams of styrene. From the second monomer emulsion 113.5 grams were removed and set aside (i). To the remaining monomer emulsion were added 7.0 grams of methacrylic acid (ii). The second monomer emulsion (ii) was added to the reactor at a rate of 5.1 grams/minute, simultaneously a mixture of 0.6 grams of ammonium persulfate in 27.9 grams of deionized water was fed to the reactor at a rate of 19.0 grams/hour at 80°C. Upon completion of the addition, the second monomer emulsion (i) was added to the reactor at a rate of 5.1 grams/minute. Upon completion of the addition, 13.1 grams of UCAR FILMER™ IBT were added to the reactor. A third monomer emulsion was prepared by mixing 96.9 grams of deionized water, 6.0. grams of RHODACAL® DSB, 191.0 grams of styrene, 42.8 grams of divinylbenzene and 21.7 grams of ammonium hydroxide. The third emulsion and a mixture of 0.6 grams of ammonium persulfate in 30.0 grams of deionized water were co-fed to the reactor over a 90 minute period at 80°C. The reaction mixture was held for four hours at 80°C and then cooled to room temperature and filtered to remove any formed grit. The final latex had a solids content of 32.5%, a pH of 9.8, and a particle size of 480 nm. Dry density was 0.69 g/mL. The contrast ratio of this polymer, determined in an 85: 15 mixture with a vinyl-acrylic latex, was 75.6%.

EXAMPLE 38

[0080] A 2-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 790.2 grams, and HITENOL® BC-1025 (25%), 1.5 grams, were added to the reactor and heated to 80°C. 122.3 Grams of the seed emulsion prepared in Example 7 were added to the heated reaction mixture. They were immediately followed by 1 gram of ammonium persulfate in 7.0 grams of deionized water. A first monomer emulsion was prepared by mixing 19.8 grams of deionized water, 1.3 grams of HITENOL® BC- 1025, 2.8 grams of butyl acrylate, 17.6 grams of methyl methacrylate, and 0.4 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 27.8 grams of deionized water were then fed to the reactor over a 30 minute period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 93.8 grams of deionized water, 20.7 grams of HITENOL® BC-1025, and 365.4 grams of styrene. From the second monomer emulsion 360 grams were removed and set aside (i). To the remaining monomer emulsion were added 3.7 grams of acrylic acid (ii). The second monomer emulsion (ii) was added to the reactor at a rate of 5.4 grams/minute, simultaneously a mixture of 0.6 grams of ammonium persulfate in 29.6 grams of deionized water was fed to the reactor at a rate of 20.1 grams/hour at 80°C. Upon completion of the addition, the second monomer emulsion (i) was added to the reactor at a rate of 5.4 grams/minute. Upon completion of the addition, 13.9 grams of UCAR FILMER™ IBT were added to the reactor. A third monomer emulsion was prepared by mixing 103.0 grams of deionized water, 6.4 grams of RHODACAL® DSB, 203.1 grams of styrene, and 28.3 grams of ammonium hydroxide. The third emulsion and a mixture of 0.6 grams of ammonium persulfate in 31.9 grams of deionized water were co-fed to the reactor over a 90 minute period at 80°C. The reaction mixture was held for four hours at 80°C and then cooled to room temperature and filtered to remove any formed grit. The final latex had a solids content of 32.9%, a pH of 10.0, and a particle size of 468 nm. Dry density was 0.69 g/mL. The contrast ratio of this polymer, determined in an 85: 15 mixture with a vinyl-acrylic latex, was 78.1%.

EXAMPLE 39

[0081] A 2-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 790.3 grams, and HITENOL® BC-1025 (25%), 1.5 grams, were added to the reactor and heated to 80°C. 121.6 Grams of the seed emulsion prepared in Example 7 were added to the heated reaction mixture. They were immediately followed by 1 gram of ammonium persulfate in 7.0 grams of deionized water. A first monomer emulsion was prepared by mixing 19.6 grams of deionized water, 1.2 grams of HITENOL® BC- 1025, 2.8 grams of butyl acrylate, 17.5 grams of methyl methacrylate, and 0.4 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 27.6 grams of deionized water were then fed to the reactor over a 30 minutes period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 96.1 grams of deionized water, 20.6 grams of HITENOL® BC-1025, and 363.4 grams of styrene. From the second monomer emulsion 360 grams were removed and set aside (i). To the remaining monomer emulsion were added 7.4 grams of acrylic acid (ii). The second monomer emulsion (ii) was added to the reactor at a rate of 5.4 grams/minute, simultaneously a mixture of 0.6 grams of ammonium persulfate in 29.5 grams of deionized water was fed to the reactor at a rate of 20.0 grams/hour at 80°C. Upon completion of the addition, the second monomer emulsion (i) was added to the reactor at a rate of 5.4 grams/minute. Upon completion of the addition, 13.8 grams of UCAR FILMER™ IBT were added to the reactor. A third monomer emulsion was prepared by mixing 102.5 grams of deionized water, 6.4 grams of RHODACAL® DSB, 201.9 grams of styrene, and 33.4 grams of ammonium hydroxide. The third emulsion and a mixture of 0.6 grams of ammonium persulfate in 31.8 grams of deionized water were co-fed to the reactor over a 90 minute period at 80°C. The reaction mixture was held for four hours at 80°C and then cooled to room temperature and filtered to remove any formed grit. The final latex had a solids content of 32.6%, a pH of 10.1, and a particle size of 443 nm. Dry density was 0.71 g/mL. The contrast ratio of this polymer, determined in an 85: 15 mixture with a vinyl-acrylic latex, was 77.1%.

EXAMPLE 40

[0082] A 2-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 790.2 grams, and HITENOL® BC-1025 (25%), 1.5 grams, were added to the reactor and heated to 80°C. 122.3 Grams of the seed emulsion prepared in Example 7 were added to the heated reaction mixture. They were immediately followed by 1 gram of ammonium persulfate in 7.0 grams of deionized water. A first monomer emulsion was prepared by mixing 19.8 grams of deionized water, 1.3 grams of HITENOL® BC- 1025, 2.8 grams of butyl acrylate, 17.6 grams of methyl methacrylate, and 0.4 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 27.8 grams of deionized water were then fed to the reactor over a 30 minutes period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 93.8 grams of deionized water, 20.7 grams of HITENOL® BC-1025, and 365.4 grams of styrene. From the second monomer emulsion 240 grams were removed and set aside (i). To the remaining monomer emulsion were added 3.7 grams of acrylic acid (ii). The second monomer emulsion (ii) was added to the reactor at a rate of 5.3 grams/minute, simultaneously a mixture of 0.6 grams of ammonium persulfate in 29.6 grams of deionized water was fed to the reactor at a rate of 20.1 grams/hour at 80°C. Upon completion of the addition, the second monomer emulsion (i) was added to the reactor at a rate of 5.3 grams/minute. Upon completion of the addition, 14.0 grams of UCAR FILMER™ IBT were added to the reactor. A third monomer emulsion was prepared by mixing 103.0 grams of deionized water, 6.4 grams of RHODACAL® DSB, 203.1 grams of styrene, and 28.3 grams of ammonium hydroxide. The third emulsion and a mixture of 0.6 grams of ammonium persulfate in 32.0 grams of deionized water were co-fed to the reactor over a 90 minute period at 80°C. The reaction mixture was held for four hours at 80°C and then cooled to room temperature and filtered to remove any formed grit. The final latex had a solids content of 33.3%, a pH of 9.7, and a particle size of 471 nm. Dry density was 0.68 g/mL. The contrast ratio of this polymer, determined in an 85: 15 mixture with a vinyl-acrylic latex, was 79.5%.

EXAMPLE 41

[0083] A 2-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 790.3 grams, and HITENOL® BC-1025 (25%), 1.5 grams, were added to the reactor and heated to 80°C. 121.6 Grams of the seed emulsion prepared in Example 7 were added to the heated reaction mixture. They were immediately followed by 1 gram of ammonium persulfate in 7.0 grams of deionized water. A first monomer emulsion was prepared by mixing 19.6 grams of deionized water, 1.2 grams of HITENOL® BC- 1025, 2.8 grams of butyl acrylate, 17.5 grams of methyl methacrylate, and 0.4 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 27.6 grams of deionized water were then fed to the reactor over a 30 minute period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 96.1 grams of deionized water, 20.6 grams of HITENOL® BC-1025, and 363.4 grams of styrene. From the second monomer emulsion 240 grams were removed and set aside (i). To the remaining monomer emulsion were added 7.4 grams of acrylic acid (ii). The second monomer emulsion (ii) was added to the reactor at a rate of 5.4 grams/minute, simultaneously a mixture of 0.6 grams of ammonium persulfate in 29.5 grams of deionized water was fed to the reactor at a rate of 20.0 grams/hour at 80°C. Upon completion of the addition, the second monomer emulsion (i) was added to the reactor at a rate of 5.4 grams/minute. Upon completion of the addition, 13.8 grams of UCAR FILMER™ IBT were added to the reactor. A third monomer emulsion was prepared by mixing 102.5 grams of deionized water, 6.4 grams of RHODACAL® DSB, 201.9 grams of styrene, and 33.4 grams of ammonium hydroxide. The third emulsion and a mixture of 0.6 grams of ammonium persulfate in 31.8 grams of deionized water were co-fed to the reactor over a 90 minute period at 80°C. The reaction mixture was held for four hours at 80°C and then cooled to room temperature and filtered to remove any formed grit. The final latex had a solids content of 33.3%, a pH of 9.9, and a particle size of 480 nm. Dry density was 0.70 g/mL. The contrast ratio of this polymer, determined in an 85: 15 mixture with a vinyl-acrylic latex, was 78.4%.

EXAMPLE 42

[0084] A 2-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 790.2 grams, and HITENOL® BC-1025 (25%), 1.5 grams, were added to the reactor and heated to 80°C. 122.3 Grams of the seed emulsion prepared in Example 7 were added to the heated reaction mixture. They were immediately followed by 1 gram of ammonium persulfate in 7.0 grams of deionized water. A first monomer emulsion was prepared by mixing 19.8 grams of deionized water, 1.3 grams of HITENOL® BC- 1025, 2.8 grams of butyl acrylate, 17.6 grams of methyl methacrylate, and 0.4 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 27.8 grams of deionized water were then fed to the reactor over a 30 minute period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 93.8 grams of deionized water, 20.7 grams of HITENOL® BC-1025, and 365.4 grams of styrene. From the second monomer emulsion 120 grams were removed and set aside (i). To the remaining monomer emulsion were added 3.7 grams of acrylic acid (ii). The second monomer emulsion (ii) was added to the reactor at a rate of 5.4 grams/minute, simultaneously a mixture of 0.6 grams of ammonium persulfate in 29.6 grams of deionized water was fed to the reactor at a rate of 20.1 grams/hour at 80°C. Upon completion of the addition, the second monomer emulsion (i) was added to the reactor at a rate of 5.4 grams/minute. Upon completion of the addition, 14.0 grams of UCAR FILMER™ IBT were added to the reactor. A third monomer emulsion was prepared by mixing 103.0 grams of deionized water, 6.4 grams of RHODACAL® DSB, 203.1 grams of styrene, and 28.3 grams of ammonium hydroxide. The third emulsion and a mixture of 0.6 grams of ammonium persulfate in 32.0 grams of deionized water were co-fed to the reactor over a 90 minute period at 80°C. The reaction mixture was held for four hours at 80°C and then cooled to room temperature and filtered to remove any formed grit. The final latex had a solids content of 33.4 %, a pH of 9.9, and a particle size of 565 nm. Dry density was 0.69 g/mL. The contrast ratio of this polymer, determined in an 85: 15 mixture with a vinyl-acrylic latex, was 79.7%.

EXAMPLE 43

[0085] A 2-liter, four necked reactor was equipped with a paddle stirrer, thermocouple, reflux condenser, and dosing pumps. Deionized water, 790.3 grams, and HITENOL® BC-1025 (25%), 1.5 grams, were added to the reactor and heated to 80°C. 121.6 Grams of the seed emulsion prepared in Example 7 were added to the heated reaction mixture. They were immediately followed by 1 gram of ammonium persulfate in 7.0 grams of deionized water. A first monomer emulsion was prepared by mixing 19.6 grams of deionized water, 1.2 grams of HITENOL® BC- 1025, 2.8 grams of butyl acrylate, 17.5 grams of methyl methacrylate, and 0.4 grams of methacrylic acid. The first monomer emulsion and a mixture of 0.7 grams of ammonium persulfate in 27.6 grams of deionized water were then fed to the reactor over a 30 minutes period at 80°C. Upon completion of the addition, a second monomer emulsion was prepared by mixing 96.1 grams of deionized water, 20.6 grams of HITENOL® BC-1025, and 363.4 grams of styrene. From the second monomer emulsion 120 grams were removed and set aside (i). To the remaining monomer emulsion were added 7.4 grams of acrylic acid (ii). The second monomer emulsion (ii) was added to the reactor at a rate of 5.4 grams/minute, simultaneously a mixture of 0.6 grams of ammonium persulfate in 29.5 grams of deionized water was fed to the reactor at a rate of 20.0 grams/hour at 80°C. Upon completion of the addition, the second monomer emulsion (i) was added to the reactor at a rate of 5.4 grams/minute. Upon completion of the addition, 13.8 grams of UCAR FILMER™ IBT were added to the reactor. A third monomer emulsion was prepared by mixing 102.5 grams of deionized water, 6.4 grams of RHODACAL® DSB, 201.9 grams of styrene, and 33.4 grams of ammonium hydroxide. The third emulsion and a mixture of 0.6 grams of ammonium persulfate in 31.8 grams of deionized water were co-fed to the reactor over a 90 minute period at 80°C. The reaction mixture was held for four hours at 80°C and then cooled to room temperature and filtered to remove any formed grit. The final latex had a solids content of 32.9%, a pH of 10.0, and a particle size of 530 nm. Dry density was 0.70 g/mL. The contrast ratio of this polymer, determined in an 85: 15 mixture with a vinyl-acrylic latex, was 78.8%.

[0086] The preceding Examples demonstrate certain features of the present invention. [0087] In Examples 1 -6, it was found that reacting a portion of the emulsion in the early stage of the process and adding the remainder in a subsequent step improves particle size control to obtain a desired particle size of the core polymer (a).

[0088] In Example 7, the core polymer with a hydrophilic ethylenically unsaturated monomer was added with the remainder portion. In order to avoid free oligomers of the hydrophilic ethylenically unsaturated monomer in the water phase, a portion of the emulsion was polymerized without the hydrophilic ethylenically unsaturated monomer and the monomer was added as a component of the later added emulsion. It is believed that the hydrophilic ethylenically unsaturated monomer inside the particle or in the particle surface region minimizes the acid content in the water phase. In the swelling step, the acid core polymer (a) is swelled with a swelling agent due to an acid-base reaction. It is believed that the particle swelling is maximized by having almost all the hydrophilic ethylenically unsaturated monomer inside the particle.

[0089] Examples 8-10 used conventional surfactants and co-fed the polymerizable aromatic monomer and the swelling agent. The encapsulation of the hydrophilic core polymer (a) within hydrophobic shells was achieved with a contrast ratio average of 68%. It is believed that co-feeding a polymerizable aromatic monomer and the swelling agent allows in one step: (i) to improve the diffusion of the swelling agent due to the plasticization of the first polymer shell (b); (ii) swelling the core polymer (a); and (iii) the particle consolidation by the polymerization of the polymerizable aromatic monomer.

[0090] Examples 11-14 used aromatic monomer (b)(ii) and/or (c)(ii) and co-fed the polymerizable aromatic monomer and the swelling agent. The aromatic monomer (b)(ii) and/or (c)(ii) is covalently bonded to the chains of the hydrophilic ethylenically unsaturated monomer (b)(i) and/or the aromatic monomer (c)(i), resulting in distribution of the hydrophilic surfactant group along the first and/or second shell polymer structure. It is believed that the hydrophilic surfactant group (polyoxyalkylene group)) bonded to the first and/or second shell polymer structure improves the swelling agent diffusion because of the polarity of the surfactant group. The hydrophilic group works as a carrier of the swelling agent and is believed to form the hydrophilic channels that enhance swelling agent diffusion. Contrast ratio is increased.

[0091] Examples 15 and 17 included an aromatic monomer (b)(ii) and/or (c)(ii) and a radical inhibitor. The radical inhibitor was used during the formation of the second shell in order to enhance the diffusion of the swelling agent. It is believed that radicals were quenched after the second shell was polymerized. Without radicals present, the third emulsion may be used only to plasticize the second shell and the swelling agent has a better diffusion through the second shell, thereby increasing the contrast ratio. As such, the swelling stage is carried out without polymerization of the aromatic monomer (b)(i).

[0092] Examples 16 and 18 used an aromatic monomer (b)(ii) and/or (c)(ii) and swelling agent was added after the polymerizable aromatic monomer to improve the contrast ratio. It is believed that the swelling agent diffusion was increased through the second shell using the third emulsion as plasticizer without the addition of a radical inhibitor.

[0093] Examples 19-21 used an aromatic monomer (b)(ii) and/or (c)(ii) and co-feeding of the polymerizable aromatic monomer and the swelling agent. The swelling agent used is a strong alkali that is almost completely dissociated into ions. It is believed that the NaOH diffusion is not as fast as other swelling agents due to highly hydrated ions which means higher temperature is needed for promoting the diffusion of Na⁺ and OH^" ions through the second shell.

[0094] Examples 22-25 used conventional surfactants and co-feeding of the polymerizable aromatic monomer and the swelling agent. The initial structuration process of the first and second shells was made with conventional surfactants but with a core polymer (a) with a small particle size. It was expected to have core-shell polymeric particles with better contrast ratio, but it was not achieved.

[0095] In Examples 26-30, the concentration of hydrophilic ethylenically unsaturated monomer in the second shell increased. As the concentration of the hydrophilic ethylenically unsaturated monomer increased in the second shell, it is believed that the polarity of the shell increased and the swelling agent diffusion through this shell is improved; hence, a better contrast ratio was obtained.

[0096] In Examples 31-33, the amount of emulsion 2 in the remainder portion of the second shell was decreased. According to the hydrophilicity of the hydrophilic ethylenically unsaturated monomer, it is believed that the monomer distribution throughout the particle is dependent on the way it is added to the emulsion. For this reason, the hydrophilic ethylenically unsaturated monomer was excluded from the initial mixture of monomers of the second emulsion and was added in different amounts of the earlier added second emulsion. A better distribution of the monomer was achieved by decreasing the amount of emulsion 2 in the remainder portion of the second emulsion. [0097] In Examples 34-37, the concentration of DVB in third shell was increased. The use of DVB in the third shell allows the core-shell polymer to have mechanical stability and chemical resistance. At higher DVB concentrations, the mechanical and chemical properties are also increased.

[0098] In Examples 38-43, the concentration of the hydrophilic ethylenically unsaturated monomer was varied by varying the amount of emulsion 2 in the remainder portion of the second shell. Due to the hydrophilicity (or water solubility) of the hydrophilic ethylenically unsaturated monomer, it is believed that the monomer distribution throughout the particle is strongly influenced by the way it is added to the emulsion. For this reason, it was excluded from the initial mixture of monomers of the second emulsion and it was added to different amounts of the earlier added second emulsion. The better results were achieved adding the hydrophilic ethylenically unsaturated monomer at about 20 to 80% of the second emulsion.

EXAMPLE 44: Coating Composition

[0099] The contrast ratio of coating compositions with the particles prepared in Example 32 was evaluated according to ASTM E 1331-96.

[00100] The components listed in Table 1 were combined to make a coating composition.

Table 1

Mixture of 1 ,2-benzisothiazolin- 2.03

3-one (2.5%) and 2-methyl-4- isothiazolin-3-one (2.5%).

Isobutyric acid, ester with 2,2,4- 7.78

trimethyl- 1 ,3-pentanediol

2,2,4-Trimethyl- 1 ,3-pentanediol

monoisobutyrate

Calcium carbonate and 116.5

Diatomite

2-(Dimethylamino)ethanol 3.33

[00101] The components were thoroughly mixed, and the contrast ratio was measured. The contrast ratio of this coating composition was determined to be 98.64%.

[00102] The following invention further includes the subject matter of the following clauses.

[00103] Clause 1: An aqueous dispersion of polymeric particles, the particles comprising: (a) a core polymer prepared from at least one hydrophilic ethylenically unsaturated monomer; (b) at least one first shell polymer at least partially encapsulating the core polymer, the first shell polymer prepared from a mixture of reactants comprising (b)(i) at least one hydrophilic ethylenically unsaturated monomer and (b)(ii) at least one aromatic monomer having a hydrophilic surfactant group and an ethylenically unsaturated group reactive with the hydrophilic ethylenically unsaturated monomer (b)(i); (c) at least one second shell polymer at least partially encapsulating the first shell polymer, the second shell polymer prepared from a mixture of reactants comprising (c)(i) at least one aromatic monomer having an ethylenically unsaturated group and (c)(ii) an aromatic monomer having a hydrophilic surfactant group and an ethylenically unsaturated group reactive with the aromatic monomer (c)(i); and (d) an optional third shell polymer at least partially encapsulating the second shell polymer, the third shell polymer prepared from at least one polymerizable aromatic monomer, wherein the polymeric particle defines a void.

[00104] Clause 2: The aqueous dispersion of clause 1 wherein the aromatic monomers (b)(ii) and (c)(ii) each comprise a phenyl group.

[00105] Clause 3: The aqueous dispersion of clause 1 or 2 wherein the aromatic monomers (b)(ii) and (c)(ii) each comprise a polyoxyalkylene group. [00106] Clause 4: The aqueous dispersion of any of clauses 1-3 wherein the aromatic monomer

(b) (ii) is present in the first shell polymer in an amount of 2 to 98 wt.% based on the total weight of the first shell polymer.

[00107] Clause 5: The aqueous dispersion of any of clauses 1-4 wherein the aromatic monomer

(c) (ii) is present in the second shell polymer in an amount of 2 to 98 wt.% based on the total weight of the second shell polymer.

[00108] Clause 6: A method of producing polymeric particles comprising: (a) forming an aqueous dispersion of a core polymer by polymerizing at least one hydrophilic ethylenically unsaturated monomer; (b) forming at least one first shell polymer at least partially encapsulating the core polymer by polymerizing onto the core polymer at least one hydrophilic ethylenically unsaturated monomer (i) and at least one aromatic monomer (ii) having a hydrophilic surfactant group and an ethylenically unsaturated group reactive with the hydrophilic ethylenically unsaturated monomer (i); (c) forming at least one second shell polymer at least partially encapsulating the first shell polymer by polymerizing onto the first shell polymer at least one aromatic monomer (iii) having an ethylenically unsaturated group and an aromatic monomer (iv) having a hydrophilic surfactant group and an ethylenically unsaturated group reactive with the aromatic monomer (iii); (d) optionally forming a third shell polymer at least partially encapsulating the second shell polymer by polymerizing onto the second shell polymer at least one aromatic monomer; and (e) adding a swelling agent to the aqueous dispersion during or after polymerization of the second or third shell polymer in steps (c) or (d).

[00109] Clause 7: The method of clause 6 wherein the swelling agent is added to the aqueous dispersion during polymerization of the third shell polymer.

[00110] Clause 8: The method of clause 6 or 7 wherein the aromatic monomers of the first shell polymer and the second shell polymer each comprise a phenyl group.

[00111] Clause 9: The method of any of clauses 6-8 wherein the aromatic monomers (ii) and (iv) of the first shell polymer and the second shell polymer each comprise a polyoxyalkylene group.

[00112] Clause 10: The method of any of clauses 6-9 wherein the aromatic monomer (ii) of the first shell polymer is added to the aqueous dispersion of core polymers in an amount of 2 to 98 wt.% based on the total weight of the first shell monomers added.

[00113] Clause 11: The method of any of clauses 6-10 wherein the aromatic monomer (iv) of the second shell polymer is added to the aqueous dispersion of first monomer encapsulated core polymer in an amount of 2 to 98 wt.% based on the total weight of the second shell monomers added.

[00114] Clause 12: A method of producing core-shell polymeric particles in a multi-stage emulsion polymerization process comprising: (a) producing core polymeric particles and a plurality of polymeric shells at least partially encapsulating the core polymeric particle, wherein the core polymeric particles are prepared from at least one hydrophilic ethylenically unsaturated monomer and at least one of the polymeric shells are produced from a mixture of reactants comprising (i) at least one hydrophilic ethylenically unsaturated monomer and (ii) an ionic ethylenically unsaturated surfactant molecule; and (b) forming an outer shell polymer at least partially encapsulating the particles from step (a) by polymerizing thereon an ethylenically unsaturated monomer in the presence of a swelling agent to swell the core polymeric particles.

[00115] Clause 13: The method of clause 12 further comprising drying the core-shell polymeric particles.

[00116] Clause 14: The method of clause 12 or 13 wherein the ionic ethylenically unsaturated surfactant monomer comprises a polar polyoxyalkylene group.

[00117] Clause 15: The method of any of clauses 12-14 wherein the ionic ethylenically unsaturated surfactant monomer comprises an aromatic group.

[00118] Clause 16: The method of any of clauses 12-15 wherein at least one of the polymeric shells is produced from an aromatic monomer.

[00119] Clause 17: A coating composition comprising the aqueous dispersion of polymeric particles of clause 1.

[00120] Clause 18: A substrate at least partially coated with the coating composition of clause 17.

[00121] Clause 19: A coating composition comprising polymeric particles produced according to the method of any of clauses 6-16.

[00122] Clause 20: A coating composition comprising core-shell polymeric particles produced according to the method of clause 12.

[00123] Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention.

Claims

THE INVENTION CLAIMED IS

1. An aqueous dispersion of polymeric particles, the particles comprising:

(a) a core polymer prepared from at least one hydrophilic ethylenically unsaturated monomer;

(b) at least one first shell polymer at least partially encapsulating the core polymer, the first shell polymer prepared from a mixture of reactants comprising (b)(i) at least one hydrophilic ethylenically unsaturated monomer and (b)(ii) at least one aromatic monomer having a hydrophilic surfactant group and an ethylenically unsaturated group reactive with the hydrophilic ethylenically unsaturated monomer (b)(i);

(c) at least one second shell polymer at least partially encapsulating the first shell polymer, the second shell polymer prepared from a mixture of reactants comprising (c)(i) at least one aromatic monomer having an ethylenically unsaturated group and (c)(ii) an aromatic monomer having a hydrophilic surfactant group and an ethylenically unsaturated group reactive with the aromatic monomer (c)(i); and

(d) an optional third shell polymer at least partially encapsulating the second shell polymer, the third shell polymer prepared from at least one polymerizable aromatic monomer, wherein the polymeric particle defines a void.

2. The aqueous dispersion of claim 1 wherein the aromatic monomers (b)(ii) and (c)(ii) each comprise a phenyl group.

3. The aqueous dispersion of claim 1 wherein the aromatic monomers (b)(ii) and (c)(ii) each comprise a polyoxyalkylene group.

4. The aqueous dispersion of claim 1 wherein the aromatic monomer (b)(ii) is present in the first shell polymer in an amount of 2 to 98 wt.% based on the total weight of the first shell polymer.

5. The aqueous dispersion of claim 1 wherein the aromatic monomer (c)(ii) is present in the second shell polymer in an amount of 2 to 98 wt.% based on the total weight of the second shell polymer.

6. A method of producing polymeric particles comprising:

(a) forming an aqueous dispersion of a core polymer by polymerizing at least one hydrophilic ethylenically unsaturated monomer;

(b) forming at least one first shell polymer at least partially encapsulating the core polymer by polymerizing onto the core polymer at least one hydrophilic ethylenically unsaturated monomer (i) and at least one aromatic monomer (ii) having a hydrophilic surfactant group and an ethylenically unsaturated group reactive with the hydrophilic ethylenically unsaturated monomer (i);

(c) forming at least one second shell polymer at least partially encapsulating the first shell polymer by polymerizing onto the first shell polymer at least one aromatic monomer (iii) having an ethylenically unsaturated group and an aromatic monomer (iv) having a hydrophilic surfactant group and an ethylenically unsaturated group reactive with the aromatic monomer (iii);

(d) optionally forming a third shell polymer at least partially encapsulating the second shell polymer by polymerizing onto the second shell polymer at least one aromatic monomer; and

(e) adding a swelling agent to the aqueous dispersion during or after polymerization of the second or third shell polymer in steps (c) or (d).

7. The method of claim 6 wherein the swelling agent is added to the aqueous dispersion during polymerization of the third shell polymer.

8. The method of claim 6 wherein the aromatic monomers of the first shell polymer and the second shell polymer each comprise a phenyl group.

9. The method of claim 6 wherein the aromatic monomers (ii) and (iv) of the first shell polymer and the second shell polymer each comprise a polyoxyalkylene group.

10. The method of claim 6 wherein the aromatic monomer of the first shell polymer is added to the aqueous dispersion of core polymers in an amount of 2 to 98 wt.% based on the total weight of the first shell monomers added.

11. The method of claim 6 wherein the aromatic monomer (iv) of the second shell polymer is added to the aqueous dispersion of first monomer encapsulated core polymer in an amount of 5 to 98 wt.% based on the total weight of the second shell monomers added.

12. A method of producing core-shell polymeric particles in a multi-stage emulsion polymerization process comprising:

(a) producing core polymeric particles and a plurality of polymeric shells at least partially encapsulating the core polymeric particle, wherein the core polymeric particles are prepared from at least one hydrophilic ethylenically unsaturated monomer and at least one of the polymeric shells are produced from a mixture of reactants comprising (i) at least one hydrophilic ethylenically unsaturated monomer and (ii) an ionic ethylenically unsaturated surfactant molecule; and

(b) forming an outer shell polymer at least partially encapsulating the particles from step (a) by polymerizing thereon an ethylenically unsaturated monomer in the presence of a swelling agent to swell the core polymeric particles.

13. The method of claim 12 further comprising drying the core-shell polymeric particles.

14. The method of claim 12 wherein the ionic ethylenically unsaturated surfactant monomer comprises a polar polyoxyalkylene group.

15. The method of claim 14 wherein the ionic ethylenically unsaturated surfactant monomer comprises an aromatic group.

16. The method of claim 15 wherein at least one of the polymeric shells is produced from an aromatic monomer. Ref. No. 15010696A1PCT

17. A coating composition comprising the aqueous dispersion of polymeric particles of claim 1.

18. A substrate at least partially coated with the coating composition of claim

17.

19. A coating composition comprising polymeric particles produced according to the method of claim 6.

20. A coating composition comprising core-shell polymeric particles produced according to the method of claim 12.