WO2015138162A1

WO2015138162A1 - Coating compositions comprising functionalized hollow silica particles with low porosity prepared using water-based silica precursors

Info

Publication number: WO2015138162A1
Application number: PCT/US2015/017912
Authority: WO
Inventors: Jelena LASIO
Original assignee: E I Du Pont De Nemours And Company
Priority date: 2014-03-11
Filing date: 2015-02-27
Publication date: 2015-09-17

Abstract

The disclosure provides a coating composition comprising functionalized hollow silica particles, wherein the functionalized hollow silica particles are prepared by a process comprising: providing a core/shell silica particle comprising a template core particle and a silica treatment, wherein the core/shell silica particle has an outer surface; and wherein the silica treatment is prepared using a water-based silica precursor; creating a functionalized surface on the core/shell silica particle, wherein the functionalized surface is prepared using sulfonic acid, phosphonic esters, carboxylic acid, amines, epoxides, or boronic acids, and removing the template core particle to form a functionalized hollow silica particle. These coating compositions comprise inorganic hollow particles which are useful as hiding or opacifying agents.

Description

TITLE

COATING COMPOSITIONS COMPRISING FUNCTIONALIZED HOLLOW SILICA PARTICLES WITH LOW POROSITY PREPARED USING WATER-BASED SILICA PRECURSORS

BACKGROUND OF THE DISCLOSURE

The present disclosure relates to coating compositions comprising functionalized hollow silica particles. More particularly, the disclosure relates to coating compositions comprising functionalized silica particles with substantially impervious silica shells prepared using water-based silica precursors.

The coating compositions of interest in the present disclosure are water-dispersible coating compositions such as latex coating

compositions, e.g. acrylic, styrene acrylic, etc.; and solvent based such as alkyd coating compositions; urethane coating compositions; and unsaturated polyester coating compositions, typically a paint, clear coating, or stain. These coatings may be applied to a substrate by spraying, applying with a brush or roller or electrostatically, such as powder coatings, etc. These coating compositions are described in Outlines of Paint Technology (Halstead Press, New York, NY, Third edition, 1990) and Surface Coatings Vol. I, Raw Materials and Their Usage (Chapman and Hall, New York, NY, Second Edition, 1984).

Inorganic powders may be added to the coating compositions. In particular, titanium dioxide pigments, have been added to coating compositions for imparting whiteness and/or opacity to the finished article. Nano core/shell particles may be added to coating compositions as hiding or opacifiying agents.

Nano core/shell particles are submicroscopic colloidal systems composed of a solid or liquid core surrounded by a thin polymer or inorganic shell. This solid or liquid core is removed to form hollow nanospheres. Such core/shell systems may be prepared by deposition of the shell material onto a template particle, wherein the shell material can be either organic, inorganic, or hybrid. The selective removal of the core (template) material without disturbing the shell generates hollow particles.

In many applications of hollow nanoparticles, for example in cases where they are used as drug delivery agents, or catalyst support, it is desired for the porosity and surface area of the material to be high, in order to ensure the delivery of the host molecule, or enough surface area for efficient catalysis. In applications in which delivery of air voids is important for the application, such as in photonic band gap materials, thermal insulators, or coatings, it is desirable that the porosity of the shell is minimized, to ensure the integrity of the central void of the hollow particle. Therefore a need exists for synthetic methods for substantially impervious hollow particles.

SUMMARY OF THE DISCLOSURE

The disclosure provides a coating composition comprising functionalized hollow silica nanospheres, typically substantially impervious hollow particles with tunable surface properties. The surface properties of the particles are tuned through grafting with a variety of functionalized alkoxysilanes.

In a first aspect, a coating composition comprises functionalized hollow silica particles, wherein the functionalized hollow silica particles are prepared by a process comprising:

(i) providing a core/shell silica particle comprising a template core particle and a silica treatment, more typically a coating, wherein the core/shell silica particle has an outer surface; and wherein the silica treatment is prepared using a water-based silica precursor;

creating a functionalized surface on the core/shell silica particle, wherein the functionalized surface is prepared using sulfonic acid, phosphonic esters, carboxylic acid, amines, epoxides, boronic acids or quarternary amines, and (iii) removing the template core particle to form a

functionalized hollow silica particle.

The template core particle from the core/shell silica particle may be removed before or after functionalization, more typically before

functionalization. If removed after functionalization, it is important the core removal does not damage the functionalized surface. For example, with a-methyl styrene, core removal is at low temperatures so no harm is done to the functionalized surface if core removal is achieved after

functionalization. Also, acid- or base-labile core materials that can be removed by hydrolysis can be removed before or after functionalization.

More typically the silica treatment is substantially impervious. By 'substantially impervious' we mean the surface area and porosity of the silica shell, typically walls, has to be tuned. Whether the silica shell is adequate can be determined by comparing the surface area of the particles with calculated surface area of a smooth sphere of the same diameter. Typically, we consider the shell substantially impervious if its surface area does not surpass about 130% of the calculated surface area of a smooth sphere of the same dimensions, i.e., it is about 30% or less higher than the surface of the core/shell silica particle compared to the calculated surface area of a smooth sphere of the same diameter, more typically about 125% of the smooth sphere surface area, and still more typically about 120% of the smooth sphere surface area of the same dimensions. Addition of various amounts of the silica precursor will lead to more or less porous silica layers, which can lead to control of the porosity and surface area of the particles. Further, the silica precursor may be added in stages to modulate the porosity of the particles as well as their surface. Lastly, calcination at temperatures higher than about 500 °C may decrease the porosity and surface area of the particles without increasing the thickness of the wall. In the first aspect, the process for preparing the core/shell silica particle comprising a template core particle and a silica treatment comprises: a) providing a template core particle, more typically prepared using emulsion polymerization;

b) coating the template particle with a water-based silica precursor such as sodium silicate, potassium silicate, ammonium silicate or pre-formed silicic acid; and

c) maintaining the pH at about 2 to about 10 to form a silica

treatment, typically a coating, on the template particle.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows the process for making hollow silica particles, as described in examples 1 -6.

Figure 2 shows functionalization of hollow silica particles with

phosphonate ester through use of diethyl-(2- (triethoxysilyl)ethyl)phosphonate, as described in Example 7.

Figure 3 shows the scheme for converting the phosphonate ester- functionalized silica from Figure 2, example 7 into phosphonic acid- functionalized silica particles through hydrolysis of phosphonic ester groups, as described in Example 8.

Figure 4 shows functionalization of hollow silica particles with (3- glycydoxypropyl)trimethoxysilane, as described in Examples 9 and 10. Figure 5 shows the process for further functionalization of the epoxy silyl- funtionalized silica with glycine, to generate carboxyl group-functionalized silica particles through an amine linkage, as described in Example 9.

Figure 6 shows the process for further functionalization of the epoxy silyl- funtionalized silica with thioglycolic acid, to generate carboxyl group- functionalized silica particles through a thioether linkage, as described in Example 10.

Figure 7 shows the process for functionalization of hollow silica particles with (diethoxyphosphoryl)methyl-2-((triethoxysilyl)ethyl)carbamate, as described in Example 1 1 . Figure 8 shows the TEM image of hollow silica particles obtained through sodium silicate deposition onto PMMA particles, followed by calcination, as described in Example 3.

Figure 9 shows the TEM image of hollow silica particles obtained through sodium silicate deposition onto PMMA particles, followed by calcination as described in Example 5.

DETAILED DESCRIPTION OF THE DISCLOSURE

In this disclosure "comprising" is to be interpreted as specifying the presence of the stated features, integers, steps, or components as referred to, but does not preclude the presence or addition of one or more features, integers, steps, or components, or groups thereof. Additionally, the term "comprising" is intended to include examples encompassed by the terms "consisting essentially of and "consisting of." Similarly, the term "consisting essentially of is intended to include examples encompassed by the term "consisting of."

In this disclosure, when an amount, concentration, or other value or parameter is given as either a range, typical range, or a list of upper typical values and lower typical values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or typical value and any lower range limit or typical value, regardless of whether ranges are separately disclosed. Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range. It is not intended that the scope of the disclosure be limited to the specific values recited when defining a range.

In this disclosure, terms in the singular and the singular forms "a," "an," and "the," for example, include plural referents unless the content clearly dictates otherwise. Thus, for example, reference to "hollow particle", "the hollow particle", or "a hollow particle" also includes a plurality of hollow particles. This disclosure is particularly suitable for producing coating compositions comprising hollow inorganic particles, typically hollow silica particles, and in particular architectural paint formulations or ink

formulations comprising hollow inorganic particles, typically hollow silica particles, having improved paint or ink performance.

The hollow inorganic particles, typically hollow silica particles, of this disclosure are produced through intermediacy of template particles, onto which the shell material is deposited, to generate core/shell particles. The process of silica deposition is such that it allows tuning of the surface area and porosity of the silica shells, thereby allowing for synthesis of impervious core/shell particles. The core material is removed to generate hollow particles. The resulting hollow particles are then functionalized with a variety of alkoxysilanes to generate functionalized hollow particles, with tunable porosity and surface area. The particles, such as template particles, described herein are between about 100 to about 900nm in size, more typically between about 100 and about 600nm, and still more typically between about 150 and about 270nm. The disclosure describes the process for hollow silica particles with tunable porosity and surface area, as well as the functional group on the hollow particles' surface. Particles of about 50 to about 100nm may be used provided they do not have a surfactant layer on the outer surface of the particle.

The coating composition comprises functionalized hollow silica particles, wherein the functionalized hollow silica particles are prepared by a process comprising:

(ii) creating a functionalized surface on the core/shell silica particle, wherein the functionalized surface is prepared using sulfonic acid, phosphonic esters, carboxylic acid, amines, epoxides, boronic acids or quarternary amines, and

(iii) removing the template core particle to form a functionalized hollow silica particle.

The template core particle may be removed before or after functionalization, more typically before functionalization. If removed after functionalization, it is important the core removal does not damage the functionalized surface. For example, with a-methyl styrene core removal is at low temperatures so no harm is done to the functionalized surface if core removal is achieved after functionalization. Also acid- or base-labile core materials that can be removed by hydrolysis can be removed before or after functionalization.

The core/shell silica particle comprising a template core particle and a silica treatment, typically a coating, is prepared by a process comprising:

(a) providing a template core particle, more typically prepared using emulsion polymerization;

(b) coating the template particle with a water- based silica precursor such as sodium silicate, potassium silicate, ammonium silicate or pre-formed silicic acid; and

(c) maintaining the pH at about 2 to about 10 to form a silica

treatment on the template particle.

The template particle or core is prepared using typically an organic monomer which is polymerized to generate template particles, or dispersed in water to generate template particles of the appropriate size. Some monomes for the template include styrene, methyl methacrylate, polyacrylic acid, a-methylstyrene, lactic acid, formaldehyde, or

copolymers like Surlyn® (copolymer of ethylene and methacrylic acid) more typically styrene, methyl methacrylate, a-methylstyrene, Surlyn®, and still more typically methyl methacrylate, styrene, or polyacrylic acid. Similarly, a group of two monomers can be chosen for a copolymerization, such as a variety of diacids and dialcohols for polyester polymers (like polyethylene terephthalate, PET), diacids and diamides for various polyamides (like Nylon 6,6, or other Nylons), etc. Typically, the particle size of the template is tunable, and the particle size distribution of the template particles achieved is narrow, which is advantageous. For example, preparation of the template particle or core by emulsion polymerization is achieved by emulsification of the water-insoluble monomer or a mixture of in water, and polymerized using radical polymerization conditions. Radical initiators such as potassium- or ammonium persulfate, and 2,2-azobis(2-methylpropionamidine) hydrochloride (AIBA) can be used. Surfactant can also typically be used. Some examples of suitable surfactants include sodium dodecylsulfate (SDS), cetyltrimethylammonium bromide (CTAB), poly-(vinylpyrrolidinone) PVP, etc. In some cases, silyl group-containing monomers, such as 3- (trimethoxysilyl)propylmethacrylate can be used, in order to facilitate the silica deposition in the subsequent step. In order to perform the

polymerization, the reaction temperature is kept between about 25 and about 100°C, more typically about 45 to about 90°C, still more typically about 55°C to about 75°C.

Alternately, the template particle or core may be inorganic, for example calcium carbonate, or other inorganic particles onto which silica can be deposited.

The template particle or core is then coated with a shell material to generate a core/shell particle. To generate a silica treatment or shell, at least one water-based silica precursor is used. Some examples of water- based silica precursors include sodium silicate, potassium silicate, ammonium silicate or pre-formed silicic acid, more typically sodium silicate or potassium silicate. Typically, in the case of a water-based silica precursor, such as sodium- or potassium silicate, the template particles are suspended in water, and the silicate agent is added either dropwise, over a period of time, or all at once.

The pH is maintained at about 2 to about 10, more typically about 5 to about 9 to form a silica layer on the recyclable template particle and the reaction times are held between about 1 to about 24 hours, more typically about 1 .5 to about 18 hours, still more typically about 2 to about 12 hours. This results in the deposition of a silica treatment or shell on the recyclable template particle or core. The core/shell particles are separated or removed from the aqueous solution by centrifugation or filtration, more typically by

centrifugation.

Typically, in order to form impervious silica shells, surface area and porosity of the silica walls have to be tuned. Whether the silica shell is adequate can be determined by comparing the surface area of the particles with calculated surface area of a smooth sphere of the same diameter. Typically, we consider the shell impervious if its surface doesn't surpass about 130% of the calculated surface area of a smooth sphere of the same dimensions, i.e., it is about 30% or less higher than the surface of the core/shell silica particle prior to functionalization, more typically about 125% of the smooth sphere surface area, and still more typically about 120% of the smooth sphere surface area of the same dimensions. Addition of various amounts of the silica precursor will lead to more or less porous silica layers, which can lead to control of the porosity and surface area of the particles. Further, the silica precursor may be added in stages to modulate the porosity of the particles as well as their surface. Lastly, calcination at temperatures higher than about 500°C can decrease the porosity and surface area of the particles without increasing the thickness of the wall. The core may then be removed before or after grafting of a variety of alkoxysilanes onto the surface of the silica particles to form hollow silica particles having a functionalized surface. In one embodiment, removal of the template may be achieved through calcination, namely heating the material to about 300 to about 800°C, more typically about 400°C to about 600°C, and most typically about 450 to about 550°C. In the case of CaCO3/silica core/shell particles, hollow particles are typically obtained through reaction with acid. If the core is made of recyclable material, it may be recycled either through thermal depolymerization, or acid- or base hydrolysis. In a specific embodiment, core materials made out of poly-(a- methylstyrene), PMMA, various polyamides, as well as styrene are depolymerized at increased temperatures, with the temperatures of depolymerization varying with the polymer used. Some suitable

temperature ranges include about 250 to about 450°C, more typically about 275 to about 400°C, still more typically from about 290 to about 325°C, to generate hollow particles as well as core monomer. For example, poly(methylmethacrylate)@silica core/shell particles can be heated above about 300°C to generate methyl methacrylate monomer and hollow silica particles. Further, poly(a-methylstyrene)@silica can be heated to about above 60°C to generate hollow silica particles and a- methylstyrene monomer.

Alternatively, acid- or base-labile core materials can be hydrolyzed instead of thermally depolymerized to generate hollow particles with possibility of monomer recycling. Polymers such as Delrin® (polyacetal), poly(lactic acid), as well as other polyesters can be depolymerized through acid hydrolysis. For example, treating polyacetal@silica with acid should generate hollow silica as well as aldehyde monomer that can be recycled in template particle synthesis. Similarly, polyesters or polyamides from core/shell particles can be recycled in the same fashion to generate diacid/dialcohol (diacid/diamine) monomer couples as well as hydroxylic or amino acids as monomers (like in the case of polylactic acid, for example).

When the core is calcium carbonate, it is removed by acid treatment, which generates hollow particles.

The functionalized surface on the silica particle may be prepared using sulfonic acid, phosphonic esters, carboxylic acids, amines, epoxides, boronic acids, quaternary amines, etc. Grafting of a variety of alkoxysilanes onto the surface of the hollow silica particles provides functionalized hollow silica particles. A large spectrum of functionalities can be introduced onto the silica surface, for example silyl phosphonates, phosphonic acids, amines, alcohols, epoxides, carboxylic acids, thiols, thioethers, carbamates, isocyanates, quarternary ammonium ions, etc. The grafting process includes mixing the grafting agent with silica particles, with or without the solvent, with optional heating of the material, in the temperature range about 25 to about 150°C, more typically about 60 to about 130°C, still more typically about 80 to about 120°C, with or without the application of vacuum, in order to remove the volatile byproducts, like water or alcohols. In one embodiment of the disclosure, the hollow silica particles were functionalized with

(diethoxyphosphoryl)methyl-2-((triethoxysilyl)ethyl)carbamate, introducing phosphonate functionality on the surface. In another embodiment of the invention, the silica particles are functionalized with diethyl [2- (triethoxysilyl)ethyl]phosphonate to generate phosphonate-functionalized silica particles. Then, in another embodiment, phosphonate ester functionality on the surface of the silica particles is hydrolyzed to generate phosphonic acid-functionalized hollow silica particles. In another embodiment of the disclosure, silica particles are treated with (3- glycidopropyl)trimethoxysilane, to generate epoxy functionality on the silica surface. The epoxy silica is then treated, in one embodiment of the disclosure, with glycine, to introduce carboxylic acid functionality through an amine linkage on the particle. In another, the epoxy silica is treated with thioglycolic acid to introduce the carboxylic functionality through a thioether group.

Coating Composition:

This disclosure is particularly suitable for producing coating compositions, and in particular architectural paint formulations or ink formulations.

Coating compositions prepared from coating bases comprising functionalized hollow silica particles and further comprising a colorant, such as an inorganic pigment, particularly a T1O2 pigment, have improved paint or ink performance. Coating Base:

The coating base comprises a dispersion of resin, functionalized hollow silica particles of this disclosure and further comprises a colorant. Other additives known to one skilled in the art may also be present. Resin:

The resin is selected from the group consisting of water-dispersible coating compositions such as latex coating compositions; alkyd coating compositions; urethane coating compositions; and unsaturated polyester coating compositions; and mixture thereof. By "water-dispersible coatings" as used herein is meant surface coatings intended for the decoration or protection of a substrate, comprising essentially an emulsion, latex, or a suspension of a film-forming material dispersed in an aqueous phase, and typically comprising surfactants, protective colloids and thickeners, pigments and extender pigments, preservatives, fungicides, freeze-thaw stabilizers, antifoam agents, agents to control pH, coalescing aids, and other ingredients. Water-dispersed coatings are exemplified by, but not limited to, pigmented coatings such as latex paints. For latex paints the film forming material is a latex polymer of acrylic, styrene-acrylic, vinyl-acrylic, ethylene-vinyl acetate, vinyl acetate, alkyd, vinyl chloride, styrene-butadiene, vinyl versatate, vinyl acetate-maleate, or a mixture thereof. Such water-dispersed coating compositions are described by C. R. Martens in "Emulsion and Water-Soluble Paints and Coatings" (Reinhold Publishing Corporation, New York, NY, 1965). Tex- Cote® and Super-Cote®, Rhopelx®, Vinnapas® EF500 are further examples of water based coating compositions comprising 100% acrylic resin.

The alkyd resins may be complex branched and cross-linked polyesters having unsaturated aliphatic acid residues. Urethane resins typically comprise the reaction product of a polyisocyanate, usually toluene diisocyanate, and a polyhydric alcohol ester of drying oil acids.

The resin is present in the amount of about 5 to about 40 % by weight based on the total weight of the coating composition. The amount of resin is varied depending on the amount of sheen finish desired.

Colorant:

The inorganic pigments, particularly the titanium dioxide pigments may be used alone or in combination with conventional colorants. Any conventional colorant such as a pigment, dye or a dispersed dye may be used in this disclosure to impart color to the coating composition. In one embodiment, generally, about 0.1 % to about 40% by weight of

conventional pigments, based on the total weight of the component solids, can be added. More typically, about 0.1 % to about 25% by weight of conventional pigments, based on the total weight of component solids, can be added.

T1O2 pigment:

In particular, titanium dioxide is an especially useful powder in the products of this disclosure. Titanium dioxide (TiO₂) powder useful in the present disclosure may be in the rutile or anatase crystalline form, more typically in predominantly rutile form, i.e., comprising at least 50% rutile. It is commonly made by either a chloride process or a sulfate process. In the chloride process, TiCI₄ is oxidized to TiO₂ powders. In the sulfate process, sulfuric acid and ore containing titanium are dissolved, and the resulting solution goes through a series of steps to yield TiO₂. Both the sulfate and chloride processes are described in greater detail in "The Pigment Handbook", Vol. 1 , 2nd Ed., John Wiley & Sons, NY (1988), the teachings of which are incorporated herein by reference. The powder may be pigmentary, nano or ultrafine particles. Pigmentary refers to median primary particles in the size range typically about 200 nm to about 450 nm, and nano refers to median primary particles in the size range typically less than 50 nm.

Conventional pigments are generally well known pigments and they may be used alone or in mixtures thereof in coating formulations of the disclosure, Suitable pigmnets are disclosed in Pigment Handbook, T. C. Patton, Ed., Wiley-lnterscience, New York, 1973. Any of the conventional pigments used in coating compositions can be utilized in these

compositions such as the following: metallic oxides, such as titanium dioxide, zinc oxide, and iron oxide, metal hydroxide, metal flakes, such as aluminum flake, chromates, such as lead chromate, sulfides, sulfates, carbonates, carbon black, silica, talc, china clay, phthalocyanine blues and greens, organo reds, organo maroons, pearlescent pigments and other organic pigments and dyes. If desired chromate-free pigments, such as barium metaborate, zinc phosphate, aluminum triphosphate and mixtures thereof, can also be used.

Other Additives

A wide variety of additives may be present in the coating

compositions of this disclosure as necessary, desirable or conventional. These compositions can further comprise various conventional paint additives, such as dispersing aids, anti-settling aids, wetting aids, thickening agents, extenders, plasticizers, stabilizers, light stabilizers, antifoams, defoamers, catalysts, texture-improving agents and/or antiflocculating agents. Conventional paint additives are well known and are described, for example, in "C-209 Additives for Paints" by George Innes, February 1998, the disclosure of which is incorporated herein by reference. The amounts of such additives are routinely optimized by the ordinary skilled artisan so as to achieve desired properties in the wall paint, such as thickness, texture, handling, and fluidity.

Coating compositions of the present disclosure may comprise various rheology modifiers or rheology additives (such as Acrysol®), wetting agents, dispersants and/or co-dispersants, and microbicides and/or fungicides. To achieve enhanced weatherability, the present coating compositions may further comprise UV (ultra-violet) absorbers such as Tinuvin®. Coating compositions of the present disclosure may further comprise ceramic or elastomeric substances, which are heat and/or infrared reflective, so as to provide additional heat reflective benefits. Preparation of the Coating Composition and its Use:

The present disclosure provides a process for preparing a coating composition, such as a paint formulation, comprising mixing the pigment- containing components and functionalized hollow silica nanospheres or particles with the resin to form a coating base. Optionally a vehicle may be present. The vehicle may be aqueous or solvent-based. Typically these coating compositions may comprise from about 30 to about 55% solids by weight and typically about 25% to about 45% solids by volume. Typically the coating compositions of this disclosure have a density of about 9.1 to about 1 1 .9 pounds per gallon, more typically about 9.5 to about 10.8 pounds per gallon. Any mixing means known to one skilled in the art may be used to accomplish this mixing. An example of a mixing device includes a high speed Dispermat®, supplied by BYK-Gardner, Columbia, MD.

Coating compositions of the present disclosure may be applied by any means known to one skilled in the art, for example, by brush, roller, commercial grade airless sprayers, or electrostatically in a particle coating. Coating compositions presented herein may be applied as many times necessary so as to achieve sufficient coating on the coated surface, for example, an exterior wall. Typically, these coating compositions may be applied from about 2 mils to about 10 mils wet film thickness, which is equivalent to from about 1 to about 5 dry mils film thickness.

Coating compositions presented herein may be applied directly to surfaces or applied after surfaces are first coated with primers as known to one skilled in the art.

The coating compositions of this disclosure may be a paint, and the paint may be applied to a surface selected from the group consisting of building material, automobile part, sporting good, tenting fabric, tarpaulin, geo membrane, stadium seating, lawn furniture and roofing material.

The examples which follow, description of illustrative and typical embodiments of the present disclosure are not intended to limit the scope of the disclosure. Various modifications, alternative constructions and equivalents may be employed without departing from the true spirit and scope of the appended claims. In one embodiment, the coating films may be substantially free of other conventional colorants and contain solely the treated titanium dioxide pigments of this disclosure. EXAMPLES

Example 1 : Polystyrene template particle synthesis

To a 2L four-neck round bottom flask, equipped with a mechanical stirrer, thermometer, a reflux condenser, and a nitrogen inlet, was added styrene (18ml_, 157.1 mmol), and 600mL of degassed water.

Polyvinylpyrrolidinone, PVP (100mg) solution in 100mL of degassed water was then added. The resulting mixture was stirred at room temperature for 15min. The mixture was degassed by bubbling nitrogen for 20min. To the reaction was then added a degassed solution of 2,2-azobis(2- methylpropionamidine) hydrochloride, AIBA(100mg, 1 .1 mmol) in 100mL water, and the reaction was heated to 70 °C overnight. Particle size analysis of the resulting suspension revealed particles with average particle size of 250nm.

Example 2: Preparation of PMMA recyclable template particle

To a three-necked 250ml_ round bottom flask with 100.0 ml_ water was added methyl methacrylate (9.5g, 94.89mmol), 2-

(methacryloxy)ethyltrimethylammonium chloride (0.125g of 80% aqueous solution, mmol), ethylene glycol dimethacrylate (0.4g, mmol), and AIBA (0.1 g, mmol). Trimethoxysilyl propyl methacrylate (0.5 g 2.01 mmol) was then added. The mixture was degassed by purging N2 for 10min, and then heated to 70 °C under nitrogen overnight, to generate a white slurry of PMMA particles. Particle size analysis of the resulting suspension revealed particles with average particle size of 280nm.

Example 3: Preparation of hollow silica particles from PMMA template particles To a 100ml three-necked round bottom flask, equipped with an overhead stirrer and a reflux condenser was added 25ml_ of PMMA suspension from example 2, and the pH of the mixture was adjusted to 9 with addition of aqueous NaOH. To this mixture was added sodium silicate (4.72g of 26.5wt% aqueous solution, diluted to 10ml_ with water), and HCI (10ml_ of 1 .40M solution), using two syringe pumps

simultaneously, to maintain the pH in the 8-9 range. The rate of addition was 2ml_/h. After the addition, the temperature of the reaction was increased to 80°C, and the mixture was left stirring overnight. After that time, the mixture was cooled down, and the solids isolated by

centrifugation, and washed with water and ethanol, to generate a while solid (2.73g), whose TEM confirmed the core/shell structure. 500mg of this material was placed in a tube furnace and heated to 500°C at a 1 °C/min rate, and kept at 500 C for ten hours. Upon cooling, 233mg of white solid was obtained, whose TEM images confirmed the hollow structure.

Example 4: Preparation of PMMA particles

To a three-necked round bottom flask, equipped with a reflux condenser, nitrogen inlet, an overhead stirrer, and a thermometer, was added water (720ml_), acetone (480ml_), and methyl methacrylate (14.2g, 0.149mol), and the mixture was degassed with nitrogen for 1 h. The reaction mixture was heated to 68°C, the 2,2'-azobis(2- methylpropionamidine)dihydrochloride was added as a solution in water (0.20g, 0.720mmol in 30.0 ml_ water), and the reaction mixture was left stirring at 68°C for 15 minutes. After that time, 3-

(trimethoxysilyl)methacrylate (4.1 g, 0.0166mol) was added via syringe, and the reaction mixture left stirring for 45 minutes, and then cooled to room temperature. The particle size of the polymer particles generated was measured to be 190nm. Example 5: Preparation of hollow silica particles from PMMA template particles The material obtained in Example 4 (150ml_ of the suspension) was concentrated in vacuo to remove acetone, until the weight of the mixture reached 100g. The material was then transferred to a 1 L three neck round bottom flask, equipped with an overhead stirrer and pH probe inlet. The pH of the mixture was adjusted to 9.5, and the mixture heated to 90 °C. Through use of a dual syringe pump, sodium silicate (7.08 ml_ of 26.2% solution in water, diluted further to 20ml_ total volume), and HCI (2.01 mL, diluted to 20ml_ with water) were added to the flask over 5h. During that time, pH of the reaction was monitored, and maintained at 9.5 with addition of either acid (dilute HCI), or base (dilute NaOH). After the addition, the reaction was left stirring at 90°C overnight, then centrifuged and washed to isolate the solids (2.78g of core/shell particles was obtained). The solid material (1 .49g) was then placed in a tube furnace, and heated to 500°C at a rate of 1 .5°C/min, and then held at that temperature for 12h to generate hollow particles (550 mg). TEM of the sample confirmed the hollow structure.

Example 6: Preparation of hollow silica particles from PS template particles

To a three-necked 250ml_ round bottom flask, equipped with an addition funnel and a reflux condenser is added 25ml_ of polystyrene slurry from Example 1 , following with sodium silicate solution (26.5 wt%, 4.72g). The resulting mixture is heated to 80°C for three or more hours, and the solids are isolated by centrifugation. Upon washing, the core/shell particles are placed inside a tube furnace and heated to 500°C to generate hollow silica particles.

Example 7: Grafting the HSP with phosphonate ester

Solid hollow particles (10g) are dispersed in 300ml_ dimethyl formamide (DMF). To this suspension is added a diethyl-(2- (triethoxysilyl)ethyl)phosphonate (10ml_, 31 .0mmol), and the mixture heated to 120°C overnight. The resulting material is centrifuged to remove the DMF solvent, and washed with ethanol. The presence of grafting groups can be measured by TGA and ESCA. Example 8: Phosphonic acid-functionalized particles

To a 1 L round bottom flask, equipped with an addition funnel and a reflux condenser are added 25.6g of phosphonate ester-functionalized particles (Example 5) and 400mL dichloromethane, and the mixture is kept under nitrogen. To the mixture is added trimethylsilyl bromide (75ml_), dropwise, via an addition funnel. Upon addition, the mixture is heated to reflux for 18h. The mixture is then cooled to room temperature and the volatiles removed in vacuo. To the residue is then added 150ml_ of methanol, and 50ml_ of dichloromethane, and the mixture left stirring at room temperature overnight. The silica material is then centrifuged to remove from the solvent and excess reagents, and washed with water and methanol. ToF SIMS data can confirm the presence of phosphonic acid functionality, and disappearance of phosphonic ester functionality.

Example 9: Epoxide-functionalized hollow silica particles, followed by reaction with glycine

To a mixture of 10mL of DMF and 50ΌμΙ_ of triethylamine (TEA) is added 38.5mg of hollow silica particles, and the mixture is sonicated in an ultrasound (US) bath for ~15min. To the mixture is then added 1 ml_ of (3- glycydoxypropyl)trimethoxysilane, and the mixture is then heated to 120 C. After three or more hours, the mixture is cooled to r.t., and 24mg glycine in 20ΌμΙ_ of water is added to the mixture, which is left stirring overnight. The sample is isolated by centrifuging and washing the solids with ethanol twice, and drying the solids. The material can be analyzed by ESCA to confirm the presence of nitrogen atoms on the silica surface. Example 10: Epoxide-functionalized hollow silica particles, followed by reaction with thioglycolic acid

To 10ml_ of DMF is added 36.5mg of hollow silica particles, and the mixture is sonicated in a US bath for ~15min. To the mixture is then added 1 ml_ of (3-glycydoxypropyl)trimethoxysilane, and the mixture is heated to 120°C overnight. The mixture is then cooled to r.t., and, 500μΙ_ of thioglycolic acid is added, and the mixture left stirring for two days. The sample is isolated by centrifuging and washing the solids with ethanol twice, and drying the solids. The material can be analyzed by ESCA to confirm the presence of sulfur atoms on the silica surface.

Example 1 1 : Phosphonic ester (carbamate) Solid hollow particles (1g) are dispersed in dilute ammonia solution

(7wt%, 20ml_), with sonication. The resulting suspension is added to 30ml_ DMF, and the water was removed in vacuo. To this suspension is added (diethoxyphosphoryl)methyl-2-((triethoxysilyl)ethyl)carbamate (1 g, 2.49mmol), and the mixture is then heated to 120°C overnight. The resulting material is centrifuged to remove the DMF solvent, and washed with ethanol. The presence of grafting groups can be measured by TGA and ESCA.

Claims

CLAIMS What is claimed is:

1 . A coating composition comprising functionalized hollow silica particles, wherein the functionalized hollow silica particles are prepared by a process comprising:

(i) providing a core/shell silica particle comprising a template core particle and a silica treatment, wherein the core/shell silica particle has an outer surface; and wherein the silica treatment is prepared using a water-based silica precursor;

2. The coating composition of Claim 1 wherein the core/shell silica particle comprising a template core particle and a silica treatment is prepared by a process comprising: a) providing a template core particle;

b) coating the template particle with a water- based silica

precursor; and

c) maintaining the pH at about 2 to about 10 to form a silica

treatment on the template particle.

3. The coating composition of Claim 2 wherein the treatment is a coating.

4. The coating composition of Claim 3 wherein the silica treatment is substantially impervious.

5. The coating composition of Claim 2 wherein the template core particle may be removed before functional ization.

6. The coating composition of Claim 2 wherein the template core particle is prepared using emulsion polymerization.

7. The coating composition of Claim 3 wherein the silica treatment has a surface area that is less than 130% higher than the surface area of a smooth sphere of identical radius.

8. The coating composition of Claim 1 wherein the functionalization of the surface of the silica is achieved through grafting.

9. The coating composition of Claim 8 wherein the grafting agent is diethyl-(2-(triethoxysilyl)ethyl)phosphonate, whereby a phosphonate ester- functionalized surface is formed .

10. The coating composition of Claim 9 wherein the phosphonate ester-functional ized surface containing particle is hydrolyzed, whereby a phosphonic acid-functionalized hollow silica particle is formed.

1 1 . The coating composition of Claim 8 wherein the grafting agent is (3-glycydoxypropyl)trimethoxysilane , whereby a epoxide-functionalized hollow silica particle is formed.

12. The coating composition of Claim 1 1 wherein the epoxide- functionalized hollow silica particle is reacted with glycine whereby a carboxylic acid-functionalized hollow silica particle with an amine linkage is formed.

13. The coating composition of Claim 1 1 wherein the epoxide- functionalized hollow silica particle is reacted with thioglycolic acid whereby a carboxylic acid-functionalized hollow silica particle with a thioether linkage is formed.

14. The coating composition of Claim 8 wherein the grafting agent is (diethoxyphosphoryl)-methyl-2-((triethoxysilyl)ethyl)carbamate.

15. The coating composition of claim 1 wherein the water-based silica precursor is sodium silicate, potassium silicate, ammonium silicate or pre-formed silicic acid.

16. The coating composition of claim 15 wherein the water-based silica precursor is sodium silicate or potassium silicate.

17. The coating composition of claim 1 wherein the template core particle comprises poly-(methylmethacrylate), poly-(alphamethylstyrene), polyamide or polystyrene.

18. The coating composition of claim 1 wherein the template core particle comprises polyacetal poly(lactic acid) or polyester.

19. The coating composition of claim 1 wherein the template core particle comprises calcium carbonate.

20. The coating composition of claim 17 wherein the template core particle comprising a silica treatment is heated to promote

depolymerization or calcination.

21 . The coating composition of claim 16 wherein the template core particle comprising a silica treatment is treated with acid.

22. The coating composition of claim 18 wherein the template core particle comprising a silica treatment is treated with acid.

23. The coating composition of claim 1 wherein the particle formed is about 100 nm to about 900 nm in size.

24. The coating composition of claim 1 wherein the particle formed is about 50 nm to about 100 nm in size.

25. The coating composition of claim 2 wherein the pH is maintained at about 8 to about 10.

26. The coating composition of claim 1 further comprising a resin.

27. The coating composition of claim 26 wherein the resin is acrylic, styrene-acrylic, vinyl-acrylic, ethylene-vinyl acetate, vinyl acetate, alkyd, vinyl chloride, styrene-butadiene, vinyl versatate, vinyl acetate- maleate, or a mixture thereof.

28. The coating composition of claim 27 wherein the alkyd resin is a complex branched or cross-linked polyester having unsaturated aliphatic acid residues.

29. The coating composition of claim 26 wherein the resin is a urethane resin.

30. The coating composition of claim 29 wherein the urethane resin comprises the reaction product of a polyisocyanate and a polyhydric alcohol ester of drying oil acids.

31 . The coating composition of claim 30 wherein the

polyisocyanate is a toluene diisocyanate,

32. The coating composition of claim 26 wherein the resin is present in the amount of about 5 to about 40 % by weight, based on the total weight of the coating composition.