Claims:We Claim:

1. Stable in-situ functionalized silica dispersion/emulsion comprising in-situ surface functionalized silica dispersion/emulsion involving acidic emulsifier catalyzed hydrolytically condensed ethylenically unsaturated alkoxysilanes on silica particle surface.

2. Stable in-situ functionalized silica dispersion/emulsion as claimed in claim 1 which is a dispersion in water including at least one ethylenically unsaturated alkoxysilanes in selective levels corresponding toselective levels of anionic and/or non-ionic surfactant favouring said stable in-situ functionalized silica dispersion/emulsion.

3. Stable in-situ functionalized silica dispersion/emulsion as claimed in anyone of claims 1 or 2 involving 8-10 wt. % alkoxysilane and anionic surfactants and/ or non-ionic surfactant of at least 2-3 wt. % on active basisand wherein said alkoxysilane concentration is limited to up to 20 wt. %, to achieve said stable in-situ functionalized silica dispersion/emulsion.

4. Stable in-situ functionalized silica dispersion/emulsion as claimed in anyone of claims 1-3 wherein said acid emulsifier as surfactant-cum-catalyst is preferably dodecylbenzenesulphonic acid.

5. Stable in-situ functionalized silica dispersion/emulsion as claimed in anyone of claims 1-4involving said hydrolytically condensed ethylenically unsaturated alkoxysilanes on silica particle surface selected from:
RnSi(OR’)4-n where, n is an integer varying from 1 to 3, R’ may be the same or different substituted or unsubstituted monovalent hydrocarbon or alkyl or acyl or aryl group and R represents a vinyl group or hydrocarbon with at least one ethylenically unsaturated group;
said alkoxysilanes having vinyl functional group on silica particle surface is adapted for hybrid latex particles with silica core and organic polymer shell preferably acrylic polymer shell via emulsion polymerization, free of any isolation and purification of said silica dispersion/emulsion and free of any further surface modification of silica.

6. Stable in-situ functionalized silica dispersion/emulsion as claimed in anyone of claims 1-5 having average particle size less than or greater than 100 nm, wherein average size >100nm is adapted for dominant core-shell morphology over occluded morphology of hybrid latex particles with silica core and organic polymer shell, and wherein with average size <100nmis adapted for dominant occluded morphology over core shell morphology of said hybrid latex particles with silica core and organic polymer shell.

7. Stable in-situ functionalized silica dispersion/emulsion as claimed in anyone of claims 1-6 wherein the average size of silica particles varies based on select said alkoxysilanes and/or their concentration.

8. Process for preparing stable in-situ functionalized silica dispersion/emulsion as claimed in claims 1-7 comprising the steps of
Providing at least one ethylenically unsaturated alkoxysilanes in selective concentrations corresponding to selective levels of anionic and/or non-ionic surfactant together with acid emulsifier as surfactant-cum-catalyst in water,
thereby yielding in-situ surface functionalized silica dispersion/emulsion comprising acid emulsifier catalyzed hydrolytically condensed ethylenically unsaturated alkoxysilanes on silica particle surface.

9. Process for preparing stable in-situ functionalized silica dispersion/emulsion as claimed in claim 8 comprising the steps of
providing (i) mixture comprising 0.1- 20 wt.% organotrialkoxysilanes containing at least one ethylenically unsaturated polymerizable group, water, anionic surfactant and/or non-ionic surfactant;
providing (ii) mixture comprising water and surfactant-cum-catalyst emulsifier preferably dodecylbenzenesulphonic acid; followed by
select sequence and select time period based controlled addition of said mixture (i) to mixture (ii) for 3-24 hours preferably 3-10 hours, more preferably for 3-5 hours at ambient temperature(20-35 °C) followed by subsequent neutralization to thereby provide for in-situ functionalized silica particles containing said ethylenically unsaturated polymerizable groups on the surface of silica particles as aqueous silica dispersion said silica dispersion being preferably obtained of 8-10 wt. % alkoxysilane as the starting material together with minimum dosage of anionic surfactants and/ or non-ionic surfactant of at least 2-3 wt. % on active basis together with surfactant-cum-catalyst emulsifier in the range of 0.1 to 10.0 wt.%, preferably 0.5 to 5.0 wt. % more preferably 0.5 to 2.0 wt.%.

10. Process for preparing stable in-situ functionalized silica dispersion/emulsion as claimed in anyone of claims 8 or 9 wherein said ethylenically unsaturated alkoxysilanes are of the type:
RnSi(OR’)4-n where, n is an integer varying from 1 to 3, R’ may be the same or different substituted or unsubstituted monovalent hydrocarbon or alkyl or acyl or aryl group and R represents a vinyl group or hydrocarbon with at least one ethylenically unsaturated group;
and are selected from vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane, 3-Methacryloxypropyl trimethoxysilane, 3-Methacryloxylmethyltrimethoxysilane, Triisopropylsilylmethacrylate, Triisopropylsilylacrylate 3-ethacryloxypropylmethyldimethoxysilane, Vinyldimethylethoxysilane, Vinylmethyldiethoxysilane, Vinylmethyldimethoxysilane3-Methacryloxypropyl triethoxysilane, 3-Methacryloxypropyl triisopropoxysilane, 3-Acryloxypropyltrimethoxysilane or mixtures thereof.

11. Process for preparing stable in-situ functionalized silica dispersion/emulsion as claimed in anyone of claims 8-10 wherein said surfactants and surfactant-cum-catalyst include sulfonic acids comprising dodecylbenzenesulphonic acid, linear alkyl benzene sulphonic acid and sulfonic acid salt derivatives like sodium lauryl sulfate, Alkyldiphenyloxide Disulfonate, sodium lauryl ether sulfate, Sodium dodecyl benzenesulfonate sold under the trade name GALAXY SLS, DOWFAX™ 2A1, GALAXY LES, RHODACAL® DS-10; commercial anionic surfactant include alkali metal salts of sulfosuccinates, alkali metal salts of a higher fatty acid, fatty alcohol sulfates, oleic acid sulfonates, alkyl sulfates, alkylethoxy sulfates, alkyl ether sulfates, higher alcohol sulfuric acid ester sodium salts, alpha-olefin sulfonates, including commercial types of anionic surfactants CALSOFT®, PENTEX® 99,AEROSOL®, STEPAN-MILD® LSB, DOWFAX™, DISPONIL®, RHODAFAC®;
said non-ionic surfactant include alkyl phenol ethoxylates, secondary Alcohol Ethoxylate, polyoxyethylenesorbitian ester trade name ATPOL 5731, TERGITOL 15S-40, TWEEN 80, TERGITOL®, TRITON™, MERPOL®, ATPOL™,ANATAROX®, SPAN® 80, IGEPAL®, Brij®, TWEEN®.

12. Hybrid latex particles having silica core and organic polymer shell comprising polymerization product of
(i) stable in-situ surface functionalized silica dispersion/emulsion precursor involving acid emulsifier catalyzed hydrolytically condensed at least one ethylenically unsaturated alkoxysilane on silica particle surface as claimed in claims 1-7; and
(ii) at least one ethylenically unsaturated polymerizable monomers.

13. Hybrid latex particles having silica core and organic polymer shell as claimed in claim 12 wherein said stable in-situ surface functionalized silica dispersion/emulsion precursor is a dispersion in water including at least one ethylenically unsaturated alkoxysilanes in selective levels corresponding to selective levels of anionic and/or non-ionic surfactanttogether with acid emulsifier adapted for said stable in-situ functionalized silica dispersion/emulsion having hydrolytically condensed at least one ethylenically unsaturated alkoxysilane on silica particle surface.

14. Hybrid latex particles having silica core and organic polymer shell as claimed in anyone of claims 12 or 13 as core-shell latex particles obtained of stable in-situ surface functionalized silica dispersion/emulsion free of any isolation and purification of said silica dispersion/emulsion and free of any added surface modification of silica.

15. Hybrid latex particles as claimed in anyone of claims 12-14 as a stable dispersion wherein said polymerization product includes silica particles that are substantially covered with polymeric shell favouring silica-core and polymeric-shell morphology.

16. Hybrid latex particles having silica core and organic polymer shell as claimed in anyone of claims 12-15 as a stable dispersion including said stable of in-situ functionalized silica dispersion/emulsionof average particle size less than or greater than 100 nm,as precursor; wherein dominant core-shell morphologyover occluded morphology of said latex particles is based on average particle size >100nm of said precursor in-situ functionalized silica dispersion/emulsion,
and wherein dominantoccluded morphology over core shell morphology of said hybrid latex particlesis based on average particle size < 100nmof said precursor in-situ functionalized silica dispersion/emulsion.

17. Hybrid latex particles having silica core and organic polymer shell as claimed in anyone of claims 12-16 wherein said polymerizable monomers (ii) includes Methylmethacrylate, n-butyl methacrylate, styrene, butyl acrylate, 2-ethyl hexyl methacrylate, methacrylic acid and 2-Hydroxyethyl methacrylate, acrylic acid esters, methacrylic acid esters and the copolymerizable monomer like methacrylamide, styrene,vinyl acetate, alkylmethacrylates, alkylacrylates, unsaturated carboxylic acids, alkenyl aromatic compounds, acrylonitrile, styrene, a-methylstyrene, acrylic acid, or derivatives or mixtures thereof.

18. A one pot process for preparing hybrid latex particles having silica core and organic polymer shell as claimed in anyone of claims 12-17 comprising a single step process involving
providing stable in-situ functionalized silica dispersion/emulsion as claimed in claims 8-11 and heating to upto desired temperature range for desired time, followed by adding pre-emulsion comprising aqueous dispersion of polymerizable monomers, deionized water, anionic and/ or non-ionic surfactant to said stable in-situ functionalized silica dispersion/emulsion for desired time of about 4 hrs and allowing it to react to thereby obtain said hybrid latex particles with silica core and polymeric shell morphology, free of anyisolation and purification step of said silica dispersion/emulsion and free of any added surface modification step of silica.

19. A one pot process for preparing hybrid latex particles having silica core and organic polymer shell as claimed in claim 18 comprising the sub-steps of
(i) Providing silica dispersion in a reactor vessel formed at room temperature followed by increasing the temperature of the reactor vessel to upto80 deg subsequently followed by PPS (initiator) addition and Pre-emulsion addition for a period of about 4 hrs in the same reactor vessel, said pre-emulsion comprising a mixture of Monomer, deionized water, anionic and / or non-ionic surfactant and free of any silica dispersion;
(ii) Digesting the reaction mixture of step (i) for about an hour at 70-80 deg post completion of pre-emulsion addition, cooling and mixing with biocide preservatives and ammonia for adjusting the pH to about 7 to thereby obtain hybrid latex particles with silica core and polymeric shell morphology therefrom by enabling first formation of silica dispersion in the reactor on which the polymer is grown on top of silica particles in the same reactor.

20. A process for preparing hybrid latex particles having silica core and organic polymer shell as claimed in anyone of claims 12-17 as a two step process comprising the steps of
(i) providing a reactor charge of demineralized water and anionic surfactant and raising the temperature to 80 deg;
(ii)(a) forming the pre-emulsion in a separate vessel by mixing pre-formed aqueous silica dispersion, demineralized water, surfactant and monomers whereby the aqueous silica dispersion is a part of pre-emulsion;
(ii)(b)adding a portion (preferably 5-10%) of said pre-emulsion to the reactor of step (i) at 80 deg followed by PPS (initiator) and buffer addition and allowing the mixture to react at 80 deg for about 15-30 minutes that is followed by continued controlled addition of the remaining pre-emulsion into said reactor at 80 deg forabout 4 hrs after completion of which said pre-emulsion addition the reaction mixture is digested for an hour at 70-80 deg for removal of unreacted monomers, further cooled and mixed with biocide preservatives and ammonia for adjusting the pH to about 8-10 to thereby obtain hybrid latex particles with silica core and polymeric shell morphology therefrom wherein in said process the silica dispersion is separately made and the same is used in step-ii (a and b)for emulsion polymerization.

21. A process for preparing hybrid latex particles having silica core and organic polymer shell as claimed in anyone of claims 18-20 comprising providing in-situ functionalized aqueous silica dispersion 1 to 15 wt.% to result in a stable hybrid latex having silica core and acrylic shell with about 40-50 wt.% solids.

Dated this the 24th day of September, 2018 Anjan Sen
Of Anjan Sen and Associates
(Applicants Agent)
IN/PA-199
, Description:FIELD OF THE INVENTION

The present invention provides for stable in-situ functionalized silica dispersion/emulsion comprising in-situ surface functionalized silica dispersion/emulsion and an emulsion polymerization process of making silica-organic hybrid latex particles with core-shell structure and a stable dispersion of the same out of said stable in-situ functionalized silica dispersion/emulsion, wherein said latex particles have silica core and polymer as organic shell. More particularly, a stable in-situ functionalized silica dispersion/emulsion comprising in-situ surface functionalized silica dispersion/emulsion is provided together with a process for manufacturing said in-situ surface functionalized stable aqueous silica dispersion at room temperature adapted for the manufacture of silica-organic hybrid latex particles with silica core and acrylic shell, preferably also provided as an emulsion. The emulsions are employed as binders for aqueous latex paints or can be used as alone to coat and protect various substrates including wood, paper, plastic, metal, concrete, ceramic.

BACKGROUND ART

In order to improve the compatibility of inorganic silica particles in the organic polymer matrix several approaches are used to do surface modification of the silica particles. Different physical and chemical approaches have been used to modify the silica surface to increase the interface adhesion with the polymer. Conventional process of forming silica core and organic shell needs multiple steps - first surface modification of silica with different organosilane coupling agents such as vinyl trimethoxysilane, 3-trimethoxysilyl propyl methacrylate, etc. This step is followed by isolation and purification of the modified silica and third is either redisperse in the organic phase or use it as seed in the seeded emulsion polymerization. On this references are drawn to several prior arts as represented hereunder:

US5856379 teaches an aqueous dispersion of core/shell-type composite particles with colloidal silica as the cores and with organic polymer as the shells and production method thereof, and describes a method of producing an aqueous dispersion of core/shell-type composite particles having colloidal silica as the cores and having an organic polymer as the shells. In the process modification of colloidal silica surface with an organoalkoxysilane as coupling agent is carried out followed by polymerization with vinyl monomers to form aqueous dispersions of particles with core/shell type composite particles having colloidal silica as the cores and having an organic polymer as the shells.

US20110263037 discloses polymeric materials incorporating core-shell silica nanoparticles that provides methods for incorporating core-shell silica nanoparticles into fibers during a fiber spinning process. Fibers, fabrics and textiles in which core-shell silica nanoparticles are incorporated are provided. Core-shell silica nanoparticles can be incorporated into fibers spun by art-known fiber manufacturing methods such as electrospinning wet spinning, dry spinning, dry-jet wet spinning, melt spinning or gel spinning.

US5188899 teaches silica-core silicone-shell particles, emulsion containing the same dispersed therein, and process for producing the emulsion. This prior art describes a process of making colloidal silica-core silicone-shell particles, an emulsion with a solid component of at least 30% by weight of the silica-core silicone-shell particles.

JP-A-61-155474 discloses an aqueous coating composition obtained by emulsion-polymerizing an acrylic monomer and an organosilicon compound having both a reactive unsaturated group and an alkoxy group in the presence of a colloidal silica, and a water-soluble or water-dispersible acrylic copolymer having an alkoxysilyl group as a binder component. These compositions has the functions such as durability, flame retardant properties, resistance to stains, dew condensation-preventive properties, and other properties, comprising an aqueous resin dispersion.

JP-A-61-271352, JP-A-61-272264 and JP-A-61-16929 disclose a process for obtaining an aqueous emulsion of a silicone reinforced with colloidal silica particles, in which hydroxyl-terminated polyorganosiloxane is condensed using a sulfonic acid-type emulsifying agent in the presence of acidic colloidal silica.

CN105489867 discloses a preparation method of porous carbon silicon material comprises thefollowing steps: adding organic polymerizable monomer, crosslinking monomer, surfactant, pyrogen and nano silica powder into the reactor to serve as continuous phase, stirring at room temperature; the aqueous solution containing initiator slowly adding dropwise to continuous phase; then stirring for 5~10 min to form stable emulsion; the vol. fraction of disperse phase accounts for 60~90% of total emulsion vol.; transferring emulsion into mold for polymerization; extracting and drying the sample to obtain the precursor of porous carbon silicon composite material; subjecting the precursor of porous carbon silicon composite material to thermal treatment in the nitrogen atm.; and carbonizing material to obtain porous carbon silicon composite material which is nano silica powder based and is used in lithium cell cathode material.

WO2014059118 relates to a process for making an oil and grease resistant cellulosic material such as paper and paperboard, the process comprising applying a homogeneous aqueous dispersion of fluorochemically surface-modified nanoparticles to a cellulosic substrate to form a treated cellulosic substrate, and subsequently drying the treated cellulosic substrate to form an oil repellent cellulosic material. Fluorochemicals used to separately modify and not in-situ modify the nanoparticles comprising silica, titania, zirconia, layered magnesium silicate, aluminosilicate, natural clay, synthetic clay, polystyrene, styrene acrylonitrile (SAN), or combinations thereof, include fluoroalkylsilanes, ionic fluorochems, or fluorinated polyacrylate obtained by seeded emulsion polymerization of fluorinated acrylates on the nanoparticles.

JP 2013059744 discloses a one step process for the preparation of microcapsules manufactured by (1) preparing aqueous dispersions containing colloidal silica as a dispersing stabilizer and aqueous N-containingcompounds as stabilizing aids, having mol. wt. 100-1000, (2) preparing emulsions comprising the dispersions, polymerizable monomers, volatile solvents, and polymerization initiators, and (3)polymerizing the monomers. Thus, microcapsules were manufactured by polymerization of acrylonitrile, methacrylic acid, methacrylonitrile, and a thermosetting resin comprising N, Nbis(2,3-epoxypropyl)-4-(2,3-epoxypropoxy)aniline and 1-chloro-2,3-epoxypropane/4,4'-isopropylidenediphenol condensate in the presence of pentane, isooctane, 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), and an aq. dispersion containing colloidal silica and Catiogen BC 50 (lauryl dimethyl benzylammonium chloride), showing av. particle size 52 µm and good expansion ratio and heat resistance. Even though, a one step a process is taught by this prior art of making an aqueous dispersion of colloidal silica the same involves use of N-containing compounds as stabilizers, volatile solvents and thermosetting resins.

CN 102702449 relates to a method comprising (1) dripping a silane coupling agent in silica sol under stirring and refluxing to obtain a silane coupling agent modified silica sol as main dispersing agent, (2) dispersing an aqueous mixed solution in an oil-phase mixed soln. under high-speed stirring to obtain a suspending emulsion, and (3) introducing the suspending emulsion into areaction kettle, carrying out suspension polymerization under stirring, naturally cooling toroom temp., filtering, cleaning, drying, sieving. The aqueous mixed solution contains the dispersing agent, pH regulator, inorganic salt, and deionized water; the oil-phase mixed solution contains polymerizable monomer (such as acrylonitrile-like monomer) 80-94.5, comonomer 5-18, crosslinking agent 0.5-2 wt%, and additional foaming agent and initiator. The dispersing agent contains main dispersing agent, and 0.2-0.5% adjuvant dispersing agent (such as PVP, or polyvinyl alc.). The foaming agent is C4-C8 alkane with low b.p.frombutane, isopentane, hexane, and/or isooctane, etc. The co-monomer contains hydrophilic unsaturated alkenes monomer 5-20 wt%, and polymer with high glass-transition temperature unsaturated alkenes monomer 80-95 wt%. The crosslinking agent is from diethylene glycoldiacrylate, dipropylene glycol dimethacrylate, polyethylene glycol diacrylate, or tripropyleneglycoldimethacrylate, etc. The silane coupling agent is selected from 3-methacryloxypropyltrimethoxysilane, vinyltrimethoxysilane, vinylmethyldimethoxysilane, etc that could modify the silica sol when used under refluxing conditions.

JP03153770 relates to adispersion, that are prepared by mixing aqueous dispersions of colloidal SiO2 with acrylic polymer emulsions prepared by emulsion polymerization of (meth)acrylic esters in the presence of poly(vinyl alcohol) with d.p.< 1,500 as emulsifiers. Thus, mixing an aqueous dispersion of 60 parts colloidal SiO2 with average diameter 10-20 nm with an aqueous dispersion of 100 parts 0.15-µm acrylic acid-Bu acrylate-Me methacrylate-vinyl alcoholic graft copolymer at 60-70° for 1 h gave a dispersion containing 40-µm particles, which was 1:1 blended with aqueous acrylic emulsion coating, spread on a substrate, and dried to give a film with 60° gloss 15, vs. 95 without the 40-µm particles. This prior art thus describes the coating composition obtained by simply mixing/ blending the colloidal silica with acrylic polymer emulsion at 60-70° for 1 h in the presence of poly (vinyl alcohol) as emulsifier and does not relate to any aqueous dispersion of in-situ functionalized silica in the process of forming hybrid latex.

JP 59217702 teaches monomers containing conjugating unsaturated bonds are polymerized in water in the presence of 0.05-5% (based on total monomers) emulsifiable monomers and 0.1-4% colloidal silica to give polymer dispersions which have excellent stability when mixed with organic solvents and form non-blocking coatings with excellent resistance to boiling water and alkalis. Thus, itaconic acid 5, styrene 110, Me methacrylate 200, 2-ethylhexylacrylate 150, and acrylonitrile 35, and Leminol JS-2 [polymerizable emulsifier; 40%RO2CCH2CN(SO3Na)CO2CH2CH:CH2] 12.5 parts were emulsion polymerization in the presence of 30% colloidal silica 12.5 (NH4)2S2O8 2, and NaHSO3 1 part, then adjusted to pH 6-9 with aqueous NH3 to give a 46%-solids emulsion, which showed no agglomeration when combined with 10% xylene, in contrast to one prepared similarly without the silica. This prior art does not relate to forming a latex (or emulsion) having silica-core and acrylic-shell type morphology but involves emulsion polymerization of monomers in the presence of colloidal silica to form water dispersed polymer composition wherein the presence of silica imparts stability to the 46% solids emulsion against 10 % xylene addition in the title composition and also includes an organic solvent xylene.

CN104017398 teaches a manufacturing method including (a) dispersing polymerizable surface modifier-modified nano-TiO2 particles in vinyl monomers to form a monomer/TiO2 dispersion (A1), (b) ultrasonically emulsifying the A1, water, an emulsifier, and hydrophobic agent, reacting at 70-80° for 6-24 h in presence of an initiator to obtain a polymer/TiO2 shell-core latex (A2), (c) reacting a silane coupler in presence of H2O and an acid at 60° for 6-8 h to form a silane coupler hydrolyzate (B1), then stirring B1 with an aqueous silica sol to form a modified sol (B2), and (d) stirring the A2, B2, a wetting agent, and a film-forming accelerator to obtain a title coating, and hence involves a post modification of polymer/TiO2 shell-core latex (A2), with silane coupler.

JP 2005023189 teaches compositions useful for buildings, steel structures, etc., contain (A) aqueous dispersions manufactured by condensation of 0.1-500 parts alkoxysilanes in the presence of 100 parts (as solids) latexes manufactured by emulsion polymerization of (meth)acrylic acid C1-10 alkyl esters 50-99.5, ethylenically unsaturated carboxylic acids 0.5-15, and other monomers 0-49.5%, (B) colloidal inorganic particles, and (C) sulfosuccinate surfactants. Thus, an aqueous dispersion containing Bu acrylate-Me methacrylate-acrylic acid-styrene copolymer, MeSi(OEt)3 condensate, and Aerosol OT 75 were mixed with Snowtex CM 40(colloidal silica), TiO2, and additives to give a coating showing gloss retention 67% andyellowness index change 4 after weathering, good adhesion to a slate plate, water resistance,and no soiling by rain after outdoor exposure for 3 months. This prior art teaches the use of alkoxysilanes in the presence of pre-formed latex prepared by emulsion polymerization and not for the preparation of aqueous silica dispersion.

JP2004292686 compositions contain (a) aqueous dispersions prepared by emulsion polymerization of unsaturated C:C linkage composition-based monomers in the presence of 1-50% organic alkoxysilanes, surfactants, polymerization initiators, polymerization accelerators, and H2O and (b) colloidal inorganic particles and/or sulfosuccinic acid surfactants. An aqueous coating composition is thereby attained involving the use of organoalkoxysilanes and colloidal silica during emulsion polymerization process containing Etacrylate-2-ethylhexyl acrylate-methacrylic acid-Me methacrylate-styrene vinyltrimethoxysilane copolymer, Latemul S 180A, Levenol WZ, Emulgen 920, and Snowtex30 (colloidal silica) gave films showing no rain-soiling after 3 months at outdoor.

JP 07157709 discloses composition of an emulsion containing colloidal silica and aqueous resin dispersions with average particle size 10-100 nm obtained by emulsion polymerization of vinyl monomers and unsaturated alkoxysilanes, to which colloidal silica is added. To this emulsion, colloidal silica is added to form the title coating composition. A dispersion was prepared by polymerizing 2-ethylhexyl acrylate343, Me methacrylate 522, methacrylic acid 45, and H2C:CMeCO2(CH2)3Si(OEt)3 90 parts at55-65° in water containing Hitenol N 08, Emulgen 920, Fe2(SO4)3, ammonium persulfate, and Na metabisulfite, adding aqueous NH3 to give pH 8-9, followed by addition of 7500 parts colloidal SiO2(40% solids). A mixture of the dispersion 170, Bu cellosolve 10, ethylene glycol 5, Primal ASE 60 (thickener) 1, aq. NH3 0.2-0.5, and H2O 12.5-12.8 parts was applied on glass and dried 7 days to give a coating showing no change during 30 min in H2O at 40°.

WO2015105189 teaches dispersions include (A) aqueous media containing water, and (B) composite particles, dispersed in A, consisting of (b1) inorganic particles or core particles at least partially coated with silica layers, and (b2) polymer layers for at least partially covering b1 surfaces, where in the composite particles show zeta potential at 60° and pH 7-11 -70 to -160 mV. Thus, feeding aqueous silica dispersion (Adelite AT 50) and sodium dioctyl sulfosuccinate (AerosolOT 75) into a reactor, heating, feeding sodium persulfate, Me methacrylate, Bu acrylate, methacrylic acid, and alkyldiphenyl ether disulfonate (Pelex SS-L), reacting, cooling, and filtering gave an aqueous dispersion showing pH 8.9, solids content 42.6%, average diameter of the composite particles 51 nm, zeta potential of the composite particles -80 mV, and good transparency retention after immersing in water at 50° for 24 h (as 80 µm-thick coating film).By adjusting the amount of the surfactant to be used and the amount of ionic ethylenic unsaturated monomer together with colloidal silica (commercial dispersion like Adelite AT 50, Cataloid SI 80 P, Snowtex ST-50) the dispersion of this prior art could be attained without any functionalization of the silica.

JP2005206701 relates to water-thinned coating compositions useful for corrosion prevention of metal surfaces, containing aqueous dispersions prepared by mixing water-soluble polymers (A) obtained by hydrolysis-condensationofsilanes (R1)mSi(OR2)n (R1 = H, lower alkyl, aryl, unsaturated fatty acid residue, functional groupdirectly linked to C atom; R2 = H, lower alkyl, acyl; m = 0, 1; n = 3, 4; m + n = 4) in H2O with water-dispersible polymers (B) obtained by emulsion polymerization of 70.0-99.9 partsmonomers having radically polymerizable groups and 0.1-30 parts monomers having radically polymerizable groups and functional groups which act as catalysts for hydrolysis-condensationof the silanes and/or monomers having radically polymerizable groups and functional groupswhich react with Si(OR2) groups of the silanes at A/B wt. ratios [by calcination of A as (R1)mSi(4-m)/2and B as solids] 0.1-10 and colloidal inorganic particles and/or sulfosuccinate surfactants. Thus, Bu acrylate, Me methacrylate, and methacrylic acid were emulsion-polymerized in the presence of Na dodecylbenzenesulfonate and (NH4)2S2O8, wherein the already formed emulsion polymer was mixed and added dropwise to a water-soluble polymer solution prepared by hydrolysis-condensation of MeSi(OMe)3 and Si(OEt)4 in H2O containing Na dodecylbenzenesulfonate, and the mixture was stirred to give an aqueous dispersion, which was mixed with Latemul S-180A (sulfosuccinate surfactant), Levenol WZ (anionic surfactant containing alkylene oxide group), Emulgen 120 (nonionic surfactant containing alkylene oxide group), and Snowtex 30 (colloidal silica) to give a waterthinned coating compositionthat showed no soiling by rain after 3-month outdoor exposure.

JP 60155762 teaches binders for glass fibers with excellent adhesion, durability, and water-, acid-, and fading-resistance consist of an aqueous colloidal silica and an aqueous copolymer dispersion obtained by emulsion polymerization of an organic Si compound containing polymerizable unsaturated groups and hydrolyzable groups which are bonded on Si atoms 0.1-40, a polymerizable unsaturated carboxylic acid 1-30, C1-18 alkyl (meth)acrylate 50-98.9,and other monomers 0-40%. Thus, CH2:CH(EtO)3Si 1, methacrylic acid 10, Me methacrylate 60, and Bu acrylate 29 parts were added to a solution of H2O 220, Na-dodecylbenzenesulfonate as emulsifier, and K2S2O8 0.5 part, which was heated 1 h at 75° to give an aqueous copolymer solution (A) with 30.0% solids. A binder consisting of 200 parts A and 15 parts Snowtex-O (aq. colloidal silica, 20% silica, particle diameter 10-20µm) showed excellent adhesion to glass plate, durability, and acid and fading resistance. This prior art thus involves post addition of functionalized silica dispersion, wherein the organoalkoxysilane with unsaturated polymerizable group are not used in the preparation of aqueous functionalized silica dispersion and is not a part of emulsion polymerization process. Instead the organoalkoxysilane with unsaturated group of this prior art are used for emulsion polymerization process and further to the above the commercial colloidal silica referred to in this prior art of Snowtex-O, is not functionalized silica.

WO 2013072769 teaches an aqueous binder mixture comprises colloidal silica free of any surface functionalization, an aqueous copolymer dispersion, and an alkoxy-substituted polysiloxane. The aqueous copolymer dispersion is prepared by emulsion polymerization of a monomer mixture comprising (i) at least 40%,based on the total monomers, of at least one of an ester of an ethylenically unsaturated carboxylic acid, a vinyl ester of a saturated carboxylic acid, and a vinyl aromatic monomer,(ii) from 0.1 to 10% of at least one of an ethylenically unsaturated mono- and/or dicarboxylic acid, an ethylenically unsaturated sulfonic acid, an unsaturated phosphoric acid, and ethylenically unsaturated phosphonic acid, and an amide of an ethylenically unsaturated mono- and/or dicarboxylic acid, and (iii) from 0.5 to 15% of an ethylenically unsaturated monomer having at least one alkoxysilyl group.

JP61089373 discloses binders with good adhesion, low-temperature curability, durability, and flame retardance based on the use of halogenated monomers comprising 100 parts (non volatiles content) aqueous copolymer dispersion [prepared by emulsion polymerization of a mixture of hydrolyzable, unsaturated silane 0.1-40, unsaturated carboxylic acid 0.1-20, unsaturated, halogenated carbonyl compound 2-80, and comonomers 0-90%], 0-40 parts colloidal silica as an aqueous dispersion, and 0-20 parts hydrolysable silane. Thus, a mixture of vinyltrimethoxysilane 1, acrylic acid 2, 2,4,6-tribromophenyl methacrylate 20, and Buacrylate 77 parts was polymerized in emulsion to give a 50.1% polymer dispersion, 200 parts of which was mixed with 20 parts 20% aqueous colloidal silica at 50°. The flame-resistant binder had yarn adhesion (in carpet backing) 4.9 kg/pile, washing resistance (in interlining cloth)90%, and abrasion resistance (in floc processing) =1000 cycles; vs. 1.5, 55, and 100-420, respectively, without acrylic acid. This prior art describes the use of aqueous colloidal silica as one of the mixture component to form the said binder composition.

Also reference is drawn to some prior art literature documents that state that in order to improve the compatibility of inorganic silica particles in the organic polymer different physical and chemical approaches have been used to modify the silica surface to increase the interface adhesion with the polymer.
Yazdimamaghanet. al. (Yazdimamaghani M. et al., Materials 2013, 6, 3727-3741) used adsorption of non-ionic surfactant based surface modification to encapsulate silica in acrylate copolymer matrix. The method involves physical interaction onto the surface of the silica particles.
To ease efficient formation of polymer on the silica surface, different functional groups that are reactive in the polymerization process (e.g., monomers, initiators or chain transfer agents) are introduced. These groups may be either chemically bound or physically adsorbed on the surface. Moreover, they can be introduced in a separate step before polymerization or during polymerization.
L. –Xavier et al. (J. Colloid Interface Sci. 2002, 250, 82–92) have synthesized silica–poly (methyl methacrylate) (PMMA) nanocomposite latex particles in emulsion polymerization using a cationic initiator, 2,2'-azobis (isobutyramidine) dihydrochloride (AIBA). Silica beads were used as the seed. Coating of the silica particles with PMMA was taking place in situ during polymerization, resulting in the formation of colloidal nanocomposites with a raspberry-like or a core–shell morphology, depending on the size and nature of the silica beads.
D. Qi et al. (Colloid and Polymer Science. (2008) 286, 233, Applied Polymer Science (2006) 99, 3425) Polyacrylate/silica nanocomposite latex particles were prepared by in situ emulsion polymerization of acrylate monomers initiated by 2,2'-azobis(2-amidinopropane)dihydrochloride (AIBA) adsorbed on silica nanoparticles. The anchoring of polyacrylate onto silica nanoparticles was achieved through the physical absorption and chemical grafting reaction.
E. Bourgeat-Lami et al. (Nanoscience and Nanotechnology. (2006) 6, 432, Colloid and Interface Science.(1998) 197, 293.)prepared Silica/polystyrene nanocomposite particles through emulsion polymerization of styrene in the presence of silica particles previously modified by gamma-methacryloxypropyltrimethoxysilane (MPS).

Zhang et al. (Macromol. Mater. Eng.2003, 288, 380–385.) used prepared silica-polymer core-shell microspheres via surface grafting and emulsion polymerization. The silica nanoparticles were grafted with 3-(trimethoxysilyl)propyl methacrylate and were employed as seeds in an emulsion polymerization to form core-shell structure.

Watanabeet al. in Journal of Polymer Science Part A: Polymer Chemistry Volume 44, Issue 16 Pages 4736–4742, 2006 discloses acrylic polymer/silica organic–inorganic hybrid emulsions synthesized by a simple method, that is, a conventional emulsion polymerization and subsequent sol–gel process, to provide water-based coating materials. The acrylic polymer emulsions contained a silane coupling agent monomer, such as methacryloxypropyltriethoxysilane, to form highly solvent-resistant hybrid films. On the other hand, the hybrid films from the surface-modified polymer emulsions, in which the silane coupling agent was located only on the surface of the polymer particles and the particle core was not crosslinked, did not exhibit high solvent resistance. The crosslinked core part and silane coupling agent containing the shell part of the polymer particles played important roles in attaining high solvent resistance.

J. Phys. Chem. C 2009, 113, 18082–18090, relates to surface modification of the silica nanoparticles with methacrylate groups wherein silica nanoparticles weremodified with 3-(trimethoxysilyl)propyl methacrylate(MPS) by taking a suspension of silica nanoparticles in ethanol and stirring at 30°C, following which MPS was added to the mixture (40µ mol of MPS/m2 of SiO2). The reaction proceeded for 48 h, and after that time the suspension was centrifuged (four cycles at 15 300 rpm of 15 min each). The MPS - silica nanoparticles were redispersed in absolute ethanol and dried at 60°C.

Reference is further drawn to J. Appl. Polym. Sci. 80: 2752–2758, 2001 teaching seeded emulsion polymerization of methyl methacrylate (MMA) or styrene (ST) carried in the presence of different vinyl-containing polysiloxanelatices (SV-*) and the core-shell particles with poly(methyl methacrylate) (PMMA) or polystyrene (PST), as the shells were obtained under different polymerization conditions. Besides the compatibility of the vinyl monomer and its polymer with polysiloxane and the reaction between vinyl monomer with vinyl group of polysiloxane, the content of vinyl group of seed polysiloxane has influence on the morphology and component of the resulted composite particles. The mechanism for the formation of core-shell structure is discussed. Even though above prior art is about core-shell morphology the core is made up of polysiloxane obtained using octamethylcylcotetrasiloxane and tetra-methyltetravinylcyclotetra-siloxane and does not involve silica particles as the core component.

As would be apparent from the state of the art above, that while several processes are known to reach to the silica-organic hybrid latex particles there is a need in the art for provision of industrially facile simple process for preparation of such silica-organic hybrid latex particles amenable to easy scale up in the existing industrial set-up. It is also a requirement of the day that in the process of manufacturing such silica-organic hybrid latex particles, there is need to explore for a provision of silica dispersion that would be pre-formed at room temperature, would not require any isolation and purification step and a further re-dispersion step to easily facilitate direct utilization as pre-formed silica dispersion for use as seed or mixed with various monomers for polymerization by conventional emulsion polymerization to result in hybrid latex particles with silica core and acrylic shell.

OBJECTS OF THE INVENTION

The primary object of the present invention is to provide for stable surface functionalized silica dispersion and hybrid latex particles with silica core and acrylic shell obtained therefrom based on a simple process for manufacturing stable in-situ functionalized silica dispersion/ emulsion preferably an aqueous dispersion at room temperature adapted for either seeded emulsion polymerization or emulsion polymerization with various proportions of monomers phase to form the hybrid latex particles with silica core and acrylic shell.

Another object of the present invention is to provide for a simple process for manufacturing stable in-situ surface functionalized silica dispersion/ emulsion that would be functionalized with ethylenically unsaturated polymerizable group to enable seeded emulsion polymerization with a monomer phase to lead to silica-organic hybrid latex particles with silica core and acrylic shell.

It is yet another object of the present invention to provide for said simple process for manufacturing stable in-situ surface functionalized silica dispersion/ emulsion which would not require multistep processing viz. isolation of modified/functionalized silica followed by its purification and then re-dispersion in the reaction medium, post surface modification of preformed silica dispersions thereby free of any isolation and purification step.

Yet another object of the present invention is to provide for a simple process of manufacturing emulsion comprising silica-organic hybrid latex particles with core shell structure involving said stable in-situ functionalized silica dispersion/ emulsion.

Still another object of the present invention is to provide for said simple process of manufacturing emulsion comprising silica-organic hybrid latex particles with core shell structure involving said stable in-situ functionalized silica dispersion/ emulsion which involving in-situ functionalized silica dispersion/ emulsion would not need nano silica material, neither any further stabilization or re-dispersion of the thus formed in-situ functionalized silica prior to emulsion polymerization with monomer phase and can be used as such to produce said silica-organic hybrid latex particles having silica core and organic polymer shell by emulsion polymerization process.

SUMMARY OF THE INVENTION

Thus in accordance with the basic aspect of the present invention there is provided a stable in-situ functionalized silica dispersion/emulsion comprising in-situ surface functionalized silica dispersion/emulsion involving acidic emulsifier catalyzed hydrolytically condensed ethylenically unsaturated alkoxysilanes on silica particle surface.

Preferably, said stable in-situ functionalized silica dispersion/emulsion is a dispersion in water including at least one ethylenically unsaturated alkoxysilanes in selective levels corresponding to selective levels of anionic and/or non-ionic surfactant favouring said stable in-situ functionalized silica dispersion/emulsion.

More preferably said stable in-situ functionalized silica dispersion/emulsion involves 8-10 wt. % alkoxysilaneand anionic surfactants and/ or non-ionic surfactant of at least 2-3 wt. % on active basisand wherein said alkoxysilane concentration is limited to up to 20 wt. %, to achieve said stable in-situ functionalized silica dispersion/emulsion.

According to another preferred aspect of the present invention there is provided said stable in-situ functionalized silica dispersion/emulsion wherein said acid emulsifier as surfactant-cum-catalyst is preferably dodecylbenzenesulphonic acid.

According to another preferred aspect of the present invention said stable in-situ functionalized silica dispersion/emulsion involving said hydrolytically condensed ethylenically unsaturated alkoxysilanes on silica particle surface selected from:
RnSi(OR’)4-n where, n is an integer varying from 1 to 3, R’ may be the same or different substituted or unsubstituted monovalent hydrocarbon or alkyl or acyl or aryl group and R represents a vinyl group or hydrocarbon with at least one ethylenically unsaturated group; said alkoxysilanes having vinyl functional group on silica particle surface is adapted for hybrid latex particles with silica core and organic polymer shell preferably acrylic polymer shell via emulsion polymerization, free of any isolation and purification of said silica dispersion/emulsion and free of any further surface modification of silica.

Preferably said stable in-situ functionalized silica dispersion/emulsion has average particle size less than or greater than 100 nm, wherein average size >100nm is adapted for dominant core-shell morphology over occluded morphology of hybrid latex particles with silica core and organic polymer shell, and wherein with average size <100nm is adapted for dominant occluded morphology over core shell morphology of said hybrid latex particles with silica core and organic polymer shell.

More preferably in said stable in-situ functionalized silica dispersion/emulsion the average size of silica particles varies based on selectsaid alkoxysilanes and/or their concentration.

According to another aspect of the present invention there is provided a process for preparing stable in-situ functionalized silica dispersion/emulsion comprising the steps of providing at least one ethylenically unsaturated alkoxysilanes in selective concentrations corresponding to selective levels of anionic and/or non-ionic surfactant together with acid emulsifier as surfactant-cum-catalyst in water,
thereby yielding in-situ surface functionalized silica dispersion/emulsion comprising acid emulsifier catalyzed hydrolytically condensed ethylenically unsaturated alkoxysilanes on silica particle surface.

Preferably said process for preparing stable in-situ functionalized silica dispersion/emulsion comprises the steps of
providing (i) mixture comprising 0.1- 20 wt.% organotrialkoxysilanes containing at least one ethylenically unsaturated polymerizable group, water, anionic surfactant and/or non-ionic surfactant;
providing (ii) mixture comprising water and surfactant-cum-catalyst emulsifier preferably dodecylbenzenesulphonic acid; followed by
select sequence and select time period based controlled addition of said mixture (i) to mixture (ii) for 3-24 hours preferably 3-10 hours, more preferably for 3-5 hours at ambient temperature (20-35 °C) followed by subsequent neutralization to thereby provide for in-situ functionalized silica particles containing said ethylenically unsaturated polymerizable groups on the surface of silica particles as aqueous silica dispersion said silica dispersion being preferably obtained of 8-10 wt. % alkoxysilane as the starting material together with minimum dosage of anionic surfactants and/ or non-ionic surfactant of at least 2-3 wt. % on active basis together with surfactant-cum-catalyst emulsifier in the range of 0.1 to 10.0 wt.%, preferably 0.5 to 5.0 wt. % more preferably 0.5 to 2.0 wt.%.

More preferably, in said process for preparing stable in-situ functionalized silica dispersion/emulsion said ethylenically unsaturated alkoxysilanes are of the type:
RnSi(OR’)4-n where, n is an integer varying from 1 to 3, R’ may be the same or different substituted or unsubstituted monovalent hydrocarbon or alkyl or acyl or aryl group and R represents a vinyl group or hydrocarbon with at least one ethylenically unsaturated group;
and are selected from vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane, 3-Methacryloxypropyl trimethoxysilane, 3-Methacryloxylmethyltrimethoxysilane, Triisopropylsilylmethacrylate, Triisopropylsilylacrylate 3-ethacryloxypropylmethyldimethoxysilane, Vinyldimethylethoxysilane, Vinylmethyldiethoxysilane, Vinylmethyldimethoxysilane3-Methacryloxypropyl triethoxysilane, 3-Methacryloxypropyl triisopropoxysilane, 3-Acryloxypropyltrimethoxysilane or mixtures thereof.

More preferably, in said process for preparing stable in-situ functionalized silica dispersion/emulsion said surfactants and surfactant-cum-catalyst include sulfonic acids comprising dodecylbenzenesulphonic acid, linear alkyl benzene sulphonic acid and sulfonic acid salt derivatives like sodium lauryl sulfate, Alkyldiphenyloxide Disulfonate, sodium lauryl ether sulfate, Sodium dodecyl benzenesulfonate sold under the trade name GALAXY SLS, DOWFAX™ 2A1, GALAXY LES, RHODACAL® DS-10; commercial anionic surfactant include alkali metal salts of sulfosuccinates, alkali metal salts of a higher fatty acid, fatty alcohol sulfates, oleic acid sulfonates, alkyl sulfates, alkylethoxy sulfates, alkyl ether sulfates,higher alcohol sulfuric acid ester sodium salts, alpha-olefin sulfonates. Commercial types of anionic surfactant can be CALSOFT®, PENTEX® 99, AEROSOL®, STEPAN-MILD® LSB, DOWFAX™, DISPONIL®, RHODAFAC®;
said non-ionic surfactant include alkyl phenol ethoxylates, secondary alcohol ethoxylate, polyoxyethylene sorbitian ester trade name ATPOL 5731, TERGITOL 15S-40, TWEEN 80, TERGITOL®, TRITON™, MERPOL®, ATPOL™,ANATAROX®, SPAN® 80, IGEPAL®, Brij®, TWEEN®.

According to another aspect of the present invention there is provided a hybrid latex particles having silica core and organic polymer shell comprising polymerization product of
(i) stable in-situ surface functionalized silica dispersion/emulsion precursor involving said acid emulsifier catalyzed hydrolytically condensed at least one ethylenically unsaturated alkoxysilane on silica particle surface; and
(ii) at least one ethylenically unsaturated polymerizable monomers.

Preferably said hybrid latex particle has silica core and organic polymer shell wherein said stable in-situ surface functionalized silica dispersion/emulsion precursor is a dispersion in water including at least one ethylenically unsaturated alkoxysilanes in selective levels corresponding to selective levels of anionic and/or non-ionic surfactant together with acid emulsifier adapted for said stable in-situ functionalized silica dispersion/emulsion having hydrolytically condensed at least one ethylenically unsaturated alkoxysilane on silica particle surface.

Said hybrid latex particles having silica core and organic polymer shell as core-shell latex particles is obtained of stable in-situ surface functionalized silica dispersion/emulsion free of any isolation and purification of said silica dispersion/emulsion and free of any added surface modification of silica.

Preferably said hybrid latex particlesis a stable dispersion wherein said polymerization product includes silica particles that are substantially covered with polymeric shell favouring silica-core and polymeric-shell morphology preferably with dominant core shell morphology over occluded morphology.

More preferably said hybrid latex particles having silica core and organic polymer shellis provided as a stable dispersion including said stable of in-situ functionalized silica dispersion/emulsionof average particle size less than or greater than 100 nm, as precursor; wherein dominant core-shell morphology over occluded morphology of said latex particles is based on average particle size >100nm of said precursor in-situ functionalized silica dispersion/emulsion,
and wherein dominantoccluded morphology over core shell morphology of said hybrid latex particlesis based on average particle size < 100nm of said precursor in-situ functionalized silica dispersion/emulsion.

Said hybrid latex particles having silica core and organic polymer shell wherein said polymerizable monomer(ii) comprises Methylmethacrylate, n-butyl methacrylate, styrene, butyl acrylate, 2-ethyl hexyl methacrylate, methacrylic acid and 2-Hydroxyethyl methacrylate. Even though only few of monomers are considered for examples, the synthesis of hybrid latex may not be restricted to only these monomers. Other ethylenically unsaturated polymerizable monomer may comprise of acrylic acid esters, methacrylic acid esters and the copolymerizable monomer like methacrylamide, styrene,vinyl acetate, alkylmethacrylates, alkylacrylates, unsaturated carboxylic acids, alkenyl aromatic compounds, acrylonitrile, styrene, a-methylstyrene, acrylic acid, or derivatives or mixtures thereof.

According to another aspect of the present invention a one pot process for preparing hybrid latex particles having silica core and organic polymer shell is provided comprising a single step process involving providing said stable in-situ functionalized silica dispersion/emulsion and heating to upto desired temperature range for desired time, followed by adding pre-emulsion comprising aqueous dispersion ofpolymerizable monomers, deionized water, anionic and/ or non-ionic surfactant to said stable in-situ functionalized silica dispersion/emulsion for desired time of about 4 hrs and allowing it to react to thereby obtain said hybrid latex particles with silica core and polymeric shell morphology, free of anyisolation and purification step of said silica dispersion/emulsion and free of any added surface modification step of silica.

Preferably in said one pot process for preparing hybrid latex particles having silica core and organic polymer shellthe same comprises the sub-steps of
(i) Providing silica dispersion in a reactor vessel formed at room temperature followed by increasing the temperature of the reactor vessel to upto 80 deg subsequently followed by PPS (initiator) addition and Pre-emulsion addition for a period of about 4 hrs in the same reactor vessel, said pre-emulsion comprising a mixture of Monomer, deionized water, anionic and / or non-ionic surfactant and free of any silica dispersion;
(ii) Digesting the reaction mixture of step (i) for about an hour at 70-80 deg post completion of pre-emulsion addition, cooling and mixing with biocide preservatives and ammonia for adjusting the pH to about 7 to thereby obtain hybrid latex particles with silica core and polymeric shell morphology therefrom by enabling first formation of silica dispersion in the reactor on which the polymer is grown on top of silica particles in the same reactor.

Further said process for preparing hybrid latex particles having silica core and organic polymer shell is provided as a two step process comprising the steps of
(i) providing a reactor charge of demineralized water and anionic surfactant and raising the temperature to 80 deg;
(ii)(a) forming the pre-emulsion in a separate vessel by mixing pre-formed aqueous silica dispersion, demineralized water, surfactant and monomers whereby the aqueous silica dispersion is a part of pre-emulsion;
(ii)(b) adding a portion (preferably 5-10%) of said pre-emulsion to the reactor of step (i) at 80 deg followed by PPS (initiator) and buffer addition and allowing the mixture to react at 80 deg for about 15-30 minutes that is followed by continued controlled addition of the remaining pre-emulsion into said reactor at 80 deg forabout 4 hrs after completion of which said pre-emulsion addition the reaction mixture is digested for an hour at 70-80 deg for removal of unreacted monomers, further cooled and mixed with biocide preservatives and ammonia for adjusting the pH to about 8-10 to thereby obtain hybrid latex particles with silica core and polymeric shell morphology therefrom wherein in said process the silica dispersion is separately made and the same is used in step-ii (a) for emulsion polymerization.

Preferably in said process for preparing hybrid latex particles having silica core and organic polymer shell comprises providing in-situ functionalized aqueous silica dispersion 1 to 15 wt.% to result in a stable hybrid latex having silica core and acrylic shell with about 40-50 wt.% solids.

BRIEF DESCRIPTION OF FIGURES

Figure 1. illustrates STEM image of in-situ functionalized silica particles as illustrated by Example 8 with average particlesize less than 100nm;

Figure 2. illustrates cryo-FESEM image showing mixed morphology (core-shell and occluded) with occluded morphology dominatingfor hybrid latex obtained using dispersion of silica particles having average size less than 100 nm (Figure 1). Both the core-shell and occluded morphology can be seen but particles with occluded morphology are more in number as compared to the hybrid particles having core-shell morphology;

Figure 3: illustrates cryo-FESEM image of hybrid latex, and the side image reveals the freeze fractured particles with silica core. Both the core-shell and occluded morphology can be seen but particles with core-shell morphology are more in number as compared to the particles having occluded morphology.

DETAILED DESCRIPTION OF THE INVENTION

As discussed hereinbefore, the present invention provides for stable in-situ functionalized silica dispersion/emulsion comprising in-situ surface functionalized silica dispersion/emulsion and hybrid latex particles with silica core and organic polymer shell preferably acrylic polymer shell and a simple industrially facile process for the manufacture of same comprising the steps of preparing a stable emulsion involving pre-formed well dispersed in-situ room temperature surface functionalized silica particles free of any isolation and purification step, which pre-formed in-situ surface functionalized silica dispersion is adapted to be used either as seed or mixed in various proportions with monomer phase for polymerization by conventional seeded emulsion polymerization to form said hybrid latex with silica core and acrylic shell.

Advantageously, the process of the present invention involves preparation of in-situ functionalized silica nanoparticles as a stable emulsion at room temperature (20-35°C) free of any requirement of additional surface modification as the particles are in-situ functionalized, and since the nanoparticles are already stabilized as a dispersion the same is free of any requirement of any further stabilization or re-dispersion and can be used as such without any isolation and purification to produce hybrid latex with silica core and acrylic polymer shell viaemulsion polymerization process.

It is surprisingly found by way of the present invention that the silica particles could be in-situ functionalized during its formation/synthesis in aqueous medium by the process comprising of slow addition of mixture-A comprising organotrialkoxy-silanes containing at least one ethylenically unsaturated polymerizable group, DI water, anionic surfactant and/ or non-ionic surfactant, at room temperature, to a reactor containing a mixture of DI water and a surfactant cum catalyst reagent viz. Dodecylbenzenesulphonic acid. The aqueous dispersion of this in-situ functionalized silica particles containing said ethylenically unsaturated polymerizable groups are further adapted to form a hybrid latex having the said morphology of silica core and polymeric shell by emulsion polymerization process.
Hence, it is thus the finding of the present invention that stable-in situ surface functionalized silica dispersion could only resultbased on the select ingredients together with involvement of select process parameters of concentration of alkoxysilane and the time employed for addition of preformed mixture of alkoxysilane and surfactant in water to surfactant-cum-catalyst reagent also taken in water.

Furthermore, the concentration of the alkoxysilane varies depending on its type for instance, Vinyltrimethoxysilane (VTMO) can be used up to 20 wt.% to form a stable in-situ functionalized silica dispersion. Experiments carried with 3 different concentrations for VTMO: 8 wt.%, 20 wt.% and 30 wt.%. revealed that 8 and 20 wt. % gave stable silica dispersion whereas, with 30 wt.% concentration the silica dispersion became unstable and formed a coagulum.
On the other hand 3-Methacryloxypropyl triethoxysilane (MAPTS) usage is restricted to up to 8 wt.% above which it does not form a stable functionalized silica dispersion but forms coagulum/ gel. For MAPTS experiments at 3 different concentrations: 6 wt.%, 8wt.% and 15 wt.% revealed that the 6 and 8 wt.% concentration gave stable silica dispersion while the 15 wt.% led to coagulation of the dispersion.
Similarly, the time for addition of preformed mixture of alkoxysilane is also very critical. The time for addition has to be minimum 3-5 hours. Fast addition of the preformed mixture leads to formation of coagulum or unstable silica dispersion.

The alkoxysilane is the most essential ingredient used in the preparation of stable in-situ functionalized aqueous silica dispersion which, are of the type RnSi(OR’)4-n where, n is an integer varying from 1 to 3, R’ may be the same or different substituted or unsubstituted monovalent hydrocarbon or alkyl or acyl or aryl group and R represents a vinyl group or hydrocarbon with at least one ethylenically unsaturated group. Said alkoxysilanes bearing vinyl functional group ensures the presence of these groups on the surface of the silica particles formed in the process of making in-situ functionalized aqueous silica dispersion/ emulsion.
Furthermore, the process of forming in-situ functionalized silica dispersion/ emulsion is carried out in the presence of surfactant cum-catalyst (acidic surfactant) selected from dodecylbenzenesulphonic acid, substituted benzene sulphonic acid, aliphatic sulphonic acids, alkyl-benzene sulphonic acid and derivatives thereof in combination with anionic and/or non-ionic surfactantto form stable in-situ functionalized aqueous silica dispersion. The acid catalyst of dodecylbenzenesulphonic acid acts as catalyst for hydrolysis condensation reaction of alkoxysilanes and at the same time it also acts as a surfactant stabilizer for the in-situ functionalized silica particles that are formed in the process. It is highly essential to synthesize the in-situ functionalized silica particles in the presence of anionic and/or non-ionic surfactant to stabilize the silica particles as they are getting formed in the process. With regard to the stability of the thus achieved in-situ functionalized silica dispersion/ emulsion during experimentation it was found through visual observation the original colour of the dispersion (bluish white or turbid white) is retained even for after 1 month when stored as such. The color of the dispersion indicates that silica particles remain in stably dispersed form in water. The proportion of each of the ingredients used in the process is critical to form a stable in-situ functionalized silica dispersion, which if not maintained results in de-stabilization of dispersion during reaction. It is highly crucial to maintain the alkoxysilane concentration in the range of 0.1 to 20 wt. % depending on its type as discussed above, beyond which the silica becomes unstable and coagulates at the bottom of reaction mixture. Based on the concentration of alkoxysilanes the surfactant dosage is selectively controlled. For instance, to form stable silica dispersion using 8-10 wt. % alkoxysilane as the starting material minimum dosage of anionic surfactants and/ or non-ionic surfactant should be at least 2-3 wt. % on active basis.
Suitable surfactants include but not limited to sulfonic acids and their salt derivatives like Sodium lauryl sulfate , AlkyldiphenyloxideDisulfonate, sodium lauryl ether sulfate, Sodium dodecyl benzenesulfonate sold under the trade name GALAXY SLS, DOWFAX™ 2A1, GALAXY LES, RHODACAL® DS-10; commercial anionic surfactant used in this invention include linear alkyl benzene sulphonic acid sold under the trade name of RHODACAL® SSA/R; non-ionic surfactant alkyl phenol ethoxylates, Secondary Alcohol Ethoxylate, polyoxyethylenesorbitian ester sold under the trade name ATPOL 5731, TERGITOL 15S-40, TWEEN 80.
Other useful anionic surfactants include but not limited to alkali metal salts of sulfosuccinates, alkali metal salts of a higher fatty acid, fatty alcohol sulfates, oleic acid sulfonates, alkyl sulfates, alkylethoxy sulfates, alkyl ether sulfates, higher alcohol sulfuric acid ester sodium salts, alpha-olefin sulfonates. Commercial types of anionic surfactant can be exemplified by different trade names such as CALSOFT®, PENTEX® 99,AEROSOL®, STEPAN-MILD® LSB, DOWFAX™, DISPONIL®, RHODAFAC®. Commercial type of non-ionic surfactants can be exemplified by TERGITOL®, TRITON™, MERPOL®, ATPOL™,ANATAROX®, SPAN® 80, IGEPAL®, Brij®, TWEEN®.

EXAMPLES
Following examples for formation of stable in-situ functionalized silica dispersion illustrates the present invention in more details and should not be construed to limit the scope of the present invention.
In these examples, the pre-emulsion is prepared by mixing the De-mineralized water with alkoxysilanes bearing ethylenically unsaturated group in the presence of anionic or non-ionic surfactant or combination thereof. The pre-emulsion is then added at controlled rate with a peristaltic pump to a reactor flask containing a mixture of De-mineralized water and dodecyl benzene sulphonic acid at room temperature of 20-35 °C. The silica average particle size and its distribution was determined using Malvern Zetasizer Nano ZS (Malvern Instruments Ltd, UK).

Example 1
The following ingredients with the proportion indicated were used to prepare the silica dispersion:

Ingredients Weight percent
Water (1st portion) 44.8
RHODACAL SSA/R(anionic surfactant) 1.5
Water (2nd portion) 35
GALAXY LES (30%, anionic surfactant) 3.3
Vinyltrimethoxysilane 8.0
Water (3rd portion) 6.7
Sodium bicarbonate (neutralizer) 0.7

In this example only anionic surfactant was used. First two ingredients (water + Dodecyl benzene suphonic acid) were added to the reactor flask and allowed to stir for 15 minutes. Then slowly with peristaltic pump controlled feeding of mixture of next two ingredients (Galaxy LES and Vinyltrimethoxysilane) in second portion of water were added to the reactor over a period of 4-5 hours. The reaction mixture was then neutralized with sodium bicarbonate pre-dissolved in the last portion of water.
The aqueous in-situ functionalized silica dispersion had the following characteristics:
Properties Value
Average particle size (nm) 25
Particle size distribution (nm) 10-100
Non volatile content (%) 6.7
pH 7.0

Example 2
Example 1 was repeated with different anionic surfactant, GALAXY SLS along with second portion of water. The proportions of different ingredients are shown below:
Ingredients Weight percent
Water (1st portion) 44.8
RHODACAL SSA/R (anionic surfactant) 1.5
Water (2nd portion) 37.3
GALAXY SLS (anionic surfactant) 1.0
Vinyltrimethoxysilane 8.0
Water (3rd portion) 6.7
Sodium bicarbonate (neutralizer) 0.7

The aqueous in-situ functionalized silica dispersion obtained in Example 2 had the following characteristics:
Properties Value
Average particle size (nm) 20
Particle size distribution (nm) 10-60
Non volatile content (%) 6.7
pH 7.0

Example 3
In this example anionic surfactant used in Example 1 was replaced with non-ionic surfactant, TERGITOL®15S-40 along with second portion of water. The proportions are as shown below:
Ingredients Weight percent
Water (1st portion) 44.8
RHODACAL SSA/R 2.0
Water (2nd portion) 37.3
TERGITOL®15S-40 (70%, non-ionic surfactant) 1.5
Vinyltrimethoxysilane 8.0
Water (3rd portion) 5.4
Sodium bicarbonate (neutralizer) 1.0

The silica dispersion obtained in Example 3 had the following characteristics:

Properties Value
Average particle size (nm) 55
Particle size distribution (nm) 25-105
Non volatile content (%) 7.3
pH 7.5

Example 4
Example 3 was repeated with different non-ionic surfactant, ATPOL™ 5720. The proportions are shown below:
Ingredients Weight percent
Water (1st portion) 44.8
RHODACAL SSA/R 2.0
Water (2nd portion) 37.3
ATPOL™ 5720 (non-ionic surfactant) 1.5
Vinyltrimethoxysilane 8.0
Water (3rd portion) 5.4
Sodium bicarbonate (neutralizer) 1.0

The silica dispersion obtained in Example 4 had the following characteristics:
Properties Value
Average particle size (nm) 57
Particle size distribution (nm) 20-300
Non volatile content (%) 7.5
pH 7.0

Example 5
Example 2 was repeated with different alkoxysilane, 3-Methacryloxypropyl triethoxysilane and the proportions are shown below:
Ingredients Weight percent
Water (1st portion) 44.8
RHODACAL SSA/R 1.5
Water (2nd portion) 37.3
GALAXY SLS 1.0
3-Methacryloxypropyl triethoxysilane (KBE-503) 6.0
Water (3rd portion) 8.7
Sodium bicarbonate (neutralizer) 0.7
The silica dispersion obtained in Example 5 had the following characteristics:
Properties Value
Average particle size (nm) 100
Particle size distribution (nm) 50-190
Non volatile content (%) 6.4
pH 7.8

Example 6
In this different combinations of anionic and non-ionic surfactant were used as shown below:
Ingredients Weight percent
Water (1st portion) 44.8
RHODACAL SSA/R 0.7
Rhodacal DS-10 0.7
Water (2nd portion) 37.3
Rhodacal DS-10 (anionic surfactant) 0.3
Atpol 5731 (non-ionic surfactant) 0.8
Dynasylan® Vinyltriethoxysilane 8.0
Water (3rd portion) 7.0
Sodium bicarbonate (neutralizer) 0.4

The silica dispersion obtained in Example 6 had the following characteristics:

Properties Value
Average particle size (nm) 63
Particle size distribution (nm) 30-140
Non volatile content (%) 5.6
pH 7.5

Example 7
Example 6 is repeated with different alkoxysilane, 3-Methacryloxypropyl triethoxysilane and the proportions of different ingredients are shown below:
Ingredients Weight percent
Water (1st portion) 44.8
RHODACAL SSA/R 0.7
Rhodacal DS-10 0.7
Water (2nd portion) 36.3
Rhodacal DS-10 (anionic surfactant) 0.3
Atpol 5731 (non-ionic surfactant) 0.8
3-Methacryloxypropyl triethoxysilane (KBE-503) 6.0
Water (3rd portion) 10.0
Sodium bicarbonate (neutralizer) 0.4

The silica dispersion obtained in Example 7 had the following characteristics:
Properties Value
Average particle size (nm) 156
Particle size distribution (nm) 90-255
Non volatile content (%) 5.6
pH 7.8

Example 8
Example 6 is repeated with different alkoxysilane, Vinyl trimethoxysilane and the proportions of different ingredients are shown below:

Ingredients Weight percent
Water (1st portion) 44.8
RHODACAL SSA/R 0.7
Rhodacal DS-10 0.7
Water (2nd portion) 37.3
Rhodacal DS-10 (anionic surfactant) 0.3
Atpol 5731 (non-ionic surfactant) 0.8
Vinyltrimethoxysilane 8.0
Water (3rd portion) 7.0
Sodium bicarbonate (neutralizer) 0.4

The silica dispersion obtained in Example 8 had the following characteristics:

Properties Value
Average particle size (nm) 50
Particle size distribution (nm) 30-120
Non volatile content (%) 6.7
pH 6.8

Example 9

Example 8 is repeated with increased concentration of vinyl trimethoxysilane
Ingredients Weight percent
Water (1st portion) 40
RHODACAL SSA/R 1.0
Rhodacal DS-10 (anionic surfactant) 1.0
Water (2nd portion) 32.5
Rhodacal DS-10 (anionic surfactant) 0.3
Atpol 5731 (non-ionic surfactant) 0.8
Vinyltrimethoxysilane 20
Water (3rd portion) 4.0
Sodium bicarbonate (neutralizer) 0.4

Properties Value
Average particle size (nm) 135
Particle size distribution (nm) 68-255
Non volatile content (%) 13.2
pH 6.6

The stable silica dispersion illustrated by the above examples (1-9) can further be used to form hybrid latex with silica core and polymeric shell.

Example 10
A typical recipe used for preparing hybrid latex is provided as illustrated by the table below:
In this example the pre-formed silica dispersion is mixed along with monomers, water and surfactant to form pre-emulsion mixture. This pre-emulsion mixture is further used for making hybrid latex following conventional seeded emulsion polymerization process. First to a reactor anionic surfactant and water is charged and allowed to stir for 15 minutes at 80°C. In a separate vessel a pre-emulsion mixture is prepared by mixing water, silica dispersion and surfactants. The mixture is stirred to form homogenous solution. To this solution then monomer mixture (Methyl methacrylate, Butyl acrylate and Methacrylic acid) are added and stirred to form pre-emulsion mixture. A seed (5 wt%) is first charged to a reactor at 80°C. The mixture is then continued to stir for another 15 minutes. The reaction mixture forms bluish white color. The remaining pre-emulsion is then fed to a reactor vessel using peristaltic pump over a period of 4 hours. The latex formed is then digested for removal of unreacted monomers further using the ingredients given in the Table below. Final latex is cooled, added with anti-microbial preservatives and filtered.

Reactor charge Proportions (%)
Demineralized water 22.1
Anionic surfactant Rhodacal DS-10 0.1
Catalyst- Potassium persulphate 0.2
Buffer- Sodiumbicarbonate 0.15
Seed 5
Pre-emulsion mixture
Demineralized water 13.3
Silica dispersion (size <100nm) 10
Anionic surfactant- Rhodacal DS-10 0.05
Non- ionic surfactant- Atpol 5731 0.7
Methyl methacrylate 28
Butyl acrylate 19.5
Methacrylic acid 0.8
Digestion
Tertiary Butyl hyderoperoxide 0.05
Sodium Formaldehyde sulphoxlate 0.05
Demineralized water 3.17
Additives
Kathon LX150 (antimicrobial preservative) 0.02
Ammonia (for adjusting pH) 0.8
Demineralized water 1.01

Typical representative Cryo-SEM image of hybrid latex showing both types of morphology core-shell and/ or occluded type of morphology is shown in Figure-2.
Figure 1 STEM image illustrates the silica dispersion (illustrated by Example 8) having average particle size less than 100nm which is used to make hybrid latex (as shown in Figure 2).
Figure 2 SEM image illustrates an example of hybrid latex obtained using dispersion of silica particles having average size less than 100 nm (Figure 1). Both the core-shell and occluded morphology can be seen but particles with occluded morphology are more in number as compared to the hybrid particles having core-shell morphology.
Figure 3 reveals cryo-FESEM image of hybrid latex, and the side image reveals the freeze fractured particles with silica core. Both the core-shell and occluded morphology can be seen but particles with core-shell morphology are more in number as compared to the particles having occluded morphology.
The reagents used in the above process especially alkoxysilane, acidic surfactant (dodecylbenzenesulphonic acid) and other nonionic and anionic surfactants are well known and often used in emulsion polymerization process. As discussed in the above section in order to obtain stable silica dispersion it was found that the critical parameters (like concentration and time of addition) are extremely crucial for the process. Equally important is the sequence in which the ingredients are added to a reaction mixture for formation of stable in-situ functionalized silica dispersion without which the silica particles loses its stability.For better understanding a brief description of the non-limiting process is as given below:
Typically, to a reactor flask first water is added followed by surfactant cum-catalyst reagent (dodecylbenzenesulphonic acid) addition. This mixture is stirred with a mechanical overhead stirrer for 15 minutes to form a homogeneous solution. In a separate vessel water is mixed with surfactant (anionic or non-ionic or their combination) and selective organoalkoxysilane to form a silane mixture. This mixture is then added slowly to a reactor containing the surfactant cum-catalyst reagent under stirring. Once the addition is completed, sodium bicarbonate is added to neutralize the formed silica dispersion. Thus,the selective sequence is necessary to obtain the stable silica dispersion such as Example 1 above without which the silica dispersion could not be attained.

The hybrid latex particles with silica-core and polymeric shell of the present invention is thus formedfree of any additional surface modification step of silicaand comprising the following steps: i) forming an aqueous dispersion of in-situ functionalized silica at room temperature using different organotrialkoxysilane having at least one ethylenically unsaturated polymerizable group and a surfactant-cum-catalyst reagent ii) mixing the aqueous dispersion with polymerizable monomers, deionized water, surfactant (anionic and nonionic)to form a pre-emulsion, iii) Adding said pre-emulsion to a reactor at 70-85 °C, and allowing it to react further to form hybrid latexparticles with silica core and polymeric shell morphology.

Especially in the present invention the select alkoxysilanes having at least one ethylenically unsaturated polymerizable group only are employed to form in-situ functionalized aqueous silica dispersion. These alkoxysilanes containing ethylenically unsaturated polymerizable group are condensed in the presence of acidic surfactant cum catalystreagentin aqueous phase to form vinyl functionalized silica particles dispersed in aqueous phase at room temperature as aqueous silica dispersion. The alkoxysilane used are selected from vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane,3-Methacryloxypropyl trimethoxysilane, 3-Methacryloxylmethyltrimethoxysilane,Triisopropylsilylmethacrylate,Triisopropylsilylacrylate3-Methacryloxypropylmethyldimethoxysilane,Vinyldimethylethoxysilane,Vinylmethyldiethoxysilane, Vinylmethyldimethoxysilane3-Methacryloxypropyl triethoxysilane, 3-Methacryloxypropyl triisopropoxysilane,3-Acryloxypropyltrimethoxysilanefor the preparation of aqueous silica dispersion.Said aqueous dispersion is further mixed with polymerizable monomers, surfactants, initiators and polymerized by seeded emulsion polymerization to form core-shell type latex particles. Further the presence of ethylenically unsaturated polymerizable groups on the silica surface ensures that the particles are completely covered with polymeric shell to form hybrid latex having silica-core and polymeric-shell morphology after emulsion polymerization.
The specific reagents used to make in-situ functionalized silica dispersion are alkoxysilanes, surfactant cum-catalyst reagent selected from dodecylbenzenesulphonic acid type sold under the Trade name of RHODACAL SSA/Rand anionic or non-ionic surfactants or combination of both anionic and non-ionic surfactants.
Effects of each of the reagents employed in the process of making silica dispersion are as follows:
1) Organoalkoxysilane: It was observed that concentration of alkoxysilane together with its type is critical to the formation of stable silica dispersion. As concentration of alkoxysilane is increased the silica particle size increases. Also the type of the alkoxysilane employed has the effect on size of the silica particles.
Additionally, the time for addition of preformed mixture of alkoxysilane is also very critical. The time for addition can be 3-24 hours preferably 3-10 hours, more preferably 3-5 hours. Fast addition of the preformed mixture leads to formation of coagulum or unstable silica dispersion.

2) For surfactant-cum-catalyst reagent: Concentration of this reagent is restrictedto 0.7, 1.5 and 2.0 wt. % which provided for the desired results.The concentration of the surfactant-cum-catalyst reagent can vary from 0.1 to 10.0 wt.%, preferably 0.5 to 5.0 wt. % more preferably 0.5 to 2.0 wt.%.
3) Surfactant: Without the use of surfactant stable silica dispersion could notbe formed. Typically, if pure organosilane is used for the preparation of silica dispersion instead of organosilane mixture with water and surfactantthen the reaction mixture tends to coagulate in to a gelly mass. It is very important to use surfactants which may be in anionic form (Examples1 and 2) or in non-ionic form (Example 3 and 4) or combination of both anionic and non-ionic forms (Examples 6,7 and 8) can be used to prepare a stable silica dispersion.

4) Sodium bicarbonate is also used as one of the ingredient at the end of the process of formation of silica dispersion to make the pH at neutral. But it has no specific role in silica formation or stabilization process and is added only at the end of the process.
According to an embodiment of the present invention the emulsion polymerization is carried out at 75-85°C with the in-situ functionalized silica nanoparticles prepared as a stable dispersion at room temperature (20-35°C). To elaborate further on the criticality of the emulsion polymerization process for forming hybrid latex with silica core and polymeric shell two different strategies are followed:
According to an embodiment of the presentinvention a one-pot synthesis of hybrid latex with silica core and polymeric shell is provided wherein the aqueous dispersion of in-situ functionalized silica particles was employed as seed component. In said one-pot process the aqueous dispersion of in-situ functionalized silica particles is first pre-formed in a reactor at room temperature. Once the silica dispersion is formed the temperature of the reactor is raised to 75-85 °C followed by initiator (K2S2O8) addition. Then pre-formed emulsion (also referred as pre-emulsion) is added slowly to the reactor at 75-85 °C over a period of 4-5 hrs and allowed to react further to form hybrid latex. The pre-emulsion mentioned is formed by mixing polymerizable monomers, surfactant (anionic and non-ionic) and deionized water. Therefore in said one-pot synthesisprocess to form the said hybrid latex both the steps i.e. first formation of aqueous silica dispersion and then subsequently emulsion polymerization is carried out in the same reactor to form the hybrid latex having silica core and polymeric shell. The criticality of this one-pot process resides in the proportion of silica dispersion used with respect to polymerizable monomers. For making a stable hybrid latex having silica core and polymeric shell with 50 wt.% solids the maximum proportion of silica dispersion can be up to 15 wt%. Above this concentration the reaction system becomes unstable to be processed further. However, from 0.1 to 15 wt. % concentration a stable hybrid latex with 50 wt.% solids can be achieved.

According to yet another embodiment of the present invention synthesis of hybrid latex with silica core and polymeric shell is provided wherein
(i) mixing the pre-formed aqueous dispersion of in-situ functionalized silica particles with polymerizable monomers, surfactants (anionic and non-ionic) and deionized water leads to a pre-emulsion wherein the portion of the pre-emulsion containing aqueous dispersion of in-situ functionalized silica particles is added as a seed to a reactor maintained at 80 °C followed by addition of initiator (K2S2O8) and pH buffer;
(ii) the mixture of step (i) added as seed, is allowed to react for 15 minutes in the reactor under stirring followed by which the remaining portion of the pre-emulsion is slowly added to the reactor over a period of 4-5hrs at 80 °C;
(iii) digesting the reaction mixture of step (ii) above for an additional hour to remove unreacted monomers, if any and after cooling to ambient is mixed with biocides (for preservation) and stored for further use.
It was significantly found by way of the present invention that in the above process involving a pre-emulsion as seed comprising polymerizable monomers, surfactants (anionic and non-ionic) and deionized water also including aqueous dispersion of in-situ functionalized silica particles, the criticality resides in the concentration of aqueous silicadispersion which when used between 1.0to 15 wt.% results in a stable hybrid latex having silica core and acrylic shell with 50 wt.% solids.

The polymerizable monomers used comprises Methylmethacrylate, n-butyl methacrylate, styrene, butyl acrylate, 2-ethyl hexyl methacrylate, methacrylic acid and 2-Hydroxyethyl methacrylate. Even though only few of monomers are considered for examples, the synthesis of hybrid latex may not be restricted to only these monomers. Other ethylenically unsaturated polymerizable monomer may comprise of acrylic acid esters, methacrylic acid esters and the copolymerizable monomer like methacrylamide, styrene,vinyl acetate, alkylmethacrylates, alkylacrylates, unsaturated carboxylic acids, alkenyl aromatic compounds, acrylonitrile, styrene, a-methylstyrene, acrylic acid, or derivatives or mixtures thereof.
If the concentration of monomer is varied then polymer shell thickness of core-shell hybrid latex changes, and moreover in employing many types of monomers the polymerization rates vary. However, since the industrial latexes usually have solid content of 45-50wt% for the sake of commercial feasibility the process of the present invention is restricted to preparing emulsions with 40-50 wt% solid content. [Solid content (wt. %): amount of solid upon drying of 100 gm of emulsion polymer].

The process embodiments of the present invention are provided as schematics below:

Scheme 1a. Schematic for silica dispersion preparation (step 1)

Scheme 1b. Schematic for preparation of silica-acrylic hybrid emulsion (step-2)

Scheme 2. Above schematic reveals preparation of silica-acrylic hybrid emulsion by single step process

Thus the present invention is directed to a simple process as it can be scaled up easily using standard emulsion manufacturing set up/plant,asto make such an emulsion it is known that to make any inorganic particle compatible with organic polymer phase surface modification of inorganic particle is required. The said surface modifications are usually carried out either with the help of different coupling agents or surfactants or cationic initiators involving a separate modification step. However, the process of the present invention is special in not requiring any of the said step of surface modification as additional step to form a silica core and polymeric shell type morphology because the silica particles are in-situ functionalized.
When commercially different colloidal silica dispersions as available such as LUDOX® HS-40,Klebosol®,Aerodisp, Snowtex and Levasil®, and the like were employed in the process of the present invention as seed to carry out emulsion polymerization, a stable core-shell hybrid latex particlecould not be produced.

Surface modification, type of surfactant, type of catalyst was found to be critical to achieve a stable hybrid latex dispersion. It was also found that even the size of silica core particles influences final hybrid latex morphology. Core-shell morphology was observed to be dominating morpholgy with silica particle size of 100-150 nm and matrix/occluded morphology is observed to be dominating with silica particle size less than 100 nm as in Figure 2 when the experiments were conducted using in-situ functionalized silica particles of the present invention.
Example 10and SEM images in the Figure 1-2 supports the abovesaid.
As illustrated in Examples 1-9the particle size of the silica particles formed may show average particle size less than or greater than 100 nm. When these silica particles are employed for making hybrid latex a mixed morphology with core-shell morphology being dominant for silica particles with average size >100nm or occluded morphology being dominated for silica particles with average size < 100nm. This can be further illustrated with Example 8 particles and Example 10 particles taken as representative example for preparing hybrid latex that clearly reveals under Figure 2 that though both core shell and occluded morphology can be seen but particles with occluded morphology is more in number to the hybrid particles with core shell morphology.
It was observed during the formation of silica particles that the average size of the silica particles can be varied by changing the type of alkoxysilanes or by changing the concentration of particular alkoxysilane employed in the process. It is evident from Table 1. below that the size of silica particles formed by using 3-Methacryloxypropyl triethoxysilanewas higher than the one obtained using vinyltriethoxysilane or vinyltrimethoxysilane. It indicated that the alkoxysilane with bulky/ larger substituent group (Methacryloxy propyl group) gave larger particle size than the smaller substituent group. Similarly, it is evident from Table 2 that as the concentration of alkoxysilane used for forming silica dispersion increases the size of the silica particle increases.

Table 1. Effect of alkoxysilane type on size of silica particles:
Alkoxysilane used Average particle size by Malvern Zetasizer Nano ZS (nm)
Vinyltriethoxysilane 63 EXAMPLE-6
3-Methacryloxypropyl triethoxysilane 156 EXAMPLE-7
Vinyltrimethoxysilane 50 EXAMPLE-8

Table 2. Effect of alkoxysilane concentration on size of silica particles:

Concentration of Vinyltrimethoxysilane (%) Average particle size by Malvern Zetasizer Nano ZS (nm)
8 50 EXAMPLE-8
20 135 EXAMPLE-9

It is thus the select and special finding of the present advancement that a stable in-situ functionalized silica dispersion/emulsion comprising in-situ surface functionalized silica dispersion/emulsion could be attained based on the process employing at least one ethylenically unsaturated alkoxysilanes in selective concentrations corresponding to selective levels of anionic and/or non-ionic surfactant together with acid emulsifier as surfactant-cum-catalyst in water also including select sequence and time period based addition methodology, which could in turn provide for silica-organic hybrid latex particles with core-shell structure as emulsions via emulsion polymerization process involving other monomers, which emulsions finds end use and application as binders for aqueous latex paints or can be used alone or in combination with other binders to coat and protect various substrates including wood, paper, plastic, metal, concrete, ceramic.