Field of the invention

The present invention relates to a process for preparing core-shell emulsion polymers. In particular, the present invention relates to a process for preparing core-shell emulsion polymers which comprise significant amount of hydrophobic monomers.

Background

One of the main requirements for protective coatings is the ability to confer water resistance to painted substrates. Current research is aimed to provide more effective barrier properties by increasing the hydrophobic nature of the polymers produced. That, in turn, requires means for effectively and efficiently polymerizing hydrophobic monomers.

Latex paint coatings typically are applied to substrates and dried to form continuous films for decorative purposes and to protect the substrate. Such paint coatings are often applied to architectural interior or exterior surfaces under conditions where the coatings are sufficiently fluid to form a continuous paint film and dry at ambient temperatures. Exterior durability requires a high degree of hydrophobicity to protect the film from water penetration and subsequent coating failure. That, in turn, also requires means for effectively and efficiently polymerizing hydrophobic monomers.

During the process of emulsion polymerization, the monomers diffuse from the monomer emulsion droplet through the water phase to the polymerizing dispersion particle. Normal monomers, like butyl acrylate and styrene, are soluble enough for such a diffusion process and have a low enough transfer barrier at the interface between the monomer droplet and the water phase. However, monomers with long alkyl chains ester (LACE), like stearyl acrylate with hydrophobic Ci8 alkyl chain, can not be polymerized in emulsion as the water solubility is too low and the interfacial resistance at the monomer droplet surface is too high. Therefore only small amounts of stearyl acrylate can be polymerized in emulsion under normal conditions. It is very difficult to copolymerize, and more so to homopolymerize, hydrophobic monomers using known techniques of emulsion polymerization, especially when they make up more than 50% of the polymer composition.

Evidence of this difficulty is the fact that it is very difficult using known techniques to polymerize such monomers to make clean latexes with a reasonable monomer conversion, i.e., latexes should be fairly homogenous and stable and, when filtered through a 250-mesh sieve for example, leave little or no residue or coagulation. German patent DE 1247659B describes a process for emulsion polymerizing octadecylacrylate by using 5% by weight of emulsifier at 50 ^e C for 16 hours in. The monomer conversion was only 40%. Moreover, emulsion was unstable and turned coagulated immediately. That, in turn, also points to the need for means to effectively and efficiently polymerize hydrophobic monomers.

Attempts to make homopolymers of very hydrophobic monomers, such as those of vinyl branched esters, have failed because of very low conversions even if the polymerization is conducted for a long time, e.g. in excess of 48 hours. There is also evidence of a curious inhibition, which is not well understood (Balic, R., deBruyn, H., Gilbert, R. G., Miller, C. M. and Bassett, D. R., "Inhibition and Retardation in Emulsion Polymerization" , Proc. 74 ^th Colloid and Surf. Sci. Symp., Lehigh University, June, p. 19 (2000)).

Many attempts to polymerize said monomers resort to costly techniques such as: use of organic solvents or other monomers to act as solvents for the hydrophobic monomer.

However, recent environmental regulations started to employ more strict measures on volatile organic solvents to require transition to emulsion polymers not to contain organic solvents.

Some attempts resort to the use of macromolecular organic compounds having a hydrophobic cavity; and use of high levels of surfactants. However, these macromolecular organic compounds will reside in the final emulsion and is difficult to be removed. For example, US Patent 5,521 ,266 describes an aqueous polymerization method for forming polymers containing, as polymerized units, at least one monomer having low water solubility, including the steps of:

1) complexing at least one monomer having low water solubility with a macromolecular organic compound having a hydrophobic cavity; and

2) polymerizing in an aqueous system from about 0.1% to about 100%, by weight of the monomer component, based on the total weight of the polymer, of the complexed monomer having low water solubility with from about 0% to about 99.9% by weight, based on the total weight of the polymer, of at least one monomer having high water solubility.

The macromolecular organic compounds with a hydrophobic cavity used in US Patent 5,521 ,266 include cyclodextrins and cyclodextrin derivatives.

US Patent 5,777,003 relates to redispersible polymer powder compositions, which comprise homo- or copolymers of ethylenically unsaturated monomers and cyclodextrins or cyclodextrin derivatives. Polymer dispersions are spray-dried and the resulting powders are formulated into mortar compositions. The flexural tensile strength and the adhesive strength of the mortars are enhanced in the presence of the cyclodextrin-containing dispersion powder, while the compressive strength is only slightly influenced.

The polymerization of stearyl acrylate, a hydrophobic monomer, using methyl-beta- cyclodextrin as a phase transfer agent and dodecyl benzene sulfonate as a surfactant is described by Leyrer, R. J. and Machtle, W. in Macromol. Chem. Phys., 201 , No. 12, 1235- 1243 (2000). Stealyl acrylate is one of the hydrophobic monomers used in the examples of both U.S. Patent 5,521 ,266 and 6,160,049.

Cyclodextrins and chemically modified cyclodextrins are very expensive compared to other components used in emulsion polymerization. In addition, cyclodextrins are water-soluble and their inclusion during the polymerization may impart undesirable properties to the polymer film such as reduced hydrophobicity. In addition, some monomers will be unable to diffuse or penetrate into the interior of the beads resulting in a reduced capacity and the need for larger amounts of cyclodextrins. This, in turn, results in undesirable attributes for the polymer films, brought about by the reduced hydrophobicity, which can be detrimental in coating applications.

U.S. Patent 5,686,518 discloses a polymerization process, referred to as miniemulsion polymerization, for polymerizing monomers and monomer mixtures which are said to be essentially insoluble in water, i.e., which have water solubility ranging from 0 to about 5 weight percent. The monomer or monomer mixture is emulsified to a very small droplet size, smaller than 0.5 microns under high shear, and is subsequently polymerized by conventional means. In order to achieve a miniemulsion, in addition to a surfactant, a polymeric co- surfactant is used at a level of 0.5 wt % to 5 wt % based on monomer. The co-surfactant accomplishes a reduction in monomer droplet size and as a result in latex particle size. Because the co-surfactant prevents monomer transfer from the small monomer droplets to the larger ones (i.e., Ostwald ripening), nucleation of the monomer droplets results in a final latex particle size similar to that of the monomer droplets.

U.S. Patent 6,160,049 discloses an emulsion polymerization process that combines macroemulsion and miniemulsion feed streams for preparing an aqueous polymer dispersion from free-radically polymerizable compounds. The process requires feeding in separate streams a monomer with a solubility of at least 0.001 wt % and a monomer with a solubility of less than 0.001 wt %, and requires emulsification of both monomer streams, The

emulsification of the monomer streams is done using high pressure homogenizers at pressures of up to 1200 bar. However, this peripheral equipment is not commonly found in conventional emulsion polymerization practice.

U.S. Patent No. 6,696,533 discloses an emulsion polymerization process for polymerizing styrene, butyl acrylate and/or acrylonitrite at a temperature higher than 100 °C in the presence of an initiator and a stable N-oxy radical. The stable N-oxyl radical was believed to be a stable free radical agent which does not irreversibly terminate, but merely temporarily block reactive free radical ends of a growing polymer chain at an elevated temperature. This process results in an average molecular weight which grows in proportion with the polymerization conversion such that a polymer having a relatively narrow polydispersity forms. This reference did not investigate the applicability of this process for core-shell emulsion polymers.

Despite the disclosure of the above references, a process is needed that is capable of preparing core-shell emulsion polymers comprising hydrophobic monomers, especially to produce latexes, especially those that are useful for hydrophobic coatings. A process capable of covering the entire monomer solubility range from hydrophobic to extremely hydrophobic monomers would be desired in order to impart the maximum possible hydrophobicity to coatings.

Summary of the invention In one aspect, the present invention provides a process for preparing a core-shell emulsion polymer, the emulsion polymer having a core and at least one shell, the process comprising:

A) polymerizing in emulsion at least one core monomer to form a core;

B) polymerizing in emulsion at least one shell monomer to form at least one shell, the at least one shell monomer is a hydrophobic monomer or a shell monomer composition comprising at least 10 wt% of at least one hydrophobic monomer, based on the weight of the shell monomer composition, the hydrophobic monomer having a water solubility not greater than 0.1 g/100 g water at 20 °C; wherein at least one step is conducted at a high temperature of 95-200 °C. In another aspect, the present invention provides a core-shell emulsion polymer obtained from the process of the present invention.

In a third aspect, the present invention provides a use of the core-shell emulsion polymer of the present invention in preparing coatings.

Detailed description of the invention

As used herein, the hydrophobic monomer has a water solubility not greater than 0.1 g/100 g water at 20 "C. Water solubility of monomers depends on their structures and polarities, also on temperature and for gaseous monomers on pressure. Hydrophobic monomers usually have lower polarity and hydrogen bond index, comparing to hydrophilic monomers having ionizable groups (such as acid, alkali and salt) or groups having higher polarity and hydrogen bond index.

Preferably, the hydrophobic monomer has a water solubility not greater than 0.02 g/100 g water, more preferably not greater than 0.01 g/100 g water, at 20 °C.

Although water solubility is not always a linear function of temperature, high temperature can increase diffusivity for low polar and non-polar monomers. By elevating temperature, it is possible to increase saturation concentration of hydrophobic monomers in water, which makes it possible for emulsion polymerizing hydrophobic monomers. Therefore, ultra high shear or ultrasound is not necessarily required to form ultra fine droplets for preparing monomer pre-emulsion in the present invention.

Preferably, the hydrophobic monomer is one or more selected from esters of (meth)acrylic acid, (meth)acrylamides, vinyl esters and partly or fully halogenated and/or silicon substituted substances of above mentioned monomers. More preferably, the hydrophobic monomer is one or more selected from alkyl (meth)acrylates, aryl (meth)acrylates, aralkyl (meth)acrylates, alkyl aryl (meth)acrylates, halothane (meth)acrylates, silane (meth)acrylates, flurosilane (meth)acrylates, alkyl acyloxy vinyl esters, fluothane acyloxy vinyl esters, silane acyloxy vinyl esters and vinyl silanes.

Example of the above hydrophobic monomers includes C _¾ -C ₄ a, preferably C ₁₀ -C24, more preferably C ₁₃ -C ₂₂ alkyl (meth)acrylates, C _e -C ₄₀ , preferably C ₁₂ -C ₂ 4, more preferably C ₁₃ -C ₂₂ alkyl acyloxy vinyl esters, C ₈ -C ₄ o, preferably Ci ₂ -C ₂ 4, more preferably C ₁₃ -C ₂₂ halothane (meth)acrylates, silane (meth)acrylates and flurosilane (meth)acrylates.

In some embodiments of the present invention, the hydrophobic monomer is one or more selected from hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethyl hexyl (meth)acrylate, n- octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, lauryl (meth)acrylate, tetradecyl (meth)acrylate, 2-methyl-7-ethyl-4-undecyl (meth)acrylate, cetyl (meth)acrylate, oleyl (meth)acrylate, stearyl (meth)acrylate, eicosyl (meth)acrylate , behenyl (meth)acryJate, cetyl-eicosyl (meth)acrylate, benzyl (meth)acrylate, phenylethyl (meth)acrylate, m-tolyl (meth)acrylate, o-tolyl (meth)acrylate, p-tolyl (meth)acrylate, (3-methoxyphenyl)methyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, 2-naphthyl (meth)acrylate, 2-(2- naphtbyloxy)ethyl (meth)acrylate, 9-anthracenyl (methyl)acrylate, 1-methylcyclohexyl (meth)acrylate, 1-methylcyclopentyl (meth)acrylate, isobornyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, 2-ethyl-2- adamantyl (meth)acrylate, 3-hydroxy-1-adamantyl (meth)acrylate, 3,5-dimethyladamantyl (meth)acrylate, 3,5-diethyladamantyl (meth)acrylate, 2-(4-(1-methyl-1- phenylethyl)phenoxy)ethyl (meth)acrylate, 3a,4,5,6,7,7a-hexahydro-4,7-methano-1 H-indenyl acrylate, 4-(meth)acryloyloxybenzo-phenone, 2-phenylphenoxyethyl (meth)acrylate, cyclohexyl (meth)acrylate, cyciododecyl (meth)acrylate, 4,7-methanooctahydro-1 h-indene-5- yl (meth)acrylate, triethylvinylsilane, trimethylvinylsilane, triphenoxyvinylsilane, vinyl tris(trimethylsiloxy)silane, 3-chloropropydimethylvinylsilane, (1-fluoro- vinyl)methyldiphenylsilane, 1 ,2,2-trifluorovinyl-triphenylsilane, (meth)acryl- oxymethyltris(trimethylsiloxy)silane. Preferably, step B) is conducted at the high temperature.

More preferably, both steps A) and 8) are conducted at the high temperature.

Preferably, the high temperature is 95-180 °C, more preferably 100-170 °C, particularly preferably 120-140 °C.

Preferably, the shell monomer composition comprises at least 20 wt%, more preferably at least 40 wt%, particularly preferably at least 50 wt% of the hydrophobic monomer, based on the weight of the shell monomer composition.

Preferably, at least one core monomer is a core monomer composition comprising not greater than 70 wt%, more preferably not greater than 50 wt%, and particularly preferably not greater than 30 wt% of the hydrophobic monomer, based on the weight of the core monomer composition.

Preferably, the solvent for the emulsion polymerization is an aqueous solvent, more preferably consists of water substantially, and particularly preferably is water.

Preferably, the emulsion polymer comprises one core and one shell.

Preferably, the weight ratio of the core to the shell is 10-90 to 90-10, more preferably 30-70 to 70-30, and particularly preferably 40-60 to 60-40. Optionally, the core or shell monomer composition can include at least one crosslinker.

Suitable crosslinkers include comonomers containing at least two addition polymerizable vinylidene groups and are alpha, beta ethylenically unsaturated monocarboxylic acid esters of polyhydric alcohols containing 2-3 ester groups. Such comonomers include alkylene glycol diacylates and dimetyacryiates, such as ethylene glycol di(meth)acrylate, 1 ,3-butylene glycol di(meth)acrylate, 1 ,4-butylene glycol di(meth)acrylate, 1 ,6-hexanene glycol di{meth)acrylate, propylene glycol di{meth)acrylate, polyethylene glycol di(meth)acrylate and triethylene glycol di(meth)acrylate; 1 ,3-glycerol di(meth)acrylate; 1 ,1 ,1-trimethylol propane di(meth)acrylate; 1 ,1 , 1-trimethylol ethane di(meth)acrylate; pentaerythritol tri(meth)acrylate; 1 ,2,6-hexane tri(meth)acrylate; sorbitol penta(meth)acrylate; methlene bis-(meth)acrylamide, divinyl benzene, vinyl (meth)acrylate, vinyl crotonate, vinyl acetylene , trivinyl benzene, triallyl cyanurate, divinyl acetylene, divinyl ethane, divinyl sulfide, divinyl ether, divinyl sulfone, diallyl cyanamide, ethylene glycol divinyl ether, dially phthalate, divinyl dimthyl silane, glycerol trivinyl ether, divinyl ahipate; dicyclopentenyl(meth)acrylate;

dicyclopentenyloxy(meth)acrylate; unsaturated esters of glycol monodicyclopentenyl ethers; allyl esters of alpha, beta-unsaturated mono- and dicarboxylic acids having terminal ethylenic unsaturation including allyl methacrylate, allyl acrylate, diallyl maleate, diallyl fumarate and diallyl itaconate.

In some embodiments of the present invention, the shell monomer composition comprises: a) 0-70 wt%, preferably 20-60 wt% of at least one monomer selected from C1-C4 alkyl (meth)acrylates, b) 30-100 wt%, preferably 40-80 wt% of at least one monomer selected from C ₁₂ -C ₂ 4, preferably C ₁₃ -C ₂₂ alkyl (meth)acrylates, and partly or fully halogenated and/or silicon substituted substances thereof.

In some embodiments of the present invention, at least one core monomer is a core monomer composition comprising: a) 30-80 wt%, preferably 40-70 wt% of at least one monomer selected from C1-C4 alkyl (meth)acrylates, b) 20-70 wt%, preferably 30-60 wt% of at least one monomer selected from C ₁₂ -C ₂ 4, preferably Ci ₂ -C ₂₂ alkyl (meth)acrylates, and partly or fully halogenated and/or silicon substituted substances thereof.

In some embodiments of the present invention, either or both of the core and shell monomer composition further comprises c) 0-50 wt%, preferably 0-10 wt% of at least one monomer selected from (meth)acrylic acid, hydroxyl esters, poly(alkylene glycol) ether esters, C,-C ₅ alkyl terminated poly(alkylene glycol) ether esters, glycidyl esters, and alkyl tertiary amine esters of (meth)acrylic acid; (meth)acrylamide, N-alkylol (meth)acrylamide, N-alkyl tertiary amine (meth)acrylamide; salt of alkyl tertiary amine esters of (meth)acrylic acid and N-alkyl tertiary amine

(meth)acrylamide; C,-C ₅ alkyl acyloxy vinyl esters; vinyl siloxane, (meth)acyloxy siloxane; self crosslinkable monomers, such as diacetone acrylamide and acetoacetoxyethyl methacrylate; and polyethylenically unsaturated monomers.

Polymerization is usually effected using at least one initiator. At least one initiator may be a peroxide. Examples of suitable peroxides are alkali metal peroxodisulfates such as, for example, potassium peroxodi sulfate, sodium peroxodisulfate, ammonium peroxodisulfate, hydrogen peroxide, organic peroxides, such as diacetyl peroxide, di-tert-butyl peroxide, diamyl peroxide, dioctanoyl peroxide, didecanoyl peroxide, dilauroyl peroxide, dibenzoyl peroxide, bis(o-toluoyl) peroxide, succinyl peroxide, tert-butyl peracetate, tert-butyl permaleate, tert-butyl perisobutyrate, tert-butyl perpivalate, tert-butyl peroctanoate, tert-butyl perneodecanoate, tert-butyl perbenzoate, di-tert-butyl peroxide, tert-butyl hydroperoxide, cumyl hydroperoxide, tert-butyl peroxy-2-ethylhexanoate and diisopropyl peroxidicarbamate. Azo compounds, such as, for example, azobisisobutyronitrile, 1-[{1 -cyano-1- methylethyl)aLZo]formamide, 2,2'-azobis{2-methyl-N-[2-(1 -hydroxybutyl)]propionamide}, 2,2 - azobis[2-methyl-N-(2-hydroxyethyl)-propionamide], 2,2'-azobis{2-methyl-N-[1 ,1- bis(hydroxymethyl)-2-hydroxyethyl]propionamide}, 2,2'-azobis(1-imino-1-pyrrolidino-2- methylpropane)dihydrochloride, azobis(2-amidopropane) dihydrochloride and 2,2'-azobis(2- methylbutyronitrile) are also suitable. Redox initiators are likewise suitable, for example comprising peroxides and oxidizable sulfur compound. Systems comprising acetone bisulfite and organic peroxide, such as tert-C Hg- OOH, Na ₂ S ₂ 0 ₅ (sodium disulfite) and organic peroxide, such as tert-C ₄ H ₉ -OOH or HO- CH ₂ S0 ₂ Na, and organic peroxide, such as tert-CHg-OOH, can be used. Systems such as ascorbic acid/H ₂ 0 ₂ can also be used.

Macro initiators having same or similar initiating groups as the above mentioned compounds can also be used. Macro initiators are, for example, 4,4'-(1 ,2-diazenediyl)bis[4-cyano-, polymer with a-hydro^-hydroxypoly(oxy-1 ,2-ethanediyl) pentanoic acid, (VPE0201 , VPE0401 , and VPE0601 , all from Wako Pure Chemical Industries, Ltd., CAS No.: 105744- 24-9), 4,4'-azobis[4-cyano-, polymer with a-[(3-aminopropyl)dimethylsilyl]-uj-[[(3- aminopropyl)dimethyl-silyl]oxy]poly[oxy(dimethylsilylene)] pentanoic acid (VPS0501 and VPS1001 , both from Wako Pure Chemical Industries, Ltd., CAS No.: 158947-07-0).

It is possible to use at least one emulsifier which may be anionic, cationic or nonionic.

Customary nonionic emulsifiers are, for example, ethoxylated mono-, di- and trialkylphenols (degree of ethoxylation: 3 to 50, alkyl radical: C ₄ -C ₁₂ ) and ethoxylated fatty alcohols (degree of ethoxylation: 3 to 80; alkyl radical: C ₈ -C ₃₅ ). Examples are Emulsogen®, Genapol® and Sapogenat® from Clariant, Lutensol® from BASF and Triton® from Dow. Emulsification capability is usually affected and limited by cloud point for nonionic emulsifiers.

Consequently, nonionic emulsifiers can be selectively comprised in recipe, or used as post- add after polymerization. Nevertheless, those ones with high cloud point are preferable for high temperature polymerization.

Customary anionic emulsifiers are, for example, alkali metal and ammonium salts of alkyl sulfates (alkyl radical: C ₈ to Ci ₂ ), of sulfuric acid monoesters of ethoxylated alkanols (degree of ethoxylation: 4 to 50, alkyl radical: C ₄ -C ₁₈ ) and of ethoxylated alkylphenols (degree of ethoxylation: 4 to 50, alkyl radical: C ₄ -Ci ₈ ), of alkanesulfonic acids (alkyl radical: C ₄ -Ci ₈ ), of alkylarylsulfonic acids (alkyl radical: C ₉ -Ci ₃ ), and of ethoxylated alkanols (degree of ethoxylation: 4 to 50, alkyl radical: C -C ₁₈ ) phosphorous acids.

Suitable cationic emulsifiers are as a rule primary, secondary, tertiary or quaternary ammonium salts having a C ₆ -C ₁₈ -alkyl, C ₆ -Ci _B -aralkyl or heterocyclic radical,

alkanolammonium salts, pyridinium salts, imidazolinium salts, oxazolinium salts,

morpholinium salts, thiazolinium salts and salts of amine oxides, quinolinium salts, isoquinolinium salts, tropylium salts, sulfonium salts and phosphonium salts.

Dodecylammonium acetate or the corresponding hydrochloride, the chlorides or acetates of various 2-(N,N,N-trimethylammonium)ethylparaffinic acid esters, N-cetylpyridinium chloride, N-laurylpyridinium sulfate and N-cetyl-N,N,N-trimethylammonium bromide, N-dodecyl-N,N,N- trimethylammonium bromide, N,N-distearyl-N,N-dimethyl-ammonium chloride and the Gemini surfactant N,N-(lauryldimethyl)ethylene-diamine dibromide may be mentioned by way of example. Numerous further examples appear in H. Stache, Tensid-Taschenbuch, Carl- Hanser-Verlag, Munich, Vienna, 1981 , and in McCutcheon's, Emulsifiers & Detergents, MC Publishing Company, Glen Rock, 1989.

Reactive emulsifiers or polymerizable emulsifiers, can also be used to form stable emulsion in the present invention. These emulsifiers have polymerizable groups like unsaturated ethylene groups and can be incorporated into the final polymer. Examples of these emulsifiers include sodium ethylenesulphonate, 2-acrylamido-2-methyl-1-propanesulfonic acid sodium salt, 3-allyloxy-2-hydroxy-1 -propanesulfonic acid sodium salt, polyethylene glycol (meth)acrylate.

In the polymerization reaction of the polymerizable monomers, a chain transfer agent may be incorporated with a purpose of controlling the molecular weight. The chain transfer agent is preferably an aromatic compound or a mercaptan, particularly preferably an alkyl mercaptan. As specific examples of the chain transfer agent, n-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, stearyl mercaptan and α-methylstyrene diner. Further additives which are customary in emulsion polymerization may be added to the reaction mixture, for example glycols, polyethylene glycols, protective colloids and buffer/pH regulators.

A duration in the range from 30 minutes to 12 hours, preferably from 2 to 8 hours, may be chosen as the duration for the emulsion polymerization.

In an embodiment of the present invention, a post polymerization is effected, for example by addition of initiator which is identical or different from the initiator used in the actual copolymerization.

In an embodiment of the present invention, the emulsion polymerization takes place substantially completely.

The emulsion polymerization process of the present invention can achieve high hydrophobic monomer conversion, preferably more than 95%, and up to 100%. Thus the incorporation of hydrophobic monomers in the final polymer can be significantly increased.

Preferably, the emulsion polymer obtained from the process of the present invention is used in preparing water resistant coatings.

The present invention is advantageous in that it provides a novel and feasible method to polymerize hydrophobic monomers into core-shell emuslion polymers. Apart from other costly techniques, high polymerization temperature makes transfer barrier low enough for hydrophobic monomers. Even larger quantities of the very hydrophobic monomers could be polymerized. These emulsion polymers and coating composition thereafter get much lower or even no VOC and no hydrophilic macro-molecular compounds like cyclodextrin. Moreover, core-shell polymer refers to the morphology of the final polymer particles. The core refers to the polymer formed by polymerizing additional monomers in the presence of the polymer formed in the first step. The monomers for the core may be varied from those of the shell to provide a core having varied characteristics from the shell. Such variations include differing hardnesses by using monomers with different glass transition temperatures, varying polarity, molecular weights of the core and shell, and include hydrophobicity of polymers.

The present invention is also advantageous in that it provides a multi-stage polymer with hydrophobic monomer in core or/and shell to achieve a high level of hydrophobicity and high tolerance to solvent.

Examples

1. Chemicals

1.1 Initiators

Abbreviation Description

APS Ammonium persulfate

1-[(1 -cyano-1 -methylethyl)azo]formamide,

V30

commercially available from Wako Pure Chemical Industries, Ltd.

1.2 Emulsifiers

Abbreviation Description

Emulsogen'"' EPA Anionic emulsifier,

073 commercially available from Clariant International Ltd.

Nonionic emulsifier,

Genapol ^® X 307

commercially available from Clariant International Ltd.

1.3 Monomers

1.4 Neutralizing agent

Ammonia

2. Water solubility test for monomers Water solubility for the above monomers was measured at 20 °C with deionized water as solvent. The solubility values were determined by Gas Chromatography and expressed as g/100 g water as below.

methacrylic acid: 8.9; methyl methacrylate: 1.59; n-butyl acrylate: 0.15; hodroxypropyl methacrylate: 10.7 ; Visiomer ^® C ₁₃ -MA: <0.001 ; Visiomer ^® C _17. «-MA: <0.001.

3. General process for emulsion polymerization

(1) A 1 -liter, jacketed pressure reactor was equipped with a paddle stirrer, a thermometer, a nitrogen inlet, a feeding line, a vent valve and a pressure meter (including a pressure relief system). Air in the kettle was replaced by nitrogen gas before experiment.

(2) As indicated in Table 1 , deionized water (DW) was charged into the reactor vessel and heated to 80-135 °C. Then, a mixture comprising DW, part of the initiator solution, one or more emulsifiers was charged to the kettle. The mixture was stirred for 15 minutes. (3) As indicated in Table 2, a monomer pre-emulsion (Core) prepared by mixing DW, one or more emulsifiers, and several monomers was then pumped into the kettle. The monomer mixture was fed for hours to form core polymer, together with a co-feed of initiator solution. After that, the mixture was held for another 0.5-1.5 hours. For comparative examples with no core-shell structure, all the monomers were pumped together during one feeding period.

(4) As indicated in Table 3, a monomer pre-emulsion (Shell) prepared by mixing DW, one or more emulsifiers, and several monomers was then pumped into the kettle. The monomer mixture was fed for hours to form shell polymer, together with a co-feed of initiator solution. After that, the reaction mixture was stirred for 0.5-1 hour.

(5) As indicated in Table 4, a chaser solution was prepared and charged to the kettle. The reaction mixture was stirred for another 1-2 hours for post-polymerization. Then the mixture was cooled to room temperature, neutralized by acid or alkali, and filtered to remove any coagulation formed.

Coagulum weight, solid content, viscosity, particle size, of Examples were calculated or measured. The resufts are reported in Table 5. For comparative example 4 and 5, polymerization was conducted at much low temperature. They were not stable with a much higher coagulum about 30-40%. These emulsion polymers were not suitable for performance evaluation.

4. Performance test for the resulting emulsion polymer

4.1 Water absorption and weight loss Water absorption is the percentage of water absorbed by the films, which represents the ability of water resistance. This value was measured by preparing a 3 ^* 3 cm ² film from the emulsions, keeping the film in water at room temperature for two days. Water absorption was calculated from the weight up-taken of film during the time. And weight loss was measured by calculating the percentage of weight loss of the film after it was dried at 80 °C for 4-6 hours. The results are reported in Table 6.

4.2 Solvent resistance

The emulsion polymers were drawn down on aluminum panels with a thickness of 150 μηι. The panels were heated up at 1 5 °C for 25 minutes. Then coatings with a thickness of 30- 40 μηη were obtained.

0.7g cotton wool absorbing 5g test liquid (brake fluid, diesel oil, 20% 2-propanol or 7% n- butanone) was placed on the testing coating. A watch glass was put on the cotton wool and a loaded weight 500g was added onto the watch glass for 15 min. Then the watch glass and cotton wool were removed. The coatings were dried for 24h in the air.

Hardness of the coatings was measured in a hardness tester (BYK pendulum hardness tester with Konig Pendulum) before and after the treatment. Hardness loss was calculated. The result is reported in Table 7.

Cross-cut test was also performed according to ISO 2409-2007. Lattice patterns were made on the coatings with a multi-cut tool (BYK Gardner, Model D-5120). Permacel tape was attached to the cross-cut area and then removed. The cross-cut area was observed through an illuminated magnifier and classified based on criteria indicated in Table 8. And the result is reported in Table 9.

Emulsion polymers with high hydrophobic monomers content can be successfully prepared by the present invention. Examples in 1-6 have a water absorption less than 0.5% after 2 days. Comparative example 1 with no hydrophobic monomer has a water absorption of 1.20%. Examples 1 and 4 have the same formulation as comparative examples 2 and 3. However, Examples 1 and 4 with core-shell structure show better water resistance than comparative examples 2 and 3. When hydrophobic monomers were polymerized into emulsion by core shell technology, the polymers show better water resistance.

Core-shell polymers with hydrophobic monomers in their composite also show better resistance to solvent, like brake fluid, diesel oil, 20% 2-propanol and 7% n-butanone. From the results of hardness loss after the treatment with test liquid, hydrophobic monomers in core or shell gave high barrier for solvent to penetrate into test coatings. These polymers have a hardness loss of less than 20%, particularly less than 15% in example 1-3. Cross-cut test shows coatings still have good adhesion to substrate with a cross-cut rating about 2-3 generally after test, only Example 5 got grade 4 to 7% butanone and Example 6 got grade 4 to 20% 2-propanol.

Table 1 Pre-charge to the reactor

Table 2 Pre aration of the core

Table 3 Pre aration of the shell

Table 4 Post ol merization and neutralization

Table 5 Index of emulsion roducts

Table 6 Water resistance test

Table 7 Hardness loss in solvent resistance test

Table 8 Classification criteria for cross-cut test result

Appearance of surface of crosscut

Classification Description area from which flaking has occurred

(Example for six parallel cuts)

The edges of the cuts are

0 completely smooth; none of the - squares of the lattice is detached.

Detachment of small flakes of the

coating at the intersections of the

1

cuts. A cross-cut area not greater

than 5 % is affected.

The coating has flaked along the 1 edges and/or at the intersections of ^■ +

2 the cuts. A cross-cut area greater ■ - >

than 5 %, but not greater than

15 %, is affected. it

The coating has flaked along the

edges of the cuts partly or wholly in I large ribbons, and/or it has flaked

3 partly or wholly on different parts of

the squares. A cross-cut area

greater than 15 %, but not greater I than 35 %, is affected.

The coating has flaked along the

edges of the cuts in large ribbons I ) 1

and/or some squares have

4

detached partly or wholly. A crosscut area greater than 35 %, but not TT i

greater than 65 %, is affected.

Any degree of flaking that cannot

5 even be classified by classification - 4.