Field

[0001] The present invention relates to methods of emulsion polymerization of at least one ethylenically unsaturated monomer in the presence of an aqueous phase comprising a water soluble chitosan salt and at least one co-stabilizer. The present invention also relates to an aqueous dispersion prepared by emulsion polymerization of at least one ethylenically unsaturated monomer in the presence of an aqueous phase comprising a water soluble chitosan salt and at least one co- stabilizer. The present invention further relates to emulsion polymers and adhesives, binders or coatings containing the emulsion polymers.

Background

[0002] Emulsion polymerization is a free-radical polymerization that is generally conducted in the presence of at least one monomer, at least one stabilizer, an initiator, and a continuous phase, typically water. The stabilizer may be an emulsifier or protective colloid, used to prevent agglomeration of particles within the emulsion and to affect viscosity and rheology. Protective colloids are preferably water-soluble and non-ionic. Known protective colloids include natural polymers, modified-natural polymers, and synthetic polymers.

[0003] Chitosan is a linear polysaccharide containing randomly distributed β-(1 - 4) linked D-glucosamine and N-acetyl-D glucosamine. It is produced through the deacetylation of chitin, the structural element in the exoskeleton of crustaceans. Chitosan is abundant in nature, is biodegradable, and has low potential for toxicity. Chitosan has been used in the agricultural, medical, and winemaking fields. See, for example, U.S. Pub. Nos. 2006/0171999 and 2002/0143081 .

[0004] However, due to its low water solubility and the expectation of only moderate emulsion stabilization, chitosan has not been pursued as an emulsion polymerization stabilizer. Instead, chitosan is added after polymerization. For example, U.S. Pat. No. 5,01 1 ,864 discloses a water absorbent latex polymer produced by the process of combining a foamed latex polymer product with both a water absorbent polymer and chitin, and drying that blend to form a foamable latex polymer containing both water absorbent polymer and chitin. U.S. Pat. No. 7,736,423 teaches an aqueous composition for outdoor, indoor, fagade and roof paints having a biocidal action. The composition comprises chitosan, chitosan derivatives, or combinations thereof, and is formed by mixing silver nitrate and chitosan to an aqueous dispersion. WO 2012/015863 teaches a low-formaldehyde binder composition for increasing wet and dry tensile strength of a nonwoven substrate, including an aqueous vinyl acetate ethylene copolymer dispersion employing a nonionic, cationic or amphoteric dispersion stabilizer, chitosan, and one or more surfactants not including the dispersion stabilizer. The chitosan is added to the copolymer dispersion after the copolymer dispersion is formed. Similar additions of chitosan after the formation of a polymer are taught in U.S. Pat. No. 8,349,343.

[0005] The need exists for emulsion polymerization processes that use an abundant modified-natural stabilizer during the polymerization process. In particular, the need exists for a chitosan derivative that may be used for its stabilizing properties during emulsion polymerization and that is retained with the polymer for use in end products.

Summary

[0006] In a first embodiment, the present invention is directed to a method of emulsion polymerization of at least one ethylenically unsaturated monomer selected from the group consisting of esters of ethylenically unsaturated monocarboxylic and dicarboxylic acids, vinyl esters, C2-C4 olefins, vinyl halides, and vinyl aromatics, the method comprising: a) forming an aqueous phase comprising conducting the emulsion polymerization in the presence of an aqueous phase comprising: i) a water soluble chitosan salt having a degree of deacetylation of chitosan of less than 95 mol.%; and ii) at least one co-stabilizer. The water soluble chitosan salt may be prepared by converting chitosan to a water soluble salt in the presence of water and a chitosan salt forming acid. The chitosan salt forming acid may be selected from the group consisting of C1 -C18 monocarboxylic acids (such as formic acid, acetic acid and propionic acid or higher acids, acetylsalicylic acid, amino acids, adipic acid, ascorbic acid, aspartic acid, citric acid, iminodiacetic acid, itaconic acid, maleamic acid, fumaric acid, glyoxylic acid, glycolic acid, glutamic acid, glutaric acid, lactic acid, maleic acid, malonic acid, N-acetylglycine, nicotinic acid, 2-pyrrolidone-5-carboxylic acid, pyruvic acid, salicylic acid, succinamic acid, succinic acid, tartaric acid, thioacetic acid, thiolactic acid, sulfonyldiacetic acid, thiodiacetic acids and thioglycolic acids, and combinations thereof. The aqueous phase may further comprise a water soluble chain transfer agent. In some embodiments, the water soluble chain transfer agent is a co-acid used to form the chitosan salt. The pH of the aqueous phase may be less than 5. The at least one co-stabilizer may be present in an amount from 0.01 to 20 wt.%, based on the total weight of the at least one monomer. The co-stabilizer may be an emulsifier and/or a protective colloid having a neutral or positive charge. The co- stabilizer may be selected from the group consisting of polyvinyl alcohols, modified polyvinyl alcohols, polyethylene glycols, polyvinyl acetals, polyvinylpyrrolidones, polysaccharides or modified polysaccharides in water soluble form, proteins and other polymers of natural origin, synthetic polymers; polyurethane stabilizers, nonionic emulsifiers and cationic emulsifiers. In some embodiments, the co- stabilizer is polyvinyl alcohol. The aqueous phase may comprise at least 0.2 wt.% water soluble chitosan salt, or from 0.2 to 5 wt.% water soluble chitosan salt based on the total weight of the at least one monomer. The water soluble chitosan salt may be selected from the group consisting of chitosan acetate, chitosan propionate, chitosan lactate and other salts with solubility of greater than or equal to 1 % in aqueous solution. The chitosan salt used in the aqueous phase may have a viscosity of less than 1000 mPa ^» s in 1 % aqueous solution. The emulsion polymerization may be performed in the presence of an initiator. The initiator may be present in an amount of at least 0.05 wt.%, based on the total weight of the at least one monomer. The initiator may be a thermal initiator or a redox initiator. The initiator may be a persulfate. The emulsion polymerization may be performed in the presence of a functional co-monomer. The emulsion polymerization may be performed at a temperature from 30 to 100°C and at a pressure from 10 to 10,000 kPa.

[0007] The emulsion polymer formed by the method described herein may be used in an adhesive, binder or coating. The emulsion polymer may also be used in agricultural coating formulations, in pharmaceutical or medical formulations, and/or in formulations for treating waste water. [0008] In a second embodiment, the present invention is directed to an aqueous dispersion prepared by emulsion polymerization of at least one ethylenically unsaturated monomer selected from the group consisting of esters of ethylenically unsaturated monocarboxylic and dicarboxylic acids, vinyl esters, C2-C4 olefins, vinyl halides, and vinyl aromatics, wherein the emulsion polymerization is conducted in the presence of an aqueous phase comprising a water soluble chitosan salt and a co-stabilizer. The aqueous dispersion may comprise from 20 to 70% solids. The aqueous dispersion may have a pH of less than 5 or of less than 4.

[0009] In a third embodiment, the present invention is directed to an emulsion polymer prepared by emulsion polymerization of at least one ethylenically unsaturated monomer selected from the group consisting of esters of ethylenically unsaturated monocarboxylic and dicarboxylic acids, vinyl esters, C2-C4 olefins, vinyl halides, and vinyl aromatics, wherein the emulsion polymerization is conducted in the presence of an aqueous phase comprising a water soluble chitosan salt having a degree of deacetylation of chitosan of less than 95 mol.% and at least one co-stabilize.

[0010] In a fourth embodiment, the present invention is directed to an adhesive, binder or coating containing the emulsion polymer prepared by emulsion polymerization of at least one ethylenically unsaturated monomer selected from the group consisting of esters of ethylenically unsaturated monocarboxylic and dicarboxylic acids, vinyl esters, C2-C4 olefins, vinyl halides, and vinyl aromatics, wherein the emulsion polymerization is conducted in the presence of an aqueous phase comprising: i) a water soluble chitosan salt having a degree of deacetylation of chitosan of less than 95 mol.% and a co-stabilizer.

Detailed Description

[0011] In general, this invention relates to emulsion polymerization conducted in the presence of a water soluble chitosan salt, and products produced therefrom. In particular, this invention relates to emulsion polymerization of at least one ethylenically unsaturated monomer in the presence of an aqueous phase formed by combining a water soluble chitosan salt with at least one co-stabilizer. The water soluble chitosan salt may have a degree of deacetylation of chitosan of less than 95 mol.%. The at least one ethylenically unsaturated monomer may be selected from the group consisting of esters of ethylenically unsaturated monocarboxylic and dicarboxylic acids, vinyl esters, C2-C4 olefins, and vinyl aromatics.

[0012] This invention also relates to an aqueous dispersion prepared by emulsion polymerization of at least one ethylenically unsaturated monomer, wherein the emulsion polymerization occurs in the presence of a water soluble chitosan salt and a co-stabilizer. This invention further relates to an adhesive, binder or coating composition containing the emulsion polymer prepared by the emulsion polymerization methods described herein. Advantageously, the present invention provides an industrially feasible emulsion polymerization method using a water soluble chitosan salt as a stabilizer.

[0013] As described herein, the first step in the emulsion polymerization method is the formation of an aqueous phase comprising a water soluble chitosan salt and at least one co-stabilizer. These components, and other optional components of the aqueous phase, are described below.

Water Soluble Chitosan Salt

[0014] The water soluble chitosan salt may be selected from the group consisting of chitosan acetate, chitosan propionate, chitosan lactate, and other chitosan salts having a solubility of greater than or equal to 1 % in aqueous solution.

[0015] The water soluble chitosan salt may be prepared by converting chitosan to a water soluble salt in the presence of water and a chitosan salt forming acid. Methods for converting chitosan to a chitosan salt are disclosed in U.S. Pat. Nos. 2,040,979 and 2,040,880, the entire contents and disclosures of which are hereby incorporated by reference. The chitosan salt forming acid may be an organic acid or an inorganic acid. In some embodiments, the chitosan salt forming acid is an organic acid. The chitosan salt forming acid may be selected from the group consisting of acetic acid, propionic acid, higher carboxylic acids, acetylsalicylic acid, amino acids, adipic acid, ascorbic acid, aspartic acid, citric acid, iminodiacetic acid, itaconic acid, formic acid, maleamic acid, fumaric acid, glyoxylic acid, glycolic acid, glutamic acid, glutaric acid, lactic acid, maleic acid, malonic acid, N-acetylglycine, nicotinic acid, nicotinic acid, 2-pyrrolidone-5-carboxylic acid, pyruvic acid, salicylic acid, succinamic acid, succinic acid, tartaric acid, thioacetic acid, thiolactic acid, sulfonyldiacetic acid, thiodiacetic acids and thioglycolic acids, and combinations thereof. [0016] The water soluble chitosan salt may have a degree of deacetylation of less than 95 mol.%, e.g., less than 93 mol.%. In terms of ranges, the water soluble chitosan salt may have a degree of acetylation from 75 to 95 mol.%, e.g., from 75 to 93 mol.%. The water soluble chitosan salt may have a water solubility from 0.5 to 5 %.

[0017] The water soluble chitosan salt may be provided in solution and may have a viscosity at 1 wt.% strength at 20°C of less than 1000 mPa ^» s, e.g., less than 500 mPa s or less than 100 mPa s. In terms of ranges, the viscosity at 1 wt.% strength at 20°C may range from 1 to 1000 mPa-s, e.g., from 10 to 500 mPa-s or from 20 to 100 mPa-s. The molecular weight of the water soluble chitosan salt may be selected to achieve this viscosity. The water soluble chitosan salt solution may have a pH of less than 5.

[0018] To form the aqueous phase, further described herein, the water soluble chitosan salt may be added to water (e.g., demineralized) in a single charge or in multiple charges. The aqueous phase may comprise at least 0.2 wt.% water soluble chitosan salt, based on the total weight of the at least one monomer, e.g., at least 0.5 wt.%, at least 1 wt.%, at least 2 wt.%, or at least 3 wt.%. In terms of ranges, the aqueous phase may comprise from 0.2 to 5 wt.% water soluble chitosan salt, based on based on the total weight of the at least one monomer, e.g., from 0.5 to 4 wt.% or from 1 to 3 wt.%.

Co-Stabilizer

[0019] The aqueous phase further comprises at least one co-stabilizer. In some embodiments, the co-stabilizer is an emulsifier and/or a protective colloid having a positive or neutral charge. In some embodiments the co-stabilizer is selected from the group consisting of polyvinyl alcohols, modified polyvinyl alcohols, polyethylene glycols, polyvinyl acetals, polyvinylpyrrolidones, polysaccharides or modified polysaccharides in water soluble form, proteins and other polymers of natural origin, synthetic polymers; polyurethane stabilizers, nonionic emulsifiers, cationic emulsifiers and combinations thereof. Generally, the co-stabilizer may be present from 0.01 to 20 wt.%.

[0020] Examples of nonionic emulsifiers include, but are not limited to, acyl, alkyl, oleyl, and alkylaryl oxyethylates. These products are available commercially, for example, under the name Genapol®, Emulsogen® or Lutensol®. They include, for example, ethoxylated mono-, di-, and tri-alkylphenols (EO degree: 3 to 80, alkyl substituent radical: C ₄ to C12) and also ethoxylated fatty alcohols (EO degree: 3 to 80; alkyl radical: Cs to C36), especially C12-C14 fatty alcohol (3-80)ethoxylates, C13C15 oxo-process alcohol (3-80)-ethoxylates, C16C18 fatty alcohol (1 1 - 80)ethoxylates, C10 oxo-process alcohol (3-80)ethoxylates, Ci 3 oxo-process alcohol (3-80)ethoxylates, polyoxyethylenesorbitan monooleate with 20 ethylene oxide groups, copolymers of ethylene oxide and propylene oxide with a minimum ethylene oxide content of 10% by weight, the polyethylene oxide (4-80) ethers of oleyl alcohol, and the polyethene oxide (4-80) ethers of nonylphenol. Especially suitable are the polyethylene oxide (4-80) ethers of fatty alcohols, more particularly of oleyl alcohol. Mixtures of nonionic emulsifiers can also be used.

[0021] Cationic emulsifiers include, but are not limited to, alkyl quaternary ammonium salts and alkyl quaternary phosphonium salts such as: alkyl trimethyl ammonium chloride, dieicosyldimethyl ammonium chloride; didocosyldimethyl ammonium chloride; dioctadecyldimethyl ammonium chloride; dioctadecyldimethyl ammonium methosulphate; ditetradecyldimethyl ammonium chloride and naturally occurring mixtures of above fatty groups, e.g. di(hydrogenated tallow) dimethyl ammonium chloride; di(hydrogenated tallow) dimethyl ammonium methosulphate; ditallow dimethyl ammonium chloride; and dioleyldimethyl ammonium chloride. Examples of useful stabilizers include, but are not limited to cationically modified polyvinyl alcohol), cationically modified starch. Specific cationic emulsifiers include alkyl trimethyl ammonium chlorides, such as cetyl trimethyl ammonium chloride and lauryl trimethyl ammonium chloride

[0022] The amount of emulsifiers, based on the total weight of the least one monomer is typically up to 10%, preferably 0.1 % to 6.0%, more preferably 0.5% to 5.0%, and very preferably 1 .0% to 4.0% by weight.

[0023] Examples of protective colloids include polyvinyl alcohols; polyvinyl acetals; polyvinylpyrrolidones; polysaccharides in water-soluble form, such as starches (amylose and amylopectin), modified starches, celluloses and their carboxymethyl, methyl, hydroxyethyl, and hydroxypropyl derivatives, in particular cationic or electroneutral derivatives, proteins, such as casein or caseinate, soy protein, gelatin; lignosulfonates; synthetic polymers such as poly(meth)acrylic acid, copolymers of (meth)acrylates with carboxyl-functional co-monomer units, poly(meth)acrylamide, polyvinylsulfonic acids, and water-soluble copolymers thereof; melamine-formaldehyde sulfonates, naphthalene-formaldehyde sulfonates, styrene-maleic acid copolymers and vinyl ether-maleic acid copolymers, or polyurethane stabilizers. A comprehensive description of further suitable protective colloids is found in Houben-Weyl, Methoden der organischen Chemie, Volume XIV/1 , Makromolekulare Stoffe, Georg-Thieme-Verlag, Stuttgart, 1961 , pages 41 1 to 420.

[0024] In some embodiments, the protective colloid is polyvinyl alcohol. Suitable polyvinyl alcohols possess degrees of hydrolysis from 60 to 100 mol%, preferably from 70 to 99 mol%, and viscosities of the 4% strength aqueous solutions at 20° C. of 2-70 mPa ^* s, more particularly 30 to 60 mPa s. Besides homopolymeric polyvinyl alcohol, i.e., polyvinyl alcohol composed only of vinyl alcohol groups and residual vinyl acetate groups, it is possible to use copolymeric and/or functionalized polyvinyl alcohols, examples being reaction products of polyvinyl alcohol with diketene or with types of polyvinyl alcohols that carry carboxyl groups, thiol groups, formamido groups, amino groups, arylamino groups, sulfate groups, sulfonate groups, phosphonate groups, quaternary ammonium groups, and other functional groups, such as partially acetalized polyvinyl alcohols. Mixtures of protective colloids may also be used.

[0025] Where protective colloids are used, their amount, based on the total weight of the at least one monomer, may range from 0.01 to 20 wt.%, e.g., from 0.1 to 15 wt.% or from 2 to 10 wt.%.

Additional Components of the Aqueous Phase

[0026] The aqueous phase may comprise additional components, including chain transfer agents. The chain transfer agent may be selected from the group consisting of monofunctional and multifunctional thiols and alkyl halides and other compounds known to be active in free radical chain transfer methods such as 2,4- diphenyl-4-methyl-1 -pentene. Suitable thiols include but are not limited to: C2-C8 alkyl thiols such as dodecane thiol. Thiol- containing oligomers may also be used such as oligo(cysteine) or an oligomer which has been post-functionalized to give a thiol group(s), such as oligoethylene glycolyl (di)thio glycolate, thiopropionic acid and esters thereof such as butyl-3-mercaptopropionate and octyl-3- mercaptopropionate,. In some embodiments, thiols include linear or branched alkylthiols such as dodecyl mercaptan, thio alcohols such as thioethanol, thio alkyl esters such as octyl-3-mercaptopropionate and thio acids such as thio lactic acid. Xanthates, dithioesters, and dithiocarbonates may also be used, such as cumyl phenyldithioacetate. More preferred chain transfer agents comprise: thiolactic acid, thioglycolic acid, thioglycerol, thioethanol, cysteine and cysteamine. The chain transfer agent may be a co-acid, e.g., an acid in addition to the acid used to convert the chitosan into a water soluble chitosan salt. In some embodiments, the chain transfer agent is thiolactic or thioglycolic acid.

[0027] The chain transfer agent may be present from 0.001 to 2 parts, based on the total weight of the at least one monomer, e.g., from 0.005 to 1 parts or from 0.01 to 0.8 parts.

[0028] The aqueous phase may have a pH of less than 5, e.g., less than 4. In terms of ranges, the pH may range from 1 to 5, e.g., from 2 to 5 or from 3 to 4. The pH of the aqueous phase may be adjusted after the addition of the water soluble chitosan salt, monomers, co-stabilizers and any other components that may affect the pH of the aqueous phase. If necessary, the pH may be adjusted by adding a buffer, such as sodium acetate, sodium citrate, disodium phosphate, and other known buffers. In some embodiments, the buffer may be sodium acetate. The pH of the aqueous phase may also be adjusted by adding alkali hydroxides, carbonates or hydrogen carbonates, carboxylic acids like formic acid or other strong organic or inorganic acids until a pH of less than 5, e.g., less than 4 is reached.

Monomers

[0029] The at least one ethylenically unsaturated monomer may be selected from the group consisting of esters of ethylenically unsaturated monocarboxylic and dicarboxylic acids, vinyl esters, C2-C4 olefins, vinyl halides, and vinyl aromatics.

[0030] Suitable vinyl esters include the vinyl esters of monocarboxylic acids containing from one to eighteen carbon atoms. Examples of these esters include vinyl formate, vinyl acetate, vinyl propionate, vinyl isobutyrate, vinyl valerate, vinyl pivalate, vinyl 2-ethylhexanoate, vinyl decanoate, Additional vinyl esters may include vinyl esters of saturated branched monocarboxylic acids having 5 to 15 carbon atoms in the acid radical, vinyl esters of Versatic™ acids, vinyl esters of relatively long-chain saturated or unsaturated fatty acids such as vinyl laurate, vinyl stearate, and also vinyl esters of benzoic acid and of substituted derivatives of benzoic acid, such as vinyl p-tert-butylbenzoate or isopropenyl acetate. In some specific embodiments, the vinyl ester is vinyl acetate.

[0031] Another group of monomers which can be used is formed by aliphatic, monoolefinically or diolefinically unsaturated, optionally halogen-substituted hydrocarbons, such as ethene, propene, 1 -butene, 2-butene, isobutene, conjugated C ₄ -Cs dienes, such as 1 ,3-butadiene, isoprene, chloroprene, and vinyl halides including vinyl chloride, vinylidene chloride, vinyl fluoride or vinylidene fluoride.

[0032] A further group of monomers which can be used is formed by esters of ethylenically unsaturated monocarboxylic or dicarboxylic acids, preferably esters of α,β-ethylenically unsaturated C3-C8 monocarboxylic or dicarboxylic acids, with preferably C1-C18 alkanols and more particularly with Ci-Cs alkanols or with Cs-Cs cycloalkanols. The esters of the dicarboxylic acids may be monoesters or, preferably, diesters. Examples of suitable Ci-Cs alkanols are methanol, ethanol, n- propanol, isopropanol, 1 -butanol, 2-butanol, isobutanol, tert-butanol, n-hexanol, and 2-ethylhexanol. Examples of suitable cycloalkanols are cyclopentanol or cyclohexanol. Examples are esters of acrylic acid, of methacrylic acid, of crotonic acid, of maleic acid, of itaconic acid, of citraconic acid or of fumaric acid, such as methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, 1 -hexyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, di-n-methyl maleate or fumarate, di-n- ethyl maleate or fumarate, di-n-propyl maleate or fumarate, di-n-butyl maleate or fumarate, diisobutyl maleate or fumarate, di-n-pentyl maleate or fumarate, di-n- hexyl maleate or fumarate, dicyclohexyl maleate or fumarate, di-n-heptyl maleate or fumarate, di-n-octyl maleate or fumarate, di(2-ethylhexyl) maleate or fumarate, di-n- nonyl maleate or fumarate, di-n-decyl maleate or fumarate, di-n-undecyl maleate or fumarate, dilauryl maleate or fumarate, dimyristyl maleate or fumarate, dipalmitoyl maleate or fumarate, distearyl maleate or fumarate, and diphenyl maleate or fumarate.

[0033] A yet further group of monomers may be formed from alkenyl aromatics, e.g., monoalkenyl aromatics. Examples include styrene, vinyltoluene, vinylxylene, a-methylstyrene or o-chlorostyrene. [0034] In addition to the at least one ethylenically unsaturated monomer discussed herein, the monomer composition may include at least one co-monomer, e.g., a functional co-monomer. Suitable functional co-monomers may include acrylic and methacrylic acids, esters of methacrylic acid, half esters of maleic acid (e.g., monoethyl, monobutyl or monooctyl maleate), beta carboxy ethyl acrylate, (meth)acrylamide, Ν,Ν-dimethyl acrylamide, hydroxyalkyl acrylate, hydroxyalkyl methacrylate, N-methylol(meth)acrylamide, N-vinylpyrrolidinone, and N-vinyl formamide), glycidyl monomers like glycidyl methacrylate, N-(2,3-epoxy)-propylacryl amide, N-(2,3-epoxy)-propylmethacryl amide, 4-acrylamidophenylglycidyl ether, 3- acrylamidophenylglycidyl ether, 4-methacrylamidophenylglycidyl ether, 3- methacrylamidophenylglycidyl ether, N-glycidoxymethyl acrylamide, N-glycidoxypropyl methacrylamide, N-glycidoxyethyl acrylamide, N-glycidoxyethyl methacrylamide, N- glycidoxypropyl acrylamide, N-glycidoxypropyl methacrylamide, N-glycidoxybutyl acrylamide, N-glycidoxybutyl methacrylamide, allylglycidyl ether, and methacrylglycidyl ether. A further group of functional co-monomers may be formed of amino group bearing co-monomers including aminoethyl methacrylate, 3-aminopropyl acrylate, 3-aminopropyl methacrylate, 4-amino-n-butyl acrylate, 4-amino-n-butyl methacrylate, 2-(N-methylamino)ethyl acrylate, 2-(N-methylamino)ethyl methacrylate, 2-(N-ethylamino)ethyl acrylate, 2-(N-ethylamino)ethyl methacrylate, 2-(N-n-propylamino)ethyl acrylate, 2-(N-n-propylamino)ethyl methacrylate, 2-(N-iso- propyl-amino)ethyl acrylate, 2-(N-iso-propylamino)ethyl methacrylate, 2-(N-tert.- butylamino)ethyl acrylate, and 2-(N-tert-butylamino)ethyl methacrylate. Yet a further group of functional co-monomers may be formed of cationic co-monomers including 2-(N,N,N-trimethylammonium)ethyl acrylate chloride, 2- (N, N, N- trimethylammonium)ethyl methacrylate chloride, 2-(N-methyl-N,N- diethylammonium)ethyl acrylate chloride, 2-(N-methyl-N,N-diethylammonium)ethyl methacrylate chloride, 2-(N-methyl-N,N-di-n-propylammonium)ethyl acrylate chloride, and 2-(N-methyl-N,N-di-n-propylammonium)ethyl methacrylate chloride. A further group of functional co-monomers is formed of carbonyl group bearing co- monomers like diacetone acrylamide and diacetone methacryl amide.

[0035] Preferably the functional co-monomers provide additional stabilization and/or have moieties that can crosslink with functional groups of other monomers, the free amino groups or other groups of the chitosan salt, and other compounds. Most preferred are electroneutral or cationic functional co-monomers as stabilizers and epoxy group (glycidyl groups), n-methylol groups, their ethers or other groups such as carbonyl group bearing monomers as crosslinking co-monomers.

[0036] The amount of the co-monomer, based on the total weight of all monomers, is, at least 0 wt.%, at least 0.5 wt.%, at least 2 wt.%, or at least 5 wt.%. In terms of ranges, all monomers may comprise from 0 to 10 wt.% of the co- monomer, based on the total weight all monomers, e.g., from 0.05 to 10 wt.% or from 1 to 5wt.%.

Preparation of the Emulsion Polymer and Polymerization

[0037] The emulsion polymer described herein is produced by free radical emulsion polymerization of the desired monomer or monomers together in the presence of an aqueous medium containing the chitosan salt and the co- stabilizer(s) in the presence of an initiator.

[0038] The initiator may be a thermal initiator or a redox initiator. Suitable initiators may include hydrogen peroxide, benzoyl peroxide, cyclohexanone peroxide, isopropyl cumyl hydroperoxide, persulfates of potassium, of sodium and of ammonium, peroxides of saturated monobasic aliphatic carboxylic acids having an even number of carbon atoms and a C8-C12 chain length, tert- butyl hydroperoxide, di-tert-butyl peroxide, diisopropyl percarbonate, azoisobutyronitrile, acetylcyclohexanesulfonyl peroxide, tert-butyl perbenzoate, tert-butyl peroctanoate, bis(3,5,5- trimethyl)hexanoyl peroxide, tert-butyl perpivalate, hydroperoxypinane, p- methane hydroperoxide. The abovementioned compounds can also be used within redox systems, using transition metal salts, such as iron(ll) salts, or other reducing agents. Alkali metal salts of oxymethanesulfinic acid, 2-hydroxy 2-sulfinato acetic acid, 2-hydroxy 2-sulfonato acetic acid, hydroxylamine salts, sodium dialkyldithiocarbamate, sodium bisulfite, ammonium bisulfite, sodium dithionite, diisopropyl xanthogen disulfide, ascorbic acid, tartaric acid, and isoascorbic acid can also be used as reducing agents.

[0039] In some embodiments, the initiator is a persulfate, such as a water- soluble persulfate, e.g., ammonium persulfate or sodium persulfate. The initiator may be present in an amount of at least 0.02 wt.%, based on the total weight of the at least one monomer, e.g., at least 0.5 wt.% or at least 0.2 wt.%. [0040] The water soluble chitosan salt may either be provided as a pre-prepared solution from the market or may be obtained as a chitosan powder that is converted to a water soluble chitosan salt. If the water soluble chitosan salt is obtained as a chitosan powder, the powder is added to water (e.g., demineralized water) and a chitosan salt forming acid to form a solution. The weight ratio between the chitosan and the chitosan salt forming acid may be from 1 :1 to 1 .2:1 , preferably 1 .1 1 :1 in case of acetic acid. Depending on the chitosan salt forming acid utilized, other weight ratios may be used, as determined by the stoichiometry of the chitosan salt to be formed. The solution may be heated, e.g., up to 100°C or 75°C, and held at the heated temperature for up to 4 hours, e.g., from 1 to 3 hours or for approximately 2 hours. The solution may then be cooled to room temperature and filtered through a sieve. The active content and viscosity of the solutions may then be measured. The active content of the solution may range from 0.1 to 10%, e.g., from 1 to 5% or from 1 .5 to 4.5%. The pH of the solution is less than 5, e.g., less than 4.5 and in terms of ranges, may range from 1 to 5, e.g., from 1 .5 to 4.8.

[0041] The water soluble chitosan salt solution may then be combined with excess water (e.g., demineralized). At least one co-stabilizer may then be added to the water soluble chitosan salt solution to form a suspension. The at least one co- stabilizer may be added in one charge or in sequential charges. The suspension may then be heated to dissolve the at least one co-stabilizer. Depending on the co- stabilizer(s), the heating time and temperature may vary. Generally, the suspension is heated for at least 1 hour, e.g., from 1 hour to 5 hours or for approximately 3 hours, to a temperature from 50°C to 150°C, e.g., from 75°C to 125°C, to form a solution. The solution is then cooled to room temperature. Additional components of the aqueous phase, including a water soluble chain transfer and/or a defoamer may be added to the solution and the pH may then be measured. The pH may be adjusted to achieve a pH of less than 5. The solution may then be transferred to a reactor unit for polymerization, e.g., a reactor unit with a stirring device, temperature control, and feed facilities.

[0042] In some embodiments the at least one ethylenically unsaturated monomer and any co-monomers are polymerized in a monomer slow-add process. A portion for kick-off reaction may be added in a single charge or in multiple charges. In some embodiments, at least a first portion of the at least one ethylenically unsaturated monomer and any co-monomers, and at least a portion of an initiator may be added to the solution. The reaction temperature may range from 50°C to 100°C, e.g., from 65°C to 80°C. At least a second portion of the at least one ethylenically unsaturated monomer, and any co-monomers may then be added to the reactor over a period from 1 to 6 hours, e.g., from 3 to 5 hours. Additional initiator may also be added during this time. During the addition of the second portion of monomer and any co-monomer, the reaction temperature may be held at the pre-determined temperature. A final amount of initiator may be added to the reactor and the temperature may be increased by at least 3°C, e.g., at least 5°C or at least 10°C and held at this temperature from 30 minutes to 2 hours. The reaction temperature is then allowed to decrease to room temperature.

[0043] In some embodiments the total amount of the at least one ethylenically unsaturated monomer, and/or any co-monomers may be added to the reactor, forming an emulsion and polymerized in a batch process.

[0044] In some embodiments the at least one ethylenically unsaturated monomer, and/or any co-monomers may be polymerized continuously in a reactor cascade or in a closed loop reactor. Upon completion of the polymerization, the residual monomer content may be lowered using demonomerization. This may be achieved using physical or chemical means. Physical means may include distillation or stripping with an inert gas. Chemical means may include adding a redox initiator system, such as a combination of tert-butyl hydroperoxide and sodium meta bisulfate, a combination of organic peroxides like tert-butyl peroxi- 3,5,5-trimethylhexanoate and disodium 2-hydroxy-2-sulfinatoacetate, or a combination of tert-butyl peroxi-3,5,5-trimethylhexanoate and a mixture of disodium 2-hydroxy-2-sulfinatoacetate with sodium sulfite and disodium 2-hydroxy-2- sulfonatoacetate. The redox initiator system may be added in one charge or in multiple charges over appropriate time periods. The residual monomer content of the polymer may be less than 10,000 ppm, e.g., less than 5,000 ppm or less than 3500 ppm.

[0045] The emulsion polymer may also be referred to as an aqueous dispersion and may have a solids content from 20 to 70%, e.g., from 50 to 70% or from 50 to 65%. The final emulsion polymer may have a pH of less than 5, e.g., less than 4.5. Uses of Emulsion Polymers

[0046] The emulsion polymers formed by the herein described methods may be used for a variety of purposes in various products, including in the manufacture of paints, including high pigment volume paints and other decorative coatings; adhesives for porous substrates such as wood, paper, paperboard or non-porous substrates such as metals, plastics or glass; binders for plastic substrates such as synthetic resin-bound plasters, paste-form tile adhesives, paste-form sealants, plaster-coated thermal insulation systems, fibrous substrates such as woven or nonwoven products including textiles, apparel in general, papers, scrim, engineered fabrics, glass or other mineral fibers, roofing or flooring materials; construction compositions including cement compositions, fibrous products, caulks and sealants; functional coatings for waterproofing, powders such as redispersible powders for waterproofing, adhesives and the like. If used in a coating composition, the coating composition is applied to the substrate to be coated in a manner dependent on the configuration of the coating composition. The application can, depending on the viscosity and the pigment content of the formulation and on the substrate, be effected by means of rolling, brushing, knife coating, dipping or as a spray. The emulsion polymers formed by the herein described methods may be further used in agricultural applications, including as part of seed coating formulations, pre-harvest or post-harvest coatings for agricultural products like fruits and vegetables, adjuvant for herbicides and may be used in pharmaceutical and medical fields or in waste water treatment.

[0047] The present invention will be better understood in view of the following non-limiting examples.

Examples

A. Preparation and characterization of Chitosan Acetate Solutions

[0048] Either pre-prepared solutions aqueous solutions of chitosan acetate or chitosan powder were obtained from the market. When chitosan powder was obtained, an aqueous solution including the powder was prepared in the presence of acetic acid according to following general procedure.

[0049] Chitosan powder was slowly added at room temperature to an appropriate amount of demineralized water containing glacial acetic acid to give active contents as listed in table 1 . The weight ratio between chitosan and acetic acid was kept at 1 .1 1 to 1 . The solution was heated up to 75°C and kept for 2 hours at this temperature. After cooling to room temperature, the mixture was filtrated over a 400 μιτι steel sieve and the active content and viscosity were measured. The pH of these solutions was in the range between 3.8 and 4.2.

[0050] In order to measure the viscosity, the solutions were adjusted to 1 wt. % and the viscosity was determined by means of a Brookfield RVT viscometer at 23°C using spindle 2 at 20 rpm. Active content was determined by determining dry matter at 105 °C for 2 hours in a drying oven.

TABLE 1

CHITOSAN ACETATE SOLUTION DATA

Chitosan Degree of Viscosity of 1 % Active Content

Sample Deacetylation (mol.%) solution (mPa s) of Solution %

Sample A 79 66 2

Sample B 83 200 3.1 1

Sample C 79 38 2

Sample D 84 37 3.25

Sample E 91 100 3.37 B. Aqueous Phase Preparation

[0051] The solutions as prepared in Table 1 were used to prepare aqueous phases in the polymerizations described in the following polymerization examples.

[0052] The aqueous phases were prepared as follows. To chitosan acetate solution samples A to E, excess parts demineralized water were added according to Table 2, followed by 4.4 parts partially hydrolyzed polyvinyl alcohol with a degree of hydrolysis of 88 mol.% and a viscosity of 18 mPa ^» s in 4% solution, 4.4 parts partially hydrolyzed polyvinyl alcohol with a degree of hydrolysis of 88 mol-% and a viscosity of 8 mPa ^» s in 4 % solution, followed by 0.12 parts sodium acetate. The suspension was heated for 3 hours at 80°C to dissolve the polyvinyl alcohols. The solution was cooled down to room temperature and the pH value of this solution was adjusted to the desired pH value by measures listed in Table 2. In Examples 4 to 6, thiolactic acid was added as a co-acid prior to pH adjustment. 0.15 parts defoamer were then added (Agitan ^® 301 ) and the solution transferred to a cylindrical glass reactor unit with a stirring device, electronic temperature control and feed facilities. TABLE 2

COMPOSITION OF AQUEOUS PHASES FOR POLYMERIZATIONS

Ex. Chitosan Chitosan Excess Thiolactic PH End

Acetate Acetate Water Acid Adjustment PH

Sample Solution (parts) (CTA/Co-

Solution (parts) Acid)

(parts)

1 A 80 21 - - 4.6

2 B 96.5 9 - Formic Acid 4.0

3 C 80 20 - Formic Acid 4.1

4 D 92.3 13 0.02 Formic Acid 3.9

5 D 92.3 13 0.03 Formic Acid 3.9

6 E 89 16 0.03 Formic Acid 3.9

Comp. A A 80 21 - NaOH 10% 5.5

C. Polymerization

[0053] About 7.2% of the total amount of 100 parts vinyl acetate or 100 parts vinyl acetate / 2 parts glycidyl methacrylate were polymerized with initiation by 0.05 parts (based on the total amount of the monomers as 100 parts) of ammonium peroxodisulfate in 0.75 parts demineralized water, at a reaction temperature of 65°C to 75°C. At 75°C the remaining monomer mixture was subsequently metered in over 4 hours, and, in parallel therewith, an aqueous solution of 0.15 parts of ammonium peroxodisulfate in 6 parts demineralized water was metered in. The reaction temperature was held at 75°C to 82°C by regulation of the feeds and by jacket cooling. An additional 0.05 parts in 0.5 parts demineralized water of ammonium peroxodisulfate was added at the end of the feed and the temperature was raised to 84°C and held for one hour. The reaction mixture was allowed to cool followed by further demonomerization with additions of tert-butyl hydroperoxide and sodium meta bisulfite (Method A) or double shots of tert-butyl peroxi-3,5,5- trimethylhexanoate and Bruggolit FF 06 below < 75 °C (Method B) with the second addition after 45 min. Residual monomer contents were < 3,500 ppm in all cases except Comparative Example A which contained > 30.000 ppm. Solids contents were 50 to 52 % except for that of Comparative Example A, which was 48.3%. End pH for all samples was 4.1 to 4.4 except for Comparative Example A which was 4.8.

[0054] The particle size distribution of Examples 1 to 6 and Comparative Example A was measured using the Mastersizer Micro Plus laser diffraction instrument from Malvern Instruments Ltd. The scatter data were evaluated using the volume-averaged "polydisperse Mie" evaluation provided by Malvern. Brookfield viscosities were measured at 23°C using an RVT viscometer at 20 rpm using the recommended spindle by the manufacturer for the respective viscosity range unless otherwise stated.

TABLE 3

RESULT OF POLYMERIZATIONS

Ex. Chitosan Amount of Co- Finish Brookfield Rheology Mass

Acetate CA related monomer Method Viscosity Average

Sample to 100 (mPa ^» s) d _w of parts Vinyl Particle Acetate Size

1 A 1 .6 - A 15,200 Shear- 1 .8

Thinning

2 B 3 2 % GMA B 47,500 Shear- 4.0

Thinning

3 C 1 .6 2 % GMA B 13,600 Shear- 1 .7

Thinning

4 D 3 2 % GMA B 27,300 Shear- 3.7

Thinning

5 D 3 2 % GMA B 16,600 Shear- 2.4

Thinning

6 E 3 2 % GMA B 43,300 Shear- 3.1

Thinning

Comp A 1 .6 2 % GMA A 1 14,200 Slightly 3.0

A Dilatant

[0055] The results for Examples 1 to 6 and for Comparative Example A show that polymerization performed below pH 5 has a strong positive impact on rheology and viscosity. Example 4 and 5 show that use of thiolactic acid as a co-acid and chain transfer agent 1 ) reduces the viscosity significantly, 2) lowers particle size and 3) allows polymerization using higher amounts of chitosan acetate and higher levels of degrees of deacetylation of the chitosan.

[0056] While the illustrative embodiments of the disclosure have been described with particularity, it will be understood that various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the spirit and scope of the disclosure. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the examples and descriptions set forth herein but rather that the claims be construed as encompassing all the features of the patentable novelty which reside in the present disclosure, including all features which would be treated as equivalents thereof by those skilled in the art to which the disclosure pertains.