Polyacrylate copolymer, polyacrylate dispersion comprising polyacrylate copolymer, and process for preparing the same

Abstract: An acrylate copolymer comprising repeating units derived from an acrylic or methacrylic ester monomer, about 0.1 to 3%, based on the weight of the total copolymer, of repeating units derived from from a water-soluble monomer having conjugated unsaturation, and about 0.1 to 3%, also based on the weight of the total copolymer, of repeating units derived from a water-soluble allyl monomer; aqueous polyacrylate dispersions comprising the copolymer; and a process of preparing the the copolymer.

Description: This invention relates to an acrylate copolymer, an aqueous polyacrylate dispersion of the polymer, and a process for preparing the same. There is a strong demand for stable polyacrylate dispersions that have good film-forming ability, high tensile strength values, and effective water resistance, for use as paint binders. The use of comonomers to improve some of those properties of the dispersions can adversely affect other properties. For instance, certain water-soluble allyl-containing monomers described in U.S. Patents 4,104,220 and 4,111,877, which improve the moisture resistance of acrylate copolymers and adhesion of latices containing them to various substrates under conditions of high humidity, have a high chain transfer constant. The tendency of those monomers (generally known as wet adhesion monomers) to undergo chain transfer can drastically reduce the latex polymer chain length, which is shown by the low reduced specific viscosity (RSV) of aqueous polyacrylate dispersions containing such acrylate copolymers, the basis of which is a reduction in the molecular weight due to carbon chain length as opposed to that due to branching. U.S. Patent No. 4,659,771 discloses that stable aqueous polyacrylate dispersions can be prepared, in the presence of protective colloids, when relatively minor amount of a substantially completely water-soluble monomer possessing conjugated unsaturation is present. In addition, European Patent Applications 252,526 and 331,011 disclose that minor amounts of water-soluble monomers possessing conjugated unsaturation are capable of stabilizing aqueous polyacrylate dispersions in the absence of a protective colloid, either in the presence or absence of comonomers, including allyl monomers that are soluble in organic solvents. The RSV of such polyacrylate dispersions is comparable to that of conventional polyacrylate dispersions. There is a need for polyacrylate dispersions having longer chains of carbon atoms and correspondently higher molecular weights, improved moisture resistance, and enhanced processability. According to the invention, an acrylate copolymer comprising repeating units derived from an acrylic or methacrylic ester monomer and from a water-soluble monomer having conjugated unsaturation, is characterized in that it comprises 0.1 to 3%, based on the weight of the total copolymer, of repeating units derived from the water-soluble monomer possessing conjugated unsaturation, and it also comprises 0.1 to 3%, also based on the weight of the total copolymer, of repeating units derived from a water-soluble allyl monomer. The acrylate copolymers according to the invention provide aqueous polyacrylate dispersions that are low in viscosity and mechanically stable, with improved film toughness and clarity. They are useful in the manufacture of latex paints, binders for nonwoven materials, water-based inks, paper coatings and water-based adhesives such as pressure-sensitive adhesives. In addition, the latex polymer molecular weight, as indicated by measurements of reduced specific viscosity (RSV), is significantly increased. Latex paints, formulated with these dispersions exhibit superior gloss and wet adhesion. Water-soluble allyl monomers useful in this invention are those allyl containing compounds (already generally referred to as wet adhesion monomers) possessing a solubility of at least 0.5 g per 100 g of water at 20°C, preferably at least 1.0 g per 100 g of water at 20°C. All such water-soluble allyl monomers possess at least one polar functional group (e.g., hydroxy, ester, ether, urethane, ureido, etc.). Examples of such monomers are allyl alcohol; mono-, di-, and tri-allylamines and their corresponding acid salts; and alkyl derivatives of mono-, di-, and tri-allylamines and their corresponding acid salts. Allyl amides, allyl carbonates, allyl carbamates and their derivatives, mono- and diallyl amine adducts of epoxides, are also useful, and preferred monomers are allyl urea and allyl derivatives of cyclic ureido compounds such as Sipomer WAM (available from Alcolac, Inc., Baltimore, MD, and particularly N-2-(allylcarbamato) aminoethyl imidazolidinone, available from Air Products and Chemicals, Inc., Allentown, PA under the trade mark WAM IV, which is more preferred and is disclosed in the above-mentioned U.S. Patent 4,111,877. Optionally, the copolymers may contain other free-radical polymerizable monomers. The term "water-soluble" with respect to the monomer having conjugated unsaturation means that it has a solubility of at least 0.4 grams per 100 ml of water, preferably 1.0 grams per 10 ml of water, at room temperature (about 20°C). The water-soluble monomers having conjugated unsaturation, i.e., conjugated double or triple bonds, suitable for use in the practice of this invention are described in the above mentioned European Patent Applications 252,526 and 331,011. They include furoic acid; linear or cyclic, nonaromatic sulfonic acids having 4 to 36 carbon atoms; metal salts, amine salts, ammonium salts and quaternary salts of rosin, or of carboxylic acids having 5 to 36 carbon atoms or of linear or cyclic, nonaromatic sulfonic acids having 4 to 36 carbon atoms; and water-soluble derivatives thereof. Such derivatives include water-soluble amine salts, amides, substituted amides, hydroxyalkyl esters and sulfoalkyl esters, aldehydes, and alcohols of said monomers. Thus, such monomers include those derivatives of, for instance, sorbic acid, cinnamic acid, abietic acid, linoleic acid, furylacrylic acid, muconic acid, 5-formyl-2-furalsulfonic acid, and furoic acid. Suitable metals for forming the metal salts of rosin and of carboxylic and sulfonic acids include sodium, potassium, lithium, magnesium, calcium and zinc. The preferred sulfonic acid monomers are the water-soluble cyclic, nonaromatic sulfonic acid monomers having conjugated unsaturation that have 4 to 24 carbon atoms. The preferred salts of sulfonic acids are salts of those sulfonic acids having 4 to 24 carbon atoms, and water-soluble derivatives thereof. By "cyclic, nonaromatic" with respect to sulfonic acids it is meant that the conjugated unsaturated moiety is present as part of a cyclic structure and will polymerize by free-radical polymerization in a 1,4 fashion (i.e., the cyclic structure is not inert to free radicals such as, for instance, phenyl, imidazolyl, and pyrrolyl structures). Examples of such moeties are 5 to 8 member rings containing all carbon atoms or including one or more hetero atoms, such as nitrogen, oxygen or sulfur atoms. Preferred are five membered rings having as a fifth atom a carbon, sulfur or oxygen atom, the most preferred of which are cyclopentadienyl, furanyl and thiophenyl. Examples of free-radical polymerizable sulfonic acid monomers useful in this invention are those having the following general formulae: in which R₁ and R₆ and, when present, R₂, R₃, R₄ and R₅, are H, -COOH, -COOR₇, -SO₃M or -R₈SO₃M, or substituted or unsubstituted alkyl, aryl or alkaryl; at least one of R₁, R₂, R₃, R₄, R₅ and R₆ which is present is -SO₃M or -R₈SO₃M; R₇ is substituted or unsubstituted alkyl, aryl, or alkaryl; R₈ is substituted or unsubstituted alkylene (e.g., methylene, ethylene, etc.), arylene, aralkylene, alkylarylene, alkyl aryl and aryl alkyl; M is H, a stoichiometric equivalent of a metal ion in an amount sufficient to neutralize the -SO₃ charge, or an amine, ammonium or quaternary ammonium group; and one or both of the double bonds may be replaced by a triple bond (in which case R₂ and R₃, R₄ and R₅, or R₂₋₅ will not be present); or in which R₂, R₃, R₄ and R₅ are defined above; at least one of R₂, R₃, R₄ and R₅ is -SO₃M or -R₈SO₃M; R₈ and M are defined above; and y is one more substituted or unsubstituted carbon or hetero atoms forming a 5 to 8 membered ring. Preferably only one of R₁₋₆ of formula (I) and R₂₋₅ of formula (II) is -SO₃M or -R₈SO₃M. The allyl monomers and conjugated monomers are readily copolymerized with acrylic esters and methacrylic esters. Exemplary acrylic and methacrylic esters per this invention include the substituted and unsubstituted alkyl, aryl, alkaryl, etc., esters of acrylic and methacrylic acid. Preferably, the acrylic esters and methacrylic esters used to make improved latices according to the invention are alkyl esters in which the alkyl group contains up to 9 carbon atoms, and most preferably are methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, isopropyl acrylate, isopropyl methacrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, t-butyl acrylate, t-butyl methacrylate, 3,3-dimethylbutyl acrylate and 3,3-dimethyl butyl methacrylate. Other alkyl esters of acrylic and methacrylic acid that can be used, containing up to 22 carbon atoms, include decyl acrylate, decyl methacrylate, hendecyl methacrylate, lauryl methacrylate, tridecanyl methacrylate, myristyl acrylate, myristyl methacrylate, pentadecanyl methacrylate, arachidyl methacrylate, behenyl methacrylate, 10-methyl hendecanyl methacrylate and 2-ethyl-lauryl methacrylate. The esters of acrylic and methacrylic acid that are suitable for use in the invention can be conventionally homopolymerized, or copolymerized with each other or with one or more different comonomers capable of addition-type polymerization, including unsubstituted and substituted styrene, acrylic or methacrylic acid, vinyl and vinylene halides, allyl esters of saturated monocarboxylic acids, vinyl esters, vinyl ethers, dialkyl esters of monoethylenically unsaturated dicarboxylic acids, ethylenically unsaturated monocarboxylic and polycarboxylic acids and the anhydrides, nitriles, unsubstituted and substituted (including N-substituted) amides of all the said acids. In the acrylate copolymers according to the invention, the units derived from acrylic or methacrylic ester monomers preferably comprise 50%, by weight of the total copolymer. However, free-radically polymerizable comonomer units can optionally be present in an amount from about 0.5% to less than 75%, preferably from 0.5% to 50%, most preferably from about 1% to about 10%, by weight of the units derived from acrylic or methacrylic esters and comonomer units (i.e., the units other than the repeating units derived from the monomer possessing conjugated unsaturation and the repeating units derived from a water-soluble allyl monomer). Reference to the "weight of the total copolymer" herein means the total weight of the units derived from alkyl esters of acrylic and methacrylic acid, the free-radically polymerizable conjugated monomers and allyl monomers, and all other comonomers. This percentage is proportional to the total monomer percentage used to form the copolymer or dispersion. The vinyl esters with which the acrylates and methacrylates used in the process according to the invention can be copolymerized include, e.g., aliphatic vinyl esters, such as vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl valerate, and vinyl caproate. The allyl esters of saturated monocarboxylic acids include, e.g., allyl acetate, allyl propionate and allyl lactate. Preferably, these comonomers are used in amounts ranging up to about 10% by weight of the total monomers. The allyl esters of saturated monocarboxylic acids are generally used in relatively small amounts together with larger amounts of one or more other vinyl comonomers, particularly with aliphatic vinyl esters such as vinyl acetate. The vinyl ethers with which the acrylates and methacrylates used in the process according to the invention can be copolymerized include methylvinyl ether, ethylvinylether and n-butylvinyl ether and typical vinyl ketones include methylvinyl ketone, ethylvinyl ketone and iso-butylvinyl ketone. The suitable dialkyl esters of monoethylenically unsaturated dicarboxylic acids include diethyl maleate, dibutyl maleate, dioctyl maleate, diisooctyl maleate, dinonyl maleate, diisodecyl maleate, ditridecyl maleate, dipropyl fumarate, dibutyl fumarate, dioctyl fumarate, diisooctyl fumarate, didecyl fumarate, dibutyl itaconate and dioctyl itaconate. The monoethylenically unsaturated monocarboxylic acids that are suitable for use as comonomers include acrylic acid, methacrylic acid, ethacrylic acid and crotonic acid; monoethylenically unsaturated dicarboxylic acids, such as maleic acid, fumaric acid, itaconic acid and citraconic acid; and monoethylenically unsaturated tricarboxylic acids, such as aconitic acid and the halogen-substituted derivatives, e.g., alpha-chloroacrylic acid, and anhydrides of these acids, such as, e.g., maleic anhydride and citraconic anhydride. Acrylonitrile, alpha-chloro-acrylonitrile and methacrylonitrile are among the corresponding nitriles of such acids that can be used as comonomers. Suitable amides of such acids include unsubstituted amides such as acrylamide, methacrylamide and other alpha-substituted acrylamides and N-substituted amides obtained by conventional reaction of the amides of the aforementioned mono- and poly-carboxylic acids with an aldehyde, such as formaldehyde. Suitable N-substituted amides include N-methylolacrylamide, N-methylolmethacrylamide, alkylated N-methylolacrylamides and N-methylolmethacrylamides, such as N-methoxymethyl-acrylamide and N-methoxymethyl-methacrylamide. Amino compounds that can be used as comonomers include substituted and unsubstituted aminoalkyl acrylates, hydrochloride salts of amino monomers and methacrylates, such as beta-aminoethylacrylate, beta-aminoethylmethacrylate, di-methylaminomethylacrylate, beta-dimethylaminoethylacrylate, dimethylaminomethylmethacrylate. Hydroxy-containing monomers that are suitable include beta-hydroxyethylacrylate, beta-hydroxypropylacrylate, gamma-hydroxypropylacrylate and beta-hydroxyethylmethacrylate. Protective colloids can be used in the process of this invention, although their presence is not necessary to achieve the objectives of this invention. Anionic, cationic, nonionic, and amphoteric surfactants, and mixtures thereof, known to the art, may be used in the process of this invention. These surfactants are conventionally used in emulsion polymerization, but are not necessary to make the copolymers of this invention. Any conventional methods of emulsion polymerization can be used including both semi-batch or continuous, as well as thermal, thermal-redox, or adiabatic-redox methods. The following examples illustrate this invention. All parts and percentages are by weight unless otherwise indicated. Example 1 This example illustrates one embodiment of this invention. A reaction vessel equipped with a stirrer, reflux condenser, thermometer, 3 feed ports, and a water jacket, was charged with 20.3 parts distilled water, 0.5 parts potassium sorbate, and 0.5 parts N-2-(allylcarbamato) aminoethyl imidazolidinone (WAM IV, Air Products) with stirring. The reaction mixture was heated to 85°C via circulating hot water, at which time three separate feeds consisting of: 1) 6 parts distilled water plus 1 part 4% aqueous sodium formaldehyde sulfoxylate, 2) 6 parts distilled water plus 0.1 part t-butyl hydroperoxide (90%), and 3) a pre-emulsion containing 1.6 parts poly(oxy-1,2-ethanediyl),alpha-sulfo-omega-(nonylphenoxy)ammonium salt (Alipal CO-436., GAF Corp., New York, NY), 14 parts distilled water, 50 parts of a mixture of monomers containing by weight 50 parts butyl acrylate, 50 parts methyl methacrylate, and 1.0 part methacrylic acid were metered into the reactor over a period of 3.5, 3.5, and 3.0 hours respectively, while maintaining the temperature at 85°C. Heating was continued for 30 minutes beyond the final addition of initiator, at which time the reactor was cooled and the resulting latex characterized. Reduced specific viscosity measurements were made by dissolving the latex into N-methyl pyrrolidone to a solids content of 0.25% by weight and measuring the viscosity at constant temperature (25°C) in a capillary viscometer, with comparisons being made to control samples without latex polymers. Example 2 The procedures of Example 1 were repeated except that N-2-(allylcarbamato) aminoethyl imidazolidinone was replaced with 0.2 parts of allylurea and 0.3 parts water. Example 3 A reaction vessel equipped with a stirrer, reflux condenser, thermometer, 3 feed ports, and a water jacket, was charged with 20.3 parts distilled water, 0.5 parts potassium sorbate, and 0.5 parts N-2-(allylcarbamato) aminoethyl imidazolidinone (WAM IV, Air Products) [allylurea] [0.1 part [allyl alcohol][alloxy-propanediol[diallyl tartardiamide], with stirring. The reaction mixture was heated to 85°C via circulating hot water, at which time three separate feeds consisting of: 1) 6 parts distilled water plus 1 part 4% aqueous sodium formaldehyde sulfoxylate, 2) 6 parts distilled water plus 0.1 part t-butyl hydroperoxide (90%), and 3) a pre-emulsion containing 1.6 parts poly(oxy-1,2-ethanediyl),alpha-sulfo-omega-(nonylphenoxy)ammonium salt (Alipal CO-436., GAF Corp., New York, NY)[sorbic acid, 0.2 parts allylamine (to neutralize and solubilize the sorbic acid as its allylammonium salt], 14 parts distilled water, 50 parts of a mixture of monomers containing by weight 50 parts butyl acrylate, 50 parts methyl methacrylate, and 1.0 part methacrylic acid were metered into the reactor over a period of 3.5, 3.5, and 3.0 hours respectively, while maintaining the temperature at 85°C. Heating was continued for 30 minutes beyond the final addition of initiator, at which time the reactor was cooled and the resulting latex characterized. The procedures of Example 1 were repeated except that both potassium sorbate and N-2-(allylcarbamato) aminoethyl imidazolidinone were replaced with 0.38 parts sorbic acid, 0.2 parts allylamine (to neutralize and solubilize the sorbic acid as its allylammonium salt), 0.1 part allyl alcohol and 0.32 parts water. Example 4 The procedures of Example 1 were repeated except that N-2-(allyl carbamato) aminoethyl imidazolidinone was replaced with 0.2 g of alloxy-propanediol and 0.3 g water. Example 5 The procedures of Example 2 were repeated except that allylurea was replaced with 0.2 g of diallyl tartardiamide. Example 6 The procedures of Example 3 were repeated except that allyl alcohol was replaced with 0.1 parts water Example 7 The procedures of Example 1 were repeated except that N-2-(allylcarbamato) aminoethyl imidazolidinone was removed from the inital charge and 1.0 part N-2 (allylcarbamato) aminoethyl imidazolidinone was added to the pre-emulsion. Example 8 The procedures of Example 1 were repeated except that the 14 parts distilled water was added to the inital charge instead of the pre-emulsion. Example 9 The procedures of Example 1 were repeated except that .3 parts of hydroxyethylcellulose (HEC), having a 5% aqueous viscosity of 75 centipoise at 25°C, and a hydroxyethyl molar substitution (average number of hydroxyethyl groups per 15 anhydroglucose units) of 2.5 was added to the initial reactor charge. Example 10 - Comparison The procedures of Example 2 were repeated except that allyl urea was replaced with 0.2 parts water. Example 11 - Comparison The procedures of Example 1 were repeated except that potassium sorbate was replaced with 0.5 parts water. Example 12 - Comparison The procedures of Example 10 were repeated except that potassium sorbate was replaced with 0.5 parts water. From the data in Table 1, it can be seen that latex polymer molecular weights imparted due to increased chain length, as assessed by RSV values, are significantly higher for latexes manufactured in the presence of both a water-soluble allyl monomer and a water-soluble conjugated unsaturated monomer, versus latexes manufactured in the presence of either water-soluble allyl monomer (Example 10) or water-soluble conjugated unsaturated monomers alone (Example 11), or latexes manufactured in the absence of both components (Example 12).

Claims: An acrylate copolymer comprising repeating units derived from an acrylic or methacrylic ester monomer and from a water-soluble monomer possessing conjugated unsaturation, is characterized in that it comprises 0.1 to 3%, based on the weight of the total copolymer, of repeating units derived from a water-soluble monomer possessing conjugated unsaturation, and 0.1 to 3%, also based on the weight of the total copolymer, of repeating units derived from a water-soluble allyl monomer. An acrylate copolymer as claimed in claim 1, further characterized in that the allyl monomer has a solubility of at least 0.5 g in 100 g of water at 20°C and contains a polar functional group. An acrylate copolymer as claimed in claim 2 further characterized in that the water-soluble allyl monomer has a solubility of at least 1.0 g in 100 g of water at 20°C. An acrylate copolymer as claimed in claim 2 or 3 further characterized in that the polar functional group is a hydroxide, ester, ether, urethane, or ureido group. An acrylate copolymer as claimed in claim 4, further characterized in that the water-soluble allyl monomer is an allyl alcohol, a mono-, di-, or tri-allylamine or acid salt of an allyl alcohol, or an alkyl derivative of a mono-, di-, or tri-allylamine, or an acid salt of a mono-, di-, or tri-allylamine. An acrylate copolymer as claimed in claim 4 further characterized in that the water-soluble allyl monomer is an allyl amide, allyl carbonate, allyl carbamate or a derivative thereof, or a mono- or di-allyl amine adduct of an epoxide. An acrylate copolymer as claimed in claim 4 further characterized in that the water-soluble allyl monomer is allyl urea or an allyl derivative of a cyclic ureido compounds. An acrylate copolymer as claimed in claim 4 further characterized in that the water-soluble allyl monomer is N-2-(allylcarbamato) aminoethyl imidazolidinone. An acrylate copolymer as claimed in any of the preceding claims, further characterized in that the monomer having conjugated unsaturation is furoic acid; a linear or cyclic, nonaromatic sulfonic acid having 4 to 36 carbon atoms; a metal salt, amine salt, ammonium salt or quaternary salt of rosin, or of a carboxylic acid having 5 to 36 carbon atoms or of a linear or cyclic, nonaromatic sulfonic acid having 4 to 36 carbon atoms; or a water-soluble derivative of one of the said monomers having conjugated unsaturation. An acrylate copolymer as claimed in claim 9, further characterized in that the water-soluble derivative of one of the said monomers is a water-soluble amine salt, amide, substituted amide, hydroxyalkyl or sulfoalkyl ester, aldehyde, and alcohol of one of the said monomers. An acrylate copolymer as claimed in claim 9 or 10 further characterized in that the water-soluble derivative of one of the said monomers is a derivative of sorbic acid, cinnamic acid, abietic acid, linoleic acid, furylacrylic acid, muconic acid, 5-formyl-2-furalsulfonic acid, or furoic acid. An acrylate copolymer as claimed in any one of claims 9 to 11, further characterized in that the monomer having conjugated unsaturation is a cyclic, nonaromatic sulfonic acid is which the the conjugated unsaturated moiety is present as a 5 to 8 member rings containing all carbon atoms or including a nitrogen, oxygen or sulfur atom. An acrylate copolymer as claimed in claim 12, further characterized in that the five membered ring forms a cyclopentadienyl, furanyl or thiophenyl group. An acrylate copolymer as claimed in any one of claims 9 to 13, further characterized in that the metal salts of rosin or of a carboxylic or a sulfonic acid is sodium, potassium, lithium, magnesium, calcium or zinc. A process for preparing an aqueous polyacrylate dispersion comprising emulsion polymerization of at least one acrylic ester or methacrylic ester in the presence of, by weight of total monomer content, (a) 0.1 to 3% of at least one water-soluble monomer possessing conjugated unsaturation and (b) 0.1 to 3% of at least one water-soluble allyl monomer. The process as claimed in claim 15 further characterized in that (a) the acrylic and methacrylic esters are selected from substituted and unsubstituted alkyl, aryl and alkaryl esters of acrylic and methacrylic acid in which the alkyl group contains up to 22 carbon atoms, (b) the water-soluble allyl monomer is selected from the group consisting of allyl alcohol; mono, di, and triallylamine and acid salts thereof; alkyl derivatives of mono, di, and triallylamines and acid salts thereof; allyl amides; allyl carbonates; allyl carbamates; mono and diallyl amine adducts of epoxides; allyl urea; and N-2-(allylcarbamato) aminoethyl imidazolidinone having a solubility of at least 0.5 g in 100 g of water at 20°C, and (c) the substantially completely water-soluble monomers having conjugated unsaturation is selected from the group consisting of furoic acid, the metal salts, amine salts, ammonium salts and quaternary salts of rosin and of carboxylic and sulfonic acids having 4 to 36 carbon atoms and water-soluble derivatives thereof having a solubility of at least 0.4 grams per 100 ml of water at 20°C. An aqueous polyacrylate dispersion comprising the acrylate copolymer as claimed in claim 1.

Inventors: CRAIG DANIEL HORACE, GOLDY HARRY JOSEPH, CRAIG, DANIEL HORACE, GOLDY, HARRY JOSEPH
Applicants: HERCULES INC, HERCULES INCORPORATED
Application year: 1990
Main classification: C08F220
IPC codes: C08F2, C09D133, C08L33, C08F236, C08F220