GB2068391A - Polyurethane Prepolymer Amine Salt Emulsifier for Emulsion Polymerization Processes - Google Patents

Abstract

A process for producing a polymer latex comprises polymerizing one or more polymerizable monomers in aqueous emulsion in the presence of a polyurethane prepolymer amine salt emulsifier prepared by reacting a first component comprising an isocyanate- capped hydrophilic polyol having a reaction functionality of two or greater with a second component comprising a ketoxime to form an oxime-blocked prepolymer, reacting said oxime- blocked prepolymer with a third component comprising a polyfunctional amine having a functionality of two or greater to form an amine reaction product, reacting said amine reaction product with a fourth component comprising an acid to produce an infinitely water- dilutable polyurethane polymer amine salt, and diluting said polyurethane polymer amine with water.

Description

SPECIFICATION Polyurethane Prepolymer Amine Salt Emulsifier for Emulsion Polymerization Processes Emulsion polymerization probably had its origin in the observations by early scientists of natural latexes or saps exuded by many plants. The most important of these is without a doubt, natural rubber latex. Natural rubber is a milklike colloidal dispersion in water of polyisoprene particles protected from coagulation by natural proteins and emulsifiers. The earliest reference to emulsion polymerization is made in German Patent DRP 250690 in 1 909. Work on emulsion polymerization continued in Germany through World War I with relatively little progress being made in the technical development.

Industrial development of emulsion polymerization appears to have started toward the end of the 1920's. In German Patent DRP 558,890 (1927) there is described the polymerization of butadiene to a synthetic latex using soaps as emulsifiers and hydrogen peroxide as the initiator.

The first significant breakthrough in the industrial development of emulsion polymerization occurred in 1 938 when it was shown that polymerization occurs in the aqueous phase and not in the monomer droplets. Understanding the mechanism of the emulsion polymerization widened knowledge so that predictions and improvements of the techniques could be made.

The advantages of emulsion polymerization over other methods such as bulk or solution polymerization are as follows: (1) An emulsion polymerized product, i.e. the latex itself, is in an ideal form for use in paints and surface coatings, adhesives, paper coating and impregnation, leather treatment, textile treatment, dipping and latex foam rubber.

(2) Control of the initiator, propagation, chain transfer, and termination reaction is easy and, in most cases, at a relatively low polymerization temperature.

(3) Emulsion polymerization lends itself to easy continuous process operation.

(4) High rates of polymerization can be obtained simultaneously with high degrees of polymerization.

(5) In contrast to solutions of polymers, the viscosity of a latex is independent of the molecular weight of the polymer it contains. Thus high polymer concentrations can be obtained at low viscosity.

(6) Emulsion polymerization uses water as the inexpensive solvent eliminating solvent recovery problems and fire risk factors.

(7) When a solid product is required, work-up of the polymer presents no problems since the latex is simply coagulated in an appropriate manner and the coagulated crumb washed with water of other aqueous solutions, pressed and dried.

It has been said that the choice of an emulsifier is probably the most important single factor in an emulsion polymerization recipe. First, the emulsifier must produce a stable emulsionbetween the monomer and water phases and later a stable latex. Second, it must not interfere adversely with the initiation system or the propagation of the reaction. Third, since the emulsifier residues will remain in the product recovered after polymerization it must impart no adverse properties to the product.

Numerous synthetic emulsifiers have been studied for their efficiency in emulsion polymerization.

According to the nature of the hydrophilic groups, surface active agents can be divided into four classes: (a) anionic, (b) cationic, (c) amphoteric, and (d) nonionic. Each of these main groups can be further subdivided chemically according to the hydrophilic group (e.g. carboxylic acids, sulfates, sulfonates) and according to the hydrophobic group (e.g. alkyl, alkylaryl, alkylamide, alkylester). Thus the choice from the number of possible permutations and combinations is very wide.

Illustrative of suitable surfactants commonly employed in emulsion polymerization processes of the prior art are the anionic surfactants such as potassium caprylate, potassium myristate, potassium palpitate, potassium stearate, potassium oleate, sodium decyl sulfonate, sodium dodecyl sulfonate, sodium tetradecyl sulfate, sodium decyl sulfate, sodium lauryl sulfate, potassium dehydroabietate, sodium rosinate, alkyl sodium sulfosuccinate esters and the like; cationic surfactants such as the long chain quaternary amine salts; and nonionic surfactants such as ethylene oxide condensates of oleyl alcohol, cetyl alcohol, lauryl alcohol etc., ethylene oxide condensates of linoleic acid, lauric acid, ricinoleic acid, caproic acid, etc., block copolymer of ethylene oxide and propylene oxide and the ethylene oxide condensates of octyl phenol or nonyl phenol.

The role of the emulsifier in emulsion polymerization is threefold: (a) an increased amount of the monomer is taken into the water phase owing to solubilization in the micelles; (b) the nonsolubilized monomer is emulsified into fine stable droplets; and (c) the latex particles created are protected against coagulation during and after the polymerization.

It is known that different emulsifiers have molar concentrations below which no micelle formation occurs. This is the critical micelle concentration, i.e. cmc. In most cases no polymerization of significance occurs below the critical micelle concentration (cmc). As the concentration of the emulsifier is lowered, the number of latex particles formed is decreased. It is known that emulsifier residue left in the latex system can leave the latex with undesirable properties i.e. the latex may lose some if its stability.

It has been recognized that an emulsifier should bring three basic properties to a latex system.

These properties are (a) good solubility at the polymerization temperature (b) good solubilizing power, and (c) imparting good stability to the latex. Further, the emulsifier must not interfere with the initiation or the propagation of the polymerization reactions.

The variety of initiator systems in emulsion polymerization processes is no less than the variety of emulsifiers described. All systems used commercially are based on the liberation of an active free radical. These active free radicals are produced by either of two means (a) thermal decomposition of a compound into free radicals or (b) interaction of chemical agents to produce free radicals.

The most commonly used initiators are those compounds containing a peroxide bond, i.e., --00--0-. The organic peroxides can be regarded as being derived from hydrogen peroxide by replacement of hydrogens by organic groups.

Some specific organic peroxide initiators are diisopropyl peroxycarbonate, caprylyl peroxide, lauroyl peroxide, benzoyl peroxide, dicumyl peroxide, tert-butyl hydroperoxide, methyl ethyl ketone peroxide, di-tert-butyl peroxide, cumene peroxide and tert-butyl peroxybenzoate. Compounds that release peroxydisulfate ions may also be used as an initiator.

Hydrogen peroxide-iron systems can be used as the initiators for the polymerization of certain monomers, e.g. methyl methacrylate and acrylonitrile while the organic hydroperoxides are preferred for the less polar monomers such as styrene and butadiene. For the manufacture of "cold" SBR recipes containing p-menthane hydroperoxide, pinone hydroperoxide, or diisopropylbenzene hydroperoxide are most frequently encountered.

In addition to emulsifiers and initiators, certain materials may be added to the emulsion polymerization reaction mixture to retard or inhibit the propagation reaction. Any substances which will trap free radicals and either destroy them, prevent them from getting to the locus of polymerization, or produce by transfer another free radical which is not active as a polymerization initiator or inhibitor may be used. Some substances may act as both retarder and an inhibitor. Some commonly used substances are diethylhydroxylamine, hydroquinone, methylether of hydroquinone, p-aminophenol, water soluble dithiocarbamates, etc.

The present invention provides a process for producing a polymer latex wherein the conventional surface active agents and/or emulsifiers are replaced by a polyurethane prepolymer amine salt. This polyurethane prepolymer amine salt eliminates the effects of the residues in the finished product by the emulsifier remaining therein since the salt upon curing of the latex becomes a part of the cured latex.

The process of the present invention comprises polymerizing one or more polymerizable monomers in aqueous emulsion in the presence of a polyurethane prepolymer amine salt emulsifier prepared by reacting a first component comprising an isocyanate-capped hydrophilic polyol having a reaction functionality of two or greater with a second component comprising a ketoxime to form an oxime-blocked prepolymer, reacting said oxime-blocked prepolymer with a third component comprising a polyfunctional amine having a functionality of two or greater to form an amine reaction product, reacting said amine reaction product with a fourth component comprising an acid to produce an infinitely water-dilutable polyurethane polymer amine salt, and diluting said polyurethane polymer amine with water.

The novel polyurethane prepolymer amine salt when used in emulsion polymerization systems has been found to act as a particle initiator and thus can be substituted for seed latex used in preparing latex compositions where a high degree of uniformity in particle size is required (for example see U.S.

Patent 3,397,1 65). It has been found that the novel polyurethane prepolymer amine salt when used in an emulsion polymerization system acts as a stabilizing medium for the latex system.

In the process of this invention latex initiation is performed in accordance with the procedures known in the art. The aqueous reaction medium is charged to the reaction zone and the monomer or monomers to be polymerized are thereafter fed continuously to the aqueous medium in the reaction zone together with a catalyst and, if desired, surfactants, buffer, etc. By the term "aqueous reaction medium" is meant water plus any other constituents, e.g. catalyst, surfactants, buffer, etc. which are present in the reaction zone in which the polymerization of this process is carried out. The temperature of initiation varies depending on the type of monomers used and the amount and type of catalyst used, and those skilled in the art will know the correct initiation temperature for any given system. Typically, when polymerizing lower alkyl acrylate or methacrylate monomers, e.g. methyl methacrylate, N-butyl acrylate, etc., it is preferred to initiate polymerization at a temperature of from about 40 to about 840C depending on the catalyst employed.

Any reactor, properly equipped, can be used in the carrying out of emulsion polymerization reactions. The different types of reactors and their suitability for emulsion polymerization are well known to those skilled in the art. Typically, a stirred tank with means for controlling temperature and pressure, means for providing a continuous feed of the monomer, catalyst, surfactant, buffer, etc., means for continuously withdrawing a portion of the tank's contents, and, where desired, means for providing an inert atmosphere (e.g. N2) above the reactants, is suitably employed as the reactor.

The emulsion polymerizable monomers which are useful in the process of our invention are any of the monomers having at least one olefinically unsaturated group of the formula

which are known to those skilled in the art to undergo addition polymerization under the conditions of emulsion polymerization in an aqueous medium. These monomers are so well known to those skilled in the art as to require no further elaboration herein.Nonetheless, one can mention as illustrative thereof, unsaturated compounds such as ethylene, propylene, 1-butene, 2-butene, isobutylene, 1-pentene, 2- methyl-2-butene, 1 -hexene, 4-methyl-i -pentene, 3,3-dimethyl- 1 -butene, 2,4,4-trimethyl- 1 -pentene, 6-ethyl-1-hexene, 1-heptene, 1-octene, 1-decene, 1-dodecene, allene, butadiene, isoprene, chloroprene, 1 ,5-hexadiene, 1 ,3,5-hexatriene, divinylacetylene, cyclopentadiene, dicyclopentadiene, norbornene, norbornadiene, methylnorbornene, cyclohexene, styrene, alpha-chlorostyrene, alphamethylstyrene, allylbenzene, phenylacetylene, 1 -phenyl-1, 3-butadiene, vinylnaphthalene, 4 methylstyrene, 2,4-dimethylstyrene, 3-ethylstyrene, 2,4-diethylstyrene, 2-methoxystyrene, 4-methoxy- 3-methyistyrene, 4-chiorostyrene, 3,4-dimethyl-alpha-m ethyistyrene, 3-bromo-4-methyl-alpha- methylstyrene, 2,5-dichlorostyrene, 4-fluorostyrene, 3-iodostyrene, 4-cyanostyrene 4-vinylbenzoic acid, 4-acetoxystyrene, 4-vinyl benzyl alcohol, 3-hydroxystyrene, 1 ,4-dihydroxystyrene, 3- hydroxystyrene, I 4-dihydroxystyrene, 3-nitro-styrene, 2-am inostyrene, 4-N,N-dimethyla minostyrene, 4-phenylstyrene, 4-chloro-1 -vinylnaphthalene, acrylic acid, methacrylic acid, acrolein, methacrolein, acrylonitrile, methacrylonitrile, acrylamide, methacryiamide, methyl acrylate, methyl methacrylate, norbornenyl acrylate, norbornyl diacrylate, 2-hydroxyethyl acrylate, 2-phenoxy-ethyl acrylate, trimethoxysilyloxypropyl acrylate, dicyclopentenyl acrylate, cyclohexyl acrylate, 2-tolyloxyethyl acrylate, N,N-dimethylacrylamide, isopropyl methacrylate, ethyl acrylate, methyl alpha-chloroacrylate, betadimethylaminoethyl methacrylate, N-methyl methacrylamide, ethyl methacrylate, 2-ethylhexyl acrylate, neopentyl glycol diacrylate, cyclohexyl methacrylate, beta-bromoethyl methacrylate, benzyl methacrylate, phenyl methacrylate, neopentyl methacrylate, butyl methacrylate, chloroacrylic acid, methyl chloroacrylic acid, hexyl acrylate, dodecyl acrylate, 3-methyl 1 butyl acrylate, 2-ethoxyethyl acrylate, phenyl acrylate, butoxyethoxyethyl acrylate, 2-methoxyethyl acrylate, isodecyl acrylate, pentaerythritol triacrylate, methoxy poly (ethyleneoxy) acrylate, tridecgxy poly (ethyleneoxy) acrylate, chioroacrylonitrile, dichloroisopropyl acrylate, ethacrylonitrile, N-phenyl acrylamide, N,N-diethylacrylamide, N-cyclohexyl acrylamide, vinyl chloride, vinylidene chloride, vinylidene cyanide, vinyl fluoride, vinylidene fluoride, trichloroethane, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl benzoate, vinyl butyral, vinyl propionate, vinyl chloroacetate, isopropenyl acetate, vinyl formate, vinyl methoxyacetate, vinyl caproate, vinyl oieate, vinyl adipate, methyl vinyl ketone, methyl isopropenyl ketone, vinyl phenyl ketone, methyl alpha-chlorovinyl ketone, ethyl vinyl ketone, divinyl ketone, allylidene diacetate, methyl vinyl ether, 2-methoxyethyl vinyl ether, 2-chloro-ethyl vinyl ether, methoxyethoxy ethyl vinyl ether, hydroxyethyl vinyl ether, aminoethyl vinyl ether, alpha-methylvinyl methyl ether, divinyl ether, divinyl ether of ethylene glycol or diethylene glycol or triethanolamine, cyclohexyl vinyl ether, benzyl vinyl ether, phenethyl vinyl ether, cresyl vinyl ether, hydroxyphenyi vinyl ether, chiorophenyl vinyl ether, naphthyl vinyl ether, dimethyl maleate, diethyl maleate, di-(2-ethylhexyl) maleate, maleic anhydride, dimethyl fumarate, dipropyl fumarate, diamyl fumarate, vinyl ethyl sulfide, divinyl sulfide, vinyl p-tolyl sulfide, divinyl sulfone, vinyl ethyl sulfone, vinyl ethyl sulfoxide, vinyl sulfonic acid, sodium vinyl sulfonate, vinyl sulfonamide, vinyl benzamide, vinyl pyridine, N-vinyl pyrollidone, N-vinyl carbazole, N-(vinyl benzyl)-pyrrolidine, N-(vinyl benzyl) piperid ine, 1-vinyl pyrene, 2-isopropenyl furan, 2-vinyl dibenzofuran, 2-methyl-5-vinyl-pyridine, 3-isopropenyl pyridine, vinyl piperidine, 2-vinyl quinoline, 2-vinyl benzoxazole, 4-methyl-5-vinyl thiazole, vinyl thiophene, 2-isopropenyl thiophene, indene, coumarone, 1-chloroethyl vinyl sulfide, vinyl 2-ethoxyethyl sulfide, vinyl phenyl sulfide, vinyl 2-naphthyl sulfide, aliyl mercaptans, divinyl sulfoxide, vinyl phenyl sulfoxide, vinyl chlorophenyl sulfoxide, methyl vinyl sulfonate, vinyl sulfoanilide, and the like.

The catalysts, buffers and any other constituents which can be employed in the emulsion polymerization reaction mixture in the process of this invention are the same as those which can be employed in the known emulsion polymerization processes of the prior art. The particular choice of the materials, other than the emulsifier, to be employed does not constitute the invention and is a matter of routine in the art of emulsion polymerization.

The catalyst employed is typically a free radical initiator or a redox catalyst. One can mention, as merely illustrative of suitable catalysts which can be employed, free radical initiators such as hydrogen peroxide, peracetic acid, t-butyl hydroperoxide, di-t-butyl peroxide, dibenzoyl peroxide, benz9yF hydroperoxide, 2,4-dichlornbenzoyl peroxide, 2,5-dimethyl-2,5-bis(hydroperoxy) hexane, perbenzoic acid, t-butyl peroxypivalate, t-butyl peracetate, azo-bis-isobutylonitrile, ammonium persulfate, sodium persulfate, potassium persulfate, sodium perphosphate, potassium perphosphate, isopropyl peroxycarbonate, etc; and redox catalyst systems such as sodium persulfate-sodium formaldehyde sulfoxylate, cumene hydroperoxide-sodium metabisulfite, hydrogen peroxide-ascorbic acid, suifur dioxide-ammonium persulphate, etc.

The catalysts are employed in the usual catalytically effective concentration which are known to those skilled in the art of emulsion polymerization.

The novel polyurethane polymer amine salt emulsifier is the subject of our Application No.

8014327 to which reference is made for a detailed description.

The polyurethane polymer amine salt consists essentially of the reaction product of an NCOterminated prepolymer blocked with an oxime reacted with an amine and then further reacted with an acid whereby infinitely water dilutable waterborne polyurethane polymer amine salts are obtained.

As used throughout this specification the term "waterborne" indicates the state or condition of the amine salts of the amine reaction product with the oxime blocked isocyanate prepolymers in an aqueous medium. It is not always apparent whether the polyurethane polymers in water is a microscopically heterogenous mixture of two or more finely divided phases, i.e., liquid in liquid, and thus a dispersion, or whether the polyurethane polymers are partially or wholly dissolved in the aqueous base and thus a solution.

We have observed the polyurethane polymers in water where the resulting product appears to be optically clear indicating a homogeneous solution. In this situation we believe that the individual molecules of polyurethane polymers are not bound together. On the other hand we have also observed polyurethane polymers in water where the resulting product is cloudy, indicating a dispersion. Thus when used in this specification the term "waterborne" means the novel amine salts in an aqueous system which may be either a homogeneous solution, a dispersion or any combination thereof.

In order to provide a satisfactory end product having adequate film forming characteristics it has been recognized that branched reactants must be included in the preparation of the waterborne polyurethane in order to get the necessary cross-linking to produce a three dimensional polymeric structure upon curing. Therefore it is understood throughout the following description that either the polyol, the polyfunctional amine, the prepolymer, a portion of each or any combination thereof shall have a reactive functionality greater than two.

The novel polyurethane polymer amine salt is made in four basic steps. First, a polyol is reacted with a polyisocyanate to prepare an NCO-terminated prepolymen The prepolymer is blocked with an oxime in the second step. Third, the oxime blocked NCO-terminated prepolymer is reacted with one or more selected polyfunctional amines as hereinafter described. The amine reaction product is reacted with an acid. We found that in order to obtain a product with useful properties that a reactant having functionality greater than two should be used in the first and/or third steps. Thus functionality of the NCO-prepolymer plus functionality of the polyfunctional amine will be at least four or greater.

It has been found that the reaction product of the polyfunctional amines with the oxime blocked NCO-terminated prepolymer tends to increase in viscosity with time until a complete gelation/setting up of the product occurs. Thus in another aspect of this invention it has unexpectedly been discovered that the gelation time and viscosity of the waterborne polyurethane polymer dispersion can be controlled and/or adjusted by the addition of a secondary amine to the reaction product.

The isocyanate capped polyoxyalkylene polyol, NCO-terminated prepolymer or urethane prepolymer useful in the invention are prepared by reacting polyoxyalkylene polyol with an excess of polyisocyanate, e.g., toluene diisocyanate. The polyol should have a molecular weight of from about 200 to about 200,000 and preferably from about 600 to about 6,000. The hydroxyl functionality following reaction is from 2 to about 8. When the isocyanate functionality of the polyol and the corresponding isocyanate functionality of the prepolymer is two the functionality of the step 3 amine reactant must be greater than two. When the isocyanate functionality of the prepolymer is greater than two the functionality of the amine reactant in step 3 may be as little as two.

The preferred isocyanate capped or NCO-terminated prepolymer consists of a mixture of (1) an isocyanate capped hydrophilic polyoxyethylene diol, said diol having an ethylene oxide content of at least 40 mole percent; and (2) an isocyanate capped polyol having a hydroxyfunctionality in the range 3 to 8 prior to capping; said isocyanate capped polyol being present in an amount in the range 2.9 to 50% by weight of(1) and (2).

The polyoxyethylene diol is the reaction product of alkylene oxides of which at least 40 mole percent is ethylene oxide with an initiator such as ethylene glycol, propylene glycol, tetramethylene glycol, hexamethylene glycol or mixtures thereof. Preferably the molecular weight of the diol is between about 400 to about 6,000.

Examples of suitable polyols (to be capped with polyisocyanates) include: (A) essentially linear polyols formed for example by reaction of ethylene oxide with ethylene glycol as an initiator. Mixtures of ethylene oxide with other alkylene oxide can be employed so long as the mole percent of ethylene oxide is at least 40 percent. Where the linear polyethers are mixtures of ethylene oxide with e.g., propylene oxide, the polymer can be either random or a block copolymer. A second class of polyol (B) includes those with a hydroxy functionality of three or more. Such polyols are commonly formed by reacting alkylene oxides with a polyfunctional initiator such as trimethylolpropane pentaerythritol, etc.

In forming the polyol B, the alkylene oxide used can be ethylene oxide or mixtures of ethylene oxide with other alkylene oxides as described above. Useful polyols can be further exemplified by (C) linear branched polyfunctional polyols as exemplified in A and B above together with an initiator or crosslinker. A specific example of C is a mixture of polyethylene glycol (m.w. about 1,000) with trimethylolpropane, trimethylolethane or glycerine. This mixture can be subsequently-reacted with excess polyisocyanate to provide a prepolymer useful in the invention. Alternatively the linear or branched polyols, (e.g., pplyethylene glycol) can be reacted separately with excess polyisocyanate. The initiator, e.g., trimethylolpropane, can also be separately reacted with polyisocyanate. Subsequently the two capped materials can be combined to form the prepolymer.

Polyoxyalkylene polyol is terminated or capped by reaction with a polyisocyanate. The reaction may be carried out in an inert moisture-free atmosphere such as under a nitrogen blanket, at atmospheric pressure at a temperature in the range of from about OOC to about 1 200C for a period of time of about 20 hours depending upon the temperature and degree of agitation. This reaction may be effected also under atmospheric conditions provided the product is not exposed to excess moisture.

Capping of the polyoxyalkylene polyol may be effected using stoichiometric amounts of reactants.

Desirably, however, an excess of isocyanate is used to ensure complete capping of the polyol. Thus, the ratio of isocyanate groups to the hydroxyl groups used is between about 2 to about 4 isocyanate to hydroxyl, and preferably about 2 to about 2.5 isocyanate to hydroxyl molar ratio.

To obtain the maximum strength, solvent resistance, heat resistance and the like, the isocyanate capped polyoxyalkylene polyol reaction products are formulated in such a manner as to give crosslinked polymer network.

Any ketoxime is effective among these being acetone oxime, butanone oxime, cyclohexanone oxime, and the like. An oxime based on a relatively volatile ketone is believed to be preferred. The most preferred oxime is butanone oxime, also commonly known as methyl ethyl ketoxime. Mixtures of oximes may be used, but there is no known merit in so doing. The proportions of oxime utilized may range from about 0.7 to about 1.2 equivalents of the isocyanate groups present. A more preferred range is 1.05 to 1.15 equivalents.

To prepare the blocked prepolymer, the oxime and prepolymer are simply admixed at temperatures of from 50 to 700C for from about 1/2 to 1-1/2 hours. A solvent is not generally necessary although materials such as butyl cellosolve acetate can be employed. Other appropriate solvents include materials which are not reactive with either the oxime or urethane groups. Based on the moles of reactive oxime and NCO groups involved, the NOH/NCO molar ratio should be from about 0.7 to about 1.2 and preferably from about 1.05 to about 1.15. Generally it is most effective to use sufficient oxime to completely react with the NCO groups.

In preparing the blocked prepolymer the oxime is selected to provide a product that will undergo curing reactions in a reasonable time at a reasonable temperature. The curing temperature is influenced by materials such as substrates and catalysts so that in curing the waterborne polyurethane dispersion temperatures outside the range of 140-1 800C can be employed. Curing temperatures of at least 1 200C have proved convenient in view of the curing times which must be employed. Lower temperatures result in longer cure times unless a catalyst is employed.Numerous oximes and catalysts which can be employed are described in: Petersen, Liebigs Ann. Chem., 562 (1949), p. 21 5; Wicks, Progress in Organic Coatings, 3 (1975), pp. 73-99; and Hill et al, Journal of Paint Tech., 43 (1971) p.

55. Oximes having the above unblocking temperatures are liquid materials at temperatures of about 800 C, and the condensation products with urethane prepolymers are miscible with water or can be dispersed in water with the aid of surfactants. Generally the oximes are aliphatic cyclic, straightchain or branched materials containing 2-8 (preferably 3-6) carbons.

The oxime blocked NCO-terminated prepolymer is reacted with an amine that is capable of causing the polymer to cure at a low temperature. Many of the amines usable within the scope of Applicant's invention are well known in the art and are referred to as polyfunctional amines. Specific examples of amines include, but are not limited to, ethylenediamine 1,3 propane-diamine, diethylenetriamine, triethylenetetramine, iminobispropyl-amine, tetraethylenepentamine, methyliminobispropylamine, 2(2-aminoethylamine)-ethanol and the polyoxypropyleneamines manufactured by Jefferson Chemical Company, Inc. and sold under the tradenames JEFFAMINE D400, D-2000 and T-403. The polyoxypropyleneamines are aliphatic polyether primary di- and trifunctional amines derived from propylene oxide adducts of diols and triols.

As can be observed from the amines listed some of the amines can be represented by general formulae NH2R'-NH21 and HO-R NH2 where R' is a C2 C8 group.

We have found in our experimental work that polyfunctional amines with a functionality of at least 2 primary amine end groups are the preferred amines in getting adequate curing of the polyurethane polymer subsequently produced.

Some of the polyfunctional amines may be represented by the formula

where z is an integer from 1 to 4, n is an integer larger than 1 and R is hydrogen, an alkyl group of 1 to 4 carbon atoms, or a hydroxyalkyl group of 1 to 4 carbon atoms.

The polyoxypropyleneamines may be represented by the formula NH2CH(CH3)CH2%OCH2CH(CH3)%xNH2 where x is greater than 2, and by the formula

where x+y+z is about 5.3. The molecular weights of these polyoxypropyleneamines range from about 200 to 2000 or larger with the preferred polyoxypropyleneamines having molecular weights of about 400 to 2000.

The amount of polyfunctional amine added to the oxime blocked NCO-terminated prepolymer should be in the range of 0.6 to 1.5 equivalents with the preferable range between 0.9 to 1.1 equivalents based on the total equivalents of all the isocyanate groups present in the NCO-terminated prepolymer.

Where the isocyanate functionality of the NCO-terminated prepolymer is two, a polyfunctional amine having a functionality of greater than two is required in order to provide a satisfactory crosslinked product When the isocyanate functionality of the NCO-terminated prepolymer is greater than two, the polyfunctional amine functionality may be as little as two. It is to be understood from this that in the same reactive system that the functionality of the NCO-terminated prepolymer and the amine or polyoxypropyleneamines will have a total functionality of greater than four.

The reaction between the oxime blocked prepolymer and the polyfunctional amine is controlled by adding an acid or a mixture of acid and water prior to the completion of the reaction. Failure to control the amine-oxime blocked prepolymer reaction at the proper time may result in an amine reaction product too viscous for the purposes of this invention. Thus the proper portions of the blocked prepolymer and polyfunctional amine are placed in a reaction vessel and reacted under controlled conditions of heating and stirring. With experience we have been able to determine the state of the reaction by observing the increase in viscosity. With proper equipment such as temperature controlled mixing head devices the reaction times can be rapid at elevated temperatures.For example reaction times can be as short as about 3 minutes at about 950C, 4 minutes at about 800C, etc. Preferred reaction times are from about one-half hour to about one hour with temperatures between about 40 and 600C. Sufficient acid or water-acid mixture is stirred into the amine reaction product to lower the pH value to about 5 or below.

The cationically stabilized waterborne polyurethane polymers are prepared by dispersing the amine reaction product in water in the presence of sufficient acid to provide a pH of from about 5 or below. In preparing the waterborne polymers the acid can be added directly to the amine reaction product and admixed therewith followed by dilution with water. This is the preferred method. However, it is also possible to first add the acid to the water followed by dispersion of the amine reaction product in the water. Other additives such as surfactants, ultraviolet absorbers, stabilizers, pigments, etc., may be formulated into the waterborne polyurethane polymers as required.

It has been found that if the pH is not controlled within the broad range set forth above, settling problems are encountered and/or portions of the amine reaction product reacts with the water to form a crust. While the pH value range is to be considered we have found that from about 1 to 10 parts or more of acid may be used for each 100 parts of amine reaction product. A more preferred range is from about 4 to 8 parts acid per 100 parts amine reaction product. These waterborne polymers have been found to be stable for periods of several months at ambient temperatures, e.g., 200C, and also exhibit excellent resistance to freeze-thaw cycles.

While any organic or inorganic acid will form the amine salt and perform the function of controlling the pH value, the acids which we have used include glacial acetic acid, acrylic acid, citric acid, ethylenediamine-tetraacetic (EDTA) acid, formic acid, glycine (aminoacetic acid), hydrochloric acid, lactic acid (alpha-hydroxypropionic acid), orthophosphoric acid (H3 PO4), phosphorous acid (H3 Pro3), sulfamic acid, sulfuric acid, tartaric acid (dihydroxysuccinic acid), paratoluenesulfonic acid and mixtures thereof.

The following specific Examples illustrate the invention.

Preparation of Polyurethane Prepolymer Amine Salt A preferred isocyanate terminated polyol prepolymer is prepared by mixing a hydrophilic polyoxyethylene diol having an ethylene oxide content of at least 40 mole percent with a polyol having a hydroxyl functionality in the range 3 to 8, said polyol being present in the admixture in an amount in the range 1.0 to 20% by weight, reacting with the mixture at a temperature in the range 0 to 1 200C an amount of a diisocyanate equal to 1.8-1.9 NCO to OH equivalents for a time sufficient to cap substantially all the hydroxyl groups of the admixture, adding additional diisocyanate to provide 0.10.3 equivalents of NCO per initial equivalent of OH in excess of the theoretical amount necessary to react with the hydroxyl groups.

To 100 grams of the NCO-terminated polyol prepolymer at 240C in a stainless steel vessel is added 22 grams of butanone oxime with stirring. The reaction of the oxime with the isocyanate is exothermic and the temperature went to 600C. A hot water bath is used to control the temperature between 80-900C for twenty minutes.

After twenty-minutes and the temperature at 900C, 12 grams of diethylenetriamine is added with stirring. The reaction with the amine is also exothermic which accelerates chain extension.

The viscosity continues to increase and after ten minutes at 90-950C, 7.1 grams of glacial acetic acid and 7.1 grams of o-phosphoric acid dissolved in 1 00 grams of deionized water is slowly added to control the viscosity. After all the acid/water mixture is in, the material is cooled and packaged. Water may be added to achieve the desired % non volatiles (% N.V) and viscosity.

Typical physical properties of the emulsifier prepared are: % N.V. 52.0 pH 4.5-6.9 Viscosity (Brookfield LVF) 600-1000 cps Appearance clear, straw colored solution Example 1 To a two liter resin kettle fitted with a condenser, thermometer, graduated addition funnel, stirrer, and a nitrogen source was added 327.5 g. of demineralized water, 2.0 g of isoascorbic acid, and 687.5 g (196.6 grams nonvolatiles) of cationic polyurethane prepolymer amine salt @ 24% nonvolatiles. The mixture was stirred and heated to 400C, under a nitrogen blanket.

At 400C, 100 g of a monomer mixture of 240.0 g of methylmethacrylate, 120.0 g of butylacrylate, 40.0 g of acrylonitrile and 8.0 g of acrylic acid was added to the kettle with stirring. To the material in the resin kettle was charged 4 cc of 30% hydrogen peroxide. The heat of reaction caused the temperature to go from 41 OC to 470C in three minutes. The remaining monomer mixture was charged at a rate to maintain a temperature of 55-600C in the resin kettle without auxiliary heating. Discrete shots of 30% H202 were added at 2 cc levels during the monomer mixture addition.

The total monomer mixture addition time was 39 minutes. When the last of the monomer mixture was charged, the temperature was 570C.

Eight minutes after the final monomer mixture addition and at a temperature of 540C, 0.1 g of isoascorbic acid dissolved in 10 cc demineralized water and 1.0 g of tertiary butylhydroperoxide were added to reduce the free monomer.

The two liter resin kettle (after packaging latex) had no solid buildup at all and required only a water rinse. The resulting latex had 39.6% Total Solids, a pH value of 4.3, a surface tension of 43.2 dynes/cm and a Brookfield LVF #1 @ 60 viscosity of 53.4 centipoises.

Example 2 Reactant % WET vinylidene chloride 67 640 butyl acrylate 15.0 144 glacial acetic acid 2 16 polyurethane prepolymer amine salt @ 40% solids 1 7 400 ascorbic acid .2 2 hydrogen peroxide 1.0 10 demineralized water 800 To a 2 liter resin kettle fitted with a thermometer, stirrer and addition funnel was added 800 g.water, 400 g. polyurethane prepolymer amine salt at 40% solids, and 2 g. ascorbic acid. This mixture was heated to 360C under a nitrogen purge.

To the above was added 200 cc of a mixture consisting of 640 g. vinylidene chloride, 144 9. butyl acrylate, and 1 6 g. glacial acetic acid followed by the addition of 2 cc of 20% hydrogen peroxide. The heat of reaction raised the temperature to 460C. The remainder of the monomer was added in 100 cc increments along with 1-2 cc shots of hydrogen peroxide to maintain a temperature range of 45500C. After the last of the monomer was added, a 2 cc parting shot of hydrogen peroxide was added and the batch was allowed to cook to reach maximum conversion.The latex had the following properties: Total Solids 39.0% Conversion 81.6% Surface Tension 52.8 dynes/cm pH Value 4.0 Examples 3-12 below illustrate emulsion polymerization using the polyurethane prepolymer amine salt as emulsifier with various monomer combinations. The procedure used in Examples 3-12 was that described in Example 2. All ingredients are indicated in weiaht Dercent.

Example 3 Weight % vinylidene chloride 32 styrene 33 acrylic acid 2 PAS 33 Example 4 Weight % vinylidene chloride 56 methylacrylate 5 acrylic acid 2 PAS 37 Example 5 Weight % methylmethacrylate 6 butylacrylate 13 methylacrylate 37 acrylic acid 6 PAS 38 Examp!es 6, 7, 8 6 7 8 methylmethacrylate 49 42 39 butylacrylate 25 21 20 acrylonitrile 8 7 6 acrylic acid 2 2 2 PAS 16 28 33 Examples 9,10 9 vinylidene chloride 33 28 styrene 33 28 butylacrylate 1 6 14 acrylic acid 2 2 PAS 16 11 Example 11 methylmethacrylate 71 PAS 29 Example 12 Weight % 12-1 1272 methylmethacrylate 42 37 butylacrylate 21 1 8 acrylonitrile 7 6 acrylic acid 2 2 PAS , 28 37 The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed.

Claims (14)

Claims

1. A process for producing a polymer latex which comprises polymerizing one or more polymerizable monomers in aqueous emulsion in the presence of a polyurethane prepolymer amine salt emulsifier prepared by reacting a first component comprising an isocyanate-capped hydrophilic polyol having a reaction functionality of two or greater with a second component comprising a ketoxime to form an oxime-blocked prepolymer, reacting said oxime-blocked prepolymer with a third component comprising a polyfunctional amine having a functionality of two or greater to form an amine reaction product, reacting said amine reaction product with a fourth component comprising an acid to produce an infinitely water-dilutable polyurethane polymer amine salt, and diluting said polyurethane polymer amine with water.

2. A process according to Claim 1 wherein the one or more polymerizable monomers are chosen from lower alkyl acrylates, lower alkyl methacrylates, acrylonitrile, acrylic acid, vinylidene chloride, styrene, and mixtures thereof.

3. A process according to Claim 1 or 2, wherein the said second component is butanone oxime.

4. A process according to any of Claims 1 to 3, wherein the said third component is diethylenetriamine, triethylenetetramine, iminobispropylamine, tetraethylenepentamine, methyliminobispropylamine, 2(2-aminoethylamino)-ethanol, ethylenediamine, 1 ,3-propanediamine, polyoxypropyleneamine, or a mixture thereof.

5. A process according to any of Claims 1 to 3, wherein the said third component is a mixture of diethylenetriamine and diethylamine, dibutylamine or dihexylamine.

6. A process according to Claim 4 wherein the said third component also includes diethylamine, dibutylamine or dihexylamine as a viscosity controlling agent.

7. A method according to Claim 4 wherein the polyfunctional amine third component is a polyoxypropyleneamine having a molecular weight of about 230.

8. A method according to Claim 4 wherein the polyfunctional amine third component has the formula:

where x+y+z is about 5.3, and has a molecular weight of about 400.

9. A process according to any of Claims 1 to 8 wherein the said fourth component is acetic, acrylic, citric, ethylenediaminetetraacetic, formic, glycine, lactic, o-phosphoric, phosphorous, ptoluenesulfonic, sulfamic, tartaric, or hydrochloric acid or a mixture thereof.

10. A process according to Claim 9 wherein the said fourth component is aqueous acetic acid, aqueous o-phosphoric acid or a mixture thereof.

11. A process according to any of Claims 1 to 10 wherein the said first component consists of a mixture of (1) from 2.9 to 50% by weight of said mixture of an isocyanate-capped polyol having a hydroxyl functionality in the range of 3 to 8 prior to capping; and (2) from 97.1 to 50% by weight of said mixture of an isocyanate-capped hydrophilic polyoxyethylene diol, said diol having an ethylene oxide content of at least 40 mole percent.

12. A process according to any of Claims 1 to 11 wherein 0.7 to 1.2 equivalents, based on NCO groups, of the ketoxime second component is reacted with the isocyanate-capped polyol first component to form an oxime-blocked prepolymer, the said oxime-blocked prepolymer is reacted with 0.6 to 1.5 equivalents, based on the blocked NCO groups, of the polyfunctional amine third component to form an amine reaction product, the said amine reaction product is reacted with from 1 to 10 parts of the acid fourth component per 100 parts of the said amine reaction product to form an amine salt, and the said amine salt is diluted with water to be less than 60% total non-volatiles content.

13. A process according to Claim 1 substantially as described in any one of the foregoing Examples 1 to 12.

14. A polymer latex produced by the process of any one of Claims 1 to 13.

1 5. A waterborne polyurethane prepolymer amine salt obtained by (1) admixing a hydrophilic polyoxyethylene diol having an ethylene oxide content of at least 40 mole percent with a polyol having a hydroxyl functionality in the range 3 to 8, said polyol being present in the admixture in an amount in the range 1.0 to 20% by weight, reacting with the admixture at a temperature in the range 0 to 1 200 C, an amount of diisocyanate equal to 1.8-1.9 NCO equivalents for a time sufficient to cap substantially all the hydroxyl groups of the admixture and thereafter adding additional diisocyanate to provide 0.1-0.3 equivalents of NCO per initial equivalent of OH in excess of the theoretical amount necessary to react with the hydroxyl groups to form an NCO-terminated prepolymer; ; (2) reacting said NCO-terminated prepolymer with from 1.05 to 1.15 equivalents of butanone oxime to form a butanone oxime-blocked prepolymer; (3) reacting said butanone oxime-blocked prepolymer with from 0.9 to 1.1 equivalents of diethylenetriamine to form an amine reaction product; and (4) reacting said amine reaction product with water containing from 4 to 8 parts of a mixture of acetic and phosphoric acids per 100 parts of said amine reaction product so that the resulting waterborne composition contains from 20 to 50% by weight non-volatiles.