Technical Field

This invention relates to hydrophilic poly- urethane polymers modified to contain carboxy groups in the polymer backbone, to processes for preparing the so-modified polyurethanes, and to uses thereof.

Background Q1 ______& Invention

Numerous polymer systems that contain free carboxy groups are known in the art. It is difficult, however, to prepare a carboxy polyurethane, that is, a

polyurethane having free carboxyl groups, because iεo- cyanate, which is a necessary component in the prepara¬ tion of any polyurethane, is quite reactive with the carboxyl groups of the carboxylic acid reactants used 5 to introduce the carboxyl group.

One approach to the introduction of carboxy groups into a polyurethane resin chain is described in U.S. Patent No. 3,412,054 to Hilligan et al. In that

•lO patent, a 2,2-di(hγdroxymethyl)alkanoic acid is reacted with an organic diisocyanate to produce a polyurethane containing unreacted carboxylic acid groups. These acids are unique because their carboxyl groups do not react to any significant extent with the isocyanateε to

15 prevent the formation of the desired carboxy resin.

However, very few carboxylic acids have this character, thus reducing the cost effectiveness of this approach.

Another approach is that of U.S. Patents 20 4,156,066 and 4,156,067 to Gould. In these patents, a polyfunctional lactone, preferably containing at least three hydroxyl groups, is reacted with an isocyanate and one or more diols to form a polyurethane having lactone groups in the polymer backbone. Upon saponifi- 5 cation or hydrolysis the lactone rings open up to form carboxyl groups. However, the amount of carboxyl which can be introduced via the lactones is limited such that the enhancement of properties attributable to the car¬ boxyl groups, e.g., water-solubility, cross-linkability

or other reactivity characteristic of carboxyl func¬ tionality, is marginal for some applications.

Summary ______ the Invention

It has now been found that hydrophilic poly- urethanes which contain carboxy (carboxylic acid or carboxylate, i.e., salt) groups in the polymer backbone can be prepared from carboxylic acids, the carboxyl functionality of which would normally be lost by reac¬ tion with organic isocyanate, by esterifying the car¬ boxyl functionality prior to reaction with the isocya¬ nate. This shields the carboxyl groups to prevent reaction with the isocyanate. Once the polyurethane is formed, the ester groups are easily converted to car¬ boxylate (salt) groups by saponification with a suit¬ able base, and to free carboxyl (acid) groups by neu¬ tralization of the saponified polymer with a suitable acid. The carboxylic acid ester reactants must also contain active hydrogen containing groups as sites for reaction with the isocyanate for urethane formation. As is known, active hydrogen groups include hydroxyl (in an aliphatic or aromatic moiety), mercaptan, oxime, amido, amino (primary or secondary), hydrazine, and the like.

The shielding afforded by the ester groups permits use of a wide variety of carboxylic acids (as

contrasted with the limited class of U.S. Patent 3,412,054), including acids having a plurality of car¬ boxyl groups and other functional groups, and thus opens up opportunity for substantial enhancement of properties attributable to higher amounts of carboxyl functionality, particularly adhesion to polar and/or polarizable substrates and the preparation of resins with differing pH and susceptibility to crosεlinking.

More particularly, the carboxy functionality of the polyurethanes supplements their hydrophilicity by providing reactive sites for introduction into the polymer of a variety of other groups, by facilitating chemical curing of films, coatings and other products prepared from the polyurethanes, and by improving ad¬ hesion to different types of substrates. The hydro- philic carboxy polyurethanes typically are low melting solids, flowing in the range of about 90°C to 250°C, and can be used as coatings or can be fabricated into a wide variety of shaped bodies including films and can- nulae using conventional thermoplastic polymer proces¬ sing procedures. The polyurethane ester intermediate is soluble in lower aliphatic alcohols, chlorinated solvents, esters, aromatic solvents and a host of other polar and non-polar solvents, but insoluble in water.

The saponified polymer is partially soluble in lower aliphatic alcohols, particularly if water is present, and soluble in water if sufficiently modified.

Accordingly, in one aspect of the invention, carboxy groups are incorporated into polyurethanes by esterifying the carboxyl group or groups of a car¬ boxylic acid having other active hydrogens for reaction with organic isocyanate, and reacting the esters in the presence of a polyol component with an organic iso¬ cyanate to form a polyurethane intermediate. Alter¬ natively, a prepolymer can be formed by reaction of the ester and isocyanate, and polyurethane is then produced by reaction of the prepolymer with polyols. By appro¬ priate selection of the polyol component and control of the ratio of isocyanate (NCO) to active hydrogen in the reaction mixture, the resulting polyurethane intermedi¬ ate polymer is hydrophilic as evidenced by its ability to absorb water to at least 10% of its weight, prefer¬ ably about 20% to 200%.

In other aspects of the invention, the ester groups of the hydrophilic polyurethane intermediate are saponified by reaction with an aqueous base and the saponified groups are neutralized to form free carboxyl groups, thereby making the carboxyl groups available for reaction with other functional groups or for im¬ proved chemical curing or adhesion.

In still other aspects of the invention, the hydrophilic carboxy polyurethanes prepared in the man¬ ner described above are used in light sensitive photo¬ graphic layers on films, paper or glass, in boat and

pipe coatings for decreasing hydrodynamic drag, as drug delivery systems, as burn and wound dressings, in cos¬ metic applications, in body implants and catheters, as coatings on cannulae, and in a host of other applica- tions where the hydrophilic character and carboxy func¬ tionality are useful properties. In general, the poly¬ urethanes can be used in any of the applications des¬ cribed in the above-cited U.S. patents but with less complicated processing such as the need, in the case of the lactone-containing polyurethanes, of removing un- reacted lactone.

Detailed Description

The polyurethanes of the present invention are prepared by the reaction of:

(A) a polyol component comprising at least one of

(a) an alkylene glycol,

(b) a long chain polyoxyalkylene glycol, and

(c) a linear polyester diol derived from the condensation of one or more diols with one or more dibasic acids;

(B) a carboxylic acid ester component comprising at least one of

(a) a hydroxy carboxylic acid ester selected from at least one of

ROOC-CH- (CH ₂ ) r-H-COOR, OH OH

HO(CH ₂ ) _n CH(CH ₂ ) _p ^* COOR

and

wherein R is an aliphatic group; m and p independently are integers of from 0 to 12 and n is an integer of from 1 to 12; and

(b) an amino acid ester having at least two active hydrogen atoms; and

(C) an organic isocyanate or isocyanate precursor containing at least two NCO groups;

the ratio of NCO to active hydrogen atoms in the reaction mixture being from 0.5/1 to 1/1, preferably about 0.7/1 to 0.95/1.

The polyol component (A) generally comprises one or more water soluble glycols having a molecular weight of at least about 50, preferably at least about 200, more preferably about 1000 to 8000 or more, and may be derived from simple alkylene glycols, long chain polyoxyalkylene glycols, and esters or ether-ester block-containing diol resins. Representative alkylene glycols (a) include the low molecular weight glycols and glycol ethers such as ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, and the like. Suitable long chain polyoxyalkylene glycols (b) consist predominantly of oxyethylene or oxypropylene groups, though a minor proportion of other oxyalkylene groups may be included, having a number average molecular weight of from about

400 to 20,000. Block copoly er polyols obtained by adding ethylene oxide to a polyoxypropylene chain are also useful.

Representative linear polyester diols (c) are derived from the condensation of one or more alkylene glycols with one or more dibasic acids and include reaction products of x moles of a difunctional acid such as adipic, sabacic, dimeric acid, phthalic and maleic etc., and x+1 moles of difunctional linear gly¬ cols such as ethylene glycol, polyethylene glycols (molecular weight 100-600, preferably 200-300), propy¬ lene glycol, polypropylene glycols (molecular weight

100-600, preferably 200-300), 1,4-butane diol, poly- butylene glycols (under 400 molecular weight) and the like. Mixtures of acids and/or glycols may be used and the value of x may vary from 1 to about 10. The mole¬ cular weight increases as x increases, the preferred value of x being 3-6. However, the molecular weight should not so high that the ester portion becomes the major portion of the polymer, an undesirable result due to the hydrophobic character of ester groups.

A minor portion (10 wt. % or less, preferably about 2 wt.% or less) of the polyol component (A) may comprise polyolε having three or more hydroxyl groups, such as glycerol or sorbitol, provided the type and amount of the polyol does not cause undue and/or prema¬ ture crosεlinking of the polyurethane.

R in the above formulas and the ester group of the amino acids typically is an alkyl or alkenyl group containing 1 to about 12 carbon atoms or more, in some cases preferably at least 4 carbon atoms, e.g., 4 to 8 carbon atoms, for the reason explained in Example 1 below.

Representative carboxylic acid esters of (B) are hydroxy mono carboxylic acid esters such as gly- ceric acid esters including D-ethyl glycerate and D- ethyl glycerate; trihydroxy n-butyric acid esters such as D-methyl erythronate; dihydroxy benzoic acid esters

such as methyl or ethyl 3,4-dihydroxybenzoate, methyl or ethyl 2,4-dihydroxybenzoate, methyl or ethyl 2,5- dihydroxybenzoate, methyl or ethyl 3,5-dihydroxyben- zoate and methyl or ethyl 2,6-dihydroxy-4-methylben- zoate; and hydroxy dicarboxylic acid esterε such as methyl or ethyl dihydroxymalonate, dimethyl or diethyl bis(hydroxymethyl)malonate, dimethyltartarate, diethyl- tartarate, dibutyltartarate, and the like, including isomerε thereof. Representative amino acids which may be esterified to form amino acid esters (b) are mono amino acids such as DL serine, glycine, alanine, val- ine, leucine and the like; amino derivatives of dibasic acids, such as aspartic acid, glutamic acid and the like, and polyamino acids such as L-lysine and argin- ine. The amino groups may be positioned anywhere on the carbon chain of the acid and thus include alpha, beta, gamma and delta amino acids.

The foregoing and a host of other carboxylic acids which may be esterified to form component (B) of the reaction mixture are described in Organic Chemistry by F.C. hitmore, second edition, Dover Publications (1961), pages 348-350, 397-404, and 497-522, incorpor¬ ated herein by reference, and in other standard tests. It will be evident from the literature that the esters may carry other active hydrogen-containing groups along with or in place of hydroxyl and/or amino, such as mercapto groups. The esters may be used singly or in mixtures of two or more, including combinations of

eεterε (a) and (b) of component (B). The type (a) esters are preferred, either as single esters or as any mixtures thereof.

The organic isocyanate used in the present invention may be represented by R(NCO) _q wherein q is an integer greater than 1, preferably 2-4, and R is an aliphatic, alicyclic, aliphatic-alicyclic, aromatic, or aliphatic-aromatic hydrocarbon compound of from 4 to 26 carbon atoms, but more conventionally from 6 to 20 and preferably from 6 to 13 carbon atoms. Representative isocyanates are: tetramethylene diisocyanate, hexa- methylene diisocyanate, trimethylhexamethylene diiso¬ cyanate, dimer acid diisocyanate, isophorone diiεocy- anate, diethylbenzene diisocyanate, decamethylene 1,10- diisocyanate, cyclohexylene 1,2-diiεocyanate, cyclohex- ylene 1,4-diisocyanate; the aromatic isocyanates such as 2,4- and 2,6-tolylene diisocyanate, 4,4-diphenyl- roethane diisocyanate, 1,5-naphthalene diisocyanate, dianiεidine diisocyanate, tolidine diisocyanate, - xylylene diisocyanate, tetrahydronapthalene-1,5 diiso¬ cyanate and neopentyl tetra isocyanate.

The preferred isocyanate is methylene bis(cy- . [-. clohexyl-4^(f-iεocyanate) sold by Mobay Chemical Corp. ° under the trademark "DESMODDR ." Other somewhat less preferred isocyanates are trimethyl hexamethylene di¬ isocyanate and isophorone diisocyanate.

Other compounds which are useful are organic isocyanate equivalentε which produce urethane linkages such as the nitrile carbonates, i.e., the adiponitrile carbonate of the formula:

The proportions in which the polyols (A) are used, particularly the preferred combination of a long chain polyoxyalkylene glycol and a low molecular weight alkylene glycol, e.g., diethylene glycol, depend on the hydrophobic-hydrophilic balance desired in the final product. Increasing the molecular weight of the long chain polyoxyalkylene glycol and/or the amount of this component, for example, contributes strong hydrophilic properties to the final product. This effect may be counter-balanced by increasing the proportion of low molecular weight alkylene glycol, i.e., diethylene glycol or dipropylene glycol.

Thus, because the number of polyalkylene oxide groups in the polyurethane primarily determines hydrophilic properties, it is a simple matter to choose mixtures of reactants such that the final product will have the desired hydrophilicity and other properties.

By choosing the molecular weight of a polyol or by using two polyols of different molecular weight, one may "tailor make" products having a wide range of properties. Other modifications of the hydrophilic polyurethane polymers may be made by adding a dialkanol tertiary amine such as diethanol methyl amine to the reaction mixture. The foregoing and other consider¬ ations relating to selection of polyol components for obtaining hydrophilic character is well known in the art, as described in U.S. patents 3,822,238, 3,975,350,

4,156,066 and 4,156,067, incorporated herein by refer¬ ence.

In one method of making the polyurethane resins of this invention, a homogeneous mixture of the polyol component and water is prepared and the organic isocyanate is reacted with the mixture. In another method of preparation, a prepolymer may first be formed by reaction of the organic isocyanate and ester, followed by reaction with the polyol components. In either case the urethane-forming reaction may be cata¬ lyzed by a known catalyst for such reaction, suitable ones being tin saltε and organo tin esters such as stannous octoate and dibutyl tin dilaurate, tertiary

amineε such aε triethyl dia ine (DABCO), N,N,N',N'- tetramethyl-l,3-butane diamine and other recognized catalyεtε for urethane reactions, with care being taken not to heat the reaction mixture unduly since undeεir- ably denεe croεεlinking may reεult.

Water in the reaction mixture cauεes evolu¬ tion of carbon dioxide, reεulting in the polymer being obtained aε a foam. Thiε is an advantage in that the foamed polymer, owing to its large surface area, exhib¬ its a high rate of diεεolution, thereby facilitating the preparation of solutions of the polymer. In adding the requisite quantity of water to the reaction mix- ture, allowance εhould be made for any moiεture that may be present in the glycol components. It iε not unuεual for commercial grades of alkylene glycols and polyoxyalkylene glycols to contain varying amounts of water. Moreover, such glycols tend to be hygroscopic and even if free of water, may become contaminated with moisture from atmospheric exposure. Preferably, how¬ ever, εufficient water will be preεent or added to cauεe foaming of the polyurethane polymer aε it iε formed. Generally, trace amounts up to about 0.5 partε by weight of water baεed on 100 partε by weight of the total reaction mixture (excluεive of catalyεt) will be effective, and for foaming, from about 0.1 to about 0.5 part by weight on the same basiε.

Upon completion of the reaction of the polyol component, ester and polyisocyanate, the polyurethane resin intermediate may be dissolved in an appropriate solvent, e.g., ethanol, and saponified with a strong aqueous base such as an alkali metal hydroxide, e.g., sodium or potassium hydroxide, while heating at reflux temperature for about 30-60 minutes. The resulting carboxylate polymer may be used directly in many of the applications described below or may be neutralized with an acidic material to a low pH (e.g., pH 3), preferably using a mineral acid such aε dilute hydrochloric acid, to form carboxyl groups. Under ambient or normal con¬ ditions of polymer formation, the carboxyl groups can react with the urethane groups of the polymer to form loose or light crosslinks comprising ester or salt groups. If the polymer is heated sufficiently (as in a molding operation), the carboxyl groups themselves can interact to cause tight, dense crosslinking, probably by elimination of water, rendering the polymer insolu- ble in solvents in which non-carboxyl group containing polyurethanes are soluble.

Upon neutralization of the carboxy1-containing polyurethane with ammonium hydroxide, the polymer will become water soluble so long aε it is not heated to a high temperature. If thus heated or cast from solu¬ tion, ammonia will be driven off, leaving a water insoluble film.

The carboxyl groupε alεo provide εiteε for light or looεe croεεlinking reactionε with the urethane groupε and other reactionε, εuch aε croεεlinking or curing with polyvalent metalε and other materialε (εuch as ammonium dichromate), and for interaction with func¬ tional groups carried on various subεtrateε contacted by the polymerε. Aside from their reactivity, the car¬ boxy groups provide for excellent adhesion to a variety of subεtrateε, eεpecially if curing agentε, εuch aε thoεe mentioned, are uεed with the polyurethaneε.

The polyurethane intermediates carrying ester groups, the saponified forms or the free carboxyl reε- inε of the present invention because of their unique physical properties may advantageously be used as burn dreεsings. The polyurethane reεin may be applied to the burn aε a powder, film, or from εolution in a volatile non-toxic εolvent and will form a barrier that iε permeable to liquids. Thus the physician has a choice of medication which may be applied to the burn prior to the resin coating or the medication may be added to the reεin for timed releaεe. A particularly advantageouε burn dreεεing iε a powder obtained by the low temperature grinding of from about 1 to about 80 parts by weight of the polyurethane resinε in their carboxyl formε and a high-boiling, water soluble non- toxic solvent for the polymer, such as glycerol, di¬ methylεulfoxide or low molecular weight polyethylene glycolε.

The above described polyurethane resins are also useful as coatings, molding compounds, absorbentε, controlled release agents, ion exchange resins, in the repair of skin abrasions and in the manufacture of dialysis membranes, denture liners, cannulae, contact lenses, solubilizing packaging components, hair sprays, cosmetics, burn dressings, contraceptive devices, su¬ tures, surgical implants, blood oxygenators, intrauter- ine devices, vascular prostheseε, perfume fixatives, deodorant compositions, antifog coatings, surgical drapes, oxygen exchange membranes, artificial finger¬ nails, finger cots, adheεives, gas permeable membranes, and in protective and drag resistant coatings for boat hulls and fluid conduits of all kinds.

The invention is further illustrated by the following non-limiting examples in which all parts and percentages are by weight unless otherwise indicated.

Example 1 illustrates the ease with which polyurethanes of the invention can be handled due to the difference in solubility of salt and acid forms of the polymers, the former being water soluble but the latter becoming water insoluble. If ammonia or other fugitive monovalent salt-forming compound iε used for neutralization of the carboxylic groups, the water- soluble resin becomes water-insoluble after drying and removal of ammonia. Addition of amino compounds of low

volatility such as di- and tri-ethanolamines, morpho- line, and the like is useful because εuch compoundε remain in the film after the water has vaporized and thereby improveε film continuity.

Example 2 deεcribeε a polyurethane eεpecially adapted for drug delivery and sustained release. The carboxy groups provide adhesion to the stomach mucosa and thuε prolong the dwell time in the εtomach of a compoεition baεed on the polyurethane carrying medica¬ tion (capεule, coated tablet, etc.) .

Exampleε 3-5 illuεtrate polyurethaneε which are particularly suitable aε permanent coatingε for boat hulls, εuch coatingε uεually being cured by the action of light on compoεitionε containing ammonium dichromate. The coatingε lower hydrodynamic drag and thuε allow increaεe in veεεel εpeed at the εame engine output or allow lowering of engine output for the εame εpeed.

Example 6 il l uεtrateε the verεatil ity of the polyurethaneε aε hard, high adhesion coatings (for example, for use in fingernail pol ishes) due to εol u- bility in a host of sol ventε both polar and non-pol ar.

.EJJ PJ J; i

In forming the ester reactants of the inven¬ tion, it is convenient to use alcohols with four or more carbon atoms, because these have a limited water solubility and the reaction can be run in an excess of alcohols under refluxing conditions, the reflux conden¬ sate going through a device which will separate the water and return the alcohol to the reaction (similar to Dean-Stark trap). If lower alcohols are used, a fractionating column iε required. Any conventional esterification catalyst may be used, such as toluene sulfonic acid, inorganic acids, ion exchange resinε, εodium alcoholates, etc. A preferred catalyst is tetrabutyl titanate and a typical esterification formu¬ lation is the following:

malic acid(hydroxy succinic acid) 134.6 parts n-butanol 205.2 parts tetrabutyl titanate 0.2 parts

These reagents are mixed in a reaction vessel equipped with a εtirrer and a reflux condenser having a Dean- Stark trap. After refluxing the mixture for 8 hours, 26.6 parts of water are collected. The acid value is 20.6. Then 30 parts of n-butanol are added with 0.1 parts of tetrabutyl titanate and the refluxing contin¬ ued for another three hours. A total of 31.8 parts of water is collected to this point and the final acid

value iε 8.3. The resulting ester iε used to prepare a hydrophilic polyurethane resin as follows.

A mixture of 60.1 parts of CARBOWAX* 1450 (a polyethylene glycol having a number average molecular weight of 1450, Union Carbide Corporation), 1.7 partε of glycerol and 25.5 parts of DESMODUR W* [methylene-

Two more εhort expoεureε (12 minuteε each) to 40°C bring the amount of reacted iεocyanate to 50.0%. The reaction mixture becomeε very viεcouε and tetrahydro- furane solvent is added in sufficient quantity to re¬ duce the viscosity.

At this point, 29 parts of the aforesaid n- butyl ester of malic acid are added with an additional

0.1 part of stannous octoate. The temperature iε brought to 55-60°C for a period of 1.5 hourε. At the end of thiε period, the iεocyante iε found to be com¬ pletely reacted.

The reacted resin iε mixed with double the amount of sodium hydroxide εtoichio etrically required to saponify the ester. An additional 18.3 parts of 50% NaOH are mixed well with the resin solution which is

then held for 24 hours at room temperature to complete the reaction. A fine precipitate of sodium carbonate forms during this time. The solution is neutralized with 10% hydrochloric acid and becomes clear at pH 5.0. The final pH is 3.0.

The resin obtained after evaporating the solvent is insoluble in water, but disεolves to a slightly turbid solution in water containing ammonium hydroxide (about 3.5% NH3). This am oniated solution dries to a clear film which is not water soluble but iε soluble in lower aliphatic alcohols and other suitable solvents.

Eu E E.2

A hydrophilic resin is made, using the fol¬ lowing formulation:

68.1 parts CARBOWAX 1450 9.7 partε diethylene glycol 0.5 parts water 40.9 partε dibutyl eεter of tartaric acid 80.8 parts DESMODUR W

0.4 parts εtannouε octoate.

The isocyanate is placed in a reaction veεsel with 0.15 partε of the εtannouε octoate. The dibutyl

eεter of tartaric acid iε then added in incrementε of approximately 2 partε each. Temperature of the reac¬ tion is maintained at 60-75°C by supplying heat or delaying the next addition of the eεter. The eεter iε added during a one hour period, at the end of which time the mass becomes so viεcouε that it can no longer be εtirred. Tetrahydrofuran εolvent iε added to reduce the viscosity.

The balance of the molten polyglycols and the rest of the catalyst is added to the batch. After heating and vigorouε mixing, the maεε becomeε homogene- ouε and iε poured into a polypropylene tray and placed into an oven at 100°C to cure. Before placing into the oven, 81.1% of the iεocyanate iε found to be reacted.

After two hourε of heating, the percent of reacted isocyanate riseε to 97%, and an additional hour at 120°C brings it to 98.3%.

The resin thus produced contains butyl ester groupε, which alter the mechanical and the εurface propertieε of the polymer. Saponification of the eεter is accomplished in solution by adding between 1.05 and 1.10 equivalent of sodium hydroxide (as a 20% solution in water) per ester group, and heating the solution to the refluxing temperature of the εolvent for εeveral hourε. The sodium salt of the carboxylic acid is formed and n-butanol is liberated.

EΣMJ__I_ _ 1

52.4 parts of CARBCWAX 1450 are heated with 8.9 parts of diethylene glycol, 0.24 parts of water and

1.5 parts of diethyl eεter of tartaric acid (Fluka Chemical Corp., Hauppauge, N.Y.) until the CARBOWAX diol melts and a homogeneouε mixture iε obtained. 37.0 parts of DESMODURW are added and mixed with the glycols, bringing the temperature of the mixture to about 50°C.

At this stage, 0.15 parts of stannous octoate are added under vigorous mixing. The reaction mixture starts to exotherm in about 1.5 minutes. When the temperature reaches 70°C, the reaction mixture is quickly poured into a polyethylene tray and placed in an oven, where it iε cured for 1.5 hours at 100°C.

For the saponification of the ethyl ester of the tartaric acid in the resin, 2N solution of sodium hydroxide iε uεed in a 5% excess of the equivalent of the ester groups. This iε effected by dissolving the resin in methyl alcohol to 20% solids, adding the proper amount of the sodium hydroxide solution and stirring the mixture under nitrogen (to remove carbon dioxide and prevent formation of sodium carbonate) for

12 hours at slightly elevated temperature (25-30°). The viscosity of the saponified solution iε much less than the εolution of the resin in the ester form.

The resulting carboxylate form of the reεin is neutral ized from pH 10 to about pH 6 with a dil uted solution of hydrochloric acid. This converts most of the sodium salt groups to carboxylic acid groups.

£X £ £

52.5 parts of CARBOWAX 1450, 8.9 parts of diethylene glycol, 0.2 parts of water and 1.9 parts of dibutyl eεter of tartaric acid (Fluka Chemical Corpora¬ tion) are reacted with 36.4 parts of DESMODUR W esεen- tially aε deεcribed in Example 3. The reεulting reεin iε 99.2% reacted after the oven curing.

The reεin iε diεεolved to 20% εolidε in methyl alcohol, and the butyl ester groups are saponi¬ fied using 2N sodium hydroxide, as described in Example 3. The viscosity of the resin solution in ester form is 925 cP (at 25°C) and the viscosity of the resin in the carboxy form is 44 cP (at 25°C).

When films are cast from the resin εolutionε, dired and then hydrated, it iε found that the eεter form of the polyurethane has an equilibrium water con¬ tent of 58.0% and expansion of 42.1%, while the sodium salt (carboxylate) form has an equilibrium water con¬ tent of 64.5% and expanεion of 51.7% on swelling. The tensile strength of the ester form material is 2500 psi

dry and 2396 pεi wet, while the carboxylate form material has a tensile εtrength of 790 pεi dry and 567 psi wet. On the other hand, the modulus at 100% elongation is 198 psi dry and 173 psi wet for the ester form material, and 538 psi dry and 263 psi wet for the carboxylate form material, showing increased stiffness in the latter form.

EXAMPLE 5_

Because the reactivity of the ester reactants is somewhat lower than that of the polyols, a prepoly¬ mer method of preparation may be utilized as follows. 36.4 partε of DESMODUR W, and 1.9 parts of dibutyl ester of tartaric acid are placed in a reaction vessel with 0.2 parts of stannous octoate and heated to 40°C for 30 minutes. This prepolymer is mixed with a glycol component (preheated to 53°C) conεiεting of 52.5 parts of CARBOWAX 1450, 8.9 parts of diethylene glycol and 0.2 parts of water. Polyurethane formation takes place and the resin is cured at 100°C for 1.5 hourε. The resulting resin is found to be 99.95% reacted.

EXAMPLE £

The physical properties of urethane resinε can be altered by the ester reactants, particularly by

dihydroxy dicarboxy acid esters, when preparing the polyurethanes of the invention. Conventional hydro¬ philic polyurethanes are generally very polar and therefore are soluble in polar solventε εuch aε alco- holε, dimethyl formamide and tetrahydrofuran, but are poorly soluble in less polar solventε εuch as aromatic solventε and eεters and are partially soluble in ketone/ alcohol mixtures. The addition of carboxy groupε to the polyurethane resin in the manner of the invention, however, reduces the overall cohesive energy and den¬ sity of the resin and reεults in increased solubility of the polymers in even the less polar solventε. Thiε iε demonεtrated aε follows.

A suitable non-polar solvent, εuch aε toluene or ethyl acetate, iε placed in a reaction veεεel equip¬ ped with stirrer, refluxing condenεer and an adding veεsel. 29.6 partε of dibutyl eεter of tartaric acid, 12 parts of diethylene glycol and 0.2 parts of εtannous octoate are then disεolved in the εolvent at tempera- tureε ranging between 70 and 80°C. The amount of the εolvent iε calculated to be between 70-75% of the final mixture (25-30% εolidε baεed on the finiεhed resin).

58.4 parts of DESMODUR W are then added drop- wise to the stirred reaction mixture at a rate which doeε not cauεe the temperature to overεhoot the choεen range. The mixture iε stirred at the choεen tempera¬ ture for another two hourε after addition of the

DESMODUR W is completed and remains liquid. The pro¬ duct is useful in a fingernail polish. A polyurethane prepared essentially as described but without the tar¬ taric acid ester forms a solid product unless the reaction is conducted in a polar solvent medium, e.g., dimethyl formamide.