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Description  |
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TECHNICAL FIELD
This invention relates to hydrophilic polyurethane polymers modified to
contain carboxy groups in the polymer backbone, to processes for preparing
the so-modified polyurethanes, and to uses thereof.
BACKGROUND OF THE 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 isocyanate, which is a
necessary component in the preparation of any polyurethane, is quite
reactive with the carboxyl groups of the carboxylic acid reactants used to
introduce the carboxyl group.
One approach to the introduction of carboxy groups into a polyurethane
resin chain is described in U.S. Pat. No. 3,412,054 to Milligan et al. In
that patent, a 2,2-di(hydroxymethyl)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 isocyanates to
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. Pat. Nos. 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 saponification 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 carboxyl groups, e.g., water-solubility,
cross-linkability or other reactivity characteristic of carboxyl
functionality, is marginal for some applications.
SUMMARY OF THE INVENTION
It has now been found that hydrophilic polyurethanes 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 reaction with organic isocyanate, by
esterifying the carboxyl functionality prior to reaction with the
isocyanate. This shields the carboxyl groups to prevent reaction with the
isocyanate. Once the polyurethane is formed, the ester groups are easily
converted to carboxylate (salt) groups by saponification with a suitable
base, and to free carboxyl (acid) groups by neutralization 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. Pat. No.
3,412,054), including acids having a plurality of carboxyl 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 crosslinking.
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 adhesion to different
types of substrates. The hydrophilic carboxy polyurethanes typically are
low melting solids, flowing in the range of about 90.degree. C. to
250.degree. C., and can be used as coatings or can be fabricated into a
wide variety of shaped bodies including films and cannulae using
conventional thermoplastic polymer processing 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 carboxylic acid having other active hydrogens for reaction
with organic isocyanate, and reacting the esters in the presence of a
polyol component with an organic isocyanate to form a polyurethane
intermediate. Alternatively, 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 appropriate selection of the polyol component
and control of the ratio of isocyanate (NCO) to active hydrogen in the
reaction mixture, the resulting polyurethane intermediate polymer is
hydrophilic as evidenced by its ability to absorb water to at least 10% of
its weight, preferably 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 improved chemical curing or adhesion.
In still other aspects of the invention, the hydrophilic carboxy
polyurethanes prepared in the manner described above are used in light
sensitive photographic 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 cosmetic applications, in body implants and
catheters, as coatings on cannulae, and in a host of other applications
where the hydrophilic character and carboxy functionality are useful
properties. In general, the polyurethanes can be used in any of the
applications described 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 unreacted 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
##STR1##
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 copolymer 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 glycols such as ethylene glycol, polyethylene glycols
(molecular weight 100-600, preferably 200-300), propylene glycol,
polypropylene glycols (molecular weight 100-600, preferably 200-300),
1,4-butane diol, polybutylene 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 molecular 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 polyols 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 premature crosslinking 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 glyceric acids esters including D-ethyl glycerate and
D-methyl 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-dihydroxybenzoate and
methyl or ethyl 2,6-dihydroxy-4-methylbenzoate; and hydroxy dicarboxylic
acid esters such as methyl or ethyl dihydroxymalonate, dimethyl or diethyl
bis(hydroxymethyl)malonate, dimethyltartarate, diethyltartarate,
dibutyltartarate, and the like, including isomers thereof. Representative
amino acids which may be esterified to form amino acid esters (b) are mono
amino acids such as DL serine, glycine, alanine, valine, 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 arginine. 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. Whitmore, second edition, Dover Publications (1961),
pages 348-350, 397-404, and 497-522, incorporated 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
esters (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).sub.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, hexamethylene
diisocyanate, trimethylhexamethylene diisocyanate, dimer acid
diisocyanate, isophorone diisocyanate, diethylbenzene diisocyanate,
decamethylene 1,10-diisocyanate, cyclohexylene 1,2-diisocyanate,
cyclohexylene 1,4-diisocyanate; the aromatic isocyanates such as 2,4- and
2,6-tolylene diisocyanate, 4,4-diphenylmethane diisocyanate,
1,5-naphthalene diisocyanate, dianisidine diisocyanate, tolidine
diisocyanate, m-xylylene diisocyanate, tetrahydronaphthalene-1,5
diisocyanate and neopentyl tetra isocyanate.
The preferred isocyanate is methylene bis(cyclohexyl-4-isocyanate) sold by
Mobay Chemical Corp. under the trademark "DESMODUR W." Other somewhat less
preferred isocyanates are trimethyl hexamethylene diisocyanate and
isophorone diisocyanate.
Other compounds which are useful are organic isocyanate equivalents which
produce urethane linkages such as the nitrile carbonates, i.e., the
adiponitrile carbonate of the formula:
##STR2##
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 considerations relating to
selection of polyol components for obtaining hydrophilic character is well
known in the art, as described in U.S. Pat. Nos. 3,822,238, 3,975,350,
4,156,066 and 4,156,067, incorporated herein by reference.
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 or
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 catalyzed by a known
catalyst for such reaction, suitable ones being tin salts and organo tin
esters such as stannous octoate and dibutyl tin dilaurate, tertiary amines
such as triethyl diamine (DABCO), N,N,N',N'-tetramethyl-1,3-butane diamine
and other recognized catalysts for urethane reactions, with care being
taken not to heat the reaction mixture unduly since undesirably dense
crosslinking may result.
Water in the reaction mixture causes evolution of carbon dioxide, resulting
in the polymer being obtained as a foam. This is an advantage in that the
foamed polymer, owing to its large surface area, exhibits a high rate of
dissolution, thereby facilitating the preparation of solutions of the
polymer. In adding the requisite quantity of water to the reaction
mixture, allowance should be made for any moisture that may be present in
the glycol components. It is not unusual 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, however, sufficient water will be present or added to cause
foaming of the polyurethane polymer as it is formed. Generally, trace
amounts up to about 0.5 parts by weight of water based on 100 parts by
weight of the total reaction mixture (exclusive of catalyst) will be
effective, and for foaming, from about 0.1 to about 0.5 part by weight on
the same basis.
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., methanol, 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 as dilute
hydrochloric acid, to form carboxyl groups. Under ambient or normal
conditions 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 insoluble in solvents in which non-carboxyl group
containing polyurethanes are soluble.
Upon neutralization of the carboxyl-containing polyurethane with ammonium
hydroxide, the polymer will become water soluble so long as it is not
heated to a high temperature. If thus heated or cast from solution,
ammonia will be driven off, leaving a water insoluble film.
The carboxyl groups also provide sites for light or loose crosslinking
reactions with the urethane groups and other reactions, such as
crosslinking or curing with polyvalent metals and other materials (such as
ammonium dichromate), and for interaction with functional groups carried
on various substrates contacted by the polymers. Aside from their
reactivity, the carboxy groups provide for excellent adhesion to a variety
of substrates, especially if curing agents, such as those mentioned, are
used with the polyurethanes.
The polyurethane intermediates carrying ester groups, the saponified forms
or the free carboxyl resins of the present invention because of their
unique physical properties may advantageously be used as burn dressings.
The polyurethane resin may be applied to the burn as a powder, film, or
from solution in a volatile non-toxic solvent and will form a barrier that
is 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 resin for timed release. A particularly
advantageous burn dressing is a powder obtained by the low temperature
grinding of from about 1 to about 80 parts by weight of the polyurethane
resins in their carboxyl forms and a high-boiling, water soluble non-toxic
solvent for the polymer, such as glycerol, dimethylsulfoxide or low
molecular weight polyethylene glycols.
The above described polyurethane resins are also useful as coatings,
molding compounds, absorbents, 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, sutures, surgical implants, blood oxygenators,
intrauterine devices, vascular prostheses, perfume fixatives, dedorant
compositions, antifog coatings, surgical drapes, oxygen exchange
membranes, artificial fingernails, finger cots, adhesives, 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 is 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, morpholine, and the like is useful because such
compounds remain in the film after the water has vaporized and thereby
improves film continuity.
Example 2 describes a polyurethane especially adapted for drug delivery and
sustained release. The carboxy groups provide adhesion to the stomach
mucosa and thus prolong the dwell time in the stomach of a composition
based on the polyurethane carrying medication (capsule, coated tablet,
etc.).
Examples 3-5 illustrate polyurethanes which are particularly suitable as
permanent coatings for boat hulls, such coatings usually being cured by
the action of light on compositions containing ammonium dichromate. The
coatings lower hydrodynamic drag and thus allow increase in vessel speed
at the same engine output or allow lowering of engine output for the same
speed.
Example 6 illustrates the versatility of the polyurethanes as hard, high
adhesion coatings (for example, for use in fingernail polishes) due to
solubility in a host of solvents both polar and non-polar.
EXAMPLE 1
In forming the ester reactants of the invention, 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 condensate 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 is required. Any conventional esterification catalyst may be used,
such as toluene sulfonic acid, inorganic acids, ion exchange resins,
sodium alcoholates, etc. A preferred catalyst is tetrabutyl titanate and a
typical esterification formulation 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 stirrer 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 continued for another three hours. A total of 31.8 parts of
water is collected to this point and the final acid value is 8.3. The
resulting ester is used to prepare a hydrophilic polyurethane resin as
follows.
A mixture of 60.1 parts of CARBOWAX.RTM. 1450 (a polyethylene glycol having
a number average molecular weight of 1450, Union Carbide Corporation), 1.7
parts of glycerol and 25.5 parts of DESMODUR W.RTM.
[methylene-bis(cyclohexyl-4-isocyanate), Mobay Chemical Corp.] is prepared
and incrementally reacted by heating at 65.degree. C. for 44 minutes,
catalyzed by 0.2 parts of stannous octoate (T-9, Air Products and
Chemicals Co.). At the end of this period, 40% of the isocyanate has
reacted. Two more short exposures (12 minutes each) to 40.degree. C. bring
the amount of reacted isocyanate to 50.0%. The reaction mixture becomes
very viscous and tetrahydrofurane solvent is added in sufficient quantity
to reduce 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 is
brought to 55.degree.-60.degree. C. for a period of 1.5 hours. At the end
of this period, the isocyanate is found to be completely reacted.
The reacted resin is mixed with double the amount of sodium hydroxide
stoichiometrically 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
dissolves to a slightly turbid solution in water containing ammonium
hydroxide (about 3.5% NH.sub.3). This ammoniated solution dries to a clear
film which is not water soluble but is soluble in lower aliphatic alcohols
and other suitable solvents.
EXAMPLE 2
A hydrophilic resin is made, using the following formulation:
68.1 parts CARBOWAX 1450
9.7 parts diethylene glycol
0.5 parts water
40.9 parts dibutyl ester of tartaric acid
80.8 parts DESMODUR W
0.4 parts stannous octoate.
The isocyanate is placed in a reaction vessel with 0.15 parts of the
stannous octoate. The dibutyl ester of tartaric acid is then added in
increments of approximately 2 parts each. Temperature of the reaction is
maintained at 60.degree.-75.degree. C. by supplying heat or delaying the
next addition of the ester. The ester is added during a one hour period,
at the end of which time the mass becomes so viscous that it can no longer
be stirred. Tetrahydrofuran solvent is 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 vigorous mixing, the mass becomes
homogeneous and is poured into a polypropylene tray and placed into an
oven at 100.degree. C. to cure. Before placing into the oven, 81.1% of the
isocyanate is found to be reacted. After two hours of heating, the percent
of reacted isocyanate rises to 97%, and an additional hour at 120.degree.
C. brings it to 98.3%.
The resin thus produced contains butyl ester groups, which alter the
mechanical and the surface properties of the polymer. Saponification of
the ester 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
solvent for several hours. The sodium salt of the carboxylic acid is
formed and n-butanol is liberated.
EXAMPLE 3
52.4 parts of CARBOWAX 1450 are heated with 8.9 parts of diethylene glycol,
0.24 parts of water and 1.5 parts of diethyl ester of tartaric acid (Fluka
Chemical Corp., Hauppauge, N.Y.) until the CARBOWAX diol melts and a
homogeneous mixture is obtained. 37.0 parts of DESMODUR W are added and
mixed with the glycols, bringing the temperature of the mixture to about
50.degree. 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.degree. C., the reaction
mixture is quickly poured into a polyethylene tray and placed in an oven,
where it is cured for 1.5 hours at 100.degree. C.
For the saponification of the ethyl ester of the tartaric acid in the
resin, 2N solution of sodium hydroxide is used in a 5% excess of the
equivalent of the ester groups. This is 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.degree.-30.degree.). The viscosity of
the saponified solution is much less than the solution of the resin in the
ester form.
The resulting carboxylate form of the resin is neutralized from pH 10 to
about pH 6 with a diluted solution of hydrochloric acid. This converts
most of the sodium salt groups to carboxylic acid groups.
EXAMPLE 4
52.5 parts of CARBOWAX 1450, 8.9 parts of diethylene glycol, 0.2 parts of
water and 1.9 parts of dibutyl ester of tartaric acid (Fluka Chemical
Corporation) are reacted with 36.4 parts of DESMODUR W essentially as
described in Example 3. The resulting resin is 99.2% reacted after the
oven curing.
The resin is dissolved to 20% solids in methyl alcohol, and the butyl ester
groups are saponified using 2N sodium hydroxide, as described in Example
3. The viscosity of the resin solution in ester form is 925 cP (at
25.degree. C.) and the viscosity of the resin in the carboxy form is 44 cP
(at 25.degree. C.).
When films are cast from the resin solutions, dired and then hydrated, it
is found that the ester form of the polyurethane has an equilibrium water
content of 58.0% and expansion of 42.1%, while the sodium salt
(carboxylate) form has an equilibrium water content of 64.5% and expansion
of 51.7% on swelling. The tensile strength of the ester form material is
2500 psi dry and 2396 psi wet, while the carboxylate form material has a
tensile strength of 790 psi 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 prepolymer method of preparation may be utilized as
follows. 36.4 parts 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.degree. C. for 30 minutes. This prepolymer is
mixed with a glycol component (preheated to 53.degree. C.) consisting 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.degree. C. for 1.5 hours. The resulting resin is found to be 99.95%
reacted.
EXAMPLE 6
The physical properties of urethane resins can be altered by the ester
reactants, particularly by dihydroxy dicarboxy acid esters, when preparing
the polyurethanes of the invention. Conventional hydrophilic polyurethanes
are generally very polar and therefore are soluble in polar solvents such
as alcohols, dimethyl formamide and tetrahydrofuran, but are poorly
soluble in less polar solvents such as aromatic solvents and esters and
are partially soluble in ketone/alcohol mixtures. The addition of carboxy
groups to the polyurethane resin in the manner of the invention, however,
reduces the overall cohesive energy and density of the resin and results
in increased solubility of the polymers in even the less polar solvents.
This is demonstrated as follows.
A suitable non-polar solvent, such as toluene or ethyl acetate, is placed
in a reaction vessel equipped with stirrer, refluxing condenser and an
adding vessel. 29.6 parts of dibutyl ester of tartaric acid, 12 parts of
diethylene glycol and 0.2 parts of stannous octoate are then dissolved in
the solvent at temperatures ranging between 70.degree. and 80.degree. C.
The amount of the solvent is calculated to be between 70-75% of the final
mixture (25-30% solids based on the finished resin).
58.4 parts of DESMODUR W are then added dropwise to the stirred reaction
mixture at a rate which does not cause the temperature to overshoot the
chosen range. The mixture is stirred at the chosen temperature for another
two hours after addition of the DESMODUR W is completed and remains
liquid. The product is useful in a fingernail polish. A polyurethane
prepared essentially as described but without the tartaric acid ester
forms a solid product unless the reaction is conducted in a polar solvent
medium, e.g., dimethyl formamide.
* * * * *
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