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BACKGROUND OF THE INVENTION
This invention relates to the field of polymer blends, or alloys, and more
particularly, to hydrophilic blends of polyurethane and poly(N-vinyl
lactam) and to the use of these blends in a variety of applications
including the formulation of lubricious coating compositions.
There has long been a need in the art for lubricious materials which are
non-slippery when dry but exhibit lubricious or slippery properties when
contacted with aqueous fluids. Applications for such materials are
numerous and diverse and include fabrication into surface coatings, foams,
fibers, films, or solid articles which absorb water, impart wettability or
reduce the coefficient of friction in aqueous environments. Uses include,
but are not limited to, coatings for catheters, condoms, invasive devices
and test probes which are lubricious only when wet, antifog coatings for
lenses, windows, etc., drag reducing coatings for ships, burn and wound
dressings, contact lenses, antistatic coatings, hydrophilic fibers and
matrices for controlled release of pharmaceuticals, dyes, fragrances,
salts and the like. It had previously been proposed to reduce the
coefficients of friction of these and similar devices and materials by the
use of non-permanent coatings of silicone or certain fluorocarbons,
neither of which are hydrophilic, and which do not have as low
coefficients of friction as are necessary or desirable for some
applications. The fluorocarbon coatings also have the disadvantage of
being difficult to handle because they are always slippery, not just when
slipperiness is desired.
Coatings and articles useful for insertion into the body, for example, are
described in U.S. Pat. Nos. 4,100,309 and 4,119,094. Articles such as
catheters and condoms described in these patents are obtained by coating a
suitable substrate with a polyvinylpyrrolidonepolyurethane interpolymer.
The coatings are obtained by a two-step procedure using first a solution
of isocyanate containing prepolymer and polyurethane followed by a
solution of polyvinylpyrollidone. The isocyanate can be modified with
chain extenders (diols, etc.) which effectively produce a linear
thermoplastic polyurethane in situ. This preparative route yields coatings
which are not of uniform composition throughout (two separate layers
intermixed at the interface) and are not suitable for the preparation of
integral articles, films, foams or matrices with regular and uniform
physical and mechanical properties. In addition, the requirement that
reactive isocyanates be present introduces unavoidable chemical
instability (pot life) and eliminates the possibility of utilizing aqueous
or alcoholic solvents for preparation. Isocyanates will also react with
and inactivate many desirable additives such as pharmaceuticals,
surfactants and dyes.
U.S. Pat. Nos. 4,373,009 and 4,472,467 describe similar composition which
can in some cases be applied from a single solution. These patents,
however, require a chemical reaction forming a covalent bond between
isocyanates and active hydrogen groups reactive toward isocyanates on the
vinyl lactam or ethylene oxide polymers to produce the objects of the
invention. These patents actually teach away from the use of chemically
inert components.
Other lubricious hydrophilic coatings for a variety of uses are described
in the prior art. For example, the practice of forming a linear
polyurethane polymer and then dispersing it in water is well known in the
art as shown in U.S. Pat. Nos. 3,412,054 and 4,094,838 which describe the
preparation of modified, water dispersible urethanes.
Polyvinylpyrrolidone, a commercially available poly(N-vinyl)lactam, is a
well known hydrophilic, polymer having numerous applications including
being a film former, protective colloid and suspending agent,
dye-receptive resin, binder and stabilizer, physiologically acceptable
polymer, etc. However, being water soluble, polyvinyl-pyrrolidone and
related poly(N-vinyl)lactams will eventually be leached from coating
compositions and other materials formulated with the polymer when
contacted with aqueous fluids. Thus, the practical value of known
compositions containing polyvinylpyrrolidone as lubricious coatings is
greatly limited due to the erosion of their lubricious properties as the
polyvinylpyrrolidone component dissolves or is leached into the
surrounding aqueous medium. Technical Bulletin 7583-033 of General Aniline
& Film Corporation describes a variety of films containing a
solvent-blended mixture of polyvinylpyrrolidone and another polymer, i.e.,
vinylchloride-vinylacetate copolymer, polyethylene, polyacrylonitrile,
vinylidene chloride polymer, polyvinylisobutyl ether, polyvinylethyl
ether, polystyrene, polyvinylchloride and polyvinyl alcohol. No suggestion
is made in the technical bulletin of a blend of polyvinylpyrrolidone and a
polyurethane.
SUMMARY OF THE INVENTION
It has been discovered that organic solvent-soluble thermoplastic
polyurethanes can be blended, or alloyed, with polyvinyl-pyrrolidone
and/or other poly(N-vinyl lactams) either by the use of a common solvent
or solvent mixture or conventional melt blending techniques. The resulting
blends generally exhibit properties intermediate those of the polyurethane
component and those of the poly(N-vinyl lactam) component, e.g. blends
which readily absorb water to become soft and slippery (predominantly made
up of the hydrophilic poly(N-vinyl lactam component) or blends which are
relatively hard but still wettable (predominantly made up of the
polyurethane component). In virtually all cases, blends containing a
sufficient quantity of poly(N-vinyl lactam) to provide useful degrees of
hydrophilicity will also exhibit significantly reduced coefficients of
friction when wet.
In accordance with the present invention, a hydrophilic polymer blend is
provided which comprises a first polymer component which is an organic
solvent-soluble, thermoplastic polyurethane and a second polymer component
which is a hydrophilic poly(N-vinyl lactam).
Unlike the procedure used for making the coatings of U.S. Pat. Nos.
4,100,309 and 4,119,094 which utilizes a solution of highly reactive
isocynate, the polymer blend of this invention is prepared with a
polyurethane, i.e., a preformed polymer having no reactive isocyanate
groups, as such being stable in solution for indefinite periods of time.
Accordingly, polymer blends herein can be readily formed at the point of
application as needed simply by evaporating any solvent(s) with which they
may be associated. This versatility makes the instant products especially
convenient for use as coatings.
Contrary to what one would expect exposure of the blends of this invention
to water, even for prolonged periods, does not result in any significant
loss of the hydrophilic poly(N-vinyl lactam) component, possibly as a
result of associative forces with the polyurethane component, chain
entanglement, or both. Whatever may, in fact, be the basis for this
property, the ability of the blends to retain their slippery properties
when wet makes them highly useful as low friction coatings which will be
in more or less constant or prolonged contact with aqueous fluids.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Organic solvent-soluble, thermoplastic polyurethanes constitute a well
known family of resins with extensive literature on the subject, e.g.,
that contained in the Encyclopedia of Polvmer Science and Technology, Mark
et al. (eds.), Wiley (1969) which is incorporated herein by reference. In
general, such polyurethanes are prepared by the reaction of aromatic
and/or aliphatic polyisocyanates with polyester and/or polyether polyols,
or in the alternative, by the reaction of substantially linear,
isocyanate-capped prepolymers with polyols of the aforestated type.
Useful polyisocyanates include toluene-2,4-diisocyanate,
toluene-2,6-diisocyanate, commercial mixtures of toluene-2,4- and
2,6-diisocyanates, cyclohexylene-1,4-diisocyanate, m-phenylene
diisocyanate, 3,3-diphenyl-4,4-biphenylene diisocyanate, 4,4-biphenylene
diisocyanate, 1,6-hexamethylene diisocyanate, 1,5-naphthalene
diisocyanate, cumene-2,4-diisocyanate, 2,4-diisocyanatodiphenylether,
5,6-dimethyl-1,3-phenylenediisocyanate,
2,4-dimethyl-1,3-phenylene-diisocyanate,
2,4-dimethyl-1,3-phenylenediisocyanate, 4,4-diisocyanatodiphenylether,
9,10-anthracene diisocyanate, 2,4-diisocyanatotoluene, 1,4-anthracene
diisocyanate, 2,4,6-toluene triisocyanate, isophorone diisocyanate and
p,p',p",-triphenylmethane triisocyanate.
Preferred organic solvent-thermoplastic polyurethanes are
polytetramethylene ether glycol-diphenylmethane diisocyanate (MDI),
polytetramethylene ether glycol tolylene diisocyanate (TDI),
polytetramethylene ether glycol-isoferrone isocyanate,
poly(1,4-oxybutylene)glycoldiphenylmethane diisocyanate (MDI),
poly(1,4-oxybutylene)glycoltolylene diisocyanate (TDI),
poly(1,4-oxybutylene)glycolisoferrone isocyanate, polyethylene
glycol-diphenylmethane diisocyanate (MDI), polyethylene glycol-tolylene
diisocyanate (TDI), polyethylene glycol-isoferone isocyanate,
polypropylene glycolidphenylmethane diisocyanate (MDI), polypropylene
glycol-tolylene diisocyanate (TDI), polypropylene glycol-isoferrone
isocyanate, polycaprolactone-diphenylmethane diisocyanate (MDI),
polycaprolactone-tolylene diisocyanate (TDI), polycaprolactoneisoferrone
isocyanate, polyethylene adipate-diphenylmethane diisocyanate (MDI),
polyethylene adipate-tolylene diisocyanate (TDI), polyethylene
adipate-isophorone isocyanate, polytetramethylene adipate-diphenylmethane
diisocyanate (MDI), polytetramethylene adipate-tolylene diisocyanate
(TDI), polytetramethylene adipate-isoferrone isocyanate,
polyethylenepropylene adipate-diphenylmethane diisocyanate (MDI),
polyethylene-propylene adipate-tolylene diisocyanate (TDI), and
polyethylene-propylene adipate-isophorone isocyanate polyurethanes.
Although the useful polyurethanes are essentially linear in order to
provide solubility and thermoplasticity, they can be crosslinked following
blending with the poly(N-vinyl lactam) component, e.g., by adding a
sufficient quantity of crosslinking agent to a solvent solution of the
polymers or by incorporating the crosslinking agent into the melt-blended
polymer mixture while it is still in the plastic state. Examples of
crosslinking agents which can be utilized for this purpose are
isocyanates, polycarboxylic acids, peroxide and organotitanates.
Useful polyester polyols include those obtained from the condensation of
polycarboxylic acids, preferably dicarboxylic acids, such as adipic,
sebacic, phthalic, isophthalic, terephthalic, oxalic, malonic, succinic,
maleic, cyclohexane-1,2-dicarboxylic, cyclohexane-1,4-dicarboxylic,
polyacrylic, naphthalene-1,2-dicarboxylic, fumaric, itaconic, etc., with
polyalcohols, preferably diols, such as ethylene glycol, diethylene
glycol, pentaglycol, glycerol, sorbitol, triethanolamine,
di(beta-hydroxyethyl)ether, etc., and/or amino-alcohols such as
ethanolamine, 3-aminopropanol, 4-aminopropanol, 5-aminopentanol-
1,6-aminohexanol, 10-aminodecanol, 6-amino-5-methyl-hexanol-1,
p-hydroxymethylbenzylamine, etc. Polyesters derived from
ring-opening/condensation of lactones with polyfunctional compounds such
as any of the aforementioned polyalcohols can also be used in providing
the organic solvent-soluble, thermoplastic polyurethane component of the
subject polymer blends.
The term "poly(N-vinyl lactam)" as used herein shall be understood to
include homopolymers and copolymers of such N-vinyl lactams as
N-vinylpyrrolidone, N-vinylbutyrolactam, N-vinylcaprolactam, and the like,
as well as the foregoing prepared with minor amounts, for example, up to
about 20 weight percent, of one or a mixture of other vinyl monomers
copolymerizable with the N-vinyl lactams. Of the poly(n-vinyl lactams),
the polyvinyl-pyrrolidone (PVP) homopolymers are preferred. A variety of
polyvinylpyrrolidones are commercially available from several sources and
of these, a polyvinylpyrrolidone having a K-value of at least about 30 is
especially preferred.
The polyurethane and poly(N-vinyl lactam) components of the blend can be
combined employing conventional melt blending techniques and apparatus,
e.g., a two-roll heated mill, helical screw extruder, etc., or, if desired
the components can be combined by dissolving them in solvent which is
subsequently evaporated to yield the blend. If the latter procedure is
selected, the choice of solvent is important. Thus, the solvent must be
capable of dissolving both polymer components in a single-phase solution
and the relative volatilities must be such that at no point during
evaporation and drying, the resulting mixture will tend to precipitate
either polyurethane, poly(N-vinyl lactam) or an association complex of
these polymers which may have different solubility characteristics than
either material by itself. Solvents which are suitable include ethyl
lactate, diacetone alcohol, methylene chloride, trichloroethylene,
N-methyl pyrrolidone and mono and di-ethylene glycol ethers. Other
solvents can be added to accelerate drying, reduce solvency toward
particular substrates, etc., provided the aforestated conditions are met.
The blends of this invention can also be prepared from aqueous polyurethane
dispersions where a coalescing solvent of lower volatility than water
and/or electrostatic attraction from ionic species on dispersed
macromolecules aids in compatibilizing the individual polymers during the
final stages of drying. Examples of such a solvent include
N-methyl(pyrollidone), dimethyl formamide, diacetone alcohol and various
mono- and diethylene glycol esters.
The blends can contain from about 10 to about 80 weight percent, and
preferably from about 25 to about 60 weight percent, of polyurethane, the
balance being made up of the poly(N-vinyl lactam) component. Minor
quantities, for example, up to about 20 weight percent, of one or a
mixture of other compatible polymers can be incorporated into the blends,
e.g., any of the polymers disclosed in General Aniline & Film Corporation
Technical Bulletin 7583-033 referred to above.
The blends can be formed into a variety of shapes and, if desired, can be
fabricated into foams employing known and conventional techniques
including the use of chemical and/or physical blowing agents. The solid
blends can also be extruded as fibers, rods, sheets, and so forth.
Many different types of additional materials can be incorporated into the
polymer blends herein including organic and inorganic salts, alcohols,
amines, acids, polymer latices, resin or wax dispersions, fillers, fibers,
cellulosics, surfactants, pigments, dyes, enzymes, proteins, chelates,
thickeners, stabilizers, dyes, fragrances, and so forth. The blends of
this invention are especially useful as carriers for a wide variety of
releasable materials including biologically active substances having
curative or therapeutic value for human beings or non-human animals.
Included among the biologically active materials which are suitable for
incorporation into the blends of the present invention are: hypnotics,
sedatives, tranquilizers, anti-convulsants, muscle relaxants,
antiparkinson agents, analgesics, antipyretic agents, anti-inflammatory
agents, local anasthetics, anti-spasmodics, antiulcer agents, antivirals,
antibacterials, antifungals, antimalarials, sympathomimetic agents,
cardiovascular agents, diuretics, antiparasitic agents, antitumor agents
and hypoglycemic agents, and so forth.
In the form of a sheet or film or as a coating, the blends can be combined
with and adhered to a virtually unlimited variety of substrates including
metal and resin foils, woven and non-woven webs of natural and synthetic
fibers, etc.
The following examples are further illustrative of the blends of this
invention.
EXAMPLE 1
To a mixture of 75 g diacetone alcohol and 25 g methyl ethyl ketone is
added 4 g polyvinylpyrrolidone (Kollidon 90, BASF Corp.) and 2 g linear
polyurethane (Estane 5703, B. F. Goodrich Co.). The resulting solution
when applied to such substrates as vinyl, epoxy and polyurethane resins
and permitted to dry forms a highly durable coating which is slippery when
wet (coefficient of friction 0.05). Continuous contact of the coated
substrates with water for six months does not degrade the coating or
diminish its lubricity to any appreciable extent.
EXAMPLE 2
To 47 g of water and 10 g N-methylpyrrolidone is added 10 g of
polyvinylpyrrolidone (Kollidon 90, BASF Corp.) and 33 g of linear
polyurethane aqueous dispersion (Neorez R940, Polyvinyl Chemical
Industries). Films cast from the resulting viscous dispersion are
lubricious when wet (coefficient of friction 0.08) and imbibe water
forming elastic, transparent films useful as burn and wound dressings. The
solution can also be used to spin fibers which are tough and elastic when
wet and can be used to produce hydrophilic foams via either mechanical
frothing or casting films with added acetone and drying with heat in
vacuo.
EXAMPLE 3
Films cast as in Example 2 and containing 2% chlorohexidine acetate (w/w/
based on polymer) exhibited long acting bactericidal action against Staph.
aureus in humid environments. Other substances which were successfully
combined with the blends include cephalosporin, ampicillin,
oxytetracycline, metaproterenol sulfate, salicylic acid and
phenolphthalein.
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