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Description  |
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BACKGROUND OF THE INVENTION
This invention relates to a method for preparing new biodegradable foams.
More particularly, the present invention provides new dental and
biomedical foams using a hydrophilic polyurethane foam having a
biodegradable moiety.
Numerous devices have been proposed in the prior art for use as dental and
biomedical foams for absorbing or removing body fluids. Typically, the
prior art approaches have relied upon natural materials such as cotton,
which is now becoming relatively expensive while providing a resultant
structure which is generally fragile in use. Also, the amount of
absorption by natural materials is relatively low.
Various polyurethanes have been used as dental and biomedical foams but
suffer a disadvantage in that such foams are not readily biodegradable. It
has now been found, however, that by practice of the present invention,
there is provided a method for preparing new, simple and highly efficient
dental and biomedical foams which are readily biodegradable after use, and
which are characterized by high absorptive ability of body fluids in use.
Various attempts have also been made in the prior art to prepare foams of
organic substances for use in cavities of the human body. However, such
organic substances typically require, for example, catalysts or the like
during the foaming reaction. These additives remain in the foam after
foaming and are readily leached into the human body when in contact with
body fluids. Thus, although artificial foams, especially those of
polyurethane, of the prior art possess the capacity of high absorptivity
of body fluids, usage within the human body typically invites
disadvantages beyond advantages realized by low cost and high
absorptivity. Thus, artificial foams such as polyurethanes of the prior
art have received limited practical acceptance by the medical, dental and
government regulatory agencies when proposed for internal usage in the
human body. There is especially a disadvantage of such foams.
DESCRIPTION OF THE INVENTION
By the present method, new biodegradable foams may be prepared having
utility in dental and biomedical applications wherein hydrophilic
crosslinked polyurethane foams are employed by reacting a particular
isocyanate capped polyhydroxyester polyol with large amounts of an aqueous
reactant. The thus generated foams may be formed in handy sizes as
desired. Such structures may be readily used in the oral cavity and while
in the oral cavity, the structure absorbs oral fluids, and thereafter may
be discarded since it is biodegradable.
The novel biodegradable foams are prepared by reacting an isocyanate-capped
hydroxyester polyether polyol having a reaction (i.e. isocyanate)
functionality of at least 2 with sufficient water to provide an H.sub.2 O
Index Value (as defined below) of from about 1300 to about 78,000. The
polyol is further characterized in that the hydroxyester linkages are
formed by condensation of an aliphatic hydroxy carboxylic acid with the
hydroxyl groups of (a) an essentially linear polyether, or (b) a monomeric
low molecular weight aliphatic alcohol containing from 3 to 8 hydroxyl
groups per mole.
Suitable acids are the monobasic aliphatic carboxylic acids having the
structure:
##STR1##
wherein n is an integer and 0 .ltoreq. n .ltoreq. 20 and preferably 0
.ltoreq. n .ltoreq. 5; R.sub.1, R.sub.2, R.sub.3, R.sub.4, and R.sub.5
independently are hydrogen, alkyl, alkylene, aryl, aralkyl, alkoxy,
carboalkoxy, acyl, acyloxy, and carboxyl with one of the groups R.sub.1,
R.sub.2 or R.sub.5 being carboxyl. Suitable alkyl groups can be straight
or branched-chain having a total of from 1 to 20 carbon atoms and
preferably being a lower aliphatic moiety having from 1 to 5 carbons. The
alkylene groups are of the same size as the alkyl groups and contain one
or more unsaturated linkages, e.g. olefinic or alkynyl and include
residues from the naturally-occurring fatty acids. Suitable aryl groups
are monocyclic and may be substituted with halogen, alkoxy or alkyl groups
having less than 4 carbons. Suitable aralkyl groups are benzyl and similar
groups corresponding to the formula:
##STR2##
where A is methylene, ethylene, isopropylene, or propylene. Alkoxy groups
include both aryloxy (e.g. phenoxy) and lower aliphatic alkoxy groups
having from 1 to 5 carbon atoms. Carboalkoxy groups are those of the
formula
##STR3##
where B is alkoxy as defined above. Acyl groups are those of the formula
##STR4##
where F is alkyl or alkenyl as defined above, and preferably contains 5
carbons or less. Acyloxy groups are those of formula O--G, where G is acyl
as defined above. Hydroxy acids that may be used in this application
include but are not limited to glycolic (hydroxy acetic) acid, lactic
acid, .alpha.-hydroxybutyric acid, .alpha.-hydroxyisobutyric acid,
.alpha.-hydroxyvaleric acid, .alpha.-hydroxyisovaleric acid,
.beta.-hydroxypropionic acid, .beta.-hydroxybutyric acid,
.beta.-hydroxyisobutyric acid, .beta.-hydroxy-n-valeric acid,
.beta.-hydroxyisovaleric acid, .gamma.-hydroxybutyric acid,
.gamma.-hydroxy-n-valeric acid, .delta.-hydroxyvaleric acid,
.epsilon.-hydroxycaproic acid, 9-hydroxystearic acid, 10-hydroxystearic
acid, 11-hydroxystearic acid, 12-hydroxystearic acid,
11-hydroxyhexadecanoic acid, 12-hydroxydodecanoic acid, and
16-hydroxyhexadecanoic acid. Also included are polyhydroxymonocarboxylic
acids such as glyceric acid, 3,12-dihydroxypalmitic acid, the erythronic
and threonic acids, trihydroxyisobutyric acid, 9,10,16-trihydroxypalmitic
acid. Also included are hydroxy unsaturated acids such as
.alpha.-hydroxyvinylacetic acid, 16-hydroxy-7-hexadecenoic acid, and
ricinoleic acid (12-hydroxy-9-octadecenoic acid). From the above
description it is apparent that the hydroxy acids are not limited to
hydroxyacetic acid but include the straight-chain and omega hydroxy acids
having 20 carbons or less.
Suitable aliphatic polyhydroxy alcohols have a molecular weight of less
than about 1000 and preferably 500 or less and include glycerol,
1,2,3-butanetriol, 1,2,4-butanetriol, trimethylolethane,
trimethylolpropane, erythritol, pentaerythritol, adonitol, arabitol,
mannitol, sorbitol, iditol, dulcitol, sucrose, dipentaerythritol,
triethanolamine and condensation products of ethylene and propylene oxides
with ethylene diamine, diethylene triamine, and triethylene tetramine.
The essentially linear polyethers have a molecular weight not exceeding
about 4000, and preferably not exceeding about 2000, and are prepared by
homopolymerization of ethylene oxide, propylene oxide, and include block
copolymers such as polyoxyethylene diol capped with polyoxypropylene
chains and polyoxypropylene diols capped with polyoxyethylene. Suitable
linear polyethers may also be prepared by condensing an alkylene oxide of
4 carbons or less (e.g. ethylene, propylene or tetramethylene oxide) with
a polyhydroxylic alcohol such as those described above. In such
condensation products the polyether chains are essentially linear and have
an average molecular weight of from 50 up to about 4000. The polyether
chains should not contain more than 50% by weight of alkylene oxide
condensation units larger than ethylene oxide (e.g. propylene glycol
units) and should not contain more than 15% by weight of tetramethylene
oxide units.
Suitable isocyanate-capped polyols or prepolymers are exemplified by the
following systems:
A. Polyether (e.g. polyoxyethylene glycol) blended with a hydroxyacid
ester, e.g. the condensation product of a polyhydroxy alcohol with
sufficient hydroxyacid to completely esterify the alcohol. The hydroxyacid
ester serves essentially as a crosslinking agent in addition to imparting
biodegradability and is employed in amounts sufficient to provide the
desired properties, i.e. if it is desired to increase rigidity, solvent
resistance and other properties associated with crosslink density, the
amount of crosslinking agent is increased. Sufficient isocyanate is added
to completely cap all the hydroxyl groups. A specific preferred system is
the blend of polyoxyethylene diol with the condensation product of
trimethylol propane or ethane with lactic or glycollic acids.
B. Essentially linear polyether completely esterified with hydroxy acid
(preferably lactic acid) and blended with a polyhydroxy alcohol.
Sufficient isocyanate is added to completely cap all the hydroxyl groups.
C. An ester is formed as in A above and the ester is condensed with
ethylene or propylene oxides to form essentially linear polyether chains
originating with the hydroxyl groups of the ester. Such chains have the
molecular weight distribution as described above. Sufficient isocyanate is
added to completely cap all the hydroxyl groups. This system may be
exemplified by the trimethylolpropane (or ethane) ester formed by
condensation with lactic acid followed by further condensation of the
hydroxyl groups of the ester (3 per mole) with ethylene oxide to provide
polyols having three essentially linear polyether chains per mole.
Sufficient isocyanate is added to completely cap the hydroxyl groups
terminating the polyether chains.
The polyether polyol used in forming the prepolymer designated as C above
may be alternatively described as corresponding to the formula:
T--L--A).sub.x wherein x is an integer from 3 to 8 and corresponds to the
number of hydroxyl groups in the alcohol designated as "T," T is the
residue of a monomeric alcohol having from 3 to 8 hydroxyl groups per
mole, L is a hydroxy carboxylic acid residue, said polyol residue bonded
to said acid residue by means of an ester linkage. A is an essentially
linear polyether residue bonded to the acid residue through an ether
linkage. The free hydroxyl group at the opposite end of the glycol is
linked by a urethane linkage to the isocyanate used in capping the polyol.
As used hereinabove the term "residue" means, for example, the portion of
the monomeric aliphatic alcohol remaining after the esterification
reaction with the hydroxy carboxylic acid. The hydroxy carboxylic acid
residue is the portion of the acid remaining after the esterification
reaction and subsequent reaction with the polyoxyethylene glycol. The
polyoxyethylene glycol residue is the portion of the glycol remaining
after bonding to the hydroxy acid and to the isocyanate used in capping.
Except for changes caused by reaction, the residues possess the same
features as the free components described above, e.g. the hydroxy acid
residue possesses the same features as the hydroxy acid described above
except for changes induced by the reaction encountered in forming the
polyether polyol.
The present foams have utility as handy expandable sponges for personal
use. The sponges are easily carried and may be readily prepared with
detergents, lotions, perfumes, biostats and the like and upon contact with
water, the sponges are found to be very soft, very hydrophilic and
biodegradable. The sponges may be used for washing, wiping, cleaning, etc.
for external body cleaning; or alternatively for internal body usage such
as is necessary in dental and medical applications. The present sponges
also have utility as intimate absorptive products, such as diapers,
sanitary napkins, incontinent pads and the like.
Polyurethane foam structures prepared herein with hydroxyester
polyisocyanates, water and certain surfactants, have an exceptionally
fine, uniform, soft, hydrophilic cell structure.
The following conditions seem to be important to obtaining foams of the
above-mentioned desirable properties. The polyether (e.g. polyoxyethylene
diol) should have a molecular weight not exceeding about 4000. In forming
the polyol (prior to capping with isocyanate) for every mole of polyether
from about 0.1 to about 4.0 moles, and preferably from about 0.2 to about
2.5 moles of the monomeric aliphatic alcohol should be employed. The
necessary hydroxyester linkage is provided by condensing the carboxylic
acid with either the hydroxyl groups on the polyether or on the monomeric
aliphatic alcohol, as described above. Preferably the carboxylic acid is
condensed with the monomeric alcohol to provide a hydroxyester
crosslinking agent having from 3 to 8 hydroxyl groups per mole, e.g.
trimethylolpropane trilactate, trimethylolethane trilactate or
trimethylolpropane triglycolate.
The polyol is next capped with a polyisocyanate (e.g. TDI). The useful
range of polyisocyanates is about 0.60 to about 1.3 moles of diisocyanate
per equivalent group in the polyol mixture. The preferred range of
diisocyanate is about 0.95 to about 1.15 moles of diisocyanate per
equivalent of the polyol mixture.
The resultant polyether polyisocyanate prepolymers are foamed by reacting
with about 10 to about 200 parts of water, preferred range of about 50 to
about 160 parts of water, to 100 parts of prepolymer in the presence of
about 0.05 to about 30 parts surfactant, preferred range of about 0.1 to
about 15 parts surfactant, per 100 parts of prepolymer. The surfactants
can be added either to the prepolymer or the water. Surfactants which are
soluble in water and/or in their own right are hydrophilic, are preferred.
The polyurethane foams made in the manner described above are exceptionally
soft, hydrophilic and biodegradable.
Trimethylolpropane trilactate or the like can be used in combination with
other polyols or trimethylolpropane trilactate can be oxyethylated or
oxypropylated to yield the appropriate polyol. Other hydroxy acids may be
used for the crosslinking agent esterification. These include but are not
limited to hydroxyacetic acid and other .alpha., .beta., .gamma., .omega.,
etc., hydroxy acids.
The polyoxyethylene polyol ester mixture is terminated or capped by
reaction with a polyisocyanate. The reaction may be carried out according
to conventional practice. The polyisocyanates used for capping the
polyoxyethylene polyol include polyisocyanates such as PAPI (the brand of
polyaryl polyisocyanate manufactured by the Upjohn Co. and defined in U.S.
Pat. No. 2,683,730), tolylene diisocyanate,
triphenylmethane-4,4',4",-triisocyanate, benzene-1,3,5-triisocyanate,
toluene-2,4,6-triisocyanate, diphenyl-2,4,4'-triisocyanate, hexamethylene
diisocyanate, xylene diisocyanate, chlorophenylene diisocyanate,
diphenylmethane-4,4'-diisocyanate, naphthalene-1,5-diisocyanate,
xylene-alpha, alpha'-diisothiocyanate, 3,3'-dimethyl-4,4'-biphenylene
diisocyanate, 2,2',5,5'-tetramethyl-4,4'-biphenylene diisocyanate,
4,4'-methylenebis (phenylisocyanate), 4,4'-sulfonylbis (phenylisocyanate,
4,4'-methylenebis (orthotolylisocyanate), ethylene diisocyanate, ethylene
diisothiocyanate, trimethylenediisocyanate and the like. Mixtures of any
one or more of the above-mentioned organic isothiocyanates or isocyanates
may be used as desired. The polyisocyanates or mixtures thereof which are
especially suitable are those which are readily commercially available,
have a high degree of reactivity and a relatively low cost, e.g. TDI. The
aromatic isocyanates are preferred.
The following examples will aid in explaining, but should not be deemed as
limiting, practice of the present invention. In all cases, unless
otherwise noted, all parts and percentages are by weight.
EXAMPLE 1
Polyethyleneglycol PEG 1000 (actual M.W. 1064) and trimethylolpropane
trilactate (361g and 60g respectively) were dried for 2.5 hours at
103.degree. C. and 4 Torr. This mixture was added to 225g of
toluenediisocyanate and 0.2g of Metal and Thermit T-9 catalyst, a catalyst
containing stannous octoate, over a period of 80 minutes at a temperature
of 60.degree. C. After completion of addition, the reaction mixture was
maintained at 60.degree. C. for an additional hour. To the reaction
mixture there was then added an additional 12g of tolylenediisocyanate and
heating continued for another hour at 60.degree. C. The final viscosity
was 24,500 cp at 25.degree. C. and the NCO was 2.38 meq/g (theory 2.33
meq/g).
From the above reaction mixture, a foam was prepared using 100g of
prepolymer, 10g of Union Carbide Silicone surfactant L-520 and 100g of
water. Aqueous solutions of enzymes, 1%, were prepared and tested on this
foam. Maxatase, H.T. proteolytic concentrate, and protease amylase, gave
essentially complete degradation after seven days at 25.degree. C. Several
others, such as mucinase, trypsin and some experimental enzyme broths,
showed some evidence of degradation. A standard polyurethane foam prepared
from 100 pts of prepolymer, isocyanate capped polyoxyethylene polyol, 1 pt
1-520 and 100 pts of water gave no change over the same period of time
with these enzymes.
The foam was buried in a compost heap for three months. On removal from the
compost heap, the foam had started to fragment and could not be washed
without falling apart.
The foam was then compared with a foam made in a similar manner with
trimethylolpropane instead of the trimethylolpropane trilactate. The
trimethylolpropane lactate based foam in ten minutes at 250.degree. F.
turned tacky and began to degrade. The trimethylolpropane based foam
showed no change in 20 minutes at 250.degree. F. Conventional
polyoxypropylene based polyurethanes show no change in three hours.
A similar comparison at 100.degree. C. in boiling water gave breakdown into
viscous lumps in 240 minutes after becoming tacky in 30 minutes for the
trimethylolpropane trilactate biodegradable polymeric foam. The
trimethylolpropane based foam showed no change in 240 minutes at
100.degree. C.
EXAMPLE 2
The procedure of Example 1 was repeated for foam generation. Next a
synthetic sewage sludge was allowed to react with the foam for one week.
The trimethylolpropane trilactate based foam had completely disintegrated.
The standard polyurethane foam was intact.
EXAMPLE 3
The trimethylolpropane trilactate that had been prepared was used with a
different polyol. A mixture of one mole each of trimethylolpropane
trilactate and Pluronic 10-R-5 (a Wyandotte polyol with a molecular weight
of 1970, an equivalent weight of 985 and end-capped with oxypropylene on
an oxyethylene backbone with approximately 50% by weight of oxypropylene
and 50% by weight of oxyethylene) was dried at 110.degree. C. and 3 Torr
for three hours. The mixture was then added to 4.75 moles of the standard
80-20 mixture of 2,4 and 2,6-tolylenediisocyanate over a period of one
hour maintaining the temperature at 60.degree. C. The reaction was
completed by heating for an additional three hours at 60.degree. C. with
the addition of Metal and Thermits' T-9 stannous octoate catalyst (5
drops). To the final prepolymer was added 0.75 moles of
tolylenediisocyanate to give a prepolymer with a viscosity of 17,250 cp.
The prepolymer was converted to a foam by the addition of 1 part of
silicone surfactant L-520 to the prepolymer (100 parts) and then adding
100 parts water to the prepolymer phase. The polymeric foam when placed in
a synthetic sewer sludge disintegrated within one week.
EXAMPLE 4
The trimethylolpropane trilactate was prepared as above in Example 1. A
mixture was prepared from one mole of trimethylolpropane lactate and 0.5
mole Pluronic P-65 supplied by Wyandotte (this polyol has a molecular
weight of 3500 and has a polyoxypropylene base, end-capped with
oxyethylene units, being 50% oxyethylene and 50% oxypropylene by weight)
and was dried by heating for a period of three hours at 115.degree. C. and
5 torr. This mixture was added to 3.8 moles of commercial TDI over a
period of one hour with the temperature maintained at 60.degree. C. After
completion of the addition, 10 drops of Metal and Thermit catalyst T-9 was
added and the reaction mixture was heated for an additional three hours at
65.degree. C. to force the prepolymer formation. Then 0.6 mole of TDI was
added to the reaction mixture and the reaction heated for an additional
two hours to give a prepolymer with a viscosity of 16,000 cp at 25.degree.
C. A foam was prepared from this prepolymer using 100 parts of prepolymer,
1.0 part of Plurafac B-26, 1.7 parts a tertiary amine of Thancat DD
catalyst by Jefferson Chemicals, and 50 parts of water (the latter three
all being in the aqueous phase). The foam that was formed decomposed in a
compost heap in two months. The conventional polyoxypropylene polyurethane
foam showed no change.
EXAMPLE 5
Trimethylolpropane hydroxyacetate (glycolate) is prepared by simple
esterification using one mole trimethylolpropane and 3.12 moles glycolic
acid (hydroxyacetic acid). The mixture was heated for four hours at reflux
and then stripped at 125.degree. C. and 12 Torr.
The prepolymer was prepared by adding a dried mixture of 2.0 moles of
PEG-1000 (molecular weight 1064) and 1.0 mole of trimethylolpropane
triglycolate to 6.7 moles of tolylenediisocyanate over a period of one
hour at a reaction flask temperature of 60.degree. C. The reaction was
continued at 60.degree. C. for an additional three hours and the measured
NCO content in meq/g. was 1.82 meq/g (theory 1.78 meq/g.). To the reaction
mixture was then added an additional 1.0 mole of TDI with heating and
stirring continued for an additional two hours at 60.degree. C. The NCO
was 2.18 meq/g (theory 2.23 meq/g.), viscosity at 25.degree. C. 19,000 cp.
A foam was prepared from this prepolymer by using 100 g. of prepolymer and
100 parts of 5% solution of Plurafac B-26 (By Wyandotte) in water. The
generated foam was found to degrade with Mexatase enzyme in six days at
25.degree. C. while the foam prepared from trimethylolpropane was intact.
In boiling water, decomposition occurred in 200 minutes with the
trimethylolpropane glycolate based material. With the trimethylolpropane
based prepolymer, no change was noted in the same time period.
EXAMPLE 6
Instead of preparing the hydroxyacid ester of the crosslinking agent as in
the previous example, the hydroxyacid ester of polyoxyalkylene glycol was
prepared. To 1 mole of polyethylene glycol having a molecular weight of
1064 (PEG-1000) there was added 2.22 moles of 88% lactic acid. The mixture
was refluxed for four hours after which the residual lactic acid was
stripped at 130.degree. C. and 4 Torr.
The product weighing 1215 g., mainly polyethylene glycol dilactate, was
combined with 67 g. of trimethylolpropane and stripped of residual water
at 105.degree. C. and 3 Torr for four hours. This mixture was then added
at 60.degree. C. flask temperature to 574 g. of tolylenediisocyanate over
a period of two hours. The reaction mixture was then heated for an
additional four hours at 60.degree. C. To the reaction mixture was then
added an additional 87 g. of tolylenediisocyanate in thirty minutes at
60.degree. C. and the reaction mixture heated for an additional two hours
at 60.degree. C. The NCO content was 2.06 meq/g. (theory 2.11 meq/g.); the
viscosity was 18,000 cp at 25.degree. C.
A foam was prepared from the prepolymer of this example using 100 parts of
prepolymer and 100 parts of 5% solution of Pluronic P-75 in water. The
final foam was dried and on treatment with a synthetic sewer sludge,
disintegrated within ten days. A similar sample was prepared from a
prepolymer containing polyethylene glycol 1000 and trimethylolpropane
showed no signs of decomposition in the same period of time.
It is understood that the foregoing detailed description is given merely by
way of illustration and that many variations may be made therein without
departing from the spirit of this invention.
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Description |
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