 |
Description  |
|
|
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to polyurethane resins, more particularly, to
water-dispersed polyurethane resins which are film formers.
2. Brief Description of the Prior Art
Water-dispersible polyurethanes are known in the art. For example, U.S.
Pat. No. 2,968,575 to Mallonee discloses emulsifying NCO-containing
prepolymers in a solution of diamine and water with the aid of detergents
and under the action of powerful shearing forces. A chain lengthening
reaction takes place as water and diamine diffuse into the droplets of the
emulsion and react with the isocyanate. The resultant poly(urethane-urea)
can then be further processed to form a coating. The process described in
U.S. Pat. No. 2,968,575 has the disadvantage associated with it that in
order to form the emulsion, a detergent must be used. The detergent
usually finds its way into the resultant coating where it can seriously
detract from the coating's overall physical and chemical properties.
Besides, insufficient shearing force often results in unstable products,
and the material can usually not be produced in typical reaction kettles
because of the high shearing forces needed.
There have also been suggestions in the prior art to prepare fully reacted
polyurethanes in organic solvent with internally contained salt groups
which permit the polyurethane to be dispersed in water. For example, U.S.
Pat. No. 3,479,310 to Dieterich et al discloses dispersing a fully chain
extended, NCO-free polyurethane having internally contained ionic salt
groups in water without the aid of detergent.
However, chain extended high molecular weight polyurethanes are very
difficult to disperse satisfactorily in water. The resultant dispersions
are fairly coarse and they require a high percentage of salt groups for
stability. These high percentages of salt groups normally result in
coatings which are moisture sensitive. In addition, because the high
molecular weight polyurethanes are generally quite high in viscosity, they
require extensive thinning with organic solvent before they have a
sufficiently low viscosity for dispersion without high shearing forces.
The excess solvent must later be removed by steam distillation or the
like. Polyurethane dispersions of the present invention, on the other
hand, which are prepared by first dispersing a low molecular weight
partially reacted NCO-containing prepolymer which contains acid salt
groups in an aqueous medium followed by chain extending in the aqueous
medium have a finely particulated dispersed phase. By chain extending in
aqueous medium, we have found that only a relatively small percentage of
salt groups is needed for satisfactory dispersion. In addition, the low
molecular weight prepolymer materials have sufficiently low viscosities
that they can be dispersed neat at room temperature or in the presence of
small amounts of organic solvents. Further chain extension in water does
not require additional solvent. It is believed that by making
polyurethanes this way, the molecules of polyurethanes are coiled.
The idea of chain extending an NCO prepolymer with internally contained
acid salt groups in water with an organic polyamine is generally expected
to give gels due to the reaction of polyacids with polyamines. In fact,
this method of making crosslinked polyurethanes was generally disclosed in
Canadian Pat. No. 837,174, to Witt et al. This reference discloses the
preparation of aqueous dispersions of highly crosslinked polyurethanes.
The polyurethanes are prepared by dispersing an NCO-containing prepolymer
which has internally contained acid salt groups in water. The prepolymer
is reacted in water with a polyamine to give a highly crosslinked product.
Crosslinking can also occur by using polyvalent counter ions of the ionic
groups in the polymer. The process and the products prepared from the Witt
et al process differ from the present invention in that they are highly
crosslinked rather than ungelled, solvent-soluble products of the present
invention. Highly crosslinked products are undesirable because they are
not solvent-soluble and will not readily coalesce to form continuous
films. For coating or adhesive usage, gel must be avoided. Witt et al do
not teach how to make ungelled film-forming polyurethanes.
U.S. Pat. No. 3,868,350 discloses sedimenting aqueous solutions of
thermoplastic polyurea powders made by reacting polyurethanes which
contain free NCO groups and ionic groups with primary and/or secondary
aliphatic diamines and/or dicarboxylic acid-bis-hydrazides at an NH to NCO
ratio of from 0.1 to 0.95 in the presence of water. U.S. Pat. No.
3,868,350 acknowledges the difficulties in forming ungelled or
uncrosslinked polyurethanes by further reaction of NCO-polymers with chain
extenders in the presence of water. The means U.S. Pat. No. 3,868,350 has
used to form ungelled products is to react an NCO-polymer of specified
salt content with a stoichiometric deficit of a specified chain extender.
The final polymer product must have specified urethane, urea and salt
group content. Although the resultant products are ungelled, they suffer
from numerous shortcomings. The products are sedimenting and not stable
dispersions. As such, the sedimented product cannot be used to make
coatings without intensive heating (e.g., powder coatings) or strong
organic solvents to dissolve the powders. Thus, conventional coating
techniques such as spraying, dipping, electrodepositing, electrostatic
spraying cannot be employed. Further, since the products of U.S. Pat. No.
3,868,350 are prepared with specified chain extender in a stoichiometric
deficit, and since the products must contain a specified urethane, urea
and salt group content, products of only a limited range of physical and
chemical properties can be produced. Finally, although the patent mentions
that the urethane dispersions can be combined with crosslinking agents,
there is no disclosed means of how this may be accomplished.
Therefore, from the above, there are numerous shortcomings in the prior art
relating to water-dispersed, ungelled polyurethanes. It is surprising that
ungelled polyurethane dispersions can be prepared by the present
invention. Besides, the polyurethane dispersions of the present invention
are also surprisingly superior to those of the prior art, overcoming many
of their shortcomings. The polyurethane dispersions of the present
invention are ungelled, solvent-soluble materials which are excellent film
formers. They can easily be prepared not requiring detergent, high
shearing forces, high temperatures or excessive amounts of organic solvent
for a satisfactory dispersion. The polyurethane dispersions of the present
invention can be prepared extremely fine, making the dispersion stable or
non-settling. By this is meant that after the dispersion is prepared, the
dispersed phase remains in dispersion and will not form hard sediments.
They cannot be filtered by regular means. Besides being non-sedimenting,
fine particle size dispersions are advantageous because they have a high
surface energy associated with them. This results in a strong driving
force for coalescing, and in coatings having surprisingly fast drying
times. The polyurethanes of the present invention, although prepared in
water, can be deposited as a coating which, when desired, is insensitive
to humidity and moisture, which is an unusual combination of properties.
Coatings prepared with the polyurethane dispersions of the present
invention can be made with outstanding elastomeric properties such as high
tensile strength, good ultimate elongation, excellent impact resistance
and hardness, in addition to excellent solvent and humidity resistance.
SUMMARY OF THE INVENTION
According to the present invention, a non-sedimenting, essentially
emulsifier-free aqueous dispersion of an ungelled polyurethane having a
particle size less than 10, preferably less than 5 microns, formed by
reacting in aqueous medium in which water is the principal ingredient:
(A) an NCO-containing polymer containing acid salt groups having monovalent
counter ions having a salt group equivalent weight of 6000 or less and
being substantially free of reactive active hydrogen formed from:
(1) an organic polyisocyanate and
(2) an active hydrogen-containing material; said organic polyisocyanate,
said active hydrogen-containing material containing a total of not more
than one gram-mole of compounds having an average functionality of 3 or
more per 500 grams of organic polyisocyanate and active
hydrogen-containing material; said NCO-containing polymer having an
NCO/active hydrogen equivalent ratio of at least 4/3;
(B) active hydrogen-containing compound having an active hydrogen
functionality of 2 or less in which the active hydrogens are more reactive
with NCO groups than water to form a polyurethane with an intrinsic
viscosity less than 2.0 deciliters per gram.
The final reaction product can be used for either thermoplastic or
thermoset coatings. For thermosetting polymers, the final reaction product
is either blended with suitable curing agents or contain suitable curing
agent groups or both such that after the coating is applied, cross-linking
can be induced to produce a durable thermoset coating.
DETAILED DESCRIPTION
The polyurethanes of the present invention are extremely dispersible in
aqueous medium, much better than would be expected from the prior art such
as U.S. Pat. No. 3,479,310 to Dieterich et al mentioned above. By better
dispersibility or improved dispersibility is meant the polyurethanes can
be dispersed in water with relatively few acid salt groups and form a
finely particulated dispersed phase. Although not intending to be bound by
any theory, the reasons we believe the products of the invention have
improved dispersibility is first, the NCO-containing prepolymer is of
relatively low molecular weight; secondly, by dispersing the low molecular
weight NCO-containing prepolymer in water, water competes with the chain
extender for reaction with the NCO groups. Although the chain extender is
more reactive with the NCO groups than water, water is believed in many
instances to react to a minor degree to form urea linkages and salt of
carbamic acid. The surprising good dispersibility and product properties
are difficult to explain. We believe these reactions can be responsible.
Determination that water participates in the reaction can be made by
dispersing an NCO-containing prepolymer in a mixture of chain extender and
water or in water itself and then adding a chain extender to the
dispersion. In either instance, when an equivalent amount of chain
extender to NCO prepolymer is used, the amount of chain extender remaining
at the completion of the chain extension reaction is an indication of side
reactions of the NCO prepolymer with water. The extent of the reaction
with water will depend on how much more active the chain extender is with
the NCO groups than water, the relative amounts of water and chain
extender present in the dispersion and the time the NCO prepolymer is
dispersed in water before a chain extender is added.
While it is relatively easy to make gelled products such as disclosed by
the aforementioned Witt et al patent, the preparation of non-gelled
products is difficult. In the practice of the invention, reaction
conditions are controlled and reactants carefully selected so as to get an
ungelled product. Whether or not a reaction mixture will gel is difficult
to determine beforehand. A method based on trial and error is the only
sure way to determine whether or not a set of reactants under specific
reaction conditions will gel. However, a few general guidelines based on
our personal experiences in working with the polyurethane dispersions of
the present invention can be given. As will be described in more detail
later, the NCO-containing polymer is prepared from reacting an organic
polyisocyanate and an active hydrogen-containing compound having an
average of at least two active hydrogens, some of which contain salt or
salt forming groups. The prepolymer is then chain extended in water with
another active hydrogen-containing compound such as an organic amine. In
the preparation of the NCO-polymer, if an approximately 4:3 equivalent
ratio of polyisocyanate to active hydrogen-containing compound is used and
the reaction permitted to go to completion, a very high molecular weight
prepolymer which is difficult to disperse will result. If either or both
of the reactants are trifunctional or of greater functionality, the
product in most instances will be a gel and not be dispersible at all.
However, if the reactants are difunctional or contain a considerable
amount of monofunctional ingredients to reduce the average functionality
of the system, and reaction conditions are controlled to limit the
molecular weight, a readily dispersible prepolymer will result. This
product can then be chain extended to form a useful product. However, the
functionality, amount of chain extender and reaction conditions must be
carefully controlled. A chain extender having an average functionality of
greater than 2 would probably gel such a high molecular weight product if
used in a stoichiometric amount with the ureacted NCO in the prepolymer.
However, gelling could probably be avoided if a sufficient excess of chain
extender were used or if a sufficient amount of monofunctional chain
extender or a chain extender with drastically different reactive groups
were used to reduce the average functionality of the chain extender. In
most instances, the use of a monofunctional chain extender along would
cause no problems and would result in an ungelled product.
Even though care must be taken to avoid gelling, we have found that the
polyurethanes of the present invention prepared in aqueous medium have
less tendency to gel than comparable polyurethanes prepared in organic
solvent. Thus, ungelled products of the invention can be prepared in
aqueous medium with trifunctional or higher functionality reactants,
whereas similar products would gel if prepared in organic solvent. This is
somewhat surprising since the aforementioned U.S. Pat. No.3,868,350 shows
only difunctional reactants in the preparation of the thermoplastic
polyurea powders.
The polyurethane dispersions of the present invention are ungelled and
essentially emulsifier free. By the term "ungelled" or "non-gelled" is
meant the dispersed resin is substantially free of crosslinking and has an
intrinsic viscosity when dissolved in a suitable solvent without
depolymerization. The intrinsic viscosity of such a product is an
indication of molecular weight. A gelled polyurethane, on the other hand,
since it has an essentially infinitely high molecular weight, will have an
intrinsic viscosity too high to measure.
The intrinsic viscosity of various resins are determined by art-recognized
methods. Thus, the intrinsic viscosity of the resins of the present
invention may be determined by first acidifying the resin. The aqueous
solvent is removed either by evaporation or decantation. The acidified
resin solid is then dissolved in N-methyl pyrrolidone or other suitable
solvent at a concentration of from 8 to 30 percent. This solution is
further thinned with dimethyl formamide to 0.5 percent and 0.25 percent
concentrations. The resins may then be passed through a capillary
viscometer to determine the reduced viscosities.
The intrinsic viscosity of the resin will then be determined by the
following equation:
[.mu.]=[.mu. reduced].sub.C=O =[.mu. reduced].sub.0.25 +[[.mu.
reduced].sub.0.25 -[.mu. reduced].sub.0.50 ]=2[.mu. reduced].sub.0.25
-[.mu. reduced].sub.0.50
where [.mu.] is intrinsic viscosity and [.mu. reduced].sub.0.25 is the
reduced viscosity of 0.25 percent concentration and [.mu.
reduced].sub.0.50 is the reduced viscosity of 0.50 percent concentration.
The general methods of determining reduced viscosities are described in
the art such as Textbook of Polymer Science, Billmeyer, Interscience
Publishers, New York, 1957, pages 79-81.
The polyurethane polymers of the present invention have intrinsic
viscosities lower than 4.0 deciliters per gram, and preferably lower than
2.0 deciliters per gram, and most preferably within the range of 0.1 to
1.5 deciliters per gram; the intrinsic viscosities being determined for
anionic polymers on the acid form of the polymer; for non-quaternized
cationic polymers on the basic form of the polymer; and for quaternized
polymers on the ionic form of the prepolymer itself.
By the term "essentially emulsifier free" is meant that the polyurethane
dispersion usually needs no externally added emulsifiers or detergent to
maintain its stability, although, of course, emulsifiers may be used if
desired. Polyurethane dispersions of the present invention are very stable
in that once they are dispersed, they will not settle or flocculate and
cannot be filtered by conventional techniques.
The organic polyisocyanate which is used in the instant invention can be an
aliphatic or an aromatic polyisocyanate or mixture of the two. Aliphatic
polyisocyanates are preferred since it has been found that these provide
better color stability in the resultant coating. Also, diisocyanates are
preferred although higher polyisocyanates can be used in place of or in
combination with diisocyanates and/or monoisocyanate. As indicated above,
the average functionality of the reactants used in making the NCO-polymer
is important in controlling the tendency of the polymer to gel. Where
higher functionality polyisocyanates are used, some monofunctional
isocyanate should be present to reduce the average functionality. Examples
of suitable higher polyisocyanates are 1,2,4-benzene triisocyanate and
polymethylene polyphenyl isocyanate. Examples of suitable monoisocyanates
are cyclohexyl isocyanate, phenyl isocyanate and toluene isocyanate.
Examples of suitable aromatic diisocyanates are 4,4'-diphenylmethane
diisocyanate, 1,3-phenylenediisocyanate, 1,4-phenylene diisocyanate and
tolylene diisocyanate. Examples of suitable aliphatic diisocyanates are
straight chain aliphatic diisocyanates such as 1,4-tetramethylene
diisocyanate and 1,6-hexamethylene diisocyanate. Also, cycloaliphatic
diisocyanates can be employed and are actually preferred because of color
stability and imparting hardness to the product. Examples include
1,4-cyclohexyl diisocyanate, isophorone diisocyanate, alpha,
alpha-xylylene diisocyanate and 4,4'-methylene-bis(cyclohexylisocyanate).
This particular polyisocyanate is preferred and is commercially available
from E. I. du Pont de Nemours and Company under the trademark HYLENE
W.RTM.. Substituted organic polyisocyanates can also be used in which the
substituents are nitro, chloro, alkoxy and other groups which are not
reactive with hydroxyl groups or active hydrogens and provided the
substituents are not positioned to render the isocyanate group unreactive.
Examples include compounds having the structure:
##STR1##
There can also be employed isocyanate-terminated adducts of diols or
polyols such as ethylene glycol, 1,4-butylene glycol, polyalkylene glycol
and the like. These are formed by reacting more than one equivalent of the
diisocyanate, such as those mentioned with one equivalent of diol or
polyalcohol to form a diisocyanate product.
Thioisocyanates corresponding to the above-described can be employed as
well as mixed compounds containing both an isocyanate and a thioisocyanate
group. The terms "polyisocyanate" and "diisocyanate," as used in the
present specification and claims, are intended to cover compounds and
adducts containing thioisocyanate groups or isocyanate groups and
compounds and adducts containing both isocyanate and thioisocyanate
groups.
Any suitable organic compound containing active hydrogens may be used for
reaction with the organic polyisocyanate to form the partially reacted
NCO-containing polymers of the present invention. The term "active
hydrogen atoms" refers to hydrogens which, because of their position in
the molecule, display activity according to the Zerewitinoff test.
Accordingly, active hydrogens include hydrogen atoms attached to oxygen,
nitrogen, or sulfur, and thus useful compounds will include those having
at least two of these groups (in any combination) --OH, --SH,
##STR2##
and --NH.sub.2. The moieties attached to each group can be aliphatic,
aromatic, cycloaliphatic or of a mixed type not including carbonyl,
phosphonyl or sulfonyl linkages.
Examples of such compounds include amines, which includes polyamines,
aminoalcohols, mercapto-terminated derivatives, and alcohols, which
includes polyhydroxy materials (polyols) which are preferred because of
the ease of reaction they exhibit with polyisocyanates. Alcohols and
amines generally give no side reactions, giving higher yields of urethane
(or urea) product with no by-product and the products are hydrolytically
stable. Also, with regard to polyols, there are a wide variety of
materials available which can be selected to give a wide spectrum of
desired properties. In addition, the polyols have desirable reaction rates
with polyisocyanates. Both saturated and unsaturated active
hydrogen-containing compounds can be used, but saturated materials are
preferred because of superior coating properties.
The amines which can be employed in the preparation of the urethanes of the
invention can be primary or secondary diamines or polyamines in which the
radicals attached to the nitrogen atoms can be saturated or unsaturated,
aliphatic, alicyclic, aromatic, aromatic-substituted aliphatic,
aliphatic-substituted aromatic or heterocyclic. Mixed amines in which the
radicals such as, for example, aromatic and aliphatic can be employed and
other non-active groups can be present attached to the carbon atom, such
as oxygen, sulfur, halogen or nitroso. Exemplary of suitable aliphatic and
alicyclic diamines are the following: 1,2-ethylene diamine, 1,2-propylene
diamine, 1,8-menthane diamine, isophorone diamine, propane-2,2-cyclohexyl
amine, methane-bis-(4-cyclohexyl amine), and
##STR3##
where x = 1 to 10.
Aromatic diamines such as the phenylene diamines and the toluene diamines
can be employed. Exemplary of the aforesaid amines are: o-phenylene
diamine and p-tolylene diamine. N-alkyl and N-aryl derivatives of the
above amines can be employed such as, for example,
N,N'-dimethyl-o-phenylene diamine, N,N'-di-p-tolyl-m-phenylene diamine,
and p-aminodiphenylamine.
Polynuclear aromatic diamines can be employed in which the aromatic rings
are attached by means of a valence bond such as, for example,
4,4'-biphenyl diamine, methylene dianiline and monochloromethylene
dianiline.
The use of amines dissolved in ketones is sometimes desirable because of
better control over reaction conditions.
Besides the amines mentioned above, hydrazines and hydrazides such as are
described later in the specification can also be employed.
Aminoalcohols, mercapto-terminated derivatives and mixtures, and the like,
hydroxy acids and amino acids can also be employed as the active hydrogen
compounds. Examples are: monoethanolamine, 4-aminobenzoic acid,
aminopropionic acid, N-(hydroxyethyl)ethylene diamine, 4-hydroxybenzoic
acid, p-aminophenol, dimethylol propionic acid, hydroxy stearic acid, and
beta-hydroxypropionic acid. When amino acids are used, additional basic
material should also be present to release NCO-reactive amines from
Zwitterion complexes.
To degress for a moment, the active hydrogen-containing compound can, if
desired, contain functional moieties which are capable of further reaction
to cure the product. Examples would be active hydrogen-containing
compounds which contained acrylic unsaturation which would enable the
coating to be cured by ultraviolet light with vinyl monomers. Various
curing mechanisms will be described in more detail later.
The polyhydroxyl materials or polyols can be either low or high molecular
weight materials and in general will have average hydroxyl values as
determined by ASTM designation E-222-67, Method B, between about 1000 and
10, and preferably between about 500 and 50. The term "polyol" is meant to
include materials having an average of two or more hydroxyl groups per
molecule.
The polyols include low molecular weight diols, triols and higher alcohols,
low molecular weight amide-containing polyols and higher polymeric polyols
such as polyester polyols, polyether polyols and hydroxy-containing
acrylic interpolymers.
The low molecular weight diols, triols and higher alcohols useful in the
instant invention are known in the art. They have hydroxy values of 200 or
above, usually within the range of 1500 to 200. Such materials include
aliphatic polyols, particularly alkylene polyols containing from 2 to 18
carbon atoms. Examples include ethylene glycol, 1,4-butanediol,
1,6-hexanediol; cycloaliphatic polyols such as 1,2-cyclohexanediol and
cyclohexane dimethanol. Examples of triols and higher alcohols include
trimethylol propane, glycerol and pentaerythritol. Also useful are polyols
containing ether linkages such as diethylene glycol and triethylene glycol
and oxyalkylated glycerol.
Also useful are low molecular weight amide-containing polyols having
hydroxyl values of 100 or above. These materials are described in U.S.
Pat. application Ser. No. 405,713, filed Oct. 11, 1973, to Chang and
assigend to PPG Industries, Inc., the assignee of the present invention,
on page 8, line 19, to page 12, line 23, the portions of which are hereby
incorporated by reference. When these low molecular weight
amide-containing polyols are incorporated into the polymer, they enhance
its water dispersibility.
Where flexible and elastomeric properties are desired, the partially
reacted NCO-containing polymer should preferably contain at least a
portion of a higher molecular weight polymeric polyol. Such a polymeric
polyol should be predominantly linear (that is, absence of trifunctional
or higher functionality ingredients) to avoid gelling of the resultant
polymeric product and should have a hydroxyl value of 200 or less,
preferably within the range of about 150 to 30.
The most suitable polymeric polyols include polyalkylene ether polyols
including thio ethers, polyester polyols including polyhydroxy
polyesteramides and hydroxyl-containing polycaprolactones and
hydroxy-containing acrylic interpolymers.
Any suitable polyalkylene ether polyol may be used including those which
have the following structural formula:
##STR4##
where the substituent R is hydrogen or lower alkyl including mixed
substituents, and n is typically from 2 to 6 and m is from 2 to 100 or
even higher. Included are poly(oxytetramethylene) glycols,
poly(oxyethylene) glycols, polypropylene glycols and the reaction product
of ethylene glycol with a mixture of propylene oxide and ethylene oxide.
Also useful are polyether polyols formed from the oxyalkylation of various
polyols, for example, glycols such as ethylene glycol, 1,6-hexanediol,
Bisphenol A, and the like, or higher polyols, such as trimethylol propane,
pentaerythritol and the like. Polyols of higher functionality which can be
utilized as indicated can be made, for instance, by oxyalkylation of
compounds as sorbitol or sucrose. One commonly utilized oxyalkylation
method is by reacting a polyol with an alkylene oxide, for example,
ethylene or propylene oxide, in the presence of an acidic or basic
catalyst.
Besides poly(oxyalkylene) glycols, any suitable polyhydric polythioether
may be used such as, for example, the condensation product of thioglycol
or the reaction product of a polyhydric alcohol, such as disclosed herein
for the preparation of hydroxyl polyesters, with thioglycol or any other
suitable glycol.
Polyester polyols can also be used as a polymeric polyol component in the
practice of the invention. The polyester polyols can be prepared by the
polyesterification of organic polycarboxylic acids or anhydrides thereof
with organic polyols. Usually, the polycarboxylic acids and polyols are
aliphatic or aromatic dibasic acids and diols.
The diols which are usually employed in making the polyester include
alkylene glycols, such as ethylene glycol and butylene glycol, neopentyl
glycol and other glycols such as hydrogenated Bisphenol A, cyclohexane
diol, cyclohexane dimethanol, caprolactone diol (for example, the reaction
product of caprolactone and ethylene glycol), hydroxy-alkylated
bisphenols, polyether glycols, for example, poly(oxytetramethylene) glycol
and the like. However, other diols of various types and, as indicated,
polyols of higher functionality can also be utilized. Such higher polyols
can include, for example, trimethylol propane, trimethylol ethane,
pentaerythritol, and the like, as well as higher molecular weight polyols
such as those produced by oxyalkylating low molecular weight polyols. An
example of such high molecular weight polyol is the reaction product of 20
moles of ethylene oxide per mole of trimethylol propane.
As has been mentioned above, some monofunctional alcohol such as n-propyl
alcohol and n-butyl alcohol can be used.
The acid component of the polyester consists primarily of monomeric
carboxylic acids or anhydrides having 2 to 18 carbon atoms per molecule.
Among the acids which are useful are phthalic acid, isophthalic acid,
terephthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, adipic
acid, azelaic acid, sebacic acid, maleic acid, glutaric acid, chlorendic
acid, tetrachlorophthalic acid and other dicarboxylic acids of varying
types. The polyester may include minor amounts of monobasic acid, such as
benzoic acid, stearic acid, acetic acid, hydroxy stearic acid and oleic
acid. In an interesting embodiment, we have found that larger amounts of a
monobasic acid such as benzoic acid can be combined with sucrose to make
effectively difunctional sucrose pentabenzoate. This difunctional material
can then be reacted with various other ingredients and isocyanates to form
polyurethanes having enhanced durability. Also, there may be employed
higher polycarboxylic acids such as trimellitic acid and tricarballylic
acid (where acids are referred to above, it is understood that the
anhydrides of those acids which form anhydrides can be used in place of
the acid). Also, lower alkyl esters of acids such as dimethyl glutarate
can be used. It is preferred that the polyester include an aliphatic
dicarboxylic acid as at least part of the acid component.
Besides polyester polyols formed from polybasic acids and polyols,
polycaprolactone-type polyesters can also be employed. These products are
formed from the reaction of a cyclic lactone such as epsilon-caprolactone
with a polyol or a hydroxy acid. Such products are described in U.S. Pat.
No. 3,169,949 to Hostettler, the portion of this patent relating to the
description of polycaprolactone polyols being incorporated by reference.
Although not disclosed in the aforementioned patent, the product of cyclic
lactone with an acid-containing polyol can also be used. The reaction of
urea and caprolactone such as described in U.S. Pat. No. 3,832,333 to
Chang et al can also be used.
While polyester polyols have been specifically disclosed, it is to be
understood that useful products are also obtainable by substituting a
polyesteramide polyol, or a mixture of polyesteramide polyols for part or
all of the polyester polyol. The polyesteramide polyols are produced by
conventional techniques from the above-described acids and diols, and
minor proportions of diamines or aminoalcohols. Suitable diamines and
aminoalcohols include hexamethylene diamine, hydrazine,
bis(4-aminocyclohexyl) methane, diethylene triamine, ethylene diamine,
ethanolamine, phenylene diamine, toluene diamine and poly(amide-amines)
such as the VERSAMIDS.RTM. sold by General Mills, and the like. It is to
be understood that the polyester polyols of the instant invention include
such polyesteramide polyo | | |
