Aqueous polyurethane compositions

A stable aqueous dispersion latex of a room temperature curing polyurethane forming films resistant to water and organic solvents is disclosed, the polyurethane containing units derived from melamine, in addition to units derived from diisocyanate and difunctional reactants, in the polymer chain, pendant water-dispersing carboxylic salt groups, and room temperature curable and cross-linking N-methylol hydrazide termini, and methods for making such dispersion.

BACKGROUND AND DISCUSSION OF PRIOR ART 
This invention relates to aqueous polyurethane compositions and more 
particularly to aqueous dispersions of room temperature curing 
polyurethane effective for depositing water resistant and organic solvent 
resistant films on any suitable substrate. 
Polyurethanes have found widespread use in coatings for fabrics, plastics, 
wood, metal, and the like, due to their advantageous properties such as 
their good chemical resistance, abrasion-resistance, toughness, elasticity 
and durability, and their ability to cure rapidly. Conventionally, such 
coatings have been applied as solutions in, for instance, polar or 
aromatic hydrocarbon solvents. When the polyurethanes are of certain 
types, they may be compatible with aliphatic hydrocarbon solvents. When 
the coating is being dried, or cured, these solvents vaporize into the 
atmosphere as an economic loss and, quite importantly, the vaporous 
solvents may pollute the atmosphere. 
Aqueous polyurethane coating compositions are, therefore, particularly 
desirable due to the low cost and availability of water. Moreover, aqueous 
coating compositions are advantageous since the evaporation of water into 
the atmosphere has little, if any, adverse effect on the environment, 
whereas conventionally employed organic solvents may be toxic, 
odoriferous, or photochemically-sensitive, and thus, may be smog-formers 
in the daylight atmosphere due to photochemical oxidation. Furthermore, 
water which is readily available can be used to thin the water-based 
coating compositions and can be used in clean-up operations. However, 
polyurethanes generally are not compatible with water unless special 
ingredients and/or particular steps of manufacture are employed in their 
synthesis. 
One approach to provide water-dispersible, polyurethane-containing 
compositions has been through the use of emulsifiers. This procedure 
generally suffers from the disadvantages that the dispersions are 
relatively unstable and the resultant films are water-sensitive. 
It has also been previously proposed to render polyurethanes dispersible in 
water by providing the polymer chain with pendant acid salt groups. Films 
produced with latices containing such polymers have not been found to be 
entirely satisfactory with respect to sufficient hardening, curing and/or 
cross-linking under ambient (e.g., room temperature) conditions, 
resistance to both water and organic solvents, elongation, flexibility, 
tensile strength, and/or impact resistance and the like. 
It is accordingly an object of this invention to provide aqueous 
polyurethane compositions and dispersions, and methods for making same, 
which will not be subject to one or more of the above deficiencies or 
disadvantages. Other objects and advantages will appear as the description 
proceeds. 
The attainment of the above objects is made possible by this invention 
which includes the provision of an aqueous dispersion of a room 
temperature curing polyurethane forming films resistant to water and 
organic solvents, prepared by: 
a. Dispersing in water an NCO-terminated polyurethane prepolymer containing 
units derived from melamine in the prepolymer chain and pendant 
water-dispersing carboxylic salt groups, 
b. chain extending the dispersed prepolymer by mixing into the dispersion 
an aliphatic polyamine chain extender more reactive with NCO groups than 
water, 
c. end capping the resulting dispersed polyurethane by mixing into the 
dispersion an organic dihydrazide, and 
d. reacting the resulting dispersed end capped polyurethane by mixing 
formaldehyde into the dispersion to convert hydrazide end caps into 
N-methylol groups; 
the resultant N-methylol terminated polyurethane containing about 1% to 
about 5% by weight of units derived from melamine. 
In the above-defined dispersions of this invention, the components 
peculiarly coact and cooperate to achieve the desired improved and 
unexpected results. The melamine performs a major role in providing 
improved resistance to organic solvents, in conjunction with the organic 
dihydrazide end caps and, preferably, diethylenetriamine chain extender. 
The methylol termini produced by reaction of the hydrazide end caps with 
formaldehyde undergo self condensation under ambient conditions upon 
drying of the latex film on the substrate. This cross linking in the dry 
state avoids the need for an external cross linker. 
NCO-terminated polyurethane prepolymers are notoriously produced by 
reacting organic material containing an average of about 2 hydrogen atoms 
per molecule, preferably a polyester polyol as in the present invention, 
with a stoichiometric excess of an organic diisocyanate. It is also known 
to include in the reaction medium a dihydroxyalkanoic acid which 
contributes randomly to the polymer backbone and provides pendant water 
dispersing carboxylic acid salt groups. 
According to a preferred embodiment of this invention, the NCO-terminated 
prepolymer is produced by sequentially reacting the dihydroxyalkanoic 
acid, preferably at a lower temperature, with the intermediate resulting 
from the previous reaction of the organic diisocyanate with melamine and 
the organic material containing an average of 2 active hydrogen atoms per 
molecule (e.g. polyester polyol). This procedure has been found to reduce 
or eliminate undesired reaction of the COOH group in the dihydroxyalkanoic 
acid, needed to provide the desired pendant water dispersing carboxylic 
salt groups, with other reactant components of said intermediate. This 
sequential procedure also yields a polymer chain with a partial block 
structure significantly different from the prior art random structure, 
apart from the further distinction of containing units derived from 
melamine in the random structure of the intermediate. 
U.S. Pat. No. 4,147,679 issued Apr. 3, 1979, to R. L. Scriven and U.S. Pat. 
No. 4,203,883 issued May 20, 1980, to D. G. Hangauer, Jr. disclose aqueous 
dispersions of polyurethanes containing pendant water dispersing 
carboxylic salt groups, but neither discloses melamine containing polymer, 
N-methylol termini, the above described sequential reaction, or the 
resulting polymer structure. 
The organic diisocyanates useful in preparing the instant polyurethanes 
comprise substantially all those known and disclosed in the prior art. 
They may be aliphatic, aromatic, cycloaliphatic, heterocyclic, or any 
mixture thereof, and may contain any substituent noninterfering groups 
e.g., containing substantially nonreactive hydrogens as determined by the 
Zerewitinoff test, J. Am. Chem. Soc., 49,3181 (1927). The term 
"diisocyanate" as employed herein and in the appended claims is inclusive 
of compounds and adducts containing thioisocyanate and/or isocyanate 
groups. Representative diisocyanates useful herein are disclosed in column 
6 of U.S. Pat. No. 4,147,679, which disclosure is incorporated herein by 
reference thereto. Preferred for use herein is 
4,4'-bis(isocyanatocyclohexyl)methane, otherwise referred to as 
4,4'-methylene-bis(cyclohexylisocyanate). 
The organic material containing an average of 2 active hydrogen atoms per 
molecule useful for reaction with the diisocyanate herein also comprises 
substantially all those known and disclosed in the prior art. The material 
may be aliphatic, aromatic, cycloaliphatic, heterocyclic, or any mixture 
thereof. The term "active hydrogen atom" refers to hydrogens which, 
because of their position in the molecule, display activity according to 
the Zerewitinoff test. Accordingly, the term includes hydrogens attached 
to O, S or N, and thus useful such material will include those monomers, 
oligomers and polymers containing any 2 of the groups --OH, --SH, --NH--, 
and --NH.sub.2. Polyols (e.g. dihydroxy) are preferred because they react 
so readily with NCO groups, give higher yields of hydrolytically stable 
urethane with minimal by-products, and are readily available in a wide 
variety of forms. Polyether polyols, and especially polyester polyols, are 
preferred, generally those having molecular weight (M.W.) ranging from 
about 400 to 5000, preferably about 1,000 to about 2,000. 
The polyether polyols include polyalkylene ether glycols such as 
polyethylene glycols, polypropylene glycols, polyoxyethylenated 
polypropylene glycols, polyoxyalkylated higher diols such as hexanediol 
and Bisphenol A, polyhydric polythioethers and the like. 
The polyester polyols are generally prepared by polyesterification 
reactions between organic diols and organic dicarboxylic acids. Especially 
preferred for use herein is the OH-terminated polyester polyol having a 
molecular weight of about 1,000 to 2,000 produced by reacting adipic acid 
with a stoichiometric excess of a mixture of hexanediol and neopentyl 
glycol. 
It will be understood that a portion of the material containing an average 
of about 2 active hydrogen atoms may contain only 1 active hydrogen, which 
deficiency would be corrected by inclusion of a complementary portion of 
material containing 3 or more active hydrogens, provided however that 
proportions materially greater than such complementary portion tend to 
yield undue and premature cross-linking, viscosity increases, and the like 
and should hence be avoided. 
Representative materials containing an average of about 2 active hydrogen 
atoms which are useful herein, including the preferred polyester polyols, 
are disclosed in the passage in U.S. Pat. No. 4,147,679 from column 7, 
line 1 to column 11, line 40, which passage is incorporated herein by 
reference thereto. 
As indicated above, melamine is included in the reaction medium in an 
amount sufficient to provide the final N-methylol terminated polyurethane 
with about 1% to about 5%, preferably about 2% to about 3.5%, by weight of 
units derived from the melamine in the polymer backbone chain along with 
units derived from the diisocyanate, from the carboxyl-providing reactant, 
and from the different, additional material, reactive with NCO, containing 
an average of 2 active hydrogen atoms per molecule. 
The insertion of pendant water dispersing carboxylic acid salt groups, in 
proportions of about 0.5% to about 10% by weight of the final 
hydroxymethylamino-terminated polymer, may be accomplished by use, for 
reaction with the diisocyanate, of a suitable portion of the organic 
material containing, in addition to the required average of about 2 active 
hydrogen atoms, at least one comparatively unreactive carboxylic group in 
salt form, or preferably in free acid form which is subsequently 
neutralized to salt form after the prepolymer formation. Carboxylic 
insertion by use of a carboxyl-substituted diisocyanate is impractical 
because such compounds are unstable. It is preferred to employ as a 
reactant for this purpose an alpha,alpha-dimethylol C.sub.2-10 alkanoic 
acid such as 2,2-dimethylol butyric, pentanoic, octanoic and/or decanoic 
acids, preferably 2,2-dimethylol propionic acid, or any mixtures thereof. 
The above-discussed carboxyl-providing reactant may be included in the 
initial reaction medium containing the organic diisocyanate reactant 
resulting in random inclusion of pendant carboxyl groups along the polymer 
chain, as disclosed in the prior art. The carboxyl-providing reactant may 
be in free acid form calling for subsequent neutralization to water 
dispersing salt form at or prior to the time of dispersion in water, or 
the reactant may be already neutralized when employed in the 
copolymerization reaction. 
According to a preferred embodiment of this invention as described above, 
the organic diisocyanate, melamine, and noncarboxyl-providing material 
containing an average of 2 active hydrogen atoms per molecule are first 
reacted to form an NCO terminated intermediate which is then reacted with 
the carboxyl-providing reactant, preferably in free acid form suitable for 
subsequent neutralization after the prepolymer formation. This sequential 
reaction also permits reaction of the carboxyl-providing reactant with 
said intermediate at relatively lower temperatures of about 50.degree. to 
about 80.degree. C. The previous reaction to form the intermediate is 
generally conducted, like the prior art reaction for producing 
NCO-terminated polyurethane prepolymers, at temperatures of about 
100.degree. to below about 150.degree. C., at which temperature 
discoloration tends to appear. The intermediate generally contains about 
8% to about 12% by weight of NCO, and the NCO-terminated prepolymer, after 
reaction with the carboxyl-providing reactant, e.g., 2,2-dimethylol 
propionic acid, generally contains about 0.5% to about 7%, usually about 
2.5% to about 4.5%, by weight of NCO. 
The NCO-containing polymer (prepolymer) can be prepared by techniques well 
known in the art. For example, the polyisocyanate is usually first charged 
to a suitable reaction vessel, followed by the active hydrogen component, 
and the mixture may then be heated if necessary until isocyanate has 
completely reacted with the active hydrogens to produce an NCO-containing 
prepolymer being essentially free of active hydrogens as determined by the 
product having an essentially constant NCO equivalent. If desired, 
catalyst such as dibutyltin dilaurate, stannous octoate and the like can 
be employed to accelerate the reaction. Reaction can take from several 
minutes to several days, depending on the reactivity of the reactants, 
temperature, presence or absence of catalyst, and the like. 
The urethane prepolymers can be prepared in the presence of a solvent which 
is essentially inert to the reaction. The solvents are generally organic 
and may be comprised essentially of carbon and hydrogen with or without 
other elements such as oxygen or nitrogen. While it may not be necessary 
to employ a solvent during formation of the urethane prepolymer, the use 
of a solvent may be desirable to maintain the reactants in the liquid 
state as well as permit better temperature control during the reaction by 
serving as a heat sink and, if desired, as a refluxing medium. The solvent 
employed should not contain active hydrogen as determined by the 
Zerewitinoff test. Solvents which may be employed include 
dimethylformamide, esters, ethers, ketoesters, ketones, e.g., methyl ethyl 
ketone and acetone, glycol-ether-esters, e.g., N-methyl pyrrolidone, 
hydrogenated furans, and the like, and mixtures thereof. The amount of 
solvent employed should be sufficient to provide a prepolymer solution 
having a sufficiently low viscosity to enhance the formation of the 
polyurethane dispersion of this invention. However, the solutions may be 
successfully employed in forming the dispersions even though the viscosity 
of the solution is relatively high at the temperature of dispersion. Such 
viscosities may be well above 10,000 centipoises, e.g., be at least about 
12,000 or 15,000 centipoises, and only mild agitation need be employed to 
form the dispersion, even in the absence of an emulsifying agent. Often 
about 0.1 to 10 parts by weight of solvent, preferably about 0.5 to 2 
parts by weight of solvent, per part by weight of the prepolymer can be 
used. The presence of a solvent for the polyurethane, however, is not 
necessary to provide a stable, infinitely dilutable aqeuous dispersion. 
Often, when solvent is employed during the preparation of the urethane 
prepolymer and/or the polyurethane polymer it is desirable to remove at 
least a portion of the solvent from the aqueous dispersion of polymer. 
Advantageously, the solvent to be removed from the dispersion has a lower 
boiling point than water and thus can be removed from the dispersion by, 
for example, distillation. The removal of the low boiling solvent is 
desirably conducted under conditions which are not deleterious to the 
urethane polymer such as vacuum distillation or thin film evaporation 
conditions. A solvent having a higher boiling point than water such as 
dimethyl formamide, N-methyl-pyrrolidone, and the like, which is a solvent 
for the urethane polymer may be employed, in which case, the higher 
boiling solvent is generally retained in the aqueous dispersion of 
urethane polymer to enhance the coalescence of the urethane polymer 
particles during film formation. 
In general, it is preferred to employ herein a water soluble organic 
solvent boiling above about 145.degree. C. (and therefore needing no 
special precautions in the polymerization reaction carried out at lower 
temperatures), N-methyl pyrrolidone being preferred. As indicated above, 
this solvent remains in the latex and final coating composition, enhancing 
coalescence of the deposited films. Usually, the solids content of the 
prepolymer in the organic solvent solution just prior to dispersion in 
water may range from about 30% to 80%, by weight. 
The organic polyisocyanate is employed in an amount sufficient to react 
with the desired amount of the active hydrogen-containing components so as 
to produce an NCO-containing prepolymer. The equivalent ratio of organic 
polyisocyanate to active hydrogen-containing compound should be at least 
4:3 and is usually within the range of about 7 to 1.5:1, preferably within 
the range of 6 to 1.8:1. To make a high molecular weight thermoplastic 
material, i.e., 10,000 or more, reaction should be complete so that 
substantially all the active hydrogen material is used up, and the 
resulting NCO-polymer is substantially free of highly active hydrogen. By 
the expression "substantially free of active hydrogen" is meant the 
resultant NCO-polymer is substantially free of active hydrogen associated 
with materials charged to the reaction mixture for the purpose of reacting 
with isocyanates to form urethanes, thiourethanes and ureas, that is, 
--OH, --SHNH, --NH.sub.2. Not included within the expression highly active 
hydrogen are the urethane, thiourethane and urea hydrogens formed in the 
NCO-polymer forming reaction, or any hydrogens associated with salt 
formation (e.g., acid groups). The determination that the product is 
substantially free of highly active hydrogen is made when reaction is 
complete and the fully reacted product has an essentially constant NCO 
equivalent. 
For high molecular weight thermoplastic prepolymers, the use of all low 
molecular weight active hydrogen-containing compounds is often undesirable 
if non-crystalline polymers are desired. Thus, some high molecular weight 
active hydrogen compound should be included in the prepolymer in order to 
make non-crystalline coatings. With low molecular weight prepolymers, such 
control on the active hydrogen-containing compound is not necessary. 
For elastomeric coatings, a high molecular weight polyester or polyether 
polyol should be present in the prepolymer formulation and constitute at 
least 20 percent by weight of the prepolymer based on total weight of the 
prepolymer reactants. Preferably, about 25 to 80 percent by weight of the 
polymeric polyol should be employed in order to get optimum elastomeric 
properties. 
Suitable salt forming agents for neutralizing the carboxylic acid groups 
include inorganic and organic bases such as sodium hydroxide, potassium 
hydroxide, and preferably tertiary amines, e.g., water soluble aliphatic 
tertiary amines of about 3 to 12 carbon atoms such as the trimethyl, 
triethyl, methyl diethyl, tripropyl, N,N-dimethylethanol and/or 
N-methyldiethanol amines and the like. Volatile amines such as 
triethylamine have the further advantage of decomposing or volatilizing 
during the drying or curing of the latex film deposit, whereby the dried 
hardened film is less sensitive to water. It should be noted that the 
carboxylic groups exert their water-dispersing function substantially only 
when neutralized in salt form with resultant pH of more than 7 up to about 
9.5-10, and that too high a proportion of carboxylic acid salt groups in 
the polymer undesirably increases the water sensitivity of the resulting 
films. Accordingly, in the interest of efficiency and economy, it is 
preferred to neutralize substantially all (100%) of the pendant carboxylic 
acid groups in the prepolymer, although lower proportions down to about 
40% may be neutralized, and to insert in the prepolymer reaction medium no 
more carboxyl-providing reactant than is needed to yield a final 
polyurethane latex containing by weight about 0.5% to about 10% of pendant 
carboxylic acid groups on the polymer chain. 
Preferably, the neutralization step is carried out by adding the base, 
preferably tertiary amine such as triethylamine, to the organic solvent 
solution of NCO-terminated prepolymer containing the desired proportion of 
pendant carboxylic acid groups. In the practice of the preferred 
sequential reaction described above, it may in some instances be feasible 
to add the carboxyl-providing reactant, e.g., 2,2-dimethylol propionic 
acid, and the preferred tertiary amine, e.g., triethylamine, substantially 
simultaneously or in closely timed sequence (post-addition of the tertiary 
amine) to the organic solvent solution of NCO-terminated intermediate. 
Salt formation may be carried out at ambient or elevated temperatures, a 
range of about 60.degree. to about 80.degree. C. being preferred to 
expedite completion of the desired reaction. 
The resulting neutralized NCO-terminated prepolymer, neat or in organic 
solvent solution as described above, is then mixed under high shear with 
water to produce an aqueous dispersion in which the remainder of the 
process, e.g., chain extension, end capping, hydroxymethylation, is 
performed. 
The amount of aqueous medium employed in the formulations of the 
dispersions of the present invention is important. When too little amount 
of aqueous medium is employed, mixtures are obtained which are often too 
thick to handle easily while, on the other hand, dispersions which are too 
dilute are uneconomical to handle due to their excessive volume. In 
general, the aqueous medium will amount to 40 to 90 percent by weight, 
preferably about 60 to 80 percent by weight, based on total weight of the 
polymer and the aqueous medium. Water is a necessary ingredient of the 
aqueous medium, being present in an amount of at least 30 and preferably 
at least 85 percent by weight based on total weight of the aqueous medium 
with a cosolvent constituting any remainder of the medium. 
The term "dispersion" as used within the context of the present invention, 
is a two-phase, aqueous polyurethane system in which the polyurethane is 
the dispersed phase. When thinned with water to form a one percent solids 
dispersion, the average particle size diameter is less than 10 and 
preferably less than 5, and most preferably 1 micron or less. The 
dispersions are generally only stable if the particle size does not exceed 
5 microns. Small particle size dispersions are advantageous because they 
are non-sedimenting and 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 term "dispersion" is also 
intended to cover homogenous aqueous solutions which appear optically 
clear. 
It should be pointed out at this point in the specification that where the 
term "polyurethane" has been used in the specification and claims, it is 
intended to cover not only polycondensates of polyisocyanates and polyols, 
but also the condensates of polyisocyanates with any active 
hydrogen-containing material mentioned above. Thus, the term 
"polyurethane" is defined as any polymer containing two or more urethane 
groups and is also intended to cover polyureas and polythiourethanes. 
The NCO-containing polymer can be dispersed in a number of ways. 
Preferably, the prepolymer, whether neat or as a solution, is added 
incrementally to the aqueous dispersing medium with agitation. 
Alternately, the aqueous dispersing medium can be added incrementally to 
the prepolymer with stirring. However, this latter method is less 
preferred because commonly upon initial addition of the dispersing medium, 
a high viscosity, grease-like material results. The main disadvantage 
associated with this grease-like viscosity is that it is very hard to stir 
in more water. Without efficient stirring there is a definite possibility 
of forming gel particles. By adding the prepolymer to water, this high 
initial viscosity is avoided, and undesired water extension reduced. 
After the NCO-polymer has been prepared, additional solvent can be added 
just before dispersion or, for that matter, after the prepolymer has been 
dispersed in the aqueous medium so as to control the viscosity of the 
medium and the particle size of the dispersed phase or enhance film 
coalescence and overall coating properties. The solvents can be selected 
from those mentioned above. Use of low molecular weight hydrophilic 
solvents such as lower alkyl alcohols (stearically hindered so as not to 
react with NCO) will sometimes increase the viscosity of the final polymer 
product acting as a thickening agent. The use of hydrophobic solvents such 
as toluene, benzene and xylene will give coarser dispersions. A 
hydrophilic solvent can be added to the prepolymer at any time in the 
process, although the effect it renders on the viscosity may be different. 
A hydrophobic solvent should preferably be added to the prepolymer before 
dispersion. 
As has been mentioned above, because of viscosity and dispersion stability 
considerations, it is preferred that the NCO-containing prepolymer be 
added to the aqueous medium. 
Usually after the salt form of the prepolymer has been dispersed, a chain 
extender is added to the dispersion fairly quickly. The prepolymer reacts 
with water at a slow rate depending upon the reaction mixture. The time 
after the prepolymer has been added to water and before chain extender is 
added will determine how much of the water reacts with the prepolymer. The 
temperature of the dispersion will also have an effect in how much 
reaction occurs. Change in temperature and time will result in different 
products. In order to get reproducible results, the time, temperature and 
amount of chain extender should be rigidly controlled. The time and 
temperature is important to determine what type of final product is 
desired. Chain extenders build molecular weight of the dispersed 
prepolymer. The chain extender can be defined as an active 
hydrogen-containing compound having at least two hydrogens more reactive 
with the NCO groups than water. Examples of suitable classes of chain 
extenders are primary and secondary organic amines, preferably diamines, 
hydrazine, substituted hydrazines and hydrazine reaction products. The 
chain extenders are preferably water-soluble, although water-dispersible 
materials may be used. Water-soluble chain extenders are preferred, 
because if the prepolymer is only marginally dispersible, a water-soluble 
chain extender will enhance the water dispersibility of the final polymer 
product. Organic diamines are often the preferred chain extenders because 
they usually build the highest molecular weight without gelling the resin. 
Examples of suitable well known chain extenders useful herein include 
ethylene diamine, diethylene triamine, propylene diamine, butylene 
diamine, hexamethylene diamine, cyclohexylene diamine, phenylene diamine, 
tolylene diamine, xylylene diamine, 3,3'-dinitrobenzidene, 
4,4'-methylenebis(2-chloroaniline), 3,3'-dichloro-4,4'-biphenyl diamine. 
2,6-diaminopyridine, 4,4'-diamino diphenylmethane, and adducts of 
diethylene triamine with acrylate or its hydrolyzed products. Also 
materials such as hydrazine, substituted hydrazines such as, for example, 
dimethyl hydrazine, 1,6-hexamethylene-bis-hydrazine, carbodihydrazide, 
hydrazides of dicarboxylic acids and sulfonic acids such as adipic acid 
mono- or dihydrazide, oxalic acid dihydrazide, isophthalic acid 
dihydrazide, tartaric acid dihydrazide, 1,3-phenylene disulfonic acid 
dihydrazide, omega-amino-caproic acid dihydrazide, hydrazides made by 
reacting lactones with hydrazine such as gamma-hydroxylbutyric hydrazide, 
bis-semi-carbazide, bis-hydrazide carbonic esters of glycols such as any 
of the glycols mentioned above. 
Of the foregoing chain extenders, certain types are preferentially employed 
as combinations of chain extenders and end cappers. More particularly, the 
polyurethane products of this invention are preferably chain extended with 
triamine-containing polyamine, especially both triamine and diamine. 
Enough triamine should be present in the chain--extending polyamine to 
provide an average of substantially more than 2, e.g., at least about 2.2, 
amine nitrogen atoms having active hydrogen per molecule of polyamine 
reacted. Advantageously, the average active amine hydrogen functionality 
of free polyamine mixture ranges between about 2.2 to 2.8 amine nitrogen 
atoms having active hydrogen per molecule of polyamine, and preferably is 
about 2.3 or 2.4 to 2.6, e.g., about 2.5 active hydrogen containing amine 
nitrogen atoms per molecule of polyamine. The chain extending polyamine 
can include components which are essentially hydrocarbon polyamines having 
2 or 3 amine groups providing reactive hydrogens in accordance with the 
Zerewitinoff test, e.g., primary and secondary amine groups, and having 1 
to about 40 or more carbon atoms, preferably about 2 to 15 carbon atoms. 
Preferably, the polyamine components each have at least 2 primary amine 
groups. Both the diamine and triamine components of the polyamine may 
contain other substituents which do not have hydrogen atoms as reactive 
with isocyanate groups as the primary or secondary amine groups. The 
polyamine components may have, for instance, an aromatic, aliphatic or 
alicyclic structure. Among the useful components of the polyamine are 
ethylene diamine, propylene diamine, 1,4-butylene diamine, piperazine, 
1,4-cyclohexyldimethylamine, hexamethylene diamine, trimethylhexamethylene 
diamine, menthane diamine, 4,4'-diaminodicyclohexylmethane, 
diethylenetriamine, dipropylenetriamine, dibutylene triamine, and the 
carboxylic dihydrazides referred to above, all of which contain 2 terminal 
primary amino groups. 
The chain extension can be conducted at elevated, reduced or ambient 
temperatures. Convenient temperatures are from about 5.degree. to 
95.degree. C. or more, preferably from about 10.degree. to about 
45.degree. C. Elevated or reduced pressures may be employed, however, the 
chain extension reaction is normally conducted at approximately ambient 
pressure. Generally, it is desired to continue the reaction until a good 
yield of the desired urea-urethane polymer is obtained. Preferably, the 
polyamine(s) employed in the method of this invention reacts rapidly with 
the urethane prepolymer such that undue reaction of water with the 
isocyanate groups is avoided. 
The polyamine may be gradually added to the reaction medium which contains 
the urethane prepolymer in order to prevent the occurrence of localized 
high concentrations of the added reactant which may lead to forming 
urea-urethanes having an unduly broad molecular weight range. When 
employing high concentrations of the reactants in the reaction medium it 
is preferred that the combination of the polyamine and prepolymer be less 
rapid than when the reactants are less concentrated. For instance, when 
the reactants are in relatively low concentration in the reaction medium 
and the medium is well agitated, the polyamine and prepolymer can be 
quickly combined. Frequently, the rate of addition of the polyamine will 
be over a period of about 0.5 to 30 minutes. The rate of addition of the 
polyamine may, in part, depend upon the degree of agitation of the 
reaction medium and the speed with which the polyamine is dissipated in 
the reaction medium. The polyamine may be added in essentially undiluted 
form or in admixture with an organic solvent or with water. Preferably, 
the polyamine is in an essentially aqueous solution. 
According to a preferred embodiment herein, initial chain extension is 
carried out by mixing into the aqueous dispersion of NCO-terminated 
prepolymer a solution in water of a mixture of about 40% to about 55% of 
ethylene diamine and about 15% to about 30% of diethylene triamine, the 
sum of said diamine and triamine in the mixture ranging from about 55% to 
about 80%, based on the weight of the free NCO in the prepolymer. After 
these polyamines have fully reacted to partially chain extend the 
prepolymer, usually requiring only a few minutes, adipic dihydrazide is 
added to the dispersion in an amount calculated to react with and chain 
extend the remaining free NCO in the prepolymer, i.e., about 45% to about 
20% of the dihydrazide based on the free NCO in the prepolymer, and an 
excess amount of about 0.5 to about 3 parts dihydrazide per part of said 
calculated amount of dihydrazide for reacting with and end capping the 
termini of the fully chain extended prepolymer. 
The resulting hydrazide end capped prepolymer is then partially or 
completely N-methylolated by adding to the dispersion for reaction with 
the --NH.sub.2 of said end caps an amount of formaldehyde about 60% to 
about 120%, preferably at least 100%, of that needed to stoichiometrically 
react with and hydroxymethylate said --NH.sub.2 in said end caps. The 
polyurethane is thus provided with internal cross linking, curable, 
hardening groups activated to self-condensation and cross-linking upon 
drying of the latex film on a substrate under ambient conditions. 
Stated otherwise, the above proportions correspond roughly, in accordance 
with particularly preferred and exemplified embodiments of this invention, 
to about 1.2% to about 2.2% of ethylene diamine, about 0.6% to about 1.2% 
of diethylene triamine, about 3.4% to about 8.0% of adipic dihydrazide, 
and about 0.4% to about 1.3% of formaldehyde, based on the weight of the 
final N-methylol-terminated polyurethane. 
The latex products of this invention are advantageously employed as coating 
compositions, for which purpose they may be further diluted with water 
and/or organic solvents, or they may be supplied in more concentrated form 
by evaporation of water and/or organic components of the liquid medium. As 
coating compositions they may be applied to any substrate including wood, 
metals, glass, cloth, plastics, foam and the like, by any conventional 
method including brushing, dipping, flow coating, spraying, and the like. 
The compositions may contain other conventional ingredients including 
organic solvents, pigments, dyes, emulsifiers, surfactants, thickeners, 
heat stabilizers, levelling agents, anti-cratering agents, fillers, 
sedimentation inhibitors, UV absorbers, antioxidants and the like 
introduced at any stage of the production process or subsequently. 
These latices may also be used in non-coating applications such as in 
adhesive, cast thin or thick films, etc. 
Coatings and films produced with these latices are curable under ambient 
conditions and have excellent resistance to water and organic solvents.

The following examples are only illustrative of preferred embodiments of 
this invention and are not to be considered limitative. All amounts and 
proportions referred to herein and in the appended claims are by weight 
and all temperatures are in .degree.C., unless otherwise indicated. 
EXAMPLES 1-3 
Table I below shows the component parts of aqueous dispersions or latices 
illustrative of this invention. In each example, the latex is prepared as 
follows: 
A. Prepolymer Preparation and Dispersion 
In a 5,000 ml. resin kettle equipped with thermometer, stirrer, water 
condenser and vacuum outlet, melt the polyester polyol and dewater under 
water aspirator vacuum at 100.degree. C. Release vacuum and at 110.degree. 
C. add melamine and diisocyanate while stirring. Adjust temperature to 
135.degree.-140.degree. C. and maintain for about 2.5-3 hours to complete 
the reaction resulting in an intermediate containing about 10.4%-10.7% 
NCO. At the beginning of the reaction the mixture is thin and white due to 
the dispersed melamine. As the reaction proceeds, the color changes to 
straw yellow and the viscosity increases. 
Stir in an amount of N-methyl pyrrolidone about 4%-7% less than the weight 
of the polyester polyol, cool to 75.degree.-80.degree. C. add dimethylol 
propionic acid and stir at same temperature for about 2 hours. 
Stir in stoichiometric amount of triethylamine (about 3/4 the weight of the 
dimethylol propionic acid) and maintain till prepolymer has an NCO content 
of about 3.5%-3.8%. 
Mix prepolymer/N-methyl pyrrolidone with an amount of water about 4.5 to 5 
times the weight of the N-methyl pyrrolidone under high shear. 
B, C Chain Extension and End Capping 
Stir in mixture of ethylene diamine and diethylene triamine prediluted with 
water. After about 5 minutes, stir in adipic dihydrazide and maintain 
until substantially devoid of NCO. 
D. Hydroxymethylation 
Add formaldehyde (stoichiometric amount to methylolate hydrazide --NH.sub.2 
end groups) and stir for about 15 minutes. 
TABLE I 
______________________________________ 
Polymer Solids (Free Acid Basis, Parts by Wt.) 
Ex. 1 Ex. 2 Ex. 3 
______________________________________ 
Polyester Polyol* 
402 422 430 
Melamine 32.7 31 29 
2,2-Dimethylol Propionic Acid 
52.2 54 55 
Diisocyanate** 411 417 411 
Diethylene Triamine 
5.6 10 10.7 
Ethylene Diamine 13 15.7 20 
Adipic Dihydrazide 
72 50 38 
Formaldehyde 10.4 7.4 6 
______________________________________ 
*Reaction product of adipic acid with about 1% stoichiometric excess of 
7/3 1,6hexanediol/neopentyl glycol, M.W. .about.1500. 
**4,4bis(isocyanatocyclohexyl)methane. 
Table II below shows proportions of chain extenders and end cappers, and 
properties of Examples 1-3 formulations. Latices are cast on acetone 
cleaned aluminum Q panels and dried at room temperature for 16 hours. 
TABLE II 
______________________________________ 
Ex. 1 Ex. 2 Ex. 3 
______________________________________ 
Diethylene Triamine %* 
15 25 25 
Ethylene Diamine %* 
40 45 55 
Adipic Dihydrazide %* Chain 
15 10 5 
Extender 
Adipic Dihydrazide %* End 
30 20 15 
Capping 
MEK (methyl ethyl ketone) Rubs 
&gt;100 &gt;100 &gt;100 
Tensile at Yield, psi 
5000 5400 4600 
Elongation % 30 45 80 
Rocker Hardness 50 44 42 
Latex pH at 25.degree. C. 
9 7.7 7.8 
______________________________________ 
*Percent of free NCO in prepolymer 
Above latices also exhibit excellent water resistance. Example 1 product 
actually passed 200 MEK and 100 ethanol ribs in addition to 8 hours in a 
pressure cooker at 15 psi and 2 weeks in a humidity oven (70.degree. C., 
95% relative humidity) without significant change. The products of Example 
2 and 3 have similarly excellent resistance properties. 
EXAMPLES 4 AND 5 
The procedure of Examples 1-3 is repeated with the following modifications: 
A. The polyester polyol is melted at 80.degree. C. and the diisocyante and 
1/3 less melamine, and a small amount of Irgonox 1010 (Ciba-antioxidant to 
inhibit darkening), stirred in at 80.degree.-90.degree. C. 
At this juncture 1/2 of the N-methyl pyrrolidone is stirred in and the 
reaction to form the intermediate carried out in N-methyl pyrrolidone at 
about 130.degree. C. for about 2 hours yielding a clear solution of the 
intermediate free of unreacted insoluble melamine particles observed in 
the Examples 1-3 procedure. This procedure enables a reduction in the 
amount of charged melamine and lower reaction times, temperatures and 
durations. The reaction to form the intermediate is run until the 
theoretical .about.8% NCO is attained which then levels off without 
significant decrease. This reaction could be run for example at 
110.degree. C. for over 5 hours or at 145.degree. C. for about 1.5 hours. 
The remainder of the N-methyl pyrrolidone is then stirred in, and the 
(exothermic) treatment with the dimethylol propionic acid and 
triethylamine carried out at a self-maintained 60.degree.-65.degree. C. 
B & C. The resulting prepolymer/N-methyl pyrrolidone dispersion in water is 
then chain extended and end capped, in Example 4 in the same proportions 
as in Example 1 and in Example 5, by modified proportions, as shown in 
Table III below which also shows the properties of the products of 
Examples 4 and 5. 
TABLE III 
______________________________________ 
Example 
Example 
4 5 
______________________________________ 
Diethylene Triamine %* 
15 30 
Ethylene Diamine %* 40 40 
Adipic Dihydrazide %* Chain Extender 
15 5 
Adipic Dihydrazide %* End Capping 
30 15 
Tensile Strength, psi 6,000 5,500 
Tensile at yield, psi 5,250 4,640 
100% modulus, psi** 5,700 5,400 
Elongation at Break, % 
95 86 
Stress-strain Curve Shape 
yield no yield 
Impact Resistance, inch-lbs. 
160 160 
MEK Rubs 150 150 
Rocker Hardness, RT, 6 hours 
14 14 
Rocker Hardness, RT, 20 hours 
44 42 
Pencil Hardness, RT, 30 min. 
6B 6B 
Pencil Hardness, RT, 75 min. 
2B 4B 
Pencil Hardness, RT, 135 min. 
B F 
______________________________________ 
*Percent of free NCO in prepolymer 
**Measured directly when reached or calculated by extrapolation 
The water resistance and other properties of the latices as in Examples 4 
and 5 are comparable to those of Examples 1-3. 
This invention has been disclosed with respect to preferred embodiments and 
it will be understood that modifications and variations thereof obvious to 
those skilled in the art are to be included within the spirit and purview 
of this application and the scope of the appended claims.