Low temperature active aliphatic aromatic polycarbodiimides

A mixed aliphatic/aromatic polycarbodiimide prepared by first polymerizing an aliphatic isocyanate or mixture thereof, optionally in the presence of a polyfunctional isocyanate; arresting polymer chain growth by reaction with a stoichiometrically deficient amount of a monofunctional isocyanate-reactive compound, followed by further polymerization with an aromatic diisocyanate.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a class of aliphatic/aromatic mixed 
polycarbodiimides having good storage stability and particularly relates 
to a method for their preparation. This invention also pertains to the use 
of such mixed polycarbodiimides as low temperature active, e.g., "low 
bake", crosslinkers in aqueous, carboxyl-containing resins. 
2. Description of Related Art 
Carbodiimides are a well-known class of organic compounds. 
Dicyclohexylcarbodiimide has been used for many years as a condensation 
agent in the preparation of peptides, as described by Sheelan and Hess (J. 
Chem. Soc., 77, 1067 (1955)). Multifunctional, linear, polydisperse 
polycarbodiimides have been prepared by Campbell from diisocyanatoalkanes 
or diisocyanatoarenes using a phospholene oxide catalyst (U.S. Pat. No. 
2,941,966 (1960)). The art is summarized in Chem. Rev., 81,589 (1981). 
The use of polydisperse polycarbodiimides as cross-linkers for carboxylated 
latex resins and neutralized carboxylated water-soluble polymers is known 
in the art. Specifically, co-assigned U.S. application Ser. No. 691,378, 
filed Jan. 15, 1985 teaches the preparation of useful polycarbodiimide 
cross-linkers from certain mono-, di-, and tri-functional cycloaliphatic 
or saturated aliphatic isocyanates. Unfortunately, the raw materials used 
to prepare the aliphatic materials are quite expensive. 
Urethane-terminated polycarbodiimides, obtained by polymerizing a 
diisocyanate in the presence of a carbodiimide-forming catalyst and 
reacting the isocyanato-terminated polymer with an alcohol, are described 
in U.S. Pat. No. 2,941,983 and in J. Organic Chemistry 28, 2069, (1963). 
All but Example 6 of U.S. Pat. No. 2,941,983 employs an equal molar amount 
of the diisocyanate and alcohol. In Example 6, 0.2 mol of 
toluene-2,4-diisocyanate is polymerized and then chain terminated using 
0.14 mol of benzyl alcohol. The former reference also suggests using 
amines for chain growth termination; while the latter reference also 
discusses the production of corresponding polycarbodiimides which are 
terminated by reacting the isocyanato-terminated polycarbodiimide with a 
monoisocyanate so that the polymer contains only carbodiimide linkages. A 
polycarbodiimide of this type, derived from toluene diisocyanate and 
terminated by reaction with p-chlorophenyl isocyanate (molar ratio of 
diisocyanate to monoisocyanate=58), is specifically exemplified. In 
addition, the formation of a polycarbodiimide of unspecified molecular 
weight from methylenebis (phenyl isocyanate) and p-tolylisocyanate (molar 
ratio of diisocyanate in monoisocyanate not specified) is postulated but 
no preparative details or properties are given. 
U.S. Pat. No. 3,450,562 teaches, in broad terms, the preparation of chain 
terminated polycarbodiimides by reacting, either sequentially or 
simultaneously, a diisocyanate and a monoisocyanate, monoalcohol or 
primary amine in the presence of a carbodiimide-forming catalyst. In 
Example I, a polymerized product of a mixture of toluene-2,4-diisocyanate 
and toluene-2,6-diisocyanate is chain terminated with isopropyl alcohol. 
In Example III, aniline is used to terminate chain growth. Example VIII of 
this patent shows the preparation of two mono-isocyanated terminated 
polycarbodiimides. The first one, polycarbodiimide 1, is obtained by 
heating a mixture of toluene diisocyanate and o-tolylisocyanate (in a 
molar ratio of 1:1) with a carbodiimide-forming catalyst. The second one, 
polycarbodiimide 2, is obtained by heating methylenebis (cyclohexyl 
isocyanate) in the presence of a carbodiimide-forming catalyst and then 
reacting the isocyanate-terminated polymer with cyclohexyl isocyanate. The 
molar ratio of diisocyanate to monoisocyanate is 1.5:1. 
Co-assigned U.S. Pat. Nos. 4,487,964 and 4,587,301 disclose the preparation 
of useful polycabodiimide cross-linkers from mixed aromatic/aliphatic 
isocyanates. According to these patents, a mixed aliphatic/aromatic 
polycarbodiimide can be prepared by simply reacting a mixture of aliphatic 
mono- and diisocynates in the presence of a phospholene oxide catalyst 
followed, in sequence, by the addition of and further reaction with 
aromatic mono- or diisocyanates under similar reaction conditions. Both 
reactions are conducted at a temperature of about 120.degree. to 
180.degree. C. and the various reactants are used in amounts to provide a 
molar ratio of mono- and diisocyanate reactants between about 2:1 to 2:10 
and a molar ratio of aliphatic to aromatic isocyanate groups in the 
reactants between about 0.5:1 to 2:1. 
Although this prior invention provided some improvement in polycarbodiimide 
resin storage stability relative to the then-existing art, excessive 
viscosity development and gellation over prolong storage, e.g., 6 months 
or longer, remains a problem in mixed polycarbodiimide resins. Due to the 
low level that these crosslinking materials generally are used in coating 
formulations, it is not uncommon for formulators to maintain these 
materials in inventory for that period of time. A more glaring 
disadvantage of this prior art invention concerns its use of 
monoisocyanates. The high toxicity and volatility of these materials makes 
them very hazardous and creates significant problems to ensure their safe 
handling and use. 
It now has been discovered that by constructing a certain polymer 
structure, for example, by using a particular reaction sequence and a 
particular molar ratio of reactants, a mixed aliphatic/aromatic 
polycarbodiimide of improved storage stability can be prepared. 
Importantly, this result can be achieved without using hazardous 
monoisocyanates. Surprisingly, the mixed polycarbodiimide resins of the 
present invention also provide solvent resistance properties to 
crosslinked resins similar to polycarbodiimide resins made solely from 
aliphatic isocyanates. 
DISCLOSURE OF THE INVENTION 
The present invention is directed to a novel class of storage stable mixed 
aliphatic/aromatic polycarbodiimides useful for crosslinking aqueous 
carboxyl-containing resins. The polycarbodiimides of the present invention 
are made by polymerizing aliphatic and aromatic diisocyanates in specific 
proportions and in a particular sequence. During the polymerization 
process, partially polymerized adducts of the aliphatic diisocyanates are 
reacted with a well-defined quantity of a monofunctional 
isocyanate-reactive compound which acts as a chain terminator to limit the 
extent of the polycarbodiimide-forming polymerization reaction. 
In one aspect, the present invention is directed to a method of preparing 
mixed aliphatic and aromatic polycarbodiimides which comprises 
(a) polymerizing a saturated aliphatic diisocyanate, or a saturated 
cycloaliphatic diisocyanate or a mixture thereof, optionally containing a 
polyfunctional isocyanate, in the presence of a polycarbodiimide 
polymerization catalyst to form a polycarbodiimide intermediate having 
free isocyanate groups, 
(b) reacting said polycarbodiimide intermediate with a monofunctional 
isocyanate-reactive compound or mixture thereof in an amount insufficient 
to react with all of said free isocyanate groups, and 
(c) further reacting said polycarbodiimide intermediate in the presence of 
an aromatic diisocyanate and said catalyst under carbodiimide-forming 
conditions until essentially all of the isocyanate groups are depleted. 
In another aspect, the present invention is directed to storage stable 
mixed aliphatic and aromatic polycarbodiimides prepared by 
(a) polymerizing a saturated aliphatic diisocyanate, or a saturated 
cycloaliphatic diisocyanate or a mixture thereof, optionally containing a 
polyfunctional isocyanate, in the presence of a polycarbodiimide 
polymerization catalyst to form a polycarbodiimide intermediate having 
free isocyanate groups, 
(b) reacting said polycarbodiimide intermediate with a monofunctional 
isocyanate-reactive compound or mixture thereof in an amount insufficient 
to react with all of said free isocyanate groups, and 
(c) further reacting said polycarbodiimide intermediate in the presence of 
an aromatic diisocyanate and said catalyst under carbodiimide-forming 
conditions until essentially all of the isocyanate groups are depleted. 
In further aspects, the present invention is directed to the use of these 
mixed polycarbodiimides for cross-linking aqueous carboxyl-containing 
resins and to mixtures of aqueous carboxyl-containing resins and the mixed 
aliphatic/aromatic polycarbodiimides of the present invention. 
As used herein, all defined groups are intended to include such groups 
containing any substitution which does not significantly interfere with 
the preparation or use of the carbodiimides for their intended purpose. 
In carrying out the process of the present invention any saturated 
aliphatic diisocyanate or saturated cycloaliphatic diisocyanate may be 
used for preparing the polycarbodiimide intermediate. While these 
aliphatic diisocyanates may contain other substituents, suitable 
substituents should not be reactive with isocyanate groups. For example, 
substituents should not contain active hydrogens as determined by the 
Zerewitinoff test. [J. Am. Chem. Soc. 49,3181 (1927)] 
Saturated aliphatic diisocyanates containing from 1 to about 18 carbon 
atoms, and saturated cycloaliphatic diisocyanates containing up to about 
18 carbon atoms, wherein the cycloaliphatic moieties contain from about 5 
to 7 carbon atoms are preferred for use in the present invention. Suitable 
saturated aliphatic and saturated cycloaliphatic diisocyanates for 
preparing the mixed polycarbodiimides of the present invention include 
isophorone diisocyanate, 1,6-hexane diisocyanate, dicyclohexylmethane 
diisocyanate, trimethylene diisocyanate 1,4-tetramethylene diisocyanate, 
decamethylene diisocyanate, 1,12-dodecane diisocyanate, cyclohexane 
diisocyanates, cyclobutane-1,3-diisocyanate, and hexahydrotolylene-2,4 and 
2,6-diisocyanates. 
It is a feature of the present invention that the aliphatic diisocyanate or 
mixture thereof may optionally include a polyfunctional isocyanate, i.e. a 
polyisocyanate. As used herein, polyfunctional isocyanates include those 
aliphatic isocyanates containing an average number of isocyanate moieties 
above 2. As will be demonstrated in subsequent examples, the amount of 
polyfunctional isocyanate optionally used in preparing polycarbodiimides 
in accordance with the present invention should be limited to avoid 
excessive crosslinking and gellation during polycarbodiimide preparation. 
Preferably, the amount of polyfunctional isocyanate should be limited so 
that such reactants contribute less than about 35 mol % of the total 
isocyanate moieties to the formation of the polycarbodiimide product, and 
preferably less than about 25 mol %. 
In accordance with the process of the present invention the saturated 
aliphatic or cycloaliphatic diisocyanate or mixture thereof, optionally 
containing a small amount of a polyfunctional isocyanate, is self-addition 
polymerized in the presence of a catalytic amount of a 
carbodiimide-forming, i.e., isocyanate addition, catalyst. 
Carbodiimide-forming catalysts which are employed in preparing the mixed 
polycarbodiimides of the present invention can be any of the 
polycarbodiimide polymerization catalysts employed in the art to convert 
organic isocyanates to carbodiimides. Catalysts which are useful in 
preparing the polymers of the present invention include phospholines, 
phospholine oxides and sulfides, phospholidines and phospholidine oxides 
and sulfides. The phospholine oxides and sulfides are described in U.S. 
Pat. Nos. 2,663,737 and 2,663,738. The phospholidine oxides are described 
in U.S. Pat. No. 2,663,739. The corresponding phospholines and 
phospholidines may be prepared by a lithium aluminum hydride reduction of 
the corresponding dichloro phospholine or phospholidine. These dichloro 
compounds are also used to prepare the above mentioned oxides and sulfides 
and are described in U.S. Pat. No. 2,663,736. 
Particularly useful classes of carbodiimide-forming catalysts are the 
phospholene-1-oxides and phospholene-1-sulfides. Representative compounds 
within these classes are 3-methyl-1-phenyl-3-phospholine 1-oxide, 
1-ethyl-phenyl-3-phospholine 1-oxide, 
3-(4-methyl-3-pentynyl)-1-phenyl-3-phospholine 1-oxide, 
3-chloro-1-phenyl-3-phospholine 1oxide, 1,3-diphenyl-3-phospholine 
1-oxide, 1-ethyl-3-phospholine 1-sulfide, 1-phenyl-3-phospholine 
1-sulfide, and 2-phenyliso-phosphindoline 2-oxide, 1-phenyl-2-phospholene 
1-oxide, 3-methyl-phenyl-2-phospholene 1-oxide, 1-phenyl-2-phospholene 
1-sulfide, 1-ethyl-2-phospholene 1-oxide, 1-ethyl-3-methyl-2-phospholene 
1-oxide, 1-ethyl-3-methyl-2-phospholene 1-oxide. Other isomeric 
phospholenes corresponding to all the above-named compounds also can be 
used. 
The amount of carbodiimide-forming catalyst employed in the preparation of 
the mixed polycarbodiimides is generally within the range of about 0.001 
to about 0.03 mol per mol of aliphatic diisocyanate but higher or lower 
amounts can be employed depending upon the activity of the particular 
catalyst chosen. Normally, an amount between about 0.003 to 0.01 mol of 
catalyst per mol of aliphatic diisocyanate should be sufficient. A 
particular advantage of the present invention is that, relative to 
commercial prior art procedures, preparation of the ultimate 
polycarbodiimide product of this invention is obtained in a shorter time 
period with the same or a lower level of polycarbodiimide polymerization 
catalyst. 
The initial polycarbodiimide polymerization reaction generally is conducted 
under atmospheric pressure conditions at a temperature between about 
125.degree. to 160.degree. C., perferably at a temperature of about 
145.degree. C. Higher temperatures can be used to reduce the reaction time 
but may result in undersired amounts of by-products; while lower 
temperatures significantly prolong the reaction period. Although 
superatmospheric or sub-atmospheric pressures can be used, it is preferred 
to use atmospheric pressures for economic reasons. The reaction mixture is 
stirred, and a small amount of nitrogen can be sparged into the reaction 
medium to assist in driving the reaction to completion by removal of 
carbon dioxide. These conditions are referred to throughout the 
specification and claims as "carbodiimide-forming conditions". 
The polymerization reaction is conducted until the desired degree of 
polymerization i.e., an average carbodiimide functionality of about 2 to 
3, has occurred, e.g., when using isophorone diisocyanate as the aliphatic 
diisocyanate the reaction is continued until the polymerized 
polycarbodiimide intermediate product attains a molecular weight of about 
650-850. Under the above-noted reaction conditions, the reaction is 
conducted for about 1 to about 3 hours, preferably for about 2 hours. As 
used herein, "molecular weight" refers to number average molecular weight, 
while "average carbodiimide functionality" refers to the average number of 
carbodiimide linkages in the polymerized polycarbodiimide intermediate per 
molecule. 
Because the resulting polycarbodiimide intermediate has free (terminus) 
isocyanate groups, and because the weight fraction of free isocyanate 
groups in the polycarbodiimide intermediate is indicative of the extent of 
polymerization, the polymerization reaction can be monitored using an 
isocyanate titration. Using the procedure described in ASTM D-1638-74, the 
weight fraction of free isocyanate groups in the intermediate product can 
be determined. When using isophorone diisocyanate as the aliphatic 
diisocyanate (equivalent weight of 111.14), the initial polymerization 
should be continued until the polycarbodiimide intermediate exhibits a 
weight percent of free isocyanate groups (--NCO) of between about 5 and 
20% by weight, and preferably between about 10 and 15% by weight. For 
other aliphatic and cycloaliphatic diisocyanates the weight fraction of 
free isocyanate groups will vary as a function of the change in equivalent 
weights of the isocyanate reactants. 
As the organic polycarbodiimide intermediate is formed, carbon dioxide is 
liberated and this carbon dioxide generally is vented from the reaction 
medium. The extent of the reaction also can be determined by measuring the 
amount of carbon dioxide which is evolved; one mol of carbon dioxide is 
evolved in the formation of each molar equivalent of carbodiimide. The 
amount of the carbon dioxide given off during the reaction can be 
continually determined, for example, by passing the gas through a suitable 
absorption column which is attached to a balance. The weight of this 
carbon dioxide can be correlated with the progress of the polymerization 
by reference to a working plot of molecular weight attained vs. weight of 
carbon dioxide evolved for the diisocyanate in question. When the amount 
of carbon dioxide evolved corresponds to the formation of the required 
number of carbodiimide groups or linkages, the reaction can be terminated. 
The reaction is effectively terminated in accordance with the present 
invention by cooling the polymerization product to a temperature below 
about 120.degree. C., preferably to a temperature of about 110.degree. C. 
and adding the monofunctional isocyanate reactive compound. 
The first polymerization step of the present invention may be carried out 
in bulk or in solution depending on the particular organic aliphatic 
isocyanate being used. Thus, when the aliphatic isocyanate is a solid, it 
may be dissolved in an inert solvent and the appropriate amount of 
phosphorus-containing catalyst added. An inert solvent is one that does 
not contain any groups reactive with isocyanates or with itself under the 
conditions of the polycarbodiimide polymerization reaction. In general, 
solvents which contain active hydrogen atoms as determined by the 
Zerewitinoff procedure should be avoided. The solvent should readily 
dissolve both the diisocyanate and the monofunctional isocyanate-reactive 
compound used as the chain-stopper. Furthermore, it should maintain the 
polymeric carbodiimide in solution during the polymerization. 
Suitable non-reactive (inert) solvents include aromatic hydrocarbons having 
6 to about 12 carbons, such as benzene, toluene, the xylenes, ethyl 
benzene, isopropyl benzene, and mesitylene. Also suitable are 
cyclopentane, n-hexane, cyclohexane, n-heptane, methyl cyclohexane, 
tetramethylethylene diisobutylene, chlorobenzene, methylene chloride, 
ethylidene chloride, chloroform, carbon tetrachloride, ethylene chloride, 
methylene bromide, o-dichlorobenzene, chloromethylether, isopropylether, 
dioxane, tetrahydrofuran, pyridine aliphatic esters or glycol diesters, 
and glycol ether esters. Additional exemplary solvents include; 
ethylbutylketone, acetophenone, propiophenone, diisobutylketone, 
cyclohexanone, N-methyl pyrrolidone, decalin, methyl CELLOSOLVE acetate, 
CELLOSOLVE acetate, butyl CELLOSOLVE acetate, CARBITOL acetate, butyl 
CARBITOL acetate, glycoldiacetate, amyl acetate, glycolether diacetate, 
dipropylene glycol ether dibutyrate, and hexylene glycol monomethyl ether 
acetate. In the cases where the aliphatic isocyanate reactant itself is a 
liquid, the use of an inert solvent is not normally necessary. In this 
case, the phosphorus-containing catalyst is added directly to the 
aliphatic isocyanate, whereupon the entire mass is converted to the 
organic polycarbodiimide intermediate. 
Any compound having only one moiety reactive with isocyanate groups can 
broadly be used as the monofunctional isocyanate-reactive compound for 
terminating the isocyanate addition polymerization in accordance with the 
present invention. Monofunctional, active hydrogen-containing compounds 
such as primary and secondary mono-alcohols, primary and secondary amines 
and mono-acids containing no other substituents reactive with isocyanates 
are particularly useful in this invention. Relative to the 
monoisocyanates, these materials are safe and easy to handle. 
Suitable active hydrogen-containing compounds include, alcohols such as the 
alkanols having 1 to 10 carbon atoms, e.g., methyl alcohol, ethyl alcohol, 
isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, isoamyl alcohol, 
n-hexanol, cyclohexanol, 2-chloro-1-propanol, and 2-octanol; benzyl 
alcohol; glycol mono ethers and glycol mono esters, e.g. diethylene glycol 
mono-n-butyl ether; alkoxy-capped polyalkylene glycols, e.g., methoxy 
polyethylene glycols,; and aliphatic and dialiphatic amines, e.g., dibutyl 
amine. 
Although not preferred from a safety perspective, aliphatic and aromatic 
mono-isocyanates also can be used as the monofunctional 
isocyanate-reactive compound according to the broad practice of the 
present invention. Suitable monoisocyanates include butyl isocyanate, 
phenyl isocyanate, hexyl-phenyl isocyanates, methoxy-phenyl isocyanates 
and the like. 
For best results, the alcohol, amine or isocyanate or mixture thereof 
selected as the polymerization chain-stopper should have a boiling point 
above the temperature at which the reaction is being conducted. 
The monofunctional isocyanate-reactive compound or mixture thereof is 
reacted with the diisocyanate self-addition polycarbodiimide intermediate 
polymer in an amount insufficient to consume or deplete all the 
free-isocyanate groups of said polymer. For linear polycarbodiimides, the 
monofunctional isocyanate-reactive compounds typically are supplied in an 
amount to provide between about 0.2 to about 0.9 mol, and most preferably 
between about 0.3 and about 0.7 mol of monofunctional isocyanate reactive 
compound per mol of isocyanate moiety ultimately used for preparing the 
mixed aliphatic/aromatic polycarbodiimide product, i.e. including both the 
aliphatic and aromatic diisocyanates. 
The termination reaction preferably is conducted at a temperature of 
between about 100.degree. to 120.degree. C., preferably at about 
110.degree. C. until completion, i.e., until essentially all of the 
monofunctional reactants are consumed. At these reduced temperatures, 
further self-addition polymerization of the polycarbodiimide intermediate 
and other isocyanates becomes quite slow. Consequently, the lower 
temperatures favor the termination reaction, especially those involving 
alcohol and amine monofunctional isocyanate-reactive compounds and further 
self-addition polymerization effectively ends. Careful temperature control 
at this stage is important for preventing an over-advancement of the 
initially polymerized polycarbodiimide intermediate. In commercial 
operations where rapid cooling of large reactors by indirect means is 
difficult, one can take advantage of the heat capacity of the various 
reactants (e.g. monoalcohols) and solvents to effect quick cooling by 
adding them rapidly to the reaction media. 
It is a preferred feature of the present invention that an alkoxy-capped 
poly(alkylene oxide) comprise at least a portion of the monofunctional 
isocyanate-reactive compound. In this way, the self-emulsifying property 
of the resulting polycarbodiimides is greatly enhanced. By improving the 
emulsifying behavior of the polycarbodiimide, its utility as a crosslinker 
for aqueous carboxyl-containing resin systems is significant improved. 
Suitable alkoxy-capped poly(alkylene oxides) are described in U.S. Pat. No. 
4,820,863, the disclosure of which is hereby incorporated by reference. 
Such alkoxy-capped polymers are well known in the art and can be readily 
prepared using familiar procedures. Useful polymers of this type include 
those described by the generic formula: R--(OCH.sub.2 CH.sub.2).sub.n 
--OH, wherein R is a C.sub.1 -C.sub.6 alkyl, preferably a C.sub.1 -C.sub.4 
alkyl, and n is about 4 to about 20, preferably about 8 to about 17. The 
degree of alkoxylation should be as close to 100 mole percent as possible. 
Various commercially available materials may be employed. For example, one 
may advantageously use those methoxy-capped poly(ethylene oxide) resins 
available from Union Carbide Corp. under the trade designation "CARBOWAX 
MPEG." Such materials are available in broad range of molecular weights. 
For purposes of this invention, the preferred molecular weight (weight 
average) range is about 300 to about 1,000, preferably about 350 to about 
750. 
The total weight of alkoxy-capped e.g., (methoxy) polyethylene glycol to 
the total weight of monofunctional isocyanate-reactive compounds should 
range from about 10 to about 50 weight percent. In order to obtain a good 
balance between dispersibility and functionality, the preferred range 
should be from about 20 to about 40 weight percent. However, if a product 
is to be used in solvent based systems, rather than with an aqueous resin, 
no alkoxy-capped polyethylene glycol would be needed. 
The reaction between the diisocyanate self-addition polymer or 
polycarbodiimide intermediate and the monofunctional isocyanate-reactive 
compounds typically is conducted in an inert solvent. Again, the choice of 
solvent is not critical. However, the boiling point of the solvent should 
be at least about 130.degree.-160.degree. C. to accommodate both this 
termination reaction and the subsequent completion of the polycarbodiimide 
polymerization reaction described below. 
The quantity of solvent used also is not critical, but should be sufficient 
to keep the product in a fluid state. As a guideline, it is recommended 
that sufficient solvent be used to produce between about a 40 and 60% 
solids concentration in the reaction media, as it may be necessary to 
remove the solvent by vaporization or other energy-intensive procedure 
before the polycarbodiimide can be used. The solvent must not contain 
active hydrogen functionality such as would react with the isocyanate 
materials or the ultimate carbodiimide product. 
As noted above, the ratio of the total moles of monofunctional 
isocyanate-reactive compound to the total moles of isocyanate functional 
groups in the reactants used to prepare the polycarbodiimide product 
should range from about 0.2 to about 0.9. The preferred range is from 
about 0.25 to about 0.9, with between about 0.3 and 0.7 most preferred for 
linear polycarbodiimides. Any composition with a ratio higher than about 
0.9 is not going to produce any noticeable effect in improving the solvent 
resistance. On the other hand, any composition with a ratio lower than 
about 0.2 is likely to gel. 
Once the termination reaction phase is essentially complete, the reaction 
temperature is again increased to within the range of 125.degree. to 
160.degree. C., preferably to about 150.degree. C. to convert any residual 
isocyanates to carbodiimides. The termination reaction should take about 
0.5 to 3.0 hours to reach completion. Neglecting the time needed to heat 
and cool the reactants and the periods of addition, the total reaction 
period will normally be between about 10 to 15 hours. At some point prior 
to initiating this final polymerization phase, an aromatic diisocyanate or 
a mixture thereof is added to the reaction medium. The aromatic 
diisocyanate typically can be added either at the same time as the 
monofunctional isocyanate-reactive compound is added to the 
polycarbodiimide intermediate or at any point thereafter, up to when 
self-addition polymerization conditions are re-established. 
As before, the progress of the final polymerization phase can be followed 
by monitoring carbon dioxide (CO.sub.2) evolution. Once CO.sub.2 evolution 
essentially ceases, the reaction is over. For convenience the final 
polymerization phase is conducted in the same solvent employed during the 
termination phase. 
Aromatic diisocyanates useful in preparing the polycarbodiimides of the 
present invention include 4,4'-diisocyanotodiphenylmethane, the toluene 
diisocyanates, naphthalenediisocyanates, and m-phenylene diisocyanate. The 
aromatic nucleus can be substituted with substituents which are inert to 
the carbodiimide linkages, including alkyl, cycloalkyl, aryl, aralkyl, 
alkoxy, aryloxy, unsaturated groups such as vinyl, allyl, butenyl groups, 
halogen particularly fluorine or chlorine, nitrile, nitro groups and the 
like. The aromatic diisocyanate is supplied in an amount to provide up to 
about 0.6 mol of aromatic diisocyanate per mol of aliphatic diisocyanate 
and preferably between about 0.2 to 0.5 mols of aromatic diisocyanate per 
mole of aliphatic diisocyanate or higher functionality aliphatic 
isocyanate. 
Incorporating a proper amount of aromatic diisocyanate in preparing the 
mixed aliphatic/aromatic polycarbodiimide improves the chemical resistance 
of the polycarbodiimide product. An excess amount of aromatic 
diisocyanate, on the other hand contributes to gelation. The total weight 
of aromatic diisocyanate to the total weight of reactants generally will 
be from about 1 to about 25 percent. For improved performance as well as 
an extended shelf life, the preferred amount of aromatic diisocyanate 
typically is from about 10 to about 20 wt %. 
It has been discovered that the stability of a mixed aliphatic/aromatic 
polycarbodiimide is related to (i) its average number of carbodiimide 
groups per molecule, or in other words the number of mols of carbodiimide 
groups in a mol of the polycarbodiimide polymer product defined as its 
functionality, and (ii) its content of aromatic diisocyanates. As 
recognized by those skilled in the art, polycarbodiimides made in 
accordance with the present invention will contain a distribution of 
molecules of differing molecular weights and each molecule will have a 
particular distribution of moieties contributed by reactions between the 
aliphatic and aromatic isocyanates, the polyfunctional isocyanates and 
between the isocyanates and the monofunctional isocyanate-reactive 
compounds. The resulting products of different molecular weights are 
relatively difficult to separate and are normally employed as a mixture. 
In this case, the functionality or number of carbodiimide groups per 
molecule is specified as an average, thus the functionality of a compound 
having two carbodiimide groups is 2; an equimolar mixture of a 
polycarbodiimide having two carbodiimide groups with a polycarbodiimide 
having three carbodiimide groups would have a functionality of 2.5; 
polymers having an average functionality of at least two are suitable for 
the practice of this invention. The theoretical functionality of 
polycarbodiimaide product which is a useful approximation of its actual 
functionality can be calculated from the reactants used during its 
preparation by the following formula: 
##EQU1## 
where: mols of isocyanate=the total number of mols of isocyanate moieties 
in the polycarbodiimide reactants 
mols of active-H=the total number of mols of active hydrogens in the 
polycarbodiimide reactants 
mols of monofunctional=the total number of mols of monofunctional 
isocyanate-reactive compounds in the polycarbodiimide reactants 
mols of polyfunctional=the total number of mols of polybodiimide reactants 
having three isocyanate groups 
The preferred functionality range for a linear carbodiimide which is 
composed of difunctional isocyanates only, is from about 2.0 to about 7.1; 
whereas the preferred functionality range for non-linear carbodiimides 
containing polyfunctional, e.g., trifunctional, isocyanate, depends upon 
the percentage of polyfunctional, e.g., trifunctional, groups. For 
example, with 5 wt. % trifunctional isocyanate, the preferred 
functionality range is about 2.0 to about 6.5, it is about 2.0 to about 
5.6 for a level of 15 percent trifunctional group, and it is about 2.0 to 
about 5.3 for a level of 25% triisocyanate. In other words, as the level 
of multi-functional isocyanate is increased, the upper limit on the 
preferred range of polycarbodiimide functionality is decreased. As a 
result of the combination of these preferred functionality ranges, a 
preferred range of the total moles of monofunctional isocyanate-reactive 
compound to the total moles of isocyanate is as noted above from about 0.2 
to about 0.9. 
The resin systems in which the polycarbodiimide crosslinkers of the present 
invention are particularly useful are those in which the resins contains 
reactive carboxyl groups, such as are typically found in aqueous latexes, 
aqueous polyurethane dispersions, or neutralized carboxylated 
water-soluble resins and carboxylated solution resins, which may for 
example be used for coatings. The polycarbodiimides will also be useful in 
such carboxyl-containing resin systems as polyesters, acrylics, epoxies 
and alkyds. All of these resins are intended to be embraced by the phrase 
"carboxyl-containing". 
The polycarbodiimides of the present invention are added as crosslinkers 
for such carboxyl-containing resins in an amount between about 0.5 to 
about 30 parts per 100 parts by weight of the carboxyl-containing resin.

EXAMPLES OF PREATION OF CARBODIIMIDES 
Nineteen examples (Examples 1-19) are presented hereafter illustrating the 
preparation of various polycarbodiimides. In connection with Example I, 
examples 1-17 demonstrate (1) the effect of the amount of aromatic 
diisocyanate (TDI) (examples 1-3, 5-8 and 13-17), (2) the effect of the 
monofunctional isocyanat-reactive compound to total isocyanate ratio 
(examples 4, 11, 13, 14 and 17), (3) the effect of various amounts of 
optional MPEG (every example) and (4) the effect of various amounts of 
optional multifunctional isocyanate monomer (examples 9-12) on the use of 
these polycarbodiimide as crosslinkers for aqueous carboxyl-containing 
resins. The resulting polycarbodiimide products of examples 1-17 were 
tested as crosslinkers in a standard carboxyl-containing aqueous latex 
formulation for their effect on solvent resistance. The results of the 
examples are summarized in Tables 1 and 2. 
EXAMPLE 1 
181.5 g isophorone diisocyanate (IPDI) and 14.3 g of a 10% solution of 
3-methyl-1-phenyl-2-phospholene-1-oxide in xylene were placed into a 
1-liter, 4-neck round-bottom flask which was equipped with a heating 
mantle, thermometer, condenser, nitrogen sparge and mechanical stirrer. 
The mixture was heated with stirring and nitrogen sparge at 145.degree. C. 
After 2 hours reaction, a mixture of 15.7 g n-butanol (BuOH), 116.5 g 
methoxy polyethylene glycol 350 (MPEG 350), and 234.0 g propylene glycol 
monomethyl ether acetate was charged into the flask, corresponding to 
about 0.24 mol of monofunctional isocyanate-reactive compound per mol of 
isocyanate moiety. Then a mixture of 56.9 g toluene diisocyanate (TDI) and 
130.0 g propylene glycol monomethyl ether acetate was added. The reaction 
temperature was held at 110.degree. C. for 1 hour and then reheated to 
150.degree. C. The reaction was completed after 8 additional hours at 
150.degree. C. The product had a solids content of 51.0%, a viscosity of 
50 cps., and a color of 6 using a Gardner Hellige Comparator. 
EXAMPLE 2 
167.5 g isophorone diisocyanate and 11.0 g of a 10% solution of 
3-methyl-1-phenyl-2-phospholene-1-oxide in xylene were placed into a 
1-liter, 4-neck, round-bottom flask which was equipped with a heating 
mantle, thermometer, condenser, nitrogen sparge and mechanical stirrer. 
The mixture was heated with stirring and nitrogen sparge at 145.degree. C. 
After 2.5 hours reaction, a mixture of 12.1 g n-butanol, 89.6 g methoxy 
polyethylene glycol 350, and 180.0 g propylene glycol monomethyl ether 
acetate was charged into the flask. Then a mixture of 21.9 g toluene 
diisocyanate and 100.0 g propylene glycol monomethyl ether acetate was 
added. The reaction temperature was held at 110.degree. C. for 1.5 hours 
and then reheated to 150.degree. C. The reaction was completed after 10 
additional hours at 150.degree. C. The product had a solids content of 
49.0%, a viscosity of 36 cps., and a color of 4 using a Gardner Hellige 
Comparator. 
EXAMPLE 3 
139.6 g isophorone diisocyanate and 10.0 g of a 10% solution of 
3-methyl-1-phenyl-2-phospholene-1-oxide in xylene were placed into a 
1-liter, 4-neck, round-bottom flask which was equipped with a heating 
mantle, thermometer, condenser, nitrogen sparge and mechanical stirrer. 
The mixture was heated with stirring and nitrogen sparge at 145.degree. C. 
After 2.5 hours reaction, a mixture of 12.1 g n-butanol, 89.6 g methoxy 
polyethylene glycol 350, and 160.0 g propylene glycol monomethyl ether 
acetate was charged into the flask. Then a mixture of 55.8 g isophorone 
diisocyanate and 100.0 g propylene glycol monomethyl ether acetate was 
added. The reaction temperature was held at 110.degree. C. for 1.5 hours 
and then reheated to 150.degree. C. The reaction was completed after 12 
additional hours at 150.degree. C. The product had a solids content of 
52.9%, a viscosity of 45 cps., and a color of 2 using a Gardner Hellige 
Comparator. 
EXAMPLE 4 
139.6 g isophorone diisocyanate and 10.0 g of a 10% solution of 
3-methyl-1-phenyl-2-phospholene-1-oxide in xylene were placed into a 
1-liter, 4-neck, round-bottom flask equipped with a heating mantle, 
thermometer, condenser, nitrogen sparge and mechanical stirrer. The 
mixture was heated with stirring and nitrogen sparge at 145.degree. C. 
After 2.5 hours reaction, a mixture of 21.5 g n-butanol, 96.0 g methoxy 
polyethylene glycol 750 (MPEG 750), and 160.0 g propylene glycol 
monomethyl ether acetate was charged into the flask, corresponding to 
about 0.2 mol of monofunctional isocyanate-reactive compound per mol of 
isocyanate moiety. Then a mixture of 72.9 g toluene diisocyanate and 100.0 
g propylene glycol monomethyl ether acetate was added. The reaction 
temperature was held at 110.degree. C. for 1.5 hours and then reheated to 
150.degree. C. The reaction was completed after 10 additional hours at 
150.degree. C. However, the product was not stable and gelled in a few 
days. 
EXAMPLE 5 
139.6 g isophorone diisocyanate and 11.0 g of a 10% solution of 
3-methyl-1-phenyl-2-phospholene-1-oxide in xylene were placed into a 
1-liter, 4-neck, round-bottom flask equipped with a heating mantle, 
thermometer, condenser, nitrogen sparge and mechanical stirrer. The 
mixture was heated with stirring and nitrogen sparge at 145.degree. C. 
After 2.0 hours reaction, a mixture of 21.5 g n-butanol, 96.0 g methoxy 
polyethylene glycol 750, and 160.0 g propylene glycol monomethyl ether 
acetate was charged into the flask. Then a mixture of 43.8 g toluene 
diisocyanate and 120.0 g propylene glycol monomethyl ether acetate was 
added. The reaction temperature was held at 110.degree. C. for 1.5 hours 
and then reheated to 150.degree. C. The reaction was completed after 10 
additional hours at 150.degree. C. The product had a solids content of 
54.9%, a viscosity of 150 cps. and a color of 6 using a Gardner Hellige 
Comparator. 
EXAMPLE 6 
167.5 g isophorone diisocyanate and 11.0 g of a 10% solution of 
3-methyl-1-phenyl-2-phospholene-1-oxide in xylene were placed into a 
1-liter, 4-neck, round-bottom flask equipped with a heating mantle, 
thermometer, condenser, nitrogen sparge and mechanical stirrer. The 
mixture was heated with stirring and nitrogen sparge at 145.degree. C. 
After 2.5 hours reaction, a mixture of 21.5 g n-butanol, 96.0 g methoxy 
polyethylene glycol 750 and 180.0 g propylene glycol monomethyl ether 
acetate was charged into the flask. Then a mixture of 21.9 g toluene 
diisocyanate and 100.0 g propylene glycol monomethyl ether acetate was 
added. The reaction temperature was held at 110.degree. C. for 1.5 hours 
and then reheated to 150.degree. C. The reaction was completed after 10 
additional hours at 150.degree. C. The product had a solids content of 
50.2%, a viscosity of 45 cps. and a color of 4 using a Gardner Hellige 
Comparator. 
EXAMPLE 7 
72.9 g toluene diisocyanate, 21.5 g n-butanol and 96.0 g methoxy 
polyethylene glycol 750 were placed into a 1-liter, 4-neck, round-bottom 
flask equipped with a heating mantle, thermometer, condenser, nitrogen 
sparge and mechanical stirrer. The mixture was heated with stirring and 
nitrogen sparge at 100.degree. C. for 1 hour. Then 275.0 g propylene 
glycol monomethyl ether acetate was charged into the flask and this 
solution was removed for later usage. 139.6 g isophorone diisocyanate and 
11.7 g of a 10% solution of 3-methyl-1-phenyl-2-phospholene-1-oxide in 
xylene were placed into the same apparatus and held at 145.degree. C. for 
1 hour. Then the previously prepared mixture of TDI, n-butanol and methoxy 
polyethylene glycol was added slowly to the flask in a dropping funnel 
over a 30-minute period. The reaction temperature was held at 145.degree. 
C. to cook out the reaction; however, the reaction mixture gelled after 18 
hours. 
EXAMPLE 8 
153.2 g isophorone diisocyanate, 32.9 g toluene diisocyanate and 180.0 g 
propylene glycol monomethyl ether acetate were placed into a 1-liter, 
4-neck, round bottom flask equipped with a heating mantle, thermometer, 
condenser, nitrogen sparge and mechanical stirrer. Then a mixture of 21.6 
g n-butanol, 96.0 g methoxy polyethylene glycol 750 and 100.0 g propylene 
glycol monomethyl ether acetate was charged into the flask slowly. The 
reaction was heated to 115.degree. C. for 2 hours, then 11.0 g of a 10% 
3-methyl-1-phenyl-2-phospholene-1-oxide in xylene was added to the flask. 
Finally, the reaction was heated to 150.degree. C. and held at that 
temperature for 20 hours. The product had a solids content of 53.8%, a 
viscosity of 44 cps. and a color of 6 using a Gardner Hellige Comparator. 
EXAMPLE 9 
120.9 g isophorone diisocyanate, 56.8 g DESMODUR N-3200 aliphatic 
polyisocyanate (N-3200) reported to have an equivalent weight of about 180 
and 10.0 g of a 10% solution of 3-methyl-1-phenyl-2-phospholene-1-oxide in 
xylene were placed into a 1-liter, 4-neck, round-bottom flask equipped 
with a heating mantle, thermometer, condenser, nitrogen sparge and 
mechanical stirrer. The mixture was heated with stirring and nitrogen 
sparge at 145.degree. C. After 1.5 hours reaction, a mixture of 21.5 g 
n-butanol, 96.0 g methoxy polyethylene glycol 750 and 180.0 g propylene 
glycol monomethyl ether acetate was charged into the flask. Then a mixture 
of 12.9 g toluene diisocyanate and 100.0 g propylene glycol monomethyl 
ether acetate was added. The reaction temperature was held at 110.degree. 
C. for 1.0 hour and then reheated to 150.degree. C. The reaction was 
completed after 10 additional hours at 150.degree. C. The product had a 
solids content of 53.1%, a viscosity of 290 cps. and a color of 3 using a 
Gardner Hellige Comparator. 
EXAMPLE 10 
93.1 g isophorone diisocyanate, 75.9 g DESMODUR N-3200 aliphatic 
polyisocyanate and 11.0 g of a 10% solution of 
3-methyl-1-phenyl-2-phospholene-1-oxide in xylene were placed into a 
1-liter, 4-neck, round-bottom flask equipped with a heating mantle, 
thermometer, condenser, nitrogen sparge and mechanical stirrer. The 
mixture was heated with stirring and nitrogen sparge at 145.degree. C. 
After 2.0 hours reaction, the viscosity increased and later gelled. 
EXAMPLE 11 
104.4 g isophorone diisocyanate, 56.8 g DESMODUR N-3200 aliphatic 
polyisocyanate and 9.0 g of a 10% solution of 
3-methyl-1-phenyl-2-phospholene-1-oxide in xylene were placed into a 
1-liter, 4-neck, round-bottom flask equipped with a heating mantle, 
thermometer, condenser, nitrogen sparge and mechanical stirrer. The 
mixture was heated with stirring and nitrogen sparge at 145.degree. C. 
After 2.0 hours reaction, a mixture of 12.1 g n-butanol, 89.6 g methoxy 
polyethylene glycol 350 and 180.0 g propylene glycol monomethyl ether 
acetate was charged into the flask. Then a mixture of 36.8 g toluene 
diisocyanate and 100.0 g propylene glycol monomethyl ether acetate was 
added. The reaction temperature was held at 110.degree. C. for 1.0 hour 
and then reheated to 150.degree. C. The reaction was completed after 10 
additional hours at 150.degree. C. The product gelled to a solid mass in a 
few days. 
EXAMPLE 12 
121.4 g isophorone diisocyanate, 42.6 g DESMODUR N-3200 aliphatic 
polyisocyanate and 9.0 g of a 10% solution of 
3-methyl-1-phenyl-2-phospholene-1-oxide in xylene were placed into a 
1-liter, 4-neck, round-bottom flask equipped with a heating mantle, 
thermometer, condenser, nitrogen sparge and mechanical stirrer. The 
mixture was heated with stirring and nitrogen sparge at 145.degree. C. 
After 1.5 hours reaction, a mixture of 12.1 g n-butanol, 89.6 g methoxy 
polyethylene glycol 350 and 180.0 g propylene glycol monomethyl ether 
acetate was charged into the flask. Then a mixture of 19.4 g toluene 
diisocyanate and 100.0 g propylene glycol monomethyl ether acetate was 
added. The reaction temperature was held at 110.degree. C. for 1.0 hour 
and then reheated to 150.degree. C. The reaction was completed after 12 
additional hours at 150.degree. C. The product had a solids content of 
50.8%, a viscosity of 100 cps. and a color of 3 using a Gardner Hellige 
Comparator. 
EXAMPLE 13 
134.8 g isophorone diisocyanate and 9.0 g of a 10% solution of 
3-methyl-1-phenyl-2-phospholene-1-oxide in xylene were placed into a 
1-liter, 4-neck, round-bottom flask equipped with a heating mantle, 
thermometer, condenser, nitrogen sparge and mechanical stirrer. The 
mixture was heated with stirring and nitrogen sparge at 145.degree. C. 
After 2.5 hours reaction, a mixture of 21.6 g n-butanol, 96.0 g methoxy 
polyethylene glycol 750 and 160.0 g propylene glycol monomethyl ether 
acetate was charged into the flask, corresponding to about 0.3 mol of 
monofunctional isocyanate-reactive compound per mol of isocyanate moiety. 
Then a mixture of 21.9 g toluene diisocyanate and 100.0 g propylene glycol 
monomethyl ether acetate was added. The reaction temperature was held at 
110.degree. C. for 1.0 hour and then reheated to 150.degree. C. The 
reaction was completed after 10 additional hours at 150.degree. C. The 
product had a solids content of 49.4%, a viscosity of 42 cps. and a color 
of 4. 
EXAMPLE 14 
111.8 g isophorone diisocyanate and 8.0 g of a 10% solution of 
3-methyl-1-phenyl-2-phospholene-1-oxide in xylene were placed into a 
1-liter, 4-neck, round-bottom flask equipped with a heating mantle, 
thermometer, condenser, nitrogen sparge and mechanical stirrer. The 
mixture was heated with stirring and nitrogen sparge at 145.degree. C. 
After 2.5 hours reaction, a mixture of 21.55 g n-butanol, 96.0 g methoxy 
polyethylene glycol 750 and 160.0 g propylene glycol monomethyl ether 
acetate was charged into the flask. Then a mixture of 21.94 g toluene 
diisocyanate and 100.0 g propylene glycol monomethyl ether acetate was 
added. The reaction temperature was held at 110.degree. C. for 1.0 hour 
and then reheated to 150.degree. C. The reaction was completed after 10 
additional hours at 150.degree. C. The product had a solids content of 
47.8%, a viscosity of 37 cps. and a color of 4. 
EXAMPLE 15 
181.5 g isophorone diisocyanate and 12.0 g of a 10% solution of 
3-methyl-1-phenyl-2-phospholene-1-oxide in xylene were placed into a 
1-liter, 4-neck, round-bottom flask equipped with a heating mantle, 
thermometer, condenser, nitrogen sparge and mechanical stirrer. The 
mixture was heated with stirring and nitrogen sparge at 145.degree. C. 
After 2.5 hours reaction, a mixture of 48.8 g dibutyl amine (DBA), 124.8 g 
methoxy polyethylene glycol 750 and 234.0 g propylene glycol monomethyl 
ether acetate was charged into the flask. Then a mixture of 47.4 g toluene 
diisocyanate and 130.0 g propylene glycol monomethyl ether acetate was 
added. The reaction temperature was held at 110.degree. C. for 1.0 hour 
and then reheated to 150.degree. C. The reaction was completed after 10 
additional hours at 150.degree. C. The product had a solids content of 
52.2%, a viscosity of 111 cps. and a color of 4. 
EXAMPLE 16 
181.4 g isophorone diisocyanate and 13.0 g of a 10% solution of 
3-methyl-1-phenyl-2-phospholene-1-oxide in xylene were placed into a 
1-liter, 4-neck, round-bottom flask equipped with a heating mantle, 
thermometer, condenser, nitrogen sparge and mechanical stirrer. The 
mixture was heated with stirring and nitrogen sparge at 145.degree. C. 
After 2.5 hours reaction, a mixture of 21.0 g dibutyl amine, 116.5 g 
methoxy polyethylene glycol 350 and 230.0 g propylene glycol monomethyl 
ether acetate was charged into the flask. Then a mixture of 47.4 g toluene 
diisocyanate and 130.0 g propylene glycol monomethyl ether acetate was 
added. The reaction temperature was held at 110.degree. C. for 1.0 hour 
and then reheated to 150.degree. C. The reaction was completed after 10 
additional hours at 150.degree. C. The product had a solids content of 
50.0%, a viscosity of 62 cps. and a color of 4. 
EXAMPLE 17 
190.7 g isophorone diisocyanate and 14.0 g of a 10% solution of 
3-methyl-1-phenyl-2-phospholene-1-oxide in xylene were placed into a 
1-liter, 4-neck, round-bottom flask equipped with a heating mantle, 
thermometer, condenser, nitrogen sparge and mechanical stirrer. The 
mixture was heated with stirring and nitrogen sparge at 145.degree. C. 
After 2.5 hours reaction, a mixture of 37.5 g dibutyl amine, 96.0 g 
methoxy polyethylene glycol 750 and 200.0 g propylene glycol monomethyl 
ether acetate was charged into the flask. Then a mixture of 32.8 g toluene 
diisocyanate and 100.0 g propylene glycol monomethyl ether acetate was 
added. The reaction temperature was held at 110.degree. C. for 1.0 hour 
and then reheated to 150.degree. C. The reaction was completed after 8 
additional hours at 150.degree. C. The product had a solids content of 
54.7%, a viscosity of 210 cps. and a color of 4. 
EXAMPLE 18 
147.6 g isophorone diisocyanate, 12.25 g of a 10% solution of 
3-methyl-1-phenyl-2-phospholene-1-oxide in xylene and 89.3 g propylene 
glycol monomethyl ether acetate were placed into a 1-liter, 4-neck, 
round-bottom flask equipped with a heating mantle, thermometer, condenser, 
nitrogen sparge and mechanical stirrer. The mixture was heated with 
stirring and nitrogen sparge at 145.degree. C. After 2.0 hours reaction, a 
mixture of 24.6 g n-butanol, 109.5 g methoxy polyethylene glycol 750 and 
130.2 g propylene glycol monomethyl ether acetate was charged into the 
flask. Then a mixture of 58.3 g toluene diisocyanate and 92.9 g propylene 
glycol monomethyl ether acetate was added. The reaction temperature was 
held at 110.degree. C. for 1.5 hour and then reheated to 150.degree. C. 
The reaction was completed after 10 additional hours at 150.degree. C. The 
product had a solids content of 49.6%, a viscosity of 107 cps. and a color 
of 5. 
EXAMPLE 19 
138.8 isophorone diisocyanate, 12.14 g of a 10% solution of 
3-methyl-1-phenyl-2-phospholene-1-oxide in xylene and 88.7 g propylene 
glycol monomethyl ether acetate were placed into a 1-liter, 4-neck, 
round-bottom flask equipped with a heating mantle, thermometer, condenser, 
nitrogen sparge and mechanical stirrer. The mixture was heated with 
stirring and nitrogen sparge at 145.degree. C. After 2.0 hours reaction, a 
mixture of 24.6 g n-butanol, 109.5 g methoxy polyethylene glycol 750 and 
129.4 g propylene glycol monomethyl ether acetate was charged into the 
flask. Then a mixture of 65.2 g toluene diisocyanate and 92.4 g propylene 
glycol monomethyl ether acetate was added. The reaction temperature was 
held at 110.degree. C. for 1.0 hour and then reheated to 150.degree. C. 
The reaction was completed after 10 additional hours at 150.degree. C. The 
product had a solids content of 49.5, a viscosity of 130 cps. and a color 
of 6. 
TABLE 1 
__________________________________________________________________________ 
Raw Material Weights 
Aromatic.sup.1 
Ex. # 
IPDI 
MPEG350 
MPEG750 
N-3200 
TDI 
BuOH 
DBA Fctlty. 
Aliphatic 
__________________________________________________________________________ 
1 181.5 
116.5 56.9 
15.7 3.2 0.40 
2 167.5 
89.6 21.9 
12.0 3.2 0.17 
3 195.4 
89.6 0.0 
12.0 3.2 0.00 
4 139.6 96.0 72.8 
21.0 4.0 0.67 
5 139.6 96.0 43.75 
21.5 3.2 0.40 
6 167.5 96.0 21.9 
21.5 3.2 0.17 
7 139.6 96.0 72.9 
21.5 4.0 0.67 
8 153.2 96.0 32.9 
21.6 3.2 0.27 
9 120.9 96.0 56.8 
12.9 
21.5 3.6 0.14 
10* 
93.1 
89.6 75.0 
43.7 
12.0 3.2 0.60 
11 104.4 
89.6 56.8 
36.8 
12.1 4.0 0.45 
12 121.4 
89.6 42.6 
19.4 
12.1 3.3 0.20 
13 134.8 96.0 21.9 
21.6 2.5 0.21 
14 111.8 96.0 21.9 
21.6 2.0 0.25 
15 181.5 124.8 47.4 48.8 
3.0 0.33 
16 181.4 
116.5 47.4 21.0 
3.4 0.33 
17 190.7 96.0 32.8 37.5 
4.0 0.22 
18 147.6 109.5 58.3 
24.6 3.2 0.50 
19 138.8 109.5 65.2 
24.6 3.1 0.60 
__________________________________________________________________________ 
*Sample gelled before the addition of MPEG, TDI and BuOH. 
.sup.1 Mol ratio of aromatic to aliphatic diisocyanates 
EXAMPLE I 
A base resin of an acrylic latex is prepared as follows: 
A mixture of 192 g water and 48.0 g Butyl Cellosolve was added to 2000.0 g 
UCAR Vehicle 443. Then the pH of resin mixture was adjusted to 8.2 with a 
14% ammonia water solution. 
The various carbodiimides of Examples 1 to 17 and a commercial 
polycarbodiimide product (XL-25SE) were added into the resin mixture at a 
level of 5% crosslinker solids to 100% resin solids. After forming a 
homogeneous dispersion, a film with 1 mil dry thickness was drawn on a 
Leneta chart and was baked at 85.degree. C. for 30 minutes. A control also 
was tested having no added crosslinker. The test of MEK and ethanol (ETOH) 
double rubs was performed after the baked film was cooled at ambient 
temperature for a few hours. According to the double rub tests, a piece of 
cheesecloth is saturated with methyl ethyl ketone (MEK) or ethanol (ETOH), 
then rubbed on the substrate until penetration occurs. One back and forth 
rub is one double rub. 
TABLE 2 
__________________________________________________________________________ 
Carbodiimide Experiments 
DOUBLE RUBS 
#Example 
##STR1## 
Wt. %MPEG 
Wt. %TDI 
Wt. %Tri-NCO 
MEKETOH@ 85.degree. C./30 Min. 
__________________________________________________________________________ 
1 0.24 31.44% 
15.35% 105 154 
2 0.24 30.79% 
7.52% 75 122 
3 0.24 30.16% 65 73 
4 0.20 29.09% 
22.09% gelled 
5 0.24 31.90% 
14.54% 105 173 
6 0.24 31.28% 
7.14% 100 160 
7 0.20 29.09% 
22.09% gelled 
8 0.24 31.61% 
10.83% 105 125 
9 0.34 31.16% 
4.19% 
18.44% 
100 164 
10* 0.24 28.51% 
13.91% 
24.14% 
gelled 
11 0.25 29.90% 
12.28% 
18.95% 
gelled 
12 0.27 31.43% 
6.80% 
14.94% 
100 197 
13 0.29 35.00% 
8.00% 103 150 
14 0.33 38.20% 
8.73% 104 133 
15 0.25 31.01% 
11.78% 110 187 
16 0.22 31.80% 
12.94% 112 191 
17 0.20 26.89% 
9.19% 105 182 
XL-25SE 100 120 
Control 35 72 
__________________________________________________________________________ 
*Sample gelled before the addition of MPEG, TDI and BuOH. 
The composition of this invention has at least three advantages over the 
prior art: stability, economy and the improvement of solvent resistance. 
The stability is demonstrated by every example within the preferred range. 
The shelf life is six months or longer. The economic advantage is a result 
of the incorporation of toluene diisocyanate for some isophorone 
diisocyanate and of butanol or dibutyl amine for butyl isocyanate. The 
improvement of solvent resistance of a carbodiimide crosslinked film 
versus an uncrosslinked film is significant in both MEK and ethanol double 
rubs test (see Table 2). In particular, the majority of aliphatic/aromatic 
polycarbodiimide crosslinkers demonstrate a substantial improvement in the 
ethanol resistance and a moderate improvement in the MEK resistance 
compared with the UCARLNK XL-25SE product, an aliphatic carbodiimide 
prepared using isophorene diisocyanate and butyl isocyanate. 
Although the invention has been described in its preferred forms with a 
certain degree of particularity, it should be understood that this 
description has been made only by way of example and that numerous changes 
may be made without departing from the spirit and the scope of the 
invention.