Oligomeric aromatic dispersing agents, method of making same, and dispersions made therefrom

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As stated above, the oligomeric aromatic dispersant is a reaction product which comprises at least 25 weight percent of a compound of the formula: ##STR5## The term "reaction product" is used with reference to any reaction by which the compound is produced.
Such patents as U.
S.
Pat.
Nos.
3,560,235 and 3,728,301 refer to reactions which produce polymers.
Of course, the statistical distribution in the degree of polymerization dictates that a very small fraction of oligomer is also produced, albeit unintentionally, in the polymerization process.
The reaction product of the present invention must be at least 25 weight percent oligomer, in contrast to the incidental production of oligomer in the '235 and '301 patents, which undoubtedly produce below 5 weight percent oligomer.
Preferably the reaction product of the present invention is at least 90 weight percent oligomer.
Although the oligomeric dispersant may be made by more than one specific reaction, the preferred reaction involves reacting an aromatic diisocyanate with a diol and/or a diamine.
In order to obtain the oligomer, there cannot be equivalent amounts of both the diisocyanate and the diol or diamine.
Equivalent amounts of the diisocyanate and the, for example, diol, produce a polymer, not an oligomer.
Rather, there must be a significant stoichiometric excess of either the diisocyanate or, for example, the diol.
"Excess", as used herein, requires that there be at least 5 mole percent more of one reactant (e.
g.
The diisocyanate) than the other reactant (e.
g.
The diol).
In the above formula, "AR" represents a residual aromatic connecting group.
Preferably the AR is the residual group left from the reaction of the aromatic diisocyanate.
Since the residue from the "--N.
dbd.
C.
dbd.
O" groups of the diisocyanate are shown beside the AR group in the above formula, it is apparent that the AR group represents only the remainder of that portion of (what was previously) the diisocyanate.
Preferred AR groups comprise: ##STR6## More preferred AR groups are (I), (II), (III), (IV), (V) and (VII) above