Dispersants resistant to color change

DETAILED DESCRIPTION OF THE INVENTION The instant invention is based on the discovery that, in block copolymers of the general type described in Hutchins et al.
, U.
S.
Pat.
No.
4,656,226, the presence of certain aromatic substituents on the A segment will provide excellent performance of the block coolymers as dispersants, and, at the same time, do not exhibit yellowing or other color change when exposed to light and aging.
Accordingly, the present compounds are exceptionally well suited for use as dispersants for pigments and in other applications where color change would not be desirable.
The block copolymers of the present invention have at least one A segment and at least one B segment.
While the block size is not critical to the present invention, each segment generally has a molecular weight of at least about 500.
The backbones of the segments consist essentially of at least one polymerized methacrylate or acrylate ester.
In the context of the present invention, both methacrylate and acrylate units are designated as acrylic moieties.
At least about 20% of the acrylic moieties of the A segment have bonded thereto a fragment derived from an acid, amide, or sulfonamide which is a substituent of a phenyl aromatic.
The term fragment is used in the usual sense of meaning that portion of the moiety remaining after bonding to the A segment.
Thus, for example, it will be understood that a phenyl aromatic having an acid group would bond to the A segment through that group, after which the acidic hydrogen would no longer be present.
The phenyl aromatic also has another substituent which is a conjugating group.
The term conjugating group will be understood to mean one having an atom attached to an aromatic ring and having a double or triple bond.
Examples of such conjugating groups include ester, nitrile, aromatic or substituted aromatic, or sulfonamide groups.
Another important characteristics of the phenyl aromatics bonded to the A segments of the present block copolymers is that they have no nitrogen, thiol, or OH group directly bonded to an aromatic ring, regardless of whether the aromatic ring is the primary component of the phenyl aromatic or a substituent