Patent ID: 7060416

Claim:
A copolymer comprising, in polymerized form: (a) about 1 wt % to about 30 wt % of N-phenylmaleimide, N-cyclohexylmaleimide, N-benzylmaleimide, or a mixture thereof; (b) about 1 wt % to about 30 wt % of acrylamide, methacrylamide, or a mixture thereof; (c) about 20 wt % to about 75 wt % of acrylonitrile, methacrylonitrile, or a mixture thereof; and (d) a total of about 20 wt % to about 75 wt % of one or more monomers selected from the group consisting of monomers of the structure: CH 2 ═C(R)-Z-X—NHC(O)NH—Y—R′ in which: X is —[C(CH 3 ) 2 ]— or —[(CH 2 ) n ]—, in which n is 0 to 12; Y is o-, m-, or p-—[C 6 H 4 ]—; Z is —[C(O)O]—, —[C(O)NH]—, or o-, m-, or p- [—C 6 H 4 ]—; R is hydrogen or C 1 to C 4 alkyl; R′ is —OC(O)—OR″, —OC(O)—Ar, or —OSO 2 —Ar; R″ is C 1 to C 12 alkyl, C 1 to C 12 arylalkyl, C 1 to C 12 aryl, C 1 to C 12 alkenyl, trimethylsilyl; Ar is C 6 H 5-n′ T n′ , in which Ar has a total of six to ten carbon atoms; each T is independently selected from the group consisting of C 1 to C 4 alkyl, fluoro, chloro, bromo, iodo, trifluoromethyl, methoxy, and cyano; and n′ is an integer from 0 to 5; and in which the copolymer is soluble in alkaline solutions having a pH greater than at least about 11.