A hydrophobe-containing alkali soluble or swellable copolymer thickener comprising an emulsion polymerization product of (A) an ethylenically unsaturated copolymerizable surfactant monomer having a cloud point of from about 65° C. to about 95° C., wherein the surfactant monomer has the formula M(EO)x(BO)zOR1 wherein M is a residue selected from the group consisting of an ethylenically unsaturated carboxylic acid, and an ethylenically unsaturated dicarboxylic acid, EO is an ethylene oxide unit; BO is a butylene oxide unit; x is from 10 to 45; z is from 5 to 35; provided that x+z is from 20 to 45; and R1 is selected from the group consisting of alkyl, alkylene, cycloalkyl, cycloalkylene, and arylalkyl group wherein the alkyl group has 1 to 4 carbon atoms; (B) an &agr;,&bgr;-ethylenically unsaturated monocarboxylic acid monomer; and (C) a nonionic &agr;,&bgr;-ethylenically unsaturated monomer. The copolymer provides aqueous compositions with constant or increased viscosity at temperatures approaching 120° C.