The terpolymers (PASA) with acrylamide (AM), butyl styrene (BST), and sodium 2-acrylamido-2-methylpropane sulfonate (NaAMPS) were synthesized by the micellar free radical copolymerization technique. The polymer composition was determined by the elemental analysis, and the block structure of PASA was characterized directly by DSC measurement. Incorporation of NaAMPS into the terpolymers may improve the water solubility and intermolecular association, and the feed amount of BST, sodium dodecyl sulfate (SDS) amount, and the total monomer concentration in the polymerization can influence apparently the viscosities of PASA. The polymer exhibits excellent viscosification effect, salt-thickening, temperature-thickening, thixotropy, pseudoplastic behavior or shear-thickening relative to the BST content in PASA, excellent anti-aging property at 85 degrees C, and a dramatic increase in solution viscosity by the addition of little amount of SDS. (c) 2006 Wiley Periodicals, Inc.