Good jetting performance and pigment-dispersing stability are necessary for pigment-based ink-jet inks. This study investigates how the chemical structures of the polymeric dispersants affect the pigment-dispersing stability and jetting performance of ink-jet inks. A series of polymeric dispersants containing styrene (hydrophobic unit) and acrylic acid (hydrophilic unit) with different ratios have been synthesized and used to disperse different pigments. Because 3000-12,000 ink drops can be expelled from the nozzle of a thermal bubble-type ink-jet printer within 1 s, the jetting behavior is related to the rheology variation of a dilute solution under a high shear. An in situ drop formation system has been used to study the high-shear-rate rheology (dynamic surface tension and dynamic viscosity) of a solution with a viscosity lower than 3 c1ps, which no commercial rheometer can measure. Excellent ink-jet inks can only be produced by the combination of pigments, dispersants, and surfactants with appropriate hydrophilicity. Moreover, the correlation of the pigment surface properties, the chemical structures of the polymeric dispersants, and ink formulation is discussed. The effects of the surfactants and firing conditions on the jetting behavior of the ink-jet ink are also examined. (C) 2003 Wiley Periodicals, Inc.