The viscosity behavior of dimethyl sulfoxide (DMSO) solutions of acrylonitrile-ammonium itaconate copolymer is discussed. The intrinsic viscosity was determined by an Ubbelohde viscometer. It is shown that an increase in the viscosity of acrylonitrile-ammonium itaconate copolymer solutions with time is considerably reduced by mechanical mixing. The viscosity of copolymer solutions with dimethyl formamide as an additive decreases monotonically. The viscosity of copolymer solutions decreases with the addition of H2O, and as the content of H2O in DMSO goes beyond 3 wt %, the viscosity shows a trend toward increase. The intrinsic viscosity decreases quickly with the addition of NaCl. As the concentration of NaCl goes beyond 0.015 mol/L, the viscosity increases solwly. The viscosity of co-polymer solutions containing sodium ethoxide and sodium hydroxide appears to increase after an initial drop. The viscosity of copolymer solutions upon the addition of diethylamine increases continuously with time and changes in viscosity become less prominent after a period of a few hours. The effects of bases on the tacticity of highly isotactic copolymers follow the order of base strength. Diethylamine is more effective for moderating the stabilization exotherm of highly isotactic copolymers compared to sodium ethoxide and sodium hydroxide. (C) 2004 Wiley Periodicals, Inc.