Methyl vinyl ketone was successfully copolymerized with acrylonitrile for the first time. This was achieved with azobisisobutyronitrile as the initiator. The viscosity behavior of solutions of the acrylonitrile/methyl vinyl ketone copolymers was determined. The solution agreed with the character of Newtonian flow at the lower shearing rate. The addition of mechanical mixing obviously prevented an increase in the viscosity of the copolymer solutions. When dimethylforrnamide was used as an additive, the solution viscosity decreased monotonically. When H2O was used as an additive, the viscosity of the copolymer solutions decreased continuously with concentrations of H2O up to 4 wt % and then increased. The viscosity of the copolymer solutions decreased continuously with concentrations of KCl and NaCl up to 0.03 mol/L and then increased. Within the first 10 h, there was a great drop in the viscosity of the copolymer Solutions containing sodium ethoxide and sodium hydroxide, and then the viscosity appeared to increase. The composition with 12 wt % acetic acid in dimethyl sulfoxide Could be considered to be a Theta solvent for the acrylonitrile/methyl vinyl ketone copolymers. (c) 2006 Wiley Periodicals, Inc.