The purpose of this study is to determine under what conditions it is possible to use CO2 to plasticize and, thereby, reduce the viscosity of an acrylonitrile (AN) copolymer in an extrusion process and render it melt processable. To assess whether it was possible to absorb adequate amounts Of CO2 in short residence times by injection into a single screw extruder, a slit-die rheometer was attached to the end of the extrusion system for the purpose of directly assessing the viscosity reduction. A chemorheological analysis was performed on 65 and 85% AN copolymers to establish the temperature at which the 85% material would be as stable as the melt-processable 65% material at its recommended extrusion temperature. This, coupled with studies correlating the degree of T. and viscosity reduction with the amount of absorbed CO2, and comparison to previous data obtained in batch processes allowed one to predict conditions for melt extrusion of the 85% AN. Preliminary studies using a pressurized chamber attached to the exit of the die allowed one to assess the conditions under which suppression of foaming is possible. POLYM. ENG. SCI., 49:1990-2004, 2009. (C) 2009 Society of Plastics Engineers