In continuation of our goal to determine the ability of CO2 to plasticize acrylonitrile (AN) copolymers and facilitate melt processing at temperatures below the onset of thermal degradation, a systematic study has been performed to determine the influence of AN content on CO2 absorption and subsequent viscosity reduction. Our previous report focused on the absorption of CO2 in a relatively thermally stable 65 mol% AN copolymer. In this study, the ability for CO2 to absorb in AN copolymers containing 85-98 mol% acrylonitrile was determined, and subsequent viscosity and equivalent processing temperature reductions were evaluated. Eighty five and 90 mol% acrylonitrile/methyl acrylate (AN/MA) copolymers were found to absorb up to 5.6 and 3.0 wt% CO2, corresponding to reductions of T-g of 37 and 27 degreesC, and subsequent viscosity reductions of 61 and 56%, respectively. CO2 absorption in these copolymers was found to occur immediately, in contrast to the time dependent absorption observed in the 65 mol% copolymer. An Arrhenius scaling analysis was used to determine the equivalent reductions in processing temperature resulting from the viscosity reductions, and reductions of up to 25 and 9 degreesC were observed for the 85 and 90 mol% AN copolymers. Based on the specific conditions used for absorption, no significant CO2 uptake was observed for AN copolymers containing greater than 90 mol% acrylonitrile. Higher temperatures than those used here may be required to absorb CO2 into AN copolymers containing greater than 90 mol% AN. (C) 2004 Elsevier Ltd. All rights reserved.