A die coated with fluoroelastomer (FE) has been used in the extrusion of thermoplastics other than conventional polyolefins, and including chlorinated polyethylene, polystyrene, polycarbonate, and an ionomer, Inverse gas chromatography was the source of acid/base interactions between FE and each of these matrix polymers, FE was found to be effective in reducing the apparent melt viscosity when the host polymer was acidic, or non-interactive. With strongly interactive, basic polymers the effectiveness of FE flow modifier was anulled. These polymers may be considered as effective purging agents for extrusion equipment containing FE residues.