Bis(trifluoroacetyl) peroxide was prepared in good yield by the reaction between trifluoroacetic anhydride and sodium peroxide under anhydrous conditions. polymers bearing benzene rings. polystyrene. poly(phenylene oxide) and poly(diphenylacetylene) were modified chemically by the peroxide. The resulting trifluoromethylated polymers have good solubilities in common organic solvents, and their cast films have good water repellency. The trifluoromethylated poly(diphenylacetylene)s have high gas and vapor permeabilities. (C) 2001 Elsevier Science Ltd. All rights reserved.