Abstract: A composition comprising: (i) a polymeric material (A) having a repeat unit of formula (O-Ph)n-O-Ph-O-Ph-CO-Ph- ??I and a repeat unit of formula —O-Ph-Ph-O-Ph-CO-Ph- ??II wherein Ph represents a phenylene moiety and n represents 0 or 1; and (ii) a polymeric additive comprising one or more of. (a) a polycarbonate; and/or (b) a polymeric material (B) which includes a repeat unit of general formula wherein R? and R?? independently represent a hydrogen atom or an optionally-substituted (preferably un-substituted) alkyl group, and R3 and R4 independently represent a hydrogen atom or an optionally-substituted alkyl group, an anhydride-containing moiety or an alkyloxycarbonyl-containing moiety.