Upper critical solution temperature behaviour in poly(ether ether sulphone)/poly(ether ether ketone-co- ether ether sulphone) blends

Upper critical solution temperature (u.c.s.t.) phase behaviour was found in blends of the homopolymer poly(oxy-1,4-phenyleneoxy-1,4-phenylenesulphonyl-1,4-phenylene) (PEES) with the copolymer poly(oxy-l,4-phenyleneoxy-l,4-phenylenecarbonyl-l,4-phenylene-co-oxy-l,4-phenyleneoxy-1,4-phenylenesul-phonyl-1,4-phenylene) (COPEEKS) for copolymer compositions ranging from 43 mol% to 56 mol% of ether ether ketone (EEK) repeat units. Blend compositions studied ranged from 25wt% to 75wt% of PEES. The consolute temperature was found to occur at a PEES/COPEEKS blend composition of about 50/50 wt% and to increase with the EEK repeat unit content of the copolymer. This miscibility behaviour was interpreted, using a mean-field theoretical approach, in terms of a single positive segmental interaction parameter which ranged from 0.054 to 0.032.