Fluorene-containing poly (arylene ether sulfone) block copolymers: Synthesis, characterization and application

A series of poly (arylene ether sulfone) block copolymers with hydrophilic segments containing fluorene groups were successfully synthesized as confirmed by 1 H NMR. The molecular weights were measured in the range 115–140   kDa by gel permeation chromatography (GPC). The hydrophilic segment showed a helical structure due to fluorene with butterfly-shaped framework in the main chain. With incorporating imidazolium groups, the microphase separation can also be achieved between the hydrophilic and the hydrophobic moieties. The membrane structure was characterized by positron annihilation lifetime spectroscopy (PALS) and small angle X-ray scattering (SAXS). The block copolymers were used to prepare membranes successfully for pervaporation separation of methanol (MeOH)/methyl tert-butyl ether (MTBE) mixture. The correlation between the membrane microstructure and the separation performance was discussed thoroughly. By increasing the hydrophilic segment proportion, the permeation flux increased while the separation factor declined. The membranes have the highest permeation flux (0.334   kg   m −2 h −1 ) and the lowest separation factor (287) for a 15   wt% MeOH feed mixture at 40   °C, and the mass fraction of MeOH in the permeate is higher than 98   wt%.