Preparation of new semifluorinated aromatic poly(ether amide)s and evaluation of pervaporation performance for benzene/cyclohexane 50/50 mixture

A series of new solution-processable aromatic poly(ether amide)s (PEAs) were prepared by the phosphorylation polyamidation reaction of terephthalic acid (TA) and four structurally different semifluorinated aromatic diamines (BTAPPI, BTAPPHI, BTAPPF, BTAPPPI). The synthesized polymers (PEA I, PEA II, PEA III and PEA IV) were characterized by FTIR, 1H and 13C NMR, TGA, DSC, DMA and WAXD techniques. The polymers showed good solubility in many organic solvents viz. NMP, DMF, DMAc and pyridine and were insoluble in CHCl3, benzene (Bz), toluene and cyclohexane (Chx). Membranes of average thickness of 42 μm of these polymers were prepared from their solutions in DMAc. The polymers showed good thermal stability, high glass transition temperatures (233–300 °C) and good mechanical strength. The membranes were investigated for separation of Bz/Chx (50/50 wt%) mixture. PEA IV containing cardo phthalimidine moiety showed the highest permselectivity and pervaporation separation index (PSI) values of 7.6 and 3616 g/m2 h for Bz/Chx mixture, respectively. PEA III containing cardo fluorene moiety in the main chain showed highest permeation flux of 569 g/m2 h in the series. The effect of temperature on the pervaporation performance of these membranes was also studied. The activation energies of pervaporation for Bz, Chx and Bz/Chx (50/50 wt%) mixtures through all the PEAs were calculated from the slopes of the respective Arrhenius plots. An attempt has been taken to draw a structure property correlation of the chemical structures of the newly prepared polymers with pervaporation performance.