Relationship between polymer structure and gas transport properties in a series of fluorine-containing aromatic polyamide membranes for oxygen enrichment

In this work, a series of fluorine-containing aromatic polyamide membranes were prepared by direct polycondensation of 4,4′-hexafluoroisopropylidene-dibenzoic acid with various aromatic diamines, and the associated gas transport and sorption properties were investigated. The properties of the prepared aromatic polyamides were examined by elemental analysis, FTIR, and X-ray diffraction. It was found that both gas diffusivity and permeability can be increased by the introduction of bulky substituted groups and arylene ether groups into the polymer backbone. Membranes with oxygen permeability of 3.8 barrers and O2/N2 selectivity of 4.6 were obtained by using the polyamide with 2,5 di-tert-butylbenzene group in the polymer backbone. It was also found that the relationship between the membrane structure and the sorption properties can be well explained by the dual sorption model.

A series of aromatic polyamide membranes having excellent solubility in polar organic solvents has been successfully prepared in this study. The polymer packing density plays an important role in determining the gas selectivity and permeability of the aromatic polyamide membranes. Therefore, the gas transport properties of the aromatic polyamide strongly depend on the specific volume of the membranes. It was observed that both the specific volume of membranes and the Langmuir capacity constant of oxygen increase with the size of the diamine segment in the polymer backbone.