Design of Pervaporation Membranes Based on Blend of Linear and Highly Branched Polyimides With Terminal Amino Groups

ABSTRACT Novel polyimide (PI) membranes for pervaporation dehydration of isopropanol/water mixtures from the blends of linear PI (based on 3,4′‐oxydianiline and 4,4′‐(4,4′‐isopropylidenediphenoxy)bis(phthalic anhydride), PI 3,4′‐ODA‐DA) and highly branched PI with terminal amino groups were obtained via evaporation induced phase separation method. New highly branched polyimide (HB PI) with terminal amino groups was synthesized by an original method of one‐pot polycondensation in a benzoic acid melt. The structure of obtained PIs was investigated by Fourier‐transform infrared (FTIR) and 1 H NMR spectroscopies. Molecular weight characteristics of HB PI were examined via gel permeation chromatography. The effect of the concentration of HB PI with terminal amino groups on the structure and pervaporation performance of the membranes from PI 3,4′‐ODA‐DA was studied. Dense membranes were investigated using differential scanning calorimetry (DSC) as well as FTIR, scanning electron microscopy (SEM) and contact angle measurements. It was found that the addition of HB PI led to hydrophilization of the membrane surface and formation of a more heterogeneous loose cellular structure compared to the reference membrane structure from linear PI. Membrane performance in the separation of water/isopropanol mixtures via vacuum pervaporation was studied. It was revealed that the introduction of HB PI to the solution of linear PI, as well as an increase in its concentration, yielded a significant increase in membrane normalized flux (from 780 to 790–900 (g μm)/(m 2 h)), selectivity (water content in permeate rose from 71% to 78%–97%) and normalized pervaporation separation index (enhanced from 12 to 19–180 (kg μm)/(m 2 h)).