Synthesis and gas transport properties of UV-cured low-viscosity fluorine-containing telechelic polyimide membranes

Abstract

A novel ultraviolet (UV) cross-linking method using fluorine-containing telechelic polyimide membranes was investigated. The base fluorine-containing polyimide was synthesized by polycondensation using the monomers, 4,4´-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and 2,3,5,6-tetramethyl-1,4-phenylene diamine (TeMPD). Both chain ends of the 6FDA-TeMPD polyimide were end-capped with either UV-reacted groups, 1,1-bis(acryloyloxy methyl) ethyl isocyanate (BEI) group or p-aminostyrene (PAS) group. The two types of telechelic polyimide membranes, 6FDA-TeMPD-BEI and 6FDA-TeMPD-PAS, were formed with UV irradiation from the low-viscosity solutions using the solvent-casting method. The base polyimide membrane was soluble in tetrahydrofuran, whereas both UV-cured telechelic polyimide membranes were partly insoluble in it. This result suggested that both telechelic polyimides reacted at the polymer chain ends through UV irradiation. The density values of the UV-cured membranes were almost the same. Thus, this cross-linking method could prevent significant membrane densification compared with other conventional cross-linking methods. As the UV irradiation time increased, the gas selectivity in both UV-cured polyimide membranes increased without a significant decrease in gas permeability. The increase in ideal gas selectivity was attributed to the increase in the gas diffusivity selectivity rather than the solubility selectivity.

Characterization and gas permeation properties of UV-cured fluorine-containing telechelic polyimide membranes with a crosslinker

“…The number average molecular weight of the telechelic polyimide was 11,000 g/mol, and the distribution was 1.6 based on GPC measurements. These values were consistent with those listed in previous literature .…”

“…Figure shows the photographs of the UV‐cured polyimide. The 6FDA–TeMPD membrane was rigid and self‐standing, whereas the unirradiated 6FDA–TeMPD–BEI (UV 0 min) was brittle because of the low molecular weight, as reported in our previous study . Therefore, we could not measure the membrane properties of the unirradiated 6FDA–TeMPD–BEI (UV 0 min).…”

“…Membrane preparation was performed via a casting method by using 6FDA–TeMPD–BEI telechelic polyimide, which was synthesized according to our previous study . In this study, BEI was added into the NMP casting solution as a crosslinker.…”

“…UV crosslinking is one of the notable methods for gas separation membrane . Previously, we reported that the synthesis and gas permeation properties of novel telechelic polyimides are composed of 6FDA and TeMPD end‐capped with the UV‐reactive group, 1,1‐bis(acryloyloxy methyl) ethyl isocyanate (BEI) . Futhermore, we obtained self‐standing membranes via casting method by exposing telechelic polyimides to UV irradiation.…”

Gas‐separation properties of amine‐crosslinked polyimide membranes modified by amine vapor

“…The permeability coefficients ( P ) of pure gases [hydrogen (H 2 ), oxygen (O 2 ), nitrogen (N 2 ), carbon dioxide (CO 2 ), and methane (CH 4 )] in the PI membranes were determined at 35 ± 1 °C using the constant‐volume/variable‐pressure method, according to the literature . The upstream pressure was maintained at approximately 76 cmHg, whereas the downstream pressure was maintained in vacuum.…”