(401h) Water Vapor Sorption and Transport in Non-Fluorinated Copolyimide Membranes

In this study, a series of non-fluorinated 6FCDA-based copolyimide (FCP) membranes were developed as promising materials for vapor separation technologies, with an emphasis on the critical correlation between polymer structure and water vapor sorption behavior. The FCPs were synthesized through a two-step polycondensation reaction between 9,9-bis(trifluoromethyl)-2,3,6,7-xanthenetetracarboxylic dianhydride (6FCDA) and non-fluorinated diamines, such as 2,4,6-trimethyl-1,3-phenylenediamine (DAM) and 4,4′-oxydianiline (ODA). The blend of methyl-substituted DAM and ether-linked flexible ODA introduced variable chain rigidity and fractional free volume (FFV), which are required for the regulation of vapor transport. Solution-cast dense membranes were also characterized using FTIR, NMR, XRD, TGA, and DSC techniques. Water vapor sorption isotherms were analyzed at 25°C, 35°C, and 55°C under different relative humidity conditions to study the temperature-sensitive absorption of vapor. Enhanced water uptake was observed in the polymers with disturbed chain packing and higher free volume, primarily attributed to steric hindrances introduced by DAM along with the flexible ether linkages present in ODA. Water permeabilities as a function of water activity were measured for all samples.