Gas separation properties of triptycene-based polyimide membranes

Abstract

Tuning of free volume element distributions and sizes in polymers is technologically important because of various applications such as microelectronics (e.g., low dielectric materials), gas storage (e.g., organic adsorbents) and membrane-based gas separation technology (e.g., high permeable, selective polymers). Here we demonstrate that the polymer design via a three-dimensional rigid structure having internal void space can create a number of free volume elements in semi-rigid or rigid glassy polymers, which help improve fast, selective mass transport. To achieve it, we considered an iptycene-based monomer, i.e., triptycene, for polymer material design, as a result, leading to the formation of high fractional free volume with proper cavity size to separate small gas molecules with high selectivity as well as high permeability. Due to rigid structure of triptycene with tiny internal free volume elements, the resultant polyimides show high glass transition temperature of 352 °C and excellent thermal stability as well as solution processibility owing to good solubility in common organic solvents used in chemical industries. We believe that this kind of polymer design will provide keen insight on the development of processable polyimides having fine microporous structures on sub-nanometric scales for high performance glassy polymer applications.