Department of Energy Engineering, College of Engineering, Hanyang University, Seoul, 04763, Republic of Korea
School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive NW, Atlanta, Georgia 30332, United States
Thermally rearranged (TR) polymers have shown outstanding gas transport properties due to their rigid polymer structure. Additionally, bulky fluorinated substituents, such as hexafluoroisopropylidene, have enhanced the gas permeability of TR polymers. Herein, the role of the fluorinated content in TR polymers in terms of their microporous structure and gas separation performance was investigated by controlling fluorine content via either a copolymerization or a polymer blending approach. A series of TR copolymers and TR polyblends were successfully prepared via post-fabrication of their precursors of copolyimides or polyimide blends, respectively. All of the precursor polyimides exhibited an imide-to-benzoxazole thermal cyclization reaction around 400 °C, regardless of the fluorinated unit contents and polymer preparation methods. The microporosity and gas permeability of the polymers were enhanced by TR conversion and the presence of hexafluoroisopropylidene moieties due to the rigid polymer backbone and the bulky units. Furthermore, the TR polymer blends exhibited distinctive thermomechanical properties with two distinct glass transition temperatures and improved gas transport properties compared to the corresponding TR copolymers synthesized from the same starting monomers. In this study, the TR polymer blend containing 90% fluorinated diamine, TR-Blend-AH91, showed the highest gas permeability (P(CO2) = 603 Barrer) among the TR polymers in this work.