Sorption and transport of small gas molecules in thermally rearranged (TR) polybenzoxazole membranes based on 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane (bisAPAF) and 4,4′-hexafluoroisopropylidene diphthalic anhydride (6FDA)

• Published in: Journal of membrane science 2013-08, Vol.441, p.1-8
• Main Authors: Kim, Seungju, Jo, Hye Jin, Lee, Young Moo
• Format: Article
• Language: English
• Subjects: Applied sciences; artificial membranes; carbon dioxide; diffusivity; Dual mode sorption; equations; Exact sciences and technology; Exchange resins and membranes; Forms of application and semi-finished materials; hydrogen; methane; nitrogen; oxygen; permeability; Polybenzoxazole; Polymer industry, paints, wood; polymers; solubility; Solubility coefficient; Solution diffusion model; sorption; sorption isotherms; Technology of polymers; Thermally rearranged
• ISSN: 0376-7388; 1873-3123
• DOI: 10.1016/j.memsci.2013.03.054

The gas solubility of thermally rearranged polybenzoxazole (TR-PBO) membranes and precursor polymer membranes was determined for five representative small gas molecules, H2, N2, O2, CH4, and CO2, at 35°C and pressures up to 23atm. Precursor membranes that thermally rearranged to TR-PBO were prepared from 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane (bisAPAF) and 4,4′-hexafluoroisopropylidene diphthalic anhydride (6FDA) using three different imidization methods. Sorption isotherms of TR-PBO followed the dual-mode sorption model, which is regarded as a typical model for glassy polymers. The Henry's law coefficient (kD), Langmuir affinity parameter (b), and Langmuir capacity parameter (C′H) were determined using the dual-mode sorption equation. During the thermal rearrangement process, excess free volume in the polymer membrane matrix increased and improved molecular transport was observed. A similar trend of increasing solubility was observed during the thermal rearrangement process. The gas permeability and diffusivity of TR-PBO membranes were also studied using the solution–diffusion model. •Two-fold increase in solubility coefficients of TR-polymers.•Ten-fold increase in the diffusivity and permeability coefficients of TR-polymers.•The permeability increase in TR-polymers due to enhanced free volume elements.