Pinnau et al present the pristine and thermally rearranged gas separation membranes.
A novel o-hydroxyl-functionalized spirobifluorene-based diamine monomer, 2,2′-dihydroxyl-9,9′-spirobifluorene-3,3′-diamine (HSBF), was successfully prepared by a universal synthetic method. Two o-hydroxyl-containing polyimides, denoted as 6FDA-HSBF and SPDA-HSBF, were synthesized and characterized. The BET surface areas of 6FDA-HSBF and SPDA-HSBF are 70 and 464 m2 g−1, respectively. To date, SPDA-HSBF exhibits the highest CO2 permeability (568 Barrer) among all hydroxyl-containing polyimides. The HSBF-based polyimides exhibited higher CO2/CH4 selectivity than their spirobifluorene (SBF) analogues (42 for 6FDA-HSBF vs. 27 for 6FDA-SBF) due to an increase in their diffusivity selectivity. Polybenzoxazole (PBO) membranes obtained from HSBF-based polyimide precursors by thermal rearrangement showed enhanced permeability but at the cost of significantly decreased selectivity.
Pristine and thermally-rearranged gas separation membranes from novel o-hydroxyl-functionalized spirobifluorene-based polyimides by Xiaohua Ma, Octavio Salinas, Eric Litwiller and Ingo Pinnau* Polym. Chem., 2014,5, 6914-6922.
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