Abstract
Three new isomeric 6FDA-based polyimide-ionenes, with imidazolium moieties and varying regiochemistry (para-, meta-, and ortho- connectivity), and composites with three different ionic liquids (ILs) have been developed as gas separation membranes. The structural-property relationships and gas separation behaviors of the newly developed 6FDA polyimide-ionene + IL composites have been extensively studied. All the 6FDA-based polyimide-ionenes exhibited good compatibility with the ILs and produced homogeneous hybrid membranes with the high thermal stability of ~380 °C. Particularly, [6FDA I4A pXy][Tf2N] ionene + IL hybrids having [C4mim][Tf2N] and [Bnmim][Tf2N] ILs offered mechanically stable matrixes with high CO2 affinity. The permeability of CO2 was increased by factors of 2 and 3 for C4mim and Bnmim hybrids (2.15 to 6.32 barrers), respectively, compared to the neat [6FDA I4A pXy][Tf2N] without sacrificing their permselectivity for CO2/CH4 and CO2/N2 gas pairs.
Highlights
Polyimides (PIs) have been extensively considered as materials for gas separation membranes because of their excellent mechanical and thermal stability as well as their intrinsic separation properties, for CO2 /CH4 and CO2 /N2 separations [1,2,3]
1 H-NMR and 13 C-NMR were utilized for structural confirmation of the monomers and polyimide-ionenes
All derivatives support the incorporation of the Tf2 N– anion (SO2 stretching vibrations at 1180 and 1050 cm−1, SNS stretching at 725 cm−1, CF3 stretching at 1370 cm−1 ), incorporated in the backbone of the neat polymers and the counter ion of all three imidazolium ionic liquids [33,38]
Summary
Polyimides (PIs) have been extensively considered as materials for gas separation membranes because of their excellent mechanical and thermal stability as well as their intrinsic separation properties, for CO2 /CH4 and CO2 /N2 separations [1,2,3]. Research into the structure-property relationships of PIs with the aim of developing enhanced gas separation application membranes has mainly focused on (1) the inclusion of flexible or contorted substituent groups into the PI backbone to enhance processability [4,5,6], (2) the incorporation of bulky and polar groups in order to improve the permeability/selectivity tradeoffs [7,8], (3) the enhancement of the inter-chain packing density and the dimensions of free volume elements [9,10], and (4) the improvement of the thermal and mechanical resistance of such membranes to harsh environments [11,12,13].
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