6FDA-APPS

Fig. 6.6a-c. Cross section of asymmetric 6FDA-APPS membranes according to evaporation time a 15, b 120, and c 600 s. Reprinted from [8], Copyright 1997, with kind permission from Elsevier... 

Scheme 3.13 Chemical structure of 6FDA-6FAP and 6FDA-APPS-based polyimide [177],...

On the contrary, the asymmetric 6FDA-APPS membrane, which did not have -CF3 groups in the diamine structure, was not plasticized by the high CO2 pressure because of the formation of the packed structure induced by strong intramolecular interactions. From this study, they postulated that the absence of bulky -CF3 groups on aromatic diamine moiety suppresses the segmental motion of 6FDA-APPS by CO2. 

Kawakami et al. prepared dense and asymmetric membranes from 2,2 -bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and bis[4-(4-aminophen-oxy)phenyl]sulfone (APPS) by solvent evaporation (dense) and by the dry-wet phase inversion technique [47]. The surface morphology was studied by AFM. They reported that the solvent evaporation method adopted for the preparation of the dense membrane influenced the formation of nodules, while the dry-wet process in which solvent/nonsolvent exchange was involved determined the roughness of the skin layer. 

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