354 HIGH PERFORMANCE POLYMERS
15.5.2 Microporous Types
Intrinsically microporous PIs have been pre-
pared from 2,2
-diamino-1,1
-binaphthalene or 4,4
-
(9-fluorenylidene)dianiline. As anhydrides pyromel-
litic dianhydride, 3,3
,4,4
-biphenyltetracarboxylic
dianhydride, 4,4
-oxydiphthalic anhydride, and 4,4
-
(hexafluoroisopropylidene)diphthalic anhydride were
used [81].
The porosity of the PIs was determined by the sorp-
tion of nitrogen, argon, hydrogen, and carbon diox-
ide for both precipitated and cast samples. Only the
stiffest and most porous PIs could adsorb nitrogen
and argon. However, almost all polymers were able
to adsorb hydrogen and carbon dioxide.
The mode of processing of the polymers has a major
influence on the porosity. Solvent cast films