Experimental results confirm the general rules for miscible polyimide
pairs containing the hexafluoroisopropylidene group if (1) the dianhyd
ride composition is the same in each pair and (2) the diamine is chang
ed from the 3,3' (meta-substituted) 6F-diamine to the 4,4' (para-subst
ituted) GF-diamine. These rules are also applicable to end-capped poly
imide pairs. This conclusion is supported with the calculations of (ch
i) values based on the Flory-Huggins theory. We also discover two inte
resting polyimide alloys: 6FDA-PMDA-3,3'-6F-diamine/6FDA-PMDA-4,4/-6F-
d forms fully miscible blends, while 6FDA-3,3'-6F-diamine/BTDA-4,4'-6F
-diamine forms partially miscible blends (6FDA = hexafluorodianhydride
, PMDA = pyromellitic dianhydride, BTDA = benzophenonetetracarboxylic
dianhydride). These surprising results confirm that the rigidity, bond
angle, space and the length of the dianhydride can significantly affe
ct the molecular packing and miscibility tendency of polyimide blends.
Copyright (C) 1996 Elsevier Science Ltd.