MISCIBILITY OF FLUORO-CONTAINING POLYIMIDE BLENDS

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.