Properties of Binary Polyimide Blends Containing Hexafluoroisopropylidene Group

Abstract

Binary polyimide (PI) blends with hexafluoroisopropylidene (-C(CF3)2-) group were prepared using three poly(amic acid) solutions derived from 4,4′‐hexafluoroisopropylidene diphthalic anhydride (6FDA), 4,4′‐oxydianiline (ODA), p‐phenylenediamine (PDA), and pyromellitic dianhydride (PMDA). Films of both blends: PI6FDA‐ODA/PI6FDA‐PDA and PI6FDA‐ODA/PIPMDA‐ODA were transparent, suggesting their homogeneity. Miscibility behavior of these polyimide pairs were characterized by DMA. The existence of single Tgs, intermediate to those of the component polyimides, indicated the blends miscibility. The introduction of the ‐C(CF3)2‐ group in the molecular structure of polyimides was found to significantly affect the optical and dielectric properties of respective polyimides and their blends. It was observed that the increase of fluorine content led to an increase in optical transparency and decrease in refractive index and dielectric constant. Thermal resistance of these polymers, based on decomposition profiles, was investigated by thermogravimetry (TG). These polyimide pairs showed good thermal stability with decomposition temperatures (10% wt loss) up to 554°C in air.