Characterization of fluorinated polyimide morphology by transition mechanical analysis.

We report the thermal transition and concomitant morphology change of polyimide films, investigated through dynamic mechanical analyses, thermo-mechanical analyses, and X-ray diffraction spectroscopy. For this study, highly transparent polyimide films composed of 3,4,3′,4′-biphenyltetracarboxylic dianhydride and fluorinated diamines, 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl, are prepared through a solvent-casting method. The films are annealed at different temperatures, and two kinds of reaction solvents (n-methyl-2-pyrrolidone and N,N-dimethylacetamide) for the polyimide precursors are compared. The mechanical analyses during thermal transition along with spectroscopic measurements reveal unusual transition behaviors and morphology differences between the polyimide films at various annealing temperatures. The results can be applied to the quantitative analysis of the imidization ratio in highly imidized polyimides when the films are imidized thermally at temperatures above 300 °C. [ABSTRACT FROM AUTHOR]