Preparation of microporous carbon films from fluorinated aromatic polyimides

Pyrolysis and carbonization behaviors of fluorinated aromatic polyimide films synthesized from fluorinated dianhydrides and diamines were investigated by thermogravimetric and mass spectrometric measurements. Evolution of fluorine compound gases and related species was observed during the pyrolysis in the temperature range from 450 to 700 °C, in addition to the evolution of CO and CO2 due to the imide ring degradation. By the carbonization of these fluorinated polyimides at 600–1000 °C, highly microporous carbons were obtained without any activation process, of which adsorption/desorption isotherm of N2 gas was typical type I and pore size distribution was sharp at around 0.55 nm in width. Surface area increased with increasing fluorine content in the repeating unit of fluorinated polyimide: the polyimide with the highest fluorine content of 31.3 mass% gave a high microporous surface area of 1342 m2 g−1 and micropore volume of 0.44 mL g−1.