Silica-containing fluorinated poly(amide-imide) hybrid films

New silica-containing hybrid films were prepared using a fluorinated poly(amide-imide) having hydroxyl groups and tetraethoxysilane, via the sol–gel technique. The polymer was synthesized by solution polycondensation reaction of a mixture of two diamines, 4,4′-diamino-4′′-hydroxy-triphenylmethane and 1,3-bis(4-aminophenoxy)benzene (molar ratio 3/7), with a fluorinated diacid chloride containing imide rings, 2,2-bis[N-(4-chloroformylphenyl)phthalimidyl]hexafluoroisopropane. To improve the compatibility between the polymer and silica, the pendant hydroxyl groups of the polymer were reacted with 3-(triethoxysilyl)propyl isocyanate. The hybrid films were flexible, tough, and exhibited high thermal stability, having the initial decomposition temperature above 420 °C. The surface morphology of the hybrid films was investigated by scanning electron microscopy. Dynamic mechanical analysis and dielectric spectroscopy revealed subglass transitions, γ and β, and an α relaxation corresponding to the glass transition temperature. Electrical insulating properties were evaluated on the basis of dielectric constant and dielectric loss and their variation with the frequency and temperature. The values of the dielectric constant at 10 kHz and 20 °C were in the range of 3.18–3.48. The influence of the silica content on the polymer properties was examined.