Precursor polymer effect on polyimide/silica hybrid nanocomposite films.

Here we report the influence of the polyimide precursor type on the surface morphology and properties of poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA PI)/silica hybrid composite films. Two types of precursor polymer were employed: poly(p-phenylene biphenyltetracarboxamic acid) (BPDA-PDA PAA) and poly(p-phenylene biphenyltetracarboxamic diethyl ester) (BPDA-PDA PES). These precursor polymers were mixed with tetraethoxysilane in the presence of HCl and H2O, which led to the precursor mixture films that contain in-situ generated silica particles via sol-gel process. Then the precursor mixture films were subject to thermal imidization to make polyimide/silica hybrid composite films. Results showed that the PAA precursor has better compatibility with silica particles, which is mainly attributed to the early making of silyl ester bonds (as evidenced by X-ray photoelectron spectroscopy) between carboxylic acid groups in the PAA and hydroxyl groups in silanol molecules. Further evidences were provided by the measurement of surface nanomorphology, crystal nanostructure, thermal/mechanical properties, and optical birefringence.