Optical and Thermal Properties of Organo-silica/Polyimide Nano-hybrids Derived from Polysiloxazane Copolymers

A new series of organo-silica/polyimide (PI) nano-hybrid materials were prepared by thermal imidization of blended precursors derived from poly (amic acid) (PAA) and polysiloxazane copolymers (DEN). 4,4'-(Hexafluoroisopropylidene) diphthalic dianhydride (6FDA) and 4,4'-diaminodiphenyl ether (ODA) were used to synthesize the PAA of a fully aromatic fluorinated PI (6FDA-ODA), and 1,2:3,4-cyclobutanetetracarboxylic dianhydride (CBDA) and ODA were chosen to prepare the PAA of semi-aromatic PI (CBDA-ODA). Compared with the traditional silica/PI hybrids prepared from sol-gel method, the novel organo-silica/PI nano-hybrids significantly improved the compatibility between PI and DEN components. The FT-IR spectra of the nano-hybrid films showed that Si?O?Si stretching peaks increased as the increase of DEN content. DEN/6FDA-ODA films exhibited higher transparency than the pristine PI, whereas DEN/CBDA-ODA films were slightly opaque due to the poor compatibility between the phenyl rings of DEN and the alicyclic CBDA structure. All the phenomena caused by the organo-silica nano- hybridization, including the slight decrease in refractive indices, the significant decrease in birefringence, and the variations in thermal diffusivity are explainable by the increase of Si?O?Si linkages which form three-dimensional cross-link networks. The DEN/PI nano-hybrids with high silica contents are promising for electronic and optical applications.