Synthesis and properties of low‐color polyimide/silica hybrid films

Abstract A series of polyimide precursors, poly(amic acid)s, containing propyltrimethoxysliane at two chain ends were prepared from 4,4′‐bis(4‐amino‐2‐trifluoromethylphenoxy)biphenyl ( I ) with six commercially available dianhydrides, followed by end‐capping with 3‐aminopropyltrimethoxysilane (APrTMOS). A new class of fluorine‐containing polyimide/silica composite films ( III ) with chemical bonds between the fluorinated polyimide backbone and the silica network has been synthesized from the APrTMOS‐terminated precursors with tetramethoxysilane via the sol‐gel process and thermal cyclodehydration. The resultant hybrid films were light‐colored, flexible, and tough. They had high levels of thermal stability associated with high glass‐transition temperatures (>251°C), 10% weight‐loss temperatures in excess of 527°C, and char yields at 800°C in nitrogen higher than 60%. For a comparative study, the analogous nonfluorinated polyimide/silica hybrid films ( III′ ), based on 4,4′‐bis(4‐aminophenoxy)biphenyl ( I′ ), and the neat fluorinated polyimide films ( IV ), based on diamine I , were also synthesized and characterized. The hybrid films of the fluorinated series III showed a higher transparency and less color intensity when compared with the nonfluorinated III′ analogs. They also revealed a lower refraction index and birefringence than pure polyimides ( IV ). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 4046–4052, 2007