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