ABSTRACT:A new type of polyimide/silica (PI/SiO 2 ) hybrid composite films was prepared by blending polymermodified colloidal silica with the semiflexible polyimide. Polyimide was solution-imidized at higher temperature than the glass transition temperature (T g ) using 3,3Ј,4,4Ј-biphenyltetracarboxylic dianhydride (BPDA) and 4,4Ј-diaminodiphenyl ether (ODA). The morphological observation on the prepared hybrid films by scanning electron microscopy (SEM) pointed to the existence of miscible organicinorganic phase, which resulted in improved mechanical properties compared with pure PI. The incorporation of the silica structures in the PI matrix also increased both T g and thermal stability of the resulting films.

ABSTRACT:To obtain polymer-modified silica (550 nm diameter), trimethoxysilyl-terminated poly(glycidyl methacrylate-co-methyl methacrylate) with epoxy ring (to prevent the formation of carboxyl group) was successfully synthesized. Then, the cross-linking of the grafted copolymer on silica was made using ethylenediamine or hexamethylenediamine of varying alkyl chain lengths, and the stability of cross-linked silica particles was investigated in alkaline aqueous solution. Cross-linked polymer-modified silica based on diamines exhibited much lower reduction rate (in wt %) of the attached polymer to silica than uncross-linked polymer-modified silica. In particular, cross-linked silica composites by ethylenediamine had more stability than cross-linked silica composites by hexamethylenediamine. Finally, the cross-linking reaction of grafted-polymer on silica particles by diamines was confirmed by the 13 C CP/ MAS NMR spectra measured on polymer-modified silica composites.