POLYIMIDE-SILICA GEL HYBRIDS CONTAINING METAL-SALTS - PREPARATION VIATHE SOL-GEL REACTION

A facile preparation of polyimide-silica gel hybrids by the simultaneo us in-situ formation of polyimides during the hydrolysis-condensation of tetramethoxysilane (TMOS) is reported here, The hydrolysis and cond ensation of TMOS was carried out in a solution of DMAc containing 5% L iCl, CaCl2 or ZnCl2 and the seven-membered cyclic polyimide intermedia te, The seven-membered cyclic intermediates, precursors of polyimides, were derived from the low-temperature polycondensation of dianhydride s [benzophenonetetracarboxylic dianhydride (BTDA), pyromellitic dianhy dride (PMDA), and 4,4-bis(hexafluoroisopropylidene)phthalic dianhydrid e (6FDA)] and di-isocyanates [isophorone di-isocyanate (IPDI), toluene di-isocyanate (TDI), hexamethylene di-isocyanate (HDI) and 4,4'-diphe nylmethane di-isocyanate) (MDI)]. These intermediates could readily be converted to the corresponding polyimides, Films were cast from the r esulting mixtures and the solvent was gradually evaporated at 130 degr ees C to result in the formation of clear, transparent, pale yellow or amber-colored hybrid films in which the salts were dispersed at the m olecular level. Pyrolysis of polyimide-silica gel hybrids at 600 degre es C gave mesoporous silica. Silica gel obtained from hybrids HPI-8 (c ontaining no salt) and HPI-11 (containing ZnCl2) had a pore radius (BJ H method) of 2.9 nm, while that from hybrid HPI-9 (containing LiCl) ha d a pore radius of 11.4 nm, The surface areas (BET method) obtained we re 203 m(2) g(-1), 19 m(2) g(-1) and 285 m(2) g(-1), while the pore vo lumes were 0.373 cm(3) g(-1), 0.158 cm(3) g(-1) and 0.387 cm(3) g(-1), respectively, for samples obtained from hybrids HPI-8, HPI-9 and HPI- 11. (C) 1997 by John Wiley & Sons, Ltd.