Polyimide–Silica Gel Hybrids Containing Metal Salts: Preparation via the Sol–Gel Reaction

✍ Scribed by C. V. Avadhani; Y. Chujo

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 102 KB
• Volume: 11
• Category: Article
• ISSN: 0268-2605
• DOI: 10.1002/(sici)1099-0739(199702)11:2<153::aid-aoc563>3.0.co;2-w

✦ Synopsis

A facile preparation of polyimide-silica gel hybrids by the simultaneous in-situ formation of polyimides during the hydrolysis-condensation of tetramethoxysilane (TMOS) is reported here. The hydrolysis and condensation of TMOS was carried out in a solution of DMAc containing 5% LiCl, CaCl 2 or ZnCl 2 and the seven-membered cyclic polyimide intermediate. The seven-membered cyclic intermediates, precursors of polyimides, were derived from the low-temperature polycondensation of dianhydrides [benzophenonetetracarboxylic dianhydride (BTDA), pyromellitic dianhydride (PMDA), and 4,4-bis(hexafluoroisopropylidene)phthalic dianhydride (6FDA)] and di-isocyanates [isophorone di-isocyanate (IPDI), toluene di-isocyanate (TDI), hexamethylene di-isocyanate (HDI) and 4,4Ј-diphenylmethane di-isocyanate) (MDI)]. These intermediates could readily be converted to the corresponding polyimides. Films were cast from the resulting mixtures and the solvent was gradually evaporated at 130 °C to result in the formation of clear, transparent, pale yellow or amber-colored hybrid films in which the salts were dispersed at the molecular level. Pyrolysis of polyimide-silica gel hybrids at 600 °C gave mesoporous silica. Silica gel obtained from hybrids HPI-8 (containing no salt) and HPI-11 (containing ZnCl 2 ) had a pore radius (BJH method) of 2.9 nm, while that from hybrid HPI-9 (containing LiCl) had a pore radius of 11.4 nm. The surface areas (BET method) obtained were 203 m 2 g Ϫ 1 , 19 m 2 g Ϫ 1 and 285 m 2 g Ϫ 1 , while the pore volumes were 0.373 cm 3 g Ϫ 1 , 0.158 cm 3 g Ϫ 1 and 0.387 cm 3 g Ϫ 1 , respectively, for samples obtained from hybrids HPI-8, HPI-9 and HPI-11.