The sol‐gel method was applied in the fabrication of homogenous polyhedral oligomeric silsesquioxane (HOMO‐POSS)‐derived silica membranes. Single gas permeation characteristics in a temperature range of 100–500°C were examined to discuss the effect of silica precursor on amorphous silica networks. HOMO‐POSS‐derived membranes showed a CO2 permeance of 1.1 × 10−7 mol m−2 s−1 Pa−1 with a CO2/CH4 permeance ratio of 131 at 100°C, which is a superior CO2/CH4 separation performance by comparison with tetraethoxysilane (TEOS)‐derived silica membranes. Normalized Knudsen‐based permeance (NKP) was applied for quantitative evaluation of pore size. HOMO‐POSS‐derived membranes had loose amorphous silica structures compared to TEOS‐derived membranes and pore size was successfully tuned by changing the calcination temperatures. The activation energy for a HOMO‐POSS‐derived membrane fired at 550°C with a uniform pore size of ∼ 0.42 nm increased linearly with the ratio of the kinetic diameter of the gas molecule to the pore diameter, λ (=dk/dp), and showed a trend similar to that of DDR‐type zeolite membranes. © 2011 American Institute of Chemical Engineers AIChE J, 58: 1733–1743, 2012

All siloxane-type siloxane-polyhedral oligomeric silsesquioxane [(HSiO 3/2 ) 8 , T 8 H ] copolymers were synthesized by the dehydrogenative condensation of T 8 H with diphenylsilanediol, tetraphenyldisiloxane-1,3-diol or silanol-terminated polydimethylsiloxanes in the presence of diethylhydroxylamine followed by trimethylsilylation. Coating films were prepared by spin-coating of the coating solutions prepared from the dehydrogenative condensation products. The hardness of the coating films was evaluated by a pencil hardness test and was found to increase up to 6H with increases in the curing temperature. Silica gels were prepared by concentrating the coating solution following by pyrolysis. These silica gels showed a specific surface area 449 m 2 /g at 650• C corresponding to the formation of a silica network in response to combustion of the phenyl groups.

Polyhedral oligomeric silsesquioxane (POSS) polymers were synthesized by the dehydrogenative condensation of (HSiO 3/2 ) 8 with water in the presence of diethylhydroxylamine followed by trimethylsilylation. Coating films were prepared by spin-coating of the coating solution prepared by the dehydrogenative condensation of POSS. The hardness of the coating films was evaluated using a pencil-hardness test and was found to increase up to 8H with increases in the curing temperature. Free-standing film and silica gel powder were prepared by aging the coating solution at room temperature. The silica gel powder was subjected to heat treatment under air atmosphere to show a specific surface area of 440 m 2 g −1 at 100• C, which showed a maximum at 400• C as 550 m 2 g −1 .