Composite membranes containing a thin-film layer of aromatic polyimides (PI
) ensure an advantageous combination of selectivity and permeability in gas
separation. A series of rigid-chain PI with different chemical structures
were studied as a thin active layer. Composite membranes were prepared by c
oating a solution of poly(amic acid) (PAA) and an imidization catalyst on a
poly(phenylene oxide) (PPO) support with pores filled by decane. The subse
quent stage of solid-state catalytic transformation of the PAA/PPO membrane
into the PI/PPO membrane determines the specific structure of the PI layer
and the transport properties of the PI/PPO composite membranes. The struct
ure of composite membranes was determined by scanning electron microscopy a
nd analyzed in the terms of the resistance model of gas transport in compos
ite membranes. (C) 2000 John Wiley & Sons, Inc.