Polyimide/polydimethylsiloxane block copolymers were prepared from oligoimides based on 2-aminopyridine-terminated 3,3’-oxybis(phthalic anhydride) and 1,4-bis(4-amino-alpha,alpha-dimethylbenzyl)benzene, and 3-aminopropyl-terminated oligo(dimethylsiloxane)s. Selectivity of homogeneous membranes prepared from the copolymers depends on the polydimethylsiloxane (PDMS) content : Selectivity of copolymers with up to approximately 20 wt % of PDMS is similar to that of polyimide homopolymer, whereas selectivity of copolymers containing more than 20 wt % of PDMS resembles that of pure PDMS.