GAS PERMEABILITIES OF POLYMERS WITH INDAN GROUPS IN THE MAIN-CHAIN - 2 - POLYIMIDES

Permeability coefficients and ideal selectivities for H-2, CO2, O-2, a nd N-2 were determined for two series of polyimides with indan groups in the main chain. The bulkiness of the indan group was varied by repl acing methyl groups at the indan ring system by bulky cyclohexyl group s. The effects of the linking group in the dianhydride part of the pol ymer repeating unit could be explained on the basis of bulkiness and f lexibility. However, the introduction of two cyclohexyl substituents a t the indan group to increase the bulkiness of this structural element had no uniform effect on permeability coefficients and selectivities. Positive or negative effects were observed, depending on the linking group in the dianhydride moiety. This was tentatively attributed to th e conformational flexibility of the cyclohexyl rings, which can result in different sterical requirements. (C) 1998 Elsevier Science B.V.