Effect of crosslinking distribution on gas permeability and permselectivity of crosslinked polyimides

Crosslinking modification of polyimide, prepared from 3,3'4,4'-benzophenone tetracarboxyl dianhydride (BTDA) and 2,3,5,6-tetramethyl-1,4-diphenylenedi amine (4MPDA), was performed by two methods, putting the polyimide in ambie nt environment for 4 months, and under UV irradiation for 2 or 8 h. The gas permeation properties of the crosslinked polyimides were investigated. The crosslinked polyimides induced by UV irradiation, in which crosslinking oc curs in the surface layer, are of much higher gas permselectivity of hydrog en to nitrogen than that induced by the ambient environment, in which cross linking takes place in the whole matrix, but their gas permeabilities for h ydrogen are similar. (C) 1999 Elsevier Science Ltd. All rights reserved.