ION-TRANSPORT ACROSS MEMBRANES PREPARED BY GEL CRYSTALLIZATION

A one-step procedure for the preparation of ion-selective membranes is described. The method employs the thermally induced gel crystallizati on of ultrahigh molecular weight poly(ethylene) (UHMW-PE) from a dilut e xylene solution. After evaporation of the xylene, a microporous UHMW -PE film remains, which can serve as the support for liquid and polyme ric ion-selective membranes. The addition of a membrane solvent and su itable receptor molecules to the xylene solution allows a onestep inco rporation of these membrane components into the UHMW-PE support. The i nfluence of the preparation conditions of the UHMW-PE support on the r ates of the p-tert-butylcalix[4] arene tetraethylester-mediated transp ort of NaClO4 was studied. Two concepts to improve the life-time of th e membranes are introduced. In a first approach, the addition of photo crosslinkable nitril-substituted siloxane copolymers to the membrane p hase has been evaluated. The enhanced viscosity of the membrane phase reduces leaching of carrier and solvent molecules from the membrane in to the aqueous phases. In a second approach, the solvent is omitted an d the membrane-phase merely consists of a benzo-15-crown-5 or calix[4] arene modified siloxane-copolymer, which is substituted to such a degr ee that ion transport no longer has to take place via diffusion of hos t-guest complexes but by jumping of the cations from one fixed carrier to a neighboring carrier. (C) 1998 John Wiley & Sons, Inc.