Synthesis and characterization of polysiloxane-bound receptor molecules for ion-selective supported polymeric membranes

The synthesis, characterization, and membrane-transport properties of a series of benzo-15-crown-5- and p-tert-butylcalix[4]arene-substitute polysiloxanes are described. Receptor-functionalized poly(dimethylsiloxane)s, randomly substituted with up to 37 mol % calix[4]arene or benzo-15-crown-5 moieties, were prepared by polymer-analogous hydrosilylation of the corresponding omega-alkenyl-substituted receptor molecules with poly(dimethylsiloxane-co-methylhydrosiloxane) copolymers of different compositions. It was attempted to increase the degree of substitution of these copolymers to such an extent that the receptor moieties no longer form isolated clusters in the bulk but associate into closely packed percolating arrays. In this way, ion transport through supported polymeric membranes containing these polymers no longer would take place by diffusion of host-guest complexes, but by hopping of the ions from one polymer-bound receptor side to another. First insight into these phenomena could be obtained from differential scanning calorimetry and transport experiments. The investigated polymeric membranes were prepared by gel crystallization of a xylene solution containing the functionalized polysiloxane and UHMW PE in a 1:1 ratio.