Novel approach of immobilization of calix[4]arene type ionophore in ‘self-plasticized’ polymeric membrane Original Research Article

The design of ion-selective membranes based on the immobilization of the calix[4]arene tetraethyl ester containing at their wider rim one polymerizable group in a linear isodecyl acrylate (IDA)/methyl methacrylate (MM) copolymer is reported. Preliminary studies were focused on an optimization of polymeric matrix based on IDA/MM copolymers to make them suitable for preparing ion-selective membranes. The effect of polymer composition (IDA:MM ratio), matrix features (glass transition temperature and molecular weight) and compatibility with electro-active components was examined. It was found that the copolymer of IDA:MM=3:7 ratio exhibited the best mechanical properties. The feasibility of the application of IDA/MM matrix for ion-selective membranes was examined using as a model ionophore, 4-tert-butyl calix[4]arene tetraethyl ester. Electrodes based on these membranes showed near theoretical sensitivity towards sodium concentration and selectivity similar to reported for classical plasticized PVC-based membranes. Methacrylamide derivative of calixarene was immobilized in IDA/MM polymer of optimized composition. Potentiometric measurements revealed that the selectivity and the slope of the response curve obtained for electrodes employing membranes with immobilized calixarene are essentially the same as for the membranes containing a free ionophore, while the lifetime was improved from 2 to 6 months.