Abstract
Potentiometric responses of polyurethane (PU)-based membranes containing valinomycin and varying amounts of plasticizer (DOA) and/or lipophilic additive (KTpClPB) were examined as a function of soft segment [poly(tetramethylene ether glycol)] contents in aromatic diisocyanate-based PU matrices. Upon increasing the weight percentages (w(soft)) of soft segments, which in part behave like a built-in plasticizer, providing the matrices with rubbery structure (glass transition temperature below -58 °C), the amounts of DOA and/or KTpClPB necessary to result in near-Nerntian response (e.g., slope > 50 mV/decade) to potassium were substantially lowered. The apparent effect of adding plasticizer to PU-based membranes was comparable to that resulting from an increase of free carrier concentration in normal PVC-based membranes. Owing to the chemical interaction between mobile anionic sites and urethane chains, plasticizer-free PU membranes could be prepared with the PU matrices with high soft segment contents (w(soft) ≥ 60 wt %). PUs composed of 60 ≤ w(soft) < 80 wt % were recommended as the matrix for fabricating ISE membranes with no or low plasticizer content.
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