POTENTIOMETRIC PROPERTIES OF ION-SELECTIVE ELECTRODE MEMBRANES BASED ON SEGMENTED POLYETHER URETHANE MATRICES

Potentiometric responses of polyurethane (PU)-based membranes containi ng valinomycin and varying amounts of plasticizer (DOA) and/or lipophi lic additive (KTpClPB) were examined as a function of soft segment [po l(tetramethylene ether glycol)] contents in aromatic diisocyanate-base d PU matrices. Upon increasing the weight percentages (w(soft)) of sof t segments, which in part behave like a built-in plasticizer, providin g the matrices with rubbery structure (glass transition temperature be low -58 degrees C), the amounts of DOA and/or KTpClPB necessary to res ult in near-Nerntian response (e.g., slope > 50 mV/decade) to potassiu m were substantially lowered, The apparent effect of adding plasticize r to PU-based membranes was comparable to that resulting from an incre ase of free carrier concentration in normal PVC-based membranes. Owing to the chemical interaction between mobile anionic sites and methane chains, plasticizer-free PU membranes could be prepared with the PU ma trices with high soft segment contents (w(soft) greater than or equal to 60 wt %). PUs composed of 60 less than or equal to w(soft) < 80 wt % were recommended as the matrix for fabricating ISE membranes with no or low plasticizer content.