Ion association effects and phase separation in poly(propylene oxide) modified poly(dimethylsiloxane) complexed with triflate salts

Abstract

Phase separation is observed in poly(propylene oxide) modified poly(dimethylsiloxane) (PPO-PDMS) with excess poly(propylene oxide) (PPO) when salts of MCF 3SO 3 (M = Li, Na) are added. The same behaviour is inferred for KCF 3SO 3. The solutions above and below the boundary layer have been studied by Raman spectroscopy and in particular by examining the non-degenerate, symmetric stretch ( A 1, SO 3) Raman mode of the CF 3SO − 3 anion. The upper part is siloxane rich; salt is present on both sides of the boundary layer with a much lower concentration in the upper part. The formation of the boundary layer is attributed to an increasing difference in surface tension between the PPO/salt/PPO-PDMS complexes and the separate PPO, PPO-PDMS components. The boundary layer moves up with increase in concentration. The number of ‘free’ ions decreases and ion association increases with increase in temperature. There is evidence of contact ion pairs, triplets and aggregates. Values of conductivity are quoted for 293 K.