Phase Behavior of Precision Polyelectrolyte/Polyether Blends

In this work we studied the miscibility of a blend of poly(ethylene oxide) (PEO) and a precision polystyrene analogue with five-carbon phenyl spacing that is converted into a polyanion by functionalizing the phenyl groups with lithium-form (trifluoromethyl)sulfonylimide. Blends were found to be miscible at high to moderate polyanion concentration ranging from 10 to 70 wt% PEO. However, as the polyanion became more dilute (90 wt% PEO and beyond) visible, macroscopic phase separation was observed. Differential scanning calorimetry was used to study trends in the primary and secondary phase transitions of each blend to better understand the phase boundaries and interactions underpinning the phase behavior. The glass transition temperature (Tg) of each blend was measured as a function of composition. A single Tg was identified at each composition. Within the miscible range, the Tg values were well fit by the Gordon-Taylor model, but significant disagreement between model and experiment was observed for two-phase blends (>90 wt% PEO). Furthermore, a clear linear relationship between melting point depression and wt% PEO was visible for all miscible, semicrystalline blends apart from those in the miscibility gap. These findings give an empirical compliment to modeling efforts that show that complicated phase diagrams can arise due to ion presence and long-range electrostatic interactions in charged polymer blends.