A study of LCST behavior is used to show that ion-dipole interactions can lead to truly thermodynamic miscibility in polymers which are immiscible in their absence. Blends of polystyrene (PS) ionomers with poly(propylene oxide) (PPrO) at low PPrO contents are miscible at low temperatures: they undergo phase separation and become opaque upon heating but recover their transparency upon cooling. The degree of miscibility enhancement (related to the strength of the interaction) can be compared in different systems by comparing the positions of the cloud point curves. Thus, an increase in the ion content of the PS ionomer shifts the cloud point curve to higher temperatures. A decrease in the counterion size in the PS ionomer (i.e., K > Na > Li) also increases the strength of the interaction and leads to an upward shift of the cloud point curves. The effect of molecular weight is similar to that seen in nonionic blends. The phase separation is a relatively fast process in a blend of styrene containing 10.4 mol % lithium methacrylate copolymer (S-0.104MAA-Li) mixed with PPrO and is completely reversible; a decrease in the ion content or an increase in the radius of the counterions slows down the phase-separation process and is accompanied by incomplete recovery of transparency upon cooling. This suggests that the lower the Miscibility the slower the phase separation process. Transparency measurements are also used to compare the strengths of the interactions between PS ionomers and PPrO on the one hand and PS ionomers and poly(ethylene oxide) (PEO) on the other. Finally, the relative strengths of ion-dipole interactions and of hydrogen bonds are also compared by transparency measurement.
All Science Journal Classification (ASJC) codes
- Organic Chemistry
- Polymers and Plastics
- Inorganic Chemistry
- Materials Chemistry