Competitive mechanism of poly(ethylene glycol) with poly(vinyl methyl ether) in complexing water molecules revealed with elastic light scattering spectroscopy

By using elastic light scattering (ELS) spectroscopy, dependences of lower critical solution temperature (LCST) of poly(vinyl methyl ether) (PVME)/poly(ethylene glycol) (PEG) solutions on concentration (C PEG) and molecular weight of PEG were analyzed. It was found that the onset temperature of phase separation (T p) decreased with increasing C PEG or molecular weight of PEG in the solutions. It indicated that PEG was competitive with PVME in complexing water molecules. The presence of PEG disturbed the hydration layer around PVME, facilitating the aggregation of PVME chains at lower temperature. Moreover, the ELS spectra revealed the aggregation and dissociation of molecular chains in PVME/PEG solutions during one heating and cooling cycle. PVME chains aggregated above the microphase transition temperature. With further increasing temperature, PVME aggregates started to contract, and then kept stable. During cooling, the chain aggregates were not immediately swelled but gradually swelled, and began to dissociate when the solution temperature was further decreased. Finally, the conformation of the molecular chains returned to its original state.