Solute–solvent friction kernels and solution properties of methyl oxazoline–phenyl oxazoline (MeOx–PhOx) copolymers in binary ethanol–water mixtures

Abstract

Solvent mixtures often alter the solubility of polymeric substances. Statistical copolymers made from 2-methyl-2-oxazoline (MeOx) and 2-phenyl-2-oxazoline (PhOx) are known for their varying solubilities in pure ethanol, pure water and in binary mixtures of ethanol-water. Constrained Molecular Dynamics (MD) simulations have been carried out with an aim to explain the varying solubilities of the statistical MeOx-PhOx copolymers. The solute-solvent dynamic friction kernels calculated through constrained MD simulations corroborate the solubility pattern in these copolymers. The solvation characteristics have been analyzed in terms of the solute-solvent radial distribution functions (RDFs). The ethanol-soluble MeOx-PhOx copolymers exhibit characteristic solute-composition dependence in the dynamic solute-solvent friction kernels, indicating the strength of the solute-solvent correlations. The aggressive solvation by the ethanol molecules in the binary solvent mixtures has been brought out by the O(solute)-H(ethanol) RDFs which exhibit a characteristic dependence on the ethanol content in the solvent composition. The corresponding O(solute)-H(water) RDFs are devoid of any such composition dependence. For all the MeOx-PhOx copolymers, the O-site solvation is strongly dominated by the water molecules and the N-sites are solvated equally by both ethanol and water molecules.