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.