Crystallization of Poly(2-isopropyl-2-oxazoline) in Organic Solutions

The crystallization of polymers from organic solvents is a common phenomenon. Poly(2-isopropyl-2-oxazoline) (PIPOx) is known to crystallize in aqueous or aqueous/organic solvent solutions. This process is associated with the dehydration of polymer chains above the polymer’s lower critical solution temperature (LCST). In this work, the ability of PIPOx to crystallize in nonaqueous media is presented. The annealing of a solution of PIPOx in organic solvents, such as acetonitrile, dimethyl sulfoxide, or propylene carbonate, leads to the precipitation of insoluble material. DSC and WAXS studies confirm the formation of a crystalline phase in the solution, with the degree of crystallinity dependent on the solvent and the polymer concentration. SEM analysis reveals micron-sized fibril structures of the PIPOx crystalline fraction. The glass transition temperature (T g) and the melting temperature (T m) of PIPOx crystallized in organic solutions are equal to those of the polymer crystallized in bulk. The enthalpy of melting (ΔH) of the PIPOx crystalline fraction versus its degree of crystallinity (χc) is shown. The value of the enthalpy of melting for hypothetical, fully crystalline PIPOx (ΔH 100%) is determined.