Temperature-responsive star-shaped poly(2-ethyl-2-oxazoline) and poly(2-isopropyl-2-oxazoline) with central thiacalix[4]arene fragments: structure and properties in solutions

Temperature-responsive star-shaped poly(2-ethyl-2-oxazoline) (star-PETOX) and poly(2-isopropyl-2-oxazoline) (star-PIPOX) with arms grafted to the lower rim of thiacalix[4]arene were studied in solutions by viscometry, sedimentation velocity, light scattering, and small-angle neutron scattering. The experiments were carried out in water and tetrahydrofuran solutions. It was revealed that in tetrahydrofuran, the studied polymers were present only as individual molecules, while in aqueous solutions, in addition to individual molecules, large polymer aggregates were found. Molecular characteristics of the star-PETOX and star-PIPOX samples were estimated; their behavior in tetrahydrofuran and water was studied over a wide temperature range. It was established that a cloud point of the aqueous solution of star-PETOX (67 degrees C) is higher than that of a solution of star-PIPOX (35 degrees C). Comparison of the data obtained by dynamic light scattering and small-angle neutron scattering turned out to be fruitful in revealing all the structural levels of the organization of star-PETOX and star-PIPOX in aqueous solutions. They include the level of the individual macromolecules and the level of supramolecular organization with a star-like architecture.