Thermosensitive Molecular Brushes With Alternating Polyoxazoline Side Chains: Synthesis, Characterization, and Solubilization Properties

Abstract

Using the “grafting through” approach, alternating polymer brushes with different lengths of the backbone and side chains are synthesized. Thermosensitive poly(2-ethyl-2-oxazoline) and poly(2-isopropyl-2-oxazoline) with styrene and maleimide moieties are used as the macromonomers. The prepared polymer brushes are characterized by molar masses in the range of 19,000–52,000 g·mol⁻¹ and have a low dispersity Ð = 1.6–1.9. The number of side chains is from 10 to 20. The LCST behavior of alternating brushes in aqueous solutions is studied by light scattering and turbidimetry. Phase separation temperatures of aqueous solutions of alternating polymer brushes are varied from 37°C to 48°C depending on the length and number of the side chains, as well as on the polymer molar mass. The critical micelle concentrations depend on molar mass and the side chain length, changing from 1.12 × 10⁻⁵ to 9.40 × 10⁻⁴ mol·L⁻¹, as established by the method of solubilization of a hydrophobic dye. Using the Benesi–Hildebrand method, the binding constants for curcumin and polymer brush samples are determined; their values range from 360 to 63,400 L·mol⁻¹. It is shown that curcumin is effectively bound by polymer brush molecules in the aqueous solutions, which ensures the solubilization of hydrophobic curcumin in water.