Synthesis of novel star-shaped calix[4]arene-based poly(2-oxazoline)s and study of their complexation with curcumin

A novel grafting-onto approach was applied to the synthesis of star-shaped poly(2-alkyl-2-oxazoline)s with macrocyclic calix[4]arene core. Cationic polymerizations of 2-ethyl-2-oxazoline and 2-isopropyl-2-oxazoline were terminated using calix[4]arene tetrahydrazide as a multifunctional termination agent. Molecular-weight and structural characteristics of obtained four-arm star poly(2-alkyl-2-oxazoline)s were determined by size exclusion chromatography and light scattering. The thermosensitivity of aqueous solutions of obtained star polymers was studied. Cloud points, determined for 1% wt. aqueous solutions were equal to tcp50% = 27.5 degrees C for CA4-PiPrOx and tcp50% = 73.1 degrees C for CA4-PEtOx. Critical micelle concentrations of aqueous solutions of star polymers were determined using UV-Vis absorption spectroscopy, they were equal to 2.20 x 10-4 g/mL for CA4-PEtOx and 1.68 x 10-4 g/mL for CA4-PiPrOx. It was shown that studied poly(2-alkyl-2-oxazoline)s form water-soluble complexes with hydrophobic curcumin. The composition of curcumin-polymer complexes and their stability in aqueous solutions were studied using UV-Vis absorption spectroscopy. Obtained Job's plots indicated the formation of bimolecular curcumin-polymer complexes. Binding constants of curcumin by studied calixarene-centered star polymers were equal to (5-7)x 104 L/mol.