Self-organization in aqueous solutions of thermosensitive star-shaped and linear gradient copolymers of 2-ethyl-2-oxazoline and 2-isopropyl-2-oxazoline

Abstract

Thermosensitive star-shaped eight-arm poly-2-alkyl-2-oxazolines (M = 21,000 g mol−1) was synthesized. The arms were gradient copolymers of 2-ethyl-2-oxazoline (EtOx) and 2-isopropyl-2-oxazoline (iPrOx). The more hydrophilic EtOx units prevailed near the calix[8]arene core. For comparison, model linear gradient copolymer (M = 3800 g mol−1) was investigated. For both polymers, comonomer molar ratio was 1/1. The aqueous solutions of copolymers were studied by light scattering and turbidimetry. Self-organization of linear and star-shaped molecules in solution was different, but the phase separation temperatures for these copolymers coincided. In order to find out the influence of the distribution of EtOx and iPrOx units along the arms on the behavior of star-shaped polyalkyloxazolines, the behavior of investigated stars was compared with that for stars, whose arms was block copolymers poly-2-isopropyl-2-oxazoline and poly-2-ethyl-2-oxazoline. It was shown that the phase separation temperature for gradient copolymer solutions was higher than one for block copolymers.