Comprehensive and Accurate Control of Thermosensitivity of Poly(2-alkyl-2-oxazoline)s via Well-Defined Gradient or Random Copolymerization

The lower critical solution temperature (LCST) of the poly(2-alkyl-2-oxazoline)s (POx) was precisely tuned over a broad range of temperatures via the well-defined gradient or random copolymerization between 2-n-propyl-2-oxazoline (nPrOx) and either 2-isopropyl-2-oxazoline (iPrOx) or 2-ethyl-2-oxazoline (EtOx). All the copolymerizations were cationically initiated by methyl p-tosylate at the optimum condition (42 °C in acetonitrile) for the living polymerization, resulting in an extremely narrow molecular weight distribution (Mw/Mn ≤ 1.05). It was determined from the composition analysis by 1H NMR and MALDI−TOF mass spectrometry that the respective monomer reactivity ratios were found to be 3.15 and 0.57 for nPrOx and iPrOx, respectively, sufficiently different to form the gradient copolymers P(nPrOx-grad-iPrOx), and 1.28 and 1.04 for nPrOx and EtOx, respectively, indicating the favorable formation of the random copolymers P(nPrOx-ran-EtOx). Both gradient and random copolymers followed a simple and practic...