Tuning the LCST of Poly(2-cyclopropyl-2-oxazoline) via Gradient Copolymerization with 2-Ethyl-2-Oxazoline

Poly(2-propyl-oxazoline)s can be prepared by living cationic ring-opening polymerization of 2-oxazolines and represent an emerging class of biocompatible polymers exhibiting a lower critical solution temperature in aqueous solution close to body temperature. However, their usability is limited by the irreversibility of the transition due to isothermal crystallization in case of poly(2-isopropyl-2-oxazoline) and the rather low glass transition temperatures (T-g<45 degrees C) of poly(2-n-propyl-2-oxazoline)-based polymers. The copolymerization of 2-cyclopropyl-2-oxazoline and 2-ethyl-2-oxazoline presented herein yields gradient copolymers whose cloud point temperatures can be accurately tuned over a broad temperature range by simple variation of the composition. Surprisingly, all copolymers reveal lower T(g)s than the corresponding homopolymers ascribed to suppression of interchain interactions. However, it is noteworthy that the copolymers still have T(g)s>45 degrees C, enabling convenient storage in the fridge for future biomedical formulations. (c) 2014 Wiley Periodicals, Inc.