Versatile synthesis of end-functionalized thermosensitive poly(2-isopropyl-2-oxazolines)

The synthesis of several end-functionalized poly(2-isopropyl-2-oxazolines) (PiPrOx) has been achieved via cationic ring-opening polymerization of 2-isopropyl-2-oxazoline. Poly(2-isopropyl-2-oxazolines) bearing primary amino groups at one chain end (Me-PiPrOx-NH2, with M. ranging from 3600 to 9700) were obtained by conversion of hydroxyl-terminated poly(2-isopropyl-2-oxazolines) (Me-PiPrOx-OH) via phthalimide activation of the hydroxl groups and subsequent hydrazine treatment. Heterotelechelic PiPrOx carrying an alpha-acetal and an omega-hydroxyl group (acetal-PiPrOx-OH) were prepared via cationic ring-opening polymerization of 2-isopropyl-2-oxazoline initiated with 3,3-diethoxy-1-propyl tosylate. The polymerizations carried out under mild conditions (40-45 degreesC) for extended periods of time yielded polymers of well-controlled molecular weight (MW) and narrow molecular weight distribution (MWD). Analysis of the polymers by H-1 and C-13 NMR spectroscopy, ion-exchange HPLC, and MALDI-TOF mass measurements indicated that nearly quantitative end-functionalization was achieved in all cases. Aqueous PiPrOx solutions (10 mM PBS (pH 7.4) containing 150 mM NaCl) possess a cloud point temperature near 37 degreesC, as determined by turbidity. Thermosensitive telechelic PiPrOx offer promising applications as smart materials including bioconjugates, hydrogels, and drug carriers.