Versatile Synthesis of End-Functionalized Thermosensitive Poly(2-isopropyl-2-oxazolines)

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Abstract

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 Mn 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 hydroxyl groups and subsequent hydrazine treatment. Heterotelechelic PiPrOx carrying an α-acetal and an ω-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 °C) for extended periods of time yielded polymers of well-controlled molecular weight (MW) and narrow molecular weight distribution (MWD). Analysis of the polymers by 1H and 13C 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 °C, as determined by turbidity. Thermosensitive telechelic PiPrOx offer promising applications as smart materials including bioconjugates, hydrogels, and drug carriers.

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