Journal of Polymer Science Part A: Polymer Chemistry, Vol.55, No.8, 1383-1396, 2017
Temperature and pH Dual Stimuli Responsive PCL-b-PNIPAAm Block Copolymer Assemblies and the Cargo Release Studies
A new atom transfer radical polymerization (ATRP) initiator, namely, 2-(1-(2-azidoethoxy)ethoxy) ethyl 2-bromo-2-methylpropanoate containing both "cleavable" acetal linkage and "clickable" azido group was synthesized. Well-defined azido-terminated poly(N-isopropylacrylamide)s (PNIPAAm-N-3)s with molecular weights and dispersity in the range 11,00019,000 g mol(-1) and 1.20-1.28, respectively, were synthesized employing the initiator by ATRP. Acetal containing PCL-b-PNI-PAAm block copolymer was obtained by alkyne-azide click reaction of azido-terminated PNIPAAm-N3 with propargyl-terminated PCL. Critical aggregation concentration (CAC) of PCL-b-PNIPAAm copolymer in aqueous solution was found to be 8.99 x 10(-6) M. Lower critical solution temperature (LCST) of PCL-b-PNIPAAm copolymer was found to be 32 degrees C which was lower than that of the precursor PNIPAAm-N-3 (36.4 degrees C). The effect of dual stimuli viz. temperature and pH on size and morphology of the assemblies of PCL-b-PNIPAAm block copolymer revealed that the copolymer below LCST assembled in spherical micelles which subsequently transformed to unstable vesicles above the LCST. Heating these assemblies above 40 degrees C led to the precipitation of PCL-b-PNIPAAm block copolymer. Whereas, at decreased pH, micelles of PCL-b-PNIPAAm copolymer disintegrate due to the cleavage of acetal linkage and precipitation of hydrophobic hydroxyl-terminated PCL. The encapsulated pyrene release kinetics from the micelles of synthesized PCL-b-PNIPAAm copolymer was found to be faster at higher temperature and at lower pH. (C) 2017 Wiley Periodicals, Inc.