A novel dual stimuli-responsive thiol-end-capped ABC triblock copolymer: synthesis via reversible addition-fragmentation chain transfer technique, and investigation of its self-assembly behavior

Abstract

A novel thermo- and pH-responsive thiol-end-capped ABC triblock copolymer, namely poly(acrylic acid)-block-poly(N-isopropylacrylamide)-block-poly(epsilon-caprolactone)-SH (PAA-b-PNIPAAm-b-PCL-SH), was synthesized using a combination of ring-opening polymerization and reversible addition-fragmentation chain transfer polymerization techniques. The chemical structures of all samples were characterized by means of Fourier transform infrared and H-1 NMR spectroscopies. The molecular weight of each segment was investigated using both H-1 NMR spectroscopy and gel permeation chromatography. The self-assembly behavior of the PAA-b-PNIPAAm-b-PCL-SH triblock copolymer under thermal and pH stimuli was fully investigated by means of fluorescence and UV-visible spectroscopies as well as dynamic light scattering measurements. The critical micelle concentration for the synthesized triblock copolymer was determined to be 0.0178 g L-1 using the fluorescence probe technique. The average size of PAA-b-PNIPAAm-b-PCL-SH micelles was determined to be 25 nm using transmission electron microscopy observations, and its lower critical solution temperature was determined to be 41-43 degrees C using UV-visible spectroscopy. (c) 2017 Society of Chemical Industry