Synthesis of stimuli responsive PEG47–b-PAA126–b-PSt32 triblock copolymer and its self-assembly in aqueous solutions

An ABC type amphiphilic triblock copolymer poly(ethylene glycol)–b-poly(acrylic acid)–b-poly(styrene), PEG47–b-PAA126–b-PSt32, was successfully synthesized by reversible addition–fragmentation chain transfer (RAFT) controlled radical polymerization, and was characterized by 1H NMR and gel permeation chromatography (GPC). The pH and salt responsive micellization of the copolymer in aqueous solution was studied using dynamic light scattering (DLS) and cryogenic-transmission electron microscopy (Cryo-TEM). The micelle is composed of a hydrophobic PSt core, PAA shell and PEG corona with hydrodynamic size (Dh) of ∼80 nm independent of the copolymer concentration at 30 °C and pH = 3.5. The complexation results from collapse of the polymer chains, which is induced by the contraction of PAA chains and the enhanced association between PAA and PEG chains. The changes in the Dh of micelles at different pH and in the presence of two salts, sodium sulfate (Na2SO4) and calcium chloride (CaCl2) are reported. Both salts increase Dh; CaCl2 interacts with PAA and Na2SO4 with PEG, making the respective polymer block less hydrophilic. We further find that in presence of the cationic surfactant dodecyltrimethylammonium bromide (DTAB), micelle size decreased. Such stimuli-responsive block copolymers may be attractive candidates as “smart” pH- and salt-responsive drug delivery systems.