Synthesis and pH-sensitive micellization of doubly hydrophilic poly(acrylic acid)-b-poly(ethylene oxide)-b-poly (acrylic acid) triblock copolymer in aqueous solutions

摘要

A doubly hydrophilic triblock copolymer poly (acrylic acid)-b-poly(ethylene glycol)-b-poly(acrylic acid) (PAA-b-PEO-b-PAA) with M_w/M_n= 1.15 was synthesized by atom transfer radical polymerization of t-butyl acrylate (tBA), followed by acidolysis of the PtBA blocks. The pH-sensitive micellization of PAA-b-PEO-b-PAA in acidic solution was investigated by potentiometric titration, fluorescence spectrum, dynamic light scattering and zeta potential. The pK_a was 6.6 and 6.0 in deionized water and in 0.1 mol/L NaCl solution, respectively. The copolymer formed micelles composed of a weakly hydrophobic core of complexed PAA and PEO and a hydrophilic PEO shell in 1 mg/mL solution at pH<5.5 due to hydrogen bonding. The critical micelle concentration was 0.168 mg/mL at pH 2.0. At pH<4.5, steady and narrow distributed micelles were formed. Increasing pH to 5.0, unsteady and broad distributed micelles were observed. At pH>5.5, the micelle was destroyed owing to the ionization of the PAA blocks.