Controlling the Dynamics of Self-Assembled Triblock Copolymer Networks via the pH

Abstract

Triblock copolymers were synthesized by ATRP with a poly(acrylic acid) (PAA) central block and random copolymer end blocks containing both AA and n -butyl acrylate ( n BA) units. Self-assembly in aqueous solution was investigated over a wide range of concentrations. The degree of ionization of the AA units (α) was varied between 0.1 and 0.9 by varying the pH. The dynamic mechanical properties of the systems were investigated using oscillatory shear measurements. With increasing pH a transition from frozen hydrogels to dynamic networks was observed at pH = 5.2 (α = 0.30). The dynamic polymer networks behaved as viscoelastic liquids with a terminal relaxation time that decreased over 7 decades with increasing pH. This remarkable feature enables fine-tuning and control of the rheology.