Charge Dependent Dynamics of Transient Networks and Hydrogels Formed by Self-Assembled pH-Sensitive Triblock Copolyelectrolytes

Abstract

Triblock copolymers of BAB type were synthesized by ATRP with a poly(acrylic acid) central block and random copolymer end blocks containing both acrylic acid (AA) and hydrophobic n-butyl acrylate (nBA) units with varied composition of the B-blocks. Visco-elastic properties of these amphiphilic polymers were investigated by oscillatory shear measurements as a function of composition, concentration, temperature and pH. Whatever the composition for each polymer the terminal relaxation time and thus the viscosity increased sharply with decreasing degree of ionization of the AA units (α) and at low values self-supporting hydrogels were formed. However, the α- (respectively pH-) dependence of the terminal relaxation time as well as the critical range of α (respectively pH) where a transition between visco-elastic solutions and self-supporting hydrogels occurs strongly depend on the composition of the B-block.

Tuning the aggregation behavior of pH-responsive micelles by copolymerization

“…7,8 However, only a few reports exist where a stimuli responsive copolymer block forms the solvophobic block(s) of the polymer. [9][10][11][12][13][14][15][16] These novel copolymer diblocks resulted in block copolymers whose aggregation and dynamics of self-assembly could be controlled by pH allowing equilibrated structures to form.…”

Asymmetric Copolymers: Synthesis, Properties, and Applications of Gradient and Other Partially Segregated Copolymers

“…These systems form dynamic associations over a wide range of degrees of ionization, allowing fine‐tuning the pH range over which the system transforms from a low viscosity liquid to a self‐supporting hydrogel ( Figure ). By contrast, fully segregated triblock systems formed kinetically frozen associations …”

“…Dependence of the relaxation time on the degree of ionization for amphiphilic copolyelectrolytes consisting of a central poly(acrylic acid) block and terminal poly( n ‐butyl acrylate‐ co ‐acrylic acid) blocks containing 40 (red), 50 (black), or 60 (blue) mol% of AA units. Reproduced with permission . Copyright 2014, American Chemical Society.…”

ARGET ATRP of Triblock Copolymers (PMMA-b-PEO-b-PMMA) and Their Microstructure in Aqueous Solution

“…8−11 When both ends of the BAB triblock copolymers associate in dilute aqueous solution, they form a hydrophobic “B” core and a hydrophilic “A” corona with a flower-like micelle microstructure. 9,11−13 The size and morphology of the flower micelle can be tuned at the molecular level by manipulating the chemical composition, architecture, and molecular weight. 6…”