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 (nBA) 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.

Self‐assembly and responsiveness of polypeptide‐based block copolymers: How “Smart” behavior and topological complexity yield unique assembly in aqueous media

“…105,106 Assembly Behavior of BAB Linear Triblock Copolymers with a Responsive Polypeptide Inner Block The aqueous self-assembly behavior of linear triblock BAB copolymers has been evaluated widely for synthetic coilcoil-coil type systems. [107][108][109][110][111] These type of systems are reported to aggregate into sunflower micelles, enabled by molecular bending of a flexible middle block, in dilute solution. 108,111 At higher concentrations, these systems often form network structures from the association of corona chains between micelles resulting in hydrogelation.…”

“…108,111 At higher concentrations, these systems often form network structures from the association of corona chains between micelles resulting in hydrogelation. 107,109,110,112,113 A few studies have been devoted to self-assembly of coil-rod-coil BAB triblock copolymers containing a functionalized, hydrophilic gold nanorod center FEATURE ARTICLE block and hydrophobic coil outer blocks. [114][115][116] This category of amphiphilic molecules exhibited self-assembly into ''doughnut-like" supramolecular barrels (similar to toroid micelles), as a result of stiffness from the center block.…”

Highlighting the Role of the Random Associating Block in the Self-Assembly of Amphiphilic Block–Random Copolymers

“…31 Their diblock architecture leads to the formation of well-defined aggregates, whereas the randomness of the associating block allows finetuning of the self-assembling properties. 32−36 The block− random architecture has been used by Bendejacq, 37 Wright, 38 Gotzamanis, 39 and ourselves 40,41 to control the structure or dynamics of self-assembly of amphiphilic block copolymers. In our research group we have studied diblock and triblock copolymers consisting of a pure hydrophilic poly(acrylic acid) (PAA) block connected, respectively, to one or two associating random blocks of n-butyl acrylate (nBA) and acrylic acid (AA): P(nBA (1−x) -stat-AA x ) 100 -b-PAA 100 (DHx) and P(nBA ( 40,41 Pure PnBA-b-PAA diblocks formed frozen aggregates 42,43 unable to exchange unimers due to the strong hydrophobic character of the pure PnBA block, but DHx and THx formed aggregates with exchange rates that could be controlled by the pH.…”

“…32−36 The block− random architecture has been used by Bendejacq, 37 Wright, 38 Gotzamanis, 39 and ourselves 40,41 to control the structure or dynamics of self-assembly of amphiphilic block copolymers. In our research group we have studied diblock and triblock copolymers consisting of a pure hydrophilic poly(acrylic acid) (PAA) block connected, respectively, to one or two associating random blocks of n-butyl acrylate (nBA) and acrylic acid (AA): P(nBA (1−x) -stat-AA x ) 100 -b-PAA 100 (DHx) and P(nBA ( 40,41 Pure PnBA-b-PAA diblocks formed frozen aggregates 42,43 unable to exchange unimers due to the strong hydrophobic character of the pure PnBA block, but DHx and THx formed aggregates with exchange rates that could be controlled by the pH. 40,41 Although preliminary results 44 highlighted the importance of x, the amount of charged units within the hydrophobic block of THx copolymers, there has been to the best of our knowledge only one investigation of the relationship between the selfassembly of a block−random copolymer (A-co-B)-b-B and that of its random associating block (A-co-B) by itself.…”

Facile fabrication method of hydrophobic-associating cross-linking hydrogel with outstanding mechanical performance and self-healing property in the absence of surfactants

“…Theoretically, a string of flowers, even macroscopic network with hydrophobic cores as cross-linking points, can occur by increasing the concentration of amphiphilic multiblock copolymers [19] Taking advantage of the concept of the self-assembly of amphiphilic multiblock copolymer, some supermolecular gels based on low-molecularweight block copolymer gelators and physical cross-linking hydrogel via hydrophobic-associating interaction in the presence of surfactants (HA gels) have been successfully realized [20,21]. However, the complicated synthesis process of multiblock copolymers and the extremely poor mechanical property of macroscopic self-assembled hydrogels limit their development.…”