pH-Controlled Rheological Properties of Mixed Amphiphilic Triblock Copolymers

Aqueous mixtures of pH-sensitive block random BAB triblock copolymers with different hydrophobic B blocks connected to the same hydrophilic A block were studied in order to investigate comicellization and the impact on the dynamic mechanical properties. The B blocks were statistical copolymers of acrylic acid (AA) and n-butyl acrylate (nBA) with varying AA contents, whereas the A block was a pure PAA. Neat triblocks self-assembled into transient networks for which the mechanical relaxation time depended both on the AA content within the B blocks and on the pH, which affected the ionization of the AA units. Static and dynamic light scattering measurements were done on mixtures of equivalent AB diblock copolymers that showed that comicellization occurred only at conditions at which both copolymers considered separately self-assemble. When comicellization occurred, the characteristic escape time of both types of B blocks from the mixed hydrophobic cores impacted the rheological properties of the binary triblock mixture. Using binary mixtures of BAB triblock copolymers exhibiting pH-controlled dynamics thus allows control and fine-tuning of the viscoelastic properties at constant pH by formulation without the need to synthesize a large number of different polymers. Moreover, the more dynamic B blocks were slowed down in the presence of the less dynamic ones, and vice versa, so that a frozen network could be transformed into a transient one by coassembly with very dynamic chains.