Translating Thermal Response of Triblock Copolymer Assemblies in Dilute Solution to Macroscopic Gelation and Phase Separation

The thermal response of semi-dilute solutions (5 w/w%) of two amphiphilic thermoresponsive poly(ethylene oxide)-b-poly(N,N-diethylacrylamide)-b-poly(N,N-dibutylacrylamide) (PEO₄₅-PDEAm_x-PDBAm₁₂) triblock copolymers, which differ only in the size of the central responsive block, in water was examined. Aqueous PEO₄₅-PDEAm₄₁-PDBAm₁₂solutions, which undergo a thermally induced sphere-to-worm transition in dilute solution, were found to reversibly form soft (G′≈10 Pa) free-standing physical gels after 10 min at 55 °C. PEO₄₅-PDEAm₈₉-PDBAm₁₂copolymer solutions, which undergo a thermally induced transition from spheres to large compound micelles (LCM) in dilute solution, underwent phase separation after heating at 55 °C for 10 min owing to sedimentation of LCMs. The reversibility of LCM formation was investigated as a non-specific method for removal of a water-soluble dye from aqueous solution. The composition and size of the central responsive block in these polymers dictate the microscopic and macroscopic response of the polymer solutions as well as the rates of transition between assemblies.