Temperature dependence of dynamics of solutions of triblock copolymer in a selective solvent

Abstract

The temperature dependence of dynamic properties of solutions of a triblock copolymer with polystyrene outer blocks and a middle block of fully hydrogenated polybutadiene (Mw=7.0×104gmol−1, mass fraction of PS 0.28) was studied in a selective solvent for the middle block, n-heptane. In dilute solutions, a gradual decomposition of the flower-like micelles was observed on heating. A more complex behavior was observed in semidilute solutions of the copolymer where three dynamic processes can be reliably extracted from the correlation functions. The fast mode corresponds to the collective diffusion mode of physically interconnected micelles, the broad middle mode is probably due to the tracer diffusion of polydispersed clusters (animal-like structures) formed by random association of the triblock copolymer and the slow mode is probably related to the diffusion of aggregates of insoluble polystyrene impurities. The crossover from relaxational to diffusive behavior was found for samples with c>5.5%(w/v). The scattered light intensity measurements revealed a phase transition for the solution with the concentration 4% (w/v) at a temperature of 79±2°C, which was related to the phase separation of polystyrene homopolymer present in a small amount in the copolymer used.