Micellization behavior of PS(PI)3 miktoarm star copolymers

We present light scattering and viscometric results from micellar solutions Of PS(PI)(3) 4-miktoarm stars (i.e. stars with chemically different arms) in two selective solvents, n-decane (selective for PI) and dimethylacetamide (DMA, selective for PS), for the different arms. A series of samples having different molecular weights and compositions were investigated in order to determine the influence of these molecular parameters as well as that of molecular architecture in the micellization behavior. Experimental results indicate that spherical micelles are formed in n-decane, a selective solvent for polyisoprene. Aggregation numbers and hydrodynamic radii of the micelles increased with increasing molecular weight and content of the insoluble component. The area of the core-corona interface per copolymer chain, A(c), was found to increase compared to the diblock case due to crowding of the three PI arms in the corona. In DMA, experimental evidence exists that points to the formation of nonspherical micelles. Aggregation numbers in this solvent are larger than n-decane. Polydispersity of the micelles is also increased. Experimental findings are discussed taking into account solvent selectivity and molecular architecture of the miktoarm stars.