The micellar behavior of linear triblock terpolymers of styrene (S), isoprene (I), and methyl methacrylate (MMA) in selective solvents for PS and PMMA

A series of linear triblock terpolymers consisting of polystyrene (PS), polyisoprene (PI) and poly(methyl methacrylate) (PMMA) were examined in tetrahydrofuran (THF), a good solvent for all the blocks and in dimethylacetamide (DMA) and dimethylformamide (DMF), selective solvents for PS and PMMA. In DMA and DMF, which are both non-solvents for PI, multimolecular micelles were formed. The micelles were characterized by low-angle laser light scattering (LALLS), dynamic light scattering (DLS) and viscometry. The aggregation number of the triblock terpolymers was greater in DMF than in DMA, reflecting the higher non-solvent strength of DMF for PI. The aggregation number was also found to increase with increasing PI content of the terpolymers in both DMA and DMF. The hydrodynamic radii depended on the aggregation number of the micelle and the length of the corona forming PS and PMMA blocks. The complexity involved in studying a system consisting of three different polymer blocks is discussed in the context of the results obtained.