Solution Properties of Architecturally Complex Multiarm Star Diblock Copolymers in a Nonselective and Selective Solvent for the Inner Block

In comparison to the behavior of linear block copolymers, much less is known about the structure and properties of highly branched polymeric materials. Motivated by this, the solution properties of a series of 26- and 40-arm polystyrene–poly(2-vinylpyridine) (PS–PVP) star diblock copolymers of different weight-average molecular weight (Mw) and styrene to 2-vinylpyridine (S/V) ratios are studied. These stars are investigated in tetrahydrofuran (THF), a thermodynamically good solvent for both blocks, and in toluene, a solvent that is selective for the inner PS blocks. It is found that in both THF and toluene, the 26- and 40-arm stars remain dispersed as unimolecular star block copolymers across the concentration range studied, 0.001< c < 10.0 mg/mL. The hydrodynamic radius, Rh, increases with PS Mw and number of arms, with the stars of highest Mw and number of arms having the largest Rh. The characteristic ρ ratio, Rg/Rh, is ∼1.0, suggesting that these stars do not behave as homogeneous hard spheres, but ra...