Hydrodynamic properties of A₈B₈ type miktoarm (Vergina) stars

The dilute solution properties of three (PS)₈(PI)₈ miktoarm (Vergina) stars were investigated by viscometry and dynamic light scattering in toluene and tetrahydrofuran (THF) (common good solvents), cyclohexane at 34.5 °C (theta solvent for PS and good for PI) and dioxane at 34 °C (theta solvent for PI and good for PS). Experimental intrinsic viscosity [η] and hydrodynamic radii, R_h, values in all solvents were larger for the miktoarm stars in comparison to the calculated ones using a simple model which describes the size of the copolymers as a weighted average of the sizes of the homopolymer stars with the same total molecular weight and number of arms as the copolymer. This expansion is discussed on the basis of the increased number of hetero-contacts, the topological constrains imposed by the common junction point in this highly branched miktoarm architecture and the asymmetry in molecular weights of the different kinds of arms. The conformation adopted in dilute solutions can explain, to some extent, the morphological results obtained on the same materials. The ratios of viscometric to hydrodynamic radii are consistent with previous investigations on linear and star polymers and in accord with the hard sphere model.