Unique Behavior of Dendritic Macromolecules: Intrinsic Viscosity of Polyether Dendrimers

Polyether dendrimers made by the convergent growth approach are characterized by size exclusion chromatography (SEC) with coupled molecular weight sensitive detection. SEC chromatograms are as narrow as those of polystyrene with M_w/M_n ≈ 1.04 and do not broaden appreciably with increasing dendrimer generation, g. Values of M_w obtained from light scattering detection are in agreement with the molecular weights of the structures anticipated from the synthetic strategy. Intrinsic viscosity, obtained from SEC viscosity detection, passes through a characteristic maximum as a function of g while the refractive index increment appears to pass through a minimum. Hydrodynamic radii, calculated from intrinsic viscosity data, increase approximately linearly with dendrimer generation. The data are in agreement with recent simulations of Lescanec and Muthukumar that predict a maximum in intrinsic viscosity as a function of g. This suggests, but does not directly prove, that the density of these dendrimers decreases monotonically from the center.