Samadi, F., Wolf, B.A., Yifei, G., Zhang, A., Schlüter, A.D.
"Branched versus Linear Polyelectrolytes: Intrinsic Viscosities of Peripherically Charged Dendronized Poly(methyl methacrylate)s and of their Uncharged Analogues"
Macromolecules 2008, 41, 8173-8180.
Abstract: Viscosities of dilute solutions were measured for four generations of peripherically charged dendronized poly(methyl methacrylate)s (CDPs) of two different chain lengths in water (no salt added) and of their uncharged analogues (UCPs) in chloroform. In all cases it was possible to describe ln (h solution/h solvent) as a function of polymer concentration by two adjustable parameters: a hydrodynamic interaction parameter B and [h ], the intrinsic viscosity of the polymer. The [h ] values for the first generation of polyelectrolytes are markedly lower (given number of monomeric units) than that of aqueous solutions of Na-polystyrene sulfonate reported earlier, despite the fact that each monomeric unit is much larger and bears two charges instead of one; as the number of generation rises, [h ] falls markedly for the CDPs as well as for the UCPs, where the effect is considerably more pronounced for the polyelectrolyte. The increase in molar mass M associated with the addition of dendrons leads to a maximum in the molar hydrodynamic volume [h ] M for the second generation of the CDP; in case of the UCPs this volume increases steadily. The interaction parameter B is normally positive but may for the higher generations become negative, corresponding to a more than exponential augmentation of h with polymer concentration. A consistent description of the findings is presented in terms of intra- and intermolecular interactions between the -NH and -O- groups of the dendrons and the distances of the charges from the polymer backbone.
preprint number: 292