Molecular Ball Bearings: The Unusual Melt Viscosity Behavior of Dendritic Macromolecules

摘要

The melt viscosity behavior of dendritic macromolecules has been investigated for the first time. For a family of dendritic polyether macromolecules based on 3,5-dihydroxybenzyl alcohol, the melt viscosity is primarily a function of molecular weight. Examination of the variation in melt viscosity with molecular weight has revealed a unique profile with no critical molecular weight, M_c, being observed with molecules having a molecular weight as high as 85 000 amu. At high molecular weights, a value for a of ca. 1.1 is obtained, which is consistent with the premise that branching and surface congestion prevent significant entanglements between separate dendritic macromolecules resulting in "ballbearing-like" molecules capable of only interdigitation and not true entanglements. We are currently extending this work to the study of the melt viscosity behavior of hybrid linear-dendritic macromolecules.