Solution rheology of hyperbranched polyesters and their blends with linear polymers

The rheological properties of different generations of hyperbranched polyesters in 1-methyl-2-pyrrolidinone solvent and their blends with a poly(2-hydroxyethyl methacrylate) are examined in this study. All the hyperbranched polyester solutions exhibit Newtonian behavior, with steady shear viscosities independent of shear rate. This indicates the absence of physical entanglements in these systems. In addition, solution viscosities are found to be only slightly affected by the different generations of the hyperbranched polymer. The polyesters have very small intrinsic viscosities, and their hydrodynamic radius scales as R-h similar to M-0.39, suggesting a less packed structure than dendrimers. All generations of the hyperbranched polyesters also show comparable apparent activation energies of now over the temperature range studied. Replacing linear polymers with hyperbranched polymers causes large reductions in the blend viscosities. This behavior can be attributed to the decrease in both the number of physical entanglements between linear polymers and the blend's intrinsic viscosity upon addition of the hyperbranched polymer.