Abstract
Hereunder a report is presented of measurement made of the viscoelastic properties of concentrated solutions of star-shaped polystyrenes. From the frequency dependence of the storage shear modulus G' and loss modulus G" the characteristic parameters in terminal zone, such as zero-shear viscosity η0 and steady-state compliance Je0, have been evaluated. The dependence of these parameters on the concentration have been discussed and compared with those of concentrated solutions of linear polystyrenes.
For the star polymers, the zero-shear viscosity reduced to the iso-free volume state, f=0.0608, is proportional to (w2ρ)6 and (w2ρ)1 at higher and lower concentrations, respectively, than the critical concentration, where w2ρ is the concentration in g/ml. The critical concentration for entanglement was evaluated to be 0.23g/ml for the star-shaped polystyrene having the molecular weight of 407000. The concentration dependence of steady-state compliance of the solutions of star polymer can be divided into three parts. The steady-state compliance is proportional to (w2ρ)-1 at low concentrations below 30wt%and to (w2ρ)-2 in the concentration range from 30 to 70wt%. In both the regions, Je0 is proportional to the molecular weight. At higher concentrations, Je0 increases rapidly passing through the minimum at about 70wt% but is independent of molecular weight. The molecular weight dependece of Je0 in the entanglement region and its rapid increase at extremely higher concentrations for the star polymers are quite different from those for linear polymers described in our recent papers. The entanglement compliance JeN0 of the solution of star polymers is proportional to (w2ρ)-2 above the critical concentration, which is similar to that of linear polymer.
