Stress Relaxation Behaviours of Blends of Monodisperse Polystyrenes

Abstract

This report covers the study of the rheological properties of polymers by stress relaxation method, especially on the effect of molecular weight and molecular weight distribution on relaxation spectra by Procedure X. Monodisperse polystyrenes and blends of them were used for the experiment.The following results were obtained:(1) The box portion of relaxation spectrum gives information on the molecular weight distribution of the polymer. Stress relaxation technique has been found to be convenient to the determination of molecular weight distribution.(2) In case of blends of monodisperse polystyrenes of molecular weights being larger than the critical molecular weight, MC, the maximum relaxation time, τm, is proportional to 3.4 powers of the mean values of the weight average molecular weight of these blends, Mw, as previously reported for monodisperse polystyrene. At the same time, however, τm has been found proportional to 2.0 powers of the average values of number average molecular weight, Mn, even when their molecular weights are lower than MC. This result is one of the important conclusion of this work.(3) The polymer with a molecular weight lower than MC acts like a plasticizer, so the wedge portion as well as the box portion in the relaxation spectrum shifts to the shorter τ region.