Effect of polydispersity in polystyrene on stress relaxation

Abstract

Abstract Stress relaxation master curves are presented for twenty‐three polystyrene samples whose weight‐average molecular weights M w varied from 20,800 to 310,000 and whose heterogeneity indices varied from 1.0 to 15.92. The maximum relaxation times τ m , the associated partial modulus E m , and the flow viscosity η were determined for these samples at 115°C. It is shown that at 115°C. the relation log τ m (minutes) = −15.10 + 3.4 M w is obeyed. It is also shown that the quantity α B = τ m E m /η correlates with the heterogeneity index of the sample. It is concluded that stress relaxation studies can be used to obtain weight‐average molecular weights and also to provide a qualitative measure of the heterogeneity index.