Results on the Correlation between Molecular Architecture and Rheological Parameters of Metallocene-Catalyzed Polyethylenes

Abstract

Dynamic rheological results of 17 commercial and noncommercial metallocene-catalyzed polyethylenes, such as shear thinning index(SHI), modulus of crossover point of store modulus and loss modulus (Gco) and flow activation energy(Ea), are presented. The effects of molecular weight distribution(MWD), and degree of short chain branching (SCB) determined by gel permeation chromatography (GPC) and FTIR, were analyzed. Plots of SHI versus MWD revealed the influence of branching level on the shear thinning behavior of polyethylenes. Gcowas observed scaling with MWD for metallocene-catalyzed polyethylenes and the correlation between them was generated by MWD=193378*Gco. Correlation between flow activation energy measured by dynamic temperature sweep at low frequency and short chain branch-0.9038was also established for metallocene polyethylenes as SCB=7*10-8*Ea6.024. Thus, an alternative single rheological method, based on the effect of molecular structural parameters on dynamic rheological behaviors, was proposed to evaluate the polydispersity and short chain branching of metallocene-catalyzed polyethylene.