Dynamic Rheological Behavior of Copolymerized Linear Low-Density Polyethylenes: Effect of Molecular Weight and Its Distribution

The change of storage moduli (G′), loss moduli (G″), zero shear viscosity, and complex viscosity were studied for a series of butene and hexene copolymerized linear low-density polyethylenes (LLDPEs) with various characteristics by investigating the dynamic rheological behaviors. It was found that: (1) the dependence of the complex viscosity on the weight average molecular weight did not follow the Raju equation; (2) the slopes of the G′～ω and G″～ω curves in the low-frequency regions not only were smaller than those of the polymers with monodisperse molecular weight, but also decreased with the relative molecular weight increasing or its distribution broadening; (3) the dynamic storage moduli G′ were more sensitive to the shear rate than the dynamic loss moduli G″; (4) the change of the dynamic moduli was directly correlated with the orientation and disorientation of the chain segments, which is influenced by the frequency or shear rate, the temperature, the molecular weight, and the molecular weight distribution; and (5) the comonomer types showed little effect on the frequency dependence of the dynamic moduli at different temperatures.