Effect of Molecular Structure on the Linear Viscoelastic Behavior of Polyethylene

Abstract

The effects of weight-average molecular weight (MW) and short and long chain branching on the linear viscoelastic behavior of polyethylene (and ethylene−α-olefin copolymers) are described. Short chain branching had no effect up to a comonomer (butene) content of 21.2 wt %. The zero shear viscosity of the linear polyethylenes scaled in the expected manner with MW. Using a high molecular weight, narrow molecular weight distribution (MWD), linear polyethylene, an estimate of the plateau modulus and molecular weight between entanglements (Me) was obtained. A solution property based technique for quantifying levels of long chain branching well below 1 LCB/104C in polyethylene is presented. Also, the applicability of 13C NMR for measuring such LCB levels is demonstrated. For metallocene polyethylene, long chain branching (LCB) increased the zero shear viscosity as compared to that of a linear material of the same molecular weight. LCB also broadened the relaxation spectrum by adding a long time relaxation mode ...