Effect of molecular structure on the linear viscoelastic behavior of polyethylene

The effects of weight-average molecular weight (M-W) and short and long chain branching on the linear viscoelastic behavior of polyethylene land ethylene-alpha-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 (M-e) was obtained. A solution property based technique for quantifying levels of long chain branching well below 1 LCB/10(4)C in polyethylene is presented. Also, the applicability of C-13 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 that was not present for the Linear polyethylene with the same MWD.