Detection of low levels of long-chain branching in polydisperse polyethylene materials

Creep experiments have been applied to probe the zero-shear viscosity, η₀, of polyethylene chains directly and precisely in a constant-stress rheometer at 190°C. Such experiments, when combined with precise measurements of the weight-average molecular weight, Mw, calibrated relative to linear chains of high-density polyethylene, are shown to provide a very sensitive approach to detect low levels (0.005 branches per 1000 carbons) of long-chain branching (LCB). This detection limit is shown to be insensitive to whether the molecular weight distribution (MWD) breadth, Mw/Mn, rises from about two to ten.