Rheology of metallocene-catalyzed polyethylenes - The effects of branching

The shear and extensional rheology of three polyethylenes(PE's) synthesized using metallocene catalysts are compared. One of the PE's is linear i.e. no long-chain branches (LCB), while the other two have different amounts of long chain branching. The shear viscosity of the linear PE is reflective of the narrow molecular weight distribution of metallocene catalyzed PE's while the apparently branched PE's exhibit a higher viscosity and an earlier onset of shear thinning. The linear polymer exhibited lower activation energy than the branched PE with similar MW. The linear PE does not show stress-strain hyesteresis while the-branched polymer does. All of them show supercooling behavior.