On the rheological footprint of branching of polyethylene

Two types of branching are relevant in polyethylene: shortand long-chain branches (SCB and LCB, respectively), whose distinction is defined by the entanglement molar mass Me.While SCB have a very distinct effect on the crystal structure and, thus, on the solid state and thermodynamic behaviour ofpolyethylenes (which will not be discussed in detail), LCBs significantly influence the melt-state properties – the rheological properties. The effect of long-chain branching onrheological properties is very distinct in both linear and nonlinear regime. Classically, one of the main ways to detect long-chainbranching is the correlation between zero shear-rate viscosity 0 and weight-average molar mass Mw, which for linearpolymers scales with approximately 3.4, while deviations sensitive to LCB-topography are found for LCB-PE. for low and medium branching levels, higher zero shear-rate viscosityby a factor  0/  0 lin up to 100000 is found, while a high level of long-chain branching leads to a decrease of  0/ 0lin to down to 10-6 (Fig. 1) Although it would be logical, SCBs do not lead to a significant deviation from the  0-Mw-relation up tosignificant SCB-levels.1-3