On the Use of Indexes for Quantifying Long-Chain Branching in Polyethylene: Can We Describe the Rheology of LCB PE and Correlate it to Processing Performance by Using a Single Number?

Numerous analytical techniques and methods have been developed in the last decades, to study macromolecular architecture, especially for the case of polyethylene. The goal was to detect with an enhanced sensitivity long-chain branching (LCB) in polyethylene and accurately quantify the branching degree and structure. These studies resulted in a large number of different methods and LCB indexes (LCBI), derived mainly from rheological techniques, as well as size-exclusion chromatographic and spectroscopical measurements (GPC-MALLS, NMR). Within this work, these were applied in a series of polyethylenes, produced by various processes and catalysts, with varying mol. weight distribution and LCB concentration. The combination of GPC-MALLS, the d vs. G* plot and elongational rheology was found to be the only possibility to realistically describe the different polyethylene structures and their distribution.