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Size-exclusion chromatography coupled to multiangle light scattering (SEC-MALS) has been used to detect long-chain branching (LCB) in polyethylene (PE) from Cr/silica catalysts for the first time. The observed LCB response to several catalyst and reactor variables mostly confirms earlier conclusions drawn from rheological measurements. However, SEC-MALS has also shed additional light on a few previously unanswered questions. Above all, SEC-MALS shows the placement of branching within the MW distribution, which was not previously known, and which may explain some of the unique molding behavior of Cr-derived PE. This new SEC-MALS data also provide insight into the mechanism of LCB formation, which is discussed. Like earlier studies based on rheology, this new study demonstrates that the commonly accepted view of macromer incorporation may be overly simplistic. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 |
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