Correlations between the Characteristic Rheological Quantities and Molecular Structure of Long-Chain Branched Metallocene Catalyzed Polyethylenes

Abstract

Different rheological quantities, such as the zero shear-rate viscosity η0 and the linear steady-state elastic compliance J e 0 of long-chain branched metallocene-catalyzed ethene homopolymers and ethene-/α-olefin copolymers with a polydispersity M w /M n ≈ 2, were correlated with the molar mass M w and degree of long-chain branching λ. A linear reference for the δ(|G * |) plot was used to show the effect of long-chain branches on this rheological property. The linear steady-state elastic compliance J e 0 correlated with the zero shear-rate viscosity increase factor η0/η0 lin and the characteristic phase angle δ c . However, the latter only works when compensating for the influence of the molar mass on J e 0 by the relationship between J e 0 and M w established elsewhere (Stadler and Münstedt, JoR, 2008). The characteristic phase angle δ c and zero shear-rate viscosity enhancement factor η0/η0 lin are linked to each other by the linear dependencies for the type I and type II viscosity functions.

Complex interplay of short- and long-chain branching on thermal and rheological properties of ethylene/α-olefin copolymers made by metallocene catalysts with oscillating ligand structure

“…While it was not possible to determine the zero shear-rate viscosity η 0 of any of the materials within the time of stability ( Figure 6), it is clear that η 0 is larger than the maximum viscosity measured η max . Figure 7 clearly shows that all data are located significantly above the η 0 -M w -relation for linear materials, [39] which has been established as an indicator for sparsely long-chain branched polymers, [41][42][43] including polyethylene [14,[44][45][46][47].…”

“…LCBs are hard to be distinguished by traditional characterization methods such as NMR, instead, they can cause significant deviation in rheological properties from their linear counterparts, namely, the zero-shear rate viscosity, terminal relaxation time and temperature dependency of rheological parameters are considerably altered [14][15][16]. Many researchers have, therefore, used these rheological fingerprints to assess the microstructure and to determine the LCB-content and topography [14,[17][18][19].…”

Deriving comprehensive structural information on long-chain branched polyethylenes from analysis of thermo-rheological complexity

“…For polyethylene, the deviation from the relation between zero shear-rate viscosity η0 and weight average molar mass Mw valid for linear materials has proven to be useful for the detection of LCBs, especially because this correlation is relatively insensitive to comonomer content within the technologically relevant range and because tacticity does not play a role for PE [26][27][28][29][30][31][32][33][34][35][36][37]. In the last years, the analysis of the complex modulus, viscosity, and compliance as a function of time or shear rate/frequency dependencies as well as the analysis of relaxation spectra have added knowledge to the behavior of LCB-PE [34,[37][38][39][40][41][42][43][44][45][46][47][48][49]. Other quantities used for the rheological analysis of LCB-PE include the recoverable compliance [43,47,[50][51][52][53][54] and the strain-hardening in elongation induced by long-chain branches [16,[55][56][57][58][59].…”

Methods of long chain branching detection in PE by triple‐detector gel permeation chromatography

“…Remarkably, thanks to the GPC advantage of focusing only on the high- Comparison of LCB from 3D-GPC and Rheology-The High LCB Case of the Janzen-Colby Plot 15 Besides 3D-GPC, another widely used method to determine LCB is rheology. 15,[17][18][19] Here, the comparison between the LCB from 3D-GPC and the rheology was reported. The rheology LCB index, called LCBi, is defined in the following equation.…”