Long chain branching (LCB) in polyethylene is one of the key microstructures that controls processing and final properties. Gel permeation chromatography (GPC) with viscometer (IV) and/or light scattering (LS) has been intensely used to quantify LCB. The widespread method to quantify LCB from GPC with IV or LS is the method of LCB frequency (LCBf) based on the Zimm-Stockmayer (ZS) random branching model. In this work, the conventional approach was compared with the recently developed method, called gpcBR. The comparison of the sensitivity of both methods is made on highly branched polymer, that is, various grades of commercial LDPE and also on polymer with very low level of LCB, that is, a commercial HDPE with no LCB, converted into several branched test samples of gradually increasing LCB by multiple extrusion. Finally, the linkages of LCB quantities from both methods to the rheological data and processing properties are illustrated. The new gpcBR index can access lower LCB level and shows obviously better relationship with both rheological data and processing properties than LCBf from the conventional ZS model.

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Ethylene/1‐olefin copolymers with controlled bimodal molecular weight distributions (MWDs) and chemical composition distributions (CCDs) have improved mechanical and rheological properties. In this work, the Stockmayer's distribution was used to develop a criterion for CCD bimodality. The proposed criterion was validated theoretically using simulation data and experimentally using crystallization analysis fractionation (CRYSTAF) and crystallization elution fractionation (CEF) of ethylene/1‐octene copolymer blends. The effect of mass fraction and number average molecular weight of copolymer produced with each metallocene catalyst on CCD bimodality was also examined. The proposed criterion was then used as a benchmark for describing cocrystallization effects in both CRYSTAF and CEF techniques.