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

Abstract

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.

Characterizing Long Chain Branching in Polypropylene

“…The theory behind the measurement of long chain branching with 3D‐GPC is based on the reduction of intrinsic viscosity and radius of gyration of a polymer chain with LCB when compared to a linear reference with the same molar mass. The difference in the slope of the Mark‐Houwink plot (Log IV × Log M) and conformation plot (Log Rg × Log M) between the linear and the branched sample is directly related to the amount of LCB, as an effect of the more compact form assumed by the branched chains …”

“…A new branching parameter, gpcBR, has been recently introduced to analyze LCB by 3D‐GPC and was also used in this study . The new parameter gpcBR is based on the differences obtained by conventional, viscometer and light scattering detectors.…”

“…Understanding the role of LCB in relation to the properties of these materials is of great academic and industrial interest . A well‐defined characterization technique for LCB capable of discriminating small LCB content differences is required to support the polymer design development …”

Analysis of Propylene‐1‐Butene Copolymer Composition by GPC with Online Detectors

“…Among them, the gpcBR index, developed by Yau et al, [31] achieves high precision and has been applied to detection of very low level of long chain branching (LCB) in PE. [32] Given that the comonomer level in a copolymer affects the coil size as the LCB does, it can be anticipated that the gpcBR index should also be useful to study the chemical composition in copolymers. In the case of P-B copolymers, the difference in size of the two constituent monomers is small, so the high sensitivity and precision of gpcBR makes it a potentially suitable method.…”

Simplified Robust Triple Detection Methods for High Temperature GPC Analysis of Polyolefins

“…Initially this gpcBR index was conceived as a bulk material property, sensitive to the presence of branching. The main purpose of developing this gpcBR index was to have a high precision index useful to detect branching, calculated from the more reliable quantities available from a triple detector GPC experiment …”