Polyolefin Microstructure Characterization Using 3D-GPC-TREF, 2005 PLACE Conference

Gel permeation chromatography (GPC) separates polymers by size, and therefore provides a measure of polymer molecular weight distribution (MWD). Since long chain branching (LCB) adds to molecular weight more than to molecular size, adding a light scattering (LS) and a viscosity detector to GPC in the form of 3D-GPC also becomes a tool to detect polymer LCB and LCB distribution. However, GPC separation is insensitive to polymer short branching (SCB). For SCB distribution, we use the temperature rising elution fractionation (TREF) technique. TREF relies on the crystallization and dissolution process to separate polymers that have different levels of SCB. Adding a LS and a viscosity detector to TREF makes it possible to detect the molecular weight (MW) dependency across the polymer SCB distribution. Therefore, a fully automated hybrid system of 3D-GPC-TREF is a very effective tool for analyzing polymer branching architectures. Such structural information is highly useful to complement the thermal analyses and the rheological results for studying many areas of polymer interests where the understanding of polymer structure-property relationship is of central importance. The following examples of problem-solving application will be discussed: LCB differences between tubular and autoclave low density polyethylene (LDPE); LCB effect on draw down, neck-in, and heat seal of LDPE in coating application; reverse MW-SCB dependency of linear low density polyethylene (LLPDE); and “gel” versus “un-melt” issues in high density polyethylene (HDPE) films.