High molecular weight tail and long-chain branching in SRM 1476 polyethylene

The composition of the high molecular weight tail in the branched polyethylene standard reference material SRM 1476 was studied in detail using size exclusion chromatography coupled with a refractive index, a viscosity, and a light scattering on-line detector. The light scattering determinations of both molecular weight and radius of gyration point at a difference in kind between the molecular species below and above 106 Da. In particular, above 106 Da, increases in molecular weight resulted in a marked “densification” process. This is consistent with a greater concentration of long-chain branching and/or with a change in molecular architecture. Previous literature results for this polymer and a critical comparison of the performance of the different detectors are also discussed.