Entanglement density of polymers is important characteristic of long chain molecules that largely determines melt viscoelasticity, the strength of interfacial adhesion in polymer composites, and dynamic and fracture properties among other critical aspects of macromolecular morphology and material performance. Two structural characteristics affect the entanglement density: 1) the primary chemical structure of polymer chains and 2) the molecular architecture, both of which are typically defined by the number- and weight-average molecular weight of polymer chains (Mn and Mw), molecular weight distribution, and the amount, average length and distribution of long chain branches. Several methods have been applied for the quantification of the entanglement density including numerous rheological methods, neutron spin-echo experiments, and NMR relaxation methods among computational treatments via Monte Carlo simulations. The aim of the present study is to revisit the characterization of entanglement density in polyethylene melts by studying a series of well-defined, high molecular weight polyethylene materials via transverse NMR relaxometry at 150oC. The comparison of the relaxometry data with high temperature SEC-MALLS characterization allows the measurement and correlation of the fraction of chain-end fragments by two independent methods. As compared with rheological methods that measure volume average characteristics, the NMR method described here offers advantages for studying entanglement molecular weight (Me) and chain dynamics in entangled polyethylene melts due to the high selectivity to dynamics of entangled chain fragments and disentangled chain end blocks.  

Chain entanglements in polyethylene melts: Why it is studied again?

245th National Meeting (2013)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.