Size exclusion chromatography

Abstract

Size exclusion chromatography (SEC) separates macromolecules according to their hydrodynamic volume and has become the dominant method for the determination of molecular weight or mass distribution (MWD or MMD) of synthetic polymers [1].Crystalline polyolefins as polypropylene (PP) with high tacticity and copolymers of propylene with ethylene and/or higher α-olefins containing sufficiently long isotactic PP blocks can only be dissolved under conditions (solvent/temperature) which cause complete melting of the crystalline domains. Therefore, SEC of PP and crystalline copolymers of propylene must be carried out at elevated temperatures which requires the special equipment of ‘high-temperature SEC (HT-SEC)’ which is commercially available from several sources, e.g. Millipore-Waters Corp. (Milford, MA, USA) and Polymer Laboratories Ltd (Church Stretton, Shropshire, UK).Keywordssize exclusion chromatography (SEC)molecular weight distribution (MWD)universal calibrationhomopolymercopolymerSchulz-Flory distributionWesslau distributioncontrolled rheology grademetallocene gradepeak broadeningweight average molecular massnumber average molecular mass