Comments on the measurement of long chain branching by size exclusion chromatography

Summary A technique for measuring long chain branching as a function of polymer molecular weight uses SEC with a low angle laser light scattering (LALLS) detector to compare M_W of an eluting species with the molecular weight of the linear counterpart that has the same retention time. This technique is correct only if all species in the SEC detector cells have the same constitution. Evidence is presented that indicates that this condition prevails for low density, high pressure polyethylene and polyvinyl alcohol. Alternative forms of data representations are suggested. A major uncertainty in the data treatment is the value to be assigned to the ratio of radii of gyration of linear and branched polymers with the same molecular weight. A method is suggested to measure this ratio directly, as a function of molecular weight, if the eluting species at any instant are uniform in branching character.