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Effect of Solvent on Concentration Dependence of Hydrodynamic Volumes and GPC Elution Volumes

A novel viscometer was devised to measure flow curves of polymer melts over a wide range of shear rates. The apparatus comprises a concentric cylinder viscometer with the inner moving piston driven axially at set speeds. Immersion depth of the moving piston increases continuously during the course of an experiment. An Instron or similar piston-operated capillary viscometer can be easily modified for this purpose.

The flow behavior of a polystyrene and a polyethylene melt has been studied during extrusion through successive capillaries arranged to produce converging and diverging flow patterns through the two orifices. Laminar flow and flow instability regions were included in the experiments.

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 MW 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.