INFLUENCE OF CHAIN CONFORMATION ON MECHANOCHEMICAL DEGRADATION OF POLYMERS IN TRANSIENT ELONGATIONAL FLOWS André M. Striegel – Department of Chemistry & Biochemistry, Florida State University On-Column, Flow-Induced Polymer Degradation During their flow through packed chromatographic media, macromolecules typically experience shear rates on the order of 104-105 sec-1, comparable to the shear rates generated during such industrial processes as gasoline engine lubrication, blade coating, or pigment milling. It is thus not surprising that ultra-high molar mass polymers, i.e., polymers of molar mass greater than 1 million g/mol, degrade during chromatographic analysis. The figures to the right show how a narrow polydispersity (Mw/Mn = 1.03) linear polystyrene of M  2 million g/mol degrades in (top) the interstitial medium of an SEC column and (middle) when the polymer has access to both the interstitial medium and the pores of the column packing material. In all cases, elution volume is plotted on the abscissa and detector response on the ordinate. The bottom figure shows the elution profiles of the same polystyrene, this time degraded under the action of ultrasonically-created transient elongational flows. The bottom set of profiles differs markedly from the top and middle set. This difference indicates that the flows responsible for macromolecular degradation in packed liquid chromatographic media are most likely steady-state elongational flows, with transient elongational and/or shear flows contribution only minorly to the degradation. Interstitial Interstitial + Pore Ultrasonic