1. 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 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