1. INFLUENCE OF CHAIN CONFORMATION ON MECHANOCHEMICAL DEGRADATION OF POLYMERS IN TRANSIENT ELONGATIONAL FLOWS André M. Striegel – Department of Chemistry & Biochemistry, Florida State University
Ultrasonic degradation of poly(-benzyl-L-glutamate), PBLG
Studying the ultrasonic degradation of PBLG allows one to explore
a polymer at the highly-extended limit of macromolecular architecture.
Furthermore, ultrasonic degradation is strictly analogous, from both
fluid mechanics and kinetics points-of-view, to the degradation
observed in other types of transient elongational flow (TEF) scenarios.
To date, our studies have demonstrated that Mlim, the limiting molar
mass beyond which polymers do not degrade in TEF, is ~114 Kg/mol
for PBLG in DMAc/LiCl. This is show in the top figure. Also shown in
this figure are the large changes that occur in the molar mass
distribution of PBLG during degradation. These are accompanied by
changes in the molar mass averages and in the size of the polymer.
The figure below plots a dimensionless size parameter, the ratio of the
viscometric and root-mean-square radii, as a function of sonication time.
Plotted also are the hard sphere limit and results for cellulose and linear
random coil polystyrene, both obtained under the same experimental
conditions as PBLG. PBLG displays the lowest value of the size
parameter, exemplifying the highly extended nature of the polypeptide.
Also, the size parameter is seen to remain relatively constant as a
function of sonication. This indicates that, while the polymer
experiences extensive changes in size, molar mass, etc., its
highly extended structure remains invariant.