Abstract
The purpose of this thesis is to detail the study of the mechanochemical degradation of a semi-flexible, highly-extended polymer, in order to create a benchmark of quantitative data for use by future investigators interested in discerning the effect of polymer conformation on the mechanochemical degradation of polymers. Polymer conformation is known to vary in solution from a random coil to a highly extended or semi-flexible conformation. To date, there are not sufficient data to explain the role that polymer conformation might play in the degradation of polymer chains as a result of sufficient applied mechanical stresses. It seems plausible that the rate, extent, and, possibly, the mechanism of polymer degradation could all be related to the conformation of a polymer in solution. This thesis will describe the results of a controlled ultrasonic polymer degradation experiment on the highly extended polymer poly(ã-benzyl-L-glutamate), PBLG. It is hypothesized that ultrasonically irradiating a solution of PBLG dissolved in N,N-dimethyl acetamide (DMAc) with 0.5% lithium chloride will produce substantial polymer degradation attributed to both the relatively high molar mass and to the rather extended state of the polymer. According to accepted theory, the degradation process should occur in a non-random fashion with near mid-chain scission and should continue until reaching a threshold known as Mlim, the limiting molar mass. The conformation of the polymer was monitored over the course of ultrasonic degradation using multi-detector size-exclusion chromatography including static multi-angle light scattering, refractometric, and viscometric detection. Because of the extended nature of the polymer, a priori reasoning was that the fractal dimensions calculated from both the light scattering and viscometric data should be similar and that both should remain invariant as a function of increased degradation. The PBLG conformation data, in the form of a dimensionless size parameter, was compared to previously published data for a random coil, linear polystyrene degraded under the same experimental conditions, to illustrate and quantify the additional information obtained from the degradation of a highly extended polymer such as PBLG.
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