Ultrasonic degradation of poly(γ-benzyl-l-glutamate), an archetypal highly extended polymer

Ultrasonic degradation provides a convenient means of studying the degradation of macromolecules in transient elongational flows. Of particular interest, because of their being a limiting architectural case, is the degradation of highly extended polymers. A classic example of a polymer with this type of architecture is poly(γ-benzyl-l-glutamate) or PBLG. Here, we monitor results of the ultrasonic degradation of PBLG using size-exclusion chromatography with a multiplicity of physical detectors. Under the given experimental conditions, the limiting molar mass (Mlim) of PBLG was found to be approximately 114,000 g/mol. The fractal dimension of PBLG, which exemplifies the highly extended nature of the macromolecule, was measured by both light scattering and viscometric means. Results from both methods demonstrated a virtual invariance in chain conformation as a function of degradation. Additional support for these observations was provided by the dimensionless ratio of the viscometric and root-mean-square radii.