| There is considerable need for the development and practical application of methods that can elucidate structural and dynamical changes associated with polymer degradation and aging. By using a suite of nuclear magnetic resonance (NMR) techniques, this thesis aims to address modification at the polymer-inorganic interface that results from radiation exposure and its associated macroscopic, structural consequences.;First, a methodology is described that allows for the spatial resolution of structural properties in these materials via 1H relaxation measurements and stray-field imaging (STRAFI). A material-specific calibration curve is generated that relates the residual 1H dipolar coupling, Dres, to the material's shear modulus, G'. Using a model "heterogeneous" sample, a sandwich of three homogeneous irradiated samples, we show that the Dres/G' correlation can be applied successfully to image shear modulus heterogeneities. Reliable performance, despite poorly optimized STRAFI conditions, is demonstrated with an error of no more than 22% between the calculated shear modulus and the measured value via DMA.;Traditional 1H relaxation analyses rely on largely empirical expressions containing a large number of (often arbitrary) independent variables. The resulting ambiguity can be circumvented largely by developing models of NMR observables that are based on basic polymer physics. To this end, we present an alternative expression that derives from the concept of the Gaussian polymer chain and compare its results to several other possible functions.;By using 29Si{1H} cross-polarization techniques we also discuss changes to the polymer-filler interface and propose a model commensurate with macroscopic data and previously-published work on similar composite materials. In this model, we propose that low levels of radiation result in a disruption of the polymer-filler interactions that dictate to a large degree the material's structural properties. At high dosages we observe behavior consistent with polymer chemisorption at the filler surface. |
