Intermolecular Structure and Dynamics in Multicomponent Glasses

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Polymeric glasses serve as the basis for many strong, lightweight materials. The engineering properties of these materials and the processing characteristics can be modified and controlled by addtion of low-molecular-weight compounds, a second polymeric component, or a reinforcing particle or fiber. The interactions between the components play a critical role in determining features such as homogeneity of the resultant material, the glass transition and the modulus. A new nuclear magnetic resonance technique based on carbon-13 spin diffusion can probe the relative intermolecular structure of the constituent components at the level of the chemical groups of the polymer repeat unit. With this level of structural data, the chemical interactions leading to properties such as compatibility or increase in modulus can be identified. Changes in the modulus typically reflect the local chain dynamics present in the glass and NMR is a particularly powerful tool for identifying these features. The influence of diluents, a second polymer or a filler on the local dynamics can reinforce the unit level structure. The materials to be studied include two polymer blends with strong interactions where compatibility is not controlled by hydrogen bonding and where NMR is the technique of choice for identifying the nature of the interaction. A special class of low molecular weight diluents which are particularly effective antiplasticizers will also be investigated. In addition, the interactions and changes in mobility of an engineering resin in the presence of a reinforcing fiber will be studied from the local structural viewpoint characteristic of NMR spectroscopy.