Wayne T. Ferrar

Two-dimensional MAS NMR of abundant spins in solids

Two-dimensional incoherent mixing experiments (I) have been used to determine the proximity of protons in solution (NOESY) (2), elucidate spin dilfusion mechanisms among dilute spins in solids (3), and determine microscopic heterogeneity in multiphase systems such as mixtures (4) and polymer blends (5). In the latter two cases, the experiments were performed with abundant spins (protons). A requirement for such experiments is the resolution of the sites between which spin exchange takes place. In the case of abundant spins, the necessary resolution has been achieved either by selecting systems with inherent mobility (4) or by the application of multiple-pulse homonuclear dipolar decoupling (5). The use of magic-angle spinning (MAS) to enhance the resolution of abundant spins in conjunction with 2D NOE experiments has not been widely explored (6). This is in part because the very fast spinning speeds required have not been available until very recently. Here, we report preliminary results from combined 19F MAS/NOESY experiments on the fluorinated polyphosphazene 1 synthesized in our laboratories.

Fatigue-resistant silicone elastomer formulations

Fatigue-resistant elastomers have been prepared using various metal oxides as fillers in poly(dimethylsiloxane) (PDMS)-based elastomers. The judicious choice of inorganic fillers produced elastomers that were stable under cyclic testing at elevated temperatures. These experiments were carried out using the Mechanical Energy Resolver, an instrument modified to reduce testing time from approximately 6 weeks to 60 h. Four elastomers showed stable storage moduli, were creep resistant, and showed less than 1% weight loss after 60 h. By comparison, a formulation prepared with alumina as the filler showed high rates of creep and greater than 10% weight loss.