Molecular Motion in Organosilanes and Silicones
HARVARD UNIV CAMBRIDGE MA MALLINCKRODT LAB
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The technique of nuclear magnetic resonance absorption was used to study the molecular motion in the solid state of organosilicon compounds. methylchlorosilanes exhibited rotation or tunneling of the Me group about the C- Si bond at 77 deg K. The line shapes and the second moment suggested some low- frequency motion of the molecule as a whole. methoxytrichlorosilane exhibited rotation or tunneling of the Me group about the C-O bond, but there was little or no motion of the molecule as a whole at 77 deg K. Hexamethyldisiloxane exhibited the usual rotation or tunneling of the Me group the low second moment suggested additional motion in the molecule. Cyclic siloxanes exhibited rotation of the Me group at 77 deg K. The cyclic trimers and tetramers showed an anomalous abrupt increase in line width and second moment at higher temperatures. Silicone rubber showed the rotation of the Me group at 77 deg K. The line width decreased abruptly at 164 deg K to about one-half the low- temperature value, and then more gradually unit it was essentially a liquid-like line at 210 deg K. This decrease in line width indicated that above 164 deg K the motion of the protons becomes rapid and random. The use of the radiofrequency spectrometer is discussed as to its applicability to this research and other problems. The theory of nuclear magnetic resonance absorption is presented as it applies to the investigation as well as facts and theories of the structure of the silicones.
- Atomic and Molecular Physics and Spectroscopy
- Physical Chemistry
- Elastomers and Rubber