Proton Magnetic Resonance Studies of Some Silicones

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Abstract
Proton magnetic resonance techniques have been used to study the molecular motions occurring in some dimethyl silicones. The substances investigated were cured Silastic 80, 400 Gum, and 200 Fluid (viscosity grade 20 centistokes at 25°C). Measurements were made of the absorption line shape from 77°K to room temperature, and of the spin‐lattice relaxation time, T1, from 160°K to 415°K. Evidence is found for the existence of methyl group reorientation about the triad axis, segmental motions about the Si–O bonds and a form of intramolecular ``spiral'' motion of the (CH3)2Si groups. The relation of the latter motion to the difference in macroscopic properties of natural and silicone rubbers is discussed.

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