Add time:08/16/2019         Source:sciencedirect.com

Deuterium, carbon-13 and proton spin-lattice relaxation times at two fields are reported for dilute solutions of 1,1-dichloro-2,2,-bis(4-hydroxyphenyl)ethylene polyformal. The carbon-13 and proton relaxation measurements were made at a concentration of 10% (w/w) in deuterated s-tetrachloroethane and as a function of temperature. A partially deuterated analog with deuterated methylene groups was used in order to remove cross-relaxation effects from the phenylene proton relaxation. In addition, deuterium relaxation measurements were made on this sample at a concentration of 10% (w/w) in tetrachloroethane as a function of temperature. The data are interpreted in terms of segmental motion arising within the bisphenol units and anisotropic internal rotations of the other structural components. Motions of the phenylene groups in the backbone are described by the Hall-Helfand segmental correlation function plus the Woessner anisotropic internal-rotation correlation function. Motions of the formal linkage are described by the same segmental correlation function plus an internal correlation function based on restricted double rotation about the two carbon/oxygen bonds. The local motion of the formal group is discussed in terms of confomational transitions that are likely in a polyformal in view of the conformational energy surface. A Helfand Type II motion of the formal group corresponding to a transition from gg′ to tg is identified as the most plausible rearrangement of this unit.

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