Internal motion in some aromatic polyesters and linear aromatic chains

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Abstract
Low‐temperature internal motions of the following polyesters have been investigated by broad line nuclear magnetic resonance: poly(methylene terephthalates) (2–6 methylene groups), poly[1,4‐(dimethylene)cyclohexylene terephthalate], poly(diethyleneglycol terephthalate), poly(1,2‐propylene terephthalate), poly(1,4‐phenylene terephthalate), poly(2,2,3,3,4,4‐hexafluoropentamethylene terephthalate), poly[1,4‐phenylenebis(dimethyl) siloxane], and poly(2,6‐dimethylphenylene oxide). No complex line structure was found for any of the samples. Molecular motions in the polyesters appear to be restricted by polar forces arising from the ester groups. Above—196°C. the line width decreases smoothly with increasing temperatures for all polymers except poly[1,4‐(dimethylene)cyclohexylene terephthalate] and poly[1,4‐phenylenebis(dimethyl)siloxane]. These two show a definite transition in line width at −20°C. and +12°C., respectively, caused by the onset of considerable internal motion. At −196°C. the lattices are rigid except for polymers containing methyl groups: poly(1,2‐propylene terephthalate), poly[1,4‐phenylenebis(dimethyl) siloxane], and poly(2,6‐dimethylphenylene oxide). Internal motion that can be ascribed to be a reorientation of the methyl groups is present at −196°C. for these three polymers, as is demonstrated by comparison of experimental second moments and those calculated on the basis of various models.

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