Rotational isomerism and physical properties of long-chain molecules in solid states

Rotational isomerism occurring in solid state of organic long-chain compounds, including synthetic linear polymers, have been concerned in connection with the macroscopic physical properties of bulk materials. The conformational order in the non-crystalline part of polyethylene has been investigated by Raman spectra, and related to the elastic behaviors of bulk samples. In the solid-state phase transition induced by mechanical forces of poly(butylene terephthalate) the macroscopic strain has been related directly to the conformational conversion of the molecules. Concerning the piezoelectric and pyroelectric activities of poly(vinylidene fluoride), polymorphism, phase transition, and structural change on the poling process have been investigated. A ferroelectric-paraelectric phase transition has been found for a series of copolymers of vinylidene fluoride and trifluoroethylene. On the phase transition a great change in molecular conformation is accompanied with the scrambling of the dipolar orientation. This is the characteristic of polymer ferroelectrics in which the dipolar units are linked with each other by covalent bonds in a molecular chain. Spectroscopic evidences are presented indicating that the thermodynamic stability of polymorphs of n-fatty acids is closely related to the rotational isomerism occurring in the carboxyl groups.