THERMAL MOTION OF ALPHA-HELICAL MOLECULES IN HIGHLY CRYSTALLINE POLY(GAMMA-METHYL L-GLUTAMATE) FILMS

Solid films of poly (γ-methyl l-glutamate) were prepared by casting solutions in chloroform, dichloromethane, and m-cresol. The mode and amplitude of thermal molecular fluctuations in the crystalline phase were studied by X-ray diffraction. All the films contain α-helical molecules and have hexagonal crystal structures, but differ from each other in their crystallinity and crystallite size. The calculated molecular fluctuation amplitudes also differ considerably. Below a threshold temperature in the range 140°-190°C (different for each sample), the segmental molecular motion is composed of translation along the chain axes coupled with rotation about the axes. At higher temperatures, the structure changes thermoreversibly into a modification, in which a screw-type motion along the α-helix axis is predominant. © 1979.