Drawing Mechanism of the Film of Poly(γ-methy D-glutamate) with α-Helical Conformation

Abstract

The solid film of poly (γ-methyl n-glutamate) (PMDG) was obtained from its chloroform solution in which a-helix form is produced. During evaporation, chloroform was replaced by ether when the concentration of PMDG in chloroform was ca.30 wt %. This sample was drawn in various extensions at 25, 75, 104, 150 and 180°C. Both α(helical chain) and β(extended chain) were found in oriented PMDG. We have studied the relationship between the true stress and the true strain and also, the mechanism of the transformation from α-form to βform.
In order to study the relationship between mechanical behavior and structual variation, the molecular chain orientation and the fraction of α and β-forms were evaluated at various temperatures and elongations. The following results were obtained about the mechanism of α and βtransformation of solid PMDG. ( 1 ) A part of α-form in the original sample transforms into fl-forms by drawing after the orientation of α-form proceeds along the drawing direction. ( 2 ) The critical strain at which β-form appears, is dependent on the drawing temperature and increases with increasing temperature. ( 3 ) Also, the fraction of β-form depends on the drawing temperature as well as the magnitude of elongation, and is a function of relative magnitude of shear stress to cause the mutual slip of α-form and that required to transform α-form into β-form. ( 4 ) During the drawing made above the viscoelastic crystalline dispersion temperature (150-170°) at which the mutual and migrational slip of α-form predominates in the relaxation mechanism, α → β transformation is not observed.