Relationships between mechanical properties and aggregated states of α-helical chains of poly(γ-methyl glutamate) films

Abstract

Abstract The states of aggregation of poly(γ-methyl glutamate) molecular chains in α-helical form were investigated. In a film cast from a gelatinized solution in pyridine (group 2 solvent), network structures of fibrils were observed and a (1010) plane of the crystallites showed a uniplanar orientation to the film surface. When the film was cast from a cholesteric liquid crystalline solution in dichloroethane (group 1 solvent), crystallites or microfibrils were dispersed separately and a planar orientation of molecular axes was induced. The dynamic mechanical properties of poly(γ-methyl glutamate) in α-helical form were studied for these specimens showing the different states of aggregation. A large tan δ peak was found in the dynamic viscoelastic measurements at around 420 K for the film cast from pyridine solution. From X-ray diffractometry and infrared spectroscopy it was confirmed that this is a crystalline relaxation and is associated with two relaxation mechanisms. The α1 relaxation process, located at around 420 K, was attributed to the process of shear deformation of α-helices in the crystalline regions accompanying the mutual slip of the α-helical chains, and the α2 relaxation process located at around 450 K was attributed to tensile deformation of α-helices permitting an accordionlike vibration of the α-helical chains along their axes. The magnitude of the crystalline relaxation was remarkable only for the film cast from pyridine solution, a feature attributed to the network structure formed by the microfibrillar connections revealed by electron microscopy.