Relaxation phenomena of poly-γ-benzyl-L-glutamate, poly-γ-methyl-L-glutamate, and copoly(γ-methyl-L-glutamate, γ-benzyl-L-glutamate)

Relaxation phenomena of poly-α-amino acids in the solid state have been investigated using poly-γ-benzyl-L-glutamate (PBLG), poly-γ-methyl-L-glutamate (PMLG), and copoly (γ-methyl-L-glutamate, γ-benzyl-L-glutamate) (PMBG) by means of dielectric, dynamic mechanical, NMR, dilatometric, and X-ray diffraction measurements at temperatures between −196 and 180°C. Each of the samples exhibits two relaxation regions, one at room temperature (β-relaxation) and the other in the range from −150 to −100°C (γ-relaxation). The γ-relaxation is attributed to motion of the side chains with small amplitude. The β-relaxation is due to large-scale motion of the side chain. It has been found that the β-relaxation is well described by the WLF-equation. The intensity of the X-ray diffraction peak at 2θ = 7° for PBLG increases with increasing temperature, which is similar to results obtained in small-angle X-ray scattering for polymer crystals consisting of two phases, amorphous and crystalline. A break point is observed at 18°C where the specific volumetemperature curve also shows a break point. It is concluded that the side chains of these polymers are almost amorphous, and that they undergo a glass-like transition while the backbones keep an α-helical conformation.