Dynamic Mechanical Properties of Poly(α-amino acid)s. I. Side-Chain Dispersions of Poly(γ-benzyl L-glutamate) and Poly(γ-methyl L-glutamate)

Abstract

Dynamic mechanical measurements for solid films of poly(γ-benzyl L-glutamate) (PBLG) and poly(γ-methyl L-glutamate) (PMLG), which were cast from helicogenic solvents, were carried out with a torsion pendulum apparatus over a frequency range of 1.0 to 0.003 Hz at various temperatures in their side-chain dispersion regions. Master curves for the real and imaginary parts of the complex rigidity and loss tangent were composed by performing suitable translations of the obtained dispersion curves along the logarithmic frequency axis. The shift factor aT derived from the superposition procedure was satisfactorily represented by the “universal” Williams—Landel—Ferry equation with Ts’s chosen as 65 and 57°C for PBLG and PMLG, respectively. The dispersions resemble those associated with glass-transition phenomena in some respects, unlike the side-chain dispersions of amorphous polymers, such as poly(alkyl methacrylate)s. This may suggest that the side chains of these poly(α-amino acid)s are randomly packed surrounding a rigid helical backbone.