Superstructure-mechanical property relationships of polyglutamic acid esters

Abstract

A study has been made of the relaxation phenomena in a series of poly-γ-n-alkyl-D-glutamates having linear side chains of different lengths in the temperature range from −170 to 250°C. The solid-state films of poly-γ-n-alkyl-D-glutamate were cast from solutions in α-helix and random coil forming solvents. The technique of dynamic mechanical relaxation at various frequencies up to 110 Hz was used in the investigation. X-ray, IR, and density measurements were used as supplements to the mechanical measurements in order to determine the relationships between the mechanical properties and superstructures. Six relaxation regions are discernible in the temperature range investigated, and these are labeled α, β, γ, δ, ε, and ζ in order of decreasing temperature. The following mechanisms are assigned to these relaxations: (1) The α-relaxation arises from the thermal molecular motion of the α-helices in the crystalline region. (2) The β relaxation arises from micro-Brownian segmental motion of the disordered region or the distorted part of the a-helices, (3) The γ and δ relaxations are associated with motions of the entire side-chain groups in the crystalline and the disordered regions, respectively. (4) The ε and ζ relaxations involve the conformational rearrangements of n-alkyl groups including carboxyl group and n-alkyl groups alone, respectively.