Structure and deformation of a crosslinked poly(α-amino acid)

Abstract

The relationship between the chain conformation and the mechanical response is an important consideration in understanding the solid state properties of block and random copolymers of α-amino acids. In order to eliminate intermolecular effects, crosslinked poly-2-hydroxyethyl-L-glutamine was prepared, and the mechanical properties of swollen films were determined. In water, the films take the random coil conformation and the mechanical behavior is elastomeric. In methanol, the chains are α-helical and plastic deformation is observed. Two molecular processes accompany the deformation of the α-helical network. At low strains, orientation of the α-helical chain segments in the draw direction is observed. At higher strains, some of the α-helical chains are converted to the β-sheet conformation. This latter process probably accounts for the observed nonrecoverable deformation. The behavior in mixed solvents showed that the nonhelical chain segments provided sufficient flexibility to the chain that the properties of films with up to 75% helicity were elastomeric.