The Structure and Properties of Copolyaspartate I. Copoly(butyl-L-aspartate-benzyl-L-aspartate)

Abstract

The α helices of copoly(butyl-L-aspartate-benzyl-L-aspartate) prepared by substituting some of the benzyl groups in the side chains of poly(β-benzyl-L-aspartate) by butyl groups, were transformed, throughout the entire range of butylation tested, into ω helices with a tetragonal packing when heated up to 140°C. The α–ω transition temperature was about 100°C for copolyaspartates of butylation less than 30% and near 130°C for copolyaspartates of butylation more than 30%. In the case of more than 30% butylation the α–ω transition was furthermore accompanied by a change from the right handed a helix to the left handed ω helix. The α–ω transition resulted in a remarkable change in the magnitude of the dynamic modulus and an exothermic peak. It was concluded that the ω helix of copoly(butyl-L-aspartate-benzyl-L-aspartate) was based on the formation of stacks between benzyl and butyl groups as well as the ω helix consisting of stacks between the benzyl groups of poly(β-benzyl-L-aspartate).