Copoly(γ, dl-glutamate)s containing short and long linear alkyl side chains

Abstract

Copoly(α-alkyl γ, dl-glutamate)s containing octadecyl and ethyl side groups were prepared from racemic poly(γ, dl-glutamic acid) of bacterial origin, and their structure in the solid state examined by DSC, polarized IR spectroscopy and X-ray diffraction methods. Copolymers with a blocky microstructure were prepared by transesterification of poly(α-ethyl γ, dl-glutamate) with octadecanol for a wide range of compositions. Random copolymers were prepared by sequential alkylation of the polyacid with ethyl bromide and octadecyl bromide in solution. All the multiblock copolymers were found to adopt the layered structure characteristic of comb-like polypeptides with the octadecyl side chains crystallized in extended conformation in a separate phase, and aligned normal to the main chains, which are arranged in helical conformation. Melting of paraffinic crystallites reversibly happened in the 50–55 °C range without significant alteration of the layered arrangement. Upon heating at 150 °C, the structure contracted but no indication on the existence of a second transition, as it is known to occur in comb-like poly(α-alkyl γ-glutamate) homopolymers, was observed by DSC. Random copolymers did show nor thermal transition neither evidence of any organized supramolecular structure.