Poly(β-L-aspartate)s containing ethylene oxide units in the side chain: Synthesis and structural studies

Abstract

Two poly(β-L-aspartate)s of general formula –[–HN–CH(COOR)–CH2–CO–]– containing ethylene oxide units in the side chain [R=–CH2CH2OCH3 (IVa), and –CH2–CH2OCH2CH2OCH3 (IVb)] have been prepared by anionic ring-opening polymerization of the corresponding optically pure β-lactams. In both cases, stereoregular polymers with molecular weights above 2×105 were obtained in satisfactory yields. These polyamides were fully characterized by combustion analysis, FTIR and1H–13C NMR spectroscopy, and DSC. Whereas polymer IVa attained was completely free of imide units, side reactions giving rise to imidation could not be entirely repressed in the polymerization of the β-lactam leading to IVb. X-Rays from oriented samples revealed that polymer IVa crystalizes in a hexagonal structure made up of 4* 13/4 helices which bear great conformational resemblance with the well known α-helix in polypeptides. A similar conformation seems to be adopted by polymer IVb, although in this case, side chains tend to remain in a disordered state hindering the crystallization of the helices. © 1994 The Society of Polymer Science, Japan. All rights reserved.