Optically active polyamides containing 1,3-dioxolane cycles in the backbone

The structure in the solid state of two optically active polyamides obtaine d from 2,3-O-methylene-L-tartaric acid and linear a,alpha-omega-alkanediami nes with 9 and 12 carbon atoms, abbreviated P9MLT and P12MLT respectively, was investigated. Two ordered phases, one of smectic liquid crystal-type an d another showing crystalline order, were characterized for P12MLT. Crystal lization of the former into the second was induced by annealing. Infrared s pectroscopy showed that hydrogen bonds are intermolecularly set in both pha ses and that they are weaker in the crystal phase. Quantum mechanical calcu lations found the O-C-C=O sequence of the tartaric unit to be in a gauche c onformation. CP-MAS C-13 NMR revealed that the dioxolane ring is a mixture of the C-2-exo and C-2-endo puckered forms in equal amounts and that the po lymethylene segment crystallizes in the all-trans conformation. X-ray diffr action of fibers and electron microscopy of solution grown single crystals afforded data consistent with a crystal lattice with orthorhombic geometry and parameters a = 7.8 Angstrom, b = 5.8 Angstrom, c = 20.0 Angstrom. Exper imental data obtained from P9MLT indicated a similar behavior for this syst em. (C) 2000 Elsevier Science Ltd. All rights reserved.