The structure in the solid state of two optically active polyamides obtained from 2,3-O-methylene-L-tartaric acid and linear a,alpha-omega-alkanediamines with 9 and 12 carbon atoms, abbreviated P9MLT and P12MLT respectively, was investigated. Two ordered phases, one of smectic liquid crystal-type and another showing crystalline order, were characterized for P12MLT. Crystallization of the former into the second was induced by annealing. Infrared spectroscopy showed that hydrogen bonds are intermolecularly set in both phases and that they are weaker in the crystal phase. Quantum mechanical calculations found the O-C-C=O sequence of the tartaric unit to be in a gauche conformation. 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 polymethylene segment crystallizes in the all-trans conformation. X-ray diffraction 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. Experimental data obtained from P9MLT indicated a similar behavior for this system. (C) 2000 Elsevier Science Ltd. All rights reserved.