Poly (2-methyl-1,8-octametyleneoxamide) (nylon-MOMD-2) was prepared from dibutyl oxalate and 2methyl-1,8-octamethylenediamine. The chemical structure was investigated by C-13 nuclear magnetic resonance (C-13 NMR). The C-13 NMR spectrum revealed that the methyl groups distribute among the four beta-sites at random. The crystal structure and its temperature dependence were also investigated by molecular mechanics calculations, X-ray diffraction, and differential scanning calorimetry. The structure was determined to be monoclinic and a = 6.26 angstrom, b = 8.80 angstrom, c = 14.7 A, and beta = 50.7. The torsion angle of the NH-CH2 bonds has a skew conformation and there are the two distinct torsion angles in the crystal structure. The crystal structure of nylon-MOMD-2 has a disordered and statistical structure. The crystal structure shows no phase transition on heating until its melting point, although the unit cell expands in the a and b axis directions. (C) 2014 Elsevier Ltd. All rights reserved.