The crystal structures of nylons X 11 under different conditions (X = 2, 4, 6, 8, 10, and 12) were investigated by wide-angle X-ray diffraction (WAXD) and electron diffraction (ED). Both the solution-and melt-crystallized samples of nylon 2 11 possess the hexagonal lattice (named gamma-form). Nylons 4 11 and 6 11 exhibit the monoclinic unit cell (termed as a-like form) for both samples characteristic of two strong diffractions at 0.44 and 0.38 nm. For nylons 8 11, 10 11, and 12 11, the a-like form are obtained for the solution-crystallized samples while the beta-like ones are obtained in the case of the melt-crystallized ones, with typical strong diffractions at 0.42 and 0.40 nm. The quenched nylon 12 11 samples annealing at different temperatures were also studied in this work to illustrate the various crystal forms obtained under different conditions. During the heating process, the a-like forms of the solution-crystallized samples for nylons 8 11, 10 11, and 12 11 transform into the high-temperature hexagonal phases prior to melting, while those of nylons 4 11 and 6 11 did not show such transformations before melting. Variable-temperature Fourier transform infrared spectroscopy was applied to investigate the crystalline transition phenomena and illustrate their essential features in the molecular level. (c) 2005 Wiley Periodicals, Inc.