Structures of X 34-nylons in chain-folded lamellae and gel-spun fibers

Structural studies and morphological features of a new family of linear, aliphatic even-even, X 34-nylons, with X = 2, 4, 6, 8, 10, and 12, are investigated with X-ray diffraction and electron microscopy. Solution-grown crystals were obtained by isothermal crystallization from N,N-dimethylformamide solutions. The thickness of lamellar-like crystals was orders of magnitude less than the chain lengths of the polymer samples used, implying that the chains fold to form chain-folded lamellae. The results bear a close resemblance, with the noticeable exception of 2 34-nylon, to those reported for nylon 6 6 and other even-even nylon chain-folded lamellar crystals. The basic structure of the straight-stem lamellar core is similar to that of the classic nylon 6 6 triclinic alpha structure, and the chains tilt approximate to42degrees relative to the lamellar normal. In the case of 2 34-nylon, the structure resembles the 2 Y nylon series, and the chain tilt angle reduces to 36.6degrees. These combined results suggest that, even with a relatively low frequency of amide units along the backbone of these molecules, hydrogen bonding is still the dominant element in controlling the behavior, structure, and properties of these polymers. In addition, gels were prepared in concentrated sulfuric acid, and gel-spun fibers were studied using X-ray diffraction. The data are interpreted in terms of a modified nylon triclinic alpha structure that bears a resemblance to the structure of even-even nylons at elevated temperatures. (C) 2002 Wiley Periodicals, Inc.