Structures for monodisperse oligoamides. A novel structure for unfolded three-amide nylon 6 and relationship with a three-amide nylon 6 6
✍ Scribed by Sharon J. Cooper; Edward D. T. Atkins; Mary J. Hill
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 359 KB
- Volume
- 36
- Category
- Article
- ISSN
- 0887-6266
No coin nor oath required. For personal study only.
✦ Synopsis
Three-amide oligomers of nylon 6 and nylon 6 6 have been investigated using electron microscopy (imaging and diffraction), X-ray diffraction, and computational modeling. A new crystal structure has been discovered for the three-amide oligomer of nylon 6. This material crystallizes from chloroform/dodecane solutions into an unfolded crystal form that has progressively sheared hydrogen bonding in two directions between polar (unidirectional) chains. This structure is quite different from the usual room temperature ␣-phase structure of chain-folded nylon 6 crystals, in which alternatingly sheared hydrogen bonding occurs between chains of opposite polarity in only one direction. The occurrence of this new structure illustrates the extent to which progressively sheared hydrogen bonding is preferred over alternatingly sheared hydrogen bonding. Indeed, the progressive hydrogen bonding scheme occurs in the threeamide nylon 6 material even though it requires a disruption to the lowest potential energy all-trans conformation of the chain backbone, and requires all the chains in each hydrogen-bonded layer to be aligned in the same direction. We believe the presence of chain folding, which necessarily incorporates adjacent chains of opposite polarity into the crystal structure, prevents the formation of this new crystal structure in the nylon 6 polymer. In contrast, the three-amide nylon 6 6 crystal structure is analogous to the polymeric nylon 6 6 ␣-phase structure, found in both fibers and chain-folded crystals, and consists of progressive hydrogen-bonded sheets which stack with a progressive shear. In both structures, the molecules (Ϸ 3 nm in length) form smectic C-like layers with well-orchestrated stacking of 2.2 nm to form a three-dimensional crystal.