Solution crystallization of nylon 12

Electron microscopy and x-ray diffraction data have been obtained on nylon 12 crystallized from 1-hexanol, 1,6-hexanediol, and hexylene glycol. Ribbonlike lamellar crystals of the γ form are obtained by crystallization from all the solutions and elongated flat crystals of the α form by crystallization from the 1-hexanol and hexylene glycol solutions. The direction of the hydrogen bond in these crystals is almost parallel to that of maximum crystal elongation. α- and γ-form crystals both grow from 1-hexanol and hexylene glycol at appropriate crystallization temperatures. γ-form crystals alone are obtained from 1,6-hexanediol solution at every crystallization temperature. The long periods measured by small-angle x-ray diffraction for the solution-grown crystals are in the range 7.6–10.6 nm. The melting behavior of the solution-grown crystals is examined and discussed. The melting temperatures of the γ form may be lower than that of the α form. An equilibrium melting temperature of 208.4°C for γ-form crystals is obtained by using a relation between thickness of lamellar crystals and their melting temperatures observed by differential scanning calorimeter measurements. Solvents affect the growth of the two crystalline forms in solution crystallization.     

Crystal structure of α-AlB12

The crystal structure of α-AlB₁₂ (tetragonal; a = 10.158(2) Å, c = 14.270(5) Å, space group P4₁2₁2 or P4₃2₁2) has been determined by the single-crystal X-ray diffraction method. It was solved by the Fourier technique initially based on a partial B₁₂ icosahedral structure, which was inferred from crystal chemical considerations. Refinement was made with the aid of a full-matrix least-squares program leading to a final R value of 3.0%. The structure is based on a three-dimensional framework consisting of B₁₂ icosahedra, B₁₉ units, and single B atoms; the B₁₉ unit is a twinned icosahedron with a triangular composition plane and a vacant apex on each side. The chemical unit is Al_3.2·2B₁₂·B·B₁₉ and its number in the unit cell is 4. The Al atoms are distributed statistically over five sites in the boron framework. The occupancies of the sites are 72, 49, 24, 15, and 2%, respectively.     

Crystal and molecular structure of benzoaza-12-crown-4 hydrochloride

Journal of Structural Chemistry - The X-ray crystallographic analysis of benzoaza-12-crown-4 hydrochloride crystals is performed for the first time: space group P1, a = 7.7497(4) Å, b =...     

Crystal structure and morphology of biaxially oriented polyamide 12 films

The structural and morphological characteristics of biaxially oriented polyamide 12 films are described on the basis of the results from differential scanning calorimetry, wide‐angle X‐ray diffraction (WAXD), polarized FT‐IR spectroscopy, and small angle X‐ray scattering (SAXS). The WAXD patterns of the oriented polyamide 12 films indicated only the monoclinic γ crystal with little dimensional changes of its unit cell depending on the stretching conditions. The crystallographic angles (α = γ = 90°, β = 121°) that were determined via the WAXD patterns confirmed the monoclinic symmetry of the γ crystal. Annealing the films stretched at 115 °C in boiling 20% formic acid solution did not result in structural changes of the crystalline unit cell. The chain‐axis repeat distance of 31.9 Å for the γ crystal was experimentally obtained with (0 26 0) planes. It was shortened as compared with that of all‐trans conformation. For films having primary orientation to MD, normals to the basal plane of folded‐chain lamellae were parallel to MD (primary stretch direction) resulting in two‐point SAXS patterns. Growth in long spacing with an increase of stretch temperature was discovered. Annealing the films induced further elongation in long spacing. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1189–1200, 2002     

Domain structure of nylon 6 fibers

Stained and unstained sections of nylon 6 fibers are examined by means of transmission electron microscopy. Data are presented regarding dimensions and shape of macrofibrils, microfibrils, amorphous, and crystalline domains of the microfibril and the spacing between the microfibrils. The new results support the conclusions of a previous SAXS and diffusion study carried out with the same fibers.     

Crystal structure of tetragonal boron related to α-AlB12

Single crystals of the so-called β-tetragonal (or tetragonal II or III) boron modification have been obtained from boron deposits prepared by hydrogen reduction of BBr₃ on tantalum filaments at 1200°C. Chemical analysis of the samples shows that this phase can be regarded as a true modification of pure elemental boron in contrast to α-tetragonal phases which require small amounts of foreign atoms to stabilize their boron framework.The lattice parameters (a = 10.14(1)Å; c = 14.17(1)Å) were obtained and refined from single crystal data. The unit cell contains four chemical units, B₂₁ · 2B₁₂ · B_2.5 resulting in d_c = 2.34 g cm^?3 (d_m = 2.36(2) g cm^?3). The systematic extinctions are compatible with space group P4₁ or P4₃.The structure was determined from 1009 independent reflexions using a model derived from the recently solved structure of α - AlB₁₂ (a = 10.161Å; c = 14.283Å; space group P4₁2₁2 or P4₃2₁2). The final R value (unweighted data) is 9.6%.Basically, the structure of this tetragonal form of boron consists of the same three-dimensional boron skeleton, built upon simple and twinned icosahedra, as that of α-AlB₁₂. However, the defective twinned icosahedral B₁₉ units in α-AlB₁₂ are now completed (B₂₁ units) in the related tetragonal boron. A number of interstitial sites, located at positions different from those occupied by aluminum in α-AlB₁₂, are totally or partially filled by boron atoms and very probably increase the stability of the boron framework.     

Crystal structure of acrylamide

The crystal structure of acrylamide is re-determined by single crystal X-ray diffraction (133(1) K, BRUKER SMART 1000 CCD, a = 8.228(1) Å, b = 5.759(1) Å, c = 9.760(1) Å, β = 120.04(1)°, V = 400.3(1) Å,³, space group P2₁/c, Z = 4, R = 0.0543 for 867 reflections). In the structure strong hydrogen bonds N-H...O join the molecules of C₃H₅NO into bi-molecular layers that make C...C molecular contacts. It is demonstrated that the process of solid phase polymerization of acrylamide should proceed through the cleavage of double bonds C(1)=C(2) in the monomers and formation of bonds C(1)-C(1) and C(2)-C(2) between the closest carbon atoms of different layers.     

Crystal structure of Li2B12H12: a possible intermediate species in the decomposition of LiBH4

The crystal structure of solvent-free Li2B12H12 has been determined by powder X-ray diffraction and confirmed by a combination of neutron vibrational spectroscopy and first-principles calculations. This compound is a possible intermediate in the dehydrogenation of LiBH4, and its structural characterization is crucial for understanding the decomposition and regeneration of LiBH4. Our results reveal that the structure of Li2B12H12 differs from other known alkali-metal (K, Rb, and Cs) derivatives.     

Crystal structure of amikacin

Amikacin is one of the important aminoglycoside antibiotics used against gram-negative bacteria. Here we report the crystal structure of amikacin that has been crystallized by vapor diffusion against polyethylene glycol. The molecule exists in a long, extended conformation, with all three six-membered rings in chair conformations and connected together by -glycosidic linkages. The orientation between the A, B and C rings of the molecule is maintained by intramolecular hydrogen bonds involving the O₅ hydroxyl group and the amide NH group.     

Crystal structure of polysulfonamides

Structures of poly(alkylene-1,3-benzenedisulfonamide)s [? HN(CH₂)_mNH? O₂SC₆H₄SO₂? ]_n (PMm: 2 ≤ m ≤ 6) were studied by x-ray diffraction and infrared spectroscopy. The crystal structure of PB6 is monoclinic, space group C2/m? C_2h³, with a = 7.70 Å, b = 7.76 Å, c (molecular axis) = 14.1 Å, and β = 117°. Two mirror-image molecules repeating with two monomeric units in an identity period 28.2 Å occupy the same lattice site with equal probability. The alkylene chains assume the planar zigzag conformation, which is the structure isomorphous with PB4. An intermolecular hydrogen bond is formed between each NH group and one of the two O = S groups of the corresponding SO₂ unit. The c axis tends to tilt from the fiber axis by an inclination angle of about 3° around the b axis.