Polymorphic forms of nylon 3

The crystal structure of nylon 3 was studied, and four crystalline modifications were observed. Modification I, as determined from the x-ray diffraction pattern of drawn fibers, is similar to the α crystal structure of nylon 6. The unit cell is monoclinic; a = 9.33 Å, b = 4.78 Å, (fiber identity period), c = 8.73 Å, and β = 60°. The theoretical density for nylon 3 with four monomeric units in the unit cell is 1.39 g/cm³, and the observed density is 1.33 g/cm³. The space group is P2₁. The nylon 3 chains are in the extended planar zigzag conformation. Although other odd-numbered nylon form triclinic or pseudohexagonal crystals when oriented, drawn nylon 3 crystals are monoclinic. In addition to modification I, modifications II, III, and IV were studied. Lattice spacings of modifications II and III are equal to those of modification I. However x-ray diffraction intensities are different. Infrared spectra of those forms indicate an extended planar zigzag conformation of the chains. Modification IV is thought to correspond to the so-called smectic hexagonal form. No γ crystals were found, and it appears that polyamide chains with short sequences of methylene groups cannot form crystals of this type.     

Crystal structure of poly(m-phenylene isophthalamide)

The crystal structure of poly(m-phenyulene isophthalamide) was determined by x-ray analysis. The triclinic cell, with a = 5.27 Å, b = 5.25 Å, c (fiber axis) = 11.3 Å, α = 111.5°, β = 111.4° and γ = 88.0° and space group P1, contains one monomeric unit. The crystal density is 1.47 g/cc. The molecules in the crystal are contracted by 1 Å per monomeric unit from the fully extended conformation, and the planes of the benzene rings and adjacent amide groups make angles of about 30°. The crystal is composed of molecular chains connected by N? H···O hydrogen bonds along the a and b axes forming a “jungle gym” network structure. The low tensile modulus of this polymer as compared with that of poly(p-phenylene terephthalamide) is attributed to the contracted molecular conformation.     

Crystal structure of nylons 2/3/3 and 1,3

The crystal structures of two polyamides, poly(glycyl-β-alanyl-β-alanine) (nylon 2/3/3) and poly(methylene malonamide) (nylon 1,3), have been investigated by x-ray diffraction and electron microscopy. Crystallization of nylon 2/3/3 from a solution in a mixture of water and formic acid yields lamellar single crystals exhibiting a triangular habit. Doughnut-shaped morphologies diffracting as single crystals are obtained in the crystallization of nylon 1,3. A helical structure of the type known as polyglycine II is found for both polyamides. In such a structure, chains are intermolecularly linked by hydrogen bonds giving a hexagonal lattice of a = 4.79 Å. Insufficient data are available to determine precisely the conformation of the chains. We assume a threefold helix having c = 35.2 Å and c = 18.0 Å for nylon 2/3/3 and nylon 1,3 respectively. No sign of the layered structure familiar in polyamides has been detected for these polymers throughout the experiments made in the present study.     

Crystal structure of poly-p-xylylene. I. The α form

The molecular conformation and the crystal structure of α-form poly-p-xylylene has been determined by x-ray diffraction. The polymer has a monoclinic unit cell with a = 5.92, b = 10.64, c (fiber axis) = 6.55 Å, and β = 134.7°. Two chains pass through the unit cell, and the space groups is C2/m. The packing fraction is 0.705. One monomer unit makes up the fiber identity period and the internal rotation angles are 0° and 90° for the ? CH₂? CH₂? and ? CH₂? ?? bonds, respectively. All benzene rings are in parallel orientation, perpendicular to the ac plane.     

Structure and thermochromic solid-state phase transition of poly (3-alkylthiophene)

In order to clarify the structural changes that occur in the thermochromic phase transition of poly (3-dodecylthiophene) [P3DT] and poly (3-hexylthiophene) [P3HT], the temperature dependence of x-ray diffraction and Fourier transform infrared spectra was measured. (1) Orthogonal unit-cell parameters were determined at room temperature: a=25.83 Å, b=7.75 Å, c (fiber axis)=7.77 Å for P3DT and a=16.63 Å, b=7.75 Å, and c=7.77 Å for P3HT. A large variation of the a-axis length between P3DT and P3HT indicates the extended trans conformation for the alkyl side chains which are oriented along the lateral a-axis direction. (2) The interplanar spacing, intensity, and integral width of the x-ray (h00) and (00l) reflections were found to change drastically in the transition region. (3) Polarized infrared measurements at high temperature revealed a marked increase of the gauche band intensity for the alkyl side group modes followed by a decrease in the band intensity of the thiophene ring modes. (4) The layer reflections of the x-ray fiber diagram become diffuse at high temperatures, indicating that the transition occurs in a liquidcrystalline manner with the orientation of the main chain axes preserved but with almost no axial correlation between the neighboring main chains. These results provide experimental support for the structural model proposed earlier: as the temperature increases, the trans-type side chains begin to disorder by introduction of gauche bonds. This disordering disrupts the regularity of the main chain conformation and decreases the effective length of the polythiophene conjugated system.     

Structural studies on the polymorphism of nylon 3

The structure and morphology of crystalline nylon 3 [poly(β-alanine)] have been studied by electron microscopy and x-ray diffraction. Two clearly defined forms are detected. Form I appears as spherulites made up of ribbonlike lamellae upon crystallization at high temperature from a solution in phenol–butanediol-1,4. They have monoclinic unit cell with a = 9.60 Å, c = 8.96 Å, and β = 122.5°. The hydrogen-bonded planes run parallel to the long dimension of the crystals. Form II is observed when the samples are prepared from formic acid solution at room temperature. A second type of spherulite with a microfibrillar structure is formed in this case. The isolated crystalline structures obtained from Form II appear to grow along the intersheet direction rather than along the hydrogen bond direction, which constitutes anomalous behaviour. Our results for this second form are consistent with an orthorhombic lattice with a = 9.56 Å and c = 7.56 Å. No clear information is obtained on the b dimension of the unit cell (chain axis) in either case. We assume a value of 4.78 Å, which corresponds to fully extended chains. The two forms coexist in films prepared from a formic acid–water solution as well as in samples recovered immediately after polymerization.     

Crystalline structure and morphology of biaxially oriented polyamide‐11 films

The effect of the uniaxial and biaxial stretching and subsequent solution annealing of extrusion‐cast polyamide‐11 films on the crystalline structure and morphology was investigated with differential scanning calorimetry, wide‐angle X‐ray diffraction (WAXD), Fourier transform infrared spectroscopy, and small‐angle X‐ray scattering (SAXS). The extrusion‐cast polyamide‐11 films exhibited elevations in the glass‐transition and cold‐crystallization temperatures with a constant crystallinity and a constant melting point during aging under room conditions (20–26 °C and 20–31% relative humidity). WAXD and SAXS suggested that chain‐folded lamellae of coexisting α‐ and β‐crystals existed in all the stretched polyamide‐11 films. WAXD pole figures indicated that hydrogen bonds in the hydrogen‐bonded sheets of these two crystalline forms apparently formed between antiparallel chain molecules. The unit cell parameters [a = 9.52 Å, b = 5.35 Å, c = 14.90 Å (chain axis), α = 48.5°, β = 90°, and γ = 74.7° for a triclinic α form and a = 9.52 Å, b = 14.90 Å (chain axis), c = 4.00 Å, α = 90°, β = 67.5°, and γ = 90° for a monoclinic β form] for polyamide‐11 crystals were proposed according to the results of this study and the results of previous investigators. The unit cell parameters of the stretched extrusion‐cast polyamide‐11 films varied, depending on the stretching conditions (the stretch temperature and stretch ratio). As the stretch temperature and stretch ratio were increased, the crystal became more similar to the form described previously and was accompanied by an increase in the long spacing of crystalline lamellae. Annealing the stretched films in a boiling 20% formic acid solution made slightly more perfected crystals. The hydrogen‐bonding α(010) + β(002) planes, which are nearly parallel to both amide group planes and zigzag methylene sequence planes of the biaxially stretched films were found to be parallel to the film surface. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2624–2640, 2002     

Crystal structure of isotactic poly(4-methyl-1-pentene)

The crystal structure of isotactic poly(4-methyl-1-pentene) was determined by x-ray analysis. The unit cell is tetragonal, P4 b2, with α = 18.70 Å and c (fiber axis) = 13.68 Å; it contains four molecular chains each consisting of seven monomeric units in the fiber period. The molecular conformation is essentially a (7/2) helix, but deviates slightly from the uniform (7/2) helix. The unusual low density is discussed from the structural point of view.     

Structural differences between two crystal modifications of poly(γ-benzyl L-glutamate)

X-ray diffraction patterns were obtained for as-cast and oriented films of poly(γ-benzyl L -glutamate) and a comparison was made of the molecular packing of the α-helices in forms B and C. Form B snowed Bragg reflections on the layer lines as well as on the equator. The spacings were explained by a monoclinic unit cell comprising two chains, with a = 29.0₆ Å, b = 13 2₀ Å, c = 27.2₇ Å α = γ = 90°. and β = 96°. The chains contained in this unit cell and consequently alternating in the crystal have opposite chain directions. Form C showed continuous scattering on the layer lines and reflections on the equator. This form, therefore, is a nematiclike paracrystal in which the packing of α-helices is periodic in the direction lateral to the chain axis (a = 14.8–115.2 Å, b = 14.3–14.8 Å, c = 27 Å, and γ = 118°–120°), but the relative levels of the chains along the chain axes are displaced. The formation of form C may be attributed to random placement of two chains with mutually opposite chain directions.     

Three-dimensional crystalline order in an atactic comblike polymer

The production of oriented “crystalline” fibers of an atactic polymer, poly{1-[6-(4-biphenylyloxy)hexyloxycarbonyl]ethylene} is reported. The x-ray diffraction is consistent with a two-chain unit cell with a = b = 23.5 Å, c = 6.48 Å, and γ = 120. Although the cell is essentially hexagonal, the absence of screw symmetry along the polymer chain reduces the crystal symmetry to P A packing model consistent with these data is proposed.     

Structural studies of polyethers. IX. Planar zigzag modification of poly(ethylene oxide)

A new crystal modification was found in poly(ethylene oxide) stretched about two-fold after necking at room temperature. An x-ray diffraction analysis indicated that the planar zigzag molecule passes through a triclinic unit cell with parameters α = 4.71 Å, b = 4.44 Å, c (fiber axis) = 7.12 Å, α = 62.8°, β = 93.2°, and γ = 111.4°. The space group is P1 ?C_i¹. Packing of the molecule is very similar to that of monoclinic polyethylene.     

The γ‐form of n‐eicosanol

In the crystal of the title compound, C₂₀H₄₂O, the mol­ecules are packed in layers parallel to the (100) plane. The alkyl chains are parallel to the [30] direction and these molecular chains are hydrogen‐bonded into chains parallel to the c axis. All C—C bonds of the alkyl chain show an antiperiplanar (trans) conformation, with a slight deviation from the ideal value (180°) in the C—C bonds close to the hydrogen bonds. The length of the alkyl chain is 27.92 (2) Å and the tilt angle is 59.7 (2)°.     

Crystal structure of α-gutta percha: Modification of the constrained least-squares method

The crystal structure of α-gutta percha has been determined by x-ray diffraction. The unit cell parameters are a = 7.98 Å, b = 6.29 Å, c (fiber period) = 8.77 Å, and β = 102.0° (monoclinic). The space group is P2₁/c–C_2h⁵. Two molecular chains of nearly trans-CTS-trans-CTS? conformation pass through a unit cell; C, T, S, and S? being the cis, trans, and two types of skew forms, respectively. The constrainedle astsquares method was modified so that the order of the least squares matrix could be reduced and was applied to the refinement of the crystal structure.     

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     

X-ray structure analysis of poly[di-(3,4-dimethylphenoxy)phosphazene]

The crystal structure of oriented poly[di-(3,4-dimethylphenoxy) phosphazene] (PDMP) was determined by x-ray diffraction. Unit-cell parameters were found to be a = 15.85, b = 19.43, and c = 9.85 Å. The unit cell is metrically orthorhombic with monoclinic space group P2₁. There were 48 refinable diffraction spots in the observed reciprocal lattice region, of which 28 were observed and 20 were unobserved. A refined model yielded the following residuals: R^(obs) = 0.162 and 0.138. It was shown that a two-chain unit cell with a [T₃C]₂ (trans, trans, trans, cis, trans, trans, trans, cis) backbone conformation was the correct structure. The dimethylphenoxy side groups were arranged in nearly parallel planes, slightly off-normal to the fiber c axis. The polymer chains are extremely tightly packed and contain close but reasonable steric contacts.     

The crystals and molecular structure of 1,1,4,4-Tetraphenyl-2,5-di-(t-butyl)-1,4-diphosphoniacyclohexadiene-2,5-dichloride

The crystal and molecular structure of the title compound has been determined by single crystal, x-ray diffraction techniques. The compound crystallizes in a monoclinic space group of C2/c symmetry with four molecules in a unit cell of dimensions a = 24.578(1), b = 10.503(1), c = 17.579(1) Å and (3 = 1.30.93 ± .01°. The unit cell also contains two waters of crystallization which are involved in hydrogen bonds to the chloride ions. The central ring has been shown to be a diene which resides in a boat conformation defined by dihedral angles of 157°. The structure has been refined to a value of R = 0.08 using the 1535 statistically significant reflections measured out ot a 2θ value of 140°.     

Crystal structure of poly(dithiotriethylene adipate)

The crystal structure of poly(dithiotriethylene adipate) has been determined through the best fitting of calculated and experimental X‐ray diffraction powder profiles. A triclinic cell was found with dimensions a = 4.942 (7) Å, b = 4.702 (2) Å, c = 20.56 (2) Å, α = 88.9 (2)°, β = 61.0 (1)°, γ = 67.8 (1)°, P‐1 space group, and one chain in the unit cell. A full extended trans conformation of the chain fitted satisfactory the experimental data, yielding to a discrepancy factor R_p = 0.073. A comparison between the crystal structures of poly(dithiotriethylene adipate) and poly (thiodiethylene adipate) is proposed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2677–2682, 2005     

Crystal Structure of the [(C5H4BMe2)2Fe]‐4,4′‐bipyridine Polymer from High Resolution X‐Ray Powder Diffraction

The crystal structure of [(C₅H₄BMe₂)₂Fe]‐4,4′‐bipyridine [ 2 · bipy]_n has been determined by the method of simulated annealing from high resolution X‐ray powder diffraction at room temperature. The compound is of interest, because it proves that highly ordered organometallic macromolecules can be formed in the solid state via the self‐assembly of N–B‐donor‐acceptor bonds. [ 2 · bipy]_n crystallizes in the triclinic space group, P 1, Z = 2, with unit cell parameters of a = 8.3366(2) Å, b = 11.4378(3) Å, c = 12.6740(5) Å, α = 112.065(2)°, β = 108.979(1)°, γ = 90.551(2)°, and V = 1047.06(6) ų. For the structure solution of [ 2 · bipy]_n 11 degrees of freedom (3 translational, 3 orientational, 5 torsion angles) were determined within several hours, demonstrating that the crystal packing and the molecular conformation of medium sized (< 50 non‐hydrogen atoms) coordination compounds can nowadays be solved routinely from high resolution powder diffraction data.     

The structure and properties of oriented fibers of poly(pentamethylene terephthalate). II. Structural analysis of two different crystalline phases by x-ray crystallography

Oriented fibers of poly(pentamethylene terephthalate) will crystallize in one of two phases. In one phase (designated α), which is preferred in the unstressed fiber at room temperature, the chain is contracted from its chemical repeat length. In the other (designated β), induced by tension, it is nearly fully extended. The structural analysis of both forms is described. The unit cells of both phases are triclinic. The parameters of the α phase are a = 4.7 Å, b = 5.8 Å, c = 24.7 Å, α = 112°, β = 94°, γ = 105°. For the β phase they are a = 5.0 Å, b = 5.8 Å, c = 28.2 Å, α = 126°, β = 74°, γ = 120°. The methylene sequence is all trans in the β phase but, surprisingly, in the α phase, three of its bonds are near the eclipsed conformation. The other surprising feature is the departure from planarity of one of the terephthaloyl residues in the β phase. These, and other features of the structures are compared with those of other chemically similar materials, both monomeric and polymeric.     

Structures for monodisperse oligoamides. A novel structure for unfolded three-amide nylon 6 and relationship with a three-amide nylon 6 6

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 α-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 three-amide 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 α-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 (≈ 3 nm in length) form smectic C-like layers with well-orchestrated stacking of 2.2 nm to form a three-dimensional crystal. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2849–2863, 1998