α–γ transition in nylon 6

The α to γ transition that occurs in nylon 6 upon iodine treatment was investigated by infrared spectroscopy, differential thermal analysis, and x-ray diffraction techniques. Thin films of nylon (0.2 mil) were treated in either iodine–potassium iodide aqueous solution or in iodine vapor. Very short treatment times, in the order of 30 sec, were found to effect the transition when a solution 0.5M with respect to iodine was used. The infrared spectra of the iodine nylon complexes formed from either the α- or γ-nylon 6 treated in vapor or dissolved iodine were all similar. This is an indication that molecular iodine is the active species in forming the complex. The temperature of the washing solution used to remove the iodine from the nylon determines whether an α-nylon 6 or γ-nylon 6 is obtained from the complex after washing. Nylon 6 plaque surfaces and thin films are similar in their behavior towards the iodine treatment. The γ-nylon 6 is a stable modification at all temperatures below its melting point. The conversion of the γ form back to the α modification can occur only if the hydrogen bonding is severely affected, e.g., by phenol treatment, iodine treatment, melting, etc. Infrared spectroscopy provided no evidence for an α–γ transition in nylon 6 on heating the sample continuously through its melting point. The shapes of the melting peaks in the above two modifications of nylon 6 were sufficiently different to provide a means of identifying the two crystalline forms.     

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.     

Bis(2‐chloro‐N‐methyl­pyridinium) iodide triiodide

The title compound, 2C₆H₇ClN⁺·I^?·I₃^?, crystallizes with undulating layers of chains containing alternate iodide and triiodide anions formed from iodine and the heterocyclic iodide salt.     

Orientation in nylon 6 films as determined by the three-dimensional polarized infrared technique

A three-dimensional polarized infrared technique was used to obtain information about molecular orientation in both uniaxially and biaxially drawn nylon 6 films. The 835 and 930 cm^?1 bands were used to describe the orientation of the A (extended chain) conformation while absorptions at 1175 cm^?1, and 1120 cm^?1 and 1075 cm^?1 were used to give some information about orientation of the B (twisted chain) conformation. On the basis of the 835 and 930 cm^?1 bands, it was shown that the hydrogen-bonded sheets made up of chains in the A conformation are parallel to the film surface in the biaxially drawn film. Uniaxially drawn films obtained by drawing both at 100 and 150°C showed a high degree of chain alignment in the draw direction for the A conformation at draw ratios greater than 2.5. Some planar orientation was also observed in these uniaxially drawn films for both the A and B conformations at high draw ratios.     

Polyiodide composition in poly(vinyl acetate)-iodine-iodide complex

Polyiodide formed by complexation of poly(vinyl acetate) (PVAc) with iodine in the presence of iodide has been investigated by chemical analysis and resonance Raman spectrophotometry. When PVAc films were immersed in iodide-iodine aqueous solutions which had different ratios of iodide to iodine concentration [I^?]/[I₂], the complex films exhibited tremendous variations of swelling degree, despite the relatively small change in the amount of bound iodine. From a quantitative chemical analysis, the composition of polyiodide bound to PVAc was found to be 1.01 ± 0.035 in the molar ratio of iodide to iodine irrespective of the composition of the iodide-iodine aqueous solution ([I^?]/[I₂] = 2–500). The polyiodide formed in PVAc-iodine-iodide complex was therefore inferred to be (I₃^?)_n. Resonance Raman spectra obtained on PVAc-iodine-iodide complexes were also identical to those of the benzamide-iodine complex, in which the polyiodide consists of (I₃^?)_n, consistent with the result from chemical analysis.     

Mechanical relaxations and moduli of oriented nylon 66 and nylon 6

The mechanical relaxations of dry and wet nylon 66 and nylon 6 with draw ratios λ = 1–3 have been studied from ?180 to 160°C and in the frequency range of 1 Hz to 10 MHz. The five independent elastic moduli C_11, C_12, C_13, C_33, and C₄₄ have also been determined by an ultrasonic method at 10 MHz. Wide-angle x-ray diffraction and birefringence measurements reveal that the crystalline orientation rises sharply at low λ and becomes saturated near λ = 3; the amorphous orientation function increases continuously, reaching values of 0.3–0.5 at λ = 3. The alignment of molecular chains and the presence of taut tie molecules in the amorphous regions lead to a lowering of segmental mobility, thereby reducing the magnitude and increasing the peak temperature and activation energy of the α relaxation. Water absorption weakens the interchain bonding and so gives rise to effects opposite to those of drawing. At low temperature, the development of mechanical anisotropy is largely determined by the overall chain orientation, with the c-shear mechanism contributing a small additional effect. However, above the α relaxation, where the amorphous region is rubbery, the stiffening effect of taut tie molecules becomes dominant and leads to increases in all moduli.     

Rotating-disc electrode studies of the anodic oxidation of iodide in concentrated iodine + iodide solutions

The anodic oxidation of iodide on platinum in concentrated iodine + iodide solutions has been investigated using a rotating disc electrode. The conventional limiting diffusion current, which is produced by the diffusion of iodide ions towards the electrode, was not observed due to the formation of an iodine film on the electrode. On the other hand, the steady-state anodic current after a current/time transient is the genuine limiting diffusion current in the anodic oxidation due to diffusion of iodine species from the electrode surface towards the bulk solution. Thus, the dissolution-diffusion control mechanism of the iodine film is confirmed. This is interesting as a typical example of an anodic process in a redox system governed by diffusion of the anodic product species from the electrode surface towards the bulk solution. When an iodine film is formed on the electrode, the maximum driving force of the iodine species is Δm_I2,max, which is defined as the extent of unsaturation of the iodine, and the limiting current of the anodic oxidation of iodide is always directly proportional to Δm_I2,max, regardless of the forms of iodine species in the solution, which may be I₂, I⁻₃, i₅⁻, etc. δm_I2,max is clearly determined by the solution composition and temperature, and it is different in definition and value from the usual degree of unsaturation of iodine.     

Lower-frequency infrared spectra and structures of some typical aliphatic polyamides

The Polarized lower-frequency infrared spectra (800–33 cm^-1) of nylon 66 (α form), nylon 77 (γ form), and nylon 6 (both α and γ form) have been examined. The spectral changes which occur on complex formation of the polyamides with iodine-potassium iodide solution and on subsequent iodine desorption have been studied in relation to the changes in the polymer structures. On the basis of these results, most of the stronger bands have been reasonably assigned to the vibrations characteristic of the amide group and the methylene chain of the polyamides, and some new structure–frequency correlations have been established for the polymers.     

Electrochemistry of iodine and iodide in chloroaluminate melts

The electrochemical behavior of iodine and iodide has been studied in AlCl₃+NaCl mixtures with compositions ranging from NaCl saturated melts to AlCl₃+NaCl (63+37 mol %) at platinum and tungsten electrodes. Iodide is oxidized in two steps to iodine and I(I); a reduction wave to iodide and an oxidation wave to I(I) are obtained in iodine solutions. The equilibrium constant for the reaction, I^?+I(I)=I₂, is 6×10⁸ l mol^?1 in molten chloroaluminate melts at 175°C.     

The Photochemistry of Ch3I in Various Matrices at Low Temperature

The photodissociation of methyl iodide in various matrices at low temperature was studied. The observed Raman spectra excited by 514.5 nm laser radiation showed that there were two different photolytically produced iodine species isolated in the matrices after illumination by a medium pressure mercury lamp. One species which was dominant at lower iodine concentrations and exhibited a progression with an ωe of 201 cm^?1, belonged to the matrix isolated iodine monomer (I₂). The other species, which was dominant at higher iodine concentrations with an ω_e of approximately 180 cm^?1, belonged to the iodine aggregate ((I₂)_n). Five progressions of resonance Raman or resonance fluorescence of these two species were also observed in the other matrices. The iodine aggregate in the methyl iodide matrix at 77 K was formed in a crystalline structure, while the photolytically generated iodine aggregate from CH₃I/Ar (2/3) matrix at 10 K, after illumination with a mercury lamp, was in amorphous form. The rearrangement of photolytically produced iodine aggregate in methyl iodide matrix was observed as a function of the duration of illumination. Local heating effects of the laser radiation might induce the iodine monomer to aggregate in matrices. The photodissociation mechanism of methyl iodide in matrices is also proposed.     

Structure of the iodine columns in iodinated nylon-6

A study of iodine-complexed nylon 6 films by polarized resonance Raman spectra shows the presence of both I ₃^? and I ₅^? species, the latter most likely in the form of an I ₂/ I ₃^? complex. Polarization characteristics of the Raman spectra show that the I ₂/ I ₃ units are orinted along the polymer chain and the I ₃^? ions are perpendicular to the chain axis. The I ₂/ I ₃^? units are in a more stable moiety than the I ₃^? species. These Raman results are consistent with the x-ray diffraction data.     

Untersuchungen an Polyhalogeniden. XXVI [1]. Über N-Propylurotropiniumpolyiodide UrPrIx mit x = 5 und 7: Strukturelle Charakterisierung eines Pentaiodids und eines Heptaiodids

Studies on Polyhalides. 26. On N-Propylurotropinium Polyiodides UrPrI_x with x = 5 and 7: Crystal Structures of a Pentaiodide and a Heptaiodide The salts UrPrI_x with x = 5 and 7 are formed by the reaction of N-propylurotropinium iodide UrPrI with excess iodine I₂ at room temperature from aqueous solution. N-propylurotropinium pentaiodide C₉H₁₉N₄I₅ crystallizes monoclinically in P2₁/n with a = 1007.6(3) pm, b = 1362.5(3) pm, c = 2899.0(9) pm, β = 91.49(3)º and Z = 8. The crystal structure is built up from parallel chains of cations UrPr⁺ and pairs of V-shaped pentaiodide anions I₅^? along [0 1 0]. N-propylurotropinium heptaiodide C₉H₁₉N₄I₇ crystallizes triclinically in P1 with a = 970.4(1) pm, b = 971.1(1) pm, c = 1357.8(2) pm, α = 106.83(1)º, β = 92.28(1)º, γ = 105.17(1)º and Z = 2. The crystal structure is stacked by alternating cationic and anionic double layers along [0 0 1]. The heptaiodide layer shows a two-dimensional network.     

Ring-disk electrode studies of the open-circuit dissolution of iodine films formed during the anodic oxidation of iodide on platinum

The open-circuit behavior of iodine films formed on platinum by electrooxidation of iodide was studied at rotating disk and rotating ring-disk electrodes. The potential transient and ring current transient at open circuit for c_I^?>0.012 M can be explained by assuming: (1) convective-diffusion controlled dissolution of the film; (2) establishment of the I₂+I^?→ I₃^? equilibrium; (3) establishment of the I₂ (solid) →I₂ (solution) equilibrium. The behavior at lower concentrations of c_I^? suggests that convective-diffusion control is absent.     

Interaction of Iodine with Hexaaza-18-crown-6 and Tetraaza-14-crown-4 in Chloroform Solution

Interactions of hexaaza-18-crown-6 (HA18C6) and tetraaza-14-crown-4 (TA14C4) with iodine have been investigated spectrophotometrically in chloroform solution. The observed time dependence of the charge-transfer band and subsequent formation of I₃ ^- in solution were related to the slow transformation of the initially formed 1:1 macrocycle. I₂ outer complex to an inner electron donor-acceptor (EDA) complex, followed by fast reaction of the inner complex with iodine to form a triiodide ion, as follows: macrocycle + I₂→_fast ^K _f macrocycle.I₂ (outer complex) macrocycle.I₂ (outer complex) →^slow (macrocycle.I⁺)I^- (inner complex) macrocycle.I⁺)I^- (inner complex) + I²→^slow (macrocycle.I⁺)I₃ ^-. The pseudo-first-order rate constants at various temperatures for thetransformation process were evaluated from the absorbance-time data. The activation parameters (E_a, Δ H^?, and Δ S^?) for thetransformation were obtained from the temperature dependence of the rate constants. The stoichiometry and formation constants of the resulting EDA complexes have also been determined. It was found that the (TA14C4.I⁺)I₃ ^- is more stable the (HA18C6.I⁺)I₃ ^- complex in chloroform solution.     

Speciation analysis of iodine and bromine at picogram-per-gram levels in polar ice

Iodine and bromine species participate in key atmospheric reactions including the formation of cloud condensation nuclei and ozone depletion. We present a novel method coupling a high-performance liquid chromatography with ion chromatography and inductively coupled plasma mass spectrometry, which allows the determination of iodine (I) and bromine (Br) species (IO ₃ ^? , I^?, Br^?, BrO ₃ ^? ) at the picogram-per-gram levels presents in Antarctic ice. Chromatographic separation was achieved using an IONPAC® AS16 Analytical Column with NaOH as eluent. Detection limits for I and Br species were 5 to 9 pg g^?1 with an uncertainty of less than 2.5% for all considered species. Inorganic iodine and bromine species have been determined in Antarctic ice core samples, with concentrations close to the detection limits for iodine species, and approximately 150 pg g^?1 for Br^?. Although iodate (IO ₃ ^? ) is the most abundant iodine species in the atmosphere, only the much rarer iodide (I^?) species was present in Antarctic Holocene ice. Bromine was found to be present in Antarctic ice as Br^?.     

Untersuchungen an Polyhalogeniden. XVI. Darstellung und Kristallstrukturen der Bipyridiniumpolyiodide Bipy · HIn mit n = 3, 5 und 7

Studies on Polyhalides. 16. Preparation and Crystal Structures of Bipyridiniumpolyiodides Bipy · HI_n with n = 3, 5, and 7 With simply protonated α,α′-Bipyridyl Bipy · H⁺ a triiodide Bipy · HI₃, a pentaiodide Bipy · HI₅ and a heptaiodide Bipy · HI₇ may be prepared in the presence of iodide ions I^? and dependent of the iodine I₂ content. Bipyridiniumtriiodide C₁₀H₉N₂I₃ crystallizes at room temperature monoclinically in P2₁/n with a = 1 122.8(1) pm, b = 1 072.7(1) pm, c = 1 200.2(3) pm, β = 98.02(2)° and Z = 4. The crystal structure is built up from mixed cationic and anionic layers. Bipyridiniumpentaiodide C₁₀H₉N₂I₅ crystallizes at room temperature monoclinically in P2₁/c with a = 887.3(5) pm, b = 2 527.9(12) pm, c = 830.7(3) pm, β = 106.78(5)° and Z = 4. The crystal structure contains triiodide ions I₃^? till now uniquely connected by iodine molecules I₂ in a trigonal planar way. Bipyridiniumheptaiodide C₁₀H₉N₂I₇ crystallizes at room temperature triclinically in P&1macr; with a = 713.1(3) pm, b = 1 007.9(3) pm, c = 1 464,8(4) pm, α = 81.07(3)°, β = 89.92(3)°, γ = 82.77(3)° and Z = 2. The crystal structure contains a V-shaped pentaiodide ion I₅^? completed by an iodine molecule I₂ to a trigonal pyramidally shaped heptaiodide ion I₇^? and at the same time connected to a zigzag chain.     

Crystal structure of nylon 12

The crystal structure of nylon 12 prepared by polymerization of dodecalactam has been determined by x-ray diffraction. Nylon 12 fiber exhibits only the γ form as its stable crystal structure. The unit cell of nylon 12 was determined with the aid of the x-ray diffraction pattern of a doubly oriented specimen. The unit cell is monoclinic with a = 9.38 Å, b = 32.2 Å (fiber axis), c = 4.87 Å and β = 121.5° and contains four repeating monomer units. The chain is planar zigzag for the most part but is twisted at the position of amide groups, forming hydrogen bonds between neighboring parallel chains. The chain conformation is similar to that of the γ form of nylon 6 proposed by Arimoto. It was deduced from the calculations that there are two chain conformations statistically coexistent according to the direction of twisting. In each conformation, hydrogen bonds are formed between parallel chains to make pleated sheetlike structures. The sheets are nearly parallel to (200) and in the sheet the directions of the neighboring chains are antiparallel, as is the case with nylon 6.     

Synthesis and x-ray study of triferrocenyliodidephosphonium triiodide

A series of iodine derivatives of ferrocenylphosphorus compounds has been obtained. An X-ray investigation of [Fc₃PI]⁺I₃^? has been carried out. All ferrocenyl fragments posses close geometric parameters, similar to those of ferrocene and its derivatives. The positive charge of the cation is localized on the phosphorus atom. Symmetrical I₃^? anions of linear configuration form zigzag-shaped chains, as is usual for triiodides. The cation—anion interaction is realized through short I…I contacts.     

(β-Cyclodextrin)2·KI7·9 H2O. Spatial fitting of a polyiodide chain to a given matrix

α-Cyclodextrin, a torus shaped molecule with a 5 Å wide central cavity, forms a number of deep green, blue and black crystals when complexed with iodine/metal iodide. In contrast, β-cyclodextrin, having a 6 Å cavity produces only one type of reddish-brown crystal, no matter what metal iodide is used. The complex (β-cyclodextrin)₂ ·KI₇·9H₂O displays space groupP2₁ (pseudo-C2) with cell constantsa=19.609(5),b=24.513(7),c=15.795(6)Å, β=109.50(2)°,Z=4. The crystal structure was solved inC2 on the basis of 3022 absorption corrected CuKα (Ni-filter) X-ray intensities and refined by full matrix least squares toR=17%. This relatively highR-factor is due to many weak reflections (pseudo-C2) and considerable disorder exhibited by water and iodine. In the complex, β-cyclodextrin adopts a ‘round’ shape with O(2)...O(3) interglucose hydrogen bonds formed and all O(6) hydroxyls pointing away from the cavity. Two molecules are arranged head-to-head to produce a dimer, and dimers are stacked such that a slightly zigzagged cylinder with a 6 Å-wide cavity is formed. In the cavity described by each dimer, an I ₇ ^? ion composed of I₂·I ₃ ^? ·I₂ units is located, with I₂ and I ₃ ^? perpendicular to each other. K⁺ ions and 9 H₂O molecules are found in interstices between the β-cyclodextrin cylinders. This zigzag polyiodide contrasts with the linear form observed in the 5 Å wide α-cyclodextrin channels. It explains differences in color of the crystals and suggests that β-cyclodextrin polyiodide is not a good model for blue starch-iodine.     

Ternary diffusion with charged-complex formation in aqueous I2+NaI and I2+KI solutions

Diaphragm cells have been used to measure ternary diffusion coefficients for I₂+NaI and I₂+KI in aqueous solution at 25°C. Although most of the iodine molecules are bound to iodide ions and are transported as the triiodide species [I₂(aq)+I^–(aq)=I ₃ ^– (aq)], diffusion of the iodide salts produces relatively small countercurrent coupled flows of the iodine component. The ternary diffusivity of the iodine component in the solutions is 10 to 20% larger than the diffusivity of the triiodide species. This behavior can be understood by considering electrostatic coupling of the ionic flows. The diffusion equations for I₂+NaI and I₂+KI components are reformulated in terns of NaI₃+NaI and KI₃+KI mixed electrolyte components.