Morphology of polypropylene crystals. III. Lamellar crystals of thermally decomposed polypropylene

Morphology and crystal structure of solution-grown and melt-grown crystals of thermally decomposed polypropylene have been studied by electron microscopy and x-ray diffraction. By crystallization from dilute α-chloronaphthalene or carbitol solutions well-defined lamellar crystals about 100–150 A. in thickness are obtained from fractions (number-average molecular weights 1600–2100) of thermally decomposed crystalline polypropylene. The structure is monoclinic as crystallized from very dilute α-chloronaphthalene or carbitol solutions (0.02–0.005 wt.-%). However crystals of the triclinic as well as of the monoclinic forms are precipitated from carbitol solutions of higher concentrations (0.05-1 wt.-%). On the other hand, the separated triclinic form has been obtained from the melt. Crystals of both modifications have similar morphology. In addition, the chain molecules cannot be expected to fold, within the thickness of lamellae in crystals of either modification prepared from the low molecular weight fractions used in this study.     

Theoretical and experimental studies of the structure and intermolecular interactions in 2-biphenylmethanole

The crystalline structure of 2-biphenylmethanol has been investigated by the radiographic method at room temperature, and its IR transmission spectra were measured in the 400–4000 cm^?1 range. Structural-dynamic models of free molecules of 2-biphenylmethanol, biphenyl and methanol, hydrogen-bonded complexes of 2-biphenylmethanol with methanol and a tetramer of methanol molecules have been built by the density functional method (B3LYP/6-31G*). The structure, the energy, mechanical and electro-optical parameters, the frequency and intensity of normal vibrations in IR spectra of each of the mentioned molecular systems were calculated. The crystalline structure of 2-biphenylmethanol, its features determined by the hydrogen bond formation in the crystal has been found, its structure-forming role and energy were assessed, and IR spectra interpreted on the basis of single crystal X-ray diffraction data, the analysis of measured IR spectra, and results of molecular modeling.     

Study of “Racemic Compound-Like” Behavior of Diastereomeric Mixture of Pinanyl Sulfoxides by X-Ray Diffraction,IR Spectroscopy,and DFT Calculations

Abstract

The oxidation of a β-hydroxysulfide in the pinane series by use of m-chloroperbenzoic acid resulted in the formation of the corresponding β-hydroxysulfoxide as a mixture of two diastereomers in 4:5 ratio. According to single-crystal X-ray diffraction (XRD) results, it is established that the diastereomeric mixture of sulfoxides crystallizes in the “racemic compound-like” manner under formation of asymmetric dimers through S=O··H–O interactions. This asymmetric dimer formed from diastereomeric molecules is a structural unit in both crystal modifications, the triclinic and the monoclinic one. The behavior of the diastereomeric mixture of pinane derived sulfoxides in crystals, melts and in tetrachloromethane solutions was studied by IR spectroscopy. The density functional theory (DFT) method with 6-31G (d, p) basis set was used to calculate the optimized geometrical parameters and vibrational frequencies of different associates in solutions. The calculated vibrational frequencies are compared with experimental IR spectra.     

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.     

Trichloromethyl chloroformate ("diphosgene"), ClCOOCCl3: structure and conformational properties in the gaseous and condensed phases

The conformational properties of gaseous trichloromethyl chloroformate (or "diphosgene"), ClC(O)OCCl3, have been studied by vibrational spectroscopy [IR (gas), IR (matrix), and Raman (liquid)] and quantum chemical calculations (MP2 and B3LYP with 6-311G basis sets); in addition, the structure of a single crystal at low temperature has been determined by X-ray diffraction. ClC(O)OCCl3 exhibits only one conformational form having Cs symmetry with a synperiplanar orientation of the C-O single bond relative to the C=O double bond. The calculated energy difference between the syn and anti forms, 5.73 kcal mol(-1) (B3LYP) or 7.06 kcal mol(-1) (MP2), is consistent with the experimental findings for the gas and liquid phases. The crystalline solid at 150 K [monoclinic, P2(1)/n, a = 5.5578(5) angstroms, b = 14.2895(12) angstroms, c = 8.6246(7) angstroms, beta = 102.443(2) degrees, Z = 4] likewise consists only of molecules in the syn form.     

Synthesis of alkyl (3-pyridyl)hydroxymethylphosphonates and their IR spectra

The reaction of dialkyl H-phosphonates with pyridine-3-carbaldehyde gives alkyl (3-pyridyl)hydroxymethylphosphonates. In liquid systems, the hydrogen atom is localized at the oxygen atom of the hydroxyl group; in crystals, the existence of a zwitter-ionic form could not be excluded. In CHCl₃ solutions, isolated molecules and cyclic dimeric H-complexes exist in an equilibrium.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1674–1676, September, 1994.     

N,N-dimethyl-selenobenzamide: two solid phases and low-temperature phase change

Two polymorphs (I: mp 49.0–50.0°C; II: mp 80.0–82.0°C) of N,N-dimethyl-selenobenzamide, (CH₃)₂NC(Se)Ph, have been observed. Both I and II can be prepared separately using the same reaction under different conditions. The phase change from phase I to phase II occurs at low temperatures and this has been confirmed by solid state NMR (¹³C), powder X-ray, and single-crystal structural studies. The single-crystal X-ray diffraction study reveals that the lower melting point form (phase I) crystallizes in the triclinic space group P-1 with two conformations in the unit cell, while the higher melting point form (phase II) crystallizes in the monoclinic space group P2₁/c with one conformation in the unit cell. Theoretical calculations on model clusters using the Universal Forcefield (UFF) show that the total energy of phase I (triclinic form) is 5.9 kcal per mol molecule higher than that of phase II (monoclinic form). Also, the immersion energy which is due to non-bonding interactions, namely Van der Waals and Coulombic (electrostatic) terms, has been calculated using UFF. The Van der Waals terms were very similar in the two crystalline forms (triclinic: −43.1 kcal mol⁻¹; monoclinic: −44.8 kcal mol⁻¹), but the Coulombic terms were significantly different (triclinic: −14.0 kcal mol⁻¹; monoclinic: −31.5 kcal mol⁻¹) and favor the monoclinic form. The triclinic form (phase I) is a kinetically favored metastable phase and upon cooling it changes to the monoclinic form (phase II), a thermodynamically stable phase.     

Disordered Nanoporous Crystalline Modifications of Syndiotactic Polystyrene

Disordered crystalline modifications formed by s(2/1)2 helices of syndiotactic polystyrene (s-PS) can be prepared by the removal of bulky guest molecules from intercalate as well as from triclinic δ clathrate forms. The X-ray diffraction pattern of the disordered crystalline modification is characterized from 2θ_CuKα < 12° by only a broad diffraction peak whose maximum is located in the 2θ_CuKα range between 8.7° and 9.8°. Films presenting disordered crystalline modifications have been used for the removal of an organic pollutant from dilute aqueous solutions. The sorption behavior of the disordered crystalline modifications are compared with that of the nanoporous-crystalline δ form as well as of the dense γ form. The disordered crystalline modifications of s-PS presents pollutant (1,2-dichloroethylene) uptake comparable to those of the nanoporous δ and ε forms and much higher than those obtained for the dense γ form. Moreover, FTIR data relative to sorption of 1,2-dichloroethane show that the guest sorption occurs essentially only in the crystalline phase. As a consequence, the obtained disordered crystalline modifications of s-PS can be fully considered disordered nanoporous-crystalline modifications.     

On the mechanical properties of poly(ethylene terephthalate). Force-field parametrization and conformational analysis for the prediction of the crystal moduli

A force-field suitable for the calculation of the mechanical properties of poly(ethylene terephthalate) and their relation with the molecular structure of the polymer has been developed. The force-field parameters were derived from quantum mechanical AM1 calculations and tested against thermodynamic and vibrational spectroscopy data available for a set of closely related small molecules. The crystal moduli of the two solid phases known for poly(ethylene terephthalate) were estimated by means of this new force-field considering both the isolated chain and the chain within the unit cell. Results were qualitatively consistent with reported x-ray data showing that the triclinic crystal form is stiffer than the mesomorphic phase provided that sample heterogeneities were taken into account. Although overestimated moduli resulted for both cases, divergences with experimental values were found to be slighter than those obtained by other theoretical methods. © 1996 John Wiley & Sons, Inc.     

Reactions of N-silylphosphoranimines with alcohols: synthesis and structure of cyclotriphosphazenes with nongeminal methyl and phenyl substituents

The reactions of Me(3)SiN=P(OR")RR'(R" = Ph, CH(2)CF(3); R, R' = Me, Ph) with alcohols were investigated. With nonequivalent amounts of CF(3)CH(2)OH, the reactions produced high yields of the cyclic phosphazene (Me(2)PN)(3) and both the cis and trans isomers of nongeminally substituted [(Ph)(Me)PN](3). The isomers of this new cyclic phosphazene were separated by column chromatography and characterized by NMR and IR spectroscopy, elemental analysis, and X-ray crystallography. Crystals of the cis isomer 6a have a monoclinic crystal system, while the trans isomer 6b has a triclinic crystal system with two different molecules in an asymmetric unit. The bond lengths and bond angles are very similar to those of the simpler cyclic trimers (Me(2)PN)(3) and (Ph(2)PN)(3.) A likely pathway for the formation of these compounds is discussed.     

Kristall- und Molekülstruktur von Bis(1,1-diethyl-3-thiobenzoyl-thioureato)nickel(II)

Crystal and Molecular Structure of Bis(1,1-diethyl-3-thiobenzoyl-thioureato)nickel(II). Bis(1, 1-diethyl-3-thiobenzoyl-thioureato)nickel(II) forms two modifications, whose structures have been determined by X-ray structure analysis. The monoclinic modification crystallizes in the space group P2₁/n with a = 13.709, b = 8.571, c = 12.803 Å, β = 68.10° and Z = 2. The triclinic modification crystallizes in the space group I1 with a = 14.406, b = 7.761, c = 11.734 Å, α = 86.10, β = 97.39, γ = 90.18° and Z = 2. The molecular structures of both modifications are nearly identical (packing polymorphism). The coordination is exactly planar, the ligands are arranged in trans position. The average Ni? S bond length is 2.153 Å in the monoclinic form and 2.163 Å in the triclinic form. The chelate rings deviate from planarity.     

n-pentanol at high pressures: rotational isomerism in the liquid phase and the liquid-solid phase transition

The vibrational spectrum of liquids constituted of chain molecules is difficult to analyze because it may have contributions of different rotational isomers. In turn, with a proper vibrational assignment, this feature allows us to extract information about the effect of temperature or pressure on the molecular conformations in the liquid state. In this regard, the information on the vibrational spectrum in the solid phase greatly simplifies the vibrational analysis of the different rotational conformers existing in the liquid, as the molecules usually present all-trans conformations in the crystalline state. Here we report room-temperature Raman experiments on n-pentanol performed in a sapphire-anvil cell up to 3 GPa. A detailed analysis of the liquid-solid phase transition occurring at 1.3 GPa is provided. The analysis of the Raman spectrum in the solid phase allows the identification of the bands due to the different rotational isomers present in the liquid. The analysis of the spectral region corresponding to skeletal vibrations of the carbon chain (800-1200 cm(-1)) indicates that gauche conformers are promoted by the application of pressure. The analysis of the intensity ratio of those bands assigned to trans and gauge conformations is used to calculate the change in molecular volume ascribed to the trans-gauge isomerization process. We find a value similar to that found in n-alkanes, i.e., -0.88 cm(3) mol(-1). In addition, we find indication that pressure varies the proportions of the different gauge conformers. Thus, it appears that the GTTt to TGTt transition in the carbon chain is favored at high pressures. As expected, a smaller change in the molecular volume accompanies this conformation change.     

H/D isotopic recognition in hydrogen-bonded systems: strong dynamical coupling effects in the polarized IR spectra of 3-methylthioacetanilide and 4-methylthioacetanilide crystals

This paper presents the investigation results of the polarized IR spectra of the hydrogen bond in crystals of 3- and 4-methylthioacetanilide. The spectra were measured at 293 and 77 K by a transmission method, with the use of polarized light. The main spectral properties of the crystals can be interpreted satisfactorily in terms of the "strong-coupling" theory, on the basis of the hydrogen bond centrosymmetric dimer model. The spectra revealed that the strongest vibrational exciton coupling involved the closely spaced hydrogen bonds, each belonging to a different chain of associated 3- and 4-methylthioacetanilide molecules. A weaker exciton coupling involved the adjacent hydrogen bonds in each individual chain. It was proven that a nonrandom distribution of the protons and deuterons took place in the lattices of isotopically diluted crystalline samples of 3- and 4-methylthioacetanilide. In each case, the H/D isotopic "self-organization" mechanism involved all four hydrogen bonds from each unit cell.     

Control of molecular structure in the generation of highly luminescent liquid crystalline perylenebisimide derivatives: synthesis, liquid crystalline and photophysical properties

We report here, for the first time, the role of the molecular design on the liquid crystalline and solid-state photoluminescent properties of soluble and thermally stable liquid crystalline perylenebisimide derivatives. A new series of perylenebisimides were designed and developed for this purpose by adopting the stoichiometry-control approach, and amine-, hydroxyl-, ester-, and amide-functionalized molecules were synthesized. Various types of spacers with different lengths (C(2) to C(12)), types (linear, cyclohexyl, and tricyclodecane), and end-capped by phenyl or tridodecyloxy gallic units were introduced in the perylenebisimide core. The molecules were completely characterized by NMR, FT-IR, SEC, and MALDI-TOF mass techniques. Thermal analysis revealed that the perylenebisimide derivatives were thermotropic liquid crystalline, and threadlike nematic phases were observed under a polarizing light microscope. The spacer length and the rigidity of the spacers play a major role in the liquid crystalline properties of the materials. In phenyl systems, the C(6) chain with ester- and the C(12) chain with amide-end-capped molecules showed a nematic phase, whereas the C(6) chain with an amide end cap and their cyclic and tricyclic counterparts did not show any LC property. The introduction of a tridodecyloxy gallic unit induced the LC property in C(12) and the cyclohexyl system; however, it failed to do so in the tricyclodecane molecule. The absorption properties of the molecules were almost unchanged by the structural variation; however, the emission quantum yield in solution and photoluminescent (PL) intensity in the solid state were significantly different. Though the gallic unit induced liquid crystallinity in the perylenebisimide core, the quantum yield and PL intensity are 4-5 times less compared to those of the simple phenyl-capped liquid crystalline system. Among the various types of spacers, the tricyclodecane induced strong molecular aggregates via pi-stacking, which in turn increased the rigidity of the entire perylenebisimide core, resulting in the absence of liquid crystallinity and low luminescence compared to their linear and cyclohexyl analogues. The molecular aggregates were very stable even at very dilute concentration and also at high temperatures. The aggregates disappeared immediately upon addition of trifluoroacetic acid, thus confirming the strong hydrogen bonding in the aggregated states. In a nutshell, the present report demonstrates the importance of molecular design for introducing liquid crystalline phases in perylenebisimides and also the development of novel highly luminescent n-type pi-conjugated material for application in optoelectronics.     

Strength of Intramolecular Hydrogen Bonding in 2-Biphenylmethanol and 4-Biphenylmethanol

Russian Journal of General Chemistry - The absolute vapor pressures over the solid and liquid 2-biphenylmethanol and 4-biphenylmethanol were measured using the transpiration method. The standard...     

Two polymorphic modifications of 1-(N-morpholiniomethyl)spirobi- (3-oxo-2,5-dioxa-1-silacyclopentan)- ate hydrate

The compound 1-(N-morpholiniomethyl)spirobi(3-oxo-2,5-dioxa-1-silacyclopentan)ate crystallizes from aqueous solution of γ-butyrolactone in the form of two crystal hydrate modifications: monoclinic (with D = 1.53 g/cm³, space group P 2₁/n) and triclinic (D = 1.45 g/cm³, space group P1^-). For the monoclinic form, an X-ray structural study at -100°C has been performed. For both structures the coordination polyhedron of the silicon atom is a trigonal bipyramid. In the crystal structures there are strong intermolecular hydrogen bonds of NH···O and OH···O types.     

Phase behavior of poly(9,9-di-n-hexyl-2,7-fluorene)

Here we report the phase behavior of poly(9,9-di-n-hexyl-2,7-fluorene) (PFH), which previously received little attention as compared to its homologues poly(9,9-di-n-octyl-2,7-fluorene) (PFO) and poly(9,9-di-(2'-ethylhexyl)-2,7-fluorene) (PFEH). By means of differential scanning calorimetry, X-ray diffraction, and electron microscopy, we show that there exist four different phases in PFH. The as-cast film is mainly composed of a mesomorphic beta phase with layer spacing of ca. 1.4 nm. This beta phase is inherently metastable and, upon heating above 175 degrees C, transforms into a crystalline (alpha) form that melts into a nematic (N) liquid above 250 degrees C. Upon stepwise cooling, the nematic melt crystallizes into the alpha phase first, followed by solid-solid transformation into another crystalline (alpha') form. Unit cell structure of the alpha form is monoclinic whereas that of the alpha' form is triclinic, but departures from strict orthogonality are slight (by ca. 6 degrees). These observations not only support our previous assignment of two crystalline forms (both orthorhombic in structure) in PFO but also provide insights to the crystalline nature of the polyfluorene series.     

Thermal investigation on polymorphism in sodium saccharine

The thermal behavior of sodium saccharin polymorphic forms was investigated using thermogravimetry and differential scanning calorimetry, while structural changes during the dehydration processes were monitored by X-ray powder diffraction. In solid state, sodium saccharine may exhibit three forms: anhydrate, 2/3 hydrate (triclinic), and 15/8 hydrate (monoclinic) ones. In this investigation, it was established that monoclinic and triclinic forms compose an entantiotropically related polymorphs system. At 82 °C, the 15/8 hydrated monoclinic form is converted to 2/3 hydrated triclinic form, which showed to be the more thermodynamically stable form at room temperature. Spontaneous solidification leads to the formation of triclinic cell setting, and additionally, spontaneous hydration of the anhydrous form leads to formation of 2/3 hydrated triclinic form.     

Crystal and molecular structure of N-(4-nitrophenyl)-β-alanine--its vibrational spectra and theoretical calculations

The N-(4-nitrophenyl)-β-alanine in crystalline form directly by the addition of 4-nitroaniline to the acrylic acid in aqueous solution has been obtained. The title β-alanine derivative crystallizes in the P2(1)/c space group of monoclinic system with four molecules per unit cell. The X-ray geometry of β-alanine derivative molecule has been compared with those obtained by molecular orbital calculations corresponding to the gas phase. In the crystal the molecules related by an inversion center interact via symmetrically equivalent O-H···O hydrogen bonds with O···O distance of 2.656(2) ? forming a dimeric structure. The dimers of β-alanine derivative weakly interact via N-H···O hydrogen bonds between the H atom of β-amine groups and one of O atom of nitro groups. The room temperature powder vibrational (infrared and Raman) measurements are in accordance with the X-ray analysis. In aqueous solution of 4-nitroaniline and acrylic acid, the double CC bond of vinyl group of acrylic acid breaks as result of 4-nitroaniline addition.     

Two polymorphs of 20‐desmethyl‐β‐carotene

Two polymorphs of 20‐desmethyl‐β‐carotene (systematic name: 20‐nor‐β,β‐carotene), C₃₉H₅₄, in monoclinic and triclinic space groups, were formed in the same vial by recrystallization from pyridine and water. Each polymorph crystallizes with the complete molecule as the asymmetric unit, and the two polymorphs show differing patterns of disorder. The β end rings of both polymorphs have the 6‐s‐cis conformation, and are twisted out of the plane of the polyene chain by angles of −53.2 (8) and 47.3 (8)° for the monoclinic polymorph, and −43.6 (3) and 56.1 (3)° for the triclinic polymorph. The cyclohexene end groups are in the half‐chair conformation, but the triclinic polymorph shows disorder of one ring. Overlay of the molecules shows that they differ in the degree of nonplanarity of the polyene chains and the angles of twist of the end rings. The packing arrangements of the two polymorphs are quite different, with the monoclinic polymorph showing short intermolecular contacts of the disordered methyl groups with adjacent polyene chain atoms, and the triclinic polymorph showing π–π stacking interactions of the almost parallel polyene chains. The determination of the crystal structures of the two title polymorphs of 20‐desmethyl‐β‐carotene allows information to be gained regarding the structural effects on the polyene chain, as well as on the end groups, versus that of the parent compound β‐carotene. The absence of the methyl group is known to have an impact on various functions of the title compound.