Monte Carlo simulations of a liquid crystal copolymer in the solid state

The condensed phase of the alternating copolyester of p-hydroxybenzoic acid (HBA) and 2-hydroxy-6-naphthoic acid (HNA) is investigated by studying the room temperature packing arrangement of the copolymer chains. A molecular modeling methodology is employed with a Monte Carlo sampling of the configurational phase space. Realistic poly(HBA-alt-HNA) polymer chains are represented by an explicit atom representation of the HBA/HNA dimers. States are sampled from the NVT ensemble using a sampling scheme consisting of (1) valence and torsional variations, (2) rigid body rotations of the chain about the chain axis, and (3) rigid body translations of the chain. The effect of chain packing on the conformation of chains, as well as the relative intra- and intermolecular orientations of aromatic rings, is investigated. Correlation of chain positioning along the chain axis is dominated by aromatic rings maintaining a center-to-center plane of registry. These layers of aromatic units pack with a preference for edge-to-face orientations in a herringbone-type pattern and have an intermolecular ring angle between the pairs of aromatic rings in the unit cell that is ca. 68°. The aromatic rings, on average, are rotated 38° out from the b–c plane. The phenylene rings of these copolyesters are less restricted in their relative orientation in comparison to the naphthalene rings. Intramolecular orientational probability density distributions indicate a preference for staggering the successive aromatic rings along the chain, with a staggering angle of ca. 66°. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 727–741, 1998     

(2S,RS)‐6‐Phenyl‐1‐(p‐tolyl­sulfinyl)­hexa‐3(E),5(E)‐dien‐2‐ol

The mol­ecule of the title compound, C₁₉H₂₀O₂S, corresponds to a chiral sulfinyldienol with two stereogenic centres, viz. the C atom susbtituted by the hydr­oxy group and the sulfinyl S atom. The mol­ecule displays a V‐shape in the solid state. The dihedral angle defined by the least‐squares planes of the aromatic rings is 72.9 (1)°. The packing pattern exhibits the following inter­molecular hydrogen bonds: one O—H⋯O [H⋯O = 1.98 Å, O⋯O = 2.785 (4) Å and O—H⋯O = 166°] and two C—H⋯O [H⋯O = 2.58 and 2.60 Å, C⋯O = 3.527 (5) and 3.347 (5) Å, and C—H⋯O = 164 and 134°]. These define a chain along b.     

The X‐ray Crystal Structures of Hg(C6F4X‐p)2 (X = NH2, OMe,or Me) – Two Examples of Supramolecular Lewis Acid/Base Complexes

The X‐ray crystal structures of Hg(C₆F₄X‐p)₂ (X = NH₂, OMe, or Me) show the compounds to have almost linear C–Hg–C stereochemistry (X = NH₂, 176.3(4)°; X = OMe, 179.5(2)°; X = Me, 176.3(2)°), and the two tetrafluoroaryl rings rotated ca. 52–62° with respect to each other. Substantial conjugation of NH₂ and OMe groups with the aromatic rings is evident from N–C and O–C(Ar) distances. For X = NH₂ or OMe, two weak N(O)–Hg coordination interactions per mercury lead to a two dimensional supramolecular chain structure containing pairs of π‐stacked aromatic rings at near van der Waals contact distances rotated at 62.2° (X = NH₂) or 52.9° (X = OMe) to each other. In Hg(C₆F₄Me‐p)₂, which does not have potential donor atoms, no supramolecular structure is obtained, the molecules being laterally displaced from one another.     

Synthesis and evaluation of properties of novel poly(benzimidazole‐amide)s

Novel aromatic polyamides have been prepared by a combination of diacids containing preformed benzimidazole rings and aromatic diamines. By the phosphorylation method of polycondensation, polymers of high molecular weight (inherent viscosities between 0.81 and 2.13 dL/g) were obtained, which showed good solubility in polar aprotic solvents. The combination of aromatic amide linkages and benzimidazole rings along the polymer chain endowed the polymers with high thermal resistance and excellent mechanical properties. Glass transition temperatures fell in the range of 290–330 °C as measured by differential scanning calorimetry, and initial decomposition temperatures under nitrogen were over 480 °C as measured by thermogravimetric analysis. Some polymer films showed outstanding tensile strength (over 150 MPa) and moduli (up to 5 GPa). The presence of benzimidazole rings in the current polyamides greatly enhanced their hydrophilicity in comparison with classical wholly aromatic polyamides; thus, although aromatic polyamide films normally show water sorption values of only 4–8%, some of the current poly(benzimidazole amide)s show water sorption up to 19% in a 65% relative humidity atmosphere. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7566–7577, 2008     

Partially bio‐based poly(amide imide)s by polycondensation of aromatic diacylhydrazides based on lignin‐derived phenolic acids and aromatic dianhydrides: Synthesis,characterization, and computational studies

Two new bio‐based diacylhydrazide monomers, namely, 4,4′‐(propane‐1,3‐diylbis(oxy))bis(3‐methoxybenzohydrazide) and 4,4′‐(propane‐1,3‐diylbis(oxy))bis(3,5‐dimethoxybenzohydrazide) were synthesized starting from lignin‐derived phenolic acids, namely, vanillic acid and syringic acid. A series of poly(amide imide)s was synthesized by polycondensation of these diacylhydrazide monomers with commercially available aromatic dianhydrides. Poly(amide imide)s showed inherent viscosity in the range 0.44–0.56 dL g^?1 and exhibited good solubility in organic solvents. Poly(amide imide)s could be cast into transparent, flexible, and tough films from their N ,N‐dimethylacetamide solutions. Poly(amide imide)s showed 10% weight loss in the temperature range 340–364 °C indicating their good thermal stability. Glass transition temperature (T _g) of poly(amide imides)s were measured by DSC and DMA which were in the range 201–223 °C and 214–248 °C, respectively. The T _g values of poly(amide imide)s were dependent on the number methoxy substituents on aromatic rings of diacylhydrazide monomers. Molecular dynamics simulation studies revealed that chain rigidity is the dominant factor for observed trends in T _g. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 3636–3645     

Hydrodynamic Properties and Unperturbed Dimensions of Polydecahydro- β -naphthyl and Poly- β-naphthyl Methacrylates in Different Solvents

Abstract

Intrinsic viscosity, sedimentation, light-scattering, and osmotic-pressure measurements have been carried out at 25° on dilute solutions of polydecahydro-β -naphthyl meth-acrylate (PDNa) and of poly-β-naphthyl methacrylate (PNa). For both polymers, the degree of polydispersity was around 1.5 and the molecular weight range was large: 10⁵ to 3 × 10⁶. Relations between [η], [S₀], A₂, and molecular weight have been established.

The applicability of the different theories (Stockmayer-Fixman, Kurata-Stockmayer, Fox-Flory, Cowie, Berry, Kamide-Moore) for the determination of the unperturbed dimensions from the viscosity data is discussed; Berry's relation best fits the experimental data.

These dimensions, calculated from the sedimentation data according to the Cowie-Bywater relation, agree with those obtained by viscosity. The flexibility factor is 2.9 for PDNa and 3.1 for PNa. These large values are a consequence of the presence of very bulky groups in the side chain; however, the higher η value for PNa led to the assumption that a specific interaction between the aromatic rings influences the rigidity of the main chain.     

Crystal and molecular structure of syndiotactic 2,4,6-triphenylheptane,a polystyrene model moleculE

The crystal and molecular structures of syndiotactic 2,4,6-triphenylheptane have been determined by direct methods and refined from X-ray diffraction data recorded with a four-circle diffractometer and Mo Kα radiation. The unit cell is monoclinic, space group P2₁/c; at room temperature, a = 16.831, b = 9.104, c = 34.390 Å and β = 128.11°. It is found that the two molecules in the asymmetric unit have the same trans conformation of the chain, with aromatic rings virtually perpendicular to the chain.     

Structure of molecular nanoparticles of petroleum asphaltenes

Ab initio RHF/3-21G** and MM+ molecular mechanics method are employed to calculate the structural chemical parameters of molecular nanoparticles of petroleum asphaltenes. It is found that naphtheno-aromatic rings have a non-planar cup-like character. The values of dihedral angles α ₁ between the planes of aromatic and naphthene rings, which are calculated by the RHF/3-21G** method, are within 156–163°. The values of dihedral angles α₂, which were calculated by the molecular mechanics method, are within 156–164°.     

DC Electrical Conductivity of Some Oligoazomethines Doped with Nanotubes

Three aromatic oligoazomethines containing seven benzene rings each were synthesized. The terminal rings were substituted with different organic groups; namely, OH, H, and NO₂. Synthesis was carried out according to the literature by condensing the para-substituted benzaldehydes with benzidine to give the three rings compound, which is then condensed with terephthaldehyde to give the respective seven benzene rings oligomer. The oligomers were used to investigate the effects of molecular structure on the electronic structure, as well as electronic and electrical properties. DC electrical conductivity variation of oligoazomethines is studied in the temperature range 300–500 K after annealing for 24 h at 100°C and after doping with 25 and 50 wt% Multi Wall Nanotubes (MWNTs). An attempt is made to relate DC electrical conductivity and electronic properties to chain length, substituted groups and coplanarity. The different groups attached to the ends showed a small effect on conductivity of the different oligomers in the following order: electron donating > neutral > electron withdrawing groups. Oligoazomethines-MWNTs gave a value of (10^?4 Scm^?1) as the highest electrical conductivity at higher temperatures. DC electrical conductivity was interpreted using the band energy model. The narrow-gap activation energies noted suggest its application in formulation of photovoltaic panels.     

Hydrogen bonding in 2‐amino‐4,6‐dimethoxypyrimidine, 2‐benzylamino‐4,6‐bis(benzyloxy)pyrimidine and 2‐amino‐4,6‐bis(N‐pyrrolidino)pyrimidine: chains of fused rings and a centrosymmetric dimer

Molecules of 2‐amino‐4,6‐di­methoxy­pyrimidine, C₆H₉N₃O₂, (I), are linked by two N—H?N hydrogen bonds [H?N 2.23 and 2.50 Å, N?N 3.106 (2) and 3.261 (2) Å, and N—H?N 171 and 145°] into a chain of fused rings, where alternate rings are generated by centres of inversion and twofold rotation axes. Adjacent chains are linked by aromatic π–π‐stacking interactions to form a three‐dimensional framework. In 2‐­benzylamino‐4,6‐bis(benzyloxy)pyrimidine, C₂₅H₂₃N₃O₂, (II), the mol­ecules are linked into centrosymmetric R(8) dimers by paired N—H?N hydrogen bonds [H?N 2.13 Å, N?N 2.997 (2) Å and N—H?N 170°]. Molecules of 2‐amino‐4,6‐bis(N‐pyrrolidino)­pyrimidine, C₁₂H₁₉N₅, (III), are linked by two N—H?N hydrogen bonds [H?N 2.34 and 2.38 Å, N?N 3.186 (2) and 3.254 (2) Å, and N—H?N 163 and 170°] into a chain of fused rings similar to that in (I).     

The syntheses and conformational studies of [n](2,4)heterophanes and [7](3,5)pyrazolophane

Synthetic sequences from (n + 3)-membered 2-cycloalkenones provide furan, thiophene and pyrrole derivatives bridged at the 2,4-positions by n-methylene chains (n = 6, 7, and 9) as well as a pyrazole derivative bridged at the 3,5-positions (n = 7). The molecular geometry as a function of the chain length has been investigated spectrometrically. The aliphatic chain of [7](2,4)pyrrolophane and [7](3,5)pyrazolophane is found to reside in the one side of the respective heteroaromatic rings even at 205°, whereas that of [7](2,4)thiophenophane flips up and down the thiophene ring upon heating, the energy barrier ΔG_c^≠ being 18·2 kcal/mol (T_c 111°C at 60 MHz). The conformational behaviour of the heptamethylene chain is thus dependent on the angle between the bonds connecting each heteroaromatic carbon with the benzylic one. Though the hexamethylene chain of the [6](2,4)heterophanes is fixed to the one side of the aromatic ring, the nonamethylene chain of the [9]-homologues is rapidly moving between the both sides even at room temperature. The red-shifts of the B-bands are attributed to the distorted, nonplanar heteroaromatic rings. The mass spectra of these heterophanes indicate the initial C(1)-C(2) fission of the polymethylene chain probably due to the steric strain of the systems.     

Linear soluble polybenzyls

Linear soluble polybenzyls, although deceptively simple in structure, have been strangely elusive. We report for the first time the synthesis of perfectly linear soluble polybenzyls by the polycondensation of 1,2,4,5‐tetrasubstituted benzenes with formaldehyde using CHCl₃/trifluoroacetic acid (TFA) as the medium, wherein TFA served both as an acidic catalyst as well as a cosolvent. The number‐average molecular weights (M_n's) of the polymers, as determined by gel permeation chromatography, varied from about 1000 to 37,000, depending on the nature of the substituent on the benzene ring; M_n was highest when all four substituents were alkoxy groups and was lowest when they were all alkyl groups. This correlated well with susceptibility of the aromatic ring toward electrophilic aromatic substitution, which is the underlying polymerization mechanism. Differential scanning calorimetry of the polymers showed that most of the samples were amorphous with glass‐transition temperatures ranging from about ?80° to +80 °C, whereas a few that were either symmetrically substituted or possessed a long alkyl substituent were partially crystalline. Preliminary studies suggested that the methylene unit linking the phenyl rings in these polybenzyls could be readily oxidized to generate conjugated polymers that may be perceived as carbon analogues of polyaniline–poly(arylmethine)s. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2345–2353, 2003     

13C NMR spectroscopy of head-to-head polystyrene: Molecular motion in solution

Head-to-head polystyrene was studied by NMR relaxation measurements in solution and these measurements were compared with those for head-to-tail polystyrene. By measuring the relaxation of the ortho and meta carbons of the phenyl rings of the polystyrenes, it was found that the head-to-head polystyrene chain is stiffer (T_m = 65°) than the head-to-tail chain (T_m = 54°). These results are in agreement with the measurements of the radius of gyration, and results from the study of the melt rheology of head-to-head and head-to-tail polystyrene.     

Estimation of the conformation of 2-hydroxy-4,6-dimethylbenzophenone and 2,4,6-trimethoxybenzophenone from electronic absorption spectra and PPP LCI ca

The twisting effect of benzene rings on the electronic spectra of derivatives of benzophenone (BPh), 2-hydroxy-4,6-dimethylbenzophenone (2-OH-4,6-diCH₃BPh) and 2,4,6-trimethoxybenzophenone (2,4,6-triOCH₃BPh) has been interpreted by the PPP method. The effect of structure, protonation, ionization and interaction with proton-acceptor solvent on the twisting of aromatic rings is discussed. The following twist angles of substituted ring (θ_I) and unsubstituted ring (θ_II) in 2-OH-4,6-diCH₃BPh were found: neutral form in cyclohexane θ_I = 39°–48°, θ_II = ?30°–(?45°); neutral form in ethanol θ_I = 66°–72°, θ_II = ?30°–0°; protonized form θ_I = 64°–6°, θ_II = ?30°–0°; ionized form θ_I = 66°–74°, θ_II = ?30°–0°. In the neutral form of 2,4,6-triOCH₃PBh the substituted ring is twisted by angle θ_I ~ 70° while in the protonated form the unsubstituted ring is twisted by angle θ_II ~ 60° and the substituted one is coplanar with the CO group.     

Low-temperature mechanical relaxations in polymers containing aromatic groups

Studies have been made of the secondary relaxation processes in the solid state of a number of polymers containing aromatic groups in the polymer chain. The polymers investigated include one, polystyrene, with the aromatic group in side-chain positions, and six high polymers in which phenylene rings lie in the main backbone chain. In polystyrene, wagging and torsional motions of the side chain phenyl rings give rise to a low-temperature δ-relaxation which is centered at 33°K (1.7 Hz) and which has an activation energy of about 2.3 kcal/mol. Most of the polymers with phenylene rings in the main chain exhibit a low-temperature relaxation in the temperature region from 100°–200°K. This relaxation process is centered at 159°K (0.54 Hz) in poly-p-xylylene, at 162°K (0.67 Hz) in polysulfone, and at 165°K (1.24 Hz) in poly(diancarbonate). In poly(2,6-dimethyl-p-phenylene oxide), two overlapping low-temperature relaxations are found, one in the range 125–140°K and the other near 277°K (ca. 1 Hz). The low-temperature secondary relaxation process in all of these polymers is believed to be associated with local reorientational motion of the phenylene, or substituted phenylene, rings or with combined motion of the phenylene rings and nearby chain units. For these low temperature relaxation processes, the activation energy is about 10 kcal/-mole. The temperature location of the relaxation appears to depend on the specific units to which the phenylene rings are attached and on steric and polar effects caused by substituents on the ring. In the poly-p-xylylenes the relaxation is shifted to much higher temperatures by a single Cl substitution on the ring but remains at essentially the same temperature position when dichlorosubstitution is made. The effects of water on the magnitude and temperature location of the observed low temperature relaxations, as well as the implications of the study for other polymers containing aromatic groups in their backbone chains, are discussed.     

Ethylene polymerization with ansa-metallocene systems rac-(Me2SiOSiMe2)[Ind]2ZrCl2-MAO and rac-(Me2SiOSiMe2)[IndH4]MtCl2-MAO; (Mt = Zr,Ti)

Ethylene was polymerized in toluene using methylalumoxane (MAO) activated rac-(Me₂SiOSiMe₂)[Ind]₂ZrCl₂ ( 1 ) and rac-(Me₂SiOSiMe₂)[IndH₄]₂MtCl₂ (Mt = Zr ( 2 ); Mt = Ti ( 3 )). All three catalyst systems polymerize ethylene with high activity. The molecular weight of polymer produced with zirconocene ( 1 ) was up to a weight-average molecular weight M̄_w = 1.1 × 10⁶ at low polymerization temperature (<20°C) under atmospheric pressure. The titanocene catalyst 3 shows lower activity and produced lower molecular weight polyethylene than zirconocenes 1 and 2. Replacement of aromatic rings in 1 by cyclohexane rings, leading to 2 , increases activity and reduces molecular weight. The catalyst systems show a dependency of the activity on temperature.     

Synthesis and characterization of spirobifluorene‐based polyimides

The synthesis and properties of organosoluble aromatic polyimides, containing spiro‐skeletal units in the polymer backbone on the basis of the spiro‐diamine monomer, 2,2′‐diamino‐9,9′‐spirobifluorene, are described. In the case of the spiro segment, the two fluorene rings are orthogonally arranged and connected through a tetrahedral bonding carbon atom, the spiro center. As a consequence, the polymer chain is periodically zigzagged with a 90° angle at each spiro center. This structural feature minimizes interchain interactions and restricts the close packing of the polymer chains, resulting in amorphous polyimides that have good solubility in organic solvents. Compared with their fluorene‐based cardo analogues, the spirobifluorene‐based polyimides have an improved solubility. Furthermore, the main‐chain rigidity of the polyimide appears to be preserved because of the presence of the spiro structure, which restricts the free segmental mobility. As a result, these polyimides exhibit a high glass‐transition temperature (T_g's) and good thermal stability. The T_g's of these polyimides were in the range of 287–374 °C, and the decomposition temperatures in nitrogen for a 10% weight loss occurred at temperatures above 570 °C. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3615–3621, 2002     

Sorption of benzene derivatives onto insolubilized humic acids

New environmental friendly sorption materials were synthesized and studied to remove organic contaminants in wastewater purification. Humic acids extracted from green-waste compost (HA_comp) and from leonardite (HA_leo) were chemically characterized by infrared spectroscopy, carbon nitrogen and hydrogen analysis, ash content, hydrophobicity tests, and molecular weight distribution. Humic acids were thermally immobilized at 330 °C for 1.5 h and their sorbent properties towards of some benzene derivatives (toluene, o-xylene, phenol, and benzyl alcohol) with the batch equilibrium method were studied. HA_comp was found to be less rich in aromatic rings and more hydrophobic than HA_leo. The maximum amount of sorbate bound at the equilibrium was consistently higher for the immobilized HA from compost than from leonardite and increased with the n-octanol/water partition coefficient of the adsorbate. The data point to hydrophobic interactions as the main force involved in the sorption of the compounds tested. The results showed that these materials can have potential applications in wastewater purification.     

Self‐inclusion structure of 5,11,17,23‐tetrakis(azidomethyl)‐25,26,27,28‐tetrahydroxycalix[4]arene,and 5,11,17,23‐tetra‐tert‐butyl‐25,27‐bis(chloroacetoxy)‐26,28‐bis(2‐pyridylmethoxy)calix[4]arene

In the structures of the two title calix[4]arene derivatives, C₃₂H₂₈N₁₂O₄, (I), and C₆₀H₆₈Cl₂N₂O₆, (II), compound (I) adopts an open‐cone conformation in which there are four intramolecular O—H...O hydrogen bonds, while compound (II) adopts a distorted chalice conformation where the two pendant pyridyl rings, one of which is disordered, are almost mutually perpendicular, with an interplanar angle of 79.2 (2) or 71.4 (2)°. The dihedral angles between the virtual plane defined by the four bridging methylene C atoms and the phenol rings are 120.27 (7), 124.03 (6), 120.14 (8) and 128.25 (7)° for (I), and 95.99 (8), 135.93 (7), 97.21 (8) and 126.10 (8)° for (II). In the supramolecular structure of (I), pairs of molecules associate by self‐inclusion, where one azide group of the molecule is inserted into the cavity of the inversion‐related molecule, and the association is stabilized by weak intermolecular C—H...N hydrogen bonds and π(N₃)–π(aromatic) interactions. The molecular pairs are linked into a two‐dimensional network by a combination of weak intermolecular C—H...N contacts. Each network is further connected to its neighbor to produce a three‐dimensional framework via intersheet C—H...N hydrogen bonds. In the crystal packing of (II), the molecular components are linked into an infinite chain by intermolecular C—H...O hydrogen bonds. This study demonstrates the ability of calix[4]arene derivatives to form self‐inclusion structures.     

Synthesis,thermal, rheological characteristics,and enzymatic degradation of aliphatic polyesters with lignin‐based aromatic pendant groups

This research aims to produce lignin‐based biodegradable polyesters with improved thermal quality. A series of aliphatic polyesters with lignin‐based aromatic side groups were synthesized by conventional melt‐polycondensation. Decent molecular weight (21–64 kg mol^?1) was achieved for the polymerizations. The molecular structures and thermal and mechanical properties of the obtained polyesters were characterized. As a result, the obtained polyesters are all amorphous, and their glass‐transition temperature (T_g) depends on the size of the pendant aromatic group (31–51 °C). Furthermore, according to the TGA results, the thermal decomposition temperatures of the polyesters are all above 390 °C, which make them superior compared with commercial biodegradable polyesters like polylactic acid or polyhydroxyalkanoates. Finally, rheological characteristics and enzymatic degradation of the obtained polyesters were also measured. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2314–2323