Packing Of Poly Research Articles

Effect of Fullerene Intercalation on the Conformation and Packing of Poly-(2-methoxy-5-(3′-7′-dimethyloctyloxy)-1,4-phenylenevinylene)

Photoluminescence (PL) and resonance Raman spectroscopy are used to track changes in the conformations and packing of poly-(2-methoxy-5-(3'-7'-dimethyloctyloxy)-1,4-phenylenevinylene) (MDMO-PPV) chains with the addition of [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) molecules. PL lineshapes of MDMO-PPV thin films as a function of annealing time were first measured to determine the spectroscopic signatures of chain conformations and packing in the absence of PCBM. Annealing results in enhanced interchain interactions leading to red-shifts of PL 0-0 transitions by up to ∼300 cm(-1) and apparent increases of the line shape Huang-Rhys factors. Wavelength-dependent PL lifetimes of as-cast and films annealed for short times (∼30 s) are nonexponential with an instrument-limited component of ∼100 ps and a ∼350 ps component. With longer annealing times, decays become single exponential with an average lifetime of ∼1 ns indicating that all excitations efficiently funnel to strongly coupled interchain sites. Addition of PCBM disrupts MDMO-PPV interchain interactions causing PL 0-0 transitions to blue-shift, increases in line width, and decreases in apparent Huang-Rhys factors. Resonance Raman spectra of MDMO-PPV/PCBM thin films with variable PCBM weight fractions (∼50:1 up to 1:8 w/w) were then measured using short (488 nm) and long (568 nm) excitation wavelengths. The out-of-plane vinylene C-H wag mode of MDMO-PPV (∼964 cm(-1)) showed pronounced increases in intensity of up to ∼30% and red-shifts of up to 5 cm(-1) with increasing PCBM content. These changes result from a decrease of planarity between chain segments that suppresses interchain interactions. Furthermore, red-shifts of up to ∼4 cm(-1) were observed for the C═C symmetric stretch of the MDMO-PPV vinylene group (∼1625 cm(-1)) with 488 nm excitation. The sensitivity of the MDMO-PPV vinylene group vibrations with PCBM indicates preferential interactions between these two molecules and is consistent with intercalation of PCBM into the polymer structure. This assignment was confirmed by thermally annealing of MDMO-PPV/PCBM films to remove intercalated PCBM molecules, which partially restores interchain interactions as seen from smaller intensity increases (∼15%) and red-shifts (∼2 cm(-1)) of the ∼964 cm(-1) mode. Overall, the spectroscopic results show that MDMO-PPV chains adopt distorted conformations (i.e., less intrachain order and shorter conjugation lengths) that have important implications for explaining the structural origins for large improvements in charge mobilities in MDMO-PPV/PCBM blends.

A spot test for nitrite and nitrate detection by color band length and number of colored zebra-bands formed in a mini-column

A detecting tube for nitrite and nitrate monitoring was developed as a spot test. The detecting tube was prepared by packing of poly(vinyl chloride) (PVC) particles coated with a quaternary ammonium salt into a mini-column. A nitrite solution was treated with sulfanilic acid and 1-naphthol; the resultant colored solution was drawn into the detecting tube by suction with a syringe, and a color band was formed in the tube. The color band length (CBL) corresponded to the nitrite concentration. Nitrate was also detected; after reduction with zinc. The nitrite and nitrate content of domestic wastewater samples was successfully detected by this method over the range of 0.5–45.3 mg-N L−1 as nitrogen concentration. Another type of detecting tube was prepared by alternately packing adsorbent and uncoated PVC particles in a mini-column. Colored zebra-bands were formed in this column, and the nitrite concentration was detected by counting the number of colored zebra-bands. Nitrite and nitrate concentrations in actual wastewater samples were detected more easily by this method, although the accuracy was somewhat lower than that obtained with the CBL method.

Packing of poly(tetrafluoroethylene) in the liquid state: Molecular dynamics simulation and theory

Molecular dynamics simulations and polymer reference interaction site model theory calculations were carried out on the C(48)F(98) oligomer of poly(tetrafluoroethylene) (PTFE) at 500 and 600 K. The exp-6 force field of Borodin, Smith, and Bedrov, was used in both the simulation and theory. The agreement between theory and simulation was equivalent to earlier studies on polyolefin melts. The intermolecular pair correlation functions of PTFE were shifted to larger distances relative to polyethylene (PE) due to the difference in the van der Waals radii of F and H atoms. A similar shift to lower wave vectors was found in the structure factor of PTFE relative to PE.

Characteristic Features of Molecular Structure and Packing of Organopolysilanes with Asymmetric Side Chains

The molecular structure and packing of poly(methyl ethyl silane), [(CH3)Si(C2H5)]n, and poly(methyl n-propyl silane), [(CH3)Si(C3H7)]n, have been examined by the X-ray diffraction method. For poly(methyl ethyl silane), several configurations are possible for the arrangement of the C2H5 group, whereas the C3H7 groups stretch along one equivalent direction for poly(methyl n-propyl silane). In both cases, the molecular structure and packing are mostly determined by the intramolecular steric hindrance and van der Waals interaction between side chains, which is the same as that of polysilanes with symmetric side chains.

Packing Studies on Poly(di‐n‐alkylsilylenemethylene)s

AbstractThe packing of poly(di‐n‐alkylsilylenemethylene) (PDASMs) chains was studied by using X‐ray, electron diffraction, and molecular modeling methods. X‐ray and electron diffraction measurements revealed unit cells in which the PDASMs were efficiently packed. The PDASM with the longer alkyl side chains, such as poly(di‐n‐propylsilylenemethylene) (PDPrSM), showed packing with the alkyl side chains interlocked with each other like cross‐shaped gears in the two‐dimensional monoclinic unit cell. The PDASM with the shorter ethyl substituent, poly(di‐n‐ethylsilylenemethylene) (PDESM), showed a lack of ability to interlock its side chains due to the short length of the alkyl groups. In these studies, we found that the length of the alkyl side chains could change the packing arrangement of PDASMs from monoclinic to orthorhombic to hexagonal with only short‐range order as the alkyl side chain length decreases at room temperature.The ab projection of a 4 × 4 chain array of poly(di‐n‐propylsilylenemethylene) (PDPSM) in the monoclinic unit cell.magnified imageThe ab projection of a 4 × 4 chain array of poly(di‐n‐propylsilylenemethylene) (PDPSM) in the monoclinic unit cell.

Conformation and packing of poly(diphenylphosphazene): the crystal structure of the α-form

The structure of the α-form of poly(diphenylphosphazene) (PDPhP) has been determined and refined from powder diffraction data, using also literature electron diffraction information. The most plausible unit cell is monoclinic, space group P2 1/ b, with a=10.23 A ̊ , b=20.00 A ̊ , c ( chain axis )=10.18 A ̊ ; γ=99.8(1)° and contains two chains with opposite side group orientation. The chain periodicity requires four monomer units, two of them non-equivalent. The standard moderately distorted (TCTC) n conformation of polyphosphazenes is stretched by nearly 4% with respect to the usual value, mainly widening the PNP bond angle to about 150°. Because only relatively weak, diffuse intensity is present on odd layer lines of fibre patterns, and due to the limited quality of the available diffraction data at higher angle, the refinement has been carried out adopting a simplified model with chain periodicity 5.09 Å, i.e. assuming equivalence of all monomer units. Two over-short contacts are found, both intermolecular suggesting that the conformation with the 5.09 Å repeat is acceptable for the isolated chain and that the doubling of the chain periodicity arises to optimise the packing. The proposed crystal structure represents a first simplified model of the organisation of PDPhP in the α-form.

Conformation and packing of poly(alkylene phosphate) chains in the crystal lattice. Part II: Temperature FTIR studies

The infra-red absorption of recrystallized samples of the polyhexa-, polyhepta-, polyocta-, polynona-, polydeca- and polydodecamethylenephosphate was measured during the heating, from the room temperature to the temperature higher than the melting temperature of the polymer examined. The heating induced changes of FTIR spectra proved, that the spatially arranged polyphosphate chains are cross-linked by the PO⋯H–O hydrogen bonds, whose properties consist with the properties of the theoretically predicted hydrogen bonds. Moreover, the strong crystal field splitting of the rocking vibrations of the polyphosphate monomer unit methylene chain and of the (P)– O–C stretching vibrations has been observed. As was founded, the dispersion curves of rocking vibrations of the polyphosphate chain (CH2)ntrans sequences may be approximated by the exponential function: ν=ν∞ exp (C/n). The crystal field splitting effects proved, that the unit cell of polyphosphate crystals contain two polyphosphate monomer unit, and that the conformation of the polyphosphate extended chains is close to the conformation of the modeled polyphosphate extended chains.

Structural data on the packing of poly(ester amide)s derived from glycine, hexanediol, and odd‐numbered dicarboxylic acids

Structural data on the packing of poly(ester amide)s derived from glycine, hexanediol, and odd‐numbered dicarboxylic acids

Structural data on the packing of poly(ester amide)s derived from glycine, hexanediol, and odd-numbered dicarboxylic acids

The crystalline structure of a series of Poly(ester amide)s derived from glycine, hexanediol, and odd-numbered dicarboxylic acids has been studied using transmission electron microscopy and X-ray diffraction. Polymers crystallize in an orthorhombic lattice with parameters a = 4.80 A, b = 22.68 A, and c in the 45–55 A interval, depending on the number of methylenes of the chemical repeat unit. The structure of the glutaric derivative can be interpreted as a singular packing of six hydrogen-bonded sheets. Amide and ester interactions between neighboring layers favor two different sheet arrangements that give rise to the observed superstructure. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2521–2533, 1999

Conformation and packing of poly(alkylene phosphate) chains in the crystal lattice. Part I: molecular modelling and wide-angle X-ray scattering

Molecular modelling of the poly(alkylene phosphates) suggests a structure in which the repeat distances appear to be in agreement with those indicated by wide angle X-ray diffraction studies of the semi-crystalline polymer. The extended zig-zag chains lie in a parallel array in stacks of pleated sheets. There are lines of phosphoryl groups, linked by hydrogen bonding, running in one direction through the structure which appear to be suitable for the selective transport of ions.

Polymorphism of poly(vinylidene fluoride): potential energy calculations of the effects of head-to-head units on the chain conformation and packing of poly(vinylidene fluoride)

Potential-energy calculations have been used to investigate the effects of head-to-head defects on the chain conformation and packing of poly(vinylidene fluoride). The calculations have demonstrated that such positional isomerism can contribute to the polymorphism exhibited by PVF2. We have shown that increased concentration of head-to-head defects or tetrafluoroethylene comonomer can cause the phase-I form to become the favored structure for poly(vinylidene fluoride). The calculations have also proven capable of reflecting some of the subtle changes arising from the insertion of such defects. Packing calculations have shown that isomorphous replacement significantly affects the way in which PVF2 chains pack into a crystalline array. The differences in the structures proposed by Tadokoro and by Doll and Lando for phase II of poly(vinylidene fluoride) have been attributed to the inclusion of head-to-head defects in the polymer chains. In general, the potential-energy functions have proven useful qualitatively, if not semiquantitatively, in investigating the relation between chains in a crystal. Finally, these calculations have shown that both conformation and packing must be considered in determining the minimum energy structure for a polymer, and that these factors cannot be treated independently.

Molecular Conformation and Packing of Poly(vinylidene fluoride). Stability of Three Crystalline Forms and the Effect of High Pressure

The formation of three crystalline forms of poly(vinylidene fluoride) was studied in detail by using an apparatus for heat treatments under high pressure up to 5000 atm. Form II consisting of TGTG-type molecular chains was the most stable under atmospheric pressure, and form I, composed of planar zigzag-type chains, was formed under special conditions, such as tension, high pressure, etc. Form III may be an intermediate modification between I and II. Based upon these experimental facts, as well as the potential energy calculations of the intra- and intermolecular interactions in the crystal lattices due to the van der Waals and electrostatic forces, the relation between the conditions of formation of the three forms and their structures was examined. The planar zigzag-type conformation (in forms I and III) is considered to be less stable than the TGTG type (form II) because of the steric hindrances and electrostatic dipole interactions. In spite of the difference in the intramolecular potential energy between these two molecular conformations, the stabilities of the three crystalline forms are not so very different because of the more favorable intermolecular interaction in form I.