Mobility of polyethylene in the inclusion complex with perhydrotriphenylene

Zhan, Yongjian; Mattice, Wayne L.

doi:10.1021/ma00042a005

Cited by 26 publications

(27 citation statements)

References 20 publications

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“…The last column on Table 3 shows the characteristic ratios defined as C n =〈r 2 〉/nl 2 , with n=40 skeletal bonds in this case. Our result of 4.8 for the isolated PE chain is slightly smaller than those of C ∞ experimentally obtained [22] or calculated [21] ; [23] that are in the range 5.2-7.0, although it should be taken into account that our chains are rather short and C n probably has not yet reached the asymptotic C ∞ limit.…”

Section: Conformational Analysis Of the Polymer Chainscontrasting

confidence: 88%

Conformations and mobility of polyethylene and trans -polyacethylene chains confined in α-cyclodextrins channels

Pozuelo¹,

Mendicuti²,

Sáiz³

2002

Polymer

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Conformational properties and mobility of two polymeric chains containing 30 repeating units of either polyethylene (PE) or trans-polyacethylene (PA) confined into the channel formed by eight α-cyclodextrins (αCDs) are studied by Molecular Dynamics simulations performed at 500 K and compared with the behavior exhibited by the same chains when they stand alone in vacuum. The rotaxane structure (i.e. polymeric chains threaded into the αCDs channel) is stabilized with respect to the separated chain and αCDs mostly because of van der Waals interactions. As it might be expected, large differences are observed in the molecular characteristics of the isolated chains as compared to their confined counterparts. The differences are in the sense of decreasing the conformational mobility in favor of extended conformations in the case of confined chains. Comparison of the results obtained for confined PE and PA chains indicates a noticeably larger mobility of the PA chain. Molecular dimensions obtained for the isolated PE chain agree with the results published in the literature.

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Section: Conformational Analysis Of the Polymer Chainscontrasting

confidence: 88%

Conformations and mobility of polyethylene and trans -polyacethylene chains confined in α-cyclodextrins channels

Pozuelo¹,

Mendicuti²,

Sáiz³

2002

Polymer

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“…This result excludes diffusion type motions of the entire chains around their axes, which have been identified as primary modes in polymer dynamics in simple inclusion compounds. [23][24][25][26] The 13 C signal of PEO in the supramolecules shows only one resonance, even down to low temperature of 180 K. This experimental result exclude another possibility of conformational transitions. 27 Considering the structural constraints along the nanochannels and uniform conformation of PEO, a two-site helical jump of PEO entire chains about their axes is further investigated.…”

mentioning

confidence: 94%

Dynamic Geometry and Kinetics of Polymer Confined in Self-Assembly via Cooperative Hydrogen Bonding: A Solid-State NMR Study under Paramagnetic Doping

Miyoshi

2010

Macromolecules

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Well-defined arrangements of the secondary intermolecular interactions play important roles for the design of new materials, which leads to unique self-assemblies consisting of multicomponent molecules with different sizes and shapes. Much work has gone into characterizing the static structures of such selfassembled systems. 1 Cooperative secondary interactions influence the molecular dynamics of the components and the bulk properties. Therefore, understanding relationship between microscopic dynamics and secondary interactions in self-assemblies is an important subject in this field. 2 Poly(ethylene oxide) (PEO) is a hydrogen acceptor and can form supramolecular crystals with a small molecule of UREA, which is a hydrogen donor, in methanol solutions. XRD revealed that two-thirds of the UREA molecules form nanochannels with a diameter of ∼1 nm, inside which isolated PEO chains and the remaining UREA molecules are included ( Figure 1a). 3 Several groups have investigated PEO dynamics in this unique morphology by conventional NMR relaxation measurements and have suggested that the dynamics of PEO is restricted by cooperative hydrogen bonding. 4,5 However, the details of the geometry and kinetics of the molecular dynamics of PEO in this supramolecular system are not well understood.Solid-state (SS) NMR techniques using magnetically anisotropic interactions can provide not only the kinetics and but also the geometry of the molecular dynamics. 6 In the past decade, various sophisticated SS-NMR techniques have been developed to investigate molecular dynamics in a wide frequency range in natural abundance. 7-11 Among them, center bands only detection of exchange (CODEX) 7,8 NMR can provide both the geometry and kinetics of molecular dynamics in a slow range and has been successfully applied to investigate the molecular dynamics of small molecules, 7 polymers, 12-14 liquid crystals, 15 and polymer blends. 16 However, this robust technique suffers from low NMR sensitivity, which has limited its application in chemically complex systems and/or systems with long T 1H values. Recently, Wickramasinghe et al. proposed a simple approach using paramagnetic doping for sensitivity enhancement. 17 Adding a small amount of a paramagnetic compound into a protein crystal could effectively shorten the T 1H value without disturbing the structures. Similar strategies may be applicable to self-assemblied systems. In this Communication, CODEX NMR and paramagnetic doping have been used to elucidate the dynamic nature of PEO in a PEO-UREA supramolecular system in natural abundance. Figure 1a shows the 13 C CPMAS NMR spectrum for PEO-UREA supramolecules at 213 K and their structures. PEO shows a very sharp 13 C signal at 70 ppm. The single resonance supports the result the PEO chains adopt a uniform 4 1 helical conformation which was obtained by XRD. 3 The observed single resonance is in stark contrast to a bulk PEO signal, which has multiple splitting on its 13 C signal (Figure 2b). Using 13 C-13 C double quantum NMR combined with relaxation...

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“…In brief, we developed initial models by packing mesogenic dimers with an antiparallel in the molecules from one stable rotational isomer to another, may also occur on a time scale of picoseconds association into periodic boxes. Relaxed models were obtained by application of cycles of energy minimization [9,10,12].…”

Section: Simulationsmentioning

confidence: 99%

“…Further molecular dynamics studies con® rm that a polyethylene chain strongly prefers a trans conformation for the chain in perhydroruns under (NPT) conditions were performed on these relaxed models at the temperature of each smectic phase triphenylene or in urea crystals. Simulations [12] of molecular dynamics found that the transitions between [7] to obtain their equilibrated structures in the smectic phase. Fluctuations of the volumes of the systems were trans and gauche states at internal CH2± CH2 bonds of an n -alkane chain are strongly suppressed by the channel observed during the equilibration, and the deviations of the corresponding densities were 0.23% for the smectic A of perhydrotriphenylene; these transitions are only allowed near the ends of the chain when the temperature phase and 0.13% for the smectic E phase.…”

Section: Simulationsmentioning

confidence: 99%

“…On the basis of 3.5. Rotational diVusion of the mesogenic molecule Rotational motions of a molecule around its long axis AM1 calculations, the dihedral angles at the bonds in the core can be classi® ed into two categories: one is near were represented by using a polar coordinate system [10,12,14] with the Z axis parallel to the C axis of the the cis conformation, such as the bonds indexed by 6 and 9, and the other is centred at the trans conformation, simulated cell. Here, we adopt the polar coordinate system to describe rotational diVusion of the mesogenic such as the bonds indexed by 7, 8, and 10.…”

Section: Simulationsmentioning

confidence: 99%

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Molecular dynamics simulations of a liquid crystalline molecule in the smectic A and E phases and in vacuum

Lee¹,

Hsiue²,

Wu³

et al. 1999

Liquid Crystals

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Molecular dynamics simulations are performed in this work at 393 and 323 K for a mesogenic molecule (R)-1-methylheptyl 4[4-(2-allyloxy ethoxy)biphenyl-4¾ -carbonyloxy]benzoate in the simulated smectics A and E, respectively, and in a vacuum at 300 K, for a period of 1.0 ns. The trajectories obtained from molecular dynamics simulations allow us to investigate the dynamical behaviour of this mesogenic molecule in the simulated smectic phases. This dynamical behaviour of a single molecule is presented using the distributions of dihedral angles and rotational diVusion around the C-axis de® ned by the simulated cells. Simulation results indicate that, except for the bonds near the end of the spacer segment, the dihedral angles all exhibit a single Gaussian-like distribution in the smectic A and E phases. Fluctuations of a dihedral angle about its mean value are more restricted in the smectics A and E than in those simulated in a vacuum. The average value of the¯uctuations of the dihedral angles at the bonds in the spacer is found to be about 2 fold larger than that of uctuations in the tail of the same molecule in the smectic A and E phases. In the smectic A phase, the distribution of orientations of a molecule about its long axis in a 36 molecule cell in which the outer molecules are ® xed is found to have three distinct peaks. This result shows that the orientational¯uctuations of single molecules are limited by con® nement due to neighbouring molecules, i.e. that the layers have short-range structural correlations. The orientational distributions show larger¯uctuations at the ends of the molecules.

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Mobility of polyethylene in the inclusion complex with perhydrotriphenylene

Cited by 26 publications

References 20 publications

Conformations and mobility of polyethylene and trans -polyacethylene chains confined in α-cyclodextrins channels

Conformations and mobility of polyethylene and trans -polyacethylene chains confined in α-cyclodextrins channels

Dynamic Geometry and Kinetics of Polymer Confined in Self-Assembly via Cooperative Hydrogen Bonding: A Solid-State NMR Study under Paramagnetic Doping

Molecular dynamics simulations of a liquid crystalline molecule in the smectic A and E phases and in vacuum

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