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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SOC POLYMER SCIENCE JAPAN  

The rotational isomeric state analysis of poly(ethylene terephthalate) (PET) was carried out by using parameters adjusted so as to reproduce the experimental results of H-1 NMR and dipole moment measurements on ethylene glycol dibenzoate. The central OC-CO bond of the ethyleneglycol unit prefers to be in the gauche form at lower temperatures, suggesting that the PET chains should contain many kink conformations in the amorphous state. In the following part, the nematic conformation of the same C-C bond was Studied by preparing a model compound which is capable of forming an enantiotropic nematic liquid crystalline (LC) phase. IR studies indicate that the trans fraction of the C-C bond increases from similar to 15% in the isotropic liquid to similar to 50% in the nematic LC state at the phase boundary. For this drastic change in the conformation at the transition, the C-C bond should be required to pay certain entropy penalty. These results are however compatible with the recent observations by SAXS and DPLS that the formation of nematic LC-like domains proceeds prior to the evolution of primary crystal nucleation during the cold-crystallization of PET. The PET chain is known to take the planar all-trans conformation in the crystalline state. Finally a possible mechanism leading to the nematic order in the amorphous PET is presented. Growth of the nematic LC-like domains in the amorphous phase may lead to a spinodal microphase separation, as suggested by Kaji et al.

DOI： 10.1295/polymj.PJ2007204

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：WILEY-V C H VERLAG GMBH  

Molecular dynamics (MD) simulations of 1,4-polybutadiene in bulk amorphous state were performed. To investigate motional coherency the relaxation rates for the collective and self motions, the collective and self relaxation rates, were evaluated for the short and long time regimes of the normalized intermediate scattering functions. The scattering vector dependence of the collective relaxation rates estimated for both fast and slow processes indicated a minimum at scattering vector q=1.3 angstrom(-1), corresponding to the position of a peak in the static structure factor. The self relaxation rates increased monotonously with q. A phenomenon known as de Gennes narrowing was reproduced well in the simulation and found to be originated from the inter-molecular correlation. The details of motional coherency and the distribution functions of relaxation time were evaluated. Keywords: amorphous; molecular dynamics; motional coherency and the distribution functions of relaxation time were evaluated.

DOI： 10.1002/masy.200750426

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

Molecular dynamics simulations of 1,4-polybutadiene in bulk amorphous state were performed. Results were compared with the recent neutron spin-echo measurements. To investigate motional coherency the relaxation rates for the collective and self-motions, the collective and self-relaxation rates, were evaluated for the short and long time regimes of the normalized intermediate scattering functions. The scattering vector dependence of the collective relaxation rates estimated for both fast and slow processes indicated a minimum at scattering vector q = 1.5 angstrom(-1), corresponding to the position of a peak in the static structure factor. The self-relaxation rates increased monotonously with q. A phenomenon known as de Gennes narrowing was reproduced well in the simulation and found to be originated from the inter-molecular correlation. The collective relaxation rate evaluated for fast process appeared to modulate around a peak of q = 2.9 angstrom(-1), corresponding to the intra-molecular correlation. (c) 2006 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.polymer.2006.06.004

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We performed thermal neutron spin echo measurements on a glass-forming polymer, deuterated polybutadiene (-[CD2-CD=CD-CD2](n)-; PB-d(6)), in a high Q range up to 3.5 angstrom(-1) covering the first and second peaks of the structure factor S(Q), and evaluated the decay rate Gamma(Q) of the coherent intermediate scattering function as a function of Q. In contrast to the previous experimental findings on the first peak of S(Q) at Q = 1.5 angstrom(-1), no 'de Gennes' type narrowing was observed on the second peak at Q = 2.9 angstrom(-1). This novel finding indicates that the narrowing is hidden by the distinct motions of the soft -CD2-CD2- and =CD-CD2- units and the self-motions of the rigid and soft units in the Q range around the second peak. The temperature dependence of the relaxation rate Gamma(Q) suggests that in the high Q range beyond the first peak of S(Q) the conformational changes in a deutrated PB chain are mainly observed.

DOI： 10.1143/JPSJ.74.3236

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A modified form of the van der Waals expression for the attractive intermolecular potential E = - η/V-m has often been used to take account of the acentric character of the potential function, where V is the volume, η a mean-field parameter representing the strength of the interaction field, and m an empirical parameter, usually a constant in the range 1-2. In this article, we have attempted to examine the validity or limitation of this expression in terms of the relevant equation of state terms such as pressure, volume, temperature, and thermal pressure coefficient. The parameters m and η in the equation were estimated separately. A series of n-alkanes including polyethylene, polyoxyethylene, and a segmented dimer compound capable of forming a liquid crystal were investigated. Strictly speaking, the accuracy of the expression was found to be guaranteed only in a limited range of temperature and volume. An interesting behavior was found for m and η in the LC state. Importance of the analysis on anisotropic liquids such as LCs is emphasized. © 2005 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.polymer.2005.02.039

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Language：English   Publishing type：Part of collection (book)   Publisher：SPRINGER-VERLAG BERLIN  

Segmented chain molecules involving mesogenic units along the backbone chain, conventionally called mainchain liquid crystals, often exhibit an enatiotropic nematic liquid-crystalline phase over a certain temperature range between the crystal and the isotropic melt. The phase transitions involved are usually of first order. Spectroscopic analyses such as X-ray and neutron diffraction, IR and Raman absorption, and H-1 and H-2 NMR demonstrated that the orientational ordering of mesogenic cores in the mesophase are strongly coupled with the spatial arrangement of the spacer. While the orientation of the molecular axis (i.e., the whole molecule) varies as a function of temperature, the well-defined nematic conformation of the spacer remains almost unaltered over the entire range of the liquid-crystalline state. In these compounds, the conformational transition takes place in the order isotropic random coil <-> nematic conformation <-> extended crystalline form, or vice versa during the crystallization/melting process. In this article, we first present a brief summary of the entropy of fusion of chain molecules. In the second part, conformational entropy changes associated with the melting via a nematic phase, or the crystallization via a nematic mesophase, are reviewed. The experimental data on liquid-crystal transitions were mostly collected from studies on oligomeric compounds such as dimer and trimer mainchain liquid crystals with neat chemical structures. Finally it is suggested that further studies on the phase transition of chain molecules via a nernatic mesophase may provide some valuable information regarding the embryonic stage of the polymer crystallization mechanism.

DOI： 10.1007/b107177

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JOHN WILEY & SONS INC  

To investigate helix-coil transition mechanisms, conformations of Glu(12)-Ala(12), EA, in aqueous solution have been studied in detail over the pH range from 2 to 8 and the temperature range from 20 to 60 degrees C using CD and NMR spectroscopy. The 750-MHz NMR spectra displayed excellent dispersion of the backbone amide proton signals, and permitted essentially complete sequence-specific resonance assignments. These assignments, together with short- and medium range nuclear Overhauser effect (NOE) constraints and coupling constants, enable us to analyze conformational characteristics of all the residues in the EA peptide individually. A combined use of CD and NMR techniques reveals that the EA peptide assumes a stable alpha-helix from Glu12 to Ala19 in 0. 1M NaCl solution at 20 degrees C above pH 7. The a-helix is getting longer as decreasing pH. Below pH 4, the peptide assumes the longest alpha-helix from Glu3 to Ala23. The important observation of the present study is that the helix- coil transition occurs stepwise, residue by residue, from both the Nand C-termini of the alpha-helix. No conformational equilibrium between the helical and random-coil states is detected for the residues in the central region of the a-helix. Quantitative analysis of temperature-induced helix-to-coil transitions at various pHs provides a pH-independent residual enthalpy change Delta H-r = 0.95 kcal res (-1). Similar values hove been reported for a 50-residue alanine-rich peptide (1.2 kcal res(-1)), poly-(L)-glutainate (1.1 kcal res(-1)), poly-(L)-lysine (1.1 kcal res(-) 1), and poly-(L)-alanine (0.86 kcal res(-1)). Those investigations, along with our present result, suggest that Delta H-r is mainly determined by the transformation of the backbone associated with the disruption of the intramolecular hydrogen bond. These results should increase our understanding of the helix-coil transition. (c) 2005 Wiley Periodicals, Inc.

DOI： 10.1002/bip.20206

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JOHN WILEY & SONS INC  

This is one of a series of studies on the reversal of the helix sense of polyaspartates originated from the pioneering work of Goodman and his associates in 1960s. Poly(beta-p-chlorobenzyl (L)-aspartate) (PClBLA) is one of the well-studied polyaspartate derivatives in both solution and the solid state. The chemical structure of PClBLA differs from those of poly(beta-benzyl (L)-aspartate) (PBLA) and poly(beta-phenethyl (L)-aspartate) (PPLA) only at the terminal of the relatively long side chain. PBLA takes a left-handed form (L) in conventional helicoidal solvents and does not exhibit any screw-sense inversion. In contrast to PBLA, both PClBLA and PPLA form a right-handed helix (R) in chlorinated alkane solvents and exhibits a reversal of a-helix sense at higher temperatures. Yet the transition behaviors in the presence of denaturant acid are quite different between these two polymers. While PPLA exhibits transitions such as R -> L -> coil by lowering temperature, PClBLA directly goes into the coil state without showing the reentrant L form. The cause of these phenomenological differences among these polymers has been investigated by constructing the phase diagram. (c) 2005 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 80: 249-257,2005.

DOI： 10.1002/bip.20207

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DOI： 10.1002/masy.200390033

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：SOC POLYMER SCIENCE JAPAN  

The dynamics of phase separation for blends of polymers containing interactive chain ends was investigated by the computational simulation with the dynamic mean field method. The attractive interaction between the chain ends was expressed by the chi parameter of a negative value. The temporal changes of the characteristic structures in the Fourier space for various values of an attractive interaction were evaluated. When an attractive interaction between chain ends becomes stronger, the phase separation is found to proceed slowly. This result suggests that the attractive chain ends behave as the virtual binding sites. When macroscopic sea-island phase constructed as the initial structure was quenched under the condition of induced micro phase separation, the dynamics of the domain structures was also investigated. In the case of more strongly segregated system, a new expanded droplet structure was found to be formed.

DOI： 10.1295/koron.60.181

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JOHN WILEY & SONS LTD  

We synthesized three partially deuterated polymer samples, namely a poly(ethylene-alt-propylene) (EP) alternating copolymer, a poly(styrene-b-EP) diblock copolymer (SEP) and a poly(styrene-b-EP-b-styrene) triblock copolymer (SEPS). The H-2 spin-lattice relaxation time, T-1, of EP soft segments above their glass transition temperature was measured by solid-state H-2 NMR spectroscopy. It was found that the block copolymers had a fast and a slow T-1 component whereas EP copolymer had only a fast component. The fast T-1 components for SEP and SEPS are similar to the T-1 value of EP above ca 20degreesC. The slow T-1 component for SEP and SEPS exhibited a minimum at 60degreesC and approached the value of the fast component near the T-g of polystyrene. The motional behavior of the EP units for SEP is similar to that of SEPS over the entire range of temperature. Copyright (C) 2001 John Wiley Sons, Ltd.

DOI： 10.1002/mrc.985

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

Molecular dynamics (MD) simulations of cis-1,4-polybutadiene in bulk amorphous state were performed to elucidate the origin of a fast relaxation process observed by quasielastic neutron scattering (QENS) measurements. The details of the torsional motion for each dihedral angle were investigated with the torsional auto- and cross-correlation functions for several temperatures in this study. Temperature dependence of the correlation between the torsional autocorrelation and cross-correlation functions is also evaluated. The origin of the fast process of cis-1,4-polybutadiene is found to be mainly the cooperative conformational transitions of two dihedral angles located at both sides of the CH2-CH2 bond when the bond is in the trans conformation. The cooperative conformational transitions exhibit even below the glass transition temperature of cis-1,4-polybutadiene. The cooperative motion appears at about 50 K below the glass transition temperature, corresponding to the Vogel-Fulcher temperature. (C) 2001 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0032-3861(01)00629-2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

Molecular dynamics (MD) calculations of cis-1,4-polybutadiene in bulk amorphous phase were performed under constant pressure and constant temperature conditions. The static and dynamic properties were evaluated from the results of MD calculations. The obtained density and coefficient of thermal expansion are in good agreement with experimental data. The feature of the calculated static structure factor is similar to the observed one. Molecular motion is examined with mean square displacements and intermediate scattering functions. An onset of a new motion, which Corresponds to so-called fast process, was clearly observed in the temperature dependence of the mean square displacement above 100 K. The dynamic structure factors obtained by the Fourier transformation of the intermediate scattering functions are compared with those obtained from quasielastic neutron scattering measurements. The peaks corresponding to the elastic scattering and the low energy excitation at around 2 meV are reproduced in the dynamic structure factors. The excessive intensity observed in the dynamic structure factor, which corresponds to the fast process, is also reproduced above 140 K in our simulation. (C) 2001 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0032-3861(01)00628-0

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DOI： 10.1295/polymj.34.450

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

A conventional method of estimating conformational entropy change at the melting point of polymers has been set forth in Mandelkern's book. The entropy separation according to this method involves a hypothetical assumption that the volume of the isotropic fluid may be compressed to that of the solid state without affecting the configurational part of the entropy of molecules. In this work, we have extensively examined the volume dependence of thermal pressure coefficient gamma = (deltaP/deltaT)(V) = (deltaS/deltaV)(T) of n-undecane. Molecular dynamic simulations were performed using the software package Insight II/Discover. In the standard calculation, a cubic box containing 30 n-undecane molecules was used under the conventional periodic boundary conditions. The experimental observations were well reproduced by the MD simulation performed as above, and accordingly the gamma vs specific volume (v(sp)) relations derived from the simulation are favorably compared with those obtained from the experimental PVT data. The gamma values remain quite insensitive to v(sp) over a wide range at given temperatures. Values of the trans fraction were found to decrease with an increase in temperature, while they tend to remain quite insensitive to pressure (0-200 MPa). It was concluded on this basis that the aforementioned treatment of the volume change at the phase transition seems to be supported by the present analysis.

DOI： 10.1021/ma001528r

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

Various conformation-dependent properties of chain molecules have been successfully treated within the rotational isomeric state approximation. The conformation entropy is one of such properties which can be readily defined by the partition function, the sum of all possible configurations of the chain. Flexible polymers often exhibit crystallization and in some cases liquid-crystallization as well. In these first-order transitions, changes in the spatial arrangement of polymer chains are considered to be a major factor involved. In order to explicitly determine the conformational contribution to the melting entropy, the latent entropy observed under the isobaric condition must be corrected for the volume change. The entropy separation involves a hypothetical assumption that the volume of the isotropic fluid may be compressed to that of the solid state without affecting the configurational part of the entropy of molecules. Finally thermodynamic significance of the conformation entropy in these transitions is emphasized on the basis of the critical studies of the entropy-volume relation of chain molecules in the liquid state.

DOI： 10.1002/1521-3900(200109)174:1<383::AID-MASY383>3.0.CO;2-C

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DOI： 10.1103/PhysRevB.64.144202

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DOI： 10.1295/polymj.33.825

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DOI： 10.1295/polymj.31.728

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

Polyoxyethylene (POE) is known to be highly flexible, a variety of spatial configurations being permitted. Like many other conventional polymers, the conformation of the POE chain can be treated within the framework of the rotational isomeric state (RIS) approximation using a limited number of RIS parameters. An unambiguous assignment of numerical values to statistical weights such as sigma and omega has not been achieved for the chain occurring under various conditions: sigma for the rotation around the C-C bond and omega for the so-called second-order interaction taking place between the methylene group and the oxygen atom separated by four bonds. In this work, we have attempted to demonstrate the role of these two parameters in determining the conformation-dependent properties of the POE chain. Various RIS parameter sets reported in literature have been compared with a model calculation, in which sigma and omega are varied over a wide range, the other parameters being kept invariant. A comprehensive analysis provides a rational explanation for the long lasting question why so many RIS parameter sets effectively reproduce the conformational characteristics of the identical polymer molecule. Finally, it is emphasised that a critical assessment of omega and/or sigma is required to establish an unambiguous RIS description of the POE chain. (C) 1998 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S1089-3156(98)00046-4

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The gas-phase NMR analysis of 5-methoxy-1,3-dioxanes was carried out. The conformational energies estimated from the observed coupling constant data were compared with the results of ab initio MO calculations using d95 + (2df,p) basis set at the MP2 level. While the energy difference between the axial-out and equatorial-out forms was in a reasonable agreement, the 1,5 interaction energy between the methoxy methyl and the ring oxygens was not in accord.

DOI： 10.1016/S0022-2860(96)09621-4

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DOI： 10.1002/(SICI)1097-0282(1997)43:6<405::AID-BIP2>3.0.CO;2-Z

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The binding properties of trivalent ions to polyacrylate and its low molecular weight analogs (monomer, dimer, and trimer) were investigated in dilute aqueous solution (10(-2)-10(-3) M) using Tb3+ ion as a fluorescent probe. The fluorescence intensity and lifetime of the Tb3+ ion depend directly on the number of water molecules bound to their inner coordination sphere. The more efficiently ligands coordinate to Tb3+ ion, the more water molecules are expelled and, consequently, the greater the fluorescence intensity and lifetime observed. Lifetime measurements in H2O and D2O showed that the number of water molecules coordinated to the Tb3+ ion are 6.5, 6.1, 4.9, and 3.6 for monomer, dimer, trimer model compounds, and polyacrylate, respectively. The viscosities of Tb3+-polyacrylate complexes were measured in the presence of a large excess of sodium bromide. Viscosities (eta(sp)/c) of the polyacrylate solutions follow Huggins' equation, and on addition of Tb3+ ion, the intrinsic viscosities decrease abruptly from 700 to 40 mL/g. The mean end-to-end distances, [r(2)]1/2, for polyacrylate in Tb3+-polymer complexes were calculated using the Flory-Fox equation and were found to be reduced from 125 to 48 nm on addition of Tb3+. These results indicate that of the nine water molecules coordinated to Tb3+ ion in aqueous solution, five to six are replaced with carboxylate groups attached to the polymer chain wrapped around the Tb3+.

DOI： 10.1021/ma960251l

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Phase behavior and ordering characteristics were reported for poly(gamma-benzyl L-glutamate) (PBLG) in a mixed solvent containing a denaturant acid, dichloroacetic acid (DCA), + dichloroethane (DCE). The solutions of PBLG prepared so as to be liquid crystal at room temperature were observed to undergo a reentrant isotropic transition at low temperature where conformational disordering of PBLG molecules takes place. The deuterium quadrupolar splitting data obtained by the H-2 NMR method were analyzed to elucidate the conformation and orientational order parameter of the ct-helix in the liquid crystalline phase. The conformation of PBLG molecules in the isotropic state was estimated from the observed C-13 NMR chemical shift. The molecular information gained through these experiments was implemented into the theoretical expression set forth by Flory and Matheson. The phase diagrams calculated on this basis have been compared with those observed. The theory has provided a reasonable picture for the high- and low-temperature phase transitions of the PBLG/DCA/DCE system.

DOI： 10.1021/ma951026r

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Infrared spectra of helical poly(beta-phenethyl-L-aspartate) (abbreviated as PPLA) dissolved in 1,1,2,2-tetrachloroethane were observed by Fourier transform-infrared spectroscopy as a function of temperature in the temperature range 30-110 degrees C. Attention was directed to the frequencies of the amide I and the ester C=O stretch bands in order to investigate the screw-sense inversion from the right-handed to the left-handed form. The amide I band was deconvolved into five components, each of which was then curve-fitted to a superposition of Gauss functions. These components were assigned to secondary structures of PPLA. At room temperature, the strongest band at 1656 cm(-1) and the second strongest one at 1659 cm(-1) (named amide I-A and I-B, respectively) were both assigned to the right-handed alpha-helical form, The intensities of these bands rapidly decreased at temperatures higher than 80 degrees C and disappeared at 100 degrees C. At the same time, a new component appeared at 1670 cm(-1) (amide I-C) above 70 degrees C, compensating for the intensity decrease of the two former components. This was assigned to the left-handed helical structure. Thus, it is concluded that the screw-sense is inverted between 80 and 100 degrees C. A weak component deconvolved at 1646 cm(-1) (amide I-D) was assigned to the random-coil structure which may exist at the N- and C-terminals of the alpha-helical chain. This component showed little intensity change with heating, indicating that the right-handed form is inverted to the left-handed form without taking on a largely unfolded structure.
The deconvolved side chain ester C=O stretch band is curve-fitted to two components at 1745 and 1735 cm(-1) (esters A and B) at 30 degrees C. Although the frequency of ester A is typical of a free ester C=O stretch mode, that of ester B is lower. Ester A disappeared at temperatures higher than 100 degrees C.

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A racemic mixture (PPDLA) comprising an equal amount of optical antipodes, Poly(beta-phenethyl L-aspartate) (PPLA)+Poly(beta-phenethyl D-aspartate) (PPDA), was found to exhibit a moderately sharp and reversible transition at around 200 degrees C. A combined use of X-ray and CP/MAS NMR methods revealed that the transition involves an interconversion of the screw-sense between the right- and left-handed alpha-helical molecules. The backbone conformation and the molecular packing (tetragonal) were found to remain nearly identical before and after the transition. The transition mechanism previously deduced in the liquid-crystalline state seems to be consistent with experimental observations in the solid state. On the other hand, PPLA alone is known to transform from the right-handed alpha-helix to the left-handed pi-helix at around 130 degrees C: the crystallographic form concurrently changes from a tetragonal to a rectangular and eventually to a hexagonal arrangement at about 200 degrees C. The difference between PPDLA and PPLA systems is discussed.

DOI： 10.1295/polymj.28.41

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Society of Polymer Science, Jpn  

The method of molecular dynamics simulation is applied to the study of glass transition, local motion of chain molecules, and local structure in amorphous polymers. The glass transition temperature, determined from the change in the thermal expansion coefficient, exhibits the expected dependency on the chain length. The local chain dynamics is investigated by evaluating the time correlation functions of bond reorientation motion and the distribution of resulting reorientation angles. The degree of success of the simulation for atactic polystyrene was examined by comparing the calculated X-ray intensity curve and neutron diffraction curves with experimental data. The calculated curves agree well. The results of the simulation were analyzed in detail to evaluate the intramolecular and intermolecular correlations. The most prominent feature in the intermolecular correlation is the strong tendency for the phenyl groups to have a separation distance of about 6A.

DOI： 10.1295/koron.53.628

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Conformation of 1,3-dimethoxypropane has been studied in the gas phase (approximately 120-180 degrees C). Vicinal coupling constants (3)J(HH) and (3)J(CH) determined by H-1 and C-13 NMR were analysed within the rotational isomeric state approximation. The trans and gauche couplings required in this analysis were set equal to J(G) = 2.8 Hz and J(T) = 13.7 Hz for H-1-C-C-H-1, and J(G) = 2.0 Hz and J(T) + J'(G) = 16.0 Hz for C-13-O-C-H-1. The conformational energy parameters of the chain were conventionally defined as E sigma and E rho for the gauche state around the CH2-CH2 and OCH2 bond, respectively, and E omega for the repulsive second-order interaction (g(+/-)g(-/+)) for the OCH2-CH2-CH2O fragment. The experimental values of the coupling constants were found to be reproduced by a variety of combinations of E sigma and E omega, E rho being kept at 1.03 kcal mol(-1). Adoption of E omega = 1.97 kcal mol(-1) as calculated by a molecular mechanics method, led to E sigma = -0.84 kcal mol(-1). Alternatively, by setting E sigma = -0.58 kcal mol(-1) as calculated, E omega = 0.40 kcal mol(-1). Assuming E omega &gt; 1 kcal mol(-1) for the gas phase, a value of E sigma from -0.7 to approximately -0.9 kcal mol(-1) was proposed. The conformation, and thus conformational energies, varied quite sensitively with the polarity of the medium. The results were compared with those observed in solution.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

A molecular dynamics simulation of bulk atactic polystyrene was performed, and the result was analyzed in detail to evaluate the intramolecular and intermolecular short range orders present. In this work the analysis was performed only on the results obtained from the united atom model, since, as was shown in the previous two publications, it gives much better agreement with experiment than the all atom model. Most of the study was performed with a system containing a single 80-monomer molecule, but some study was also made with a system containing two 40-monomer molecules. The short range order was examined by evaluating the radial distribution functions and orientational order parameters of pairs of aliphatic backbone segments and of phenyl group centers. In the case of intramolecular phenyl pairs, these quantities were evaluated individually according to the monomeric distance along the chain by which the two phenyls are separated. The conformation of the molecule was examined by evaluating the population distribution of backbone bond torsional;angles in meso and racemic diads. The result resembles the conformational energy maps previously prepared by others, but some differences were also noted. The most prominent feature in the intermolecular correlation is the strong tendency for the phenyl groups to have a separation distance of about 6 Angstrom. A detailed analysis was given to define the relative orientation that the pair of phenyls adopt at this separation. Intermolecular pairs of backbone segments were found to be oriented mostly randomly at separation distances larger than 6 Angstrom.

DOI： 10.1021/ma00112a028

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Dipole moments and optical anisotropies of alpha,omega-bis[(4,4'-cyanobiphenyl)oxy]alkanes NCPhPhO(CH2)(n)- OPhPhCN (CBA-n) with n = 9 or 10 have been determined in 1,4-dioxane. In the latter measurements, the molecular optical anisotropy gamma(2) was determined by using a depolarized Rayleigh apparatus equipped with a Fabry-Perot interferometer to facilitate the exclusion of the collision-induced contributions. The compounds studied are composed of two mesogenic groups joined by a flexible spacer and known to form nematic Liquid crystals when heated in the bulk state. In contrast to the configurational characteristics observed in the Liquid crystalline state, the (isotropic) solution properties studied in this work exhibited only a moderate odd-even trend with the number of flexible methylene units n; dipole moment mu = 6.67 (n = 9) and 6.76 D (n = 10), optical anisotropy gamma(2) 1089 (n = 9) and 1362 Angstrom(6) (n = 10) are all values measured at 25 degrees C. The temperature coefficient of the dipole moment d In mu(2)/dT was found to be positive for both compounds. The corresponding values of the optical anisotropy d ln gamma(2)/dT exhibited a small odd-even effect. These results have been satisfactorily interpreted within the framework of the rotational isomeric state approximation. The relative orientation of the two terminal mesogenic groups was elucidated for given conformations, and spatial distribution curves were constructed for the individual molecular systems. By the use of the molecular parameters thus established in the isotropic solution, mean-square values of the optical polarizability (gamma(2)) were further estimated for the ensemble of the conformers adopted in the nematic state. The bimodal character of the orientational distribution was shown to be responsible for the odd-even effect observed in the isotropic as well as in the anisotropic states.

DOI： 10.1021/j100017a031

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

RIS analysis of the deuterium quadrupolar splitting data was performed for alpha,omega-bis[(4,4'-cyanobiphenylyl)oxy]alkane dimer liquid crystals having -O(CH2)(n)O- flexible spacers (n = 9 (CBA-9) and n = 10 (CBA-10)) between the 4,4'-cyanobiphenylyl ends according to the scheme previously established. The analysis indicates that most of the conformers involved in the range 0 &lt; psi(1),psi(2) &lt; 45 degrees adopt spatial configurations reasonably consistent with the nematic arrangement of mesogenic cores in both dimer LC systems, where psi(1), and psi(2) denote the inclination angles of the terminal mesogenic cores with respect to the molecular axis. The conformational entropy changes at the crystal-nematic (CN) and nematic-isotropic (NI) interphases estimated on this basis are as follows: CBA-9, Delta S-en(conf) = 59.6, Delta S-ni(conf) = 13.3; CBA-10, Delta S-ni(conf) = 64.2, Delta S-ni(conf) = 15.6 (J mol(-1) K-1 units). The values of the entropies Delta S-tr(conf) thus derived were compared with the constant-volume transition entropies (Delta S-tr)(v) determined by the PVT measurements reported in the accompanying paper: CBA-9, (Delta S-cn)(v) = 53.9, (Delta S-ni)(v) = 7.9; CBA-10, (Delta S-cn)(v) = 62.4, (Delta S-ni)(v)) = 13.3 (J mol(-1) K-1 units). In view of the uncertainties involved in the estimation of the entropies both in theory and in experiments, the correspondence is quite favorable. The conformation of the spacer undoubtedly plays an important role in determining the phase behaviors of these main chain liquid crystals. It is pointed out that the discrepancy between the calculation and experiment may be further improved by considering other contributions such as (1) the entropy changes due to the orientation of the anisotropic molecules in the liquid crystalline state and (2) the possibility of the entropy loss during the compression to achieve constant-volume transitions. It is concluded that the observed increase in the quadrupolar and dipolar splittings with decreasing temperature arises mainly from the variation of the order parameter of the molecular axis.

DOI： 10.1021/ma00105a012

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The magnetic susceptibilities of some ether-type liquid-crystalline polymers such as -[PhOC-(O)PhO(CH2)nOPhC(O)OPhO(CH2)nO]x-(Ether-PLC-n) with n = 9 and 10 have been measured by a SQUID magnetometer. Variations of DELTA-chi at the isotropic to nematic transition were found to occur more gradually as compared with those observed for the dimer liquid crystals. The DELTA-chi values estimated for the stable nematic state were analyzed according to the RIS scheme developed in the previous work. The order parameters of the mesogenic core axis S(M) were elucidated for the nematic conformation derived independently from the H-2 NMR analysis. The same treatment has been extended to include ester-type main-chain liquid crystals such as -[Ph(CH3)N(O)NPh(CH3)OOC(CH2)(n)COO]x-(Ester-PLC-n) with n = 7 and 10, for which experimental data are available from Esnault et al.'s work. For both Ether- and and Ester-PLCs, the values of S(M) estimated from SQUID were found to be reasonably consistent with those obtained by the other measurements.

DOI： 10.1021/ma00010a056

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

DOI： 10.1021/ma00220a015

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DOI： 10.1021/ma00197a018

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