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  • 1
    Electronic Resource
    Electronic Resource
    Effect of Chain Flexibility on Selectivity in the Gas Separation Process: Molecular Dynamics Simulation (1995)
    s.l. : American Chemical Society
    Macromolecules 28 (1995), S. 8598-8603 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00129a019
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  • 2
    Electronic Resource
    Electronic Resource
    A Monte Carlo simulation of polymer/polymer interface in the presence of block copolymer. I. Effects of the chain length of block copolymer and interaction energy (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 12193-12201 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A Monte Carlo simulation for the segregation behavior of symmetric diblock copolymer at the interface between immiscible homopolymers was performed on a simplified lattice model. The simulation results show that the segregation behavior of block copolymer is significantly dependent on the molecular parameters, such as the chain length Nc of block copolymer and the interaction energy εAB between A and B segments. In a weakly repulsive system with εAB=0.1, the block copolymers are more strongly segregated at the interface with increasing the chain length when the block length is shorter than and comparable to the homopolymer length. However, when the block length becomes longer than the homopolymer length, the concentration of copolymer segments at the interface rather decreases and its distribution becomes broadened. In a strongly repulsive system with εAB=0.5, the distribution of copolymer segments at the interface becomes broader as the chain length of block copolymer increases. This behavior is closely related to the stretching and orientation of block copolymer chains at the interface and to the extent of penetration of homopolymers into the copolymer layer. These simulation results are in excellent agreement with the numerical predictions by the self-consistent mean field theory. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479156
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  • 3
    Electronic Resource
    Electronic Resource
    Monte Carlo simulation of the order–disorder transition of a symmetric cyclic diblock copolymer system (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 1712-1720 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The microphase separation of symmetric cyclic diblock copolymer with decreasing temperature is simulated using the Monte Carlo method. In order to investigate the effect of the ring-shape chain architecture on order–disorder transition (ODT), the microphase separation of the cyclic diblock copolymer is compared with that of a symmetric linear diblock copolymer with the same chain length. For both systems, the ODT is observed as a first-order transition, and the ordered structure formed through the ODT is lamellar. The ratio of the domain spacing in the cyclic diblock copolymer to that in the linear one is 0.7 at the ODT, and the scattering intensity of the former is weaker than that of the latter. The ring-shape chain architecture suppresses the random thermal force, so that the cyclic diblock copolymer still shows a mean-field behavior at the temperature at which the linear diblock copolymer does not obey the mean-field prediction. The value of (χeffN)ODT of the linear diblock copolymer is calculated to be in the range of 25.36〈(χeffN)〈26.04, which is in good agreement with the theoretical prediction, (χeffN)ODT=25.61, indicating that this simulation properly describes the ODT of the diblock copolymer. The value of (χeffN)ODT of the cyclic diblock copolymer is predicted to be in the range of 40.83〈(χeffN)〈43.02. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479431
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  • 4
    Electronic Resource
    Electronic Resource
    Analysis of the mechanical behavior of poly(trimethylene terephthalate) in an amorphous state under uniaxial extension–compression condition through atomistic modeling (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 7524-7532 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The mechanical behavior of poly(trimethylene terephthalate) (PTT) in an amorphous state was simulated under uniaxial extension–compression conditions through atomistic modeling. The elastic properties obtained from the well-defined structure were comparable with those obtained from experiments. Typical stress–strain curves showing yielding and plastic behaviors were obtained under both extension and compression conditions. It was observed that the stress under uniaxial compression is higher than the stress under uniaxial extension with the same strain. The absence of structural defects in samples for simulation leads us to conclude that the difference of stress levels between two conditions is not intrinsically related to structural defects. Various analyses of chain conformation such as bond orientation, the dihedral angle, and Voronoi volume tessellation shows that the PTT chain under extension undergoes conformational changes different from those under the compression condition. When the change in the energetic state of PTT is calculated as a function of strain, it is revealed that the dihedral angle torsion energy and the van der Waals interaction energy play more important roles in deformation under extension than under compression. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478655
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  • 5
    Electronic Resource
    Electronic Resource
    Monte Carlo simulation of the phase separation dynamics of polymer blends in the presence of block copolymers. IV. Effects of chain length and composition of repulsive block copolymer (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 4267-4281 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Monte Carlo simulation was used to study the effects of C-b-D block copolymers with repulsive interaction on the phase separation dynamics of A/B immiscible homopolymer blend. It is found that a repulsive block copolymer can significantly suppress the rate of phase separation of an immiscible binary blend when its interaction energies with the homopolymers satisfy a proper condition. It is also found that the longer the chain length of block copolymer, the better such a retardation effect. When the chain extension of block copolymer at the interface is examined, each block in the repulsive block copolymer is contracted in its corresponding homopolymer phase, whereas the attractive copolymer chain is extended at the interface. This may lead to less retardation effect of repulsive block copolymer as compared with attractive block copolymer. Unlike the attractive block copolymer, the repulsive block copolymer with an asymmetric composition (f=0.7) does not show better retardation than the symmetric one. However, in spite of some difference in retardation effect, both types of block copolymers (attractive and repulsive) obey the dynamic scaling law, and the scaled structure factors are universal with time, irrespective of copolymer structure. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475826
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  • 6
    Electronic Resource
    Electronic Resource
    Effect of the molecular structure of graft copolymer on the interfacial behavior between two immiscible homopolymers: A Monte Carlo simulation (1998)
    Springer
    Polymer bulletin 40 (1998), S. 607-612 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The effects of molecular structure of graft copolymer on the interfacial properties are investigated using a Monte Carlo simulation. The interfacial activity is analyzed by calculating the surface coverage and the concentration profile of graft copolymer at the interface. At low interaction energy between two segments, the graft copolymer having fewer grafting sites and longer grafting chains locates better at the interface than the graft copolymer having more grafting sites and shorter grafting chain. At high interaction energy, this situation is reversed: the graft copolymer with more grafting sites locates better than the copolymer with fewer grafting sites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002890050297
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  • 7
    Electronic Resource
    Electronic Resource
    Molecular dimensions of poly(ethylene isophthalate) and poly(ethylene naphthalene-2,6-dicarboxylate) (1997)
    Springer
    Polymer bulletin 39 (1997), S. 257-263 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract. The rotational isomeric state (RIS) model was used to calculate the molecular dimensions of poly(ethylene isophthalate) (PEI) and poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) by introducing new description for aromatic segments and by adopting the statistical weight parameters of PET. The mean square dimension ratios ((〈r2〉0/M)∞) of PEN and PEI were 0.653 and 1.167, respectively, and the entanglement molecular weight (Me) of PEI and PEN were 1850 and 1810, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002890050146
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  • 8
    Electronic Resource
    Electronic Resource
    The effect of crystalline morphology of poly (butylene terephthalate) phases on toughening of poly(butylene terephthalate)/epoxy blends (1999)
    Springer
    Journal of materials science 34 (1999), S. 161-168 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In an effort to investigate the effect of the crystalline morphology of a poly(butylene terephthalate) (PBT) phase on the toughening of PBT/epoxy blends, the blends, having different degrees of perfectness of the PBT crystalline phase, were prepared by blending PBT and epoxy at various temperatures ranging from 200 to 240 °C. As the blending temperature decreases, the degree of perfectness of the PBT crystalline phase increases as a result of the increase of crystal growth rate. For PBT/epoxy blends, the change in crystalline morphology induced by processing may be the most important cause for the dependency of the fracture energy on blending temperatures. It has been found that PBT phases with a well-developed Maltese cross are most effective for epoxy toughening. This dependency reveals the occurrence of a phase transformation toughening mechanism. Also, the higher relative enhancement of fracture energy of a higher molecular weight epoxy system is further indirect evidence for a phase transformation toughening mechanism. Some other toughening mechanisms observed from the fracture surfaces, such as crack bifurcation, crack bridging, and ductile fracture of PBT phases, have been found to also be affected by the blending temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004410901853
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  • 9
    Electronic Resource
    Electronic Resource
    Microstructure effect in the coupling reactions of polymeric organolithium compounds using chlorosilanes (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1743-1753 
    Details
    ISSN: 0887-624X
    Keywords: coupling reaction ; living polymer ; microstructure ; coupling yield ; 1,4-enchainment ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The most important variable affecting the yield in the coupling reactions of polymeric organolithium compounds with chlorosilane compounds has been investigated through size-exclusion chromatographic (SEC) analysis. The coupling reaction of poly(styryl)lithium with dichlorodimethylsilane as a silane-coupling agent provided 44 wt % of the coupling yield. The coupling yield, depending on the chain end reactivity of active polymers, was not greatly affected. The addition of a Lewis base such as N,N,N′,N′-tetramethylethylenediamine (TMEDA) even after complete polymerization of the dienes in hydrocarbon seems to affect the coupling reaction, resulting in decreasing the yield. The 1,2- or 3,4-enchain contents in the polydiene backbones affected the reduction of the linking efficiency in the coupling of the poly(dienyl)lithiums with chlorosilanes as the linking agent. The linking yields of the active polymers including over 75 mol % of 1,2- or 3,4-enchainment on the polydiene segment were below 20 wt %. The linking yields exhibited a dependence not only on the steric requirement of the chain end, but also the microstructure of the polydiene segment. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1743-1753, 1998
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Comparison of activities of homogeneous Ti-based catalysts in the presence of methylaluminoxane (MAO) for synthesis of syndiotactic polystyrene by UV/visible spectroscopic study (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1733-1741 
    Details
    ISSN: 0887-624X
    Keywords: homogeneous Ti-based catalyst ; methylaluminoxane ; catalytic activity ; UV/visible spectroscopy ; syndiotactic polystyrene ; polymorphic structure ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The catalytic activities in syndiospecific polymerization of styrene in hydrocarbon using homogeneous Ti-based catalysts in the presence of methylaluminoxane (MAO) were investigated through UV/visible spectroscopic analysis. A strong UV absorption band of CpTiCl3, itself, incipiently appeared at λmax = 400 nm in toluene, followed by a bathochromic shift with its remarkable decrease by the addition of MAO. The absorption band intensity at λmax = 400 nm arising from delocalization of π-electrons on the cyclopentadienyl ring decreased by methylation in the presence of MAO with regard to the mechanism for production of an active center (“cation-like”), for example, the change of the ionic nature. The intensity decrease at λmax = 400 nm was suppressed over 2000 of the [Al]/[Ti] ratio. In the case of Ti(OC4H9)4 having a σ-ligand, new and broad UV absorption bands were developed at λmax = 340 nm and 410 nm in the presence of MAO in contrast with the CpTiCl3/MAO system. Comparison between the relative absorption intensities at λmax = 340 nm and 410 nm led to the determination of a maximum catalytic activity of Ti(OC4H9)4 in the presence of MAO related to the polymerization yield. The maximum polymerization yield was observed with regard to the relative maximum value of the absorption intensity at λmax = 410 nm with the [Al]/[Ti] ratio (500). From observation for polymorphism of the final products via differential scanning calorimetric analysis (DSC), the thermally unstable β-form seemed to be produced by the CpTiCl3/MAO system independent of the MAO concentration, the Ti(OC4H9)4/MAO system produced a thermally stable α-form in the low MAO concentration (up to 100 of the [Al]/[Ti] ratio), and a mixture of α- and/or β-forms over 200 of the [Al]/[Ti] ratio under our experimental conditions. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1733-1741, 1998
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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