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| 2. |
- Guo, J.-H., et al.
(författare)
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How the phenyle rings (benzene) act as building blocks in pi conjugated polymers
- 1998
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Ingår i: Advanced Light Source. - Berkeley : Ernest Orlando Lawrence Berkeley National Laboratory, University of California Berkeley, California, USA. ; , s. 129-132
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Organic conjugated polymers have the electronic structure of semiconductors and can be doped to become good conductors (1). Conjugated polymers are now used as active materials in a wide variety of prototype applications such as light emitting diodes [2] and organic transistors [3,4]. Most of the interesting chemistry and physics of conjugated polymers is associated with the details of the electronic structure at the valence and conduction band edges and, in this connection, various electron spectroscopies can be used as tools for diagnosis of the relevant electronic and geometric properties....
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| 3. |
- Guo, J.-H., et al.
(författare)
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Resonant and nonresonant x-ray scattering spectra of some poly(phenylenevinylene)s
- 1998
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 108:14, s. 5990-5996
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of some poly(phenylenevinylene)s have been investigated by resonant and nonresonant x-ray inelastic scattering spectroscopies. The nonresonant as well as all resonant spectra for each polymer demonstrate benzene-like features, indicating a local character of the x-ray emission in which the phenyl ring acts as a building block. Theoretical simulations of x-ray energies and intensities taking the repeat unit as a model molecule of the polymer agree with the experimental spectra fairly well. The edges of the occupied bands have been identified in the nonresonant spectra of each polymer. By subtracting the emission energy of the highest occupied molecular orbital in the nonresonant spectrum from the core excitation energy in the resonant spectrum an alternative way to determine the optical band gap is obtained. As for free benzene the outer π band in the polymer spectra show a depletion of the emission going from the nonresonant to the resonant x-ray emission spectra. It is demonstrated that this transition, which is strictly symmetry forbidden for free benzene, becomes effectively forbidden in the polymer case as a result of strong interference effects, and it is argued that this is the general case for resonant x-ray emission of conjugated polymers as far as the frozen orbital approximation holds.
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| 4. |
- Guo, JH, et al.
(författare)
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Resonant and nonresonant x-ray scattering spectra of some poly(phenylenevinylene)s
- 1998
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Ingår i: JOURNAL OF CHEMICAL PHYSICS. - 0021-9606. ; 108:14, s. 5990-5996
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The electronic structure of some poly(phenylenevinylene)s have been investigated by resonant and nonresonant x-ray inelastic scattering spectroscopies. The nonresonant as well as all resonant spectra for each polymer demonstrate benzene-like features, ind
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| 6. |
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| 7. |
- Yang, Y-W, et al.
(författare)
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Association and phase behaviour of statistical and block copolymers of ethylene oxide and butylene oxide in water
- 1997
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Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 38, s. 1659-1668
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Tidskriftsartikel (refereegranskat)abstract
- Three copolymers of ethylene oxide (EO) and 1,2-butylene oxide (BO) were prepared by anionic polymerization to have similiar molar masses (Mn ≈ 7000 g mol-1), molar mass distributions (Mw/Mn<1.1) and compositions (80mol% oxythylene) but different chain structures. A triblock copolymer was prepared by sequential copolymerization of EO followed by BO, and two statistical copolymers were prepared from mixed monomers, either to low (15%) or to high (93%) conversion. The disparity in reactivity ratios in the EO/BO copolymerization resulted in pronounced composition drift along the chains of the high conversion statistical copolymer, giving it the character of a block copolymer. This composition profile was checked by 13C n.m.r. spectroscopy. The association behaviour of the statistical copolymers in aqueous solution at 25°C was studied by dynamic and static light scattering. The low conversion statistical copolymer remained in its molecular state across the concentration range studied (up to 100 g dm-3), but the high conversion statistical copolymer associated into molecular clusters and micelles. Cloud point curves were determined for solutions of the three copolymers. The effect of associations on phase behaviour is discussed.
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