Analysis of Raman-active low-frequency bands observed for syndiotactic polystyrene

Savage, John D.; Wang, Ying Kang; Stidham, Howard D.; Corbett, Max; Hsu, Shaw Ling

doi:10.1021/ma00038a022

Cited by 18 publications

(9 citation statements)

References 11 publications

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“…polymer mixtures in this region only a few experimental results are described in the literature. Omar et al zo reported an excess of the dielectric loss in the far-infrared (FIR) spectra of polystyrene (PS) mixtures with various methyl-substituted benzene derivatives and Savage et al 21 have found a small maximum shift towards higher wave numbers of the lowfrequency Raman (LFR) band at 50 cm ···1 in crystalline syndiotactic PS when the solvent ethylbenzene is integrated in the crystal structure. Both observations may be compared with recently published excess absorption and maxima shifts in the FIR spectra of CSz/benzene mixture in the liquid phase.…”

Section: Introductionmentioning

confidence: 99%

Line shape analysis of the depolarized Rayleigh spectra of CS2/PS mixtures

Silveira¹,

Stassen²,

Dorfmüller³

1994

The Journal of Chemical Physics

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Section: Introductionmentioning

confidence: 99%

Line shape analysis of the depolarized Rayleigh spectra of CS2/PS mixtures

Silveira¹,

Stassen²,

Dorfmüller³

1994

The Journal of Chemical Physics

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“…It is expected that these torsional vibrations can improve the alignment between the transition dipoles during vibrations in 4th4Q also. These torsional dynamics can explain the observed degradation in core-PL intensity of both dendrimers below ~100 K. At temperatures higher than 100 K, torsional vibrations of the aromatic rings are definitely activated, because the thermal energy at 100 K (~9 meV) is larger than the energy quantum (~6 meV [13,14]) of torsional vibrations. Such vibrations can mediate exciton transfer from the outer aromatic rings to the inner ones and finally to the porphyrin core, by dynamic recovery of the energy transfer rate.…”

Section: Plmentioning

confidence: 89%

Depression of excitonic energy transfer by freezing molecular vibrations in meta ‐linked branching dendrimers

Akai¹,

Kato²,

Okada³

et al. 2006

Phys. Status Solidi (c)

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The temperature dependence of excitonic energy transfer is investigated in both small and large dendrimers having meta-linked light-harvesting peripheries. In these dendrimers, highly efficient excitonic energy transfer takes place from peripheries to core at room temperature and gives rise to intense core photoluminescence (PL) upon selective excitation of the peripheries. Upon direct photo-excitation of the core chromophore, the intensity of core-PL increases monotonically with decreasing temperature. However, during selective excitation of the peripheries, the enhancement of the core-PL is markedly suppressed at temperatures lower than 100 K in both dendrimers. This result demonstrates that torsional vibrations of adjoining aromatic rings in the peripheries mediate excitonic energy transfer, and that the freezing of such vibrations at low temperature strongly inhibits the transfer in these meta-linked dendrimers.1 Introduction Highly efficient excitonic energy transfer from the photo-excited peripheries to corechromophore has been found to occur at room temperature (RT) in several types of light-harvesting dendrimers [1][2][3]. In these hyper-branched dendrimers, the light-harvesting peripheries consist of aromatic rings in a meta-linked branching architecture. At RT, the branching peripheries vibrate actively, and it is expected that these vibrations play an important role in excitonic energy transfer.We have demonstrated quenching of energy transfer in a quasi-planar dendrimer by freezing molecular vibrations and have pointed out the importance of torsional vibrations that alter the co-planarity between core and peripheries [4]. In dendrimers with meta-linked branching peripheries, the wavefunctions of the excited states involved in energy transfer between adjoining aromatic rings are nearly orthogonal to each other because these rings are nearly right angles to each other. It was thought that torsional vibrations between these aromatic rings play an important role in the highly efficient energy transfer in such dendrimers because these vibrations dynamically change the orientational configuration of adjoining aromatic rings [5].In this study, we employed small and large dendrimers with branching peripheries in the meta-position and investigated the temperature dependence of their excitonic energy transfer processes in order to study the role of torsional vibrations between adjoining aromatic rings in the peripheries.

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“…Similar results have also been described in several previous papers. [3,4] Like sPS/1,1,2,2-tetrachloroethane or other sPS crystal/solvent complexes, [4,[13][14][15][16][17][18] the g ! a 0 transition always occurs at about 200 8C resulting in an obvious exothermic peak that is associated with recrystallization of the melted g-type crystal during the course of DSC scanning upon further heating.…”

Section: Thermal Evidence For the D-type Crystalmentioning

confidence: 99%

“…Recently, subjects of polymorphism of sPS have been widely investigated by using differential scanning calorimetry (DSC), [1,2] X-ray diffraction, [3][4][5] transmission electron microscopy, electron diffraction, [6][7][8] Raman scattering and Fourier-transform infrared spectroscopy (FTIR), [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] etc. There are four known crystals (a-, b-, d-, and g-crystals) in sPS.…”

Section: Introductionmentioning

confidence: 99%

“…Thus, the crystal phases and chain conformations in the polymersolvent complexes or polymer crystals can be effectively analyzed using FTIR spectroscopy. [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] Fourier-transform infrared spectroscopy (FTIR) technique has been commonly and widely used to investigate crystal polymorphism and chain conformations in semicrystalline polymers, [18][19][20][21][22][23] and numerous applications have been demonstrated on investigating the vibrational spectra changes with polymorphism alteration in sPS during various solvent/thermal treatments. By using X-ray diffraction characterization, the preliminary evidences show the different phase transition mechanisms for various polymer-solvent complexes depending on the type of the solvent included in the crystal of the d-type.…”

Section: Introductionmentioning

confidence: 99%

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Thermal‐Induced Crystal/Conformation Transformations in Syndiotactic Polystyrene Films Treated with Different Solvents

Sun

Woo

2003

Macro Chemistry & Physics

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Solution‐crystallized or solvent‐induced crystal forms and transitions of these crystals upon post‐annealing in solvent‐treated syndiotactic polystyrene (sPS) (films cast from o‐dichlorobenzene or immersed in 1,2‐dichloroethane, respectively) were investigated via wide‐angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), and Fourier‐transform infrared (FTIR) spectroscopy. IR spectra in the frequency range of 720–820 cm−1, which is attributed to the CH out‐of‐plane bending of the phenyl ring for neat syndiotactic polystyrene (sPS) and their crystal/solvent complexes (sPS/o‐dichlorobenzene or sPS/1,2‐dichloroethane), were examined for the freshly as‐cast samples in comparison with those having been subjected to post‐annealing by heating to high temperatures. Three bands centered at approximately 779, 769, and 750 cm−1 were observed, the intensity and wavenumber being sensitive to the helical structural changes as a function of the annealing temperature. The band at 769 cm−1, being associated with the intramolecular interactions of the helical chains of the γ‐crystal, was used to confirm the formation of such a phase. The bands at 779 cm−1 and 769 cm−1 disappeared and the sharper band at 750 cm−1 remained upon further annealing above the γ → α′ transition temperature. Thus, by examining the temperature dependency as revealed in the IR spectra, the thermal‐induced phase transition from the δ‐ to an ordered γ‐ and then to an α′‐phase was successfully proven for the sPS/o‐dichlorobenzene complex. Similarly, the other sPS/1,2‐dichloroethane complex underwent transition (from a δ‐ to a disordered γ‐ and then to an α′‐phase) upon the same thermal treatments, except that the intermediate phase is a disordered γ‐phase.FTIR spectra in the frequency ranging from 720 to 820 cm−1 for the δ‐type sPS/o‐dichlorobenzene complex subjected to increase of the temperature by 5 °C steps in the range of 60–245 °C.magnified imageFTIR spectra in the frequency ranging from 720 to 820 cm−1 for the δ‐type sPS/o‐dichlorobenzene complex subjected to increase of the temperature by 5 °C steps in the range of 60–245 °C.

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Analysis of Raman-active low-frequency bands observed for syndiotactic polystyrene

Cited by 18 publications

References 11 publications

Line shape analysis of the depolarized Rayleigh spectra of CS2/PS mixtures

Line shape analysis of the depolarized Rayleigh spectra of CS2/PS mixtures

Depression of excitonic energy transfer by freezing molecular vibrations in meta ‐linked branching dendrimers

Thermal‐Induced Crystal/Conformation Transformations in Syndiotactic Polystyrene Films Treated with Different Solvents

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