Effect of cold-drawing on the secondary dielectric relaxation of bisphenol-A polycarbonate

Mitxelena, Olatz; Colmenero, Juan; Alegría, Ángel

doi:10.1016/j.jnoncrysol.2005.03.072

Cited by 4 publications

(8 citation statements)

References 19 publications

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“…However, the comparison of the loss curves recorded at the same temperature evidences a significant reduction of the dielectric loss peak intensity, in agreement with literature results. 12,[16][17][18] Neverthe-less, this is an unbalanced effect since, for instance, the reduction of the dielectric losses at 200 K is significantly less pronounced in the low frequency flank of the loss peak (see Figure 4). Moreover, when the same kind of comparison is performed for samples with different level of orientation, it is found that the loss reduction depends almost linearly on the molecular orientation as determined by birefringence measurements, irrespective of the frequency range considered (see inset of Figure 4).…”

Section: Resultsmentioning

confidence: 99%

“…The corresponding values of the birefringence index ∆n (∆n ) n |n ⊥ ) were in the range 0.03-0.05. 16 To avoid any moisture absorption, all the samples were stored under a dry nitrogen atmosphere before the subsequent dielectric experiments.…”

Section: Methodsmentioning

confidence: 99%

“…In this temperature range, the contribution of the relaxation component previously associated with the librations of the isolated carbonyl group is found to be dominant. 16 Therefore, the QENS results put into question the independence of the carbonyl group motions and instead, they again point to the cooperative character among the motions of the different molecular groups forming the BPA-PC unit.…”

Section: Introductionmentioning

confidence: 99%

“…Nevertheless, early dielectric relaxation investigations on the γ-relaxation of BPA−PC already evidenced that it can be hardly associated with a single molecular motion. , Indeed, in a recent work where DS technique has been used to investigate a series of poly(ester carbonates) it was concluded that there are two main contributions to the dielectric γ-relaxation of BPA−PC, one assigned to the libration of the carbonyl group alone (as it was previously suggested 13 ) and the other to the combined motion of the carbonyl and phenylene groups. On the other hand, some other dielectric investigations have shown a significant effect of small molecule plasticizers and the molecular orientation ,− on the secondary γ-relaxation of BPA−PC.…”

Section: Introductionmentioning

confidence: 99%

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On the Molecular Motions Originating from the Dielectric γ-Relaxation of Bisphenol-A Polycarbonate

2006

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We have investigated the molecular motions responsible for the dielectric γ-relaxation of bisphenol A polycarbonate (BPA-PC) by taking advantage of the unbalanced influence of cold-drawing in the dielectric losses. The direct comparison of the dielectric relaxation curves measured on the BPA-PC samples uniaxially stretched below the glass transition temperature with those corresponding to the nonstretched samples allowed us to resolved two main components of the dielectric γ-relaxation. The characteristic times of each of these components nearly coincide with those derived by neutron scattering and deuterium nuclear magnetic resonance for two welldefined jumps of the phenylene rings, evidencing the cooperativity among the motions of the different molecular groups forming the polycarbonate repeating unit. A more detailed analysis of the orientation effects on the dielectric γ-relaxation reveals a weaker third component with characteristic time scales close to those reported in the literature for the fast phenylene ring oscillations. On the basis of these three components we have been able to accurately describe the relaxation behavior of both oriented and nonoriented samples over an extremely wide temperature interval (50-350 K). From these results, we conclude that the low temperature dielectric behavior is mainly driven by the phenylene π-flips, but at temperatures above 200 K, the dielectric relaxation becomes increasingly governed by the concurrent rotation of the carbonate/phenylene units, being these motions those more strongly hindered by chain orientation. Some implications of these finding on the mechanical properties of polycarbonate are discussed.

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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On the Molecular Motions Originating from the Dielectric γ-Relaxation of Bisphenol-A Polycarbonate

2006

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“…Earlier investigations on PC ascertained that beta relaxation is a single, unresolved relaxation that involves rotation of carbonate groups [51,55]. Later several studies were performed on beta relaxation over a broad frequency range and at the wide temperatures where the secondary transition separated into two or three regions resulting from phenyl ring motion, carbonate group motion, and coupled phenyl ring and carbonate motion [61][62][63][64][65][66]. Our DEA studies for PC reveal a broad relaxation observed at higher frequencies (1 kHz-100 kHz).…”

Section: Dielectric Analysismentioning

confidence: 99%

Processing and Performance of Polymeric Transparent Conductive Composites

Jain

Muralidharan

Sedloff

et al. 2013

International Journal of Polymer Science

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Recent advances in microelectronic and optoelectronic industries have spurred interest in the development of reticulate doped polymer films containing "metallic" charge transfer complexes. In this study, such reticulate doped polymer films were prepared by exposing solid solutions of bis(ethylenedioxy) tetrathiafulvalene (BEDO-TTF) in polycarbonate (PC) to iodine, forming conductive charge transfer complexes. The resulting films exhibited room temperature conductivities ranging from 6.33 to 90.4×10 −5 S ⋅ cm −1. The colored iodine complexes in the film were reduced by cyclic voltammetry yielding conductive, colorless, transparent films. We were intrigued to examine the dielectric properties of BEDO-TTF in solid solution in PC prior to formation of the charge transfer complex as no such studies appear in the literature. Dielectric analysis (DEA) was used to probe relaxations in neat PC and BEDO-TTF/PC. BEDO-TTF plasticized the PC and decreased the glass transition temperature. Two secondary relaxations appeared in PC films, whereas the transitions merged in the BEDO-TTF/PC film. DEA also evidenced conductivity relaxations above 180 ∘ C which are characterized via electric modulus formalism and revealed that BEDO-TTF increased AC conductivity in PC.

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Effect of stretching on the sub-Tgphenylene-ring dynamics of polycarbonate by neutron scattering

et al. 2008

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We have investigated the effect of cold drawing on the motion of phenylene rings in bisphenol-A polycarbonate by neutron scattering. The intensity scattered by isotropic and stretched polycarbonate is different, the quasielastic broadening being larger for the isotropic sample. This difference can be well accounted for by considering that preferentially oriented rings in the stretched polymer have their motion sterically hindered. The extent of the effect of stretching on the phenylene-ring motion obtained from this neutron-scattering investigation is in good agreement with that obtained when studying the effect of cold drawing on the ␥ relaxation by dielectric spectroscopy.

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Effect of cold-drawing on the secondary dielectric relaxation of bisphenol-A polycarbonate

Cited by 4 publications

References 19 publications

On the Molecular Motions Originating from the Dielectric γ-Relaxation of Bisphenol-A Polycarbonate

On the Molecular Motions Originating from the Dielectric γ-Relaxation of Bisphenol-A Polycarbonate

Processing and Performance of Polymeric Transparent Conductive Composites

Effect of stretching on the sub-Tgphenylene-ring dynamics of polycarbonate by neutron scattering

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