Local Mechanism of Phenyl Ring π-Flips in Glassy Polycarbonate

Whitney, Duane; Yaris, Robert

doi:10.1021/ma9611432

Cited by 35 publications

(63 citation statements)

References 23 publications

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“…Therefore, it seems unlikely to be the origin of the secondary relaxation unless it is cooperatively linked to the motions or is part of the mechanism a͒ Electronic mail: wapcolej@sq.ehu.es causing the relaxations and therefore monitoring them, as has been repeatedly suggested in the literature. 13,[15][16][17][18][19][20][21][22][23][24][25][26][27] NMR studies of the molecular motions taking place in glassy polycarbonates below T g show that the main characteristic motions in these systems consist of -flips of the phenylene rings around the C1C4 axis ͑see Fig. 1͒, oscillations of the ring about the same axis, and some small amplitude main-chain reorientation.…”

Section: Introductionmentioning

confidence: 99%

“…On the other hand, theoretical calculations and molecular dynamics simulations on systems containing phenylene rings qualitatively agree with the type of motions observed experimentally by NMR depending on the time range examined. [25][26][27][35][36][37][38][39][40] However, the exact mechanism leading to the occurrence of these flips or the role of the flips on the mechanical properties is not yet clear. There is not a consensus on questions like, up to which extent and in which way do the inter-and intrachain interactions affect the flipping process, or whether the ring flip needs cooperative motion of different units along the chain or not.…”

Section: Introductionmentioning

confidence: 99%

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Phenylene ring dynamics in bisphenol-A-polysulfone by neutron scattering

Arrese-Igor

Arbe

Alegría

et al. 2004

The Journal of Chemical Physics

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We have investigated the dynamics of phenylene rings in a glassy polysulfone (bisphenol-A-polysulfone) by means of quasielastic neutron scattering. Nowadays it is well known that these molecular motions are directly connected with the mechanical properties of engineering thermoplastics in general. The particular system investigated by us has the advantage that by selective deuteration of the methyl groups, the neutron scattering measured is dominated by the incoherent contribution from the protons in the phenylene rings. In this way, the dynamics of such molecular groups can be experimentally isolated. Two different types of neutron spectrometers: time of flight and backscattering, were used in order to cover a wide dynamic range, which extends from microscopic (10(-13) s) to mesoscopic (10(-9) s) times. Moreover, neutron diffraction experiments with polarization analysis were also carried out in order to characterize the structural features of the sample investigated. Fast oscillations of increasing amplitude with temperature and pi-flips are identified for phenylene rings motions. Due to the structural disorder characteristic of the amorphous state, both molecular motions display a broad distribution of relaxation times, which spreads over several orders of magnitude. Based on the results obtained, we propose a model for phenylene rings dynamics, which combines the two kinds of molecular motions identified. This model nicely describes the neutron scattering results in the whole dynamic range investigated.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Phenylene ring dynamics in bisphenol-A-polysulfone by neutron scattering

Arrese-Igor

Arbe

Alegría

et al. 2004

The Journal of Chemical Physics

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“…10 in reference [1], and associated text). However, kHz-MHz regime small-amplitude oscillations about the ring C 2 axis are also likely to be present [20]. The 2-bond C-F coupling in fluoro-polycarbonate has been estimated as 1800 Hz using a constant-time 8-T r version of 13 C{ 19 F} REDOR [21].…”

Section: Correction To Single-pulse-observe Redormentioning

confidence: 99%

Compensating for pulse imperfections in REDOR

Weldeghiorghis

Schaefer

2003

Journal of Magnetic Resonance

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“…DMS of (B x t) n copolymers (x ϭ 3, 5, 7, 9) at 1.0 Hz. 14 chains, 27 as shown schematically in Figure 15. Furthermore, it is the motions of polymer chains that give rise to the ␥-relaxation peaks.…”

Section: Bdt Temperatures and Molecular Motionsmentioning

confidence: 99%

Controlling molecular mobility and ductile–brittle transitions of polycarbonate copolymers

Wu¹,

Xiao²,

Yee³

et al. 2001

J Polym Sci B Polym Phys

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ABSTRACT:To control molecular mobility and study its effects on mechanical properties, we synthesized two series of poly(ester carbonate) and polycarbonate copolymers with different linkages: (B x t) n (x ϭ 3, 5, 7, 9) and (B x T) n (x ϭ 1, 3, 5, 7, 9), where t represents the terephthalate, T represents the tetramethyl bisphenol A carbonate linkages, and B is the conventional bisphenol-A (BPA) carbonate. These two series of materials have distinct differences in their relaxation behaviors and chain mobility, as indicated by the -flip motion of the phenylene rings in the B x blocks. Uniaxial tensile tests of the copolymers indicate that the brittle-ductile transition (BDT) temperatures of the copolymers are correlated to whether the ␥-relaxation peaks due to the B x sequence is fully established. The materials possessing more fully established lowtemperature ␥ peaks give rise to a lower BDT. Also, the locations of the ␥ peaks are correlated to the ring flips of the B x blocks of polymer chains.

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Local Mechanism of Phenyl Ring π-Flips in Glassy Polycarbonate

Cited by 35 publications

References 23 publications

Phenylene ring dynamics in bisphenol-A-polysulfone by neutron scattering

Phenylene ring dynamics in bisphenol-A-polysulfone by neutron scattering

Compensating for pulse imperfections in REDOR

Controlling molecular mobility and ductile–brittle transitions of polycarbonate copolymers

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