Viscoelastic behavior of low molecular weight polystyrene

Plazek, D. J.; O’Rourke, V. M.

doi:10.1002/pol.1971.160090202

Cited by 281 publications

(314 citation statements)

References 32 publications

(7 reference statements)

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“…The estimated value of R f for L-PS and 8-arm-47K-star is (5.7 ( 1) × 10 -4 K -1 ( Figure 2). [44][45][46] On the other hand, R f for 10K-HBPS and 5K-HBPS seems to be higher and was estimated to be 6.5 × 10 -4 and 10.9 × 10 -4 K -1 , respectively ( Figure 2). The larger coefficient of thermal expansion obtained for 5K-HBPS in present study is consistent with weaker temperature dependence of its horizontal shift factor (a T ).…”

Section: Resultsmentioning

confidence: 99%

Role of Architecture on the Conformation, Rheology, and Orientation Behavior of Linear, Star, and Hyperbranched Polymer Melts. 1. Synthesis and Molecular Characterization

Kharchenko¹,

Kannan²,

Cernohous³

et al. 2002

Macromolecules

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In the preceding publication, we showed that the hyperbranched polystyrenes (HBPS) synthesized as part of this study may be viewed as starlike molecules with a high branch density, which are either unentangled or weakly entangled. In this paper, the role of architecture, especially the branch density, on the rheological and orientation behavior is investigated using simultaneous, quantitative stress and flow birefringence measurements in the melt state. Linear PS and eight-arm symmetric PS stars follow the stress-optical rule (SOR) over a wide dynamic range, with the stress-optical coefficient (C) governed by the arm molecular weight. When the branch density is "moderate" (greater than ∼20 arms), there is only a hint of nonterminal behavior in the viscoelastic moduli, while the C drops by 30% compared to a star with eight arms of comparable length. When the branch density is "high" (∼50 arms), and the arms are unentangled, the nonterminal behavior in G* is clearly apparent, and there is a dramatic breakdown in the stress-optical rule in these homopolymer melts. The quantitative birefringence measurements suggest that the "excess" birefringence may be due to the "form" contributions from the core-shell structure. Such a structure may be formed by the preferential radial stretching of the chain segments near the core, as suggested by other studies on hyperstars. For comparable chain density, the core would be bigger than the shell when the arm length is smaller. Therefore, the 5K-HBPS exhibits a more severe breakdown compared to the 10K-HBPS.

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Section: Resultsmentioning

confidence: 99%

Role of Architecture on the Conformation, Rheology, and Orientation Behavior of Linear, Star, and Hyperbranched Polymer Melts. 1. Synthesis and Molecular Characterization

Kharchenko¹,

Kannan²,

Cernohous³

et al. 2002

Macromolecules

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“…In Figure 3 relaxation times 14 and viscosities 11 are plotted for a lower molecular weight polystyrene, PS2K (M w ) 2 kg/mol). The steady-state recoverable compliance displayed in the inset was obtained by interpolation (J s ∝ M w ) between published values 15 for PS having molecular weights bracketing 2 kg/mol. The conspicuous decrease in J s corresponds to a value of τ 1 ∼ 6 × 10 -4 s at T ∼ 370 K. At temperatures below this, the viscosity (+) varies more with temperature than does τ 1 (×), while the curves for η and τ seg (9) are roughly parallel.…”

Section: Resultsmentioning

confidence: 99%

“…The 15 The inset shows the steady-state recoverable compliance. ) behavior is reflected in the temperature variation of J s .…”

Section: Discussion and Summarymentioning

confidence: 99%

Modes of Molecular Motion in Low Molecular Weight Polystyrene

2004

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The variations with temperature of the viscosity, η, and the relaxation times for various low molecular weight, unentangled polystyrenes (PS) are analyzed. We find that the temperature dependence of η does not directly reflect the behavior of the global chain modes. Depending on molecular weight and temperature, η can exhibit a stronger temperature dependence than even the local segmental modes. However, this is only a consequence of the strong temperature dependence of the recoverable compliance J s. The Rouse relaxation time, τ1, deduced from the product of the viscosity and the recoverable compliance, has the expected behavior. For example, this Rouse time for a PS of molecular weight equal to 2 kg/mol has the same temperature dependence as that for self-diffusion; hence, there is no enhancement of translational diffusion in the polymer. The same conclusion was reached by Urakawa et al. [Urakawa, O.; Swallen, S. F.; Ediger, M. D.; von Meerwall, E. D . Macromolecules 2004, 37, 1558], although the analysis leading to it was different. The conclusion is consistent with two extant explanations of the enhancement of translational diffusion in small molecular glass-formers, one which invokes spatially heterogeneous dynamics and the other ascribing the effect to the different coupling parameters for the translational and rotational correlation functions.

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“…In particular, PS has been the focus of several studies, because of conflicting results in the literature. 22,23 However, mechanical spectroscopy, 24 dynamic light scattering, 25 thermal analysis, 26 and dielectric spectroscopy 27 have demonstrated unambiguously that for M n Ͻ 1 kg/mol the fragility decreases with decreasing chain length. The appeal of fragility as a means to characterize temperature dependences arises from its correlation with the shape of the segmental relaxation function (or the ␣ dispersion in dielectric spectra), as shown for many molecular and polymeric glass formers.…”

Section: Introductionmentioning

confidence: 99%

Local segmental relaxation in bidisperse polystyrenes

Robertson

Roland

2004

J Polym Sci B Polym Phys

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Dynamic mechanical results are reported for segmental relaxation of monodisperse polystyrenes (PSs) with molecular weights of 0.7, 3, 18, and 104 kg/mol and bidisperse PSs created from blending pairs of these materials. The data for the monodisperse polymers confirm previous findings; namely, there is an increase in the glass-transition temperature normalized temperature dependence of the segmental relaxation times (fragility) with increasing molecular weight, along with a breakdown of the correlation between the fragility and the breadth of the relaxation function. For both the monodisperse and bidisperse PSs, the glass-transition temperature is a single function of the average number of chain ends, independent of the nature of the molecular weight distribution. It is also found that these materials exhibit fragilities that uniquely depend on the number-average molecular weight, that is, on the concentration of chain ends. In blends with linear PS, cyclic PS with a low molecular weight behaves as a high polymer, similar to its neat behavior, reflecting the overriding importance of chain ends.

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Viscoelastic behavior of low molecular weight polystyrene

Cited by 281 publications

References 32 publications

Role of Architecture on the Conformation, Rheology, and Orientation Behavior of Linear, Star, and Hyperbranched Polymer Melts. 1. Synthesis and Molecular Characterization

Role of Architecture on the Conformation, Rheology, and Orientation Behavior of Linear, Star, and Hyperbranched Polymer Melts. 1. Synthesis and Molecular Characterization

Modes of Molecular Motion in Low Molecular Weight Polystyrene

Local segmental relaxation in bidisperse polystyrenes

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