The Molecular Structure of Polyethylene. VII. Melt Viscosity and the Effect of Molecular Weight and Branching<sup>1</sup>

Peticolas, Warner L.; Watkins, JJ

doi:10.1021/ja01576a002

Cited by 54 publications

(14 citation statements)

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“…However, despite extensive work on the effects of LCB on the viscoelastic properties of these types of material in the melt in the 1960s, there is no unified picture of their dependence on molecular variables. The following general properties were established for a moderate to high degree of LCB (>> 1 LCB/10 4 carbon atoms): a) lower Newtonian or zero-shear viscosity η o and a higher critical shear rate o γ& for the onset of shear thinning behaviour than linear polymers of the same weightaverage molecular weight, M w [3][4][5][6][7][8][9][10][11][12][13][14]; b) less intense pseudoplastic behaviour [11,[15][16][17]; c) increased activation energy of flow, E a [18][19][20][21][22][23][24][25][26][27][28][29]; and d) enhanced melt elasticity expressed in terms of first normal stress difference N 1 , steady-state compliance J e o and extrudate swell d j /D [4,5,12,13,16,17,[30][31][32].…”

Section: Conventional Polymersmentioning

confidence: 99%

Effect of long chain branching on linear-viscoelastic melt properties of polyolefins

et al. 2002

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Abstract:The aim of this review is to provide evidence that rheological testing is a potent tool for characterising polymers in the melt. An effort has been made in order to gather results in conventional and model polyolefins, and correlating them with phenomena occurring at the molecular level. We have focused our interest on long chain branching (LCB). In the case of materials containing long side-chain branches, strong effects on viscosity, elastic character and activation energy of flow are general features. Literature results mostly indicate that the effect of polydispersity on these parameters could be very similar to that expected due to the presence of LCB -notwithstanding that the effects of LCB seem to be stronger than those due to polydispersity for a given molecular weight. Different relaxation processes appear as a consequence of the presence of LCB: slower terminal relaxation behaviour than of linear counterparts, and faster additional branch relaxation at higher frequencies, clearly distinguishable from polydispersity effects. To measure the amount of LCB from limited viscoelastic data and molecular properties seems to be a suitable instrument to explain the rheological features of the different polymers, but it fails when the results are compared with measured values of LCB density in model polymers. The actual framework leads us to say that the number of branches is less important than the topology itself. Therefore, the position and architecture of the branches along the polymer main chain are the main factors that control the rheology of the material.

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Section: Conventional Polymersmentioning

confidence: 99%

Effect of long chain branching on linear-viscoelastic melt properties of polyolefins

et al. 2002

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“…In many experimental investigations the molecular weight dependence of the zero-shear viscosity r/was found to be different above and below the critical molecular weight Me [3], [4], [62] - [64]. The empirical power laws are q -M (M < Mc and constant density) with respect to molecular weight.…”

Section: Zero-shear Viscositymentioning

confidence: 99%

“…The power laws below M c must be considered to represent average molecular weight dependences 8 ~/ // ~ calc. from directly measured nmr data (PS [66]; PE [60], [64], (this work) [73], [74] So far, we have derived formulae for diverse observables from the same basis, given by the three-component description of chain fluctuations. However, nuclear magnetic relaxation times depend on more components than zero-shear viscosity does.…”

Section: ~ ~ Ngc(t )mentioning

confidence: 99%

NMR field-cycling relaxation spectroscopy, transverse NMR relaxation, self-diffusion and zero-shear viscosity: Defect diffusion and reptation in non-glassy amorphous polymers

Kimmich

Bachus

1982

Colloid & Polymer Sci

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Molecular weight and frequency dependences, respectively, of the nuclear magnetic relaxation times and the self-diffusion coefficient of polyethylene and polystyrene have been investigated over several orders of magnitude. The relation to viscous behaviour is established. A closed concept is developed. Conclusions are: a) The y-process in amorphous polyethylene can be described by the aid of the limited defect diffusion model. b) The fl-process in the same material is interpreted as limited reptation. The intensity function of this process depends on the amorphous content. c) The three-component description of chain fluctuations already presented in previous papers has been modified in order to account for the precise molecular weight dependences, which now have been measured. Especially we distinguish between internal and whole-chain reptation. A correlation function is derived, which predicts the right limiting behaviour inspite of its semi-empirical character. The three components can be identified by the frequency and molecular weight dependences of the nuclear magnetic relaxation times. d) The molecular weight dependences are subdivided by 3 (spin lattice relaxation), 2 (transverse relaxation), 1 (zero-shear viscosity) and 0 (self-diffusion coefficient) characteristic molecular weights (Me, MBo MA~ ). All of them can be derived as dynamic case transitions. Especially the classical critical molecular weight of the viscosity can be explained by the transition between tube fluctuations governed by internal and wholechain reptation, respectively. The assumption of a structural transition is unnecessary. e) A semi-empirical expression for the zero-shear viscosity is derived for the whole range of chain lengths. The analysis of the molecular weight dependences of the NMR relaxation times straightforwardly leads to those of the zero-shear viscosity. f) Using a NMR field-gradient method, it is shown again that the self-diffusion coefficients of both melt examples obey D ~ M~72~ g) Matrix effects predominantly are due to changes in the free volume.

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“…One possible explanatiori may be that the melt viscosity of long chain branched polymers does not increase with molecular weight as much as in linear polyniers. [13][14][15][16] This hypothesis was strengthened by crystallization at cooling rates from 1.23 to 20°C/min on fractions from BPE-11. The supercooling curves from BPE 11-3 and BPE 11-18 are virtually parallel, indicating that molecular weight changes do not strongly affect primary crystallization rates in these branched polymers.…”

Section: Resultsmentioning

confidence: 99%

“…The crystallization and melting temperatures reported were determined as the point of maximum departure from the baseline. 13 The instrument was periodically calibrated with p-dibromobenzene, benzoic acid and indium melting point standards. The heats of fusion A H , were determined by planimetric integration of the area under the melting endotherm, using the AH, of an indium sample as a calibration standard.…”

Section: Crystallization Behavior Of Low-density Polyethylene: Eflectmentioning

confidence: 99%

Crystallization behavior of low‐density polyethylene: Effects of molecular weight and branch concentration

Otocka¹,

Roe²,

Bair³

1974

J. Polym. Sci. Polym. Phys. Ed.

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The Molecular Structure of Polyethylene. VII. Melt Viscosity and the Effect of Molecular Weight and Branching¹

Cited by 54 publications

References 1 publication

Effect of long chain branching on linear-viscoelastic melt properties of polyolefins

Effect of long chain branching on linear-viscoelastic melt properties of polyolefins

NMR field-cycling relaxation spectroscopy, transverse NMR relaxation, self-diffusion and zero-shear viscosity: Defect diffusion and reptation in non-glassy amorphous polymers

Crystallization behavior of low‐density polyethylene: Effects of molecular weight and branch concentration

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The Molecular Structure of Polyethylene. VII. Melt Viscosity and the Effect of Molecular Weight and Branching1

Cited by 54 publications

References 1 publication

Effect of long chain branching on linear-viscoelastic melt properties of polyolefins

Effect of long chain branching on linear-viscoelastic melt properties of polyolefins

NMR field-cycling relaxation spectroscopy, transverse NMR relaxation, self-diffusion and zero-shear viscosity: Defect diffusion and reptation in non-glassy amorphous polymers

Crystallization behavior of low‐density polyethylene: Effects of molecular weight and branch concentration

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The Molecular Structure of Polyethylene. VII. Melt Viscosity and the Effect of Molecular Weight and Branching¹