ISSN:
1435-1536
Keywords:
NMR field-cycling relaxation spectroscopy
;
transverse relaxation
;
self-diffusion
;
NMR field-gradient method
;
zero-shear viscosity
;
defect diffusion
;
reptation
;
tube renewal
;
contour length fluctuation
;
critical molecular weight
;
matrix effects
;
amorphous polymers
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract 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) Theγ-process in amorphous polyethylene can be described by the aid of the limited defect diffusion model. b) Theβ-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 (M C, MBC, MAB). 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 obeyD ∼M w −2.0 . g) Matrix effects predominantly are due to changes in the free volume.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01413127
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