Pulsed Gradient Spin−Echo (PGSE) Diffusion and1H,19F Heteronuclear Overhauser Spectroscopy (HOESY) NMR Methods in Inorganic and Organometallic Chemistry:  Something Old and Something New

2005 ◽  
Vol 105 (8) ◽  
pp. 2977-2998 ◽  
Author(s):  
Paul S. Pregosin ◽  
P. G. Anil Kumar ◽  
Ignacio Fernández
Keyword(s):  
Organometallic Chemistry ◽  
Spin Echo ◽  
Nmr Methods

Pulsed and Steady Field Gradient NMR Diffusion Measurements in Polymers

1985 ◽  
Vol 58 (3) ◽  
pp. 527-560 ◽  
Author(s):  
Ernst D. von Meerwall
Keyword(s):  
Spin Echo ◽  
Concentrated Solutions ◽  
Free Volume Theory ◽  
Polymer Systems ◽  
Polymer Molecules ◽  
Self Diffusion ◽  
Semidilute Solutions ◽  
Nmr Diffusion ◽  
Nmr Methods ◽  
And Diffusion

Abstract Some twenty years after the development of the steady and pulsed gradient spin-echo NMR methods of measuring self-diffusion, these techniques are now maturing and experiencing a surge of interest, much of it concentrated on polymer systems. The methods are briefly reviewed here, together with the most important results in polymers, with particular concentration on work described within the last few years. The research is divisible into three categories: diffusion of diluent and penetrant molecules in rubbery high polymers, diffusion of polymer molecules in dilute and semidilute solutions with liquid solvents, and diffusion of macromolecules dissolved in concentrated solutions or melts of equivalent or different polymers of arbitrary molecular weight. The review includes the main theoretical interpretations of the experiments, particularly the free-volume theory in its various forms and power-law behaviors postulated by recent refinements of tube/reptation and scaling theory. This article represents an updated elaboration of an earlier review.

Ultrasound Devulcanization of SBR: Molecular Mobility of Gel and Sol

1997 ◽  
Vol 70 (2) ◽  
pp. 183-193 ◽  
Author(s):  
S. T. Johnston ◽  
J. Massey ◽  
E. von Meerwall ◽  
S. H. Kim ◽  
V. Yu Levin ◽  
...  
Keyword(s):  
Glass Transition ◽  
Main Chain ◽  
Molecular Level ◽  
Spin Echo ◽  
Mean Diffusivity ◽  
Nmr Relaxation ◽  
Butadiene Rubber ◽  
Ultrasound Technique ◽  
Large Molecules ◽  
Nmr Methods

Abstract In an effort to support the recycling of rubbery polymers and composites, 1H NMR relaxation and pulsedgradient spin echo diffusion measurements have been performed on virgin and unfilled vulcanized strene-butadiene rubber (SBR), and networks after various extents of devulcanization using an ultrasound technique. The NMR methods recognize unentangled light molecules (e.g. sol), but do not distinguish between unattached entangled large molecules and chemical network segments. Devulcanization generates additional sol with a wide mass distribution, thus increasing both sol and gel mobility, but decreasing sol mean diffusivity. The latter effect is accounted for by the increasing mean sol molecular mass but also by the increasing glass transition temperature, which is related to main-chain stiffening seen in our earlier 13C NMR experiments. In addition to improving the molecular-level understanding of devulcanization, this study provides guidance for the optimization of the devulcanization parameters.

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