Solid-state carbon-13 and proton NMR imaging studies of the accelerated-sulfur cured high vinyl poly...

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" Solid-state carbon-13 and proton NMR imaging studies of the accelerated-sulfur cured high vinyl polybutadiene "
M. A. Rana J. L. Koenig

Document Type	:	Latin Dissertation
Language of Document	:	English
Record Number	:	1113354
Doc. No	:	TLpq304013869
Main Entry	:	J. L. Koenig
	:	M. A. Rana
Title & Author	:	Solid-state carbon-13 and proton NMR imaging studies of the accelerated-sulfur cured high vinyl polybutadiene\ M. A. RanaJ. L. Koenig
College	:	Case Western Reserve University
Date	:	1993
student score	:	1993
Degree	:	Ph.D.
Page No	:	295
Abstract	:	Solid-state C NMR and H Imaging methods have been used to follow the progress of accelerated-sulfur vulcanization of unfilled high vinyl polybutadiene. Different NMR pulse sequences have been used to characterize the micro-network structures present in the bulk of the finally cured rubber samples. These studies were made as a function of formulation and processing variables. The time-resolved, integrated data have been used to interpret the development of the crosslinked rubber network. Mono-sulfidic as well as the residual accelerator fragments were differentiated from the polysulfidic crosslinks in a finally cured material. Dynamic studies of these network structures were made using spin-spin relaxation (T{\rm 2c}) measurements. The activation energies calculated based on T2 were used to verify different carbons, directly attached to the sulfur atoms. A swelling method based on Flory-Rehner's equation was also used to determine the crosslink densities and the number-average molecular weight between the nodal junctions in different formulations. Different spatially resolved structural features have been detected in the swollen samples using NMR imaging method. The voids, no-voids and other impurities were differentiated on the basis of magnetic susceptibility differences. Cyclohexane was used as a swelling solvent to probe the morphological defects in these materials. The T2-weighted images were used to evaluate the crosslink densities in different samples. The quantitative estimations based on histogram was also employed to determine the average volume per crosslink region. The contrast based on H-1 spin-density or mobility was highlighted in T2-weighted images. The variations were found to be closely related to variation in both concentration and mobility of the network.
Subject	:	Applied sciences
	:	Chemical engineering
	:	polybutadiene
	:	Polymers
	:	Pure sciences
	:	sulfur vulcanization