Rotational correlation times for ethanol by deuteron magnetic spin–lattice relaxation

Deuterium nmr spin–lattice relaxation times have been measured for dilute solutions of adamantane-d16 in CH2I2, CHBr3, CCl4, CHCl3, and CH2Cl2. The reorientation correlation times, τ2, calculated from the experimental data are used to calculate τJ, the angular momentum correlation times, assuming both the J-diffusion and Hubbard relations. The derived τJ values suggest that adamantane executes small step diffusion in CH2I2 and CHBr3, and large step diffusion in CCl4, CHCl3, and CH2Cl2. The calculated τJ values do not appear to be related to the mean times between collisions calculated using a hard sphere model. Both variable solvent and variable temperature experiments indicate 1 ps/cP for the viscosity dependence of the adamantane reorientation time, about 1/36th the value predicted using the familiar Stokes–Einstein equation.Carbon-13 and 1H nmr T1 data indicate that reorientation of hexamethylenetetramine in H2O (28 ps/cP), CHCl3 (27 ps/cP), and CHBr3 (18 ps/cP) is severely hindered because of inter-molecular hydrogen bonding.

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Solid-State Carbon-13 NMR Studies of Vulcanized Elastomers. VI. Relaxation in Sulfur-Vulcanized Natural Rubber

Rubber Chemistry and Technology ◽

10.5254/1.3536237 ◽

1989 ◽

Vol 62 (1) ◽

pp. 82-97 ◽

Cited By ~ 6

Author(s):

Mladen Andreis ◽

Juwhan Liu ◽

Jack L. Koenig

Keyword(s):

Experimental Data ◽

Solid State ◽

Variable Temperature ◽

Lattice Relaxation ◽

Spin Lattice Relaxation ◽

Relaxation Techniques ◽

Nmr Studies ◽

Time Curve ◽

Correlation Times ◽

Spin Lattice

Abstract Molecular motions in sulfur-vulcanized NR are investigated by solid state 13C NMR relaxation techniques. Since the high-resolution spectra of crosslinked samples exhibit overlapping in the aliphatic region, a combined application of variable temperature spin-lattice relaxation measurements and the computer simulation of the overlapped spectral region is used in order to detect resonance signals. Motional restrictions introduced by crosslinks are investigated from the temperature dependence of nT1 relaxation times for individual carbons. The V-curves for all polyisoprene signals and for the detectable signals arising from the network units exhibit a similar general trend with increased curing time: curve broadening, shift of the minima to higher temperatures, and increase of the T1 min values. All the backbone carbons show quantitatively similar effects of vulcanization on the spin-lattice relaxation. At shorter curing times, motional restrictions for the methyl side group are more pronounced compared to the main-chain carbons. The experimental data suggest that the isotropic motion is strongly affected by the crosslinking. Librational motion is less affected, while the change in rotational motion has no significant influence on the relaxation curve. Although experimental data cover a relatively narrow temperature range, not sufficiently wide for a more accurate quantitative analysis, the results indicate that concepts of plural correlation times and a distribution of correlation times are applicable.

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