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1H NMR spin-lattice (T1) and spin-spin (T2) relaxation times have been measured for the residual CHCl3 component of deuterochloroform (99.8 atom% D) in neat solvent samples and in a series of isotropic solutions of the ionic surfactant n-octylammonium-n-octadecanoate and also in degassed/dried and aerated solvent systems at 298 K. Analysis of the proton relaxation times as composite values from various relaxation mechanisms suggests that the spin-lattice process is predominantly via spin-rotation while spin-spin relaxation principally involves 1H-Cl scalar coupling. Rotational correlation times from relaxation rates via the dipolar and spin-rotation mechanisms reveal similar fast picosecond molecular rotation of chloroform in the different samples. The presence of surfactant in the solution appreciably affects the 1H NMR spin-lattice relaxation time of CHCl3 and the chemical shift, which is concentration dependent owing to weak intermolecular interactions. Effects of sample condition and solvent degassing, drying, and aeration treatments on the NMR relaxation times and line shape properties of the residual CHCl3 isotopomers are also examined. [ABSTRACT FROM AUTHOR]

H NMR chemical shift, line width, indirect nuclear splitting value, peak area integration value, and spin-lattice and spin-spin relaxation times at 298 K are compared for low-concentration isotropic solutions of n-octylammonium n-octadecanoate prepared via different techniques and conditions using dried, distilled, and degassed deuterochloroform and the nontreated solvent containing tetramethylsilane. The nature of the variation of observed spectral parameters and relaxation/rotational behavior with chemical composition (presence of oxygen and other paramagnetic species, stabilizer, impurities, and degradation products) of the solvent, history of the solution, and sample containment are analyzed. Relaxation times are interpreted in terms of monomer structure and reorientation and internal rotation modes as a function of atomic position along the n-alkyl chains. Collectively, the relaxation behavior of the surfactant complies with the two-step model of fast picosecond internal rotations of different size segments containing methylene groups separated in timescale from slower large segment and overall molecular tumbling modes of the monomer. Fast motional phenomena do not appear to be appreciably influenced by the chemistry of the solvent in contrast to spectral parameters such as chemical shift and line width of the labile ammonium protons. A model is also presented to explain anomalous variation of the peak area integration value with chemical shift of the ammonium resonance peak. [ABSTRACT FROM AUTHOR]

Highlights: [•] Segmental dynamics in molten polymers was studied by the PGSE method. [•] PGSE attenuation dependence on the gradient pulse width reduces artifacts. [•] Spectral analysis gives the effect of motion on spin dephasing. [•] Model of tube Rouse motion explains the measurements on the polyethylene. [Copyright &y& Elsevier]

The aim of this work was to study the effect of the type of substituent of the cellulose ethers and the molecular mass on the state and dynamics of water in the respective hydrogels to specify the quantity of adsorbed water on the polymers or, more explicitly, to calculate the average number of water molecules bound to a polymer repeating unit (PRU).1H NMR relaxation experiments were performed on equilibrated systems of cellulose ether polymers (HEC, HPC, HPMC K4M, and HPMC K100M) with water. In particular, the water proton spinlattice ( T 1) and spin-spin ( T 2) relaxation times were measured in these systems at room temperature. The observed proton NMR T 1 and T 2 of water in hydrogels at different cellulose ether concentrations at room temperature were shown to decrease with increasing polymer concentration. The relaxation rate 1/ T 1 is sensitive to the type of polymer substituent but insensitive to the polymer molecular mass. The rate 1/ T 2 appears much less influenced by the polymer substitution. The procedure developed for calculating the amount of water bound per PRU, based on the analysis of the T 1 and T 2 data, shows that this amount is the largest for HPC followed by HEC, HP MC K4M, and HPMC K100M. The results correlate well with the degree of hydrophilic substitution of the polymer chains. This NMR analysis deals with a single molecular layer of adsorbed water for the investigated cellulose ether polymers at all concentrations, while the rest of the water in the hydrogel is bulk-like. Therefore, the mesh size of polymer network in the view of a single molecular layer is not effectively changed. [ABSTRACT FROM AUTHOR]