Nuclear spin relaxation, poly

Nuclear spin relaxation, poly(methacrylonitrile peroxide), 709... 

Froix MF, Beatty CL, Pochan JM, Hinman DD (1975) Nuclear spin relaxation in poly(diethyl-siloxane). J. Polymer Sci., Polymer Phys. Ed. 13 1269... 

C Spin lattice relaxation times, Tj, spin-spin relaxation times, T2, and nuclear Overhauser enhancements, NOE, for the a-carbons of PBLG of various molecular weights have been used to study transitions from rigid to flexible forms of this polymer (Allerhand and Oldfield, 1973). Effective rotational correlation times, reff, calculated from 7 - and NOE-values, for the a-carbons were 24-32 nanoseconds for the helical form and approximately 0-8 nanoseconds for the random coil (Allerhand and Oldfield, 1973). The transition from the a-helix to the random-coil of PLM causes the resonances of the a- and carbonyl carbons to move upfield 2-3 and 3-4 ppm respectively (Tadokoro et al., 1973), which is consistent with results obtained for PBLG and PCBO. Further work is required before the reasons for the chemical shift differences between the corresponding carbons in the helical and random-coil forms in deuterochloroform-TFA systems can be elucidated. Plots of chemical shifts and relaxation times vs. pH have been used to study the helix-coil transition of poly-L-lysine hydrochloride in aqueous solution (Saito and Smith,... 

The relaxation dynamics of junctions in polymer networks have not been well known until the advent of solid-state P NMR spin-lattice relaxation measurements in a series of poly(tetrahydrofuran) networks with tris(4-isocyanatophenyl)-thiophosphate junctions (Shi et al., 1993). The junction relaxation properties were studied in networks with molecular weights between crosslinks, Me, ranging from 250 to 2900. The dominant mechanism for P nuclear spin lattice relaxation times measured over a wide range of temperatures were fit satisfactorily by spectral density functions, 7([Pg.225]

McBrierty and Douglass have studied cross-relaxation between and F spins in poly(vinylidene fluoride) by means of the transient nuclear Overhauser effect. The results provided valuable additional data in support of previous interpretations of relaxation, in particular the measurement of motional frequencies at the hitherto inaccessible frequency of the difference between H and F frequencies (2 MHz). The same authors have used this technique to study compatibility in blends of poly(vinylidene fluoride) with poly(methyl and ethyl methacrylate)s. The cross-relaxation data indicate substantial intimate mixing. 

The combined effects of temperature and pressure on nuclear magnetic relaxation have been studied to obtain the derivative (dr/dP), from spin-lattice relaxation time measurements as well as dT/bP at constant line width in the region of line narrowing.Even at a single frequency, the determination can be made at various temperatures. The spin-lattice measurement corresponds to frequencies of the order of 10 Hz the spin-spin or line width measurement, of lO Hz. The lower the temperature, the more short range is the character of the motions reflected at a given frequency and the numerical values for (ibT/bP) appear to decrease with decreasing temperature for natural rubber, cw-polybutadiene, and other poly-... 

Spin dynamics studies in poly pyrrole-perchlorate (PPy-CIO4) have been performed by Devreux and Lecavellier [8]. At first, observation of the Overhauser effect proved the existence of a direct dynamic coupling between electronic and nuclear spins [104]. The frequency dependence of the proton relaxation rate is shown in Fig. 5.19. The data can be fitted with Ti" a for temperatures r < 150 K. For T > 150 K, the data deviate from 1-D diffusion behavior. They also cannot be fitted with the law of a pseudo-one-dimensional diffusion [Eq. (10)] with the introduction of a cutoff frequency o>c. Instead, they can be accounted for by taking the spectral density... 

The ionic association induced by the addition of potassium iodide to poly(ethylene oxide) in methanol produces large changes in the nuclear spin-lattice relaxation (Tj) of the polymer protons. These changes can be described quantitatively in terms of free and charged units along the polymer chain. Long-range interactions, as evidenced in... 

The presence of four kinds of nuclear magnetic resonance (NMR) observable nuclei ( H, uB, 13C, and 29Si) allows poly(m-carborane-siloxane) to be readily investigated using NMR spectroscopy. In addition, H spin-echo NMR relaxation techniques can provide an insight into polymer segmental chain dynamics and therefore useful information on material viscoelastic characteristics. 

Dynamics of Poly(oxyethylene) Melts Comparison of 13C Nuclear Magnetic Resonance Spin-Lattice Relaxation and Dielectric Relaxation as Determined from Simulations and Experiments. 

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