Polymer studies spin lattice time measurement

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]

Molecular motions not only affect the NMR line shape, but also determine the spin-lattice relaxation time T. Measurement of the T relaxation provides information about fast motions with frequencies near the NMR fiequency of deuterons, i.e., 46 MHz [25]. Moreover, Ti relaxation experiments are very useful for detecting motional heterogeneity in polymers [25]. Motional effects in both relaxation and line shape studies are completely dominated by reorientations of C-D bonds. Therefore, in motionally heterogeneous polymers, different T] relaxation times can be related to chain units with different mobility as reflected in different line shapes. 

The local dynamics of polymer chains can be studied by C NMR through measurements of J e spin-lattice magnetic relaxation time, T. The spin of a given relaxes by dipolar relaxation... 

The dynamics of intact lime cuticle and its two major component polyesters, cutin and wax, have been studied by the MAS NMR experiment [134]. By the measurements of spin-lattice relaxation times and spin-lattice relaxation times in the rotating frame which characterize respectively the megahertz- and kilohertz-regime motions, it is indicated that motional restrictions are present at the crosslinks of the cutin polymer and along the alkyl chains of the wax. The values of relaxation times, which differ for analogous carbon sites of cutin and wax individually, approach common values for the two materials in the intact lime cuticle. These results are considered to provide evidence for hydrophobic association within the plant cuticle of the long aliphatic chains of cutin and wax. 

Relaxation parameters of interest for the study of polymers include 1) 13C and H spin-lattice relaxation times (T1C and T1H), 2) the spin-spin relaxation time T2, 3) the nuclear Overhauser enhancement (NOE), 4) the proton and carbon rotating-frame relaxation times (T p and T p), 5) the C-H cross-relaxation time TCH, and 6) the proton relaxation time in the dipolar state, T1D (2). Not all of these parameters provide information in a direct manner nonetheless, the inferred information is important in characterizing motional frequencies and amplitudes in solids. The measurement of data over a range of temperatures is fundamental to this characterization. 

In the previous section, drug stability was shown to depend on the physical state of water in excipients. Detailed information on the physical state of water can be obtained by measuring the dynamics or the mobility of water molecules. The effect of water mobility on drug stability has been studied by determining water mobility in mixtures of water and polymers used as pharmaceutical excipients. Methods used include the measurement of spin-lattice relaxation time and spin-spinrelaxation time by nuclear magnetic resonance (NMR) spectroscopy as well as of dielectric relaxation time by dielectric relaxation spectroscopy. 

In heterogeneous polymer systems, nuclei with different mobilities and environments may have different relaxation times. This property has been widely exploited to study the partitioning of semi-crystalline polymers in their different phases. For example, measurements of the spin-lattice relaxation times of the crystalline portion of a set of polyethylenes have shown that the... 

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