Segmental motion line narrowing

Since quantitation is crucial in many polymer analyses, it is important to obtain data with T l and NOE in mind. Highly flexible polymers undergoing rapid segmental motion typically give narrow l c lines. Often these carbons can have Tj s of several seconds and full or nearly full NOE. Other, more rigid polymers may exhibit broad lines and little NOE. In the case of ethylene-l-hexene copolymer there is considerable NOE for the 1-hexene portion (Figure 2). Relative peak areas can produce good concentrations only if and NOE are properly considered. ... 

C-NMR studies have complemented the above H-NMR results (Sears, 1975 Ribeiro and Dennis, 1976). The phospholipid in mixed micelles also exhibit similar Ti values to the phospholipid in the unsonicated multilamellar vesicles, corresponding to similar fast segmental motions on the phospholipid fatty acid chains in all of these systems. However, the phospholipid in mixed micelles very clearly exhibits narrower lines (longer T relaxation times) than in the bilayer systems. 

Since quantitation is crucial in many polymer analyses, it is important to obtain data with T] and NOE in mind. Highly flexible polymers undergoing rapid segmental motion typically give narrow lines. Often these carbons can have s of several... 

The overall rotational mobility of the polymer, rather than segmental motions, is primarily responsible for the motional averaging of the dipolar and chemical-shift interactions to their isotropic values. The viscosity can be decreased and the motion can be increased by making more dilute polymer solutions and by increasing the measurement temperature. In this manner, narrower lines for high-resolution speetra can be obtained for polymers in solution. Special techniques are required to obtain high-resolution spectra of polymeric solids [21,22]. 

In order to investigate the dynamics of an electrolyte system, the line width of the central Li transition as a function of P(E0-EC)/LiCF3S03 electrolyte content (P(EO-EC) = poly(ethylene oxide-co-ethylene carbonate)) as well as temperature were measured by Jeon and Kwak on solvent-free polymer electrolyte materials based on poly(vinylidene fluoride) (PVdF) membranes fllled with P(EO-EC). As seen in Fig. 7.8 a typical temperature dependence is observed for this system with broad spectral lines below and narrow Unewidths above Tg, indicating Li ion mobilities closely associated with segmental motion of P(EO-EC) polymer. 

The molecular interpretation of this result is as follows above the glass temperature T0 the molecular segments are in vigorous motion and change their positions frequently. Hence, the average nuclear spin interaction is reduced to a minimum. This causes a narrow absorption line. As the kinetic motion of the molecules is decreased by cooling, the frequency of position changes is reduced, and... 

The spectral line shape is concentration dependent, but remains motionally narrowed until relatively high polymer concentrations are reached (Figure 1-B,C and reference 27). Loop and tail segment density near the surface may be large, but falls off rapidly with distance above the surface. We therefore expected tails and all but the smallest loops (and surface extended loops) would exhibit three line spectra similar to that observed with the free, isolated polymer molecule. 

In NMR terminology the words solid and liquid are used to describe the local motion of the nuclear environment. In that sense spins belonging to liquid molecules absorbed in a solid-state matrix or to mobile polymer segments in a rubbery solid are considered to be in a liquid state. Liquid-state imaging techniques are experimentally less demanding the same techniques can be used for investigations of solids with narrow lines. Suitable mate-... 

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