Cross-polarisation dynamics

Figure 4.15. Cross-polarisation dynamics for S0.3MHz spectra of a copolymer of nylon-6 and 40% polyether/polyesteramide (see the text) [14] variation of peak height S with contact time CT A, nylon-6-carbons (diamonds indicate the C4/CS peak, squares are for C2, and circles are for Cl, see III) B, polyether carbons (the symbols are for the peaks at the following chemical shifts triangles 18.2 ppm, circles 75.8 ppm, squares 73.9 ppm, diamonds 71.2 ppm). S is expressed relative to the peak height of the most intense signal, extrapolated to zero CT. A theoretical curve is shown for Cl in A...

A detailed analysis of the cross-polarisation behaviour showed that quantitative results can be obtained. The amount of unreacted units, typically 0-15%, was found to depend on the polymerisation parameters. Conditions favouring mobility, i.e., higher temperatures or increased solvent quality, resulted in lower content of residual double bonds. Bromine addition values are 2-3% higher than the NMR data. The reactivity toward bromine further indicates that the mobility is reasonably high. This has also been confirmed by measurements of the rotating-frame relaxation time constant, Tj ( C) Most likely, Tjp is dominated by spin-lattice processes i.e., it can be interpreted in terms of molecular dynamics. The values obtained for C=0 and >C =CH2 in unreacted units are about twice that of C=0 in reacted units, indicating increased mobility. The reactivity of the remaining double bonds in a radical polymerisation with a chiral monomer was also demonstrated. 

Schneider and Klein(5) have pointed out that the early stages of cross-flow microfiltration often follow such a pattern although the growth of the cake is limited by the cross-flow of the process liquid. There are a number of ways of accounting for the control of cake growth. A useful method is to rewrite the resistance model to allow for the dynamics of polarisation in the film layer as discussed by Fane 6. Equation 8.3 is then written as ... 

Whilst most measurements are of the total chemiluminescent emission from a reaction, the angular distribution of chemiluminescence has been recently studied [82, 83] in crossed-molecular beam experiments. An additional property of the chemiluminescence observed in beam experiments that may contain information about the reaction dynamics is the degree of polarisation of the emission [84, 85], There have been several recent reviews dealing with the topic of chemiluminescence [3, 77, 86-88]. 

The first term represents the usual mechanism for radiative capture, while the second results from the polarisation mechanism. The ratio r/ of the partial cross sections of the two mechanisms of capture is approximately p 4 arf(w) 2 jir2R3f, where Rf is the radius of the final state orbit of the electron. Within a giant resonance, the dipole dynamical polarisability is mainly determined by its imaginary part Jmad(oj) = cct (u )/4-k, where cr7(co) is the photoabsorption cross-section of the cluster. 

Many previous authors have ignored the cross terms that occur between the various dielectric components in a biopolymer/water system. Steinhauser and co-woricers have analysed the situation theoretically and with molecular dynamics simulations. Their model may be summarised by the following equation for the total polarisation, tp, of the system. 

A novel approach for solid-state NMR characterisation of cross-linking in polymer blends from the analysis of polarisation transfer dynamics is... 

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