How does dense phase CO2 influence the phase behaviour of block copolymers synthesised by dispersion polymerisation?

Using a CO₂ continuous phase for dispersion synthesis of block copolymers can provide a useful handle to control phase behaviour.

MAS double-quantum filtered dipolar shift correlation spectroscopy

A carbon-13 magic angle spinning double-quantum filtered dipolar shift correlation NMR experiment which can be used to establish through-space connectivities in solids is analyzed. The main advantage of the double-quantum filtered approach is the removal of intensity arising from natural abundance background signals. The variation in intensity of the cross and diagonal peaks observed in the two-dimensional spectrum as a function of mixing time is investigated experimentally for model systems. The observed behavior is compared with analytical expressions derived for three coupled spins, as well as with simulations based on average Hamiltonian theory. Copyright 2000 Academic Press.

Electron spin density distribution in the polymer phase of CsC60: assignment of the NMR spectrum

We present high resolution 133Cs-13C double resonance NMR data and 13C-13C NMR correlation spectra of 13C enriched samples of the polymeric phase of CsC60. These data lead to a partial assignment of the lines in the 13C NMR spectrum of CsC60 to the carbon positions on the C60 molecule. A plausible completion of the assignment can be made on the basis of an ab initio calculation. The data support the view that the conduction electron density is concentrated at the C60 "equator," away from the interfullerene bonds.

Isotropic mixing, sign discrimination, and sensitivity in solid-state wideline heteronuclear correlation experiments

A variant of the solid-state wideline heteronuclear NMR correlation experiment is described which overcomes some of the drawbacks associated with the routine experiment. The modified experiment results in spectra which are sign-discriminated in the omega(1) dimension, but without the loss in sensitivity expected for a standard hypercomplex implementation. In favorable cases sensitivity enhancements over comparable routine experiments are obtained. As well as these advantages, the method retains the selectivity of modified WISE experiments proposed previously which give spectra containing correlations between directly bonded nuclei only.

Spin counting with fast MAS

A novel magic angle spinning (MAS) multiple-quantum spin counting experiment based on the C7 recoupling sequence of Lee et al. is described. In contrast to previous approaches the new experiment is applicable at fast MAS rates and can be used to follow the multiple-quantum excitation dynamics with fine time resolution. The new method is illustrated by experiments on adamantane at spinning speeds comparable to the nonspinning dipolar linewidth. The sizes of the clusters of dipolar-coupled spins measured using the new experiment are compared to those obtained using the original nonspinning spin counting technique of Baum et al. Copyright 1999 Academic Press.