1. I. R. Peat and W. F. Reynolds, Tetrahedron Lett. 14, 1539 (1972).
2. J. R. Lyerla, Jr., T. T. Horikawa and D. E. Johnson, J. Amer. Chem. Soc. 99, 2463 (1977).
3. For a recent review see V. J. McBrierty, Polymer 15, 503 (1974).
4. J. Schaefer, E. O. Stejskal and R. Buchdahl, Macromolecules 10, 384 (1977), and references therein.
5. E. R. Andrew in “Progress in Nuclear Magnetic Resonance Spectroscopy,” J. W. Emsley, J. Feeney and L. H. Sutcliffe, Eds., Pergamon Press, New York, N.Y., 1972, Vol. 8, Chapter 1.