1. IRC in Polymer Science and Technology, Department of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, U.K.; Department of Chemistry, University of Sheffield, Sheffield, S2 2UN, U.K.; Institut für Festkörperforschung, FZ Jülich GmbH, 52425, Jülich, Germany; ISIS, Rutherford-Appleton Laboratory, Chilton, Oxon, OX11 0QX U.K.; and Department of Physics, University of Sheffield, Sheffield, S2 2UN, U.K.