1. Department of Chemistry, University of Bath, Bath, BA2 7AY U.K., Centre for Self-Organising Molecular Systems, University of Leeds, Leeds, LS2 9JT, UK, Max-Planck-Institut für Polymerforschung, Ackermannweg 10, 55128 Mainz, Germany, and Forschungszentrum Jülich, 52425 Jülich, Germany