1. Max-Planck-Institut für Polymerforschung, Ackermannweg 10, 55128 Mainz, Germany; Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovsky Sq. 2, 162 06 Prague 6, Czech Republic; Institut für Physik, Universität Potsdam, Am Neuen Palais 10, 14469 Potsdam, Germany; and Bayer, 51368 Leverkusen, Germany