1. Department of Physics and Geosciences, University of Leipzig, Linnéstr. 5, 04103 Leipzig, Germany; Inst. Macromolecular Compounds, Bolshoi pr. 31, 199004 St. Petersburg, Russia; and University of Freiburg, Inst. Macromolecular Chemistry, Sonnenstr. 5, 79104 Freiburg, Germany