1. Empa, Swiss Federal Laboratories for Materials Science and Technology, Feuerwerkerstrasse 39, CH-3602 Thun, and Ueberlandstrasse 129, CH-8600 Duebendorf, Switzerland, Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany, and Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, CH-3012 Bern, Switzerland