1. Contribution from The W. M. Keck Laboratories for Organic Synthesis, Department of Macromolecular Science, Case Western Reserve University, Cleveland, Ohio 44106-7202, Institut für Physikalische Chemie, Johannes Gutenberg-Universität, Jakob-Welder-Weg 11, D-55128 Mainz, Germany, Organische Chemie II, Makromolekulare Chemie, Universität Ulm, D-89069 Ulm, Germany, Maurice Morton Institute of Polymer Science, University of Akron, Akron, Ohio 44325-3909, and Department of Engineering Materials and Center for...