1. Laboratoire de Chimie des Polymères Organiques (LCPO), ENSCPB−CNRS-Université Bordeaux 1, 16 Avenue Pey-Berland, 33607 Pessac Cedex, France, and The George and Josephine Butler Polymer Research Laboratory, Department of Chemistry, University of Florida, P.O. Box 117200, Gainesville, Florida 32611-7200