1. Laboratory of Polymer Chemistry, CP 206/1, Université Libre de Bruxelles, Boulevard du Triomphe, 1050 Bruxelles, Belgium, Laboratory for Chemistry of Novel Materials, Université de Mons-Hainaut/Materia Nova, Place du Parc, 20, B-7000 Mons, Belgium, and Department of Physics, IFM, Linköping University, S-58183 Linköping, Sweden