1. Foundation for Research and Technology-Hellas (FO.R.T.H.), I.E.S.L., P.O. Box 1527, 711 10 Heraklion Crete, Greece, and Physics Department, University of Ioannina, 45 110 Ioannina, Greece; T.U. Graz, Institute of Chemical Technology of Organic Substances (ICTOS), 8010 Graz, Austria; and Max-Planck Institut für Polymerforschung, Postfach 3148, D-55021 Mainz, Germany