1. Centre for Education and Research on Macromolecules (CERM), University of Liège, B6, Sart-Tilman, 4000 Liège, Belgium, Service des Matériaux Polymères et Composites, University of Mons-Hainaut, Place du Parc 20, 7000 Mons, Belgium, and DOW Benelux N.V., P.O. Box 48, 4530 AA Terneuzen, The Netherlands