1. Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands, Department of Physical Chemistry, University of Duisburg-Essen, D 45117 Essen, Germany, and Netherlands Organisation for Scientific Research (NWO), DUBBLE@ESRF, Grenoble F-38043, France