1. Chimie ParisTech, UMR CNRS 7223, 75005 Paris, France, Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York, 14853-1301, Borealis Polymers Oy, FI-06101 Porvoo, Finland, and Centre de Diffractométrie X, Université de Rennes 1, 35042 Rennes, France