1. Institute for Chemical Technology and Polymer Chemistry, University of Karlsruhe, Engesserstrasse 18, 76131 Karlsruhe, Germany, Fax: (+49) 721‐608‐3151
2. On leave from the School of Chemistry and Materials Engineering of Yunnan University, China.
3. Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
4. Present address: Department of Chemical Engineering, Materials Research Laboratory, University of California, Santa Barbara, CA 93106, USA