1. Department of Chemistry and the Herman F. Mark Polymer Research Institute, Polytechnic University, Six Metrotech Center, Brooklyn, NY 11201, USA.
2. Department of Macromolecular Science, Faculty of Science, Osaka University, Toyonaka, Osaka 560, Japan
3. Lawrence Livermore National Laboratory, Livermore, CA 94550, USA.
4. Department of Chemical Physics, Weizmann Institute of Science, Rehovot, 76100, Israel