1. Contribution from the Department of Chemical Engineering, University of California, Santa Barbara, California, 93106, Materials Research Laboratory, University of California, Santa Barbara, California, 93106, Max-Planck-Institute für Polymerforschung, Postfach 3148, D-55021 Mainz, Germany, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, and Laboratoire de Chimie de la Matière Condensée, Université Pierre et Marie Curie, CNRS-UMR 7574, 4 Place Jussieu, 75252 Paris CEDEX 05 France