1. Contribution from the Materials Research Laboratory, University of California, Santa Barbara, California 93106, IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120, Department of Polymer Science and Engineering, University of Massachusetts, Amherst, Massachusetts 01003, and Leibniz-Institut für Polymerforschung Dresden e.V., Hohe Strasse 6, D-01069 Dresden, Germany