1. Department of Chemical Engineering, University of California at Santa Barbara, Santa Barbara, California 93106, Institute of Polymer Research Dresden, P.O. Box 120411, D-01005 Dresden, Germany, Guidant Corp., 26531 Ynez Road, Temecula, California 92589-9018, Department of Chemistry, Tulane University, New Orleans, Louisiana 70118, and Department of Chemistry and Biochemistry, University of California at Los Angeles, Los Angeles, California 90095