1. Department of Chemical and Biological Engineering, Korea University, Seoul 136-713, Republic of Korea, Materials Research Laboratory and Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, Department of Polymer Science and Engineering, University of Massachusetts, Amherst, Massachusetts 01003, and Laboratoire des Matériaux Polymères et Biomatériaux - UMR CNRS 5627, Université Claude Bernard Lyon, 15, Bd Latarjet, F− 69 622 VILLEURBANNE, France