1. Department of Polymer Science and Engineering, Hannam University, 133 Ojeong Dong, Daedeog Ku, Taejeon, Korea 306-791; School of Life Sciences and Biotechnology, Korea University, 1,5-ka, Anam Dong, Sungbuk Ku, Seoul, Korea 136-701; Advanced Materials Division, Korea Research Institute of Chemical Technology, P.O. Box 107, Yusung, Taejeon, Korea 305-600; and School of Electrical, Electronic and Computer Engineering, Hongik University, Jochiwon, Chungnam, Korea 339-701