1. Department of Applied Chemistry, Kumoh National Institute of Technology, Kumi 730-701, Korea, Department of Polymer Science and Engineering, Chungju National University, Chungju 380-702, Korea, Electronic Materials Lab., Samsung Advanced Institute of Technology, P.O. Box 111, Suwon 440-600, Korea, and Basic Research Lab., ETRI, Taejon 305-350, Korea