1. a R & D Center , Korea Petrochemical Industrial Company, Limited , Ulsan, 680-110, Korea
2. b Department of Chemistry , Pusan National University , Pusan, 609-735, Korea
3. c Department of Polymer Science , Kyungpook National University , Taegu, 702-701, Korea
4. d Research Laboratory of Resources Utilization , Tokyo Institute of Technology , Yokohama, 226, Japan