1. Key Laboratory of Polymer Ecomaterials Changchun Institute of Applied Chemistry; Chinese Academy of Sciences; 5625 Renmin Street Changchun 130022 P. R. China
2. University of Chinese Academy of Sciences; Beijing 100049 P. R. China
3. Department of Materials Science and Engineering; University of Illinois at Urbana-Champaign; MC 246, 1304 West Green Street Urbana Illinois 61801 USA