1. Research Center for Engineering Technology of Polymeric Composites of Shanxi Province School of Materials Science and Engineering North University of China Taiyuan 030051 P. R. China
2. Department of Chemistry and the Materials Research Center Northwestern University 2145 Sheridan Road Evanston IL 60208 USA
3. Flexterra Inc. 8025 Lamon Avenue Skokie IL 60077 USA