1. Key Laboratory of Advanced Materials Ministry of Education Department of Chemical Engineering Tsinghua University No. 1, Tsinghua Garden, Haidian District Beijing 100084 P. R. China
2. Key Laboratory of Carbon Fiber and Functional Polymers Ministry of Education College of Materials Science and Engineering Beijing University of Chemical Technology No. 15, North Third Ring Road, Chaoyang District Beijing 100029 P. R. China