1. State Key Laboratory of Chemical Resource Engineering College of Materials Science and Engineering Beijing University of Chemical Technology Beijing 100029 China
2. Chemistry Department Durham University South Road Durham DH1 3LE UK
3. Physics Department Durham University South Road Durham DH1 3LE UK
4. Key Laboratory of Rubber-Plastics Ministry of Education Qingdao University of Science & Technology Qingdao 266042 P.R. China