1. School of Petrochemical Engineering, Liaoning Petrochemical University, Fushun 113001, P. R. China
2. School of Physics and Information Engineering, Shanxi Normal University, Taiyuan 030031, P. R. China
3. State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, P. R. China