1. Institute of Materials Science & Technology, Analytical & Testing Center, Sichuan University, Chengdu 610064, P. R. China
2. College of Polymer Science and Engineering, Sichuan University, Chengdu 610065, P. R. China
3. Provivi, Inc, Santa Monica, CA, USA
4. State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu 610065, P. R. China