1. Dept. of Polymer Science and Engineering, Shanghai Jiao Tong Univ., Shanghai 200240, P.R. China (corresponding author).
2. Shanghai Key Laboratory of Electrical Insulation and Thermo Aging, Shanghai Jiao Tong Univ., Shanghai 200240, P.R. China.
3. Shanghai Road and Bridge Group Co. Ltd., No. 36, Guoke Rd., Yangpu District, Shanghai 200433, P.R. China.