1. Shaanxi Key Laboratory of Macromolecular Science and Technology School of Chemistry and Chemical Engineering Northwestern Polytechnical University Xi'an Shaanxi, 710072 P. R. China
2. College of Chemistry and Chemical Engineering Key Laboratory of Auxiliary Chemistry and Technology for Chemical Industry Ministry of Education, Shaanxi Key Laboratory of Chemical Additives for Industry Shaanxi University of Science and Technology Xi'an Shaanxi, 710021 P. R. China