1. Faculty of Physics, St. Petersburg State University, Ulyanovskaya Str. 1, Petrodvorets, St. Petersburg, 198504 Russia
2. Institute of Macromolecular Compounds, Russian Academy of Sciences, Bolshoy pr. 31, V.O., St. Petersburg, 199004 Russia
3. Theoretical Polymer Physics, University of Freiburg, Hermann-Herder-Str. 3, D-79104 Freiburg, Germany