1. a Laboratory on Structure and Properties of Polymers , Sofia University , Sofia, 1126, Bulgaria
2. b Institut für Technische und Makromolekulare Chemie, Universität Hamburg , Bundesstr. 45, Hamburg, 20146, Germany
3. c Department of Polymer Engineering , University of Minho , Guimaraes, 4800, Portugal
4. d Institute for Composite Materials, University of Kaiserslautern , Kaiserslautern, 67663, Germany