1. Institute of Polymers, Bulgarian Academy of Sciences, Acad. G. Bonchev 103-A, 1113 Sofia, Bulgaria, Centre of Polymer and Carbon Materials, Polish Academy of Sciences, M. Curie-Skłodowskiej 34, 41-819 Zabrze, Poland, and Institute of Chemistry, University of Opole, Oleska 48, 45-052 Opole, Poland