1. Department of Polymer Chemistry and Material Science, Institute of Chemistry, Chemical Research Center, Hungarian Academy of Sciences, H-1525 Budapest, Pusztaszeri u. 59-67, P.O. Box 17, Hungary; The Danish Polymer Centre, Risø National Laboratory, DK-4000 Roskilde, Denmark; and The Danish Polymer Centre, Department of Chemical Engineering, Technical University of Denmark, Building 229, DK-2800 Lyngby, Denmark