1. Department of Engineering Physics and Mathematics, and Center for New Materials, Helsinki University of Technology, P.O. Box 2200, FIN-02015 HUT, Espoo, Finland, Laboratory of Polymer Chemistry, Materials Science Centre, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands, and Department of Physical Sciences, University of Helsinki, P.O. Box 64, FIN-00014, Helsinki, Finland