1. School of Biotechnology, Department of Biochemistry, AlbaNova University Center, Royal Institute of Technology, SE-106 91 Stockholm, Sweden, School of Chemical Science and Engineering, Department of Fiber and Polymer Technology, Teknikringen 56-58, Royal Institute of Technology, SE-100 44 Stockholm, Sweden, and Department of Polymer Chemistry, PO Box 513, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands