[1] Univ Cambridge, Cavendish Lab, Cambridge CB3 0HE, England
[2] Riso Natl Lab, Mat Res Dept, DK-4000 Roskilde, Denmark
[3] Riso Natl Lab, Danish Polymer Ctr, DK-4000 Roskilde, Denmark
[4] Max Planck Inst Polymer Res, D-55128 Mainz, Germany
[5] CNRS, Ctr Rech Macromol Vegetales, F-38041 Grenoble, France