1. UNESCO Centre for Macromolecules and Materials, Department of Chemistry and Polymer Science, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa; Nuclear Magnetic Resonance Laboratories, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa; and Laboratory of Polymer Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands