1. Melville Polymer Laboratory, Department of Chemistry, University of Cambridge, Lensfield Rd, CB2 1EW, UK; National Starch, Wexham Rd, Slough, SL2 5DS, UK; ICI Uniqema, PO Box 90, Wilton Centre, Middlesbrough, Cleveland, TS90 8JE, UK; and ICI Technology, PO Box 90, Wilton Centre, Middlesbrough, Cleveland, TS90 8JE, UK