Novel possibilities by cationic ring-opening polymerisation of cyclodextrin derivatives:: Preparation of a copolymer bearing block-like sequences of tri-O-methylglucosyl units

Equimolar mixtures of O-permethylated and O-perdeuteromethylated cyclodextrins were submitted to cationic ring-opening polymerisation (CROP) with Et3OPF6 or BF3.Et2O as initiator in dichloromethane, Reaction started after an incubation time and yielded a polymeric product, which was partially degraded again during competing chain transfer reaction. Average block length was determined by ESI-MS after partial methanolysis and was found to be close to the theoretical value of 14 for beta-cyclodextrin in the early stage of the reaction, but decreased to 2-5 during further chain transfer reactions accompanied by an equilibration of alpha- and beta-configurated glucosidic linkages to a ratio of 64:36. Molecular weight was estimated from end group analysis and GPC to reach about 29 000 as a maximum. From P-31 NMR spectra of the initiator it was obvious that PF6- is partly hydrolysed to PO2F22- under participation of the glass surface.