Synthesis of (S)-BINOL-Terminated Poly(ethylene glycol) Polyrotaxane Including α-Cyclodextrin

a,omega-Dimesyl-terminated poly(ethylene glycol) (PEG-Ms2) and alpha,omega-ditosyl-terminated PEG (PEG-Ts2) were prepared from PEG (PEG(1000); M-n = 1000 and PEG(4000); M-n = 4000) and methanesulfonyl chloride or p-toluenesulfonyl chloride. alpha,omega-Ditosyl-terminated PEG4000 pseudorotaxane (PEG(4000)-TS2-pseudorotaxa-alpha-cyclodextrin (alpha-CD) was prepared from PEG(4000)-TS2 and alpha-CD in H2O. (S)-(-)-1,1'-Bi (2-naphthol) ((S)-BINOL) was added to the pseudorotaxanes in the presence of sodium hydride to give PEG-rotaxa-alpha-CDs end-capping (S)-BINOL (PEG-BINOL2-rotava-alpha-CD). The purified PEG(4000)-BINOL2-rotaxa-alpha-CD was isolated in 38% yield. For a PEG4000-TS2, the average number of alpha-CD's per chain is 29, which corresponds to 64% coverage. After end-capping reaction, the average number of alpha-CD's per chain is 14, which corresponds to 31% coverage. The threading level in the polyrotaxane is limited by the coverage of the poly-pseudorotaxane and by the competition between the end blocking reaction and dethreading. In DMF a rapid dethreading occurs.