Synthesis of polypseudorotaxanes and polyrotaxanes with multiple α- and γ-cyclodextrins co-threaded over poly[(ethylene oxide)-ran-(propylene oxide)]

A series of novel polypseudorotaxanes, in which multiple α-cyclodextrin (α-CD) and γ-cyclodextrin (γ-CD) rings were randomly co-threaded over a poly[(ethylene oxide)-ran-(propylene oxide)] (P(EO-r-PO)) copolymer chain, were prepared by reacting the copolymer simultaneously with α-CD and γ-CD in aqueous solution. X-ray diffraction studies demonstrated that both α-CD and γ-CD molecules in the inclusion complexes (ICs) assumed a channel-type structure. 1H NMR spectra revealed that the compositions of the polypseudorotaxanes were strongly dependent on the molar ratio between α-CD and γ-CD in the feed. More interestingly, when we used the moderately bulk 2,4,6-trinitrophenyl (TNP) group, which is larger than the cavity of α-CD but smaller than that of γ-CD, to cap the two ends of the polypseudorotaxanes, we obtained polyrotaxanes with both α-CD and γ-CD randomly co-threaded over the P(EO-r-PO) chain, but the compositions of the polyrotaxanes were different from the corresponding polypseudorotaxanes because some γ-CD rings dethreaded since the cavity of γ-CD is larger than TNP. However, some γ-CD rings were sandwiched by α-CD rings, and these γ-CD and α-CD rings were both entrapped over the P(EO-r-PO) chain by the TNP ends. Our results revealed that how the compositions of the polypseudorotaxanes and the polyrotaxanes were different, and how their compositions were affected by the feed ratio between α-CD and γ-CD.