A series of novel polypseudorotaxanes, in which multiple alpha-cyclodextrin (alpha-CD) and gamma-cyclodextrin (gamma-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 alpha-CD and gamma-CD in aqueous solution. X-ray diffraction studies demonstrated that both alpha-CD and gamma-CD molecules in the inclusion complexes (ICs) assumed a channel-type structure. H-1 NMR spectra revealed that the compositions of the polypseudorotaxanes were strongly dependent on the molar ratio between alpha-CD and gamma-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 alpha-CD but smaller than that of gamma-CD, to cap the two ends of the polypseudorotaxanes, we obtained polyrotaxanes with both alpha-CD and gamma-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 gamma-CD rings dethreaded since the cavity of gamma-CD is larger than TNP. However, some gamma-CD rings were sandwiched by alpha-CD rings, and these gamma-CD and alpha-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 alpha-CD and gamma-CD. (C) 2009 Elsevier Ltd. All rights reserved.