Polyrotaxane structure stability

The stability of the polyrotaxane structure can result from both the intermolecular interaction (of the type of hydrogen, donor-acceptor, and Van der Waals bonds) between the macrocydes and polymer and a conformation change due to mobility... 

Recently, we have also prepared nanosized polymersomes through self-assembly of star-shaped PEG-b-PLLA block copolymers (eight-arm PEG-b-PLLA) using a film hydration technique [233]. The polymersomes can encapsulate FITC-labeled Dex, as model of a water-soluble macromolecular (bug, into the hydrophilic interior space. The eight-arm PEG-b-PLLA polymersomes showed relatively high stability compared to that of polymersomes of linear PEG-b-PLLA copolymers with the equal volume fraction. Furthermore, we have developed a novel type of polymersome of amphiphilic polyrotaxane (PRX) composed of PLLA-b-PEG-b-PLLA triblock copolymer and a-cyclodextrin (a-CD) [234]. These polymersomes possess unique structures the surface is covered by PRX structures with multiple a-CDs threaded onto the PEG chain. Since the a-CDs are not covalently bound to the PEG chain, they can slide and rotate along the PEG chain, which forms the outer shell of the polymersomes [235,236]. Thus, the polymersomes could be a novel functional biomedical nanomaterial having a dynamic surface. 

On the other hand, the chenucal structure of the polymer chain penetrating into macrocydes is also sential for the formation of polyrotaxaiKs. If the size of a monomer unit exceecte the dze of the macrocycle interior, the formation of polyrotaxanes becomes impossible, and if the monomer unit size is much less than that of the interior, the stability of polyrotaxanes is poor. A prerequidte for obtaining a stable polyrotaxa-iK is the optimum ratio between the macrocyde interior size and the geometric... 

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