Synthesis of parallel double stranded polyrotaxanes comprising γ-CDs and distal azido-terminated PEG via Click reaction using propargylamine monosubstituted β-CDs as end stoppers

When γ-CDs were self-assembled with a distal 2-chloropropionyl terminated poly (ethylene glycol) (PEG-2Cl) in aqueous solution, two distinct polypseudorotaxanes (PPRs), a single stranded one and a double stranded one were identified from the upper clear solution and the lower precipitates, respectively. Moreover, if the chlorine groups in PEG-2Cl were converted into the azido groups to give a bifunctional azido terminated PEG (PEG-2N₃) and then subjected to the inclusion complexation with γ-CDs, two similar double stranded PPRs were lyophilized from the upper and lower layer products. To probe whether the parallel or bent double stranded PPRs were created from the self-assembly of γ-CDs with PEG-2N₃, the in situ copper-catalyzed azide/alkyne cycloaddition (CuAAC) was conducted to transform the resulting PPRs into the PRs using propargylamine monosubstituted β-CDs (PA-β-CDs) as bulky stoppers. After thorough purification, both the upper and lower layer products lyophilized therefrom were revealed the same parallel double stranded PRs by spectral and thermal analyses.