Synthesis,Characterization,and pH-Triggered Dethreading of alpha-Cyclodextrin-Poly(ethylene glycol) Polyrotaxanes Bearing Cleavable Endcaps

摘要

The synthesis,characterization,and degradation kinetics of three alpha-cyclodextrin (alpha-CD)-poly(ethylene glycol) (PEG) polyrotaxanes with endcaps that were installed using Cu(I)-catalyzed Huisgen cyclization is reported.PEG 1500,azidated with azidoacetic acid,was threaded with alpha-CD to form a pseudopolyrotaxane that was then capped in up to 82% yield with three different substituents to provide polyrotaxanes that were either acid-,base-,or fluoride-sensitive.NMR,GPC,XRD,and ARM methods were used to characterize the polyrotaxanes.Dethreading rates upon exposure to mild deprotection conditions were monitored by turbidity analysis.The vinyl ether-endcapped polyrotaxane is stable at pH 7 for 16 h but is solubilized at approximately 0.0211 min~(-1) at pH 4.The ester-endcapped polyrotaxane is solubilized at 0.0122 min~(-1) at pH 12.1.Our results show that pH-triggerable polyrotaxanes can be readily and efficiently prepared from pseudopolyrotaxanes in high yield by Huisgen cyclization of azido-and alkynyl-modified precursors in the presence of Cu(I).