End-capping double-chain stranded polypseudorotaxanes using lengthily tunable poly(2-hydroxyethylmethacrylate) blocks via atom transfer radical polymerization

Owing to a large cavity, γ-cyclodextrin (γ-CD) can form double-chain inclusion complexes with linear polymeric chains such as poly(ethylene glycol) (PEG) and poly(ε-caprolactone). However, to date few reports have focused on the end-capping of these kinds of fascinating supramolecular entities. In this study, atomtransfer radical polymerization (ATRP) was employed toprepare double-chain stranded polyrotaxanes (PRs) with lengthily tunable poly(2-hydroxyethyl methacrylate) (PHEMA) blocks as bulky end-cappers. ATRP of HEMAwas carried out using pseudopolyrotaxanes (PPRs) self-assembled from a distal 2-bromoisobutyryl end-capped PEG (BriB-PEG-iBBr) with varying amounts of γ -CDs as macroinitiator in the presence of Cu(I)Br/N,N,N',N",N"-pentamethyldiethylenetriamine in aqueous solution at room temperature. The resulting PRswere demonstrated by the unique H-like double-chain stranded supramolecular architecture end-capped with lengthily tunable PHEMA blocks. When the feed molar ratio of γ-CD: BriB-PEG-iBBr varied from 5 to 60 in PPRs, the feed molar ratio in PRs was found to remain at around 20 with a higher yield. ATRP was successfully applied to prepare double-chain stranded PRs end-capped with lengthily tunable PHEMA blocks. This provides a protocol for the preparation of novel H-like PR-based block copolymers.