Novel polyrotaxanes comprising γ-cyclodextrins and Pluronic F127 end-capped with poly(N-isopropylacrylamide) showing solvent-responsive crystal structures

Herein novel polyrotaxanes (PRs) comprising γ-CDs and Pluronic F127 end-capped using poly(N-isopropylacrylamide) blocks were prepared via the atom transfer radical polymerization in aqueous medium at room temperature. The structure was characterized in detail by ¹H NMR, 2D NOESY NMR, FTIR, GPC, WXRD and DSC analyses. Solvent treatments were conducted on the resulting PRs via incubation in water and DMF, respectively. Interestingly the treatments resulted in two crystal structures: the DMF-incubated PRs appeared to give a novel crystal structure, while the water treated samples yielded a typical channel-type crystal structure. The entrapped γ-CDs were found to be aggregated mainly around the central PPO segment in the DMF-incubated PRs while some of γ-CDs were randomly dispersed on the PEO segments in the water treated samples. The two crystal structures exhibited a strong solvent dependence and were convertible through solvent incubation. The solubility and flexibility were greatly changed with the crystal structure conversion. Hence this provides an opportunity to alter the physical properties of PRs without any chemical modification of entrapped CDs. The aggregated/dispersed state of γ-CDs along the Pluronic F127 chain as a result of response to solvent treatment renders the PRs great potential to be used as smart materials.