Preparation of β-Cyclodextrin-based Polyrotaxane Block Copolymers and Their Solvent-responsibily

A kind of polyrotaxane (PR)-based block copolymers was synthesized via the atom transfer radical polymerization (ATRP) of hydroxylethylene acrylate (HEA) initiated by polypseudorotaxanes (PPRs) built from a distal 2-bromoisobutyryl end-capped polypropylene glycol-polyethylene glycol-polypropylene glycol (PPO-PEO-PPO) with a varying amount of-cyclodextrins (-CDs) in the presence of Cu(I)Cl and N, N, N', N', N-pentamethyldiethylenetriamine (PMDETA) as catalyst at 20 ℃ in aqueous solution. The supramolecular structure of the resulting copolymers was characterized by means of ¹H-NMR, GPC, FTIR, WXRD, DSC and TGA measurements. It was shown that the PHEA segments were attached to two ends of PPRs to give rise to the PR-based block copolymers featured by a characteristic channel-type crystal structure. The entrapped-CD number was increased with the feeding molar ratio, but only about one third added-CDs were retained on the polymer chain after the ATRP process. However, the polymerization degree of PHEA (DP) segments was well controllable with changing the molar feed ratio. In addition,-CDs were observed to favourably aggregate around the PPO segments and nearly cannot accommodate with the PEG segments after incubation in water and freeze-drying. However, according to TGA analyses, there were around one-third of the threaded-CDs enabling to slide to the PEO segments after being treated with DMF and anhydrous ether. The results suggested that these PR-based block copolymers exhibit the solvent-responsibility with the potential to be used as solid smart materials.