Novel triblock copolymers comprising a polyrotaxane middle block flanked by PNIPAAm blocks showing both thermo- and solvent-response

Two kinds of polyrotaxane (PR)-based triblock copolymers were synthesized via the in situ ATRP of NIPAAm initiated by self-assemblies of β- and γ-cyclodextrins (CDs) with a distal 2-bromopropionyl end-capped poly(propylene glycol) bis(2-aminoproyl ether) in water at 25 °C. The structure was characterized in detail by ¹H NMR, FTIR, WXRD and GPC techniques. The number of entrapped CDs was found to be tunable by varying the molar feed ratios. Their thermo-responsive and self-aggregation behavior in aqueous solution were demonstrated by turbidity measurements and TEM observations, respectively. Furthermore, solvent treatments were carried out on these copolymers. As evidenced by WXRD analyses, they also exhibit a solvent-response by aggregating or dispersing the CDs along the central PPG chain, in which both β- and γ-CDs entrapping copolymers give a typical channel-type crystal structure after water treatment, while the β-CD based ones produce a dispersed state structure and the γ-CD derived ones yield a novel mosaic crystal structure after DMF treatment with anhydrous ether. Here the key to the solvent-response is the coverage ratio rather than the type of CD. Given their thermo-responsive behavior in aqueous solution and their unique solvent-response, these PR-based triblock copolymers show great potential to be used as smart materials for controlled drug delivery systems, molecular detectors, and the like.