Dual thermo-responsive polyrotaxane-based triblock copolymers synthesized via ATRP of N-isopropylacrylamide initiated with self-assemblies of Br end-capped Pluronic F127 with beta-cyclodextrins

Dual thermo-responsive polyrotaxane (PR)-based triblock copolymers were synthesized via the atom transfer radical polymerization (ATRP) of N-isopropylacrylamide (NIPAAm) initiated with self-assemblies made from a distal 2-bromopropionyl end-capped Pluronic F127 with a varying amount of beta-cyclodextrins (beta-CDs) in the presence of Cu(I)Cl/N, N, N', N '', N ''-pentamethyldiethylenetriamine at 25 degrees C in aqueous medium. The structure of the copolymers was characterized in detail by means of H-1 NMR, GPC, FTIR, and XRD analyses. The number of entrapped beta-CDs and the degree of polymerization (DP) of attached NIPAAm oligomers appeared to be tunable. A two-step thermo-responsive transition arisen from a combination of a polypseudorotaxane middle block and poly(N-isopropylacrylamide) (PNIPAAm) flanking blocks was demonstrated by turbidity measurements. The number of entrapped beta-CDs and DP of PNIPAAm are crucial for this dual thermo-responsive transition. The aggregates of one selected PR-based triblock copolymer were evidenced by TEM observations exhibiting a morphology change from core-shell particles to worm-like aggregates with increasing temperature. Furthermore, this sample can encapsulate and separate a negatively charged dye Coomassie Brilliant Blue G-250 from the aqueous solution when heated up to its deposition temperature.