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

Abstract

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 β-cyclodextrins (β-CDs) in the presence of Cu(I)Cl/N,N,N′,N′′,N′′- pentamethyldiethylenetriamine at 25 °C in aqueous medium. The structure of the copolymers was characterized in detail by means of ¹H NMR, GPC, FTIR, and XRD analyses. The number of entrapped β-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 β-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.