Temperature- and pH-responsive star amphiphilic block copolymer prepared by a combining strategy of ring-opening polymerization and reversible addition–fragmentation transfer polymerization

The star-shaped poly(ε-caprolactone)-b-poly(2-(dimethylamino)ethyl methacrylate) (HPs-Star-PCL-b-PDMAEMA) was synthesized by ring-opening polymerization and reversible addition–fragmentation chain transfer (RAFT) polymerization. Star-shaped polycaprolactones (HPs-Star-PCL) were synthesized by the bulk polymerization of ε-caprolactone (CL) with a hyperbranched polyester initiator and tin 2-ethylhexanoate as a catalyst. The number-average molecular weight of these polymers linearly increased with the increase of the molar ratio of CL to hyperbranched initiator. HPs-Star-PCL was converted into a HPs-star-PCL-RAFT by an esterification of HPs-Star-PCL and 4-cyanopentanoic acid dithiobenzoate. Star amphiphilic block copolymer HPs-Star-PCL-b-PDMAEMA was obtained via RAFT polymerization of 2-(dimethylamino)ethyl methacrylate (DMAEMA). The molecular weight distribution of HPs-Star-PCL-b-PDMAEMA was narrow. Furthermore, the micellar properties of HPs-Star-PCL-b-PDMAEMA in water were studied at various temperatures and pH values by means of dynamic light scattering (DLS). The results indicated that the star copolymers had the pH- and temperature-responsive properties. The release behaviors of model drug aspirin from the star polymer indicated that the rate of drug release could be effectively controlled by pH value and temperature.

Graphical abstract(HPs-Star-PCL-b-PDMAEMA) was synthesized by ring-opening polymerization and RAFT polymerization.Figure optionsDownload full-size imageDownload as PowerPoint slide