Thermoresponsive poly(epsilon-caprolactone)-graft-poly(N-isopropylacrylamide) graft copolymers prepared by a combination of ring-opening polymerization and sequential azide-alkyne click chemistry

摘要

A straightforward strategy is described to synthesize poly(E-caprolactone)-graft-poly(N-isopropylacrylamide) (PCL-g-PNIPAAm) amphiphilic graft copolymers consisting of potentially biodegradable polyester backbones and thermoresponsive grafting chains. PCL with pendent chlorides was prepared by ring-opening polymerization, followed by conversion of the pendent chlorides to azides. Alkyne-terminated PNIPAAm was synthesized by atom transfer radial polymerization. Then, the alkyne end-functionalized PNIPAAm was grafted onto the PCL backbone by a copper-catalyzed azide-alkyne cycloaddition. PCL-g-PNIPAAm graft copolymers self-assembled into spherical micelles comprised of PCL cores and PNIPAAm coronas. The critical micelle concentrations of the graft copolymers were in the range 7.8-18.2mgL(-1), depending on copolymer composition. Mean hydrodynamic diameters of micelles were in the range 65-135nm, which increased as the length of grafting chains grew. PCL-g-PNIPAAm micelles were thermosensitive and aggregated upon heating. (c) 2014 Society of Chemical Industry