Thermally responsive polymeric micellar nanoparticles self-assembled fromcholesteryl end-capped random poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide):synthesis,temperature-sensitivity,and morphologies

摘要

Cholesteryl end-capped thermally responsive amphiphilic polymers with two different hydrophobic/hydrophilic chain-length ratios were synthesized form thehydroxyl-terminated random poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) and cholesteryl chloroformate.Thehydroxyl-terminated precursor polymers wiht narrow molecular weight distributions were synthesized by free-radical poymerization using 2-hydroxyethanethiol as a chain-transfer agent.The aqueous solutions of the cholesteryl end-capped copolymers exhibited reversible phase transitons at termperatures slightly above human body temperature,with the lower critical solution temperature values being 37.7 adn 38.2 deg C,respectively.The critical micelle concentration values of the two cholesteryl end-capped polymers were 9 and 25 mg/L,respectively.Polymeric micellar nanoparticles were prepared form the amphiphilic polymers using a dialysis method as well as a direct disslution mehtod.Transmission electron microscope studies showed that themicellar nanoparticles existed indifferent morphologies,including spherical,starlike,like,and cuboid shapes.Pyrene as a model hydrophobic compound counld be readily encapsulated in these polymeric nanoparticles,at loading levels of 1.0 and 0.8 mg/g for the two cholesteryl end-capped polymers,respectively.The temperature sensitivity and unusual morphlology of these novel polymeric nanoparticles would make an intresting drug delivery system.