Perparations And Properties Of Star Amphiphilic Copolymers Initiated On The Surface Of Magnetic Nanoparticles

First，magnetic nanoparticles of Fe₃O₄were synthesized through co-precipitation, usingFe2+and Fe3+in alkaline conditions. The surface of nanoparticles was modified with KH-560,Fe₃O₄-（OH）_nwith much-OH on surface was synthesized. The structure and thermal stabilityof Fe₃O₄-（OH）_nwere proved by IR, XRD and TGA.Second, Sn（OCt）2as the catalyst, magnetic star-shaped polymers of Fe₃O₄-PLA weresynthesized by L,D-lactide ring-opening reaction initiated by-OH on the surface of magneticFe₃O₄-（OH）_n. The composition and structure of Fe₃O₄-PLA was characterized by IR, TGAand DSC. We can prove that the method is feasible. The molecular weight is proportional tothe ratio of lacide, and molecular weight distribution is narrow by the result of GPC, whichprovided that the reaction is part of Living Polymerization. And then, magnetic star-shapedamphiphilic copolymers of poly （L,D-lactide-b-monomethyl polyethylene glycol）（Fe₃O₄-PLA-MPEG） and poly （L,D-lactide-b-malic acid）（Fe₃O₄-PLA-PMA） weresynthesized by the esterification of PLA with MPEG and PMA, the Fe₃O₄-PLA as cores andMPEG or PMA as shell. The structure of the star block copolymers were studied by FT-IR,TGA, XRD. The results show that the method is feasible. Magnetic responsibility were testedby vibrating sample magnetometer（VSM）, the result show that remanence and coercivity ofFe₃O₄nanoparticales,Fe₃O₄-PLA20,Fe₃O₄-PLA20-MPEG are zero, a typical superparamagneticand the saturated magnetic instensity is decreased with the increase of polymer content.The nano micelle formed from the amphiphilic star copolymer. Fe₃O₄-PLA-MPEGmicelles and Fe₃O₄-PLA-PMA micelles were analysis through TEM, AFM and DLS. Theresults show that they have stable core-shell structure, and the diameter is100nm-300nm, thesize of nano-micelle increased with the increase of hydrophobic segment’s content. Thecytotoxity grade of the nano-micelles was determined by the RGR analysis of cytotoxicty andconditions of cell growth, the result show that micellar solution has no cytotoxicity to thehuman body.The control-release behavior of Fe₃O₄-PLA-MPEG micelles and Fe₃O₄-PLA-PMAmicelles as drug carrier were researched by choosing Ibuprofen as a model. Because of theself-catalytic action of-COOH, the drug’s cumulative release amount and shaking frequencyof Fe₃O₄-PLA-PMA micelles are higher than Fe₃O₄-PLA-MPEG micelles.