Metal-centered star block copolymers: Amphiphilic iron tris(bipyridine)-centered polyoxazolines and their chemical fragmentation to bipyridine-centered BAB triblock copolymers

Amphiphilic metal-centered six-arm star block copolymers were prepared by t he sequential addition of two different oxazoline monomers to the hexafunct ional metalloinitiator, [Fe(4,4'-bis(chloromethyl)-2,2'-bipyridine)](PF6)(2 ). Polymers of the form [Fe{bpy(PEOX-PUOX)(2)}(3)]X-2, [Fe{bpy(PUOX-PEOX)(2 )}(3)]X-2, and [Fe{bpy(PEOX- PPOX)(2)}(3)]X-2 (PEOX = poly(2-ethyl-2-oxazol ine); PUOX = poly(2-undecyl-2-oxazoline); PPOX = poly(2-phenyl-2-oxazoline) ; X = Cl, I, or PF6) were generated by reaction of the appropriate 2-R-2-ox azolines (R = Et, Ph, undecyl). In some cases sodium iodide was added to ac tivate the initiator, and dipropylamine was used for termination. Since the labile core polymers fragment during GPC analysis, the iron was removed by reaction with aqueous K2CO3 for MW characterization by multiangle laser li ght scattering in CHCl3 solution. The resulting bpy-centered telechelic BAB triblock copolymers, bpy(PEOX-PUOX)(2), bpy(PUOX-PEOX)(2), and bpy(PEOX-PP OX)(2), exhibit narrow molecular weight distributions (PDIs < 1.1) and mole cular weights close to targeted values. For polymers prepared from ethyl an d undecyl monomers, differential scanning calorimetry (DSC) measurements me re performed for Fe-centered star homopolymers and block copolymers as well as for the corresponding metal-free bpy-centered linear polymers. DSC runs of block copolymers show T-g and T-m values that correlate well with those observed for the respective ethyl- and undecyloxazoline homopolymers.