Metal-Centered Star Block Copolymers: Amphiphilic Iron Tris(bipyridine)-Centered Polyoxazolines and Their Chemical Fragmentation to Bipyridine-Centered BAB Triblock Copolymers

Abstract

Amphiphilic metal-centered six-arm star block copolymers were prepared by the sequential addition of two different oxazoline monomers to the hexafunctional metalloinitiator, [Fe(4,4‘-bis(chloromethyl)-2,2‘-bipyridine)](PF6)2. Polymers of the form [Fe{bpy(PEOX−PUOX)2}3]X2, [Fe{bpy(PUOX−PEOX)2}3]X2, and [Fe{bpy(PEOX−PPOX)2}3]X2 (PEOX = poly(2-ethyl-2-oxazoline); 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-oxazolines (R = Et, Ph, undecyl). In some cases sodium iodide was added to activate 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 light scattering in CHCl3 solution. The resulting bpy-centered telechelic BAB triblock copolymers, bpy(PEOX−PUOX)2, bpy(PUOX−PEOX)2, and bpy(PEOX−PPOX)2, exhibit narrow molecular weight distributions (PDIs < 1.1) and molecular weights close to targeted values. For polymers prepared from ethyl and undecyl monomers, differential scanning calorimetry (DSC) measurements were 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 Tg and Tm values that correlate well with those observed for the respective ethyl- and undecyloxazoline homopolymers.