Iron cluster and microstructure formation in metal-centered star block copolymers: Amphiphilic iron tris(bipyridine)-centered polyoxazolines

The microstructure of a metal-centered six-arm star block copolymer, amphiphilic iron tris(bipyridine)-centered poly(2-ethyl-2-oxazoline)-b-poly(2-undecyl-2-oxazoline), [Fe{bpy(PEOX-PUOX)(2)}(3)](2+), was investigated with small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), transmission electron microscopy (TEM), and atomic force microscopy (AFM). Cylindrical PEOX microdomains were observed in a matrix of PUOX. A similar cylindrical morphology was noted for bpy(PEOX-PUOX)(2), the metal-free macroligand subunit of which the Fe star is comprised. Thin films simple-cast from chloroform solution onto carbon substrates annealed at 160 degreesC for approximate to2 days revealed in both TEM and AFM the formation of nanoscale iron clusters (approximate to 20-40-nm diameter) distributed randomly across the surface of the film. No clusters were evident in as-cast films subjected to TEM analysis without the annealing step, suggesting the importance of thermal treatment for nanocrystal formation. For bulk films, larger micrometer-scale (1-2 mum) iron aggregates formed and segregated to the surface of the film after thermal treatment for l week. A liquid crystallike mesophase due to undecyl alkyl side chain ordering was evidenced by SAXS and WAXS in the bulk sample.