Effect of Chemical Oxidation on the Thermodynamics of
Organometallic Block Copolymers

H. Eitouni

University of California, Berkeley

Diblock copolymers, because of their ability to self assemble into interesting and useful morphologies, have received much attention for use as lithographic materials, photonic crystals, filters, and many other applications. Paramount to controlling the structures and properties of diblock copolymers is an understanding of the factors that describe the interactions of the blocks. The thermodynamic interactions in anionically synthesized poly(styrene-block-ferrocenyldimethylsilane) (SF) copolymers were examined using birefringence, small angle X-ray scattering (SAXS), and small angle neutron scattering (SANS). The location of the order-disorder transition determined from birefringence measurements is in agreement with SAXS results measured on the same material. The temperature-dependence of the Flory-Huggins parameter, c of SF copolymers, determined by SAXS, is similar in magnitude to that between polystyrene and polyisoprene chains. We find that c is independent of block copolymer composition (within experimental error) as predicted by the Flory-Huggins theory. We also demonstrate that the neutron scattering length densities of styrene and ferrocenyldimethylsilane moieties are identical due to a surprising cancellation of factors related to density and atomic composition. The thermodynamic interactions in SF copolymers were systematically adjusted by oxidation of the ferrocene moiety with silver nitrate and examined using small angle X-ray scattering. The polymer retained a microphase separated ordered structure upon oxidation and showed a systematic change in the location of the order-disorder transition as a function of ferrocenium nitrate content. By controlling the redox properties of the ferrocene moiety in the backbone of the polymer, we will provide a novel method of control over microstructure and hence bulk properties.

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