Phase Behavior of Alkyne-Functionalized Styrenic Block Copolymer/Cobalt Carbonyl Adducts and in Situ Formation of Magnetic Nanoparticles by Thermolysis

A series of polystyrene-block-poly(4-(phenylethynyl)styrene) (PS-b-PPES) diblock copolymers with a range of compositions were prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization. Block copolymer/cobalt carbonyl adducts (PS_x-PPES_y[Co₂(CO)₆]_n) were subsequently prepared by reaction of Co₂(CO)₈ with the alkyne groups of the PPES block. Phase behavior of the block copolymer/cobalt carbonyl adducts (PS_x-PPES_y[Co₂(CO)₆]_n, 8% ≤ wt % PS ≤ 68%) was studied by small-angle X-ray scattering and transmission electron microscopy (TEM). As the composition of PS_x-PPES_y[Co₂(CO)₆]_n copolymers was shifted from PS as the majority block to PPES_y[Co₂(CO)₆]_n as the majority block, the morphology was observed to shift from lamellar with larger PS domains to cylindrical with PS as the minority component and then to spherical with PS as the minority component. These observations have been used to map out a partial phase diagram for PS_x-PPES_y[Co₂(CO)₆]_n diblock copolymers. Heating of PS_x-PPES_y[Co₂(CO)₆]_n samples at relatively low temperatures (120 °C) results in the formation of nanoparticles containing crystalline cobalt and cobalt oxide domains within the PPES_y[Co₂(CO)₆]_n regions as characterized by TEM, X-ray diffraction (XRD), and X-ray scattering.