Preparation and Morphology Control of Block Copolymer/Metal Salt Hybrids via Solvent-Casting by Using a Solvent with Coordination Ability
journal contributionposted on 22.06.2010, 00:00 by Atsushi Noro, Yoshio Sageshima, Shigeo Arai, Yushu Matsushita
We report a systematic study on preparation and morphology control of macroscopically homogeneous hybrid films composed of a block copolymer and a metal salt, where one block interacts with a metal salt by metal-to-ligand coordination. Hybrids were prepared by blending a polystyrene-b-poly(4-vinylpyridine) (PS−P4VP, Mn=37K, ϕs=0.79) block copolymer and iron(III) chloride (FeCl3) with changing the mole fraction of FeCl3. To prevent the rapid cross-linking formation between P4VP and FeCl3, pyridine as a polar solvent with the coordination ability was used at the solvent-casting stage, which turned out to be effective to prepare macroscopically homogeneous films with a large amount of FeCl3. Transmission electron microscopy and small-angle X-ray scattering measurements were carried out to observe the morphology of thermally annealed samples at the nanoscopic scale. It was revealed that simple two-phase nanostructures were observed due to homogeneously mixing of FeCl3 into a P4VP phase up to 0.9 mol equiv of FeCl3 to pyridine units in P4VP. This indicates FeCl3 works as a filler in a P4VP phase just as small homopolymers: domain expansion and morphology transition were observed as the amount of added FeCl3 increases. However, overflow of FeCl3 was observed in the hybrid with an amount of 1.0 mol equiv of FeCl3. This is probably due to the saturation of incorporated FeCl3, indicating that morphology of the present system can be controlled by stoichiometric balance between 4-vinylpyridine units and FeCl3.