비대칭 믹토암 스타 블록공중합체의 합성 및 상거동 분석

Abstract

Block Copolymers (BCPs) self-assemble into various nanostructures like spheres, cylinders, gyroids, and lamellae, depending on Flory-Huggins segmental interaction parameter (χ), degree of polymerization (N), and volume fraction of one block (fA). BCPs have been received great attention for their applicability to various fields like next-generation lithography and functional membranes but have a limitation that those microdomains are strongly restricted by the volume fraction of each block. Many studies have been done to shift the phase boundaries to form nanostructures unrestricted by volume fractions. Above all, BCPs with complex architecture such as miktoarm star copolymers are regarded as an efficient and effective method. Because they have an architecture where several linear chains are connected at a junction point, a large amount of entropy is generated from chain stretching or packing frustration. Therefore, they form the structures that have not been observed in linear BCPs. In this thesis, I synthesized polystyrene-[polystyrene-b-poly(2-vinylpyridine)]3 miktoarm star copolymer [PSL-(PSS-b-P2VP)3], where PSL and PSS are long and short PS chains, respectively, and investigated the phase behavior changed by the volume fraction of the PS block (fPS) and the chain asymmetry of the PS chain (τ = fPS,L / (fPS,L+fPS,S)). Inverted gyroids consisting of PS chains were observed at fPS = 0.64 and τ = 0.65, while asymmetric lamellae were formed at fPS = 0.81 and τ = 0.79. Because a long PS chain (PSL) and three short diblock chains (PSS-b-P2VP) are linked at a single junction point, a large configurational entropy penalty was expected, resulting in shifting the original phase boundaries observed for conventional AB linear block copolymer. Interestingly, the phase behavior was greatly affected by τ at a fixed fPS. At a fixed fPS (0.64), an inverted gyroid structure was observed at τ = 0.65, while a lamellar structure was formed at τ = 0.46. When the difference of molecular weight between PSL and PSS gets smaller, the interfacial curvature is not expected because all short diblock chains (PSS-b-P2VP) have no need to be arranged in the same direction anymore. The experimental results were consistent with the predictions based on self-consistent field theory (SCFT).