Tetragonally Packed Inverted Cylindrical Microdomains from Binary Block Copolymer Blends with Enhanced Hydrogen Bonding

Hexagonally packed (HEX) cylindrical microdomains can be obtained through the self-assembly of block copolymers (BCPs) with a moderately asymmetric volume fraction of one block (f), resulting in the formation of minor cylinders. However, for next-generation lithography and high-density memory devices, it is desirable to obtain densely and tetragonally packed inverted cylindrical microdomains, which are composed of the major block in the minor matrix. The inverted cylinders differ from conventional HEX cylinders, which consist of the minor block in the matrix of the major block. In this study, we achieved this objective by utilizing a binary blend of a polystyrene-b-poly(4-vinylpyridine) copolymer (S4VP) and polystyrene-b-poly(4-hydroxystyrene) copolymer (SHS), where the P4VP block exhibited a strong hydrogen bonding interaction with the PHS block. By carefully controlling the molecular weight ratio of S4VP and SHS as well as the blend composition, we successfully observed tetragonally packed inverted PS cylinders with a square cross-section at a volume fraction of PS of 0.69.