Perforated lamellar (PL) microphase structure of block copolymers in the bulk is rarely observed. Herein, formation of the PL structure from simple block copolymer, poly(tert-butyl methacrylate)-block-polystyrene (PtBMA-b-PS) prepared by reversible additionefragmentation chain transfer (RAFT) mediated radical polymerization, is reported. The PL phase consists of alternating layers of PS and PtBMA microdomains, among which the PS layers contain ordered cylindrical domains of PtBMA. It is confirmed that the PL phase is located between the cylindrical phase and lamellar phase. In methanol, the microphaseseparated sample is readily split into individual core/shell nanosheets with perforated glassy PS core. The PtBMA domains are densely attached both as the shells along PS sheets and as passages with a hexagonal pattern. The passage has a diameter of ca. 12 nm and an average periodic distance of 31 nm. (C) 2016 Elsevier Ltd. All rights reserved.