A one-pot "grafting-from" strategy is presented to prepare AB-and ABA-type bottlebrush block copolymers (BBCPs). Precursor block copolymers with pendant dithiocarbamate and hydroxyl groups were synthesized as the macroinitators. Polylactide (PLA) and poly(N-vinylpyrrolidone) (PVP) side chains were grafted by ring-opening polymerization (ROP) and reversible addition-fragmentation chain-transfer (RAFT) polymerization in one pot, respectively. Molecular weight control was achieved as evidenced by gel permeation chromatography (GPC) and H-1 nuclear magnetic resonance (H-1 NMR). The length of side chains in each block (DP from 8 to 113) could be facilely tuned by polymerization conditions such as the reaction time and the feed ratio of monomer to initiator, leading to various molecular morphologies observed by atomic force microscopy (AFM). This synthetic strategy is flexible and adaptable, allowing convenient access to customized macromolecular architecture. (C) 2018 Elsevier Ltd. All rights reserved.