As a kind of novel material, nanotubes with special one-dimensional hollow structure have attracted more and more attention and investigation. Compared with widely studied carbon nanotubes or small amphiphilic molecular nanotubes, block copolymer nanotubes show advantages in dimension scales, functionalization of both inner and outer spaces and structure stability. Recent progress in preparation of nanotubular aggregates via direct self-assembly of block copolymer in selective solvent is reviewed in this paper. According to properties of blocks, block copolymers that can form nanotubes are divided into three categories, including coil-coil block copolymers, rod-coil block copolymers, and pseudo-block copolymers with specific structures. For each category, the preparation procedures, structure characterizations and formation conditions of the nanotubes are introduced. Moreover, mechanisms and regularities of such hollow one-dimensional structure formation are discussed as well. It is proposed that nanotube formation required highly ordered molecular packing and anisotropic intermolecular interactions; thus rod-coil block copolymers are more likely to form polymer nanotube than coil-coil blockcopolymers. Based on these studies, potential applications and possible trends for future research are briefly described finally.

Contents
1 Introduction
2 Preparation methods and structure characterizations of self-assembled nanotubes
2.1 Direct dissolution
2.2 Selective solvent addition
2.3 Film rehydration
2.4 Solution temperature control
2.5 Characterization of nanotubular structures
3 Classification of nanotube-forming block copolymers
3.1 Coil-coil block copolymers
3.2 Rod-coil block copolymers
3.3 Pseudo-block copolymers with specific structures
4 Conclusions and outlook