As an important research field of chiral polymers, chiral polyimides have attracted much attention from polymer community for their potential applications in molecular recognition, enantioselective separation, and asymmetric catalysis. This paper reviews the advance on chiral polyimides in past 20 years. Optically active polyimides are divided into three types according to the position and type of the chiral groups, which are the chirality on side chain, the central chirality on main chain, and the axial chirality on main chain. Each type of chiral polyimides is summarized in details with representative structure, synthesis, properties, the formation of secondary structure, and applications related to the chiro-optical activity of the polymers. Chiral polyimides prepared by post-derivation on the side chains of the achiral backbones supplied chiral alignment surfaces to induce the alignment of liquid crystals in forms with enantiomeric excess or with specific directions. Chiral polyimides with chiral groups in main chains are prepared from chiral dianhydrides or chiral diamines that are usually derived from amino acids, trans-1,2-cyclohexanediamine, spirocyclic compounds, and binaphthyl derivatives. Studies have shown that both central chiral monomers and axial chiral monomers induced the formation of secondary structure by the chiral polyimides. Optical rotation and circular dichroism (CD) are still the few tools for the investigations to the chiral secondary structure of chiral polyimides. At the end of the review, we present the challenges and the future directions of the developments on chiral polyimides. Despite quick developments in recent years, preparations, structures, and applications of chiral polyimides, as well as scrutiny on the chiral secondary structure with rationale models and methodologies, are worthy of paying much attention.

Contents
1 Introduction
2 Polyimides with chiral groups in side chains
3 Polyimides with central chirality in main chain
3.1 Chiral polyimides from amino acids
3.2 Chiral polyimides from trans-1, 2-cyclohexanediamine
3.3 Chiral polyimides from chiral dianhydride
4 Polyimides with axial chirality in main chain
4.1 Chiral polyimides from binaphthyl compounds
4.2 Chiral polyimides from spirobifluorene
5 Conclusion and outlook