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Challenges and Perspectives in the Macromolecular Flatland.

Polymer chemistry has recently welcomed a new addition to its field: the planar macromolecules known as two-dimensional polymers (2DPs). These topologically planar and crystalline monolayer covalent sheets are reminiscent of molecular fishermen's nets and apart from being conceptually very interesting for the field of macro-molecular chemistry, they also show some potential applications as novel 2D materials. This article reviews how the field has developed five years after the first 2DP was synthesised in 2012. After a brief historical introduction, the main synthetic approaches will be discussed providing concrete examples of 2DPs and highlighting the challenges associated with the synthesis and especially structural characterisation of these fascinating macro-molecules. Finally an overview on their potential applications such as membranes for gas separation, rewritable molecular paper and miniaturisation of optical devices will be presented.