Clathrates

Polymer clathrates are a fascinating class of crystalline host–guest compounds in which at least one component consists of a polymer species. In these compounds, the main component acts as the host, forming a cage-like structure around the molecules of the guest. Polymer host–guest compounds can be distinguished in “polymer clathrates,” “crystalline polymer-inclusion complexes,” “crystalline-polymer molecular complex,” or “polymer intercalates.” Polymer clathrates are crystalline solids in which low molecular mass guest species are hosted inside cages or cavities of molecular size, generated by polymer chains. Crystalline polymer-inclusion complexes are crystals comprising a polymer guest within a low molecular mass host whereas crystalline-polymer molecular complexes are the crystalline molecular complex between different polymers. Finally, polymer intercalates are sandwich-type inclusion compounds in which the guest molecules are entrapped in between layers of closely packed polymer chains. In the present article, the crystal structure and the main features of the most studied systems of each class, together with those of the nanoporous polymer crystals (ie, a polymer crystal presenting empty volume elements that can host low molar mass guest species) that can be obtained by removing the low molar mass guest species from some polymer host–guest compounds, are discussed. A review of the most promising applications in material science and technology of this class of host–guest compounds is also presented.