Polymer interleaved layered double hydroxide: A new emerging class of nanocomposites

The present paper describes the synthesis and characterization of nanocomposite materials built from the assembly of organic polymers and two-dimensional host materials, particularly reviewing those composed of layered double hydroxide (LDH) inorganic frameworks. When the meaning commonly adopted for nanocomposites is narrowed, the system is constituted of sheets lying on top of each other in which covalent forces maintain the chemical integrity and define an interlamellar gap filled up with the polymer guest. The situation is different from an inorganic filler dispersed into a polymeric matrix. The incorporation of polymer between the galleries proceeds via different pathways such as coprecipitation, exchange, in situ polymerization, surfactant-mediated incorporation, hydrothermal treatment, reconstruction, or restacking. The latter method, recently effective via the exfoliation of the LDH layers, appears to be more favorable, in terms of crystallinity, to capture monomer entities than the whole polymer. The nanocomposites are enlisted according to the preparation pathways. It is found that these multicomponent systems are thermally more stable than the pristine inorganic compounds, leading, for example, to potential applications in flame-retardant composites. A large variety of LDH/polymer systems may be tailored considering the highly tunable intralayer composition coupled to the choice of the organic moiety. The paper concludes with a brief discussion underlining the perspectives. Despite their appeal, the polymer/LDH class of nanocomposites has not yet been extensively studied for applications.