In situ polymerization and intercalation of polymers in layered double hydroxides

This chapter is intended to provide a state-of-the-art review of nanocomposite materials prepared by the assembly of layered double hydroxides (LDH) and polymers, including their synthesis and characterization, and point out their potential applications. Owing to the highly tunable LDH intralayer composition coupled with the wide possible choice of organic moiety, a large variety of LDH/polymer systems may be tailored. The incorporation of a polymer in the interlayer galleries may proceed via different pathways such as coprecipitation, exchange, surfactant-mediated incorporation, hydrothermal treatment, reconstruction, or restacking. Alternatively, various monomers can be intercalated and polymerized in situ within the interlamellar space of LDH. The spatial confinement is believed to increase the degree of polymerization, and, in addition, this type of in situ radical polymerization process makes it possible to tune the tacticity and the molecular weight of the resulting polymer by varying the layer-charge density and the particle size of the host structure, respectively. From several studies, it has been observed that the multi-component LDH/polymer systems are thermally more stable than the pristine inorganic compounds, leading to potential applications such as flame-retardant composites. Bio-related polymers and large bio-macromolecules such as poly(aspartate), alginate, and deoxyribonucleic acid (DNA), have also been incorporated within the galleries of LDH materials. One obvious interest for these bio-organoceramics is the drug release aspect, but acquiring a fundamental understanding of biomechanisms and other biomimetic phenomena is also important. The incorporation of polymers into hydrocalumite-like LDHs, known collectively as AFm phases in the literature of cement science, is of current concern in relation to the macro-defect-free (MDF) cement concept. Another incentive aspect is the use of LDH materials as nanolayers for fillers in polymeric matrices. Largely studied for the case of smectite-type materials, some recent results show similar trends for LDH nanofillers, i.e., an enhancement of the mechanical properties and increase in the polymer glass transition temperature.