Multifunctional metal oxocluster/polymer hybrid nanoparticles
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Abstract
The design and the applications of novel metal oxocluster/polymer hybrid nanoparticles is the main focus of the present PhD thesis. The targeted hybrid materials are characterized by the covalent incorporation of structurally well-defined and functionalized oxoclusters of group 4 metals (zirconium and titanium) in organic polymers (e.g., methyl methacrylate, N-isopropylacrylamide). Free radical copolymerization, initiated either by using thermo- or photoactivation, occurs in the confined space of miniemulsion droplets, providing a degree of control of size and size distribution of the resulting hybrid particles. Because of the nanometric dimensions of the synthesized hybrid systems, higher surface area, an enhanced dispersibility, and processability are achieved. The formation of a strong chemical bond between the organic and the inorganic counterparts has the advantage of protecting the guest species (oxoclusters), increasing its stability towards hydrolysis, and providing a homogeneous distribution in the polymer particles. Moreover, because of the functionalization with a high number (6–24) of polymerizable bonds, metal oxoclusters act as cross-linking units for the resulting hybrid polymer matrix. The advantages of using inorganic-based cross-linkers over the “traditional” organic ones are: (i) the enhancement of thermal and mechanical properties of polymers by the inorganic component; (ii) the introduction of specific functional properties (e.g., catalytic properties of Zr4O2(OMc)12); and (iii) a higher cross-linking efficiency due to their multiple docking points. Linear polymers are turned into cross-linked polymers, thus being able to swell in appropriate solvents. The consequent swelling of the resulting hybrid polymer matrix is exploited for applications ranging from the regulation of the catalytic activity to the thermo-responsive fluorescence of encapsulated dyes. The use of different surfactants shows major differences on morphology, cross-linking efficacy, and catalytic performances of the nanoparticles. The choice of the atomic ratio between the oxocluster and the monomer is crucial for tuning structural and functional properties according to the final applications of the material. The synergic outcome, given by the embedding of an inorganic metal oxocluster into a polymer matrix, gives enhanced functionality to the resulting materials, when compared to the individual starting counterparts.