8/22/2019 Conte Carotenuto Pepe Abstract

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NMR-ANALYSIS OF MECHANISM INVOLVED IN THE MERCAPTIDE

DECOMPOSITION IN POLYMER MEDIUM FOR NANOCOMPOSITE

PREPARATION

P. Conte, G. Carotenuto, G. Pepe

Dipartimento di Scienze del Suolo, della Pianta e dellAmbiente, Universit di Napoli Federico II, via

Universit 100, 80055, Portici (Na) Italy

Institute of Composite and Biomedical Materials, National Research Council, Piazzale Tecchio, 80,

80125, Napoli Italy

Dipartimento di Scienze Fisiche, Universit di Napoli Federico II, Piazzale Tecchio, 80 80125 Napoli

Italy

Polymer-embedded nano-sized metals are an important class of functional materials. In

fact, such systems can be applied in material chemistry for their unique optical,

magnetic, photonic, and high chemical stability properties. These materials behave justlike polymers and therefore they can be processed in a number of ways. Large-scale

production of these nanocomposite materials requires metal precursors that can be

mixed with polymer to generate clusters by thermal decomposition during the material

hot-processing stage. Some organic precursors have been investigated for this purpose,

however a general compound class is not available yet. It has been recently found that

homoleptic mercaptides (i.e., Mex(SR)y) can be conveniently used as metal or metal-

sulfide precursors, in the preparation of polymer-based nanocomposites. Mercaptides of

transition metals are covalent organic compounds, characterized by a high compatibility

with polymers, because of their hydrophobic nature, in addition to interesting

thermolytic characteristics. In particular, mercaptides are quite thermally stable at room-temperature and therefore they can be handled and stored without special care, but

quantitatively decompose at little higher temperatures (180-250C) to produce zero-

valence metal or metal sulfides, depending on the mercaptide nature. Here, the

mechanism involved in the preparation of silver/polystyrene nanocomposites has been

investigated by NMR. In particular, the mechanism for silver cluster formation should

involve the homolysis of Ag-S bonds, with formation of zero-valence silver atoms and

sulfur radicals, SR. When the polymer phase is saturated by silver atoms, clusters may

precipitate. Sulfur radicals removed hydrogen from the polymer matrix producing thiol

molecules, which partially evolved during the annealing treatment. Benzyl radicals

should be preferentially generated because of their high stabilization by resonance; then,these carbon radicals combined together, cross-linking the polystyrene chains.