Sonochemical Synthesis of a Polymer-Metal Composite

The use of ultrasound radiation for polymerizing various monomers was reviewed in [la]. Here we will discuss how ultrasound waves have been used successfully been to embed ultrafine metallic partides in a polymeric matrix. The first report was by Wizel and coworkers [57]. They used ultrasound radiation to prepare a composite material made of polymethylacrylate and amorphous iron nanopartides. 

Two preparation methods are described [57], in which the monomer, methylacrylate, is the starting material. 

In the first, Fe(CO)5 and distilled methylacrylate were sonicated as a mixture of neat liquids. During the sonication, the glass cell was wrapped in a dark cover to avoid photopolymerization. After 30 min of irradiation (avoiding degradation) at a dry ice-acetone temperature, the solution was treated with cold methanol, precipitating the polymeric product. In the second method, amorphous iron nanoparticles were prepared following Suslick s recipe [6]. The dried amorphous iron powder was introduced into the sonication cell without exposure to air and mixed with a solution of the methylacrylate monomer in N,N -dimethylformamide (DMF). The concentration of the methylacrylate solution in DMF was 5.5 M. 35 ml of this solution was mixed with various amounts of amorphous iron nanoparticles. The amounts of the iron powder were changed from 50 mg to 200 mg. The chemical analysis of polymers prepared by the two methods is presented in Table 6.1. 

When the molecular weight (Mw) values of the polymeric composite material are compared with those of the polymeric product obtained from the irradiation of the monomer alone at the same irradiation time and concentration of the monomer, a 20% reduction is detected. This can be ascribed to the influence of the iron on the growth of the polymer. This would mean that the recombination of the iron 

Wizel later extended her study and included another metallic nanopartide, cobalt, and an additional polymer, poly(methylmethacrylate), in her metal-polymer composite research [58]. A significant difference in the solubility of the iron-poly(methylacrylate) and cobalt-poly(methylacrylate) in various solvents was observed. While the iron-poly(methylacrylate) composite (FePMA) and iron-poly(methylmethacrylate) composite (FePMMA) dissolved in chloroform, acetone, and toluene at room temperature, the corresponding cobalt-poly(methylacrylate) composite (CoPMA) was insoluble in these solvents at room temperature. At elevated temperatures (45 °C), dissolution of CoPMA in these solvents was observed. This difference is accounted for by the stronger interaction existing between the cobalt and the surrounding polymer. For iron-poly(methylacrylate) this interaction is weakened due to the formation of an iron complex. The Mw of the various polymers and composites as a function of the metal-to-monomer weight ratio was measured and reported. 

---