pentacarbonyl dissociation products disturbs the growth of the polymeric radical.
Thus, the dissociation products serve as a quenching agent for the creation of the
polymer. The magnetic properties of the composite material are measured and
reveal a super-paramagnetic behavior.
Wizel later extended her study and included another metallic nanoparticle,
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 M w of the various polymers and composites as a function of the metal-to-monomer weight ratio was
measured and reported.
The general features observed are that the molecular weights of the CoPMA are
always larger than those of the corresponding FePMA. This comparison is made
for equal amounts of starting materials. The second observation is that the larger
the amount of the metal, the smaller the molecular weight of the PMA. The opposite is observed for the FePMMA, where a larger molecular weight is obtained
for higher amounts of iron clusters. This phenomenon is explained as due to the
presence of the oxidized iron, especially Fe
þ3 . These ions accelerate the polymerization of the methylmethacrylate [59], and a higher amount of metal will favor a
higher molecular weight polymer. The presence of oxidized iron is supported by
XPS and X-ray absorption near-edge spectroscopy (XANES) measurements. Nanosized amorphous iron was also imbedded in polystyrene [60] similarly.
A different approach was taken by Kumar and associates [61]. He also embedded
metals in polymers, but used as his precursor the polymer and not the monomer.
In his first study a composite material containing amorphous Cu nanoparticles
and nanocrystalline Cu 2 O embedded in polyaniline matrices was prepared by a
sonochemical method. These composite materials were obtained from the sonication of copper (II) acetate when aniline or 1% v/v aniline–water was used as the
solvent. Mechanisms for the formation of these products are proposed and discussed. The physical and thermal properties of the as-prepared composite materials are presented. A band gap of 2.61 eV is estimated from optical measurements
for the as-prepared Cu 2 O in polyaniline.
In a similar way, well-dispersed nickel nanoparticles in polystyrene were obtained by a sonochemical method [62]. The first step in this synthesis was the
preparation of nickel formate, which was prepared according to a previously described method. The preparation of the nickel–polystyrene composite was carried
out by the sonochemical method. Typically, 500 mg of nickel formate and 1 g of
polystyrene (Aldrich; M w ¼ 350,000) are dissolved in 100 mL of N,N-dimethylform6 Sonochemistry and Other Novel Methods Developed for the Synthesis of Nanoparticles
126
Thus, the dissociation products serve as a quenching agent for the creation of the
polymer. The magnetic properties of the composite material are measured and
reveal a super-paramagnetic behavior.
Wizel later extended her study and included another metallic nanoparticle,
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 M w of the various polymers and composites as a function of the metal-to-monomer weight ratio was
measured and reported.
The general features observed are that the molecular weights of the CoPMA are
always larger than those of the corresponding FePMA. This comparison is made
for equal amounts of starting materials. The second observation is that the larger
the amount of the metal, the smaller the molecular weight of the PMA. The opposite is observed for the FePMMA, where a larger molecular weight is obtained
for higher amounts of iron clusters. This phenomenon is explained as due to the
presence of the oxidized iron, especially Fe
þ3 . These ions accelerate the polymerization of the methylmethacrylate [59], and a higher amount of metal will favor a
higher molecular weight polymer. The presence of oxidized iron is supported by
XPS and X-ray absorption near-edge spectroscopy (XANES) measurements. Nanosized amorphous iron was also imbedded in polystyrene [60] similarly.
A different approach was taken by Kumar and associates [61]. He also embedded
metals in polymers, but used as his precursor the polymer and not the monomer.
In his first study a composite material containing amorphous Cu nanoparticles
and nanocrystalline Cu 2 O embedded in polyaniline matrices was prepared by a
sonochemical method. These composite materials were obtained from the sonication of copper (II) acetate when aniline or 1% v/v aniline–water was used as the
solvent. Mechanisms for the formation of these products are proposed and discussed. The physical and thermal properties of the as-prepared composite materials are presented. A band gap of 2.61 eV is estimated from optical measurements
for the as-prepared Cu 2 O in polyaniline.
In a similar way, well-dispersed nickel nanoparticles in polystyrene were obtained by a sonochemical method [62]. The first step in this synthesis was the
preparation of nickel formate, which was prepared according to a previously described method. The preparation of the nickel–polystyrene composite was carried
out by the sonochemical method. Typically, 500 mg of nickel formate and 1 g of
polystyrene (Aldrich; M w ¼ 350,000) are dissolved in 100 mL of N,N-dimethylform6 Sonochemistry and Other Novel Methods Developed for the Synthesis of Nanoparticles
126