6 research outputs found
Exploration of Iron and Cobalt Core-Shell Nanoparticles via Thermal and Microwave Polyol Synthesis
Thermal and microwave polyol methods were investigated in the synthesis of various iron and cobalt core-shell nanoparticles. The reaction involved 1 mmol of an Fe+2 or Co+2 salt, bis-acetylacetanato [(Acac)2] iron (II), cobalt (Acac)2 or iron (II) acetate along with 1 mmol of a surfactant capping agent. The salt was reduced with 2 mmol of a 1,2 diol. When 1,2-hexadecanediol solid was used as a reducing agent, it was dissolved along with the metal salt and capping agent in octyl ether. When 1,2-hexanediol liquid was used as the reducing agent, it was also the solvent, and octyl ether was eliminated. For reactions in which octyl ether acted as the solvent, the capped nanoparticles were precipitated using ethanol. For reactions in which the solvent also acted as the reducing agent, the particles precipitated after nucleation and supersaturation of the polyol solvent/reducing agent
Mechanically Induced Scission and Subsequent Thermal Remending of Perfluorocyclobutane Polymers
Perfluorocyclobutane (PFCB) polymer solutions were subjected to pulsed ultrasound, leading to mechanically induced chain scission and molecular weight degradation. <sup>19</sup>F NMR revealed that the new, mechanically generated end groups are trifluorovinyl ethers formed by cycloreversion of the PFCB groups, a process that differs from thermal degradation pathways. One consequence of the mechanochemical process is that the trifluorovinyl ether end groups can be remended simply by subjecting the polymer solution to the original polymerization conditions, that is, heating to >150 °C. Stereochemical changes in the PFCBs, in combination with radical trapping experiments, indicate that PFCB scission proceeds via a stepwise mechanism with a 1,4-diradical intermediate, offering a potential mechanism for localized functionalization and cross-linking in regions of high stress
Tension Trapping of Carbonyl Ylides Facilitated by a Change in Polymer Backbone
Epoxidized polybutadiene and epoxidized polynorbornene
were subjected
to pulsed ultrasound in the presence of small molecules capable of
being trapped by carbonyl ylides. When epoxidized polybutadiene was
sonicated, there was no observable small molecule addition to the
polymer. Concurrently, no appreciable isomerization (<i>cis</i> to <i>trans</i> epoxide) was observed, indicating that
the epoxide rings along the backbone are not mechanically active under
the experimental conditions employed. In contrast, when epoxidized
polynorbornene was subjected to the same conditions, both addition
of ylide trapping reagents and net isomerization of <i>cis</i> to <i>trans</i> epoxide were observed. The results demonstrate
the mechanical activity of epoxides, show that mechanophore activity
is determined not only by the functional group but also the polymer
backbone in which it is embedded, and facilitate a characterization
of the reactivity of the ring-opened dialkyl epoxide