Zirconocene Dichloride: An Efficient Cleavable Photoinitiator Allowing the in Situ Production of Zr-Based Nanoparticles Under Air

Cp₂ZrCl₂ is presented as both an effective photoinitiator and additive for radical photopolymerization reactions in aerated conditions. This compound is characterized by remarkable properties: (i) an efficiency higher than that of a reference Type I photoinitiator (2,2-dimethoxy-2-phenylacetophenone, DMPA), (ii) an excellent ability, when added to DMPA, to overcome the oxygen inhibition of the polymerization, and (iii) a never reported in situ photoinduced and oxygen-mediated formation of zirconium-based nanoparticles (diameter ranging from 50 to 70 nm). The photochemical properties of Cp₂ZrCl₂ are investigated by steady state photolysis and electron spin resonance (ESR) experiments. The high reactivity of this compound is ascribed to a bimolecular homolytic substitution S_H2 (clearly characterized by molecular orbital calculations) which converts the peroxyls into new polymerization-initiating radicals and oxygenated Zr-based nanoparticles

Design of Waterborne Nanoceria/Polymer Nanocomposite UV-Absorbing Coatings: Pickering versus Blended Particles

Nanoparticles of cerium dioxide (or nanoceria) are of interest because of their oxygen buffering, photocatalytic ability, and high UV absorption. For applications, the nanoceria can be incorporated into a polymer binder, but questions remain about the link between the nanoparticle distribution and the resulting nanocomposite properties. Here, the thermal, mechanical, and optical properties of polymer/ceria nanocomposites are correlated with their nanostructures. Specifically, nanocomposites made from waterborne Pickering particles with nanoceria shells are compared to nanocomposites made from the blending of equivalent surfactant-free copolymer particles with nanoceria. Two types of nanoceria (protonated or citric acid-coated) are compared in the Pickering particles. A higher surface coverage is obtained with the protonated ceria, which results in a distinct cellular structure with nanoceria walls within the nanocomposite. In the blend of particles, a strong attraction between the protonated nanoceria and the acrylic acid groups of the copolymer likewise leads to a cellular structure. This structure offers transparency in the visible region combined with strong UV absorption, which is desired for UV-blocking coating applications. Not having an attraction to the polymer, the citric acid-coated nanoceria forms agglomerates that lead to undesirable light scattering in the nanocomposite and yellowing. This latter type of nanocomposite coating is less effective in protecting substrates from UV damage but provides a better barrier to water. This work shows how nanoparticle chemical functionalization can be used to manipulate the structure and to tailor the properties of UV-absorbing barrier coatings

Smoothing and Cicatrization of Isotactic Polypropylene/Fe₃O₄ Nanocomposites via Magnetic Hyperthermia

We prepare industrially relevant magnetoresponsive thermoplastic nanocomposites capable of being cicatrized and smoothed after additive manufacturing through the application of an oscillatory magnetic field (OMF). The materials are made of an isotactic polypropylene (iPP) matrix filled with magnetite nanoparticles (NPs; 2–22 wt %, 75 nm in diameter) synthesized from steel waste, providing them with a limited ecological impact on top of their ability to be repaired. NPs are found to have no significant impact on the thermal properties of iPP, which allows one to compare directly the magnetothermal effects measured on the different nanocomposites. Beyond the primary temperature increase generated by magnetic hysteresis loss, we show that the OMF irradiation triggers a second heating mechanism from the iPP melting. This phenomenon, which was assigned to NP magnetization and subsequent rotation causing high-frequency mechanical friction, is investigated here in a systematic way. Our results indicate that while the specific power generated by NP friction is (expectedly) proportional to the irradiation time, it is independent of the NP content as long as the temperature is well above the polymer melting point. These observations therefore suggest that the (local) filler–polymer interfacial rheology dictates the amount of heat generated through friction. From an application point of view, 7 wt % of the NPs is found to be enough to induce iPP melting from the magnetothermal effect, which enables the postprocessing of a hot-pressed and 3D-printed specimen through “cicatrization” and “smoothing” experiments. In the former case, rewelding a sample cut into two pieces is found to provide a Young modulus and a yield point similar to those in native hot-pressed samples (exhibiting, however, a lower strain at failure). In the latter case and beyond the improved specimen appearance, smoothing is found to double both the stress and strain at failure of large 3D-printed samples that present, nevertheless, significantly lower properties than those of their hot-pressed counterparts