Synergistic effect of ultrasonication and phase transfer catalysts in radical polymerization of methyl methacrylate - A kinetic study

Sonochemical fabrication of inorganic nanoparticles for applications in catalysis

Catalysis covers almost all the chemical reactions or processes aiming for many applications. Sonochemistry has emerged in designing and developing the synthesis of nano-structured materials, and the latest progress mainly focuses on the synthetic strategies, product properties as well as catalytic applications. This current review simply presents the sonochemical effects under ultrasound irradiation, roughly describes the ultrasound-synthesized inorganic nano-materials, and highlights the sonochemistry applications in the inorganics-based catalysis processes including reduction, oxidation, degradation, polymerization, etc. Or all in all, the review hopes to provide an integrated understanding of sonochemistry, emphasize the great significance of ultrasound-assisted synthesis in structured materials as a unique strategy, and broaden the updated applications of ultrasound irradiation in the catalysis fields.

Synthesis and Characterization of a Core-Shell Copolymer with Different Glass Transition Temperatures

The aim of this study is to synthesize an organic core-shell co-polymer with a different glass transition temperature (Tg) between the core and the shell that can be used for several applications such as the selective debonding of coatings or the release of encapsulated materials. The co-polymer was synthesized using free radical polymerization and was characterized with respect to its morphology, composition and thermal behavior. The obtained results confirmed the successful synthesis of the co-polymer copolymer poly(methyl methacrylate)@poly(methacrylic acid-co-ethylene glycol dimethacrylate), PMMA@P(MAA-co-EGDMA), which can be used along with water-based solvents. Furthermore, the Tg of the polymer’s core PMMA was 104 °C, while the Tg of the shell P(MAA-co-EGDMA) was 228 °C, making it appropriate for a wide variety of applications. It is worth mentioning that by following this specific experimental procedure, methacrylic acid was copolymerized in water, as the shell of the copolymer, without forming a gel-like structure (hydrogel), as happens when a monomer is polymerized in aqueous media, such as in the case of super-absorbent polymers. Moreover, the addition and subsequent polymerization of the monomer methyl methacrylate (MAA) into the mixture of the already polymerized PMMA resulted in a material that was uniform in size, without any agglomerations or sediments.

Role of External Field in Polymerization: Mechanism and Kinetics

The past decades have witnessed an increasing interest in developing advanced polymerization techniques subjected to external fields. Various physical modulations, such as temperature, light, electricity, magnetic field, ultrasound, and microwave irradiation, are noninvasive means, having superb but distinct abilities to regulate polymerizations in terms of process intensification and spatial and temporal controls. Gas as an emerging regulator plays a distinctive role in controlling polymerization and resembles a physical regulator in some cases. This review provides a systematic overview of seven types of external-field-regulated polymerizations, ranging from chain-growth to step-growth polymerization. A detailed account of the relevant mechanism and kinetics is provided to better understand the role of each external field in polymerization. In addition, given the crucial role of modeling and simulation in mechanisms and kinetics investigation, an overview of model construction and typical numerical methods used in this field as well as highlights of the interaction between experiment and simulation toward kinetics in the existing systems are given. At the end, limitations and future perspectives for this field are critically discussed. This state-of-the-art research progress not only provides the fundamental principles underlying external-field-regulated polymerizations but also stimulates new development of advanced polymerization methods.

The influence of a hydrophobic carrier, reactant and product during H2O adsorption on Pd surface for the oxidative esterification of methacrolein to methyl methacrylate

Taking the one-step oxidative esterification of methacrolein (MAL) to methyl methacrylate (MMA) as a model reaction and because H2O that was generated easily formed a film of water on the catalyst surface, which restricted the diffusion of the reactants to the active sites, the effects of the hydrophobic carrier styrene-divinylbenzene (SDB) copolymer, the reactant CH3OH and the product MMA during the adsorption of H2O on a Pd surface were investigated. For a Pd/SDB catalyst, the interactions between the active component and the carrier were first calculated using Pd4 clusters. The results implied that Pd4 clusters were chemisorbed on the SDB carrier. By comparing the adsorption energy of H2O molecules on Pd4 clusters with or without SDB, it was found that the adsorption energy of the former was reduced by about 50%, indicating that the hydrophobic carrier SDB reduced the adsorption of H2O on Pd4 clusters. This was also confirmed by the results for the partial density of states, differences in charge density and comparative Mulliken charge analysis. The influences of the reactant CH3OH and the product MMA on the adsorption of H2O were investigated using the Pd(111) surface. The results of co-adsorption simulations showed that some of the electrons on CH3OH molecules were transferred to H2O molecules that strengthened the electronic interaction between H2O molecules and the Pd surface and led to a change in the adsorption of isolated H2O molecules from physisorption to chemisorption. However, the product MMA when chemisorbed on the Pd surface had little effect on the adsorption of H2O molecules on the Pd(111) surface.