Precision Chemistry最新文献

Dual control of the molecular weight and tacticity in proton transfer anionic polymerization (PTAP) of methyl methacrylate (MMA) was investigated by using various ligands in the presence of a bulky potassium base catalyst and an organic compound with a weakly acidic C–H bond as dormant species in toluene at 0 °C. The tacticity of the resulting poly(MMA) (PMMA) produced without ligands was nearly atactic (rr/mr/mm = 22/54/24). However, the use of 18-crown-6 as a ligand afforded predominantly syndiotactic PMMA (rr ≈ 58%), whereas the use of chiral bis(oxazoline) ligands gave slightly isotactic-rich PMMA (mm ≈ 32%). Molecular weight control of PMMA was achieved (Đ = 1.1–1.2) by adding 1,1-diphenylethanol as a reversible terminator while maintaining control of the tacticity with the above ligands. Stereoblock PMMA consisting of atactic and syndiotactic segments was successfully synthesized via sequential PTAP using macroinitiator/macro-CTA methods.

Dual control of the molecular weight and tacticity in proton transfer anionic polymerization (PTAP) of methyl methacrylate (MMA) was investigated by using various ligands in the presence of a bulky potassium base catalyst and an organic compound with a weakly acidic C-H bond as dormant species in toluene at 0 °C. The tacticity of the resulting poly(MMA) (PMMA) produced without ligands was nearly atactic (rr/mr/mm = 22/54/24). However, the use of 18-crown-6 as a ligand afforded predominantly syndiotactic PMMA (rr ≈ 58%), whereas the use of chiral bis(oxazoline) ligands gave slightly isotactic-rich PMMA (mm ≈ 32%). Molecular weight control of PMMA was achieved (Đ = 1.1-1.2) by adding 1,1-diphenylethanol as a reversible terminator while maintaining control of the tacticity with the above ligands. Stereoblock PMMA consisting of atactic and syndiotactic segments was successfully synthesized via sequential PTAP using macroinitiator/macro-CTA methods.

While photocatalytic CO₂ reduction has been intensively investigated, reports on the influence of anions coordinated to catalytic metal sites on CO₂ photoreduction remain limited. Herein, different coordinated anions (F^–, Cl^–, OAc^–, and NO₃^–) around single Co sites installed on bipyridine-based three-component covalent organic frameworks (COFs) were synthesized, affording TBD-COF-Co-X (X = F, Cl, OAc, and NO₃), for photocatalytic CO₂ reduction. Notably, the presence of these coordinated anions on the Co sites significantly influences the photocatalytic performance, where TBD-COF-Co-F exhibits superior activity to its counterparts. Combined experimental and theoretical results indicate that the enhanced activity in TBD-COF-Co-F is attributed to its efficient charge transfer, high CO₂ adsorption capacity, and low energy barrier for CO₂ activation. This study provides a new strategy for boosting COF photocatalysis through coordinated anion regulation around catalytic metal sites.

While photocatalytic CO₂ reduction has been intensively investigated, reports on the influence of anions coordinated to catalytic metal sites on CO₂ photoreduction remain limited. Herein, different coordinated anions (F^-, Cl^-, OAc^-, and NO₃ ^-) around single Co sites installed on bipyridine-based three-component covalent organic frameworks (COFs) were synthesized, affording TBD-COF-Co-X (X = F, Cl, OAc, and NO₃), for photocatalytic CO₂ reduction. Notably, the presence of these coordinated anions on the Co sites significantly influences the photocatalytic performance, where TBD-COF-Co-F exhibits superior activity to its counterparts. Combined experimental and theoretical results indicate that the enhanced activity in TBD-COF-Co-F is attributed to its efficient charge transfer, high CO₂ adsorption capacity, and low energy barrier for CO₂ activation. This study provides a new strategy for boosting COF photocatalysis through coordinated anion regulation around catalytic metal sites.

One-dimensional (1D) functional nanowires are widely used as nanoscale building blocks for assembling advanced nanodevices due to their unique functionalities. However, previous research has mainly focused on nanowire functionality, while neglecting the structural stability and damage resistance of nanowire assemblies, which are critical for the long-term operation of nanodevices. Biomaterials achieve excellent mechanical stability and damage resistance through sophisticated structural design. Here, we successfully prepared a mechanically stabilized monolamella silver nanowire (Ag NW) film, based on a facile bubble-mediated assembly and nondestructive transfer strategy with the assistance of a porous mixed cellulose ester substrate, inspired by the hierarchical structure of biomaterial. Owing to the closely packed arrangement of Ag NWs combined with their weak interfaces, the monolamellar Ag NW film can be transferred to arbitrary substrates without damage. Furthermore, freestanding multilamellar Ag NW films with impressive damage resistance can be obtained from the monolamellar Ag NW film, through the introduction of bioinspired closely packed crossed-lamellar (CPCL) structure. This CPCL structure maximizes intra- and interlamellar interactions among Ag NWs ensuring efficient stress transfer and uniform electron transport, resulting in excellent mechanical durability and stable electrical properties of the multilamellar Ag NW films.

One-dimensional (1D) functional nanowires are widely used as nanoscale building blocks for assembling advanced nanodevices due to their unique functionalities. However, previous research has mainly focused on nanowire functionality, while neglecting the structural stability and damage resistance of nanowire assemblies, which are critical for the long-term operation of nanodevices. Biomaterials achieve excellent mechanical stability and damage resistance through sophisticated structural design. Here, we successfully prepared a mechanically stabilized monolamella silver nanowire (Ag NW) film, based on a facile bubble-mediated assembly and nondestructive transfer strategy with the assistance of a porous mixed cellulose ester substrate, inspired by the hierarchical structure of biomaterial. Owing to the closely packed arrangement of Ag NWs combined with their weak interfaces, the monolamellar Ag NW film can be transferred to arbitrary substrates without damage. Furthermore, freestanding multilamellar Ag NW films with impressive damage resistance can be obtained from the monolamellar Ag NW film, through the introduction of bioinspired closely packed crossed-lamellar (CPCL) structure. This CPCL structure maximizes intra- and interlamellar interactions among Ag NWs ensuring efficient stress transfer and uniform electron transport, resulting in excellent mechanical durability and stable electrical properties of the multilamellar Ag NW films.

Using density functional theory, we carefully calculated the relative stability of monolayer, few-layer, and cluster structures with Penta PdSe₂, T-phase PdSe₂, and Pd₂Se₃-phase. We found that the stability of Penta PdSe₂ increases with the number of layers. The Penta PdSe₂, T-phase PdSe₂, and Pd₂Se₃ monolayers are all semiconducting, with band gaps of 1.77, 0.81, and 0.65 eV, respectively. The formation energy of palladium selenide clusters with different phase structures is calculated, considering the cluster size, stoichiometry, and chemical environment. Under typical experimental conditions, Pd₂Se₃ phase clusters are found to be dominant, having the lowest formation energy among all of the phases considered, with this dominance increasing as cluster size grows. Adjusting the Pd-Se ratio in the environment allows for controlled synthesis of specific palladium selenide phases, providing theoretical insights into the nucleation mechanisms of PdSe₂ and other transition metal chalcogenides.

Using density functional theory, we carefully calculated the relative stability of monolayer, few-layer, and cluster structures with Penta PdSe₂, T-phase PdSe₂, and Pd₂Se₃-phase. We found that the stability of Penta PdSe₂ increases with the number of layers. The Penta PdSe₂, T-phase PdSe₂, and Pd₂Se₃ monolayers are all semiconducting, with band gaps of 1.77, 0.81, and 0.65 eV, respectively. The formation energy of palladium selenide clusters with different phase structures is calculated, considering the cluster size, stoichiometry, and chemical environment. Under typical experimental conditions, Pd₂Se₃ phase clusters are found to be dominant, having the lowest formation energy among all of the phases considered, with this dominance increasing as cluster size grows. Adjusting the Pd–Se ratio in the environment allows for controlled synthesis of specific palladium selenide phases, providing theoretical insights into the nucleation mechanisms of PdSe₂ and other transition metal chalcogenides.

Synthesis of functional polyethylene from ethylene alone is tricky and heavily dependent on both the type and structure of the precatalyst and the choice of cocatalyst used in the polymerization. In the present study, a series of cobalt precatalysts was prepared and investigated for ethylene polymerization under various conditions. By incorporation of strong electron-withdrawing groups (F and NO₂) and a steric component (benzhydryl) into the parent bis(imino)pyridine ligand, the catalytic performance of these precatalysts was optimized. On activation with MAO or MMAO, these precatalysts with relatively open structure achieved unprecedented ethylene polymerization rates at 60 °C (up to 27.6 × 10⁶ g mol^–1 h^–1) and remained effective at temperatures up to 100 °C. Chain growth reactions were moderate, resulting in polyethylene with molecular weights up to 61.0 kg/mol and broad bimodal dispersity index. High crystallinity and melt temperature indicated a strictly linear microstructure, as further confirmed by high-temperature ¹H/¹³C NMR measurements. Of significant note that chain termination predominantly occurred through β-elimination (up to 84.5%), yielding vinyl-terminated long-chain olefins. These functional α-macro-olefins are valuable as precursors for postfunctionalization, expanding the potential applications of polyethylene across various sectors.

Synthesis of functional polyethylene from ethylene alone is tricky and heavily dependent on both the type and structure of the precatalyst and the choice of cocatalyst used in the polymerization. In the present study, a series of cobalt precatalysts was prepared and investigated for ethylene polymerization under various conditions. By incorporation of strong electron-withdrawing groups (F and NO₂) and a steric component (benzhydryl) into the parent bis(imino)pyridine ligand, the catalytic performance of these precatalysts was optimized. On activation with MAO or MMAO, these precatalysts with relatively open structure achieved unprecedented ethylene polymerization rates at 60 °C (up to 27.6 × 10⁶ g mol^-1 h^-1) and remained effective at temperatures up to 100 °C. Chain growth reactions were moderate, resulting in polyethylene with molecular weights up to 61.0 kg/mol and broad bimodal dispersity index. High crystallinity and melt temperature indicated a strictly linear microstructure, as further confirmed by high-temperature ¹H/¹³C NMR measurements. Of significant note that chain termination predominantly occurred through β-elimination (up to 84.5%), yielding vinyl-terminated long-chain olefins. These functional α-macro-olefins are valuable as precursors for postfunctionalization, expanding the potential applications of polyethylene across various sectors.