Nanostructure and Linear Rheological Response of Comb-like Copolymer PSVS‑<i>g</i>‑PE Melts: Influences of Branching Densities and Branching Chain Length

Comb-like poly­(styrene-<i>co</i>-4-(vinylphenyl)-1-butene)-<i>g</i>-polyethylene copolymers (PSVS-<i>g</i>-PE) with various branching parameters were synthesized to study the influence of branch chains on morphology (at melt state) and linear rheological response of the copolymers. The results showed that both the branching density and branch chain length of PSVS-<i>g</i>-PE copolymers strongly affected linear rheological behavior of the copolymers, resulting from the formation of different microphase separation structure in the melt state. PSVS-<i>g</i>-PE copolymers with low branching density (2.3–3.5 branch chains per 100 repeating units of the backbone) showed a microphase-separated structure at the melt state, and a typical rheological characteristic for network-like structure was observed. Furthermore, the type of microphase-separated structure at the melt state strongly influences the applicability of the time–temperature superposition (TTS) principle. As a result, the TTS failure was observed in the modulus curves for PSVS52.7-3.5-PE4.9 (poor-order lamellar structure) and PSVS54.4-2.7-PE10.7 (long tubular structure). In contrast, the PSVS-<i>g</i>-PE sample with high branching density (16.6–24.5 branch chains per 100 repeating units of the backbone) showed homogeneous phase structure and normal rheological behavior, similar to linear or comb-like homopolymers. The gel-like state appeared in a limited frequency regime (a plateau regime of tan δ versus ω) during decreasing the frequency from the high frequency regime in these comb-like copolymers

Synthesis of Diverse Well-Defined Functional Polymers Based on Hydrozirconation and Subsequent Anti-Markovnikov Halogenation of 1,2-Polybutadiene

For the first time, hydrozirconation and halogenolysis of 1,2-polybutadiene (1,2-PBD, by living anionic polymerization) were studied to synthesize reactive polyhalohydrocarbons, which provide a platform for preparing well-defined functional polymers via macromolecular substitution. Hydrozirconation and halogenolysis afforded quite convenience for anti-Markovnikov hydrohalogenation of 1,2-PBD with controllable degree of functionalization. Diverse functional polymers and branched polymers were synthesized after macromolecular substitution reaction with a broad range of commercially available nucleophiles (amines, phenols, alcohols, carbanions, carboxylates, and azide) or macromolecular nucleophiles. NMR and GPC characterizations confirmed high conversion in substitution reaction and narrow molecular weight distribution of the resultant functional polymers, respectively. The methodology utilizing Schwartz’s reagent for hydrozirconation of macromolecules could greatly facilitate the modification of vinyl groups containing polymers with high efficiency

Atomically Dispersed Dual Metal Sites Boost the Efficiency of Olefins Epoxidation in Tandem with CO₂ Cycloaddition

Tandem catalysis provides an economical and energy-efficient process for the production of fine chemicals. In this work, we demonstrate that a rationally synthesized carbon-based catalyst with atomically dispersed dual Fe–Al sites (ADD-Fe-Al) achieves superior catalytic activity for the one-pot oxidative carboxylation of olefins (conversion ∼97%, selectivity ∼91%), where the yield of target product over ADD-Fe-Al is at least 62% higher than that of monometallic counterparts. The kinetic results reveal that the excellent catalytic performance arises from the synergistic effect between Fe (oxidation site) and Al sites (cycloaddition site), where the efficient CO2 cycloaddition with epoxides in the presence of Al sites (3.91 wt %) positively shifts the oxidation equilibrium to olefin epoxidation over Fe sites (0.89 wt %). This work not only offers an advanced catalyst for oxidative carboxylation of olefins but also opens up an avenue for the rational design of multifunctional catalysts for tandem catalytic reactions in the future

Si/Ag/C Nanohybrids with <i>in Situ</i> Incorporation of Super-Small Silver Nanoparticles: Tiny Amount, Huge Impact

Silicon (Si) has been regarded as one of the most promising anodes for next-generation lithium-ion batteries (LIBs) due to its exceptional capacity, appropriate voltage profile, and reliable operation safety. However, poor cyclic stability and moderate rate performance have been critical drawbacks to hamper the practical application of Si-based anodes. It has been one of the central issues to develop new strategies to improve the cyclic and rate performance of the Si-based lithium-ion battery anodes. In this work, super-small metal nanoparticles (2.9 nm in diameter) are <i>in situ</i> synthesized and homogeneously embedded in the <i>in situ</i> formed nitrogen-doped carbon matrix, as demonstrated by the Si/Ag/C nanohybrid, where epoxy resin monomers are used as solvent and carbon source. With tiny amount of silver (2.59% by mass), the Si/Ag/C nanohybrid exhibits superior rate performance compared to the bare Si/C sample. Systematic structure characterization and electrochemical performance tests of the Si/Ag/C nanohybrids have been performed. The mechanism for the enhanced rate performance is investigated and elaborated. The temperature-dependent <i>I–V</i> behavior of the Si/Ag/C nanohybrids with tuned silver contents is measured. Based on the model, it is found that the super-small silver nanoparticles mainly increase charge carrier mobility instead of the charge carrier density in the Si/Ag/C nanohybrids. The evaluation of the total electron transportation length provided by the silver nanoparticles within the electrode also suggests significantly enhanced charge carrier mobility. The existence of tremendous amounts of super-small silver nanoparticles with excellent mechanical properties also contributes to the slightly improved cyclic stability compared to that of simple Si/C anodes