Bromoalkyl-functionalized poly(olefin)s were synthesized by copolymerization of 4-(4-methylphenyl)-1butene with 11-bromo-1-undecene using Ziegler−Natta polymerization. The resulting bromoalkyl-functionalized poly-(olefin)s were converted to quaternary ammonium-containing anion-conductive copolymers by reacting the pendant bromoalkyl group with trimethylamine or a custom-synthesized tertiary amine containing pendant quaternary ammonium moieties. Poly(olefin)-based AEMs with three cations per side chain showed considerably higher hydroxide conductivities, up to 201 mS/cm at 80 °C in liquid water, compared to that of samples with only one cation per bromoalkyl site (68 mS/cm, 80 °C, liquid water), likely due to phase separation in the triple-cation structure. More importantly, triple-cation side-chain poly(olefin) AEMs exhibited higher hydroxide conductivity under relative humidity conditions (50%−100%) than typical AEMs based on benzyltrimethylammonium cations. The triple-cation the triple-cation side-chain poly(olefin)-based AEM exhibited an ionic conductivity as high as 115 mS/cm under 95% RH at 80 °C and 11 mS/cm under 50% RH at 80 °C. In addition to high ionic conductivity, the triple-cation side-chain poly(olefin) AEMs exhibited good chemical and dimensional stability. High retention of ionic conductivity (>85%) was observed for the samples in 1 M NaOH at 80 °C over 1000 h. Based on these high-performance poly(olefin) AEMs, a fuel cell with a peak power density of 0.94 W cm −2 (1.28 W cm −2 after iR correction) was achieved under H 2 /O 2 at 70 °C. The results of this study suggest a new, low-cost, and scalable route for preparation of poly(olefin)-based AEMs for anion exchange membrane applications.
It is very challenging to improve the catalytic activity of Pt-based catalysts since the strong CO chemisorption on Pt inhibits oxygen activation leading to poor activity at low temperature. Here, we report that introducing MO x (M = Fe, Co, Ni) to modify Pt catalysts (0.5 wt % Pt/CeO2) is a facile way to improve catalytic activity for CO oxidation at ambient temperature. The chemical state of Pt and the reducibility of doped MO x dominate the activity for CO oxidation. The electron-deficient Pt due to the strong interaction between Pt and MO x leads to the weaker CO adsorption strength. Meanwhile, the higher reducibility of FeO x and CoO x extends the reaction routine due to the improved activity of oxygen with the help of the redox cycle between FeO x /CoO x and CeO2. However, the stability of catalyst depends on the ability to recover consumed oxygen, and the reversible compensation of consumed oxygen species makes CoO x /Pt/CeO2 and NiO x /Pt/CeO2 remain stable with time on stream. Our study shows that CoO x is a potential candidate to increase Pt atom efficiency for CO oxidation on Pt/CeO2 catalysts.
A new series of polyethylene (PE) containing arylene ether units as defects in the main chain, which were precisely separated by 20 CH 2 units, were synthesized via acyclic diene metathesis (ADMET) polymerization. The thermal stability, crystallization, and melting behaviors, crystal structure, and chain stacking were investigated with TGA, DSC, WAXD, and SAXS. It is found that the substitution position in the arylene units has a remarkable influence on the chain stacking and their location in the solid phase. The ortho-substituted phenylene units are excluded from the crystal phase, leading to a low melting temperature (T m ). In contrast, the para-substituted phenylene units can be included into the crystal, leading to a high T m . The meta-substituted phenylene units can be partially included into the crystal, resulting in mixed crystal structures and an intermediate T m . Such an effect of substitution position in precision PEs is different from that in poly(ethylene oxide) reported in the literature, which can be ascribed to the matchable configuration of the defects in the main chain with the conformation of PE in the crystals. When the defects become naphthylene ether units, the crystallization and melting behaviors of the polymers are similar to or different from those of the precision PEs with phenylene ether defects, depending on the substitution position. This shows that both the substitution position in the arylene ether defects and the defect size exert effects on crystallization, melting behaviors, and chain stacking of precision PEs.
Fiber-like (1D) core-crystalline micelles of uniform length can be obtained in protocols involving multiple steps from block copolymers (BCPs) in which crystallization of the core-forming polymer drives the self-assembly. Here we report a systematic study that shows that adding small amounts (<5 w/w%) of a homopolymer corresponding to the core-forming block of the BCP enables uniform 1D micelles (mean lengths L n = 0.6 to 9.7 μm) to be obtained in a single step, simply by heating the mixture in a selective solvent followed by slow cooling. A series of poly(ferrocenyldimethylsilane) (PFS) BCPs with different corona-forming blocks and different compositions as well as PFS homopolymers of different lengths were examined. Dye labeling and confocal fluorescence microscopy showed that the homopolymer ends up in the center of the micelle, signaling that it served as the initial seed for epitaxial micelle growth. The rate of unimer addition was strongly enhanced by the length of the PFS block, and this enabled more complex structures to be formed in one-pot self-assembly experiments from mixtures of two or three BCPs with different PFS block lengths. Furthermore, BCP mixtures that included PFS-b-PI (PI = polyisoprene) and PFS-b-PDMS with similar PFS block lengths resulted in simultaneous addition to growing micelles, resulting in a patchy block that could be visualized by staining the vinyl groups of the PI with Pt nanoparticles. This approach also enabled scale up, so that uniform 1D micelles of controlled architecture can be obtained at concentrations of 10 w/w % solids or more.
A crystalline-coil block copolymer with an amphiphilic corona-forming block affords a variety of different 2D structures in different self-assembly media.
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