Ultrahigh molecular weight polyethylene (UHMWPE) exhibits outstanding properties and widespread application requirements, yet its processing challenges remain a major concern. In this study, a series of β-diketonate titanium catalysts were developed for the one-reactor synthesis of bimodal polyethylene (polyethylene wax/UHMWPE). The content of the polyethylene wax component (2–60 wt %) could be regulated by varying polymerization conditions and catalyst structure. Optimal catalytic activity was achieved at low temperatures (0 °C), yielding bimodal polymers with less than 5 wt % polyethylene wax content, where the UHMWPE component was confirmed to be in a disentangled state. The resulting polymer exhibited ultradrawability, with draw ratios reaching up to 300, yielding tapes with superior mechanical properties. This is the first report of β-diketonate titanium catalysts for disentangled UHMWPE. The catalysts were readily synthesized in one step from inexpensive industrial precursors, demonstrating excellent potential for industrial application. This system supports both melt and solid-state processing, providing a practical pathway to overcome UHMWPE processing limitations.
We investigate the kinetics of self-assembly in solutions of polyampholytes (PAs) with identical net charge but differing charge sequences, using coarse-grained molecular dynamics simulations under moderately poor solvent conditions. Three representative sequence types─forming micelles with polyelectrolyte (PE) tails, micelles with sticky (telechelic) corona, and droplets─are studied to elucidate how charge patterning affects aggregate formation, stability, and dynamic restructuring. We identify three dominant mechanisms of mass redistribution: (1) direct binding and release of unimers, (2) merging of preassembled aggregates, and (3) bridging between cores via polyampholytic tails, which facilitates unimer exchange during inelastic collisions between larger aggregates. At low concentrations, a population of small aggregates forms that equilibrates easily through reversible association, whereas at higher concentrations, the kinetics are strongly influenced by sequence-dependent barriers and corona structures. Micelle-forming sequences exhibit kinetic trapping and minimal mass exchange, whereas droplet-forming sequences show frequent transitions and extended lifetimes of double-core aggregates. The interaction potential between aggregates is quantified and used to estimate association and dissociation times via a Fokker–Planck approach, in good agreement with simulation results. In addition, simulations of biologically relevant ProTα sequences reveal a dynamic gel-like network characterized by frequent unimer exchange. Our study highlights the crucial role of charge sequence in controlling the pathways of PA aggregation, offering insight into phase behavior in biological system and the design of functional polymeric materials.
Lignin-derivable para-phenolic acids (syringic, vanillic, and 4-hydroxybenzoic acids, with number of methoxy groups per molecule ranging from 0 to 2) were epoxidized using a two-stage allylation–epoxidation procedure and cured into resins with an anhydride curing agent. During epoxidation of allylated syringic acid with a peracid, a significant hydroxylated epoxy side-product was formed via aromatic ring oxidation, which was not observed in the vanillic acid or 4-hydroxybenzoic acid systems. Shortening the reaction time reduced the hydroxylated product formation and also decreased epoxy conversion. Importantly, the presence of the hydroxylated product in the curing mixture did not impact the curing kinetics or the glass transition temperature (Tg) of the resin. Thermomechanical analysis of the resins showed that increasing methoxy groups in the monomer raised the glassy storage modulus (E′) but lowered the Tg of the resin. This Tg decrease correlated with reduced cross-link density and rubbery E′. When Tg was plotted against cross-link density, the resin derived from para-phenolic acid followed a consistent linear trend, distinct from that of the petroleum-derived diglycidyl ether of bisphenol A (DGEBA) resin, suggesting a different structure–property relationship. In summary, epoxy monomers derived from para-phenolic acids represent promising biobased alternatives to DGEBA. The number of methoxy groups on the lignin-derivable monomer critically influences the cross-link density, Tg, and thermomechanical properties of the resulting resins.
Polymer capacitors have garnered extensive attention in modern electronic and power systems. Nonetheless, the relatively low energy density of the polymer dielectric limits its application. Herein, sulfobetaine methacrylate (SBMA) was grafted onto poly(vinylidene fluoride) (PVDF) through free-radical polymerization, resulting in the formation of PVDF-g-SBMA. Dielectric films of PVDF-g-SBMA were then fabricated using a casting method. The grafting of SBMA enhances the polarization of the graft copolymer dipoles, its electron-withdrawing ability, and mechanical strength, thereby improving the dielectric characteristics of the copolymer films. At a grafting level of 7 wt %, the copolymer film demonstrates a relatively high dielectric constant (∼11.3) and a high electrical breakdown field strength (∼346 kV/mm) at 1 kHz, representing about a 16% increase in dielectric constant with respect to pure PVDF films (∼9.7) and a 71% increase in breakdown field strength (∼202 kV/mm). At the highest applied field strength, the energy density of the material (∼8.38 J/cm3) is approximately 390% greater compared to pure PVDF films, which exhibit an energy storage density of approximately 1.71 J/cm3. This study offers a practical approach to achieving a high energy storage capacity in polymer-based dielectrics.
The efficient separation of hydrogen (H2) and carbon dioxide (CO2) mixtures represents a critical step in clean H2 production, where environmentally friendly and energy-saving membrane technology serves as a promising solution. The key to realizing practical applications of membrane separation technology lies in the rational design and development of polymeric membrane materials that simultaneously exhibit high permeability and high selectivity. However, polymeric membrane materials face challenges in efficiently separating H2 and CO2 with similar molecular sizes. This review systematically summarizes recent research progress in polymeric membrane materials for H2 and CO2 separation. It focuses on analyzing the characteristics and separation performance of various material systems, including poly(ethylene oxide) (PEO), polyimides (PIs), polybenzimidazoles (PBIs), carbon molecular sieve membranes (CMSMs), polyamides (PAs) and polyarylates (PARs), and covalent organic framework (COF) membrane. The review thoroughly discusses current key challenges and technical bottlenecks of polymer membranes for hydrogen and carbon dioxide separation, while also providing insights into future development directions.
Reduction of nonbonded steric interactions within the supporting cyclopentadienyl, amidinate (CPAM) ligand environment of group 4 metal dimethyl complexes of general formula, (η5-C5R5)[κ2-(N,N)-N(R1)C(R2)N(R3)]MMe2 (I), render these capable of serving as initiators for the living coordination polymerization (LCP) and living coordinative chain-transfer polymerization (LCCTP) of challenging alkene monomers, such as vinylcyclohexene (VCH). More specifically, the active ion pair initiator derived from the Cs-symmetric Hf preinitiator 1 (M = Hf; R = R1 = R3; R2 = Ph) and the anilinium borate co-initiator, [PhNHMe2][B(C6F5)4] (B1), provides isotactic poly(vinylcyclohexane) (iPVCH) through LCP via a chain-end stereocontrol mechanism, and in the presence of 5 equiv of diethylzinc (ZnEt2) as a chain-transfer agent, the LCCTP of VCH provides end-group-functionalized atactic PVCH using a reactive quench with I2. Finally, the active initiator obtained from the CPAM Ti preinitiator 2 (M = Ti; R = H, R1 = R3 = Me, R2 = Ph) and either B1, [Ph3C][B(C6F5)4] (B2), or B(C6F5)3 (B3) as a co-initiator, was shown to be competent for the nonliving coordination polymerizations of ethene, propene, and 1-hexene.
Perfluorosulfonic acid ionomer (PFSA) dispersions are essential to the coating processes used to fabricate membranes, catalyst layers, and thin films for hydrogen fuel cell and water electrolyzer applications. The PFSA dispersion viscosity can significantly affect coating parameters including wetting, leveling, and compatibility with coating equipment. The effect of PFSA concentration, chemical structure, and solvent composition on dispersion viscosity is examined as a function of five different PFSAs and three different binary alcohol–water solvent systems, using n-propanol, isopropanol, or ethanol as the alcohol. The zero-shear viscosity, η0, is observed to increase with decreasing side chain length, increasing side chain content, and increasing alcohol concentration in the binary alcohol–water solvent. A direct comparison is made between the PFSA colloidal morphology discussed in a previous publication by the present authors and η0. At a fixed, nondilute PFSA concentration, two regimes of weak and strong dependence of η0 on alcohol concentration in the solvent are identified. In the regime where η0 weakly depends on alcohol concentration, an increase in η0 is associated with an increase in the aggregate surface area normalized by side chain content. The orders of magnitude increases in η0 with increasing alcohol concentration in the regime of strong dependence of η0 are attributed to both aggregate morphology and interaggregate ionic associations. By independently considering the PFSA side chain and backbone solubility parameters, two regimes corresponding to relatively favorable solvent-side chain and relatively favorable solvent-backbone interactions are defined as a function of alcohol–water solvent composition. An analysis of PFSA-solvent interaction parameters shows that interaggregate ionic associations occur when solvent-side chain interactions are unfavorable relative to solvent-backbone interactions─for example, at high alcohol concentrations in the solvent. The alcohol concentration corresponding to the crossover between the weak and strong regimes of η0 is found to agree within ±5 wt % alcohol with the crossover between the regimes of favorable solvent-side chain and favorable solvent-backbone interactions.
Statistical copolymers of ethylene oxide (EO) and propylene oxide (PO) are widely used in industry and academia. Despite their decade-long use, the influence of the polymerization conditions on reactivity ratios is underexplored, and surprisingly solution and bulk properties of the resulting polyether copolymers have not been reported in a systematic manner. In this study we examined the copolymerization of EO and PO in a variety of solvents (dimethyl sulfoxide, toluene, anisole) and at different temperatures (25–60 °C), correlating reaction conditions with the thermal and solubility properties of the resulting P(EO-co-PO) copolymers. The copolymerization was monitored online by in situ 1H NMR spectroscopy to determine the reactivity ratios for the full conversion range. The results show a temperature-dependent trend in reactivity ratios (r) for different solvents. In toluene, the reactivity ratios converge with increasing temperature, changing from rPO = 0.26 and rEO = 3.78 at 40 °C to rPO = 0.31 and rEO = 3.21 at 60 °C. A similar pattern is observed in anisole, with the reactivity ratios shifting from rPO = 0.28 and rEO = 3.52 at 40 °C to rPO = 0.30 and rEO = 3.32 at 60 °C, respectively. In contrast, the reactivity ratios in DMSO are generally slightly more similar, with rPO = 0.32 and rEO = 3.10 at 40 °C. Thermal characterization of the polyether copolymers revealed similar melting points of approximately 10 °C and enthalpies of around 40 J·g–1. Cloud point measurements of the copolymers showed decreased aqueous solubility as the differences in reactivity ratios decreased. These findings demonstrate that the statistical EO/PO copolymerization reaction conditions affect the gradient and thereby significantly influence copolymer physical properties, highlighting the need to consider these parameters for applications.
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：