4-苯乙炔基苯胺封端聚酰亚胺树脂的合成与性能研究

使用4-苯乙炔基苯胺(4-PEA)作为反应性封端剂,和3,3′,4,4′-二苯醚四酸二酐(ODPA),3,3′,4,4′-联苯四酸二酐(BPDA),1,4-双(4′-氨基-2′-三氟甲基苯氧基)苯(BTPB)和3,4′-二氨基二苯醚(3,4-′ODA)反应合成了系列4-苯乙炔基苯基封端的聚酰亚胺低聚物,对低聚物的化学结构、热性能和熔体粘度以及固化后树脂的热性能等进行了研究.实验结果表明,低聚物均具有一定的结晶性,含有ODPA的聚酰亚胺低聚物较之含有BPDA的低聚物具有更低的熔体粘度,且出现最低熔体粘度的温度更低;固化后的树脂表现出良好的热性能,含有BPDA的树脂具有更高的玻璃化转变温度;系列低聚物中二胺单体的比例对于低聚物的熔体粘度和固化后树脂的热稳定性有一定影响.     

Flat polymer ribbons and other shapes by electrospinning

In addition to round nanofibers, electrospinning a polymer solution can produce thin fibers with a variety of cross‐sectional shapes. Branched fibers, flat ribbons, ribbons with other shapes, and fibers that were split longitudinally from larger fibers were observed. The transverse dimensions of these asymmetric fibers were typically 1 or 2 μm, measured in the widest direction. A correlation of the branches and bends, observed in high‐frame‐rate videography of the electrified jets of polymer solutions from which the ribbons and branched fibers were produced, suggest that these phenomena occur at scales ranging from around 1 mm to 1 μm. The observation of fibers with these cross‐sectional shapes from a number of different kinds of polymers and solvents indicates that fluid mechanical effects, electrical charge carried with the jet, and evaporation of the solvent all contributed to the formation of the fibers. The influence of a skin on the jets of polymer solutions accounts for a number of the observations. The observed shapes can be used as guides for the extension of mathematical or computer‐generated models for the electrospinning process. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2598–2606, 2001     

Molecular Bridging Enables Isolated Iron Atoms on Stereoassembled Carbon Framework To Boost Oxygen Reduction for Zinc-Air Batteries

Realizing the synergy between active site regulation and rational structural engineering is essential in the electrocatalysis community but still challenging. Here, a matrix-confined co-pyrolysis strategy based on molecular bridging is demonstrated to realize highly dispersed Fe atoms on stereoassembled carbon framework. Both polyacrylonitrile matrix and organic linker from metal–organic frameworks (MOFs) provide sufficient N-anchoring sites for the generation of Fe−N₄ moieties. A high Fe loading of 2.9 wt.% is readily achieved based on the scalable approach without post-treatment. Owing to the presence of highly exposed Fe−N−C sites and well-tuned pore structures, isolated Fe atoms on porous carbon nanofiber framework (Fe−SA/NCF) exhibits decent oxygen reduction activity and stability in alkaline conditions via a near four-electron path, demonstrating superior performance as air cathode for zinc-air batteries (ZABs) to commercial Pt/C catalyst.     

Synthesis and properties of thermoplastic propyl-etherified amylose

Amylose was etherified with 1-bromopropane in DMSO. The degree of substitution (DS) was varied by altering the feed ratio of 1-bromopropane. The structures of the products were characterized by IR and 1H-NMR spectroscopy. When the molar feed ratio of 1-bromopropane to hydroxyl groups of amylose was beyond 7.5, the hydroxyl groups were completely substituted with propyl ether groups. The etherified amylose with DS 1.9 showed a glass transition temperature (T_g), and that with DS 2.3 or 3.0 showed both T_g and melting temperature (T_m) (DS 3.0 means complete substitution). The etherification imparted melt processability and solubility in nonpolar organic solvent to amylose.     

Electrospun Nanofibers from a Tricyanofuran‐Based Molecular Switch for Colorimetric Recognition of Ammonia Gas

A chromophore based on tricyanofuran (TCF) with a hydrazone (H) recognition moiety was developed. Its molecular‐switching performance is reversible and has differential sensitivity towards aqueous ammonia at comparable concentrations. Nanofibers were fabricated from the TCF–H chromophore by electrospinning. The film fabricated from these nanofibers functions as a solid‐state optical chemosensor for probing ammonia vapor. Recognition of ammonia vapor occurs by proton transfer from the hydrazone fragment of the chromophore to the ammonia nitrogen atom and is facilitated by the strongly electron withdrawing TCF fragment. The TCF–H chromophore was added to a solution of poly(acrylic acid), which was electrospun to obtain a nanofibrous sensor device. The morphology of the nanofibrous sensor was determined by SEM, which showed that nanofibers with a diameter range of 200–450 nm formed a nonwoven mat. The resultant nanofibrous sensor showed very good sensitivity in ammonia‐vapor detection. Furthermore, very good reversibility and short response time were also observed.     

Sol-Gel Co-Electrospun LiNiO2 Hollow Nanofibers

Using a coaxial capillary spinneret electrospinning technique combined with the sol-gel method, the nickelic xerogel hollow nanofibers first were prepared and the polycrystalline LiNiO₂ hollow nanofibers were obtained after sintering. The obtained hollow nanofibers were about 500 nm to 4 µm in outer diameter, and were made up of 20 ～ 30 nm nanocrystals. The xerogel hollow nanofibers and those calcined at different temperatures were characterized by thermogravimetric (TG) analysis, Fourier transform infrared (FTIR) spectrum, x-ray diffractometry (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM).     

Preparation of poly(propylene carbonate)/organo-vermiculite nanocomposites via direct melt intercalation

Intercalated nanocomposites comprised of poly(propylene carbonate) (PPC) and organo-vermiculite (OVMT) was first prepared via direct melt compounding of the alkali-vermiculite intercalated host with PPC in a twin rotary mixer. The dispersion and morphologies of OVMT within PPC were investigated by X-ray diffraction and transmission electron microscopic techniques. The results revealed the formation of intercalated-exfoliated vermiculite sheets in the PPC matrix. Because of the thermally sensitive nature of PPC, thermal degradation occurred during the melt compounding. The degradation led to a deterioration of the mechanical properties of the nanocomposites. Tensile test showed that the yield strength and modulus of the nanocomposites decrease with increasing vermiculite content. The degradation mechanism was discussed according to the results of GPC and TGA measurements.     

Biocompatibility Study of Electrospun Nanocomposite Membranes Based on Chitosan/Polyvinyl Alcohol/Oxidized Carbon Nano-Onions

In recent decades, the number of patients requiring biocompatible and resistant implants that differ from conventional alternatives dramatically increased. Among the most promising are the nanocomposites of biopolymers and nanomaterials, which pretend to combine the biocompatibility of biopolymers with the resistance of nanomaterials. However, few studies have focused on the in vivo study of the biocompatibility of these materials. The electrospinning process is a technique that produces continuous fibers through the action of an electric field imposed on a polymer solution. However, to date, there are no reports of chitosan (CS) and polyvinyl alcohol (PVA) electrospinning with carbon nano-onions (CNO) for in vivo implantations, which could generate a resistant and biocompatible material. In this work, we describe the synthesis by the electrospinning method of four different nanofibrous membranes of chitosan (CS)/(PVA)/oxidized carbon nano-onions (ox-CNO) and the subdermal implantations after 90 days in Wistar rats. The results of the morphology studies demonstrated that the electrospun nanofibers were continuous with narrow diameters (between 102.1 nm ± 12.9 nm and 147.8 nm ± 29.4 nm). The CS amount added was critical for the diameters used and the successful electrospinning procedure, while the ox-CNO amount did not affect the process. The crystallinity index was increased with the ox-CNO introduction (from 0.85% to 12.5%), demonstrating the reinforcing effect of the nanomaterial. Thermal degradation analysis also exhibited reinforcement effects according to the DSC and TGA analysis, with the higher ox-CNO content. The biocompatibility of the nanofibers was comparable with the porcine collagen, as evidenced by the subdermal implantations in biological models. In summary, all the nanofibers were reabsorbed without a severe immune response, indicating the usefulness of the electrospun nanocomposites in biomedical applications.     

Effect of Polythiophene Content on Thermomechanical Properties of Electroconductive Composites

The thermal, mechanical and electrical properties of polymeric composites combined using polythiophene (PT) dopped by FeCl₃ and polyamide 6 (PA), in the aspect of conductive constructive elements for organic solar cells, depend on the molecular structure and morphology of materials as well as the method of preparing the species. This study was focused on disclosing the impact of the polythiophene content on properties of electrospun fibers. The elements for investigation were prepared using electrospinning applying two substrates. The study revealed the impact of the substrate on the conductive properties of composites. In this study composites exhibited good thermal stability, with T₅ values in the range of 230–268 °C that increased with increasing PT content. The prepared composites exhibited comparable PA T_g values, which indicates their suitability for processing. Instrumental analysis of polymers and composites was carried out using Fourier Transform Infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and scanning electron microscopy (SEM).     

聚碳酸酯合成工艺开发的新进展

本文从工艺开发的角度，简要评介了目前聚碳酸酯两大工业生产工艺，即光气化界面缩聚工艺和熔融酯交换缩聚工艺的研究开发新动向。