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81.
Joung Heo 《Journal of Coordination Chemistry》2017,70(23):3837-3858
The reaction of [ZnCl2] with N-cyclopentyl-1-(quinolin-2-yl)methanimine (LA), N-cyclohexyl-1-(quinolin-2-yl)methanimine (LB), N-cyclohexyl-1-(pyridin-2-yl)methanimine (LC), 2,6-diethyl-N-(pyridin-2-ylmethylene)aniline (LD), N-cyclopentyl-1-(pyridin-2-yl)methanimine (LE), and N-phenyl-(pyridin-2-yl)methanimine (LF) in ethanol produced the bidentate [(NN′)ZnCl2] complexes, [LAZnCl2], [LBZnCl2], [LCZnCl2], [LDZnCl2], [LEZnCl2] and [LFZnCl2], respectively. The molecular structures revealed that the zinc in [LnZnCl2] (Ln = LA ? LD) showed a distorted tetrahedral geometry involving two nitrogens of N,N’-bidentate ligands and two chloride ligands. Most of these initiators were effective for polymerization of methyl methacrylate (MMA) and polymerization of rac-lactide (rac-LA). [LCZnCl2] (with N-cyclohexyl substituted at imine-pyridine moiety) exhibited the highest catalytic activity for MMA polymerization in the presence of modified methylaluminoxane (MMAO) with an activity of 3.33 × 104 g PMMA/mol·Zn·h at 60 °C, giving moderate syndiotactic poly methyl methacrylate (PMMA) with high molecular weight (9.62 × 105 g/mol). The dimethyl derivatives [LnZnMe2] (Ln = LA ? LF), generated in situ, polymerized rac-LA with moderate activity and yielded a polylactide (PLA) with good number-average molecular weights and narrower polydispersity indices (PDIs). [LAZnMe2] effectively initiates the ring-opening polymerization (ROP) of rac-LA to attain heterotactic PLA (Pr = 0.91). 相似文献
82.
The mechanical properties of surface treated UHMWPE fibers and TiO2 reinforced PMMA composite
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Mechanical properties of hybrid PMMA composites reinforced with UHMWPE fiber and nano‐titanium dioxide (2, 4, 6, and 8 wt%) was investigated. In this work, the effect of UHMWPE fiber surface treatment on tensile, flexural, and impact properties of PMMA composites was studied. The fiber loadings were varied from 0% to 20%. The addition of UHMWPE fiber had caused a decline in the tensile strength of the PMMA composite. Results revealed that the presence of titanium dioxide on the surface treated UHMWPE fiber has further enhanced the efficiency of stress transfer from the matrix to the fiber thus improved the interfacial adhesion between the UHMWPE fiber and PMMA matrix. 相似文献
83.
Improvement of interfacial adhesion in PP/PS blends enhanced with supersonic atmosphere plasma spraying surface‐treated carbon fiber
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The effects of surface treatment of a carbon fiber (CF) by supersonic atmosphere plasma spraying (SAPS) on the interfacial adhesion behavior and morphology of polypropylene/polystyrene (PP/PS) matrix blends filled CF composites were investigated. Effects of surface treated a commercial CF on mechanical properties are studied. Contact angle was measured to examine the changes in wettability of the CF. The chemical and morphological changes were characterized by using X‐ray photoelectron spectroscopy and scanning electron microscopy. PP/PS/CF composites were fabricated with and without SAPS treatment, and their interlaminar fracture toughnesses were compared. The results showed that the interlaminar shear strength of composites has been greatly improved filled SAPS modification CF. The water contact angle of resin sample decreased 50% after addition of SAPS surface‐treated CF. Scanning electron microscopy results on the fractured surface exhibited PP/PS blends adhered well around the CFs of the SAPS‐treated specimen compared with that of the untreated specimen. This attributed to the CF interlock, and it improves the wetting between fibers and resins. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
84.
Inorganic nanoparticles are widely used to improve space charge behavior, DC breakdown strength and other electrical properties of polymer insulating materials, but the uniform distribution of inorganic nanofillers in matrix is difficult due to their agglomeration and bad compatibility with the polymeric matrix. In this paper, polypropylene (PP)/polystyrene (PS) blends were prepared to suppress space charge accumulation and improve DC breakdown strength. Polypropylene-g-polystyrene (PP-g-PS) graft copolymer was used as compatibilizer to improve the compatibility of PP matrix and PS filler. The evolution of microstructure of PP/PS blends were investigated by scanning electron microscope (SEM), the space charge distributions were measured by a pulsed electro-acoustic (PEA) system, and DC breakdown strength was also tested. The morphologies show that the size of PS particles reduced to 310 nm when the content of PP-g-PS graft copolymer increased to 24 wt%, and the interaction between PP matrix and PS particles enhanced. The presence of PS particles in all PP/PS blends suppressed the space charge accumulation compared to neat PP, but the DC breakdown strength in uncompatibilized blend was lower than neat PP. The increasing of content of PP-g-PS improved the DC breakdown strength with the maximum value of 408.9 kV/mm was obtained. This may attribute to excellent interface structure formed between PP matrix and PS particles. 相似文献
85.
86.
87.
In this paper, a desirably simple, convenient and inexpensive saturable absorber mirror has been fabricated based on graphene, which has no wavelength selectivity. Moreover, there are no changes in the structure and characteristics of graphene. By inserting the graphene-PMMA SA mirror to the Nd: YAG laser, the shortest pulse width of 260 ns can be obtained with the single-pulse energy of about 8.32 μJ. The experimental results prove that our graphene-PMMA SA mirror is feasible and suitable for Q-switched lasers. 相似文献
88.
Structure and photoluminescence properties of ZnS films grown on porous Si substrates 总被引:1,自引:0,他引:1
ZnS films were deposited on porous silicon (PS) substrates with different porosities. With the increase of PS substrate porosity, the XRD diffraction peak intensity decreases and the surface morphology of the ZnS films becomes rougher. Voids appear in the films, due to the increased roughness of PS structure. The photoluminescence (PL) spectra of the samples before and after deposition of ZnS were measured to study the effect of substrate porosity on the luminescence properties of ZnS/PS composites. As-prepared PS substrates emit strong red light. The red PL peak of PS after deposition of ZnS shows an obvious blueshift. As PS substrate porosity increases, the trend of blueshift increases. A green emission at about 550 nm was also observed when the porosity of PS increased, which is ascribed to the defect-center luminescence of ZnS. The effect of annealing time on the structural and luminescence properties of ZnS/PS composites were also studied. With the increase of annealing time, the XRD diffraction peak intensity and the self-activated luminescence intensity of ZnS increase, and, the surface morphology of the ZnS films becomes smooth and compact. However, the red emission intensity of PS decreases, which was associated with a redshift. White light emission was obtained by combining the luminescence of ZnS with the luminescence of PS. 相似文献
89.
90.
Huanhuan KouXin Zhang Yongling DuWeichun Ye Shaoxiong LinChunming Wang 《Applied Surface Science》2011,257(10):4643-4649
Well-aligned ZnO nanoflowers and nanosheets were synthesized on porous Si (PS) at different applied potentials by electrodeposition approach. The deposits were grown using the optimized program and were characterized by means of cyclic voltammetry (CV), amperometry I-t (I-t), open-circuit potentiometry. X-ray diffraction (XRD) analysis proved a strong preferential orientation (1 0 0) on PS. Scanning electronic microscopy (SEM) observation showed the deposits consist of nanoflowers with uniform grain size of about 100 nm in diameter and nanosheets, which may have potential applications in nanodevices and nanotechnologies. Thus, ZnO grown on PS can be used as photoelectric materials due to its larger photoelectric effect compared to Si wafer according to open-circuit potential (OCP) study. Optical band gap measurements were made on samples using UV-visible spectrophotometer thus giving a band gap of 3.35 eV. 相似文献