The substituted pyrazole palladium complexes, (3,5-tBu2pz)2PdCl2 (1) (3,5-Me2pz)2PdCl2 (2), (3-Mepz)2PdCl2 (3) and (pz)2PdCl2 (4) (pzH=pyrazole), can be prepared from the reaction of (COD)PdCl2 with the appropriate pyrazole. The chloromethyl derivative, (3,5-tBu2pz)2PdCl(Me) (5), was prepared from (COD)PdClMe and tBu2pzH. X-ray crystal structure determination of 1 and 5 established their structures in the solid state to be the trans-isomer. After activation of 1-4 and 5 with methylaluminoxane (MAO) the resulting palladium complexes were used as catalysts in ethylene polymerization, yielding linear high-density polyethylene (HDPE). The highest activity was observed for (3,5-tBu2pz)PdClMe. 相似文献
Composites of high density polyethylene, HDPE, filled with submicrometric particles of BaTiO3, BT, have been prepared. Uniform dispersion of the particles was achieved by high energy ball milling and subsequent hot pressing. Using SEM, FTIR, TGA-DTA and stress-strain tests, studies of the structural, morphological and mechanical features of the composites have been carried out. Frequency response analysis, dielectric strength and resistivity measurements were also performed to evaluate the final electrical properties as a function of the processing and the amount of BaTiO3 particles. From the analysis of the microscopic structure, it can be deduced that any change in the properties of the materials must be solely ascribed to the presence of the BT particles. A balance between an enhancement of space charge polarization with the presence of BT and the existence of permanent dipoles associated to them might explain an initial increase in the dielectric losses with the BT content, and its later decrease at higher BT content. The observed decrease in resistivity and breakdown voltage when increasing the amount of BaTiO3 can be explained by the lower resistivity of BT particles at room temperature and the growing accumulation of space charge. 相似文献
The mechanical and physical properties of blends based essentially on nitrile butadiene rubber (NBR) and different ratios of high density polyethylene (HDPE) up to 25 parts per hundred part of rubber (phr) before and after electron beam irradiation were investigated. The values of tensile strength (TS), tensile modulus at 50% elongation (M50), hardness and gel fraction % (GF%) of NBR/HDPE blends were increased with both irradiation dose and by increasing the content of HDPE in the blends. On the other hand, the values of elongation at break (Eb) were decreased with both irradiation dose and the content of HDPE in the blends. By loading NBR/HDPE (100/25) blend with ethylene vinyl acetate (EVA) copolymer the mechanical and physico-chemical properties were improved. Moreover, the degree of improvement is proportional to the loading content of EVA. 相似文献
Acrylonitrile-butadiene copolymer (NBR) nanocomposites were prepared with varied silicate loadings by the melt mixing between NBR and organoclays (OCs) containing intercalants with different polarity and chain length. WXRD exhibited that the NBR nanocomposites had an intercalated structure with distinct differences in gallery height depending on the intercalant characteristics. However, WXRD failed to show a structural change with increasing silicate contents. Hence, tensile strain-stress measurements were carried out at various strain rates (0.162, 0.0975, and 0.0187 s−1), and then the results of tensile measurement applied to the strain-time correspondence (STC) principle, resulting in the tensile modulus master curves of the NBR nanocomposites as a function of time. For pure NBR, a master curve was constructed using only the horizontal shift factor, indicating that the material was structurally homogeneous. However, the NBR nanocomposites required both vertical shift (modulus shift, Γ(α)) and horizontal shift to form the master curves, indicating structural heterogeneity ascribed to the domain structure such as silicate tactoid. From master curves, we found that NBR nanocomposite with OC having polar organic intercalant, NBROC30B, had the lowest n value in the nanocomposites. This indicates that NBROC30B had the most dispersive silicate structure in the nanocomposites due to the polar interaction, being in good agreement with WXRD results. In particular, STC was not applicable at all nanocomposites with silicate loadings over 8 wt%, regardless type of organoclay, and tensile strength and toughness of the nanocomposites with silicate loading of 8 wt% were better than expected. These could be explained as the network-like percolation of the silicate tactoids in all nanocomposites with silicate loadings over 8 wt%, which were consistent with the results observed from HR-TEM. 相似文献
HDPE is a semi-crystalline thermoplastic polymer, with remarkable physical properties such as high chemical resistivity, high impact strength, and high modulus. Compared to the other semi-crystalline polymers, HDPE mostly possesses a high crystallinity, due to which, it exhibits a unique combination of mechanical and chemical resistance properties. In the present work, we have characterized the crystalline spherulites of neat and formulated HDPE compositions thoroughly characterized by different electron microscopy techniques such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM). One of the critical steps to obtaining well-resolved SEM images is the sample preparation that typically involves the etching process to elucidate the crystalline spherulites. Though such traditional methodology can effectively be used for neat HDPE, it leads to the creation of undesirable experimental artifacts when used to investigate formulated HDPE compositions. An alternate TEM-based method provides clear images without any artifacts, apart from being a direct and green method and taking relatively a lesser measurement time. 相似文献
In the current work we present results on the controlled/living radical copolymerization of acrylonitrile (AN) and 1,3‐butadiene (BD) via reversible addition fragmentation chain transfer (RAFT) polymerization techniques. For the first time, a solution polymerization process for the synthesis of nitrile butadiene rubber (NBR) via the use of dithioacetate and trithiocarbonate RAFT agents is described. It is demonstrated that the number average molar mass, , of the NBR can be varied between a few thousand and 60 000 g · mol−1 with polydispersities between 1.2 and 2.0 (depending on the monomer to polymer conversion). Excellent agreement between the experimentally observed and the theoretically expected molar masses is found. Detailed information on the structure of the synthesized polymers is obtained by variable analytical techniques such as infrared spectroscopy (IR), nuclear magnetic resonance (NMR) spectroscopy, differential scanning calorimetry, and electrospray ionization‐mass spectrometry (ESI‐MS).