共查询到20条相似文献,搜索用时 153 毫秒
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对甲基酚醛树脂热裂解产物的固体~(13)CNMR谢德民,张建国,王存国,王荣顺(东北师范大学化学系,长春,130024)关键词对甲基酚醛树脂,裂解,固体~(13)C,NMR酚醛树脂经热裂解制备的聚并苯导电材料在空气中稳定,由裂解温度可控制碳化程度,其本... 相似文献
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用~(13)C和~1HNMR波谱,探讨了聚环氧氯丙烷(PEPCH)的辐射效应,结果表明随着辐射剂量的增加,本体聚合物的~(13)CNMR谱中各基团的分辨率得以提高,~1HNMR谱中出现了裂解产物共振峰,T~1变短,表明PEPCH在限量空气氛中的辐射效应以大分子裂解反应为主,并通过特性粘度的测定,得到了证实。 相似文献
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以五甲基茂基三苄氧基钛[Cp* Ti(OBz)3] 和甲基铝氧烷( MAO) 组成的催化体用本体法合成出苯乙烯 乙烯共聚物Poly(S co E) .考察了共聚温度,共聚时间,Al/Ti 摩尔比,主催化剂浓度[Ti] 等条件对共聚反应的影响.共聚产物经沸丁酮,沸四氢呋喃(THF) 连续抽提分离,发现共聚物主要存在于THF 可溶级分中.可溶级分经DSC,13C NMR,WAXD,DMA 等手段分析,证明苯乙烯 乙烯共聚物为具有单一玻璃化转变温度( Tg) 无熔融温度的无规共聚物,显示弹性体的粘弹性行为. 相似文献
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以五甲基茂基三苄氧基钛〔Cp*Ti(OBz)3〕和甲基铝氧烷(MAO)组成的催化体 用本体法合成出苯乙烯-乙烯共聚物Poly(S-co-E)。考察了共聚温度,共聚时间 ,A1/Ti摩尔比,主催化剂浓度〔Ti〕等条件对共聚反应的影响。共聚产物经沸丁酮,沸四氢呋喃(THF)连续抽提分离,发现共聚物主要存在于THF可溶级分中。可溶级分经DSC,^13C-NMR,WAXD,DMA等手段分析,证明苯乙烯-乙烯共聚物为 相似文献
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双(环戊二烯基)二氯化锆载体催化剂催化乙烯/α—烯烃共聚合 总被引:7,自引:1,他引:7
合成了3种Zr/甲基铝氧烷(MAO)/SiO2型载体催化剂,考察了不同MAO投料量对载锆反应及催化活性的影响,研究了乙烯聚合及乙烯/α-烯烃共聚合,结果表明,该催化剂对己烯和辛烯有很强的共聚作用,而对癸烯的共聚能力较弱,解释了α-烯烃碳链增长对乙烯/α-烯烃共聚催化活性的影响,SEM分析表明,α-烯烃的加入有利于聚合物形态原改善。 相似文献
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Thor Kamfjord Thale Sofie Wester Erling Rytter 《Macromolecular rapid communications》1998,19(10):505-509
Silica supported (butylcyclopentadienyl)2ZrCl2/MAO catalysts were synthesized according to the “incipient wetness” method from a solution of metallocene in a liquid monomer. The monomer was allowed to polymerize yielding a catalyst containing polyhexene (PH), polystyrene (PS) or polyoctadiene (PO). One catalyst containing no polymer was also synthesized. The catalysts were used to polymerize ethene at 70°C and 4 bar total pressure. The measured average activities were 5 300 kg PE/(mol Zr · h) for (BuCp)2ZrCl2/MAO/PH/SiO2, 8 600 kg PE/(mol Zr · h) for (BuCp)2ZrCl2/MAO/PS/SiO2, 3 400 kg PE/(mol Zr · h) for (BuCp)2ZrCl2/MAO/PO/SiO2 and 5 700 kg PE/(mol Zr · h) for (BuCp)2ZrCl2/MAO/SiO2. The polyhexene, polystyrene or polyoctadiene in the catalyst forms a protective layer around the active sites. Even after exposure to air for five hours these catalysts retain some polymerization activity. 相似文献
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James C. W. Chien Bor-Ping Wang 《Journal of polymer science. Part A, Polymer chemistry》1988,26(11):3089-3102
Ethylene was polymerized by Cp2ZrCl2–methylaluminoxane (MAO) catalysts where a portion of the MAO was replaced with trimethyl aluminum (TMA). At a total Al to Zr ratio of 1070, there is neither appreciable loss of productivity nor change in polymerization profile for TMA/MAO ≤ 10. The productivity is reduced only by two- to three-fold for TMA/MAO ≤ 100 accompanied by a 10 min induction period. Aging of this catalyst did not affect the induction period, but improves its productivity. The kinetic isotope effect for radiolabeling with tritiated methanol is 2.0. About 40% of the Zr is active for the catalyst with {99 [TMA] + 1[MAO]} to Zr ratio of 100. The rate constants for propagation and chain transfer were obtained. The mechanisms for the mixed TMA and MAO cocatalyst system are discussed. The results of this work have important practical significance. MAO is a hazardous material to synthesize and only in low yields. The replacement of > 90% of MAO with TMA represents a substantial saving since as much as 0.1M of the former is commonly used for a polymerization. 相似文献
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As one of the most important catalysts in polyethylene industry,Phillips catalyst(CrO_x/SiO_2)was quite unique for its activation by ethylene monomer without using any activator like alkyl-aluminium or MAO.In this work,the density functional theory(DFT)calculation combined with paired interacting orbitals(PIO)method was applied for the theoretical studies on coordination reaction mechanism between ethylene monomer and two model catalysts namely Cr(Ⅱ)(OH)_2(M1) and silsesquioxane-supported Cr(Ⅱ)(M2)as sur... 相似文献
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K. M. Bichinho Gilvan P. Pires F. C. Stedile J. H. Z. dos Santos 《Spectrochimica Acta Part B: Atomic Spectroscopy》2002,57(12):1877-1884
Metal contents in polymerization catalysts were comparatively determined by Rutherford backscattering spectrometry (RBS), X-ray photoelectron spectroscopy (XPS) and X-ray fluorescence (XRF) spectroscopy. Catalysts were prepared by grafting metallocene onto bare silica or onto silica chemically modified with methylaluminoxane (MAO). Catalysts were compressed as self-supporting pellets (RBS and XRF), or mounted on adhesive copper tape (XPS). The proximity of the mass of the atomic nuclei did not allow resolution by RBS of the signals corresponding to Zr and Nb, nor Si and Al in catalyst systems such as (nBuCp)2ZrCl2/Cp2NbCl2/MAO/SiO2. On the other hand, Zr, Nb, Si and Al lines were completely resolved in an XRF spectrum. For supported metallocenes on bare silica, XPS measurement was ca. 40% higher than that obtained by RBS. Silica-supported zirconocene showed good agreement in Zr content determination by XRF and RBS. 相似文献
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Horst Schneider Gerd T. Puchta Franz A. R. Kaul Gabriele Raudaschl-Sieber Frdric Lefebvre Guillaume Saggio Dimitrios Mihalios Wolfgang A. Herrmann Jean Marie Basset 《Journal of molecular catalysis. A, Chemical》2001,170(1-2):127-141
The modification of a mesoporous silica surface with Si(Ind)(CH3)2Cl and the immobilization of CpZr(NMe2)3 on this surface was studied via IR-spectroscopy. To reduce side reactions, the indenyl-modified silica was reacted with hexamethyldisilazane (HMDS) under IR-control before the CpZr(NMe2)3-immobilization. The role of the hydroxyl group protection with HMDS is discussed. The surface modifications have been repeated via Schlenk technique at the same conditions and the surface modifications were studied with 13C CP MAS–NMR, 1H MAS–NMR, elemental-, SEM- and BET-analysis. The surface species of the resulting catalysts are discussed. The precatalysts have been treated with methylaluminoxane (MAO) (Al:Zr (mol:mol)=500:1) and the resulting Zr contents (leaching-effect) are discussed. All catalysts have been tested in ethylene and propylene polymerization. 相似文献
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James C. W. Chien Abbas Razavi 《Journal of polymer science. Part A, Polymer chemistry》1988,26(9):2369-2380
Bis(neomenthyl cyclopentadienyl)zirconium dichloride/methyl aluminoxane (η5-(NMCp)2ZrCl2/MAO) catalyst has been investigated for ethylene polymerization. About 51% of the Zr forms active sites more or less instantaneously according to quenching with tritiated methanol. There is an initial drop of rate of polymerization, Rp, of about 30% which remains constant thereafter. The catalytic activity increases monotonically with temperature; it is proportional to [MAO]1.75 at a constant [Zr] = 1.5 μM and proportional to [Zr]?1.2 at a constant [MAO] = 64.5 mM. At very large [MAO]/[Zr], the catalyst has extremely high activity; κp = 5 × 103 (Ms)?1 at 50°C. There is also facile chain transfer to aluminum, κ = 0.14 s?1 at 50°C. Both κp and κ are about 30 times greater than the corresponding rate constants for MgCl2 supported TiCl3 catalysts. The TiCl3/MgCl2 and (NMCp)2/MAO catalysts have nearly the same activation energy for propagation (ca. 7 kcal/mol?1). The higher activity of the latter is due to its larger preexponential factor in κp. The dependence of catalytic activity on the [MAO]/[Zr] ratio may be explained by rapid association-dissociation equilibria of MAO involving acid-base and/or electron deficient bridge complexation. 相似文献
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《Journal of molecular catalysis. A, Chemical》1998,128(1-3):191-200
The evolution of methane from methylaluminoxane (MAO) solutions is enhanced in the presence of homogeneous metallocenes. This reaction serves as a model for the deactivation of metallocene catalysts. By supporting different metallocenes on a silica/MAO carrier the deactivation reaction by alpha-hydrogen transfer among metallocene active sites and aluminum alkyls can be suppressed. The suppression of alpha-hydrogen transfer is proven for different Al/Zr ratios and by near independence of the polymerization activity on the catalyst aging time, after reaching maximum activity. Aluminum alkyls and MAO leach Cp2ZrCl2 from the carrier, the leached metallocene is only active in polymerization if MAO is present. 相似文献
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A silica-magnesium bisupport (SMB) was prepared by a sol-gel method for use as a support for the impregnation of TiCl4 and rac-Et(Ind)2ZrCl2. The prepared rac-Et(Ind)2ZrCl2/TiCl4/MAO(methylaluminoxane)/SMB catalyst was applied to the ethylene-hexene copolymerization under the conditions of variable Al(MAO)/Zr ratio and fixed Al(TEA, triethylaluminum)/Ti ratio. The effect of Al(MAO)/Zr ratio on the physical properties and chemical composition distributions of ethylene-hexene copolymers produced by a rac-Et(Ind)2ZrCl2/TiCl4/MAO/SMB catalyst was investigated. The catalytic activity of rac-Et(Ind)2ZrCl2/TiCl4/MAO/SMB was steadily increased with increasing Al(MAO)/Zr ratio from 200 to 500. The ethylene-hexene copolymer produced with Al(MAO)/Zr = 300, 400, and 500 showed two melting points at around 110 °C and 130 °C, while that produced with Al(MAO)/Zr = 200 showed one melting point at 136 °C. The number of chemical composition distribution (CCD) peaks was increased from 4 to 7 and the short chain branches of ethylene-hexene copolymer were distributed over lower temperature region with increasing Al(MAO)/Zr ratio. The lamellas in the copolymer were distributed over lower temperature region and the small lamellas in the copolymer were increased with increasing Al(MAO)/Zr ratio. The rac-Et(Ind)2ZrCl2/TiCl4/MAO/SMB catalyst preferably produced a ethylene-hexene copolymer with non-blocky sequence ([EHE]) with increasing Al(MAO)/Zr ratio. 相似文献
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Henri Cramail Alain Deffieux Jean-Noêl Pédeutour Karunakaran Radhakrishnan 《Macromolecular Symposia》2002,183(1):113-120
In this paper, we investigate different routes to lower drastically the amount of methylaluminoxane (MAO) required to activate racEt(Ind)2ZrX2 catalysts towards olefin polymerization. A first approach consists in replacing Cl ligands by more easily extractable X groups such as Me, CH2Ph or NMe2 groups. A second method focuses on the preparation of TMA-depleted MAO either by pumping off TMA from commercial MAO or by exploring new synthetic source to MAO via non-hydrolytic processes such as the reaction of TMA with benzophenone. Both methods allowed us to produce polyolefins with a maximal catalytic activity for Al/Zr ratios not exceeding 150, i.e. ratio 20 times lower than those required in the presence of commercial MAO. 相似文献