共查询到20条相似文献,搜索用时 296 毫秒
1.
2.
Using 70 mol % norbornene in the monomer mixture before polymerization, the influences of different polymerization conditions were studied. It was found that by increasing the temperature from 10 to 70°C, the yield increased and the molecular weight decreased; and when increasing the ethylene pressure from 2 to 6 atm, yield and molecular weight increased. The highest glass transition temperatures, however, were achieved at 30°C and 4 atm. Further improvements could be obtained by increasing the amount of catalyst or Al/Zr ratio. Using the conditions of 30°C, 4 atm, 4 mg catalyst, 3000 Al/Zr, 250 mL toluene solution, and 30 min, the amount of norbornene was increased from 31.1 to 90 g, resulting in an increase in the glass transition temperature from 98 to 155°C. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1063–1070, 1997 相似文献
3.
《国际聚合物材料杂志》2012,61(10):776-786
The late transition metal catalyst of [2,6-diacethylpyridinebis(2,6-diisopropylphenylimine)]cobalt(II) dichloride was prepared under controlled conditions and used for polymerization of ethylene. Methylaluminoxane (MAO) and triisobuthylaluminum (TIBA) were used as a cocatalyst and a scavenger, respectively. The highest activity of the catalyst was obtained at about 30°C; the activity decreased with increasing temperature. At polymerization temperatures higher than 50°C not only was a sharp decrease in the activity observed but also low molecular weight polyethylene product that was oily in appearance was obtained. The polymerization activity increased with increasing both of the monomer pressure and [MAO]:[Co] ratio. However, fouling of the reactor was strongly increased with increasing both of the monomer pressure and the amount of MAO used for the homogeneous polymerization. Hydrogen was used as the chain transfer. The activity of the catalyst and the viscosity average molecular weight (Mv) of the polymer obtained were not sensitive to hydrogen concentration. However, the viscosity average molecular weight of the polymer decreased with the monomer pressure. The (Mv), the melting point, and the crystallinity of the resulting polymer at the monomer pressure of 1 bar and polymerization temperature of 20°C were 1.2 × 105, 133°C, and 67%, respectively. Heterogeneous polymerization of ethylene using the catalyst and the MAO/SiO2 improved morphology of the resulting polymer; however, the activity of the catalyst was also decreased. Fouling of the reactor was eliminated using the supported catalyst system. 相似文献
4.
5.
Propylene is polymerized in a slurry over a TiCl3 · ?AlCl3 catalyst with a DEAC cocatalyst, approaching conditions of industrial relevance. The effects of various parameters such as temperature, pressure, cocatalyst-to-catalyst ratio, hydrogen concentration, and polymerization time are investigated with particular emphasis on the yield, tacticity, molecular weight, bulk density, and particle size of the resulting polymer. The highest yield and isotactic content are obtained at an Al/Ti ratio of 6, temperature of 70°C, and pressure of 9 kg/cm2g. The polymerization rate is found to be first order up to a monomer concentration of 2.5 mol/L. The overall activation energy of polymerization calculated from an Arrhenius plot is found to be 11.6 kcal/mol. A correlation between MFI and molecular weight is also presented. © 1994 John Wiley & Sons, Inc. 相似文献
6.
Four cocatalysts, referred to as ethylaluminoxanes, were synthesized by the reaction between triethylaluminium (AIEt3) and water under various molar ratios of H2O/Al at ?78°C. Aluminoxanes were used as cocatalysts for a MgCl2‐supported Ziegler–Natta catalyst for propylene polymerization at temperatures ranging from 70 to 100°C. When the polymerization was activated by AlEt3, the activity as well as the molecular weight and isotacticity of the resulting polymer gradually dropped as the temperature varied from 70 to 100°C. When ethylaluminoxane was employed as the cocatalyst, good activity and high molecular weight and isotacticity were obtained at 100°C. Furthermore, when the cocatalyst varied from AlEt3 to ethylaluminoxane, the atactic fraction and polymer fraction with moderate isotacticity decreased and the high isotactic fraction slightly increased, which indicated that the variation of the cocatalyst significantly affects the isospecificity of active sites. It was suggested that the reactivity of the Al‐Et group and the size of the cocatalyst were correlated to the performance of the Ziegler–Natta catalyst at different temperatures. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1978–1982, 2006 相似文献
7.
tert‐Butyl vinyl ether (tBVE) was polymerized with the catalyst dimethyl[rac‐ethylenebis(indenyl)] zirconium (ansa‐zirconocene) with tri(pentafluorophenyl) borane [B(C6F5)3] as a cocatalyst. The effects of various polymerization conditions, such as the polymerization time, type of polymerization solvent, polymerization temperature, and catalyst concentration, on the conversion of tBVE into poly(tBVE), its molecular weight and molecular weight distribution, and its stereoregularity were investigated. The maximum conversion of tBVE into poly(tBVE) was over 90% at a polymerization temperature of ?30°C with an ansa‐zirconocene and B(C6F5)3 concentration of 3.0 × 10?7 mol/mol of tBVE, respectively. The number‐average molecular weights of poly(tBVE) ranged from approximately 14,000 to 20,000, with a lower polydispersity index (weight‐average molecular weight/number‐average molecular weight) ranging from 1.48 to 1.77, at all polymerization temperatures. The number‐average molecular weight of poly(tBVE) increased with decreases in the polymerization temperature and catalyst concentration. The mm triad sequence fraction of poly(tBVE) polymerized with ansa‐zirconocene/B(C6F5)3 at ?30°C was much higher than that of poly(tBVE) polymerized with the B(C6F5)3 catalyst at ?30°C, and this indicated that the ansa‐zirconocene/B(C6F5)3 catalyst system affected the isospecific polymerization of tBVE. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
8.
Ricardo Baumhardt-Neto Griselda B. Galland Raquel S. Mauler Raul Quijada 《Polymer Bulletin》1998,40(1):103-109
The copolymerization of ethylene with 1-hexene using Et[Ind]2ZrCl2/MAO as catalyst was studied by multivariate methods. Three complete factorial designs were performed to study the influence
of 1-hexene concentration, reaction temperature and [Al]/[Zr] ratio on catalytic activity, copolymer viscosity, crystallinity
and melting point. Since the [Al]/[Zr] ratio has a small effect on the catalytic activity, a fourth design with 1-hexene and
temperature was developed, giving higher catalytic activities. Temperature and 1-hexene concentration were the main effects
found in the system. A second order effect arising from 1-hexene versus [Al]/[Zr] ratio was also detected. Polymer viscosity,
crystallinity and melting points decreased with 1-hexene concentration. Viscosity decreased with temperature whereas crystallinity
increased when the temperature was raised from 30 to 60 °C.
Received: 13 June 1997/Revised version: 2 November 1997/Accepted: 21 November 1997 相似文献
9.
Summary Ethylene and propylene were copolymerized in n-heptane in the presence of high activity heterogeneous Ziegler-Natta catalyst to study the effect of the cocatalyst on the microstructure and molecular weight of the copolymer. Seven aluminium alkyls of structure Al((CH2)nCH3)3, where n = 0—3, 5, 7 or 11, and one of structure Al(C(CH3)3)3, were used as cocatalysts. The effect of the Al/Ti mole ratio was also studied. Modern molecular modelling techniques were used to calculate the volume of the cocatalyst and the electron density around aluminium. The size of the cocatalyst molecule was found to have a marked effect on the activity of the catalyst: the smaller the cocatalyst the higher the activity. Higher electron density around aluminium increased the randomness of the copolymer. 相似文献
10.
在WCl_6-C_4H_(?)OH催化体系中各种助催化剂对聚合活性的影响表明,以Al(i-Bu)_(?)为助催化剂体系的聚合活性最高,AlEt_2Cl和AlEt_3体系的聚合活性相近;CH_3PhOH/Al(i-Bu)_3=1(mol比)的助催化剂体系和Al(i-Bu)_3体系的聚合活性相近,但适宜Al/W(mol比)的范围增宽,醇类作助催化剂的配位体时,体系的聚合活性降低;在实验条件下,Al(i-Bu)_2H体系无聚合活性;以AlEt_3、Al(i-Bu)_3、Al(i-Bu)_2OPhCH_3和Al(i-Bu)_2OC_4H_(?)分别作助催化剂时,对产物分子量影响较小,并均能得到1,2-结构含量大于85%的1,2-聚丁二烯。 相似文献
11.
Observation on different reducing power of cocatalysts on the Ziegler–Natta catalyst containing alkoxide species for ethylene polymerization 下载免费PDF全文
Goond Hongmanee Saovalak Sripothongnak Bunjerd Jongsomjit Piyasan Praserthdam 《应用聚合物科学杂志》2014,131(20)
In this work, the effects of three types of cocatalyst having different alkyl groups, such as triethylaluminium (TEA), triisobutylaluminum (TiBA), and trioctylaluminium (TnOA), and their concentrations on the catalytic activity and polymer properties were investigated for the Ziegler–Natta catalyst containing alkoxide species. The drastic escalation of catalytic activity was observed when the ratio of Al/Ti was increased only for TEA because of its good diffusivity as proven by the electron spin resonance technique. Moreover, it was found that the characteristic of the alkyl group in cocatalyst affected on the chain transfer ability. The chain transfer ability of TnOA was found to be equal to the TiBA in spite of its concentration was higher. By the way, the cocatalyst types and their concentrations did not affect on the variety of active sites as seen in molecular weight distribution of polymer. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40884. 相似文献
12.
M. Pérez-Luna A. Cosultchi J. A. Toledo-Antonio L. Díaz-Garcia 《Catalysis Letters》2009,128(3-4):290-296
Sulfated mixed oxides, SO 4 = /Ni–Al–O and SO 4 = /Zr–Al–O were evaluated for double bond isomerization (DBI) of 1-hexene using helium and hydrogen as carrier gases. The increase of temperature from 100 to 200 °C seems to favor the deprotonation pathway and contribute to increase the 1-hexene conversion for both catalysts and without regard of the carrier gas. The results indicate that temperature it is the main factor that contributes to improve both conversion and selectivity towards (cis + trans)-2-hexene, while the reductive atmosphere beneficiate only the SO 4 = /Ni–Al–O catalyst performance, as hydrogen prevents this catalyst from a fast deactivation. 相似文献
13.
《Polymer-Plastics Technology and Engineering》2013,52(4):601-618
Polymerization methods of ethylene include the slurry, solution, and gas-phase processes. This study investigates polymerization conditions and kinetics under slurry process. Typical metallocene catalyst/cocatalyst Cp2ZrCl2/MAO system was used for ethylene polymerization. Two kinds of polymerization kinetics were compared in this study, multiple active-site model and transfer-effect model. The kinetic studies used metallocene-type polymerization kinetics, including catalyst activation, initiation, chain propagation, chain transfer, and termination steps. In addition, kinetic constants of polymerization reaction model were calculated. Calculation results of catalyst activity and molecular weight were compared with experimental results, indicating their good correlation. Moreover, the conventional polymerization was modified to accurately predict the molecular weight behaviors under various reaction conditions with the proposed transfer-effect model. Exactly, how reaction time, pressure, catalyst concentration, and cocatalyst ratio affect catalyst activity and molecular weight of the polymer were also discussed. 相似文献
14.
A study has been made of ethylene polymerization in pseudo-solution with a catalyst system TiCl4/Al(C2H5)2Cl/Mg(C6H5)2 in the presence of hydrogen as a regulator of polyethylene molecular weight. The polymerization process in pseudo-solution by adjustment of hydrogen makes it possible to produce polyethylene having a wide range of molecular weights. For this purpose melt indices between 0°–50°C/min are desirable and these values are not reached with a suspension type of ethylene polymerization with a catalyst system TiCl4/Al(C2H5)2Cl/Mg(C6H5)2. The effect of the molar ratio cocatalyst/catalyst (Al/Ti and Mg/Ti) on the catalyst activity and on the polyethylene molecular weight was studied, together with the content of hydrogen as a regulator of the molecular weight. The catalyst productivity increased to some limiting molar ratio Mg/Ti and Al/Ti and further increase of organometallics in the catalyst system did not influence the polymer molecular weight. In the case of ethylene polymerization with this catalyst combination in the presence of hydrogen, some activation of the catalyst was observed. Two mechanisms, which may account for the activation effect of the hydrogen are discussed. 相似文献
15.
16.
Zhi Ma Yucai Ke Hang Wang Cunyue Guo Mingge Zhang Wen‐Hua Sun Youliang Hu 《应用聚合物科学杂志》2003,88(2):466-469
A supported iron‐based diimine catalyst (SC) was prepared by immobilization of 2,6‐bis[1‐(2,6‐diisopropylphenylimino)ethyl]pyridine iron chloride (I) on silica and employed in ethylene polymerization. The kinetic behavior of ethylene polymerization with SC was studied. The effects of the Al/Fe molar ratio, reaction temperature, and cocatalyst on the catalytic activity as well as the melting temperature, molecular weight, and morphology of the polymers obtained were also investigated. The results showed that good catalytic activities can be obtained even with a small amount of the cocatalyst methylaluminoxane (MAO) or triethylaluminum (AlEt3). The polyethylenes obtained with a supported catalyst had higher molecular weight, higher melting temperature, and better morphology than those obtained with a homogeneous catalyst. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 466–469, 2003 相似文献
17.
Summary The influence of various cocatalysts on the activity and stereospecificity of a supported magnesium–titanium catalyst, generated
by in situ reduction of titanium (IV) chloride using a Grignard reagent (MgCl2/TiCl3) or prepared by the recrystallization method (MgCl2/2M2P/ED/TiCl4, 2M2P= 2-methyl-2-pentanol, ED= dibutyl phthalate or ethyl benzoate), in the 1-hexene polymerization was investigated. The
MgCl2/TiCl3 catalyst showed the highest activity but the lowest stereospecificity in the 1-hexene polymerization with all investigated
cocatalysts. The MgCl2/2M2P/ED/TiCl4 catalyst with dibutyl phthalate as an internal electron donor was characterized by the highest stereospecificity and led
to the polymers with high molecular weight. All catalysts showed the highest activity and stereospecificity when triisobutylaluminium
was used as a cocatalyst. The addition of a small amount of ethyl benzoate as an external electron donor ([Al]/[ED] 10:1)
led to considerable improvement of the stereospecificity of the MgCl2/TiCl3 catalyst in comparison with the catalysts prepared by the recrystallization method. 相似文献
18.
Hossein Mahdavi Alireza Badiei Gholam Hossein Zohuri Abbas Rezaee Roghieh Jamjah Saied Ahmadjo 《应用聚合物科学杂志》2007,103(3):1517-1522
An iron‐based catalyst of 2,6‐bis‐[1‐(2‐methylphenylimino)ethyl]pyridine iron dichloride was prepared. The ligand was prepared using 2,6‐diacetylpyridine as the starting chemical under controlled conditions. The preparation procedure was followed using 13C‐NMR, 1H‐NMR, FT‐IR, MS (mass spectroscopy), and elemental analysis methods. The homogeneous polymerization of ethylene was carried out using the prepared catalyst in toluene media. Methyl aluminoxane (MAO) was used as a cocatalyst. The effect of the [Al] : [Fe] molar ratio, polymerization temperature, and monomer pressure of 202,000 to 454,500 Pa on the polymerization behavior were studied. The highest activity of the catalyst was obtained at 30°C, the activity decreased with increasing temperature, while increasing pressure linearly increased its activity. The molecular weight distribution of the polyethylene obtained was 1.25 to 1.72. A weight average molecular weight of 7.1 × 104 and 1.5 × 103 were obtained. The crystallinity of the polymer was about 19% and its melting point was about 65°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1517–1522, 2007 相似文献
19.
The bisupported Ziegler–Natta catalyst system SiO2/MgCl2 (ethoxide type)/TiCl4/di‐n‐butyl phthalate/triethylaluminum (TEA)/dimethoxy methyl cyclohexyl silane (DMMCHS) was prepared. TEA and di‐n‐butyl phthalate were used as a cocatalyst and an internal donor, respectively. DMMCHS was used as an external donor. The slurry polymerization of propylene was studied with the catalyst system in n‐heptane from 45 to 70°C. The effects of the TEA and H2 concentrations, temperature, and monomer pressure on the polymerization were investigated. The optimum productivity was obtained at [Al]/[DMMCHS]/[Ti] = 61.7:6.2:1 (mol/mol/mol). The highest activity of the catalyst was obtained at 60°C. Increasing the H2 concentration to 100 mL/L increased the productivity of the catalyst, but a further increase in H2 reduced the activity of the catalyst. Increasing the propylene pressure from 1 to 7 bar significantly increased the polymer yield. The isotacticity index (II) decreased with increasing TEA, but the H2 concentration, temperature, and monomer pressure did not have a significant effect on the II value. The viscosity‐average molecular weight decreased with increasing temperature and with the addition of H2. Three catalysts with different Mg/Si molar ratios were studied under the optimum conditions. The catalyst with a Mg/Si molar ratio of approximately 0.93 showed the highest activity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1177–1181, 2003 相似文献
20.
Suspension polymerization of ethylene with the catalyst system TiCl4/Al(C2H5)2Cl/Mg(C6H5)2, at different molar ratios Mg/Ti and Al/Ti, was studied. The transition metal compounds in the catalyst complex formed in this system were found to consist only of Ti(II) and Ti(III), without free Ti(IV); but even with a Ti(II) content of 30% the catalyst was highly active. The influence of the molar ratio cocatalyst/catalyst (Al/Ti and Mg/Ti) on the catalyst activity and on the polyethylene molecular weight was studied, together with the reduction of TiCl4 by Al(C2H5)2Cl and Mg(C6H5)2 in the reduction step. The polymer yield increased to some limiting molar ratio Mg/Ti and to some limit ratio Al/Ti and further increase of organometal concentration in the system has practically no influence on the catalyst productivity. Dependence of the polyethylene molecular weight on the molar ratios Mg/Ti and Al/Ti was observed, proving the presence of chain transfer reactions with organometallics. 相似文献