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采用Material Studios对二氧化硅形成的三种晶面进行计算,并模拟甲基铝氧烷(MAO)在不同晶面产生的吸附行为。结果表明,当形成不同的晶面时,二氧化硅晶体的带宽变宽,表明频带中电子的有效质量越小,非局域性越大,并且频带的原子轨道扩展越强。MAO在SiO_2(100)面吸附形成的带隙为0.016eV,在Si(110)面吸附形成的带隙为0.086eV,而在SiO_2(111)面形成的带隙为0.180eV,表明MAO在SiO_2(111)面产生的吸附最强。MAO在SiO_2(111)形成的吸附行为与自由羟基形成映衬,而自由羟基的减少是由桥连羟基随机缩合反应导致。 相似文献
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基于传统釜式反应器的烷基铝氧烷生产技术仍存在过程危险、控制难、收率低、经济性差等问题,首先回顾了传统烷基铝水解路线中将水以不同方式引入反应体系的过程,重点介绍了应用3D打印和流动化学技术的烷基铝氧烷合成系统设计,包括甲基铝氧烷(MAO)与异丁基铝氧烷(IBAO)合成、产物在线监测、反应焓测定以及改性甲基铝氧烷(MMAO)合成。流动化学系统将水以单分散微水滴的形式引入反应体系,提高了反应的传热、传质性能,实现了烷基铝氧烷的小型化、连续化、安全化生产,产品收率高,其助催化活性均达到或超过市售产品水平,并可通过微反应器放大技术进一步扩大生产能力。流动化学合成烷基铝氧烷的技术具有广阔应用前景,也为其他快速、强放热、多相反应提供了解决方案。 相似文献
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硅铝氧烷溶胶复合PMMA增强NBR 总被引:3,自引:0,他引:3
用2-甲基丙烯酸与硅酸钠,硝酸名反应,制得硅铝氧溶胶,。在该溶胶存在下进行甲基丙烯酸甲酯无皂乳液聚合,蜊硅铝氧烷溶胶复合聚甲基丙烯酸甲酯填充到丁腈橡胶中,其硫化胶性能与填充硅铝氧溶胶者相比,拉伸强度有明显提高,硫化促进作用也很明显。从拉伸断裂面的SEM照片可以看出前者呈韧性裂,而后者为脆性断裂。 相似文献
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以Nd(Oi-Pr)3/MAO为催化体系进行月桂烯聚合。结果表明,该催化体系具有高活性和高顺式-1,4选择性,所得聚合物顺式-1,4-结构摩尔分数可达95.6%。聚合温度的升高可显著提高聚合速率,在0℃下聚合24 h,聚合物收率仅为15.8%;而在70℃下聚合1 h,聚合物收率可达99.0%。随着聚合温度的升高,链转移反应增强,聚合物的相对分子质量下降;同时由于体系中所形成的对式Nd-η^3-烯丁基转变为热力学上更为稳定的同式异构体,使得顺式-1,4-结构含量下降。 相似文献
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硅铝氧烷溶胶是一种能使水泥等无机材料与有机颜料牢固结合的物质。本文介绍在超声波的作用下制得的硅铝氧烷溶胶。在自制的彩色水泥加加入硅铝氧烷溶胶并对彩色水泥的耐候性,耐溶剂性,耐热老化性进行测试,效果良好。 相似文献
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Butadiene was polymerized using a monotitanocene complex of η5‐pentamethylcyclopentadienyltribenzyloxy titanium [Cp*Ti(OBz)3] in the presence of four types of modified methylaluminoxanes (mMAO), which contained different amounts of residual trimethylaluminum (TMA). The titanium oxidation states in Cp*Ti(OBz)3/mMAO and Cp*Ti(OBz)3/mMAO/triisobutylaluminum (TIBA) catalytic systems were determined by redox titration method. The effects of various oxidation states of titanium active species on butadiene polymerization were investigated. It was found that Ti(III) active species is more effective for preparing polybutadiene with high molecular weight. The addition of TIBA to the Cp*Ti(OBz)3/mMAO system could reduce a greater number of Ti(IV) complexes to Ti(III) species and lead to significant increases of polymerization activity and molecular weight of polymer, whereas the polybutadiene microstructure was only slightly changed. On the basis of microstructure and property characterization by FTIR, 13C‐NMR, DSC, and WAXD, all resultant polymers were proved to be amorphous polybutadiene with mixed 1,2; cis‐1,4; and trans‐1,4 structures. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2494–2500, 2004 相似文献
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The effects of residual trimethylaluminum (TMA) in methylaluminoxane (MAO) and external alkylaluminum (AlR3) on styrene syndiotactic polymerization with CpTi(OBz)3 as a catalyst precursor have been investigated by comparison of the polymerizations using a series of MAOs containing various amounts of residual TMA. The results indicated that the residual TMA plays a deciding role in the reduction of Ti and promotes formation of the active centers for styrene polymerization. The variations in the catalytic activity and molecular weight of the polymer caused by additions of external AlR3, AlMe3, AlEt3, Al(i-Bu)3, and AlEt2Cl, into the catalyst systems are quite different, depending the properties of MAO used and the type of the external AlR3. It was found that there is an optimum range of concentration ratio of the free AlR3, including the residual TMA and external AlR3, to the total Al compounds, 25–35 mol %, for maximum catalytic activities. The catalytic activities decrease at the ratios either above or below the range. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 765–770, 1998 相似文献
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The effect of different aluminum‐based cocatalysts (MAO, pMAO, and TMA) on butadiene (Bd) polymerization catalyzed by VO(P204)2 was investigated. The bimodal dependence of the polymer yield on the [MAO]/[V] molar ratio was revealed, and an highest polymer yield was achieved at a rather low [MAO]/[V] molar ratio ([MAO]/[V] = 13). The microstructures of the resulting poly(Bd)s were also significantly influenced by the ratio. In the TMA or pMAO system, the polymer yields were also very sensitive to the [Al]/[V] molar ratio. However, the microstructures of the resulting poly(Bd)s were almost independent of the ratio. In relation to the microstructures of poly(Bd)s obtained by the MAO and TMA systems at various temperatures, the 1,2‐unit contents were found to be the most abundant microstructure for both systems. In the pMAO system, the trans‐1,4‐units were the most abundant. The results of the additions of Lewis bases (THF and TPP) into Bd polyerization system comfirmed the existing of the two types of the reactions of VO(P204)2‐MAO catalyst and had the polymerization process controlled to some extent. The different thermal behaviors of these catalytic systems also show that multiple types of active centers were formed during the reaction between VO(P204)2 and MAO. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 相似文献
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Syndiotactic polystyrene (sPS) was synthesized with a novel monotitanocene complex of η5‐pentamethylcyclopentadienyltri‐4‐methoxyphenoxy titanium [Cp*Ti(OC6H4OCH3)3] activated by methylaluminoxane (MAO) in different polymerization media, including heptane, toluene, chlorobenzene, and neat styrene. In all cases bulk polymerization produced sPS with the highest activity and molecular weight. Solution polymerization produced much better activity in heptane than in the other solvents. Using a solvent with a higher dipole moment, such as chlorobenzene resulted in lower activity and syndiotacticity because of the stronger coordination of solvent with the Ti(III) active species, which controlled syndiospecific polymerization of styrene. With bulk polymerization at a higher polymerization temperature the Cp*Ti(OC6H4OCH3)3–MAO catalyst produced sPS with high catalytic activity and molecular weight. The external addition of triisobutylaluminum (TIBA) to the Cp*Ti(OC6H4OCH3)3–MAO system catalyzing styrene polymerization led to significant improvement of activity at a lower Al:Ti molar ratio, while the syndiotacticity and molecular weight of the yields were little affected. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1243–1248, 2001 相似文献
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Liqiang Cui Xiaowei Ba Hongxiang Teng Laiqiang Ying Kechang Li Yingtai Jin 《Polymer Bulletin》1998,40(6):729-734
Summary
The polymerization of butadiene(Bd), isoprene(Ip) and styrene(St) has been examined using the six catalyst systems composed
of lanthanocene, (C5H9Cp)2NdCl(I), (C5H9Cp)2SmCl(II), (MeCp)2Sm OAr'(III), (Ind)2NdCl(IV), Me2Si(Ind)2NdCl(V) and (Flu)2NdCl(VI), and methylaluminoxane(MAO) respectively.
All of them can be used to form the polyisoprene with molecular weights of 1 to 10 thousand and cis-1,4-unit contents of 41
to 47%. (I), (II) and (III) of them can be also used to form the polybutadiene with molecular weights of 10 to 20 thousand
and cis-1,4-unit contents of 62 to 78%. In addition, the catalysts from (II) to (V) are still active for St polymerization
and (II) of them gives a syndio -rich random polystyrene. It is noteworthy that (II) and (III) are active for homopolymerization
of Bd, Ip and St in the same polymerization condition.
Received: 16 December 1997/Revised version: 17 March 1998/Accepted: 24 March 1998 相似文献
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The polymerization of styrene with two pyrazolylimine nickel (II) complexes of (2-(C3HN2Me2-3, 5)(C(Ph) = N(4-R2C6H2(R1)2-2, 6)NiBr2 (Complex 1 , R1 = iPr, R2 = H; Complex 2 , R1 = H, R2 = NO2)) activated by methylaluminoxane was studied. The influences of polymerization parameters such as polymerization temperature, Al/Ni molar ratio, and reaction time on catalytic activity and molecular weight of the polystyrene (PS) were investigated in detail. The electron-withdrawing of nitro group in Complex 2 could not enhance the catalytic activity for styrene polymerization; however, the molecular weights of polymers were increased. Both of the two catalytic systems exhibited high activity [up to 8.45 × 105 gPS/(mol Ni h)] for styrene polymerization and provide PS with moderate to low-molecular weights (Mw = 2.21 × 104∼ 5.71 × 103 g/mol) and narrower molecular weight distributions about 2.0. The obtained PS were characterized by means of IR, 1H NMR, and 13C NMR techniques. The results indicated that the PS was atactic polymer. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献
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The polymerization of styrene with a series of bispyrazolylimine dinickel (II) complexes of bis‐2‐(C3HN2(R1)2‐3,5)(C(R2) = N(C6H3(CH3)2‐2,6)Ni2Br4 (complex 1 : R1 = CH3, R2 = Ph; complex 2 : R1 = CH3, R2 = 2,4,6‐trimethylphenyl; complex 3 : R1 = R2 = Ph; complex 4 : R1 = Ph, R2 = 2,4,6‐trimethylphenyl) in the presence of methylaluminoxane (MAO) was studied. The influences of polymerization parameters such as polymerization temperature, Al/Ni molar ratio, reaction time, and catalyst concentration on catalytic activity and molecular weight of the polystyrene were investigated in detail. The influence of the bulkiness of the substituents on polymerization activity was also studied. All of the four catalytic systems exhibited high activity (up to 10.50 × 105 gPS/(mol Ni h)) for styrene polymerization and provide polystyrene with moderate to low molecular weights (Mw = 4.76 × 104–0.71 × 104 g/mol) and narrower molecular weight distributions about 2. The obtained polystyrene was characterized by means of FTIR, 1H‐NMR, and 13C‐NMR techniques. The results indicated that the polystyrene was atactic polymer. The analysis of the end groups of polystyrene indicated that styrene polymerization with bispyrazolylimine dinickel complexes/MAO catalytic systems proceeded through a coordination mechanism. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011. 相似文献
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Anna Maria Raspolli Galletti Mohammad Hayatifar Yogesh Patil 《Polymer International》2010,59(8):1148-1153
Polymerization catalysts based on copper precursors appear particularly interesting due to the low metal cost, limited toxicity and modest sensitivity to deactivation by polar species. To date, α‐olefin and polar monomer coordination polymerization catalysed using copper catalysts has been scarcely investigated, and a good part of the literature is represented by patents. Here this research has been expanded to the study of the performances of bis(salicylaldiminate)copper(II)/methylaluminoxane (MAO) catalysts in the polymerization of n‐butyl methacrylate. The study of the catalytic activity of bis(salicylaldiminate)copper(II)/MAO systems in n‐butyl methacrylate polymerization was focused on the relationship between the catalytic behaviour and the main reaction conditions and ligand structures. The electronic and steric characteristics of the chelate ligands play an important role in the catalytic performances. The presence of electron‐withdrawing nitro groups on the chelate ligands increased the catalytic activity which reached 36 kgpolymer mol?1 h?1, the highest value up to now reported for copper systems in methacrylic or acrylic monomer polymerization. These performances were ascribed to copper catalysts activated by MAO: without copper precursor, working in the presence of MAO and free salicylaldimine ligand, complete inactivity was ascertained. Copyright © 2010 Society of Chemical Industry 相似文献