ESR studies on vanadocene/cocatalyst systems for ethylene polymerization

Three vanadocene–cocatalyst catalytic systems for ethylene polymerization—Cp₂ZrCl₂/Al₂Et₃Cl₃ [dichlorobis(η‐cyclopentadienyl)vanadium/ethylaluminumsesquichloride], Cp₂ZrCl₂/MAO [dichlorobis(η‐cyclopentadienyl)vanadium/methylaluminoxane] and Cp₂ZrCl₂/AlEt₃ [dichlorobis(η‐cyclopentadienyl)vanadium/triethylaluminum]—were monitored by electron spin resonance (ESR) spectroscopy. It was found that at least a certain kind of vanadium complex is formed after mixing dichlorobis(η‐cyclopentadienyl)vanadium with ethylaluminumsesquichloride. After introducing ethylene, a new kind of vanadium complex is detected by ESR. Ethylene can be polymerized by using a dichlorobis(η‐cyclopentadienyl)vanadium/ethylaluminumsesquichloride catalytic system. These results possibly indicate that the vanadium complex exists in the forms ClCp₂VClEtAlCl₂ and ClCp₂VClEtAlClEt, which are responsible for forming active centers. The Dichlorobis(η‐cyclopentadienyl)vanadium/methylaluminoxane and dichlorobis(η‐cyclopentadienyl)vanadium/triethylaluminum systems also were monitored by ESR. Completely different spectra were recorded compared to those of the dichlorobis(η‐cyclopentadienyl) vanadium/ethylaluminumsesquichloride system. Ethylene almost cannot be polymerized by the dichlorobis(η‐cyclopentadienyl)vanadium/methylaluminoxane and dichlorobis(η‐cyclopentadienyl)vanadium/triethylaluminum catalytic systems, showing that resultant vanadium complexes of dichlorobis(η‐cyclopentadienyl)vanadium/methylaluminoxane and dichlorobis(η‐cyclopentadienyl)vanadium/triethylaluminum catalytic systems are different from that arising from the dichlorobis(η‐cyclopentadienyl)vanadium/ethylaluminumsesquichloride system. Plausible mechanisms are suggested for this. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1188–1194, 2001     

Recycling of methylaluminoxane (MAO) cocatalyst in ethylene polymerization with supported metallocene catalyst

The economy of the metallocene catalyst system in olefin polymerization depends more on the cost of methylaluminoxane (MAO) cocatalyst rather than on the catalyst cost since high ratio of cocatalyst to catalyst is required to have sufficient activity. The conditions to minimize the consumption of MAO have been studied for the ethylene polymerization with supported metallocene catalyst. By introducing the prepolymerization step, in which the supported metallocene catalyst is activated at high MAO concentration before polymerization, the MAO could be recovered after the prepolymerization and recycled repeatedly for the subsequent activation with marginal decrease in activity. No extra MAO was needed during the main polymerization. The addition of small amount of MAO or less expensive alkylaluminum at each recycle step kept the catalyst activity to the initial level. It compensates the MAO losses occurring both by the incomplete decantation of MAO solution and by the reaction with metallocene complex or impurities. As a result, the actual consumption ratio of Al/Zr in moles in commercial applications could be reduced to about 30 without sacrificing the activity. This value is significantly low considering that conventionally an Al/Zr ratio of 1,000 is required for sufficient activity. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

丁基改性的甲基铝氧烷助催化乙烯聚合

采用丁基改性的甲基铝氧烷(MMAO-Bu)与茂金属或后过渡金属配合物组成催化体系并催化乙烯聚合或齐聚。考察了MMAO-Bu的助催化活性及其对聚乙烯分子量和齐聚产物分布的影响。结果表明,适宜组成的MMAO-Bu可表现出比MAO更高的助催化活性;在MMAO-Bu的助催化作用下,所得聚乙烯具有较宽的分子量分布,而齐聚产物分布向高碳数的方向移动。     

溶剂对rac-Et[Ind]_2ZrCl_2/MMAO催化体系催化乙烯-降冰片烯共聚合的影响

采用乙基桥连二茚基二茚基二氯化锆(rac-Et[Ind]2ZrCl2)/MMAO催化体系催化乙烯/降冰片烯共聚合,比较了甲苯、苯、正己烷、环己烷及其混合溶剂作为反应介质对共聚合活性及共聚物结构的影响。通过差示扫描量热分析(DSC)对共聚产物进行了热力学性质的表征。结果表明,聚合活性和产品的玻璃化转变温度(Tg)在不同溶剂体系中有着显著的差异,在相同聚合条件下,当甲苯/苯体积比为80/20时,聚活活性达到最高,但产品的Tg和降冰片烯的插入率较低。     

Surface modification of polyurethane by plasma-induced graft polymerization of poly(ethylene glycol) methacrylate

A new approach, plasma-induced graft polymerization of poly(ethylene glycol) methacrylate (PEGMA), was used to introduce PEG graft chains with hydroxyl end groups onto a polyurethane (Tecoflex) surface. After argon plasma treatment and subsequent exposure to air, graft polymerization onto Tecoflex films was allowed to proceed in deaerated aqueous solutions of PEGMA at 60°C. The virgin, plasma-treated, and grafted films were characterized comparatively by means of attenuated total reflection infrared spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy, measurement of contact angle, and protein adsorption. The Tecoflex film undergoes etching during argon plasma treatment, surface oxidation when exposed to air after plasma treatment, and surface restructuring in response to environment upon storage in air. The plasma-induced graft polymerization of PEGMA proved to be successful in introducing PEG graft chains with reactive hydroxyl end groups onto the surface. Grafted films with different surface grafting density of PEG were prepared. Grafted films with higher PEG content exhibit higher hydrophilicity, smoother topography, and lower fibrinogen adsorption. The hydroxyl end groups built onto the surface offer further possibilities of improving its biocompatibility by immobilizing bioactive molecules. © 1996 John Wiley & Sons, Inc.     

助催化剂对新型球形丙烯聚合用催化剂性能的影响

丙烯聚合时,研究了3种不同的烷基铝助催化剂对丙烯聚合用新型球形催化剂的活性、聚丙烯(PP)等规指数、熔点、相对分子质量及其分布的影响。结果表明:使用三异丁基铝作助催化剂时,催化剂活性最高,活性衰减最慢,所制PP等规指数最低、重均分子量最大;使用三甲基铝作助催化剂时,催化剂活性最低,活性衰减最快,所制PP的重均分子量最小;使用三乙基铝作助催化剂时,PP等规指数和熔点最高。     

Influence of cocatalyst on the stereoselectivity and productivity of styrene polymerization reactions

Influence of different cocatalysts on the polymerization reaction of styrene using heterogeneous nanoparticle NA-MgO and NA-TiO2 (anatase) supported bis (cyclopentadienyl) zirconium dichloride catalysts is studied. Methyaluminoxane, trityl tetrakis(pentafluorophenyl)borate(1), dimethylanilinium tetrakis (pentafluoro-phenyl)borate (2) and tris(pentafluorophenyl)borane (3) are used as cocatalysts for this study. The productivity and stereoselectivity of the catalysts systems are found to be highest with MAO and lowest with the borane 3 (MAO > 1> 2 > 3). Catalysts derived from the borane 3 yield amorphous atactic polystyrenes but those from cocatalysts MAO, 1, or 2 yield crystalline, syndiotactic polystyrenes under the same reaction conditions. Effects of addition of various scavengers and solvents with different polarities on styrene polymerizations are also reported here. Characterization of the obtained polymers is done by Gel Permeation Chromatography, ¹³C-NMR spectroscopy and Differential Scanning Calorimetry.     

Low-pressure polymerization of ethylene. II

This paper presents the kinetic study of polymerization of ethylene with VOCl₃ and aluminum alkyls such as Et₃Al and Et₂AlCl. The effect of various parameters like the [Al]/[V] ratio, catalyst concentration, reaction time, temperature, solvents, and additives on rate of the reaction, yield, and molecular weight is reported. Each of these parameters has a remarkable effect on the yield and the rate of polymerization for both catalyst systems. Triethylamine is found to increase the catalyst efficiency and the rate. It is also observed that aliphatic hydrocarbons acted as a better polymerization medium than did the aromatic ones.     

FI Zr-type catalysts for ethylene polymerization

Two FI-type catalysts of Bis[N-(3,5-dicumylsalicylidene)-naphthylaminato]zirconium(IV) dichloride (catalyst (a)) and Bis[N-(3,5-dicumylsalicylidene)-anthracylaminato]zirconium(IV) dichloride (catalyst (b)) were prepared and used for ethylene polymerization comparatively. Methylaluminoxane (MAO) was used as cocatalyst. Polymerization reactions of ethylene using the prepared catalysts at the different conditions of polymerization were carried out. Plurality of the fused aromatic rings on the N atom of the imine in the catalyst structure affected the polymerization activity and molecular weight of the resulting polymer as well. Productivity of the prepared catalysts increased with the addition of [Al]/[Zr] molar ratio. The highest activity was observed at about 35–40 °C for the catalysts. The catalyst (b) produced higher viscosity average molecular weight (M_v) of the obtained polyethylene, while generally the activity of the catalyst (a) was higher than the catalyst (b). Similar behavior was observed for the polymerization carried out at the monomer pressure of 2 to 6 bars using the catalysts. The higher the pressure the more activity of the catalysts obtained, in the range studied. Crystallinity and melting point of the obtained polymer were between 55–65% and 120–135 °C respectively. Higher pressure increased both the crystallinity and the M_v values of the resulting polymer. The polymerization was carried out using different amounts of hydrogen. Higher amount of hydrogen could increase the activity of the catalysts. A linear dependence between the polymerization time and the molar weight was observed, however the polydispersity was broadened with the time.     

乙烯水相配位聚合反应的研究进展

综述了用于乙烯水相配位聚合反应的有机铑络合物、中性Ni(II)阴离子P-0配体络合物、中性Ni(Ⅱ)水杨醛亚胺配体络合物和阳离子α-二亚胺配体络合物的合成及所得的聚合物的特性以及Ni络合物催化的乙烯水相乳液聚合反应。水作为反应介质具有很好的应用前景。水相聚合反应催化剂的研究今后将会成为聚烯烃催化剂研究的一个重要组成部分。     

Butadiene polymerization with a rare earth compound using a magnesium alkyl cocatalyst: 1

High trans polybutadiene was obtained using a catalyst system comprising rare earth compounds plus magnesium dialkyl. The polymer appeared to contain some ‘live’ chain ends and block polymerization and coupling experiments were carried out. High cis polybutadienes formed when aluminium alkyl halides were used as a third catalyst component.     

Butadiene polymerization with a rare earth compound using a magnesium alkyl cocatalyst: 2

A catalyst was developed for the preparation of high cis polybutadiene consisting of ‘didymium’ versatate — aluminium alkyl halide — magnesium dialkyl. By altering the order of component addition and using neodymium versatate, the catalyst activity and cis content of the polymer were both increased. The aluminium alkyl halide could be replaced by mixtures of aluminium trialkyl plus silicon halides or organic halides. Various additives were tried in order to reduce polymer molecular weight and to alter the molecular weight distribution.     

TH-1L高效气相法浆液催化剂催化乙烯聚合

开发了一种新型高效气相法浆液聚合催化剂TH-1L,研究了该催化剂的制备工艺及其在气相法中试装置上的催化聚合。TH-1L不仅催化性能优良,而且聚合过程中避免使用复杂昂贵的在线还原系统,可降低生产成本,适于工业化生产。     

Polymer-supported metallocene catalysts for gas-phase ethylene polymerization

The use of hydroxylated chloromethylated-styrene/divinylbenzene copolymer as a support for three different catalysts, Cp₂ZrCl₂, [Ind]₂ZrCl₂ and (CH₃)₂Si[Ind]₂ZrCl₂ has been examined for the polymerization of ethylene in gas phase. The gas phase polymerization experiments were performed in a horizontal reactor by using Box-Behnken experimental design [Box and Wilson, 1951] to study the effects of temperature, ethylene partial pressure, and MAO cocatalyst level on polymerization. The measured average catalyst activities were empirically correlated with these three factors. Temperature appears to be the most important factor, which shows a first and second order effect on activity and also interacts with pressure and MAO. The kinetic study shows that these supported catalysts might contain two types of active sites, and the deactivation of sites follows a first order kinetic. This paper is dedicated to Professor Wha Young Lee on the occasion of his retirement from Seoul National University.     

Effect of the cocatalyst on the copolymerization of ethylene and propylene with high activity Ziegler-Natta catalyst

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.     

乙丙橡胶接枝改性的研究进展

总结了乙丙橡胶接枝改性的研究进展，对接枝方法、接枝物的性能及其应用进行了介绍。常见的乙丙橡胶接枝改性方法包括：（1）对乙丙橡胶进行官能化处理引入过氧等官能团，然后进行自由基或阳离子接枝聚合；（2）在过氧化物引发剂存在下直接进行熔融或溶液接枝聚合；（3）用电子束或γ射线辐照进行接枝聚合；（4）在乙丙橡胶的第三单体上引入原子转移自由基聚合引发活性点，进行活性自由基接枝聚合；（5）将乙丙橡胶溶液乳化后进行“假乳液”接枝聚合。接枝了不同单体的乙丙橡胶可以在热稳定性、机械性能、耐油性、染色性、生物相容性、阻燃性等方面得到改善，从而大大拓宽了乙丙橡胶的应用范围。     

Heterogeneous catalyst mixtures for the polymerization of ethylene

Heterogeneous cocatalysts, catalysts, and catalyst mixtures for the polymerization of ethylene were prepared applying “fumed silica” and mesoporous MCM-41 support materials and zirconocene dichloride, titanocene dichloride, and a bis(arylimino)pyridine iron complex as catalyst precursors. The catalyst mixtures produced polyethylenes which exhibit the properties of two single polymers. Polyethylenes with the desired bimodal molecular weight distributions could be obtained with a series of ternary Zr/Ti/Fe catalysts. The ability of the zirconium and titanium species to copolymerize short-chain 1-olefins produced by the iron centers (“in situ” copolymerization) is useful for the production of copolymers from only one monomer (ethylene).     

Preparation of highly active Cr-catalysts for ethylene polymerization

A Cr(CH₃COO)₃ · (CH₃CO)₂O/MgCl₂/AlEt₂Cl/2-EHA catalyst was prepared by modifying the Battelle catalyst with MgCl₂ in 2-ethyl-1-hexanol(2-EHA), and the polymerization of ethylene was carried out in toluene at 20–60°C. The rate of polymerization increased to reach an individual stationary value during the course of polymerization, and the stationary rate markedly increased with an increase in the molar ratio of Mg/Cr. The polyethylene obtained without MgCl₂ had a rather low molecular weight with a very broad polydispersity, whereas those obtained in the presence of MgCl₂ had extremely high molecular weights with narrow polydispersities.Polymerization of ethylene was subsequently performed under similar conditions using various types of metal chlorides in place of MgCl₂. A clear relation was found between the polymerization activity and the electronegativity X(M^x+) of metal ion in Mclx:metal chlorides having the electronegativities below X(Cr²⁺) accelerated the activity, whereas those above X(Cr²⁺) retarded it. A plausible mechanism for the enhancement of the activity by metal chlorides was proposed on the basis of these results.     

LH-1型催化剂催化乙烯聚合的性能

评价了LH-1型催化剂催化乙烯均聚合,乙烯-丙烯、乙烯-1-丁烯共聚合的性能.与国内工业化生产的催化剂进行对比,研究了LH-1型催化剂的粒径分布、催化活性、氢调敏感性.结果表明:LH-1型催化剂的粒径分布均匀,细粉含量少,且具有较高的氢调敏感性;在聚合温度80℃、压力0.8 MPa、氢气分压0.2 MPa的乙烯淤浆聚合工艺下聚合2h,LH-1型催化剂的活性较高,达5.36×104 g/g,优于对比催化剂;用LH-1型催化剂制备的高密度聚乙烯的堆密度较大,达0.350g/cm3,乙烯-丙烯、乙烯-1-丁烯共聚合性能好.