Controlling molecular weight distributions of polyethylene by combining soluble metallocene/MAO catalysts

A critical look at the possibility of controlling the molecular weight distribution (MWD) of polyolefins by combining metallocene/methylalumoxane (MAO) catalysts is offered. Catalysts investigated were bis(cyclopentadienyl)zirconium dichloride (Cp₂ZrCl₂), its titanium and hafnium analogues (Cp₂TiCl₂ and Cp₂HfCl₂), as well as rac-ethylenebis(indenyl)zirconium dichloride (Et(Ind)₂ZrCl₂). As observed by other researchers, the MWD of polyethylene can be manipulated by combining soluble catalysts, which on their own produce polymer with narrow MWD but with different average molecular weights. Combined in slurry polymerization reactors, the catalysts in consideration produce ethylene homopolymer just as they would independently. Unimodal or bimodal MWDs can be obtained. This effect can be mimicked by blending polymers produced by the individual catalysts. We demonstrate how a variability in catalyst activity translates into a variability in MWD when mixing soluble catalysts in polymerization. Such a variability in MWD must be considered when setting goals for MWD control. We introduce a more quantitative approach to controlling the MWD using this method. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 831–840, 1998     

异丁烯聚合催化体系研究 Ⅰ.均聚与共聚反应

用苯甲酰氯(BC)／TiCl4引发异丁烯(IB)聚合及与苯乙烯(St)的共聚反应，得到分子量高、分布窄的聚异丁烯及其共聚物，并控制了BC的高活性。对IB均聚及其与ST共聚反应影响因素(体系浓度、残余水、第3组分三乙胺(TEA))进行优化，得到最佳条件为：[BC]=2．6mmol／L、[TEA]／[BC]=1.0(均聚)和n(TiCl4)／n(BC)=80、[TEA]／[BC=4．0(共聚)，BC／TiCl4／TEA是最佳体系，对水不敏感，可以制备分子量高及分子量分布(MWD)为1．5(均聚)和2．0(共聚)的窄分布聚合物(GPC曲线均为单峰)。     

环烷酸亚铁-烷基铝-邻菲咯啉-卤化物体系催化丁二烯聚合的研究

本文研究了Fe(naph)_2(环烷酸亚铁)-Al(i-Bu)_3(三异丁基铝)-Phen(邻菲咯啉)-卤化物体系催化丁二烯聚合的一般规律。实验证实:卤化物可以提高体系的催化活性,调节聚合物的分子量,并能增加体系活性中心的稳定性;加料方式对体系的催化活性有显著的影响。催化剂的紫外-可见光谱研究表明:510nm处的吸收代表了此体系活性中心的特征吸收。     

Population Balance Model for Emulsion Polymerisation Under Pseudo-Bulk Conditions: Combined Particle Size Distribution and Molecular Weight Distribution

A comprehensive model for emulsion polymerisation is presented, accounting for particle size distribution (PSD) and molecular weight distribution (MWD). The PSD information is incorporated through a population balance framework. A mechanistic formulation is adopted in modelling the average number of radicals/particle under pseudo-bulk compartmentalisation conditions. The method of moments is adopted to simplify the MWD equations over each discrete size class. The impact of the pseudo-bulk assumption on the PSD and MWD results is assessed. An identification of potential manipulated variables for control of PSD and MWD is done through sensitivity analysis.     

Fe-Zn双金属氰化物催化环氧丙烷开环聚合的研究

用Fe Zn双金属氰化物 (DMC)催化剂合成了数均分子量 30 0 0～ 12 0 0 0的聚氧化丙烯二元醇 .着重考察了聚合反应的温度、加料方式等对聚合物分子量及分布的影响 ,并初步探讨了Fe Zn双金属氰化物催化环氧丙烷开环聚合的反应特征 .实验发现 ,采用Fe ZnDMC催化剂 ,聚合物分子量可控 ;在较高温度下聚合所得的聚合物分子量分布呈双峰形 ,显示反应体系中至少存在两类活性中心 ,这可能与催化剂中存在两种价态的络合物有关 ,当降低聚合温度时 ,聚合物分子量分布呈单峰形 ,可能是一类活性中心没有引发 ;实验中还发现单体分批加料时聚合物分子量分布较窄 ,而一步加料法所得聚合物分子量分布则很宽     

MgCl_2负载双金属复合催化剂制备宽分子量分布聚乙烯

聚乙烯的分子量和分子量分布对其熔体的流变性能和产品的力学性能有显著影响．分子量分布的变化,尤其是分子量分布末端部位的变化,都会对材料的注塑行为产生大的影响［１］．为了控制Ｚｉｅｇｌｅｒ催化剂制备的聚乙烯分子量分布而改善聚合工艺的报道很多［２～４］,工业生产中可利用多步聚合工艺来获得宽分子量分布的聚乙烯［５,６］,但这种方法工艺复杂,成本高．美国ＵＣＣ公司利用复合的ＴｉＶ和ＺｒＶ催化剂在气相法Ｕｎｉｐｏｌ工艺装置上首次成功的合成出了双峰高分子量聚乙烯产品［７,８］,由于采用Ｕｎｉｐｏｌ生产工艺…     

Theoretical Consideration of the External Donor of Heterogeneous Ziegler–Natta Catalysts Using Molecular Mechanics,Molecular Dynamics,and QSAR Analysis

In the previous paper we calculated the most stable structure of the catalyst and cocatalyst of metallocene catalyst systems using molecular dynamics and molecular mechanics. In this paper we postulate the active site of the heterogeneous Ziegler–Natta catalyst, and analyze it by the same methods to clarify the main factors that control the activity and molecular weight distribution of the heterogeneous catalyst systems. The roles of the external donor were also considered, and we found that the interaction energy between an external donor and the active site of the catalyst, as well as the structural factors of the external donor itself, are strongly related to both activity and molecular weight distribution. These results reveal that molecular dynamics and molecular mechanics calculations are also effective methods to screen the heterogeneous catalyst systems.     

Kinetic features of ethylene polymerization over supported catalysts [2,6‐bis(imino)pyridyl iron dichloride/magnesium dichloride] with AlR3 as an activator

The effects of polymerization temperature, polymerization time, ethylene and hydrogen concentration, and effect of comonomers (hexene‐1, propylene) on the activity of supported catalyst of composition LFeCl₂/MgCl₂‐Al(i‐Bu)₃ (L = 2,6‐bis[1‐(2,6‐dimethylphenylimino)ethyl] pyridyl) and polymer characteristics (molecular weight (MW), molecular‐weight distribution (MWD), molecular structure) have been studied. Effective activation energy of ethylene polymerization over LFeCl₂/MgCl₂‐Al(i‐Bu)₃ has a value typical of supported Ziegler–Natta catalysts (11.9 kcal/mol). The polymerization reaction is of the first order with respect to monomer at the ethylene concentration >0.2 mol/L. Addition of small amounts of hydrogen (9–17%) significantly increases the activity; however, further increase in hydrogen concentration decreases the activity. The IRS and DSC analysis of PE indicates that catalyst LFeCl₂/MgCl₂‐Al(i‐Bu)₃ has a very low copolymerizing ability toward propylene and hexene‐1. MW and MWD of PE produced over these catalysts depend on the polymerization time, ethylene and hexene‐1 concentration. The activation effect of hydrogen and other kinetic features of ethylene polymerization over supported catalysts based on the Fe (II) complexes are discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5057–5066, 2007     

α-萘基丁二亚胺氯化镍/MAO制备双(宽)峰聚乙烯

合成了一种新型α 二亚胺镍配合物———α 萘基丁二亚胺氯化镍 ,此配合物作为催化剂在MAO的活化下催化乙烯聚合得到支化聚乙烯 ,聚合活性高达 7 18× 10 5gPE molNi·h ,1 3C NMR、FTIR测试结果表明制备的聚乙烯含有末端双键 ;GPC结果表明所制备的聚乙烯分子量呈双 (宽 )峰分布 ,其原因有两个 ,一是此催化剂能产生分子量较低的α 烯烃 ,在聚合过程中一部分α 烯烃会“就地”与乙烯原位共聚形成分子量较高的聚合物 ,二是此催化剂存在立体异构体 ,而不同异构体在MAO活化下形成的活性中心的配位环境不同 ,因而得到的聚乙烯的分子量也不同 .研究了聚合温度、聚合压力、铝镍摩尔比 (nAl nNi)对催化活性、聚乙烯分子量、支化度的影响 .聚乙烯的分子量随聚合温度的升高而下降 ,支化度增大 ,熔点则降低 .     

Steady State Simulation of Ethylene Polymerization Using Multiple-Site Coordination Catalysts

Summary: Simulation models are important tools for the development and optimization of polymerization processes because they can describe catalyst performance and polymer properties as a function of polymerization kinetics and process conditions. As the polyolefin industry moves towards the production of resins with more complex microstructures, these models become essential for process understanding and product design. A simulation model has been developed for the polymerization of ethylene in a process with n reactors working in series. The model can predict raw material conversions and product properties like the molecular weight distribution (MWD) coupled with short chain branching distribution (SCBD), melt index, density and fluff morphology. Model parameters have been obtained from laboratory data. The model predictions are in good agreement with experimental results.     

Effect of cocatalyst on the chain microstructure of polyethylene made with CGC‐Ti/MAO/B(C6F5)3

This investigation studied the solution polymerization of ethylene in Isopar E in a semibatch reactor using CGC‐Ti as catalyst and methylalumoxane (MAO) and tris(pentaflourophenyl)borane [B(C₆F₅)₃] as cocatalysts. The effects of cocatalyst type and amount on the chain microstructure were investigated. ¹³C NMR and gel permeation chromatography were used to determine the long‐chain branching (LCB) content and molecular weight distribution (MWD), respectively, of the samples. It was observed that higher concentrations of MAO increased the LCB content and decreased the molecular weight of the polymer. On the other hand, increasing the amount of B(C₆F₅)₃ lowered the LCB content, increased the molecular weight, and broadened MWD significantly. We believe that this approach can be used as an efficient way to control the microstructure of polyolefins made with these catalytic systems. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3055–3061, 2004     

球形MgCl_2负载钛催化剂催化苯乙烯等规聚合与产物分子量分布研究

采用球形高效负载ZieglerNatta催化体系(TiCl4MgCl2AlR3二苯基二甲氧基硅烷(DPDMS)合成等规聚苯乙烯(iPS),催化效率最高可达7.7×103gPSgTi·h.通过多个SchulzFlory最可几分布对产物的分子量分布曲线拟合分峰来研究iPS的分子量及分子量分布的变化,AlEt3能使产物中低分子量部分含量增加,Al(iBu)3则倾向于形成高分子量的活性中心.体系中加入氢气不仅能显著提高催化效率,而且使iPS的分子量分布显著增宽.     

Kinetic Study of the Copolymerisation of Ethylene with a Single Site Catalyst in Propane Slurry Polymerisation

Summary: The kinetic behaviour of a supported metallocene catalyst in slurry polymerisation of ethylene with 1-hexene under industrially relevant reaction conditions has been studied. Polymerisation experiments were carried out in a 5-litre stirred tank reactor in a temperature range from 60 to 80 °C and ethylene partial pressures from 5 to 15 bar. Comonomer and hydrogen amounts were varied as well. The catalyst showed pronounced activation and slow deactivation during runtimes of about 1 hour. Strong influences of 1-hexene (“hexene effect”) and hydrogen (“hydrogen effect”) on the activity profiles were observed. Based on the experimental results, a kinetic model has been derived in order to describe and predict important polymerisation data such as activity profile, comonomer content and molecular weight distributions with respect to the reaction conditions. The presented kinetic model is able to describe the observed effects of 1-hexene and hydrogen on the activity profiles, as well as the comonomer incorporation across a broad range of polymerisation conditions. The molecular weight distributions can be simulated with good qualitative agreement to the experimental data.     

Development of Amino–Oxazoline and Amino–Thiazoline Organic Catalysts for the Ring‐Opening Polymerisation of Lactide

The ring‐opening polymerisation of lactide by a range of amino–oxazoline and amino–thiazoline catalysts is reported. The more electron‐rich derivatives are demonstrated to be the most highly active and polymerisation is well controlled, as evidenced by the linear relationship between the molecular weight and both the monomer conversion and the monomer‐to‐initiator ratio. Mechanistic studies reveal significant interactions between the monomer, initiator and catalyst and that the polymerisation is first order with respect to each of these components. These observations indicate that the polymerisation operates by a general base/pseudo‐anionic mechanism.     

Influence of Metal-Alkyls on Early-Stage Ethylene Polymerization over a Cr/SiO2 Phillips Catalyst: A Bulk Characterization and X-ray Chemical Imaging Study

The Cr/SiO₂ Phillips catalyst has taken a central role in ethylene polymerization since its invention in 1953. The uniqueness of this catalyst is related to its ability to produce broad molecular weight distribution (MWD) PE materials as well as that no co-catalysts are required to attain activity. Nonetheless, co-catalysts in the form of metal-alkyls can be added for scavenging poisons, enhancing catalyst activity, reducing the induction period, and tailoring polymer characteristics. The activation mechanism and related polymerization mechanism remain elusive, despite extensive industrial and academic research. Here, we show that by varying the type and amount of metal-alkyl co-catalyst, we can tailor polymer properties around a single Cr/SiO₂ Phillips catalyst formulation. Furthermore, we show that these different polymer properties exist in the early stages of polymerization. We have used conventional polymer characterization techniques, such as size exclusion chromatography (SEC) and ¹³C NMR, for studying the metal-alkyl co-catalyst effect on short-chain branching (SCB), long-chain branching (LCB) and molecular weight distribution (MWD) at the bulk scale. In addition, scanning transmission X-ray microscopy (STXM) was used as a synchrotron technique to study the PE formation in the early stages: allowing us to investigate the produced type of early-stage PE within one particle cross-section with high energy resolution and nanometer scale spatial resolution.     

SUPPORTED ZIEGLER-NATTA CATALYSTS FOR ETHYLENE SLURRY POLYMERIZATION AND CONTROL OF MOLECULAR WEIGHT DISTRIBUTION OF POLYETHYLENE

The effect of chemical composition of highly active supported Ziegler-Natta catalysts with controlled morphology on the MWD of PE has been studied.It was shown the variation of transition metal compound in the MgCl_2-supported catalyst affect of MWD of PE produced in broad range:Vanadium-magnesium catalyst(VMC)produce PE with broad and bimodal MWD(M_w/M_n=14-21).MWD of PE,produced over titanium-magnesium catalyst(TMC)is narrow or medium depending on Ti content in the catalyst(M_w/M_n=3.1-4.8).The oxidati...     

Polyethylene with Reverse Co‐monomer Incorporation: From an Industrial Serendipitous Discovery to Fundamental Understanding

A triethylaluminium(TEAl)‐modified Phillips ethylene polymerisation Cr/Ti/SiO₂ catalyst has been developed with two distinct active regions positioned respectively in the inner core and outer shell of the catalyst particle. DRIFTS, EPR, UV‐Vis‐NIR DRS, STXM, SEM‐EDX and GPC‐IR studies revealed that the catalyst produces simultaneously two different polymers, i.e., low molecular weight linear‐chain polyethylene in the Ti‐abundant catalyst particle shell and high molecular weight short‐chain branched polyethylene in the Ti‐scarce catalyst particle core. Co‐monomers for the short‐chain branched polymer were generated in situ within the TEAl‐impregnated confined space of the Ti‐scarce catalyst particle core in close proximity to the active sites that produced the high molecular weight polymer. These results demonstrate that the catalyst particle architecture directly affects polymer composition, offering the perspective of making high‐performance polyethylene from a single reactor system using this modified Phillips catalyst.     

Modification of the(SiO_2/MgO/MgCl_2)·TiCl_x Ziegler-Natta Polyethylene Catalysts Using the Third Metal Elements

Various(SiO_2/MgO/MgCl_2)·Ti Clx Ziegler-Natta catalysts modified by the third metal elements were synthesized by the co-impregnation of water-soluble magnesium and the third metal salts. Several key factors including the electronegativity of the third metal elements, catalyst performances in ethylene homo-polymerization, ethylene/1-hexene copolymerization and hydrogen response were systematically investigated. Both the catalyst performance and the polymer properties are influenced by the introduction of the third metal elements. Compared with the unmodified(SiO_2/MgO/MgCl_2)·Ti Clx Ziegler-Natta catalyst, activity and 1-hexene incorporation are enhanced by the introduction of zirconium, vanadium, aluminum and chromium, while deteriorated by the addition of ferrum, nickel, molybdenum and tungsten. Correlations of the catalyst activities and 1-hexene incorporation ability with the electronegativity of the third metal elements are discovered. It is found that the lower electronegativity of the third metal elements leads to the catalyst with higher activity and higher α-olefin co-polymerization ability. The polyethylene produced by a nickel modified catalyst showed broad molecular weight distribution(MWD) and the lowest average molecular weight(MW), while by using a ferrum modified catalyst, the resulting polyethylene had the highest MW, reaching the ultra-high MW area. Vanadium and chromium modified catalysts demonstrated the best hydrogen response.     

Use of hydrogen for the tailoring of the molecular weight distribution of polyethylene in a bimetallic supported metallocene catalyst system

The shape of the molecular weight distribution (MWD) of polyethylene produced with a bimetallic supported metallocene catalyst was controlled with hydrogen in a semi-batch slurry reactor. Polymers produced at different hydrogen pressures have MWD's varying from unimodal to bimodal, with high or low molecular weight shoulders.     

The effect of molecular weight and catalyst concentration on catalytic activity in mechanochemically activated transesterification using silver(I)‐N‐heterocyclic carbene latent catalysts

We have investigated the effect of the concentration and molecular weight on the activity of polymeric silver(I)‐NHC (NHC = N‐heterocyclic carbene) catalyst complexes in ultrasound‐induced mechanochemical catalyst activation. A strong dependence of the turnover number (TON) on initial catalyst concentration was observed in the transesterification of vinyl acetate with benzyl alcohol. The main findings of this study are that the concentration and molecular weight effects on TON are caused by competition between mechanochemical catalyst activation and deactivation, most likely by reactive species produced during the sonication process. Performing the transesterification reaction under radical‐suppressing conditions resulted in a significant increase of TON. This result clearly demonstrates the increased catalyst lifetime when reducing the amount of sonochemical impurities, and it highlights the importance of controlling and suppressing secondary, sonochemical processes when using ultrasound‐induced mechanochemical generation of reactive species such as catalysts. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012