Study of the morphology and kinetics of novel Ziegler–Natta catalysts for propylene polymerization

The morphological and kinetic characteristics of novel Ziegler–Natta catalysts were studied. Catalysts were prepared by Borealis Polymers Oy using a new synthesis technique (emulsion technology). Video microscopy was used to study the growth of single catalyst particles during polymerization in the gas and liquid phases. The distribution of single particle activity was very narrow in the catalyst without external support and was rather broad in the the silica‐supported catalyst. Video microscopy of molten polymer particles allowed observation of the process and degree of fragmentation of the catalyst particles. A correlation between the activation period during the initial stage of polymerization and catalyst fragmentation was found. Fragmentation was faster and more uniform with the catalyst without external support than with the silica‐supported catalyst. Scanning electron microscopy provided information on morphology evolution and shape replication of the catalyst particles. With the catalyst without external support, good shape replication was observed, and compact and spherical particles were formed. With the silica‐supported catalyst, shape replication was poor, and nonspherical porous polymer particle were formed. Modeling of the kinetics of propylene polymerization was done using a simple three‐step reaction scheme neglecting mass and heat transport effects. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2191–2200, 2005     

Preparation of novel microspherical MgCl2‐based titanium catalyst for propylene polymerization

Lowering the particle size of support is one of methods to reduce breakage of supported catalyst during polymerization, which may cause serious problems for fine polymer particles from those broken catalysts. Microspheric MgCl₂ support could be obtained by emulsion way, but we found that they easily aggregated after emulsification and they are difficult to keep good spherical morphology. Up until now, hardly paper on the morphology improvement of micro size supports has been published. With the addition of an amount of Poly(propylene glycol)(PPG), microspheric MgCl₂ supports with good morphology were obtained. 1, 3, 15, 35, 80% PPG were added, respectively, and the results of SEM study on obtained particles showed that appropriate addition of PPG obviously improved the morphology of supports. The optimist dosage was 3% in our experiment and the activity of catalyst supported on obtained support was 32.3 kg PP/g cat h. The function of PPG was explored preliminarily. In spite of the improvement of morphology the activity of supported catalyst was decreased gradually compared to those without PPG. So the further XRD and IR analysis were carried out to find reasons. The results indicated that PPG might plug pores of support and interfere with the reaction between supports and TiCl₄. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

MgCl2‐supported catalyst containing mixed internal donors for propylene polymerization

A MgCl₂‐supported catalyst containing diisobutyl phthalate (DIBP) and 2,4‐pentadiol dibenzoate (PDDB) as internal donors was prepared. Propylene polymerizations were carried out using the catalyst in the absence or presence of an external donor. The resulting polymers were characterized by ¹³C‐NMR, crystallization analysis fraction (CRYSTAF) and gel permeation chromatography (GPC). The performance of the catalyst was compared with that of other catalysts containing donor‐free, DIBP and PDDB as internal donors respectively. The results demonstrated that the catalyst containing mixed internal donors not only had high activity and stereospecificity but also produced the polymer with relatively broad molecular weight distribution and the highest [mmmm] value. ¹³C‐NMR analysis results indicated that strongly coordinating donors gave more stereoregular polymers, which was further confirmed by CRYSTAF data. The effects of mixed internal donors on the catalyst properties were discussed systematically. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis of highly improved Ziegler‐Natta catalyst

The effects of media viscosity, mixing speed, and injection time on catalyst average particle size (APS), particle size distribution (PSD), and morphology in both conditions, with and without emulsifier, were investigated. Supports were prepared using a so‐called recrystallization method; then they were catalyzed under the same condition. To show the effects of emulsifier on the final product's properties such as catalyst activity, polymer isotacticity, and so on, two types of catalysts were polymerized and finally their results were compared. Scanning electron microscopy micrographs were used for morphological study. Results show that by increasing the media viscosity and injection time, APS of the catalyst support was decreased. But by increasing the mixing speed, APS was decreased and PSD was broadened. It was found that emulsifier reduces the sensitivity of APS and PSD of catalyst when the support preparation conditions are changed. Consequently, by employing emulsifier, highly improved catalyst was produced. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of internal donors in propylene polymerization analyzed with the two‐site model

The effect of internal donors of Ziegler‐Natta catalyst on stereoregularity in propylene polymerization was analyzed with the aid of the two‐site model analysis system. The amount of internal donor and that of external donor were varied. The probability in the selection of d (or l) monad in asymmetric site is contributed by both the amount of internal donor and that of external donor. With respect to the fraction of asymmetric site, the two‐site model enabled us to conceive that the new kinds of active centres are generated in specific cases where external donor is believed to be replacing weaker internal donor during polymerization. The effect of hydrogen concentration during polymerization is also discussed. © 2002 Society of Chemical Industry.     

Synthesis of polypropylene/clay nanocomposites using bisupported Ziegler‐Natta catalyst

In this article, preparation of polypropylene/clay nanocomposites (PPCNC) via in situ polymerization is investigated. MgCl₂/montmorillonite bisupported Ziegler‐Natta catalyst was used to prepare PPCNC samples. Montmorillonite (MMT) was used as an inert support and reinforcement agent. The nanostructure of the composites was characterized by X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy techniques. Obtained results showed that silica layers of the MMT in these PPCNC were intercalated, partially exfoliated, and uniformly dispersed in the polypropylene matrix. Thermogravimetric analysis showed good thermal stability for the prepared PPCNC. Differential scanning calorimetric was used to investigate both melting and crystallization temperatures, as well as the crystallinity of the PPCNC samples. Results of permeability analysis showed significant increase in barrier properties of PPCNC films. Effective parameters on molecular weight and flow ability of produced samples such as Al/Ti molar ratio and H₂ concentration were also investigated. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Highly active Ziegler–Natta catalyst for propylene polymerization

Polymerization of propylene was carried out by using a MgCl₂–EtOH–TiCl₄–ID–TEA–ED catalyst system in n‐heptane, where ID (internal donor) was an organic diester, ED (external donor) was a silane compound, and TEA (triethyl aluminum) was the activator. The influences of temperature, pressure, time, hydrogen, and the molar ratios of Al/Ti and ED/Ti on polymer isotacticity and catalyst activity were studied by solubility in boiling n‐heptane and measuring the polymer produced, respectively. The morphology of the polymers was evaluated through scanning electron microscopy and particle size distribution. The rheological properties of the poly(propylene) were determined by the melt flow index. It was found that the catalyst showed good morphology and high activity and also the produced polymers were characterized by high isotacticity and globulelike shapes. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1744–1749, 2005     

Investigations of the initial state polymerization of propylene with Ziegler–Natta catalysts in slurry

The initial state polymerization of propylene with Ziegler–Natta catalysts has been investigated and discussed at very low polymerization yields under adiabatic industrial prepolymerization conditions in diluted slurry regarding the effects of significant process parameters like monomer pressure, aluminum alkyl, and donor kind and concentration including the morphology of the catalyst/polymer particles formed. A sharp temperature increase in the first minutes of the initial state polymerization is followed by a temperature maximum and a slow decrease. With cocatalyst triethyl aluminum (TEAL), high prepolymerization yields were already achieved at a molar ratio TEAL/Ti of 3.0, remaining about constant until ratios of at least 300. The external donor dicyclopentyl dimethoxy silane leads to higher polymerization yields than the donor cyclohexyl dimethoxymethyl silane in the initial state polymerization too; however, both show a remarkable decreasing effect on polymerization yield above a specific molar ratio donor/Ti obviously correlated with the bulkiness of the alkyl groups. The particle size of the catalyst and the catalyst/prepolymer particles is increasing with polymerization yield until about 22 g PP/g Cat with particles almost perfectly spherical. The particle size distribution is rather broad at lower prepolymerization stages but unifying with lower polymerization rates at higher polymerization times. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Advantages of an Emulsion‐Produced Ziegler‐Natta Catalyst Over a Conventional Ziegler‐Natta Catalyst

Summary: Self‐supported and MgCl₂‐supported Ziegler‐Natta catalysts, produced by two catalyst synthesis methods are compared. Borealis Polymers OY (Finland), who supplied the catalysts, developed the catalyst synthesis methods. The first method (Method One) is based on an emulsion system and consists of an in situ single step preparation. The second method (Method Two) consists mainly of two steps: formation of the catalyst carrier particles, and their subsequent impregnation with the active material. The results showed that Method One produced catalysts of compact, spherical particles with good intra‐particle homogeneity and a narrow particle size distribution. On the other hand, Method Two produced catalyst particles whose properties depended directly on that of the catalyst carrier: they were spherical but very porous, with a broad particle size distribution. Polymer particles produced with the two catalyst systems are perfect replicas of the catalyst particles. Fines formed either during catalyst preparation or during polymerization were observed only with the catalyst prepared using Method Two. The particles of the catalysts produced using Methods One and Two had similar activities, independent of the initial particle size. Fragmentation of catalyst particles was very fast for both catalyst systems and was only observed to be 100% completed using the catalyst produced with Method One. Studies of the thermal properties showed that the catalyst prepared using Method One produced poly(propylene) of higher crystallinity and with a narrower melting peak.

SEM images of polymer particles produced by (A) Method One and (B) Method Two.     

Multiple active site Monte Carlo model for heterogeneous Ziegler‐Natta propylene polymerization

In this study, the kinetics of propylene polymerization catalyzed with the fourth heterogeneous Ziegler‐Natta catalyst is studied. More than one type of active site is present in the propylene polymerization based on an analysis of the GPC curves. A multiple active site kinetic model (MSmodel) is proposed by using Monte Carlo technique. Good agreements in the polymerization kinetics are achieved for fitting the kinetic profiles with the MSmodel. In addition, the MSmodel is used to describe the dynamic evolutions of the active sites and their effects on the propylene polymerization. The simulated results indicate that different types of active sites have different polymerization kinetics and the site type can affect the propylene polymerization kinetics. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The influence of the nature of organoaluminum compound on kinetic heterogeneity of active sites in lanthanide‐based diene polymerization

The influence of organoaluminum compound on kinetic heterogeneity of active sites in lanthanide‐based diene polymerization was investigated. It was shown that heterogeneity of investigated catalytic systems was displayed in the existence of four types of active centers. They are formed at the beginning of the polymerization process and produce macromolecules with lengths that are definite for each type of active centers. The organoaluminum compound's nature greatly influences the kinetic activity of polymerization centers. The method of analysis of the curves' maximum distribution on kinetic activity and the change of kinetic activity of every active centers' type were proposed, which permits the calculation of values of concentration for each type of active center separately. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 358–368, 2003     

Coupled‐single‐particle and Monte Carlo model for propylene polymerization

A coupled‐single‐particle and Monte Carlo model was used to simulate propylene polymerization. To describe the effects of intraparticle transfer resistance on the polymerization kinetics, the polymeric multilayer model (PMLM) was applied. The reaction in each layer of the PMLM was described with the Monte Carlo method. The PMLM was solved together with the Monte Carlo model. Therefore, the model included the factors of the mass‐ and heat‐transfer resistance as well as the stochastic collision nature of the polymerization catalyzed with single‐site‐type/multiple‐site‐type catalysts. The model presented results such as the polymerization dynamics, the physical diffusion effect, and the polymer molecular weight and its distribution. The simulation data were compared with the experimental/actual data and the simulation results from the uniform Monte Carlo model. The results showed that the model was more accurate and offered deeper insight into propylene polymerization within such a microscopic reaction–diffusion system. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Kinetic and morphological study of a magnesium ethoxide‐based Ziegler–Natta catalyst for propylene polymerization

BACKGROUND: Kinetic and morphological aspects of slurry propylene polymerization using a MgCl₂‐supported Ziegler–Natta catalyst synthesized from a Mg(OEt)₂ precursor are investigated in comparison with a ball‐milled Ziegler–Natta catalyst. RESULTS: The two types of catalyst show completely different polymerization profiles: mild activation and long‐standing activity with good replication of the catalyst particles for the Mg(OEt)₂‐based catalyst, and rapid activation and deactivation with severe fragmentation of the catalyst particles for the ball‐milled catalyst. The observed differences are discussed in relation to spatial distribution of TiCl₄ on the outermost part and inside of the catalyst particles. CONCLUSION: The Mg(OEt)₂‐based Ziegler–Natta catalyst is believed to show highly stable polymerization activity and good replication because of the uniform titanium distribution all over the catalyst particles. Copyright © 2008 Society of Chemical Industry     

Preparation of porous spherical MgCl2/SiO2 complex support as precursor for catalytic propylene polymerization

The MgCl₂/SiO₂ complex support was prepared by spray drying using alcoholic suspension, which contained MgCl₂ and SiO₂. The complex support reacted with TiCl₄ and di‐n‐butyl phthalate, giving a catalyst for propylene polymerization. The catalyst was spherical and porous with high specific surface area. TEA was used as a cocatalyst, and four kinds of alkoxysilane were used as external donors. The bulk polymerization of propylene was studied with the catalyst system. The effect of the reaction conditions and external donor on the polymerization were investigated. The results showed that the catalyst had high activity, high stereospecificity, and sensitive hydrogen responsibility. Polypropylene has good grain morphology because of duplicating the morphology of the catalyst. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1296–1299, 2005     

Surface modification of single‐walled carbon nanotubes with polyethylene via in situ Ziegler–Natta polymerization

Single‐walled carbon nanotubes (SWNTs) were modified with polyethylene (PE) prepared by in situ Ziegler–Natta polymerization. Because of the catalyst pretreated on the surface of the SWNTs, the ethylene was expected to polymerize there. Scanning electron microscopy images and solubility measurements showed that the surface of the SWNTs was covered with a PE layer, and a crosslink may have formed between the SWNTs and PE. When the SWNTs covered with a PE layer were mixed with commercialized PE by melt blending, the resulting composite had better mechanical properties than the composite from the SWNTs without a PE layer. The yield strength, the tensile strength and modulus, the strain at break, and the fracture energy of the modified‐SWNT/PE composites were improved by 25, 15.2, 25.4, 21, and 38% in comparison with those of the raw‐SWNT/PE composites. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3697–3700, 2004     

Effect of high polymerization temperature on the microstructure of isotactic polypropylene prepared using heterogeneous ticl4/mgcl2 catalysts

The effects of alkylaluminum and polymerization temperature on propylene polymerization without an external donor in the use of a TiCl₄–MgCl₂–diether(BMMF) catalyst were investigated. The results indicated that with increasing polymerization temperature the concentrations of [mmmm] of heptane‐insoluble poly(propylene) (PP) fraction increased. Crystallization analysis fractionation (CRYSTAF) results showed the fractions of different crystallization temperatures were changed according to various polymerization temperatures. The activity with Et₃Al as cocatalyst at 100°C was much lower than that at 70°C. However, the activity with i‐Bu₃Al at 100°C was as high as that at 70°C. The fraction of high‐crystallization temperature of PPs obtained with i‐Bu₃Al increased with increasing polymerization temperature, which was opposite to that with Et₃Al, thus implying that the copolymerization of propylene with the monomer arising from Et₃Al led to the lower crystallization ability of PPs obtained with Et₃Al. The terminal groups of PP suggested that the chain‐transfer reaction by β‐H abstraction was the main chain‐transfer reaction at 120°C. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3980–3986, 2003     

Three‐site mechanism and molecular weight: Time dependency in liquid propylene batch polymerization using a MgCl2‐supported Ziegler‐Natta catalyst

This article demonstrates that the molecular weight of propylene homopolymer decreases with time, and that the molecular weight distribution (MWD) narrows when a highly active MgCl₂‐supported catalyst is used in a liquid pool polymerization at constant H₂ concentration and temperature. To track the change in molecular weight and its distribution during polymerization, small portions of homo polymer samples were taken during the reaction. These samples were analyzed by Cross Fractionation Chromatograph (CFC), and the resulting data were treated with a three‐site model. These analyses clearly showed that the high molecular weight fraction of the distribution decreases as a function of time. At the same time, the MWD narrows because the weight‐average molecular weight decreases faster than the number‐average molecular weight. A probable mechanism based on the reaction of an external donor with AlEt₃ is proposed to explain these phenomena. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1035–1047, 2001     

丙烯预聚合工艺的研究进展

综述了有关丙烯预聚合的最新进展,包括新的预聚合工艺及其对聚合过程、聚丙烯(PP)产品性能等的影响以及在“超临界”聚合上的应用等。丙烯预聚合对于PP颗粒形态、主聚合阶段的聚合动力学以及聚合工艺都会产生影响。     

Butadiene polymerization in the presence of VOCl3–dialkylmagnesium catalytic system

The butadiene polymerization in toluene at 25°C on VOCl₃? (n‐C₄H₉)Mg(iso‐C₈H₁₇) catalytic system was investigated. The kinetic parameters of polymerization and molecular characteristics of polybutadiene were determined. It was shown that substitution of traditional organoaluminum cocatalysts in trans‐regulating vanadium systems does not have an effect on its stereospecificity, but significantly influences on the active centers reaction ability. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 596–600, 2003     

Correlation of Arrhenius parameters for UHMWPE synthesis with ethylene solubility characteristics in different polymerization media

The effect of different polymerization media like n‐hexane, cyclohexane, isooctane, n‐decane, toluene, varsol, and light normal paraffin (LNP) on the kinetics of the slurry polymerization of ethylene using a highly active Ziegler Natta (ZN) catalyst for synthesizing UHMWPE was studied. Attempts have been made to determine the solubility of ethylene in the above polymerization media in a very basic manner and to correlate same with the process activation energy based on the Arrhenius plots. The ethylene solubility seemed to depend on the number of carbon atoms in the media, besides other parameters like geometry, dipole moment, etc. It is obvious and well understood that the monomer (ethylene) concentration has a direct bearing on the polymerization kinetics, which influenced the activation energy (Ea) besides other parameters like catalyst/cocatalyst concentration, temperature, etc which were kept constant during the study. The role of the catalyst system in controlling the activation energy was also further exemplified by employing a different ZN catalyst system wherein higher activation energy was observed. This was ascribed to restricted activation pathways for the catalyst under the comparable experimental conditions employed. As soon as better activation pathways for the catalyst were enabled the activation energy dropped down remarkably. The Ea for the synthesis of ultra‐high molecular weight polyethylene (UHMWPE) using traditional MgCl₂ supported Ti catalyst was found to be 5–12 kcal/mol which compared well with the values obtained by other researchers using other similar catalyst systems for different ethylene polymerization processes. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011