In situ formation of nanocomposites based on polyethylene and silica nanospheres

Polyethylene nanocomposites containing silica nanospheres, synthesized by the sol–gel method, were produced via in situ polymerization. The silica nanospheres were added together with the catalytic system [metallocene catalyst and methylaluminoxane (MAO) as cocatalyst] directly to the reactor and used for the polymerization of ethylene. The polymerization activity increased slightly in the presence of 1 wt % silica nanospheres in comparison to the homogeneous polymerization sans filler. The Young's modulus of the nanocomposites increased 19–25% without a significant decrease in the elongation at break with respect to the neat polyethylene. The polymer particle morphology was also significantly improved with the incorporation of silica nanospheres. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Experimental proof of the existence of mass‐transfer resistance during early stages of ethylene polymerization with silica supported metallocene/MAO catalysts

The size of a silica supported metallocene/MAO (methylaluminoxane) catalyst plays an important role in determining its productivity during ethylene polymerization. From a chemical engineering point of view, this size dependency of catalytic activity of supported metallocenes is mathematically connected with the different levels of mass‐transfer resistance in big and small catalyst particles but no experimental evidence has been provided to date. The results of this systematic experimental study clearly demonstrate that the intraparticle monomer diffusion resistance is high in bigger catalyst particles during initial instants of ethylene polymerization and diminishes with the polymer particle growth. Two different silica supported metallocene/MAO catalysts provided the same results while highlighting the fact that catalyst chemistry should be carefully considered while studying complex chemical engineering problems. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4476–4490, 2017     

New clay‐supported Ziegler–Natta catalyst for preparation of PE/Clay nanocomposites via in situ polymerization

Polyethylene/clay (PE/Clay) nanocomposites were prepared by the in situ polymerization of ethylene using the new Clay/butyl octyl magnesium (BOM)/Chloroform/EtOH/TiCl₄/tri ethyl aluminum (TEA) catalyst system in heptane where BOM and TEA were the support for the clay modification and cocatalyst, respectively. The influence of the modified clay using BOM on the catalyst and polymerization was investigated. Also, the effect of temperature, pressure, hydrogen, and the molar ratios of TEA/Ti on the catalyst yield and ethylene consumption (polymerization rate) were studied. It was found that the above clay‐supported catalyst was an efficient Ziegler–Natta type catalyst due to its suitable yield for the polymerization of ethylene toward the production of the PE/Clay nanocomposites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Video Microscopy for Fast Screening of Polymerization Catalysts

Video microscopy has been used as an effective tool for fast screening of six different metallocene/MAO supported catalyst samples. The different techniques employed for supporting the metallocene on silica gels can have an influence on the overall catalyst activity and on the activity of single catalyst particles. The kinetics of gas‐phase polymerization of ethylene with supported metallocene/MAO catalysts can be modeled by using a simple reaction scheme and neglecting mass and heat transport effects.     

PE/OMMT nanocomposites catalyzed by the OMMT‐intercalated Et[Ind]2ZrCl2 in slurry polymerization: Effects of organic solvent on ethylene polymerization behaviors and the nanocomposite structures

In situ intercalative polymerization for ethylene monomers was carried out to produce PE‐based hybrids through a slurry polymerization method. In this approach, organic solvent for olefin polymerization was found to be one of the most significant factors for the dispersion of the OMMT‐intercalated Et[Ind]₂ZrCl₂ catalysts, which determines that whether olefin monomers polymerize is in a well‐defined confinement environment or not. Understanding the olefin polymerization occurring in between the nanoscale silicate layers of OMMT as well as the corresponding structure of OMMT in an organic polymerization solvent is a critical step toward tailoring and characterizing nanocomposites formed by OMMT in a polyolefin matrix. As we know, the Et[Ind]₂ZrCl₂ catalyst and MAO are both better dissolved in toluene than that in hexane because of the larger polarity of toluene. Thus, in hexane the active sites of the OMMT/Et[Ind]₂ZrCl₂ catalyst exist in the silicate layers of OMMT and the PE chains grow in the middle of them, while in toluene the active specimens are exposed in the gel formed by the OMMT‐intercalated catalyst with MAO, which cause that the PE chains propagated in the mixture liquids. Consequently, when hexane is selected as the polymerization solvent, the formed PE‐based nanocomposites have a good dispersion of OMMT and the nanofiller content (TGA measurement residue at 600°C) is thus higher (>7.0 wt %). However, in toluene, most of the silicate layers of OMMT are agglomerated in the PE matrix. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation of multifunctional supported metallocene catalyst using organic multifunctional modifier for synthesizing polyethylene/clay nanocomposites via in situ intercalative polymerization

A new type of multifunctional ammonium modifier with carbonyl group and vinyl group was synthesized to prepare multifunctional montmorillonites (F-MMTs), which were used as multifunctional catalyst supports for in situ ethylene polymerization. High loading of metallocene catalyst in the galleries of F-MMT had been achieved due to the presence of carbonyl group in the multifunctional modifier. XRD profiles and TEM images showed that polyethylene/montmorillonite (PE/F-MMT) nanocomposites with exfoliated structure could be synthesized using the intercalated catalyst described above, even when the content of MMT was very high (more than 15.1 wt%). The as-produced PE/F-MMTs nanocomposites were composed of flower-like particles with a diameter of about 5 μm. A thermal stable monoclinic phase was observed in PE/F-MMT nanocomposites. Comparatively, the resultant PE/F-MMT nanocomposites showed low gas permeability. Interfacial interaction between PE matrix and F-MMT was enhanced due to the chemical linking between the two components via copolymerization of ethylene with vinyl group of F-MMT. Thus the resultant PE/F-MMT nanocomposites showed good structural stability.     

Characterization of polyethylene/kaolin composites by polymerization filling with Cp2ZrCl2/MAO catalyst system

In this work, the preparation and characterization of metallocene‐catalyzed polyethylene (PE)/kaolin composites were presented. The composites was prepared by the so‐called polymerization‐filling method in which the PE matrix was formed directly on the kaolin surface by ethylene polymerization with the prefixed Cp₂ZrCl₂/methylaluminoxane (MAO) catalyst system on the kaolin surface. SEM, FTIR, and DMA were carried out to characterize the composites. The experimental results showed the new composites had homogeneous distribution of kaolin particles in the PE matrix and strong interfacial interaction between the PE matrix and kaolin particles. At the molecular level, the interfacial interaction caused the decrease of the mobility of PE molecular chains. In addition rheological testing showed that the introduction of kaolin by polymerization filling could improve the rheological behavior of prepared composites. The relationship between the rheological behaviors and the interfacial conditions were discussed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2913–2921, 2002     

In situ polymerization of polyethylene/clay nanocomposites using a novel clay‐supported Ziegler‐Natta catalyst

Polyethylene/clay nanocomposites (PECNC) were synthesized via in situ Ziegler‐Natta catalyst polymerization. Activated catalyst for polymerization of ethylene monomer has been prepared at first by supporting of the cocatalyst on the montmorillonite (MMT) smectite type clay and then active complex for polymerization formed by reaction of TiCl₄ and aluminum oxide compound on the clay. Acid wash treatment has been used for increasing hydroxyl group and porosity of the clay and subsequently activity of the catalyst. The nanostructure of composites was investigated by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Obtained results show that silica layers of the mineral clay in these polyethylene/nanocomposites were exfoliated, intercalated, and uniformly dispersed in the polyethylene matrix even at very high concentration of the clay. Thermogravimetric analysis (TGA) shows good thermal stability of the PECNCs. Differential scanning calorimeter (DSC) results reveal considerable decrease in the crystalline phase of the PECNC samples. Results of permeability analysis show an increase in barrier properties of PECNC films. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers     

Syndiotactic Polystyrene/Organoclay Nanocomposites: Synthesis via In Situ Coordination‐Insertion Polymerization and Preliminary Characterization

Summary: Syndiotactic polystyrene (sPS)/organophilic clay nanocomposites were obtained by in situ coordination‐insertion polymerization of styrene. Two cationic surfactants (alkylammonium and alkylphosphonium) were used for the intercalation of montmorillonite (MMT). For each organically modified clay, three protocols were performed using an MAO‐activated hemi‐metallocene catalyst, in order to compare the influence of experimental conditions on the composite microstructure and on its thermal stability. The microstructures of nanocomposites were investigated by wide angle X‐ray scattering and DSC. Partially exfoliated or intercalated materials were obtained in all cases and a decrease of crystallinity is observed. Thermal properties were also studied by DSC and thermogravimetric analysis. The presence of clay does not have a strong influence on the sPS thermal transitions but the thermal decomposition process of the material was slowed down in the presence of few organoclay percents, particularly in the degradation beginning. The influence of these two organically modified clays on the thermal stability of the material is discussed.

Gel and suspension formed from the combination of cloisite with toluene (left) and styrene (right), respectively.     

Polymerization of ethylene: Some aspects of metallocene catalyst stabilization under homogeneous and heterogeneous reaction conditions

The development of metallocene‐based catalysts is an important advance on the study of polyolefinic materials. However, due to the rather different conditions that are established in actual applications, only around 3% of these polymers are obtained from metallocene technology. In view of this, novel strategies must be developed to produce metallocene‐based catalysts that are more thermally stable, which is a fundamental requirement to establish metallocene technologies. Homogeneous and heterogeneous polymerizations of ethylene were compared, using the Ph₂C(Cp)(Flu)ZrCl₂/MAO system. Homogeneous polymerizations were more active than the corresponding supported reactions. At low ethylene pressure, the addition of 1‐hexene increases the activity under homogeneous conditions. Nevertheless, this is not observed on the respective supported systems. At higher pressure conditions, all polymerizations attained higher yields. However, when the reaction temperature increases the activity significantly decreases under homogeneous conditions. Furthermore, when the polymerization was performed under heterogeneous conditions the deactivation was lower. The homogeneous and supported catalytic systems show different characteristics and, in all attempted reactions, immobilization of the molecular catalyst reduces the activity. However, the deactivation ratio was lower when the polymerization was performed under heterogeneous conditions. This means that immobilization of Ph₂C(Cp)(Flu)ZrCl₂ on silica can improve the thermal stability of the catalytic species. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Cp2TiCl2/坡缕石黏土负载型催化剂催化乙烯聚合的特性

利用浸渍法制备了两种二氯二茂钛（Cp₂TiCl₂）/坡缕石黏土负载型催化剂Cat-A 和Cat-B,并进行了乙烯淤浆聚合评价。对热活化黏土进行表征的结果表明,坡缕石黏土在热活化过程中由于配位结晶水的脱除表面主要由Lewis酸性位占据。黏土载体所具有的表面酸性使其具有完全不同于硅胶载体的负载茂金属催化剂聚合行为。在相同的聚合条件下,直接负载型催化剂的活性高于载体化学修饰型催化剂,甚至高于均相Cp₂TiCl₂催化剂。直接负载催化剂所得聚合产物的分子量和熔点低于载体化学修饰催化剂,且其产物性质受温度影响更为显著。以硅胶负载型茂金属催化剂作为对比,分析了表面具有较强Lewis酸性的载体活性中心性质,以此解释了直接负载型催化剂的乙烯聚合特性。对直接负载型催化剂不同时间段的聚合产物形态进行了扫描电镜观察,发现最终聚合产物中聚合物“纤维”和“纤维”聚集体形态的形成,并进一步分析了聚合物形态演化过程的特点。     

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.     

In‐situ synthesis of poly(ethylene terephthalate)/clay nanocomposites using TiO2/SiO2 sol‐intercalated montmorillonite as polycondensation catalyst

A novel organic montmorillonite, which could act as both polycondensation catalyst of poly(ethylene terephthalate) (PET) and filler of PET/clay nanocomposites, was prepared. Original montmorillonite was first treated with different amounts of poly(vinylpyrrolidone) (PVP), and then intercalated by TiO₂/SiO₂ sol to gain polycondensation catalytic activity. The acquired clay possessed excellent thermal stability and would not degrade during the polycondensation step. PET/clay nanocomposites were prepared via in‐situ polymerization using the organo‐clay as polycondensation catalysts. The morphologies of the nanocomposites were characterized by X‐ray diffraction and transmission electron microscope. The results indicated that the amount of PVP and TiO₂/SiO₂ sol strongly affected the dispersion state of the clay, and finally, partially exfoliated PET/clay nanocomposites were obtained. The nanocomposites had better properties than pure PET due to the incorporation of the delaminated clay layers. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

α-二亚胺镍溴化物/凹凸棒黏土负载催化剂催化乙烯聚合研究

A nickel-diimine catalyst [N, N'-bis(2,6-diisopropylphenyl)-1,4-diaza-2,3-dimethyl-1, 3-butadiene nickel dibromide, DMN] was supported on palygorskite clay for ethylene slurry polymerization. The effect of supporting methods on the catalyst impregnation was studied and compared. Pretreatment of the support with methylalumi-noxane (MAO) followed by DMN impregnation gave higher catalyst loading and catalytic activity than the direct impregnation of DMN. Catalyst activity as high as 5.42×105g PE·molNi-1·h-1 was achieved at ethylene pressure of 6.87×105 Pa and polymerization temperature of 20℃. In particular, the morphological change of the support during MAO treatment was characterized and analyzed. It was found that nano-fiber clusters formed during the support pretreatment, which increased the surface area of the support and favored the impregnation of the catalyst. The investigation of polymerization behavior of supported catalyst revealed that the polymerization rate could be kept at a relatively h     

Preparation of polypropylene‐based nanocomposites using nanosized MCM‐41 as support and in situ polymerization

MCM‐41 nanoparticles were used for preparing nanocomposites through the in situ polymerization of propylene. The performance of the catalytic system and the final properties of the materials obtained are highly dependent on the methodology used for impregnation of the catalyst onto the support particles, and therefore an optimization study for the impregnation methodology of the catalyst (Me₂Si(Ind)₂ZrCl₂) was carried out. Two different methodologies were used; the results in terms of catalytic activity and polymer molecular masses indicated that the most promising one involved the pre‐activation of the catalyst with the cocatalyst, methylaluminoxane, followed by impregnation onto the MCM‐41 nanoparticles. Thus, an optimized route for the preparation of polypropylene nanocomposites achieving significant improvements in catalyst activity was developed. The nanocomposite materials were characterized by GPC, TGA and DSC. The dispersion state and the size of the nanoparticles incorporated in the polypropylene matrix were investigated by transmission electron microcopy. Additionally, this methodology allows simultaneous control of the desired amount of support and the concentration of catalyst to be used in the in situ polymerization. © 2015 Society of Chemical Industry     

Propylene polymerization using combined syndio‐ and isospecific metallocene catalysts supported on silica/MAO

Syndiotactic and isotactic polypropylene were produced using the metallocene compounds Ph₂C(Flu)(Cp)ZrCl₂ and SiMe₂(2‐Me,4‐Ph‐Ind)₂ZrCl₂ in homogeneous system and supported on silica/MAO. These catalysts were evaluated either isolated or as a binary system. In the latter case, the iso‐ and syndiospecific metallocene complexes were immobilized together during the preparation of the supported catalyst. In a further experimental set, the syndio‐ and isospecific isolated heterogeneous catalysts were mixed at the moment of propylene polymerization. The polypropylenes obtained were evaluated using differential scanning calorimetry. The catalytic activities were also investigated. At all the studied polymerization temperatures, the results showed that the binary catalyst produced polypropylenes with lower melting temperatures in comparison with those obtained when the mixture of isolated supported syndio‐ and isospecific catalysts was employed. Moreover, the activation energies for the polymerization of all catalysts systems were calculated, resulting in a lower value for the binary system when compared to that employing the catalyst mixture and to both the isolated supported metallocene catalysts. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 628–637, 2006     

Influence of supported vanadium catalyst on ethylene polymerization reactions

BACKGROUND: In the research area of homogeneous Ziegler–Natta olefin polymerization, classic vanadium catalyst systems have shown a number of favourable performances. These catalysts are useful for (i) the preparation of high molecular weight polymers with narrow molecular weight distributions, (ii) the preparation of ethylene/R‐olefin copolymers with high R‐olefin incorporation and (iii) the preparation of syndiotactic polypropylenes. In view of the above merits of vanadium‐based catalysts for polymerization reactions, the development of well‐defined single‐site vanadium catalysts for polymerization reactions is presently an extremely important industrial goal. The main aim of this work was the synthesis and characterization of a heterogeneous low‐coordinate non‐metallocene (phenyl)imido vanadium catalyst, V(NAr)Cl₃, and its utility for ethylene polymerization. RESULTS: Imido vanadium complex V(NAr)Cl₃ was synthesized and immobilized onto a series of inorganic supports: SiO₂, methylaluminoxane (MAO)‐modified SiO₂ (4.5 and 23 wt% Al/SiO₂), SiO₂? Al₂O₃, MgCl₂, MCM‐41 and MgO. Metal contents on the supported catalysts determined by X‐ray fluorescence spectroscopy remained between 0.050 and 0.100 mmol V g^?1 support. Thermal stability of the catalysts was determined by differential scanning calorimetry (DSC). Characterization of polyethylene was done by gel permeation chromatography and DSC. All catalyst systems were found to be active in ethylene polymerization in the presence of MAO or triisobutylaluminium/MAO mixture (Al/V = 1000). Catalyst activity was found to depend on the support nature, being between 7.5 and 80.0 kg PE (mol V)^?1 h^?1. Finally, all catalyst systems were found to be reusable for up to three cycles. CONCLUSION: Best results were observed in the case of silica as support. Acid or basic supports afforded less active systems. In situ immobilization led to higher catalyst activity. The resulting polyethylenes in all experiments had ultrahigh molecular weight. Finally, this work explains the synthesis and characterization of reusable supported novel vanadium catalysts, which are useful in the synthesis of very high molecular weight ethylene polymers. Copyright © 2007 Society of Chemical Industry     

Effect of clay platelet dispersion as affected by the manufacturing techniques on thermal and mechanical properties of PMMA‐clay nanocomposites

In this work, the properties of Poly(methyl methacrylate) (PMMA)‐clay nanocomposites prepared by three different manufacturing techniques viz., solution mixing, melt mixing, and in‐situ bulk polymerization in presence of clay were studied. Morphological analysis revealed that the extent of intercalation and dispersion of the nanoclay were relatively higher in the in‐situ polymerized nanocomposites than those of solution and melt blended nanocomposites. Differential Scanning Calorimetric study indicated maximum increment in T_g of the PMMA in the in‐situ polymerized PMMA‐clay nanocomposites. Thermo gravimetric analysis showed improved thermal stability of PMMA in all the nanocomposites and the maximum improvement was for in‐situ polymerized nanocomposites. The storage moduli of all the nanocomposites were higher than the pure PMMA. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Modified preparation of HDPE/clay nanocomposite by in situ polymerization using a metallocene catalyst

In this study, preparation of high-density polyethylene (HDPE)/clay nanocomposite by in situ polymerization of ethylene using a zirconocene catalyst (bis-(cyclopentadienyl) zirconium dichloride (Cp₂ZrCl₂)) was investigated. To obtain higher efficiency, nanoclay particles (Na-montmorillonite) were modified by ammonia (NH₃), NH₃/methylaluminoxane (MAO), NH₃/dodecylamine (DDA), and NH₃/MAO/DDA systems. The results showed that the activity of the catalyst supported on the nanoclay particles modified by NH₃/MAO (762 g_p/mmol (Zr) t [atm]) was higher than that of the one supported on the unmodified nanoclay as well as the other prepared modified nanoclay-supported catalyst systems. The catalyst activities versus MAO concentration in NH₃/MAO treatment system and versus DDA concentration in NH₃/DDA system showed a maximum. Unexpectedly, a very low catalyst activity (180 g_p/mmol(Zr) t [atm]) was obtained using NH₃/MAO/DDA system. X-ray diffraction patterns showed that the HDPE/clay nanocomposites prepared by NH₃/MAO/DDA treatment system had less intercalated structure. Fourier transform infrared (FTIR) spectroscopy confirmed that water molecules of the nanoclay particles were reduced by NH₃ modification. DSC results revealed that crystallinity of the HDPE/clay nanocomposites increased with the modification of the nanoclay particles. The maximum degree of crystallinity of 80.8% was obtained for HDPE/clay nanocomposites prepared by the nanoclay modified by NH₃. In addition, nanoclay modification with NH₃, NH₃/MAO, and NH₃/DDA systems resulted in higher thermal decomposition temperature (~30 °C higher than 480 °C of the unmodified one). Such increase was not observed for the NH₃/MAO/DDA treatment system. Dynamic mechanical analysis showed an increase in the elastic modulus of the nanocomposite samples prepared by modified nanoclay particles, as well. Meanwhile, modification of the nanoclay particles by NH₃ led to the highest elastic behavior compared to the other modification systems. It was about 4.6 GPa which was 28% higher than the elastic modulus of the nanocomposite prepared by unmodified nanoclay particles.     

The effect of aluminum alkyls and BHT‐H on reaction kinetics of silica supported metallocenes and polymer properties in slurry phase ethylene polymerization

In slurry and gas phase catalytic ethylene polymerization processes, aluminum alkyl (AlR₃) compounds are usually present inside the reactor and their role either as co‐catalyst or scavenger is of considerable importance. Silica supported metallocene/methyl aluminoxane (MAO) catalysts show specific interactions with AlR₃ compounds. Therefore, this study shows an attempt to analyze and compare the effect of concentration as well as type of commonly used AlR₃ on slurry phase ethylene homopolymerization kinetics of silica supported (n‐BuCp)₂ZrCl₂/MAO catalyst. The obtained results indicate that the lower the concentration of smaller AlR₃ compounds, the higher the instantaneous catalytic activity. Concerning the polymer particle size distributions, a rise in fines generation has been observed with increasing AlR₃ content inside the reactor. Finally, it has been shown that the addition of 2,6‐di‐tert‐butyl‐4‐methylphenol (a substituted phenol) into the reactor containing AlR₃ reduces the influence of AlR₃ compounds on the reaction kinetics of silica supported metallocene/MAO catalysts. Polyethylene properties remain similar in all the studied scenarios. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45670.