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Rice husk is an agricultural waste abundantly available from rice production. It was due to the high content of silica (SiO2) inside rice husk, burning it under the control condition provides ash with the silica content up to 97% which can be simultaneously or consequently extracted to obtain rice husk-derived silica (RHS). In order to valorize the RHS, in this study it was used as a support for zirconocene/MMAO catalyst in ethylene polymerization, compared with commercial silica (CMS). It was found that rice husk-derived silica (RHS) has a larger surface area and lower amount of impurities than CMS. After immobilizing MMAO cocatalyst onto the silicas, it was observed that both silicas exhibit good distribution of MMAO all over the particles, but RHS has a higher content of MMAO. When using both silicas in the polymerization systems, it was observed that RHS gave a higher catalytic activity to the polymerization system than CMS (202 and 150 kg pol/mol Zr h). This is due to RHS having the lower amount of impurities especially Na2O which remains only in CMS from the production of commercial silica. The polymer obtained from the polymerization system with RHS has a good morphology suggesting that RHS still retains the advantage of providing a polymer with a good morphology as same as the conventional silica supports. [ABSTRACT FROM AUTHOR]

In this study, four Ziegler-Natta (ZN) catalysts with the absence and presence of Lewis acids including TiCl4/MgCl2/THF (None-THF), TiCl4/ZnCl2/MgCl2/THF (Zn-THF), TiCl4/ZnCl2/AlCl3/MgCl2/THF (ZnAl-THF), and TiCl4/ZnCl2/FeCl2/MgCl2/THF (ZnFe-THF) were synthesized, characterized, and used for ethylene polymerization. This research aims to elucidate the hydrogen effects in different Lewis acid-doped ZN catalysts on ethylene polymerization behaviors in terms of catalytic activity and polymer properties. With the absence of hydrogen during polymerization, it was found that ZnCl2 decreased the catalytic, because it acted as a catalyst poison. The catalytic activity was in the order of None-THF > ZnFe-THF > ZnAl-THF > Zn-THF. Thus, the addition of second Lewis acids such as AlCl3 and FeCl2 was able to improve the catalytic activity of Zn-THF catalyst. In addition, ZnFe-THF catalyst exhibited slightly higher activity than ZnAl-THF catalyst. This is because FeCl2 may better participate in MgCl2 structure due to similar atomic radius, leading to more efficiently removal of the remaining THF in the final catalyst. With the presence of hydrogen during polymerization, the decrease in catalytic activity was in the order of ZnFe-THF < ZnAl-THF < Zn-THF < None-THF with increasing H2/C2H4 molar ratio from 0.08 to 0.60. The hydrogen response on molecular weight was also observed for all catalysts in this study. [ABSTRACT FROM AUTHOR]

Abstract: Ethylene homopolymerization by two types of Ziegler‐Natta catalyst including ZN‐THF and ZN‐EtOH catalysts was compared. The influences of hydrogen pressure and reaction time on catalytic activity using different types of catalyst were investigated. The EDX analysis and surface area measurement confirmed that ZN‐EtOH catalyst had better active center distribution than that of ZN‐THF. Thus, the ZN‐EtOH catalyst could retard the effect of hydrogen and show higher activity with increased hydrogen pressures. However, catalytic activity was lower with high hydrogen pressure. Moreover, polymerization time also has an influence on activity. Both catalysts showed the similar result where an increase in polymerization time can improve yield of polymer, but it decreased activity. In addition, it is seen that the increase in hydrogen pressure leads to decrease the melting temperature for polyethylenes, but it increases the crystallinity. [ABSTRACT FROM AUTHOR]

In this research, the modification of TiCl4/MgCl2/THF catalyst system with various metal chlorides was investigated on ethylene polymerization. Experimentally, metal chlorides (CaCl2, FeCl2 and ZnCl2) were simultaneously introduced different with TiCl4/MgCl2/THF catalyst. ICP analysis was used to determine the total amount of each metal in the catalyst. For polymerization reaction, TEA was used as cocatalyst and hexane was used as a medium solvent. The Al/Ti molar ratio was 140. The activity result of Ca-Al, Zn-Al and Fe-Al was 979, 1009 and 1476 kgPE/molTi.h, respectively. The coaddition of AlCl3 and FeCl2 in TiCl4/MgCl2/THF catalyst system exhibited the highest activity. It suggested that the co-addition of AlCl3 and FeCl2 has higher electronegativity (EN) and the radius of Fe2+ is closer to Mg2+ resulting in an increased efficiency of the THF removal. This result led to improve the catalyst performance. [ABSTRACT FROM AUTHOR]

ABSTRACT In this work, the effects of three types of cocatalyst having different alkyl groups, such as triethylaluminium (TEA), triisobutylaluminum (TiBA), and trioctylaluminium (TnOA), and their concentrations on the catalytic activity and polymer properties were investigated for the Ziegler-Natta catalyst containing alkoxide species. The drastic escalation of catalytic activity was observed when the ratio of Al/Ti was increased only for TEA because of its good diffusivity as proven by the electron spin resonance technique. Moreover, it was found that the characteristic of the alkyl group in cocatalyst affected on the chain transfer ability. The chain transfer ability of TnOA was found to be equal to the TiBA in spite of its concentration was higher. By the way, the cocatalyst types and their concentrations did not affect on the variety of active sites as seen in molecular weight distribution of polymer. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40884. [ABSTRACT FROM AUTHOR]

Highlights: [•] Methylaluminoxane was supported on ZrO2 unmodified and modified with SiCl4. [•] The supported cocatalysts were applied for living polymerization of propylene. [•] The modification effect with SiCl4 was clarified by using the living character. [•] The catalysts also conducted controlled copolymerization of ethylene and 1-hexene. [Copyright &y& Elsevier]

ABSTRACT In this research, ethylene polymerization was carried out in the presence of different additives (ZnCl2, SiCl4, and the combined ZnCl2-SiCl4) on TiCl4/MgCl2/THF catalytic system. The presence of ZnCl2-SiCl4 mixtures showed higher activity in ethylene polymerization when compared with the catalytic activity in the presence of single Lewis acids, ZnCl2, or SiCl4. The modified catalyst with ZnCl2-SiCl4 demonstrated the highest activity, which was more than three times the activity of the system without Lewis acid modification. The enhanced activity can be attributed to the reduction in the peak intensity of MgCl2/THF complexes with Lewis acid compounds as proven by XRD. This was reasonable because of some THF removal from the structure of MgCl2/THF by Lewis acid compounds. In addition to the effect of modification with additives on the partial elimination of THF, the catalytic activities could be increased due to the titanium atoms that have been locally concentrated on the surface as seen by energy dispersive X-ray spectroscopy measurement. On the basis of the in situ electron spin resonance measurement, the mixed metal chlorides (ZnCl2-SiCl4) addition could promote the amount of Ti3+after reduction with triethylaluminum. It revealed that the modification of TiCl4/MgCl2/THF catalytic system with mixed metal chlorides (ZnCl2-SiCl4) is very useful for ethylene polymerization. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1588-1594, 2013 [ABSTRACT FROM AUTHOR]

Bis [N-(3-tert-butylsalicylidene) cyclooctylamine] titanium dichloride (C8 FI; complex 1) was synthesized by the Schiff base reaction and formed complex with TiCl4. This catalyst is highly active for producing polyethylene having high molecular weight (1.1×106–1.97×106 g/mole) and narrow polydispersity (1–2) in the presence of MAO as co-catalyst under atmospheric pressure. Comparing with the bis[N-(3-tert-butylsalicylidene) cycloheptylamine] titanium dichloride (C7 FI; complex 2), complex 1 exhibits higher activity upon the same polymerization condition over the temperature from 20°C to 60°C. Polyethylene obtained from the complex 1 has molecular weight lower than that obtained from the complex 2 due to steric bulky congestion. Additionally, the molecular weight of polymer obtained from the complex 1 increased with increasing the polymerization time from 10 to 60min. It is evident that the complex 1 has a living fashion in ethylene polymerization. [ABSTRACT FROM AUTHOR]

Two commercial nanoclays were used here as catalytic fillers for production of polyethylene (PE) and linear low-density polyethylene (LLDPE) nanocomposites via in situ polymerization with zirconocene/MAO catalyst. It was found that both types of nanoclays designated as clay A and clay B can improve thermal stability to the host polymers as observed from a thermal gravimetric analysis (TGA). The distribution of the clays inside the polymer matrices appeared good due to the in situ polymerization system into which the clays were introduced during the polymer forming reaction. Upon investigating the clays by X-ray diffractometer (XRD) and Fourier transform infrared spectroscopy (FTIR), it was observed that the crucial differences between the two clays are the crystallite sizes (A < B) and the amounts of amine group (A < B). The higher amount of amine group in clay B was supposed to be a major reason for the lower catalytic activity of the polymerization systems compared to clay A resulting from its deactivating effect on zirconocene catalyst. However, for both clays, increasing their contents in the polymerization systems reduced the catalytic activity due to the higher steric hindrance occurring. [ABSTRACT FROM AUTHOR]

Nano-TiO particles with a range of crystallite sizes were synthesized by a conventional sol-gel method, and then used as nanoparticle substrates in the synthesis of LLDPE/TiO nanocomposites via in situ polymerization of ethylene/1-hexene with zirconocene/MMAO catalyst. It was found that the size of the nano-TiO crystallite nanoparticles can influence the catalytic activity in the polymerization system. The larger nano-TiO crystallites provided better catalytic activity in the polymerization system due to more space for monomer attack. In addition, by thermo-gravimetric analysis, it can be seen that the larger nano-TiO crystallites also exhibited lower interaction with available MMAO. Consequently, the MMAO reacted more efficiently with the zirconocene catalyst during the activation process, and enhanced polymerization catalysis. All the polymer nanocomposites products did not have well defined melting temperature indicating non-crystalline polymers. This is due to the high amount of hexene incorporation (based on C NMR). The difference in crystallite sizes of the nano-TiO also affected how 1-hexene became incorporated into the polymer nanocomposites. The smaller crystallite size of nano-TiO allowed greater 1-hexene incorporation due to depression of the reactivity of the ethylene. The contribution of this work helps develop a better understanding of the role of nano-TiO in the catalytic activity of the polymerization system and in the microstructure of the polymer composite product. However, this study only considers work on the laboratory scale, so for commercial application of these results, it is necessary to scale up the polymerization process. It is only at this stage, that other physical properties, such as the mechanical properties of these materials can be sensibly determined. [ABSTRACT FROM AUTHOR]

In this study, the influences of the Ti oxidation state on the catalytic properties of MgCl-supported Ziegler-Natta catalysts in ethylene homo- and co-polymerization with 1-hexene were investigated. Three catalysts having different Ti oxidation states were synthesized by milling TiCl, TiCl, or TiCl together with MgCl. With these catalysts having different Ti oxidation states, the polymerization conditions such as the Al concentration, temperature, and 1-hexene concentration were varied to figure out their catalytic abilities in ethylene homo- and co-polymerization. The Ti oxidation state affected the catalyst activity largely, having unique dependences on the polymerization conditions. A higher oxidation state led to a higher activity, slightly larger comonomer incorporation, and lower molecular weight as well as its narrower distribution. However, rough characteristics of copolymers were similar among the different Ti oxidation states. [ABSTRACT FROM AUTHOR]

MgCl2-SiO2/TiCl4 Ziegler-Natta catalysts for ethylene polymerization were prepared by impregnation of MgCl2 on SiO2 in heptane and further treatment with TiCl4. MgCl2·nEtOH adduct solutions were prepared with various EtOH/MgCl2 molar ratios for preparation of the MgCl2-supported and MgCl2-SiO2-supported catalysts in order to investigate the effect on polymerization performance of both catalyst systems. The catalytic activities for ethylene polymerization decreased markedly with increased molar ratios of [EtOH]/[MgCl2] for the MgCl2-supported catalysts, while for the bi-supported catalysts, the activities only decreased slightly. The MgCl2-SiO2-supported catalyst had relatively constant activity, independent of the [EtOH]/[MgCl2] ratio. The lower [EtOH]/[MgCl2] in MgCl2-supported catalyst exhibited better catalytic activity. However, for the MgCl2-SiO2-supported catalyst, MgCl2 can agglomerate on the SiO2 surface at low [EtOH]/[MgCl2] thus not being not suitable for TiCl4 loading. It was found that the optimized [EtOH]/[MgCl2] value for preparation of bi-supported catalysts having high activity and good spherical morphology with little agglomerated MgCl2 was 7. Morphological studies indicated that MgCl2-SiO2-supported catalysts have good morphology with spherical shapes that retain the morphology of SiO2. The BET measurement revealed that pore size is the key parameter dictating polymerization activity. The TGA profiles of the bi-supported catalyst also confirmed that it was more stable than the mono-supported catalyst, especially in the ethanol removal region. [ABSTRACT FROM AUTHOR]

Copolymerization of ethylene and 1-hexene for obtaining the linear low-density polyethylene was conducted along with silicas as supports for [ t-BuNSiMeFlu]TiMe/MMAO catalyst. Two silicas with different pore sizes were used to investigate the effect of pore sizes on copolymerization. In addition, gallium was also introduced into both silicas to improve their properties and enhance the catalytic activities of the system. It was found that before modification, the larger pore silica exhibited higher catalytic activity than the smaller one due to low internal diffusion resistance. After modification, both silicas exhibited higher catalytic activity comparing to their pristine condition. However, 1-hexene incorporation in the obtained copolymers was lower. The reduced surface area of silica after modification was the main reason for the decrease in 1-hexene incorporation. The properties of the copolymers by means of differential scanning calorimetry, gel permeation chromatography, and C NMR spectroscopy were further discussed in more detail. [ABSTRACT FROM AUTHOR]

In the present study, copolymerization of ethylene and 1-hexene was conducted with a series of ansa-fluorenylamidodimethyltitanium complexes, including [t-BuNSiMe2Flu]TiMe2 (complex 1), [cyclododecylNSiMe2Flu]TiMe2 (complex 2) and [t-BuNSiMe2(2,7-t-Bu2Flu)]TiMe2 (complex 3), activated by MMAO. The effect of these catalysts on catalytic behavior, namely activity, molecular weight and monomer reactivity ratios, has been investigated. The results showed that all of them acted by a single site polymerization mechanism and the molecular weight distribution is independent of catalyst structure. Based on the study, it revealed that the introduction of a t-butyl at the 2,7 position on the fluorenyl ligand is able to enhance both catalytic activity and copolymer molecular weight more than introducing a cyclododecyl on the amine, which is probably associated with the electronic effect exerted by the t-butyl substituent. The comonomer incorporation content was controllable over a wide range by adjusting the comonomer feed ratio. Moreover, referring to monomer reactivity ratio exploration, it seems that the substitution on the ansa-fluorenylamidodimethyltitanium complex tends to hinder the insertion of 1-hexene into the polymer chain, leading to the highest 1-hexene content for traditional complex 1. [ABSTRACT FROM AUTHOR]

This article reveals the dependence of crystalline phases in titania on the intrinsic activity during in situ polymerization of ethylene/1-hexene using the zirconocene/dMMAO catalyst to produce LLDPE/TiO nanocomposites. First, the TiO nanoparticles having different crystalline phases were employed as the nanofillers by impregnation with dMMAO to obtain dMMAO/TiO. Then, copolymerization of ethylene/1-hexene using zirconocene catalyst was performed in the presence of dMMAO/TiO. It was found that the catalytic activity derived from the anatase TiO (A) was about four times higher than that obtained from the rutile TiO (R). This was likely due to higher intrinsic activity of the active species present on the TiO (A). In addition, increased [Al]/[Zr] ratios apparently resulted in enhanced activities for both TiO (A) and TiO (R). However, the TiO (R) showed less deactivation upon increased [Al]/[Zr] ratios. This can be attributed to strong interaction between dMMAO and TiO (R) as proven by the TGA measurement. The microstructure of the LLDPE/TiO obtained was found to be random copolymer for both TiO (A) and TiO (R). [ABSTRACT FROM AUTHOR]

The present research focuses on investigation of the catalytic behaviors of MgCl2-SiO2/TiCl4/THF Ziegler-Natta (ZN) catalysts_ with fumed SiO2 variously treated with silane compounds. The non-treated silica (NTS) and other silicas treated with dimethylsilicone fluid (TSDMSF), dimethyldichlorosilane (TSDMDCS), and hexamethyldisilazane (TSHMDS) were employed. It was found that the Cat-TSDMDCS and Cat- TSHMDS exhibited remarkably high activity, even with a similar bulk Ti content as the others. Thus, the more powerful technique of XPS analysis was used to determine the Ti content at the catalyst surface. It was evident that the surface concentrations of Ti could play important role on the catalyst activity. As the result, the increased activity is proportional to the surface concentration of Ti. It was mentioned that the change in surface concentration of Ti with different treated silica can be attributed to the effect of silane spacer group and steric hindrance. The distribution of Ti on the external surface can be also proven by means of EDX mapping, which matched the results obtained by XPS analysis. The treated silica also resulted in narrower molecular weight distribution (MWD) due to the more uniform active sites produced. There was no significant change in polymer morphology upon treatment of the silica. [ABSTRACT FROM AUTHOR]

The present research focuses on investigation of the catalytic behaviors of MgCl2-SiO2/TiCl4/THF Ziegler-Natta (ZN) catalysts_ with fumed SiO2 variously treated with silane compounds. The non-treated silica (NTS) and other silicas treated with dimethylsilicone fluid (TSDMSF), dimethyldichlorosilane (TSDMDCS), and hexamethyldisilazane (TSHMDS) were employed. It was found that the Cat-TSDMDCS and Cat- TSHMDS exhibited remarkably high activity, even with a similar bulk Ti content as the others. Thus, the more powerful technique of XPS analysis was used to determine the Ti content at the catalyst surface. It was evident that the surface concentrations of Ti could play important role on the catalyst activity. As the result, the increased activity is proportional to the surface concentration of Ti. It was mentioned that the change in surface concentration of Ti with different treated silica can be attributed to the effect of silane spacer group and steric hindrance. The distribution of Ti on the external surface can be also proven by means of EDX mapping, which matched the results obtained by XPS analysis. The treated silica also resulted in narrower molecular weight distribution (MWD) due to the more uniform active sites produced. There was no significant change in polymer morphology upon treatment of the silica. [ABSTRACT FROM AUTHOR]

This research aimed to investigate the copolymerization of ethylene and various 1-olefins. The comonomer lengths were varied from 1-hexene (1-C6) up to 1-octadecene (1- C18) in order to study the effect of comonomer chain length on the activity and properties of the polymer in the metallocene/MAO catalyst system. The results indicated that two distinct cases can be described for the effect of 1-olefin chain length on the activity. Considering the short chain length comonomers, such as 1-hexene, 1-octene and 1-decene, it is obvious that the polymerization activity decreased when the length of comonomer was higher, which is probably due to increased steric hindrance at the catalytic center hindering the insertion of ethylene monomer to the active sites, hence, the polymerization rate decreased. On the contrary, for the longer chain 1-olefins, namely 1-dodecene, 1- tetradecene and 1-octadecene, an increase in the comonomer chain length resulted in better activity due to the opening of the gap aperture between Cp(centroid)-M-Cp-(centroid), which forced the coordination site to open more. This effect facilitated the polymerization of the ethylene monomer at the catalytic sites, and thus, the activity increased. The copolymers obtained were further characterized using thermal analysis, X-ray diffraction spectroscopy and 13C-NMR techniques. It could be seen that the melting temperature and comonomer distribution were not affected by the 1-olefin chain length. The polymer crystallinity decreased slightly with increasing comonomer chain length. Moreover, all the synthesized polymers were typical LLDPE having random comonomer distribution. [ABSTRACT FROM AUTHOR]

This article reveals the effects of mixed activators on ethylene polymerization and ethylene/1-hexene copolymerization over MgCl2/SiO2-supported Ziegler-Natta (ZN) catalysts. First, the conventional ZN catalyst was prepared with SiO2 addition. Then, the catalyst was tested for ethylene polymerization and ethylene/1-hexene (E/H) co-polymerization using different activators. Triethylaluminum (TEA), tri-n-hexyl aluminum (TnHA) and diethyl aluminum chloride (DEAC), TEA+DEAC, TEA+TnHA, TnHA+ DEAC, TEA+DEAC+TnHA mixtures, were used as activators in this study. It was found that in the case of ethylene polymerization with a sole activator, TnHA exhibited the highest activity among other activators due to increased size of the alkyl group. Further investigation was focused on the use of mixed activators. The activity can be enhanced by a factor of three when the mixed activators were employed and the activity of ethylene polymerization apparently increased in the order of TEA+ DEAC+TnHA > TEA+DEAC > TEA+TnHA. Both the copolymerization activity and crystallinity of the synthesized copolymers were strongly changed when the activators were changed from TEA to TEA+DEAC+TnHA mixtures or pure TnHA and pure DEAC. As for ethylene/1-hexene copolymerization the activity apparently increased in the order of TEA+DEAC+TnHA > TEA+TnHA > TEA+DEAC > TnHA+DEAC > TEA > TnHA > DEAC. Considering the properties of the copolymer obtained with the mixed TEA+DEAC+TnHA, its crystallinity decreased due to the presence of TnHA in the mixed activator. The activators thus exerted a strong influence on copolymer structure. An increased molecular weight distribution (MWD) was observed, without significant change in polymer morphology. [ABSTRACT FROM AUTHOR]

Abstract: The study showed that the use of silica-supported aluminoxanes as coactivator can alter the catalytic behaviors of MgCl2/diethylphthalate (DEP)/TiCl4 catalyst with triethylaluminum (TEA) as an activator for propylene polymerization. It was found that the catalytic activities were ranged between 380 and 760kg PP/mol.Ti.h within the order of dMMAO/SiO2 >MAO/SiO2 >MMAO/SiO2 >dMMAO>no coactivator>SiO2. The TGA analysis revealed that the strong interaction between aluminoxane compounds and support apparently resulted in a decreased catalytic activity. Based on the polymer microstructure, it indicated that an enhanced activity can be attributed to the increase in active site concentration. [Copyright &y& Elsevier]

Abstract: In the present study, the polymerization behaviors of ethylene–propylene (EP) copolymerization with a zirconocene/MAO catalyst upon the addition of a small amount of diene were investigated. It indicated that besides the addition of dienes, the polymerization behaviors were also dependent on the E/P ratios and types of diene. Apparently, diene addition resulted in decreased activity, especially at high E/P ratio (E/P=3). In all cases, the addition of 1,4 hexadiene (1,4 HD) resulted in the lowest activities. It seemed that there was no significant change in the microstructure of EP elastomers upon different E/P ratios. The characteristics of polymer obtained by means of DSC and 13C NMR were further discussed in more detail. [Copyright &y& Elsevier]

Abstract: The present study revealed the effect of different TiO2 nanoparticles employed on catalytic and characteristic properties of LLDPE/TiO2 nanocomposites synthesized by the in situ polymerization with zirconocene/dMMAO catalyst. It was found that the presence of rutile phase in titania apparently resulted in decreased activities due to low intrinsic activity of active sites being present. Based on 13C NMR results, all LLDPE/TiO2 samples exhibited the random copolymer having different degree of 1-hexene insertion. The highly dispersion of titania can enhance the degree of 1-hexene insertion resulting in decreased crystallinity. [Copyright &y& Elsevier]

Abstract: Here, the copolymerization of ethylene/1-octene with zirconocene/dMMAO catalyst using different pore sized silica-based supports was investigated. It revealed that the large pored silica [SiO2 (LP)] exhibited the highest polymerization activity due to both highest amount of available active sites present along with the moderate interaction between dMMAO and the support. The strong interaction between dMMAO and the support as proven by TGA analysis apparently resulted in dramatically decreased polymerization activity for the bimodal pored silica–alumina [Si–Al (BP)]. The copolymers produced were further characterized by means of DSC and 13C NMR. Although they exhibited the similar triad distribution, the degree of 1-octene insertion was different. [Copyright &y& Elsevier]

A TiCl4/ethylbenzoate/MgCl2 Ziegler-Natta catalyst was pretreated with chemically different poisoning compounds to investigate their effects on the catalyst activity and stereospecificity for propylene polymerization. The poisoning power on the activity was in the order of methanol > acetone > ethyl acetate. A kinetic analysis using the stopped-flow method revealed that addition of the poisoning materials decreased the activity through the reduction of the number of active sites, whereas the catalyst isospecificity was hardly affected by these materials. [ABSTRACT FROM AUTHOR]

Abstract: The LLDPE/Al2O3 nanocomposites synthesized by the in situ polymerization with dried-modified methylaluminoxane (d-MMAO)/zirconocene catalyst were investigated. First, after vacuum heated the Al2O3 nanofiller, the d-MMAO as the cocatalyst was impregnated onto it. Then, ethylene/1-hexene copolymerization was carried out with the presence of different amounts of d-MMAO/Al2O3 in a 100mL semi-batch stainless steel autoclave reactor. After filtration, the obtained LLDPE nanocomposite was characterized by means of scanning electron microscopy (SEM)/energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), gel permeation chromatography (GPC), differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR). It was found that the polymerization activity strongly depended on the [Al]dMMAO/[Zr]cat ratios. The addition of Al2O3 nanofiller apparently resulted in increased melting temperature and molecular weight of LLDPE without any change in molecular weight distribution (MWD). [Copyright &y& Elsevier]

The bimodal polyethylene obtained from TiO2-supported zirconocene/MAO catalyst was observed during polymerization of ethylene and ethylene/1-hexene. By means of XPS, it revealed that TiO2 consisted of Ti3+ (BE = 462.6 eV) and Ti4+ (BE = 464.9 eV). The dual catalytic sites were attributed to the presence of Ti3+ and Ti4+ in TiO2. [ABSTRACT FROM AUTHOR]

Abstract: In the present study, the characteristics and catalytic properties of [t-BuNSiMe2Flu]TiMe2/dMMAO catalyst dispersed on various supports towards ethylene/1-octene copolymerization were investigated. First, the dMMAO was impregnated onto various supports, such as SiO2, SiO2–TiO2, and TiO2. Then, copolymerization of ethylene/1-octene was conducted with and without the presence of supports in different solvent mediums. The SiO2–TiO2 support exhibited the highest activity among all the supports. The high activity observed for the SiO2–TiO2 support can be attributed to fewer interactions between the support and dMMAO, as confirmed by XPS and TGA results. The different solvents can alter the nature of the catalyst in two ways: (i) changing the interactions between the support and cocatalyst and/or (ii) changing the form of active species i.e., active ion-pair and solvent-separated ion-pair, as seen in the homogeneous system. However, there was no effect with regards to activity of the solvent mediums employed for the homogeneous system. It is worth noting that the Ti-complex made possible high incorporation of 1-octene having the triblock (OOO) and diblock (EOO) copolymers. The properties of copolymers by means of GPC, DSC, and 13C NMR were further discussed in more detail. [Copyright &y& Elsevier]

Abstract: Here, we revealed the effect of particle size of the nanoscale SiO2 on catalytic and characteristic properties of LLDPE/nano-SiO2 composites synthesized via the in situ polymerization with a zirconocene/MAO catalyst. In the experiment, SiO2 (10 and 15nm) was first impregnated with MAO. Then, copolymerization of ethylene/1-hexene was performed in the presence of nano-SiO2/MAO to produce LLDPE/nano-SiO2 composites. It was found that the larger particle exhibited higher polymerization activity due to fewer interactions between SiO2 and MAO. The larger particle also rendered higher insertion of 1-hexene leading to decreased melting temperature . There was no significant change in the LLDPE molecular structure by means of 13C NMR. [Copyright &y& Elsevier]

A certain amount of CaO enhanced the activity of Ziegler–Natta catalyst during propylene polymerization, but decreased isotacticity. The results indicated that CaO accelerated the initial polymerization rates and improved catalyst against deactivation without effects on melting point, crystallinity and morphology of polypropylene. The electron spin resonance (ESR) results revealed that CaO facilitated the reduction of Ti4+ species. [ABSTRACT FROM AUTHOR]

Abstract: In the present study, the impact of diene addition during copolymerization of ethylene and propylene using a metallocene/MAO catalyst was investigated. It showed that with a small amount of diene added, the dienes (except for ENB) did not incorporate in the polymer backbone pronouncedly. However, the addition of dienes can alter the incorporation of ethylene and propylene in the polymer backbone according to different types of dienes used. The catalytic behaviors and yields were not significant changes with the addition of dienes. The characteristics of polymer obtained using 13C NMR, SEM, and DSC were also further discussed in more detail. [Copyright &y& Elsevier]

The present study showed enhanced activities of ethylene/1-octene copolymerization via TiO2-SiO2 mixed oxides-supported MAO with a zirconocene catalyst. It was proposed that titania was decorated on silica surface and acted as a spacer to anchor MAO to the silica support resulting in less steric hindrance and less interaction on the support surface. [ABSTRACT FROM AUTHOR]

Effect of SiCl4-modified silica/MAO-supported Et[Ind]2ZrCl2 metallocene catalyst on copolymerization of ethylene with α-olefins was investigated. Effect of SiCl4 on activities was diminished with higher α-olefins. Molecular weights of copolymers decreased with SiCl4 modification. SiCl4 modification also resulted in a lower molecular weight distribution. 13C NMR showed that ethylene incorporation in all systems gave copolymers with similar triad distribution. In addition, a narrow branching distribution can be achieved with SiCl4 modification. [Copyright &y& Elsevier]

Activities of ethylene/α-olefin copolymerization were found to increase with silane-modified silica-supported MAO using ansa-zirconocene catalyst. The increase in activities was less pronounced when higher α-olefins were used. However, silane modification resulted in the narrower molecular weight distribution of polymers. 13C NMR revealed that ethylene incorporation in all systems gave polymers with the similar triad distribution. [ABSTRACT FROM AUTHOR]

Polyethylene-cellulose biocomposites were synthesized here via the ethylene polymerization with metallocene as a catalyst along with methylaluminoxane (MAO) as a cocatalyst. The immobilization method in which the catalyst or cocatalyst is fixed onto the catalytic filler (cellulose) can be classified into 3 methods according to the active components fixed onto the filler surface: 1) only metallocene catalyst (Cellulose/Zr), 2) only MAO cocatalyst (Cellulose/MAO) and 3) mixture of metallocene and MAO (Cellulose/(Zr+MAO)). It was found that the different immobilization methods or different fillers altered the properties of the obtained composites and also the catalytic activity of the polymerization systems. It was found that Cellulose/MAO provided the highest catalytic activity among all fillers due to a crown-alumoxane complex, which caused the heterogeneous system with this filler behaved similarly to the homogeneous system. The different fillers also produced the biocomposites with some different properties such as crystallinity which Cellulose/Zr provided the highest crystallinity compared with other fillers as observed by a thermal gravimetric analysis-differential scanning calorimetry (TGADSC). Nevertheless, the main crystal structure indicated to the typical polyethylene was still observed for all obtained biocomposites with different fillers as observed by an X-ray diffractometer (XRD). [ABSTRACT FROM AUTHOR]

Abstract: In the present study, the solvent effects on the catalytic behaviors of [t-BuNSiMe2Flu]TiMe2 complex during ethylene/1-hexene (EH) copolymerization were investigated. Based on the study, it revealed that activities of polymerization strongly depended on the solvent medium used regarding to its dielectric constant value (ε). In fact, four solvent mediums such as heptane, chlorobenzene, toluene, and dichloromethane were selected. It was found that at 70°C, the catalytic activity was the highest when toluene was employed during ethylene polymerization and EH copolymerization. However, with changing the polymerization temperature to 0°C, the solvent effect was less pronounced and low activities were obtained. In order to give a better explanation, the contact ion-pair model was applied. The microstructure of polymer was further discussed in more details. [Copyright &y& Elsevier]