Synthesis of polyethylene using ultrasonic energy with a metallocene catalyst

Ethylene polymer was synthesized by the treatment of a metallocene catalyst Zr(CP)₂Cl₂ solution with ultrasonic energy. Ultrasonic energy irradiation was used to change the polymer structure of the formed polymer. Different ultrasonic energy irradiation times were applied to the metallocene catalyst solution. The ultrasonic energy had an effect on the average molecular weight, molecular weight distribution, and polymer productivity. A lower average molecular weight and a narrower molecular weight distribution were produced with a longer ultrasonic irradiation time. The polymer productivity was almost constant when the metallocene catalyst was treated with ultrasonic energy. Finer polyethylene particles were produced with longer ultrasonic irradiation times. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 756–759, 2006     

Dimethylsilylbis(1‐indenyl) zirconium dichloride/methylaluminoxane catalyst supported on nanosized silica for propylene polymerization

A dimethylsilylene‐bridged metallocene complex, (CH₃)₂Si(Ind)₂ZrCl₂, was supported on a nanosized silica particle, whose surface area was mostly external. The resulting catalyst was used to catalyze the polymerization of propylene to polypropylene. Under identical reaction conditions, a nanosized catalyst exhibited much better polymerization activity than a microsized catalyst. At the optimum polymerization temperature of 55°C, the former had 80% higher activity than the latter. In addition, the nanosized catalyst produced a polymer with a greater molecular weight, a narrower molecular weight distribution, and a higher melting point in comparison with the microsized catalyst. The nanosized catalyst's superiority was ascribed to the higher monomer concentration at its external active sites (which were free from internal diffusion resistance) and was also attributed to its much larger surface area. Electron microscopy results showed that the nanosized catalyst produced polymer particles of similar sizes and shapes, indicating that each nanosized catalyst particle had uniform polymerization activity. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Nano‐sized silica supported Me2Si(Ind)2ZrCl2/MAO catalyst for ethylene polymerization

Nano‐sized and micro‐sized silica particles were used to support a zirconocene catalyst [racemic‐dimethylsilbis(1‐indenyl)zirconium dichloride], with methylaluminoxane as a cocatalyst. The resulting catalyst was used to catalyze the polymerization of ethylene in the temperature range of 40–70°C. Polyethylene samples produced were characterized with scanning electron microscopy (SEM), X‐ray diffraction (XRD), differential scanning calorimetry (DSC), and gel permeation chromatography (GPC). Nano‐sized catalyst exhibited better ethylene polymerization activity than micro‐sized catalyst. At the optimum temperature of 60°C, nano‐sized catalyst's activity was two times the micro‐sized catalyst's activity. Polymers obtained with nano‐sized catalyst had higher molecular weight (based on GPC measurements) and higher crystallinity (based on XRD and DSC measurements) than those obtained with micro‐sized catalyst. The better performances of nano‐sized catalyst were attributed to its large external surface area and its absence of internal diffusion resistance. SEM indicated that polymer morphology contained discrete tiny particles with thin long fiberous interlamellar links. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Influence of support friability and concentration of α‐olefins on gas‐phase ethylene polymerization over polymer‐supported metallocene/methylaluminoxane catalysts

The effects of support friability (Φ) and ethylene/comonomer ratios were investigated over supported metallocene/methylaluminoxane catalysts prepared with nine different porous polymeric supports and various comonomer concentrations with a 2‐L reactor operated in the semibatch gas‐phase mode at 80°C and 1.4 MPa. Φ of the supports was measured with a newly devised method. The performance of the supported catalysts depended on support Φ as follows. The average homopolymerization activities varied from less than 6 t of polyethylene (PE) (mol of Zr)^?1 h^?1 for low‐Φ catalysts to 10–20 t of PE (mol of Zr)^?1 h^?1 for moderate‐Φ catalysts and up to 100 t of PE (mol of Zr)^?1 h^?1 for the high‐Φ catalysts. The presence of 1‐hexene and propylene comonomers increased the activity of the low‐Φ catalysts by up to 20‐fold and 50‐fold, respectively; that is, there were very marked comonomer effects. Activity enhancement by 1‐hexene was less than 3‐fold for the moderate‐Φ catalysts, whereas the high‐Φ catalysts showed little activity enhancement. Sometimes, 1‐hexene even resulted in activity reductions. Very different particle morphologies were obtained with the catalysts of different Φ's. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 514–527, 2007     

Synthesis of reactor blend of linear and branched polyethylene using metallocene/Ni‐diimine binary catalyst system in a single reactor

This work reports the synthesis of a series of reactor blends of linear and branched polyethylene materials using a combination of [1,4‐bis(2,6‐diisopropylphenyl) acenaphthene diimine nickel(II) dibromide] ( 1 )/MMAO, known as an active catalyst for the production of branched polyethylene, and [rac‐ethylenebis(indenyl) zirconium dichloride] ( 2 )/MMAO, which is active for the production of linear polyethylene. The polymerization runs were performed at various levels of temperature, pressure, and catalyst 2 molar fractions. At 5°C, there was very low influence of catalyst 2 molar fraction on the overall catalyst activity. However, at 30°C and 50°C, the overall catalyst activity increased linearly with catalyst 2 molar fraction. The same linear dependency was also found for the polymerization reactions carried out at 60°C and 100°C. At various levels of temperature and ethylene pressure, higher melting temperature and crystallinity were observed with an increase in catalyst 2 molar fraction. At 60°C and 100 psig, the DSC thermograms of the polymers produced with 1 / 2 /MMAO exhibited two distinct peaks with melting temperatures closely corresponding to the melting temperatures of the polymers produced with the individual catalysts, 1 /MMAO and 2 /MMAO. The GPCV analysis of all polyethylene samples showed monomodal molecular weight distributions with low polydispersities. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2212–2217, 2005     

Influence of branch content,comonomer type,and crosshead speed on the mechanical properties of metallocene linear low‐density polyethylenes

The effects of branch content (BC) and comonomer type on the mechanical properties of metallocene linear low‐density polyethylene (m‐LLDPEs) were studied by means of a stress–strain experiment at room temperature. A total of 16 samples with different BCs and comonomer types were used. In addition, the effect of crosshead speed on the mechanical properties of m‐LLDPEs with different BCs was examined. The degree of crystallinity (X_t) of these copolymers was determined by differential scanning calorimetry. In addition, Ziegler–Natta linear low‐density polyethylenes (ZN‐LLDPEs) were also studied for comparison purposes. The increase in BC of m‐LLDPEs decreased X_t and the modulus. However, the ZN‐LLDPEs showed higher small‐strain properties but lower ultimate properties than the m‐LLDPEs with similar weight‐average molecular weights and BCs. In comparison with low‐BC resins, m‐LLDPEs with high BCs exhibited a stronger strain hardening during the stress–strain experiments. Strain hardening was modeled by a modified Avrami equation, and the order of the mechanically induced crystal growth was in the range of 1–2, which suggested athermal nucleation. The crosshead speed was varied in the range 10–500 mm/min. For low‐BC m‐LLDPEs, there existed a narrow crosshead speed window within which the maxima in modulus and ultimate properties were observed. The location of the maxima were independent of BC. The effect of the crosshead speed on the mechanical properties of the m‐LLDPEs was a strong function of BC. However, highly branched m‐LLDPE in this experiment showed a weak dependence on the crosshead speed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 5019–5033, 2006     

Ethylene polymerization with a silica‐supported iron‐based diimine catalyst

A supported iron‐based diimine catalyst (SC) was prepared by immobilization of 2,6‐bis[1‐(2,6‐diisopropylphenylimino)ethyl]pyridine iron chloride (I) on silica and employed in ethylene polymerization. The kinetic behavior of ethylene polymerization with SC was studied. The effects of the Al/Fe molar ratio, reaction temperature, and cocatalyst on the catalytic activity as well as the melting temperature, molecular weight, and morphology of the polymers obtained were also investigated. The results showed that good catalytic activities can be obtained even with a small amount of the cocatalyst methylaluminoxane (MAO) or triethylaluminum (AlEt₃). The polyethylenes obtained with a supported catalyst had higher molecular weight, higher melting temperature, and better morphology than those obtained with a homogeneous catalyst. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 466–469, 2003     

Effect of diatomite/polyethylene glycol binary processing aids on the rheology of a metallocene linear low‐density polyethylene

Flow performance of metallocene linear low‐density polyethylene (mLLDPE) containing small amounts of polyethylene glycol (PEG) diatomite and diatomite/PEG binary processing aids respectively was investigated. The mLLDPE melt viscosity is increased by the addition of diatomite, but is decreased by addition of PEG or the diatomite/PEG binary processing aids. It was also found that the viscosity reduction of mLLDPE with the addition of diatomite/PEG binary processing aid was significantly greater than that obtained with the addition of only PEG. The flow curves of mLLDPE containing diatomite/PEG binary processing aid show extremely lower value and stronger dependence on shear rate than the others. It is suggested that the rheological improvement of mLLDPE with diatomite/PEG binary processing aids resulted not entirely from the wall slip promoted by PEG; the intrinsic structure may have changed under the application of shear flow. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1546–1552, 2004     

Cocatalyst‐originated aluminum residues in fibrous,very high molar mass polyethylene

In this work, fibrous very high molar mass polyethylene was prepared by Cp₂TiCl₂, which was supported on methylaluminoxane (MAO) pretreated mesoporous silica fiber. After the polymerization, an “ordinary” washing procedure was not sufficient to remove the aluminum residues of the cocatalyst MAO from the polymerization product. When hydrochloric acid was used in the termination of the polymerization, the aluminum existed as [Al(H₂O)₆]Cl₃, the presence of which causes additional signals to DSC and XRD grams of the polyethylene. These signals have previously been interpreted to be attributed to the extended chain crystal structure of the polyethylene. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1812–1815, 2004     

Ethylene polymerization with methylaluminoxane/(nBuCp)2ZrCl2 catalyst supported on silica and silica‐alumina at different AlMAO/Zr molar ratios

Methylaluminoxane (MAO)/(nBuCp)₂ZrCl₂ metallocene catalytic system was supported on silica and silica‐alumina. The Zr loading was varied between 0.2–0.4 wt %, and the MAO amount was calculated to get (Al_MAO/Zr) molar ratios between 100 and 200, suitable for the industrial ethylene polymerization of supported metallocene catalysts. Catalytic activity was statistically analyzed through the response surface method. Within the ranges studied, it was found that Zr loading had a negative effect on polymerization activity, which increases with the (Al_MAO/Zr) molar ratio. Catalysts supported on silica‐alumina are more active than those supported on silica, needing less MAO to reach similar productivity, which constitutes an important advantage from an economical and environmental point of view. Supported catalysts were characterized by ICP‐AES, SEM‐energy‐dispersive X‐ray spectrometer, and UV‐Vis spectroscopy, whereas polyethylenes were characterized by GPC and DSC. Molecular weight and crystallinity are not influenced by Zr loading or (Al_MAO/Zr) ratio, in the range studied. In general, silica‐supported MAO/(nBuCp)₂ZrCl₂ catalysts give polyethylenes with higher molecular weight and polydispersity but lower crystallinity. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Ethylene polymerization by phenylenedimethylene‐bridged homobinuclear zirconocene/methylaluminoxane systems

In the presence of methylaluminoxane (MAO), ethylene polymerization was successfully performed with homobinuclear zirconocene complexes {[(C₅H₅)ZrCl₂](C₅H₄CH₂ C₆H₄CH₂C₅H₄)[(C₅H₅)ZrCl₂]; 3o , 4m , and 5p }, which were prepared conveniently by the reaction of disodium(phenylenedimethylene)dicyclopentadienide [C₆H₄(CH₂C₅H₄Na)₂] with 2 equiv of (N⁵‐Cyclopentadienyl)trichlorozirconium dimethoxyethane (CpZrCl₃(DME)) in tetrahydrofuran and characterized by ¹H‐NMR and elemental analysis. The effects of the polymerization parameters, such as the temperature, time, concentration of the catalyst, MAO/catalyst molar ratio, and isomeric difference of the homobinuclear metallocene complexes 3o , 4m , and 5p were studied in detail. The results showed that all three catalytic systems had moderate activities in ethylene polymerization and afforded polyethylene with relatively broad polydispersities. The catalytic activity of 4m was somewhat higher than that of 3o and 5p but lower than that of 4,4′‐bis(methylene)biphenylene‐bridged zirconocene catalysts; this indicated that the distance between the two metal centers was too short in comparison with a 4,4′‐bis(methylene)biphenylene bridge to increase the catalytic activity. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Nonisothermal crystallization kinetics of linear metallocene polyethylenes

The effect of weight‐average molecular weight (M_w) on the nonisothermal crystallization kinetics of linear metallocene polyethylene (m‐PE) was studied with modulated differential scanning calorimetry. Six linear m‐PEs of molecular weights in the range 122–934 kg/mol were prepared by gas‐phase polymerization. The cooling rate (R) was varied in the range 2–20°C/min, and it significantly affected the crystallization behavior. M_w had a weak influence on both the peak crystallization temperature and the crystallization onset temperature. All m‐PEs showed primary and secondary crystallizations. At both low and high R's, the crystallinity showed a significant drop (～ 30%) when M_w was increased from 122 to 934 kg/mol. At low R's (< 10°C/min), the rate parameters in the modified Avrami method [primary rate constant (k_R)] and Mo method [F(T)] of analyses agreed in suggesting that an increased M_w slowed the rate of crystallization. The M_w dependency of k_R followed the Arrhenius type (k_R = k_Roe²⁸¹/M_w, where k_Ro is a rate‐dependent constant). However, at higher R's, k_R approached a constant value. The order parameters obtained by the different methods of analysis (n and α) were independent of M_w, which suggests that the crystal type remained the same. Hoffman–Lauritzen theory was used for data analysis, and activation energy per segment showed a significant decrease, from 225.0 to 11.8 kJ/mol, when M_w was increased from 152 to 934 kg/mol. Finally, all methods of analysis suggested a significant effect of M_w on slowing the overall crystallization process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Copolymerization of ethylene/nonconjugated dienes over a Bis(2‐methyl indenyl) zirconium dichloride/methylaluminoxane catalyst system

Ethylene was copolymerized with 1,5‐hexadiene (1,5‐HD), 1,4‐hexadiene (1,4‐HD) and 1,7‐octadiene (1,7‐OD) with bis(2‐methyl indenyl) zirconium dichloride/methylaluminoxane. 1,5‐HD units formed the trans‐structured cyclopentane rings and 1‐butenyl side chains, and cross‐linking took place during ethylene/1,5‐HD (E15HD) copolymerizations. The lower the polymerization temperature was, the larger the amount of hot xylene (XYL)‐insoluble faction was. Copolymers of ethylene/1,7‐OD (E17OD) did not have any cyclic structures and were nearly insoluble in XYL when produced below 60°C. In contrast, all the copolymers of ethylene/1,4‐HD (E14HD) were completely soluble in XYL. The broadest differential scanning calorimetry melting peak was found for E15HD and then for E17OD, and the narrowest was found for E14HD due to the presence or the absence of the cyclic structures and cross‐linking. Addition of 1,7‐OD or 1,4‐HD as a comonomer reduced the polymerization rate and the molecular weight of the respective copolymers much more than that of 1,5‐HD. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1048–1058, 2002; DOI 10.1002/app.10397     

Use of silica from rice husk ash as an antiblocking agent in low‐density polyethylene film

In packaging applications, blocking is always found in low‐density polyethylene (LDPE) films. Practically, such problems can be solved by incorporation of antiblocking agents, for example, silica and talc. The objective of this research was to explore the possibility of using silica from rice husk ash (RHA silica) as an antiblocking agent in LDPE film. Properties of RHA silica were compared with commercial silica, Sylo‐1. The appropriate amount of silica to be used as an antiblocking agent in LDPE film was also investigated. The results indicate that RHA silica has a smaller particle size and a higher specific surface area but a higher bulk density than those of Sylo‐1 silica. In the plastic film industry, 500–1000 ppm of silica is added in LDPE films as an antiblocking agent. It was also found that LDPE film with 2000–3000 ppm RHA silica showed similar properties to LDPE film filled with commercial silica in terms of its blocking behavior, mechanical strength, and film clarity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 848–852, 2003     

Preparation of shish‐kebab and nanofiber polyethylene with chromium/Santa Barbara amorphous silica‐15 catalysts

Cr/SBA‐15 catalysts were prepared by the grafting of chromium nitrate nonahydrate [Cr(NO₃)₃·9H₂O] complexes onto SBA‐15 mesoporous materials. Shish‐kebab and nanofiber polyethylenes (PEs) were prepared under different temperatures via ethylene extrusion polymerization with the Cr(NO₃)₃·9H₂O catalytic system. The diameter of a single nanofiber was 100–250 nm. Scanning electron microscopy images showed that the polymer obtained from the SBA‐15‐supported catalyst under different polymerization temperatures produced nanofiber and/or shish‐kebab morphologies. X‐ray diffraction and differential scanning calorimetry were used to characterize microstructures of the materials. Polymers obtained with all of the catalysts showed a melting temperature, bulk density, and high load melt index; this indicated the formation of linear high‐density PE. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Partially hydrolyzed trimethylaluminum (PHT) as heterogeneous cocatalyst for the polymerization of olefins with metallocene complexes

A method for the preparation of a novel heterogeneous cocatalyst, partially hydrolyzed trimethylaluminum (PHT), has been developed and optimized for ethylene polymerization reactions. It is possible to generate PHT on nearly any support without much loss of catalyst activity. The carrier material can be SiO₂, AlF₃, B₂O₃, starch, cellulose, active carbon, polyethylene, polypropylene, polystyrene, etc. This new type of partially hydrolyzed trimethylaluminum (PHT) is synthesized by reacting such a carrier material with trimethylaluminum (TMA) in toluene to block all surface Lewis basic centers that could poison a cationic metallocene polymerization center. The subsequent addition of a calculated amount of water gives a heterogeneous PHT that is different from the common methylalumoxane (MAO). Various PHT cocatalysts were studied by ¹³C and ²⁷Al MAS NMR, scanning electron microscopy (SEM), and infrared spectroscopy (IR), and compared with solid MAO. Surface areas and porosities were determined according to the BET method. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 454–466, 2001     

Application of chemiluminescence to probe miscibility in metallocene‐catalyzed polyethylene blends

Chemiluminescence (CL) monitoring has successfully been applied to the study of the oxidative degradation of two‐component polyethylene blends made with commercially available low‐density polyethylene, linear low‐density polyethylene, high‐density polyethylene, and metallocene‐catalyzed linear low‐density polyethylene (mLLDPE) formulations. The emphasis in the analysis of the results is placed on blends containing mLLDPE to address the lack of CL information on these blends. The CL data are consistent with the thermal and physicomechanical properties of the blends, with a decreased blend miscibility being reflected in the CL data as a departure from the idealized behavior observed for more miscible blends. Furthermore, the results suggest that immiscibility in the solid state is reflected to some extent in the behavior of the melt. Preliminary experiments conducted to determine the level of consistency of CL results with respect to both variability between instruments and variability between techniques indicate a high degree of correlation in each case. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3006–3015, 2003     

Synthesis and characterization of polybutadiene with monotitanocene/methylaluminoxane catalyst

Butadiene was polymerized using a monotitanocene complex of η⁵‐pentamethylcyclopentadienyltribenzyloxy titanium [Cp*Ti(OBz)₃] in the presence of four types of modified methylaluminoxanes (mMAO), which contained different amounts of residual trimethylaluminum (TMA). The titanium oxidation states in Cp*Ti(OBz)₃/mMAO and Cp*Ti(OBz)₃/mMAO/triisobutylaluminum (TIBA) catalytic systems were determined by redox titration method. The effects of various oxidation states of titanium active species on butadiene polymerization were investigated. It was found that Ti(III) active species is more effective for preparing polybutadiene with high molecular weight. The addition of TIBA to the Cp*Ti(OBz)₃/mMAO system could reduce a greater number of Ti(IV) complexes to Ti(III) species and lead to significant increases of polymerization activity and molecular weight of polymer, whereas the polybutadiene microstructure was only slightly changed. On the basis of microstructure and property characterization by FTIR, ¹³C‐NMR, DSC, and WAXD, all resultant polymers were proved to be amorphous polybutadiene with mixed 1,2; cis‐1,4; and trans‐1,4 structures. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2494–2500, 2004     

Ziegler-Natta/茂金属复合催化剂制备双峰聚乙烯

通过把茂金属催化剂负载在Ziegler-Natta催化剂上制备了ZM复合催化剂,在单一聚合反应器内研究了ZM催化剂用于乙烯聚合制备双峰聚乙烯的性能。考察了催化剂中茂金属化合物的含量、聚合过程中反应温度、助催化剂的用量和共聚单体1-己烯的用量对催化剂乙烯聚合性能的影响规律。结果表明：采用ZM催化剂可以在单反应器内催化乙烯聚合得到分子量分布呈双峰的聚乙烯,聚乙烯的分子量分布达到155,聚合活性可达2.52×10⁷ g/molMt·h。     

Improvement in processability of metallocene polyethylene by ultrasound and binary processing aid

The effect of ultrasonic vibration and binary processing aid in improving the processability of metallocene linear low‐density polyethylene (mLLDPE) was investigated. During extrusion, ultrasonic vibration clearly reduced the die pressure and apparent viscosity of mLLDPE but had only a slight effect on its melt fracture. The effect of diatomite/PEG binary processing aid (BPA) was excellent in reducing the viscosity and eliminating the sharkskin fracture of mLLDPE. The effect of ultrasonic vibration and binary processing aid in improving the processability of mLLDPE was synergetic. With a combination of ultrasonic vibration and a small amount of processing aid, the flowability of mLLDPE was further improved, and the critical shear rate for the onset of sharkskin fracture was increased. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1927–1935, 2007