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     

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     

Mechanical,rheological, thermal,and morphological properties of blends based on poly(propylene)/poly(propylene‐co‐1‐octene)/poly(ethylene‐co‐1‐octene)

The effect of addition of propylene copolymer, produced by metallocene catalysts, on the mechanical, rheological, and morphological properties of blends based on poly(propylene) (PP) and ethylene–1‐octene copolymer (EOC) was evaluated. It was observed that the addition of 2 wt % propylene–1‐octene copolymer (POC) improved the impact strength of the EOC/PP blends. The rheological analysis indicated that the addition of propylene copolymer produced materials with improved processability. Thermal and morphological analysis showed that the POC acts as a compatibilizer on the EOC/PP blends. © 2003 Wiley Periodicals, J Appl Polym Sci 89: 1690–1695, 2003     

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     

Comparative study of propylene polymerization using monosupported and bisupported titanium‐based Ziegler–Natta catalysts

Heterogeneous Ziegler–Natta systems—MgCl₂ (ethoxide type)/TiCl₄/di‐n‐butyl phthalate (DNBP)/triethylaluminum (TEA)/dimethoxymethylcyclohexylsilane (DMMCHS) and SiO₂/MgCl₂ (ethoxide type)/TiCl₄/DNBP/TEA/DMMCHS—were studied for the polymerization of propylene. The slurry polymerization of propylene was carried out with the catalyst systems in n‐heptane. Both systems performed with optimum activity at a particular [Al]/[DMMCHS]/[Ti] molar ratio. The ratio to reach the highest activity was much lower for the bisupported catalyst system. The productivity of the bisupported catalyst was higher than that of the monosupported one. Polypropylene of a high isotacticity index (II; >96%) was obtained with both systems and did not significantly change with an increasing [Al]/[DMMCHS]/[Ti] molar ratio. The addition of hydrogen as a chain‐transfer agent reduced II of the polymers obtained with both systems. The effect of the polymerization temperature (40–75°C) on the viscosity‐average molecular weight (M_v) and II showed a decrease in both cases. The bisupported catalyst system produced a polymer with higher M_v. The effect of temperature on II was similar for both the monosupported and bisupported systems. A monomer pressure of 2.02 × 10⁵ to 0.8 × 10⁶ Pa increased M_v of the obtained polymer. II of the polymer slightly decreased with increasing monomer pressure. The titanium content of the catalyst was 1.70 and 3.55% for the monosupported and bisupported systems, respectively. The surface area of the bisupported catalyst was higher than that of the monosupported catalyst. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2220–2226, 2006     

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     

Characterization and evaluation of supported rac‐dimethylsilylenebis(indenyl)zirconium dichloride on ethylene polymerization

rac‐Dimethylsilylenebis(indenyl)zirconium dichloride was grafted onto commercial methyl aluminoxane modified silica (SMAO) at different loadings (0.1–1.5 wt % Zr/SMAO). Supported catalysts were evaluated in ethylene polymerization with isoprenylaluminum as a cocatalyst. The characterization of two supported catalysts bearing 0.3 and 0.8 wt % Zr/SiO₂ by extended X‐ray absorption fine structure indicated that the number and the intensity of the peaks beyond the coordination shell, associated with the next nearest neighbors, depended on the Zr concentration. For the catalyst with a higher Zr content, only one peak (2.8 Å) was observed. The catalyst with 0.3 wt % Zr/SMAO presented two small peaks at 2.8 and 3.8 Å. Polymers produced with the supported catalysts presented lower crystallinity and higher molar mass and polydispersity values in comparison to that produced by the homogeneous one. Gel permeation chromatogram deconvolution suggested the presence of four catalyst sites for the supported systems. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Suppression of metallocene catalyst leaching by the removal of free trimethylaluminum from methylaluminoxane

The leaching of the catalyst zirconocene dichloride (Cp₂ZrCl₂) from an SBA‐15 silica support during ethylene polymerization was studied; severe leaching was observed when commercial methylaluminoxane (MAO) was used as the cocatalyst. However, the removal of free trimethylaluminum (TMA) from an MAO solution with a sterically hindered phenol reduced the catalyst leaching by 97–100%. The results obtained from the leaching experiments with TMA‐free MAO suggested that the major reason for catalyst leaching was the free TMA in the commercial MAO solution, not the pure MAO itself. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4632–4635, 2006     

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     

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     

Nanosized silica‐supported metallocene/MAO catalyst for propylene polymerization

A nanosized silica particle was used as the support to prepare an Et[Ind]₂ZrCl₂/MAO catalyst for propylene polymerization of polypropylene. The catalyst and the polymer produced were characterized with nitrogen adsorption, ICP, DSC, SEM, TEM, XRD, solution viscometer, ¹³C NMR and optical microscopy. The effects of polymerization temperature and [Al]/[Zr] ratio on catalyst activity and polymer melting point were investigated. Under identical reaction conditions, nanosized catalyst exhibited better polymerization activity than the microsized catalyst (e.g., the former had 64% higher activity than the latter at the optimum polymerization temperature (50°C) and [Al]/[Zr] = 570). DSC results indicated that polymer melting point increased with the increase of [Al]/[Zr] ratio and with the decrease of polymerization temperature. XRD results showed that the percentage of γ crystals increased with decreasing [Al]/[Zr] ratio. Electron microscopic results showed that the polymer particle size increased with increasing polymerization temperature. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2573–2580, 2006     

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 and characterization of propylene‐α‐olefin random copolymers with isotactic propylene sequence. II. Propylene–hexene‐1 random copolymers

A series of novel hexene‐1–propylene random copolymers with isotactic sequence of propylene was synthesized with a MgCl₂‐supported Cr(acac)₃ catalyst. The molecular weight distribution of copolymers and homopolymers was considerably narrower than that of typical polyolefins produced by heterogeneous Ziegler–Natta catalysts. The crystallizability of the copolymers having a propylene‐unit content of more than 50 mol % drastically decreased with decreasing propylene‐unit content, and the copolymers with a propylene content of less than 50 mol % were completely amorphous. In the present novel type of random copolymers with crystallizable and noncrystallizable units, a single glass transition was observed between pure polypropylene and polyhexene‐1, and a major component was found to govern the final morphology and the mechanical characteristics. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2949–2954, 2004     

Structural and ultraviolet‐protective properties of nano‐TiO2‐doped polypropylene filaments

Textiles, with appropriate light absorbers and suitable finishing methods, can be used as ultraviolet (UV) protection materials. In this study, we investigated the effects of nano‐TiO₂ particles on the UV‐protective and structural properties of polypropylene (PP) textile filaments. Master batches of PP/TiO₂ nanoparticles were prepared by melt compounding before spinning, and filaments incorporating 0.3, 1, and 3% TiO₂ nanoparticles were spun in a pilot melt‐spinning machine. The structural properties of the nanocomposite fibers were analyzed with scanning electron microscopy, X‐ray diffractometry, differential scanning calorimetry, and tensile tests. The UV‐protection factor was determined to evaluate the UV‐protective properties of the filaments. In conclusion, although the structure and mechanical properties of the nanocomposite filaments were slightly affected by the addition of nano‐TiO₂, the UV‐protective properties of the PP filaments improved after treatment with nano‐TiO₂, and the nanocomposite filaments exhibited excellent UV protection. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

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     

Gas‐phase ethylene polymerization using zirconocene supported on mesoporous molecular sieves

Mesoporous molecular sieves, with pore diameters of 2.6–25 nm, were impregnated with methylaluminoxane and bis(butylcyclopentadienyl)zirconium dichloride and tested as catalysts for the gas‐phase homopolymerization of ethylene at ethylene pressures of 200 psi and temperatures of 50–100°C and for 1‐hexene/ethylene copolymerization at 70°C. The activities and activity profiles, at constant Zr and Al contents, depended on the pore size of the supports and the polymerization temperature. Maximum activities for both the homopolymerizations and copolymerizations were observed for catalysts made with supports having pore diameters of 2.6 and 5.8 nm. Homopolymerization activities were highest at temperatures of 70–80°C; average homopolymerization and copolymerization activities up to 9000 kg of polyethylene/(mol of Zr h) were obtained. The weight‐average molecular weights (M_w's) were not a function of the support pore size but decreased with increasing reaction temperatures, from about 260,000 at 50°C to about 165,000 at 100°C. The polydispersities were essentially constant at 2.5 ± 0.2 for the homopolymers. M_w's for the 1‐hexene/ethylene copolymers had an average value of 117,000 with an average polydispersity of 2.8. The amount of triisobutyl aluminum added to the reactor significantly affected the activity and activity profiles. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1161–1177, 2003     

Novel preparation of poly(propylene)–layered silicate nanocomposites

We used a novel approach to prepare poly(propylene)–clay nanocomposite starting from pristine montmorillonite and reactive compatibilizer hexadecyl trimethyl ammonium bromide. The nanocomposite structure was revealed by X‐ray diffraction and high‐resolution electronic microscopy. The thermal properties of the nanocomposite were investigated by thermogravimetric analysis. An increase of thermal stability was observed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2586–2588, 2003     

Poly(propylene)–poly(propylene)‐grafted maleic anhydride–organic montmorillonite (PP–PP‐g‐MAH–Org‐MMT) nanocomposites. II. Nonisothermal crystallization kinetics

The nonisothermal crystallization kinetics of poly(propylene) (PP), PP–organic‐montmorillonite (Org‐MMT) composite, and PP–PP‐grafted maleic anhydride (PP‐g‐MAH)–Org‐MMT nanocomposites were investigated by differential scanning calorimetry (DSC) at various cooling rates. Avrami analysis modified by Jeziorny and a method developed by Mo well‐described the nonisothermal crystallization process of these samples. The difference in the exponent n between PP and composite (either PP–Org‐MMT or PP–PP‐g‐MAH–Org‐MMT) indicated that nonisothermal kinetic crystallization corresponded to tridimensional growth with heterogeneous nucleation. The values of half‐time, Z_c; and F(T) showed that the crystallization rate increased with the increasing of cooling rates for PP and composites, but the crystallization rate of composites was faster than that of PP at a given cooling rate. The method developed by Ozawa can also be applied to describe the nonisothermal crystallization process of PP, but did not describe that of composites. Moreover, the method proposed by Kissinger was used to evaluate the activation energy of the mentioned samples. The results showed that the activation energy of PP–Org‐MMT was much greater than that of PP, but the activation energy of PP–PP‐g‐MAH–Org‐MMT was close to that of pure PP. Overall, the results indicate that the addition of Org‐MMT and PP‐g‐MAH may accelerate the overall nonisothermal crystallization process of PP. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3093–3099, 2003     

Propylene/1‐Hexene Copolymer as a Tailor‐Made Poly(propylene) for Membrane Preparation via the Thermally Induced Phase Separation (TIPS) Process

Summary: Poly[propylene‐co‐(1‐hexene)], one example of a “tailor‐made poly(propylene)”, was synthesized using an iso‐specific metallocene catalyst in order to study the influence of copolymer composition on the pore size of isotactic poly(propylene) (iPP) membranes prepared by the TIPS process. The structure of the copolymers and their properties in solution were analyzed and discussed in relation to the polymer‐diluent phase diagram, the droplet growth kinetics during the TIPS process, the viscosity of the system and the final pore size of the membranes. The crystallization curve in the phase diagram was found to shift significantly as comonomer content increased and thus the droplet growth period was drastically increased. The resulting increase of the characteristic pore size in the membranes demonstrated that it is possible to use tailor‐made poly(propylene)s to control the pore size in porous membranes prepared via the TIPS process (under otherwise constant conditions).

Porous size is controlled by the polymer and the TIPS process.     

Investigation of styrene/1‐hexene copolymerization by homogeneous and heterogeneous bisindenyl ethane zirconium dichloride catalyst system

Homogeneous copolymerization of styrene and 1‐hexene was carried out in toluene at room temperature using bisindenyl ethane zirconium dichloride/methylaluminoxane (MAO). The supported catalyst was prepared with immobilization of Et(Ind)₂ZrCl₂/MAO on silica (calcinated at 500°C) with premixed method. Heterogeneous copolymerization of styrene/1‐hexene with different mole ratios was carried out in the presence of supported catalyst system. The copolymers obtained from homogeneous and heterogeneous catalyst system were characterized by ¹H NMR and ¹³C NMR. Composition of the resulting copolymers was determined by ¹H NMR data. Analysis of ¹³C NMR spectra of obtained copolymers by homogeneous and heterogeneous catalyst systems present isotactic olefin‐enriched copolymers. Molecular weight and thermal behavior of resulting copolymers was investigated. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 4008–4014, 2007