Preparation and application of a novel core–shell‐particle‐supported zirconocene catalyst

The use of functional groups bearing silica/poly(styrene‐co‐4‐vinylpyridine) core–shell particles as a support for a zirconocene catalyst in ethylene polymerization was studied. Several factors affecting the behavior of the supported catalyst and the properties of the resulting polymer, such as time, temperature, Al/N (molar ratio), and Al/Zr (molar ratio), were examined. The conditions of the supported catalyst preparation were more important than those of the ethylene polymerization. The state of the supported catalyst itself played a decisive role in both the catalytic behavior of the supported catalyst and the properties of polyethylene (PE). IR and X‐ray photoelectron spectroscopy were used to follow the formation of the supports. The formation of cationic active species is hypothesized, and the performance of the core–shell‐particle‐supported zirconocene catalyst is discussed as well. The bulk density of the PE formed was higher than that of the polymer obtained from homogeneous and polymer‐supported Cp₂ZrCl₂/methylaluminoxane catalyst systems. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2085–2092, 2001     

Novel polystyrene‐supported zirconocene catalyst for olefin polymerization and its catalytic kinetics

Through the Diels–Alder reaction between cyclopentadiene groups attached to polystyrene in the presence of zirconocene, novel polystyrene‐supported metallocene catalysts were prepared. A novel method for immobilizing metallocene catalysts was investigated, and the resultant polystyrene‐supported metallocene for olefin polymerization was studied. The results of olefin polymerization showed that different crosslinking degrees of support in the catalyst system had significant effects on the catalytic behavior. The influence of the [Al]/[Zr] molar ratio and the temperature on the (co)polymerization activity was studied. When 1‐hexene and 1‐dodecene were used for copolymerization with ethylene, an obvious positive comonomer effect was observed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2650–2656, 2005     

Preparation of macroporous functionalized polymer beads by a multistep polymerization and their application in zirconocene catalysts for ethylene polymerization

Macroporous functionalized polymer beads of poly(4‐vinylpyridine‐co‐1,4‐divinylbenzene) [P(VPy‐co‐DVB)] were prepared by a multistep polymerization, including a polystyrene (PS) shape template by emulsifier‐free emulsion polymerization, linear PS seeds by staged template suspension polymerization, and macroporous functionalized polymer beads of P(VPy‐co‐DVB) by multistep seeded polymerization. The polymer beads, having a cellular texture, were made of many small, spherical particles. The bead size was 10–50 μm, and the pore size was 0.1–1.5 μm. The polymer beads were used as supports for zirconocene catalysts in ethylene polymerization. They were very different from traditional polymer supports. The polymer beads could be exfoliated to yield many spherical particles dispersed in the resulting polyethylene particles during ethylene polymerization. The influence of the polymer beads on the catalytic behavior of the supported catalyst and morphology of the resulting polyethylene was investigated. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 873–880, 2003     

Poly(4‐vinylpyridine)‐supported cationic bis(cyclopentadienyl)zirconocene catalyst: Development of a new simple method to prepare polymer‐supported cationic zirconocene and its application to ethylene polymerization

Bis(cyclopentadienyl)zirconocene dimethyl (Cp₂ZrMe₂) combined with triphenylcarbenium tetrakis(pentafluorophenyl)borate ([Ph₃C][B(C₆F₅)₄]) was brought into contact with a suspension of 2% cross‐linked poly(4‐vinylpyridine) to give a new type of polymer‐supported cationic zirconocene catalyst. The resulting polymer‐supported catalyst system combined with Al(i‐Bu₃) showed markedly high activity for ethylene polymerization in even a non‐polar solvent like hexane at 25–60°C and [Al]/[Zr] molar ratio 40–200. By the analysis of Zr content of the hexane solution, it was found that no Zr was detected in the solution, i. e. no leaching of the cationic catalyst into the hexane medium. The catalytic activity was found to increase with an increase of polymerization temperature and showed the highest at [Al]/[Zr] = 100. The molecular weight, crystalline melting temperature, crystallinity, and bulk density of polyethylene formed were higher than those of the polymer obtained from the homogeneous system.     

Synthesis,characterization, and heterogeneous catalysis of polymer‐supported poly(propyleneimine) dendrimer stabilized gold nanoparticle catalyst

We report here, the synthesis of two types of heterogeneous nanoparticle catalysts viz., polymer‐supported poly(propyleneimine)‐G2 dendrimer stabilized gold nanoparticle catalysts using crosslinked poly(4‐vinylpyridine) matrix (PSP4VP) as support material. The grafting of dendrimer on the surface of P4VP beads was characterized by FTIR spectrophotometer and CHN analyses. The immobilization of AuNPs was characterized by UV‐Vis spectrum, SEM, and HRTEM studies. The resultant polymer‐supported dendrimer stabilized AuNPs were used as a heterogeneous catalyst for the reduction of 4‐nitrophenol. The catalytic activity is found to be excellent and it can also be reused many times by simple filtration and activity remains maintained. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2525–2532, 2010     

Syndiospecific polymerization of styrene using fluorinated indenyltitanium complexes

Nine new fluorinated half-sandwich titanocene complexes (1b–9b) based on substituted alkylindenes were synthesized, by reacting Me₃SnF with the corresponding chloride species, and employed as catalyst precursors for the syndiospecific polymerization of styrene. When activated with methylaluminoxane (MAO), the new precursors 1b–9b exhibited increased activities by factors of 15-40 compared with the corresponding chlorinated compounds and provided improved syndiotacticity, enhanced melting temperature, and higher polymer molecular weights. The activities of indenyl and methyl- or phenyl-substituted indenyl complexes were found to be higher by factors of 4-12.5 than those of CpTiF₃ and Cp*TiF₃. More importantly, the amount of MAOcan be reduced to an Al : Ti molar ratio of 300 in the temperature range of 10-90°C. It is likely that Ti F, more polarized than the Ti Cl bond in the half-sandwich titanocenes, allows the formation of more active and stable active sites of Ti(III) complexes needed for the syndiospecific polymerization of styrene. Evidence in this direction is brought via the electron paramagnetic resonance (EPR) spectrum and redox titration. The higher activity and syndiospecificity of the fluorinated catalysts are attributable to a greater number, more stable Ti(III) active sites, and/or higher propagation rate constant. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2481–2488, 1999     

Synthesis of polyethylene and polypropylene containing fluorene units in the side chain

Copolymerizations of ethylene or propylene and allyl monomers containing 9‐fluorenyl group, diallyl‐di‐9‐fluorenylsilane (DAFS), 9,9‐diallylfluorene (DAF), and 9‐allylfluorene (AF), were investigated with various zirconocene catalysts using methylaluminoxane as a cocatalyst. The bridged zirconocene catalysts, especially a syndioselective catalyst, showed a higher reactivity for all the comonomers than the nonbridged catalysts. DAFS was mainly incorporated into the polymer chain via cyclization insertion, whereas DAF was copolymerized via both 1,2‐ and cyclization insertions. Cyclization selectivity, ratio of cyclized insertion unit, of DAF in the copolymerization with propylene was higher than that in the copolymerization with ethylene. Copolymerization with AF yielded low‐molecular weight copolymer because of frequent chain transfer reaction. Optical properties of the propylene based‐copolymers were investigated by UV‐vis and photoluminescence spectroscopy, and absorption‐ and emission‐derived from fluorenyl groups were detected in the copolymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3542–3552, 2010     

Synthesis of polyethylene with bimodal molecular weight distribution by supported iron‐based catalyst

Through immobilization of two iron‐based complexes, [((2,6‐MePh)N = C(Me))₂C₅H₃N]FeCl₂ ( 1 ) and [((2,6‐iPrPh)N = C(Me))₂C₅H₃N]FeCl₂ ( 2 ), on SiO₂ pretreated with tetraethylaluminoxane (TEAO), two supported iron‐based catalysts, 1 /TEAO/SiO₂ ( 3 ) and 2 /TEAO/SiO₂ ( 4 ), were prepared. These two supported catalysts 3 and 4 could be used to catalyze ethylene polymerization with moderate polymerization activity and prepare linear high‐density polyethylene with bimodal molecular weight distribution (MWD). It was demonstrated that immobilization of catalyst could significantly improve molecular weight (MW) of high‐MW fraction of the resultant polyethylene, as well as maintain bimodal MWD of polyethylene produced by the corresponding homogeneous catalysts. Such bimodal MWD of polyethylene produced by supported iron‐based catalysts could be well tailored by varying polymerization conditions, such as ethylene pressure and molar ratio of Al to Fe. It has been proven that TEAO is an efficient activator for both homogeneous and heterogeneous iron‐based catalysts for producing polyethylene with bimodal MWD. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5662–5669, 2004     

Preparation of poly(alkylenebenzimidazole) by ruthenium complex catalyzed polycondensation of 3,3′‐diaminobenzidine with α,ω‐diols

The reactions of 3,3′‐diaminobenzidine with 1,12‐dodecanediol in 1 : 1–1:3 molar ratios in the presence of RuCl₂(PPh₃)₃ catalyst give poly(alkylenebenzimidazole), [ (CH₂)₁₁ O (CH₂)₁₁ Im / (CH₂)₁₀ Im ]_n (Im: 5,5′‐dibenzimidazole‐2,2′‐diyl) (I_a‐I_d) in 71–92% yields. The relative ratio between the [(CH₂)₁₁ O (CH₂)₁₁ Im ] unit (A) and the [‐ (CH₂)₁₀ Im ] unit (B) in the polymer chain varies depending on the ratio of the substrates used. The polymer I_a obtained from the 1 : 3 reaction contains these structural units in a 98 : 2 ratio. The polymers are soluble in polar solvents such as DMF (N,N‐dimethylformamide), DMSO (dimethyl sulfoxide), and NMP (N‐methyl‐2‐pyrrolidone) and have molecular weights M_n (M_w) of 4,200–4,800 (4,800–6,500) by GPC (polystyrene standard). The polymerization of the diol and 3,3′‐diaminobenzidine in higher molar ratios leads to partial cross‐linking of the resulting polymers I_e and I_f via condensation of imidazole NH group with CH₂OH group. Similar reactions of 3,3′‐diaminobenzidine with α,ω‐diols, HO(CH₂)_mOH (m = 4–10), in a 1 : 3 molar ratio give the polymers containing [ (CH₂)_m−1 O (CH₂) _m−1 Im ] and [ (CH₂) _m−2 Im ] units with partial cross‐linked structures. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1383–1392, 1999     

High‐temperature ethylene/α‐olefin copolymerization with a zirconocene catalyst: Effects of the zirconocene ligand and polymerization conditions on copolymerization behavior

Copolymerizations of ethylene and α‐olefin with various zirconocene compounds at a high temperature were carried out to study the relationship between the ligand structure of zirconocene compounds and the copolymerization behavior. All of the indenyl‐based zirconocene compounds in combination with dimethylanilinium tetrakis(pentafluorophenyl)borate/triisobutylaluminum produced only low molecular weight copolymers at a high temperature, regardless of the substituents and bridged structures of the zirconocene compounds. However, zirconocene compounds with a fluorenyl ligand gave rise to a significant increase in the activity and molecular weight of the copolymers by the selection of a diphenylmethylene bridge structure even at a high temperature. Ethylene/1‐hexene copolymers obtained with the fluorenyl‐based catalysts contained inner double bonds accompanied by the generation of hydrogen, presumably because of a C H bond activation mechanism. The contents of the inner double bonds were significantly influenced by the polymerization conditions, including the 1‐hexene feed content, polymerization temperature, and ethylene pressure. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4641–4648, 2000     

ESR studies on oxidation state of titanocene and zirconocene catalysts

An on‐line electron spin resonance (ESR) technique was applied to investigate the oxidation states of the metallocene catalysts CpTiCl₃, CpZrCl₃, Cp₂TiCl₂, and Cp₂ZrCl₂. These metallocene catalysts were activated by modified methylaluminoxane (MMAO). It was found that the titanocene catalysts (CpTiCl₃ and Cp₂TiCl₂) were readily reduced to the trivalent state while the zirconocene catalysts (CpZrCl₃ and Cp₂ZrCl₂) were quite stable with respect to reduction. The concentrations of the trivalent species Ti(III) and Zr(III) showed linear relationships with the concentrations of metallocene catalyst precursors. However, their slopes were always smaller than unity indicating the existence of bimetallic interactions of the active sites. The ESR detectable Ti(III) and Zr(III) concentrations initially increased with the MAO/catalyst ratio and then leveled off after an 800–1000 Al/catalyst molar ratio. The deactivation processes were followed as a function of aging time over a range of temperature (25–100°C). The decay curves strongly depended on aging temperature with higher temperature giving faster decay rates. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1465–1472, 1999     

Internal stress in plasma polymer films prepared by cascade arc torch polymerization

Thin plasma polymer films were deposited from several liquid monomers (mainly siloxane‐type monomers) in a low‐temperature cascade arc torch (CAT) reactor. The effects of monomer structures and plasma parameters on internal stress in the films were experimentally studied. By appropriately adjusting these factors, the internal stress in the film was reduced nearly two orders of magnitude from 10⁹ to 10⁷ dyn/cm². It was noted that the polymer films prepared from siloxane‐type monomers showed lower internal stress than their hydrocarbon counterpart. Fourier transform‐infrared spectroscopy (FTIR) studies indicated that a large amount of Si O Si structure from siloxane monomers, which are very flexible bonds, was preserved in the resultant plasma polymers. Ellipsometry results suggested that the internal stress can be qualitatively correlated with the refractive index of the plasma polymer film. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1577–1587, 1999     

Transport properties of anion exchange membranes prepared by the reaction of crosslinked membranes having chloromethyl groups with 4‐vinylpyridine and trimethylamine

The electrodialytic transport properties of new anion exchange membranes were evaluated that included the transport numbers of various anions, sulfate, bromide, fluoride, and nitrate ions, relative to chloride ions and current efficiency. The anion exchange membranes were prepared by the reaction of copolymer membranes crosslinked to different extents having chloromethyl groups with 4‐vinylpyridine to form a ladder‐like polymer in the membranes and then with trimethylamine to convert the remaining chloromethyl groups to benzyl trimethylammonium groups. The transport numbers of the sulfate and fluoride ions relative to the chloride ions were markedly less for the membranes that had been reacted with 4‐vinylpyridine and then with trimethylamine compared with those of the membranes that had been reacted only with trimethylamine. On the other hand, the selective permeation of nitrate and bromide ions through the membranes was enhanced by the reaction with 4‐vinylpyridine although the membranes became tighter by the reaction. The decrease in permeation of the sulfate ions was attributed to a synergistic effect involving the decrease in sulfate ions ion‐exchanged with the membranes and the decrease in mobility of the sulfate ions in the membranes with a low degree of crosslinking. Though the ion‐exchanged sulfate ion content was the lowest in the highly crosslinked membranes, the mobility ratio between the sulfate ions and chloride ions did not decrease in the membranes. However, the increase in the permeation of nitrate ions was based on the increase in the ion‐exchanged amount of nitrate ions with the membrane, and not the change in the mobility ratio between the nitrate and chloride ions. The formation of the ladder‐like polymer in the membrane matrix brought on a decrease in the hydrophilicity of the membranes due to pyridine groups and an increase in their tightness. The current efficiency of all membranes was greater than 99% during the electrodialysis of 0.50 N salt solutions. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1773–1785, 1999     

Polymer‐supported half‐titanocene catalysts for the syndiospecific polymerization of styrene

Monocyclopendienyltitanium trichloride (CpTiCl₃) was supported on polymer carriers with different hydroxyl contents, and the supported catalysts were used for styrene polymerization. The supported catalysts exhibited high activity even at low Al/Ti ratios and increased the molecular weight of the products, indicating that polymer carriers could stabilize the active sites. The polymers prepared with unsupported and supported catalysts were extracted with boiling n‐butanone and characterized by carbon nuclear magnetic resonance (¹³C NMR) and differential scanning calorimetry. The polymers obtained by supported catalysts had a high fraction of boiling n‐butanone‐insoluble part and high melting temperatures, but ¹³C NMR results showed that syndiotacticity decreased compared with that of polymers prepared with an unsupported catalyst. ESR study on the supported catalysts confirmed that the active sites supported on the carrier dropped into the solution and formed active sites the same as those in the unsupported system when they reacted with methylaluminoxane. ¹³C NMR analysis showed that the polymerization mechanism of the supported active sites was an active‐site controlled mechanism instead of a chain‐end controlled mechanism of the unsupported active sites. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 127–135, 2000     

Copolymerization of propylene with 1,3‐butadiene using isospecific zirconocene catalysts

Poly(propylene‐ran‐1,3‐butadiene) was synthesized using isospecific zirconocene catalysts and converted to telechelic isotactic polypropylene by metathesis degradation with ethylene. The copolymers obtained with isospecific C₂‐symmetric zirconocene catalysts activated with modified methylaluminoxane (MMAO) had 1,4‐inserted butadiene units ( 1,4‐BD ) and 1,2‐inserted units ( 1,2‐BD ) in the isotactic polypropylene chain. The selectivity of butadiene towards 1,4‐BD incorporation was high up to 95% using rac‐dimethylsilylbis(1‐indenyl)zirconium dichloride (Cat‐A)/MMAO. The molar ratio of propylene to butadiene in the feed regulated the number‐average molecular weight (M_n) and the butadiene contents of the polymer produced. Metathesis degradations of the copolymer with ethylene were conducted with a WCI₆/SnMe₄/propyl acetate catalyst system. The ¹H NMR spectra before and after the degradation indicated that the polymers degraded by ethylene had vinyl groups at both chain ends in high selectivity. The analysis of the chain scission products clarified the chain end structures of the poly(propylene‐ran‐1,3‐butadiene). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5731–5740, 2007     

Kinetic features of ethylene polymerization over supported catalysts [2,6‐bis(imino)pyridyl iron dichloride/magnesium dichloride] with AlR3 as an activator

The effects of polymerization temperature, polymerization time, ethylene and hydrogen concentration, and effect of comonomers (hexene‐1, propylene) on the activity of supported catalyst of composition LFeCl₂/MgCl₂‐Al(i‐Bu)₃ (L = 2,6‐bis[1‐(2,6‐dimethylphenylimino)ethyl] pyridyl) and polymer characteristics (molecular weight (MW), molecular‐weight distribution (MWD), molecular structure) have been studied. Effective activation energy of ethylene polymerization over LFeCl₂/MgCl₂‐Al(i‐Bu)₃ has a value typical of supported Ziegler–Natta catalysts (11.9 kcal/mol). The polymerization reaction is of the first order with respect to monomer at the ethylene concentration >0.2 mol/L. Addition of small amounts of hydrogen (9–17%) significantly increases the activity; however, further increase in hydrogen concentration decreases the activity. The IRS and DSC analysis of PE indicates that catalyst LFeCl₂/MgCl₂‐Al(i‐Bu)₃ has a very low copolymerizing ability toward propylene and hexene‐1. MW and MWD of PE produced over these catalysts depend on the polymerization time, ethylene and hexene‐1 concentration. The activation effect of hydrogen and other kinetic features of ethylene polymerization over supported catalysts based on the Fe (II) complexes are discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5057–5066, 2007     

Effects of methylaluminoxane immobilization on silica on the performance of zirconocene catalysts in propylene polymerization

Investigation of the characteristics and performance in propylene polymerization of silica‐immobilized methylaluminoxane (MAO), in combination with a moderately and a highly isospecific zirconocene catalyst, has revealed that a simple impregnation of silica with MAO at ambient temperature is insufficient to obtain uniform distribution of MAO throughout the support particle. Homogeneous Al distribution throughout the support, giving increased catalyst activity, was achieved by a more rigorous impregnation of silica with MAO at elevated temperatures. The highest catalyst activities were obtained by precontacting the MAO with the zirconocene to generate the activated species before immobilization on silica. Polymer particle morphology was strongly dependent on the characteristics of the silica used for catalyst immobilization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2734‐2748, 2005     

Fluorescence,ion binding,and viscosity properties of poly[2‐ and 4‐vinylpyridine]s in methanol and in sulfuric acid

Fluorescence intensities of poly(2‐vinylpyridine) (P2VP) and poly(4‐vinylpyridine) (P4VP) in H₂SO₄/H₂O solutions were increased with increasing acid concentration. The intensities for P2VP were found to be six times stronger than that of P4VP. These differences were accounted for by the microenvironment of protonated pyridinium group. The ion binding properties of 4‐methylpyridine (4MP), P2VP, and P4VP were investigated in methanol using Tb³⁺ as a fluorescence probe. The increase of fluorescence intensity of Tb³⁺ in [P2VP–Tb³⁺] and [P4VP–Tb³⁺] complexes is due to both the replacement of the inner coordinated methanol molecules and ligand‐to‐metal energy transfer. The model compound 4MP was inefficient from this point of view, and the results were attributed to the polymer cooperative effect. Reduced viscosities of poly(vinylpyridine)s (PVP) in methanol were similar to nonionic polymers; however, when TbCl₃ was added into the solution, the viscosities increased upon dilution. These results also indicated that PVP form complexes with Tb³⁺ in methanol. When diluted, the counterions Cl⁻ are allowed to dissociate and the charged polymer expands. Consequently, the solution's viscosity increases. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1341–1345, 1999     

Synthesis of zirconocene-acetylene and zirconocene-diacetylene polymer

A new class of organometallic polymer having a backbone of conjugated Poly-yne and Zr-metal atoms has been prepared. Trichloroethylene (TCE) and Hexachlorobutadiene (HCB) are quantitatively converted by n-butyllithium to dilithioacetylene (LiCCLi) and dilithiodiacetylene (Li CC CC Li) respectively. Quenching with Cp₂*ZrCl₂ affords high yields of the polymers Zr(Cp₂*)CC_n and Zr(Cp₂*)CC CC_n where Cp* = C₅(CH₃)₅ = pentamethyl cyclopentadienyl. The Cp₂*ZrCl₂ and the polymers were characterized by viscosity, molecular weight, elemental analysis, FTIR, NMR spectra, and TGA. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3899–3902, 1999     

Titanium (IV) chloride complexes with salen ligands supported on magnesium carrier: Synthesis and use in ethylene polymerization

The magnesium support with the formula MgCl₂(THF)_0.32(Et₂AlCl)_0.36 was used for immobilization of salen complexes of titanium [Ti(salen)Cl₂, Ti(salen(OMe)₂)Cl₂]. The effects of the catalyst composition (i.e. type of titanium complex and type of activator), polymerization temperature, polymerization time, and the effect of comonomer (1‐octene) on the activity of the obtained supported catalysts, on the polymer characteristics (molecular weight, molecular weight distribution, melting point), and on the polymer morphology were studied. The findings were compared to those obtained for corresponding unsupported systems. Catalysts immobilization results in considerable changes in catalysts activity and in properties of resultant polymers. The studied supported catalysts are highly active in ethylene polymerization, their activity increases with increasing temperature and lasts at least 2 hours. Their copolymerizing ability towards 1‐octene is rather low. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6693–6703, 2009