Synthesis and photophysical properties of polyethylene containing pyrenyl units in the side chain

Copolymerization of ethylene and diallyl‐bis(pyren‐1‐yl)‐silane (APyS) was investigated with zirconocene catalysts, rac‐ethylenebis(indenyl)zirconium dichloride ( 1 ) and diphenylmethylene(cyclopentadienyl)(9‐fluorenyl)zirconium dichloride ( 2 ), using methylaluminoxane as a cocatalyst. APyS was copolymerized via both 1,2‐insertion and cyclization insertion, and cyclization selectivity, ratio of cyclized insertion unit, of APyS in the copolymers obtained with Catalyst 1 was higher than that obtained with Catalyst 2 . Catalyst 2 showed a higher reactivity for APyS than Catalyst 1 . Photophysical properties of the copolymer were investigated by UV–vis and photoluminescence (PL) spectroscopy, and absorption and fluorescence derived from pyrenyl groups were detected in the copolymers. Chloroform solution of the copolymer showed emission derived from both monomer and eximer of pyrenyl units. Only the emission derived from eximer of pyrenyl units was observed in the cast film. The polarized PL spectrum of an oriented film showed anisotropy, and the polarization excitation parallel to the drawing direction showed high fluorescence intensity. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

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     

Composition distribution of ethylene or propylene–norbornene copolymers obtained with zirconocene catalysts

Copolymerization of ethylene or propylene and norbornene (NB) was carried out with stereospecific zirconocene catalysts rac‐ethylenebis(indenyl)zirconium dichloride, rac‐dimethylsilylenebis(indenyl)zirconium dichloride ( 2 ), rac‐dimethylsilylenebis(2‐methylindenyl)zirconium dichloride, and diphenylmethylene(cyclopentadienyl)(9‐fluorenyl)zirconium dichloride combined with cocatalysts at 40 °C. Temperature‐rising elution fractionation of the copolymers was carried out with cross‐fractionation chromatography with o‐dichlorobenzene as a solvent, and a broad distribution of the copolymer composition was detected. The fraction eluted at lower temperature contained higher NB. The effect of the polymerization time was examined in the ethylene–NB copolymerization with catalyst 2 , and the higher‐temperature elution fraction increased with increasing polymerization time. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 441–448, 2003     

Copolymerization of propylene and disubstituted diallylsilanes involving intramolecular cyclization with stereoselective zirconocene catalysts

The copolymerization of propylene and disubstituted diallylsilanes [(CH₂ ?CH? CH₂? )₂R₂Si (R = CH₃ or C₆H₅)] was investigated with isoselective and syndioselective zirconocene catalysts with methylaluminoxane as a cocatalyst. The syndioselective catalyst showed a higher reactivity for disubstituted diallylsilanes than the isoselective catalysts. Diallyldimethylsilane was incorporated into the polymer chain via cyclization insertion preferentially and formed 3,5‐disubstituted dimethylsilacyclohexane units in the polypropylene main chain. In the copolymerization with diallyldiphenylsilane, diallyldiphenylsilane was copolymerized via both cyclization insertion and 1,2‐insertion, which formed a pendant allyl group. The structures of isolated silacyclohexane units, determined by ¹³C NMR and distortionless enhancement by polarization transfer spectroscopy, proved that the 1,2‐insertion of diallylsilanes proceeded with enantiomorphic site control; however, the diastereoselectivity of the cyclization reaction was independent of the stereoselectivity of the catalysts used, and cis‐silacyclohexane units were mainly formed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6083–6093, 2006     

High molar mass ethene/1‐olefin copolymers synthesized with acenaphthyl substituted metallocene catalysts

The influence of ligand structure on copolymerization properties of metallocene catalysts was elucidated with three C₁‐symmetric methylalumoxane (MAO) activated zirconocene dichlorides, ethylene(1‐(7, 9)‐diphenylcyclopenta‐[a]‐acenaphthadienyl‐2‐phenyl‐2‐cyclopentadienyl)ZrCl₂ ( 1 ), ethylene(1‐(7, 9)‐diphenylcyclopenta‐[a]‐acenaphthadienyl‐2‐phenyl‐2‐fluorenyl)ZrCl₂ ( 2 ), and ethylene(1‐(9)‐fluorenyl‐(R)1‐phenyl‐2‐(1‐indenyl)ZrCl2 ( 3 ). Polyethenes produced with 1 /MAO had considerable, ca. 10% amount of trans‐vinylene end groups, resulting from the chain end isomerization prior to the chain termination. When ethene was copolymerized with 1‐hexene or 1‐hexadecene using 1 /MAO, molar mass of the copolymers varied from high to moderate (531–116 kg/mol) depending on the comonomer feed. At 50% comonomer feed, ethene/1‐olefin copolymers with high hexene or hexadecene content (around 10%) were achievable. In the series of catalysts, polyethenes with highest molar mass, up to 985 kg/mol, were obtained with sterically most crowded 2 /MAO, but the catalyst was only moderately active to copolymerize higher olefins. Catalyst 3 /MAO produced polyethenes with extremely small amounts of trans‐vinylene end groups and relatively low molar mass 1‐hexene copolymers (from 157 to 38 kg/mol) with similar comonomer content as 1 . These results indicate that the catalyst structure, which favors chain end isomerization, is also capable to produce high molar mass 1‐olefin copolymers with high comonomer content. In addition, an exceptionally strong synergetic effect of the comonomer on the polymerization activity was observed with catalyst 3 /MAO. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 373–382, 2008     

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     

Copolymerization of isoprene with ethylene catalyzed by cationic half‐sandwich fluorenyl scandium catalysts

Isoprene polymerization and copolymerization with ethylene can be carried out by using cationic half‐sandwich fluorenyl scandium catalysts in situ generated from half‐sandwich fluorenyl scandium dialkyl complexes Flu'Sc(CH₂SiMe₃)₂(THF)_n, activator, and AlⁱBu₃ under mild conditions. In the isoprene polymerization, all of these cationic half‐sandwich fluorenyl scandium catalysts exhibit high activities (up to 1.89 × 10⁷ g/mol_Sc h) and mainly cis?1,4 selectivities (up to 93%) under similar conditions. In contrast, these catalysts showed different activities and regio‐/stereoselectivities being significantly dependent on the substituents of the fluorenyl ligands in the copolymerization of isoprene with ethylene under an atmosphere of ethylene (1 atm) at room temperature, affording the random copolymers with a wide range of cis?1,4‐isoprene contents (IP content: 64 ? 97%, cis?1,4‐IP units: 65 ? 79%) or almost alternating copolymers containing mainly 3,4‐IP‐alt‐E or/and cis?1,4‐IP‐alt‐E sequences. Moreover, novel high performance polymers have been prepared via selective epoxidation of the vinyl groups of the 1,4‐isoprene units in the IP‐E copolymers. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2898–2907     

C2‐symmetry dimethylated zirconocenes activated with triisobutyl aluminum as effective homogeneous catalysts for copolymerization of olefins

We investigated the catalytic performance of both bridged unsubstituted [rac‐EtInd₂ZrMe₂, rac‐Me₂SiInd₂ZrMe₂] and 2‐substituted [rac‐Et(2‐MeInd)₂ZrMe₂), rac‐Me₂Si(2‐MeInd)₂ZrMe₂] dimethylbisindenylzirconocenes activated with triisobutyl aluminum (TIBA) as a single activator in (a) homopolymerizations of ethylene and propylene, (b) copolymerization of ethylene with propylene and hexene‐1, and (c) copolymerization of propylene with hexene‐1 (at Al_TIBA/Zr = 100‐300 mol/mol). Unsubstituted catalysts were inactive in homopolymerizations of ethylene and propylene and copolymerization of propylene with hexene‐1 but exhibited high activity in copolymerizations of ethylene with propylene and hexene‐1. 2‐Substituted zirconocenes activated with TIBA were active in homopolymerizations of ethylene and propylene and exhibited high activity in copolymerization of ethylene with propylene and hexene‐1, and in copolymerization of propylene with hexene‐1. Comparative microstructural analysis of ethylene‐propylene copolymers prepared over rac‐Me₂SiInd₂ZrMe₂ activated with TIBA or Me₂NHPhB(C₆F₅)₄ has shown that the copolymers formed upon activation with TIBA are statistical in nature with some tendency to alternation, whereas those with borate activated system show a tendency to formation of comonomer blocks. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2934–2941, 2010     

Copolymerization of ethylene or propylene with α‐olefins containing hydroxyl groups with zirconocene/methylaluminoxane catalyst

Copolymerization of olefins (ethylene and propylene) and 5‐hexen‐1‐ol pretreated with alkylaluminum was performed using [dimethysilylbis(9‐fluorenyl)]zirconium dichloride/methylaluminoxane as the catalyst. The copolymerization required extra addition of alkylaluminum to prevent deactivation of the catalyst when 5‐hexen‐1‐ol was pretreated with trimethylaluminum, whereas the triisobutylaluminum‐treated system did not require any addition of alkylaluminum. The molecular weight of the copolymer depended on the kind of alkylaluminum compound (masking reagent, additive, and cocatalyst). ¹³C NMR analysis proved that poly(ethylene‐co‐5‐hexen‐1‐ol) containing 50 mol % of 5‐hexen‐1‐ol acted as an alternating copolymer, whereas the poly(propylene‐co‐5‐hexen‐1‐ol) acted as a random copolymer. The surface property of the copolymers was simply evaluated by means of water drop contact angle measurement. It was found that the copolymers containing large amounts of 5‐hexen‐1‐ol units showed good hydrophilic properties. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 52–58, 2004     

Synthesis of polyolefins with unique properties by using metallocene-type catalysts

Copolymerization of ethylene and 1,5-hexadiene (HD) by zirconocene catalysts proceeded via cyclization-addition mechanism to form 1,3-didsubstituted cyclopentane structure in the polyethylene chain. The 1,3-cyclopentane structure was found to be taken in the crystalline structure of polyethylene (isomorphism) by partially chainging the trans zigzag chain into gauche conformation, thereby, inducing a transformation of orthorhombic crystal to pseudohexagonal crystal. Copolymerization of ethylene and cyclopentene (CPE) by zirconocene catalysts yielded copolymers having 1,2-disubstituted cyclopentane structure in the polyethylene chain. The 1,2-cyclopentane structure was not taken into the crystalline structure of polyethylene. The melting point (T_m) and the crystallinity (X_c) of polyethylene decreased by copolymerization of HD or CPE, and the T_m- and X_c-decreasing effect of CPE was stronger than HD. For copolymers of propylene and HD or CPE obtained with isospecific zirconocene catalyst, the isomorphism was not ovserved.     

Unconstrained geometry complexes: Ethylene/α‐olefin copolymerizations with a tetramethyldisilyl‐bridged Cp‐amido titanium complex

A new disilyl‐bridged complex, [(N‐tert‐butylamido)(3‐indenyl)tetramethyldisilyl]titanium dichloride ( 3 ), was synthesized and activated with methylaluminoxane (MAO) for propylene homopolymerization and ethylene/propylene and ethylene/1‐hexene copolymerizations. A polypropylene with a slight isotactic enrichment was obtained. The number of regioerrors present in the polypropylene was somewhat smaller than that found in most polypropylenes made from monosilyl‐bridged [(N‐tert‐butylamido)(3‐indenyl)dimethylsilyl]titanium dichloride. The regioerrors detected in the copolymers obtained from 3 /MAO were on the order of the amounts observed in polymers made with the monosilyl‐bridged constrained geometry catalysts. Ethylene copolymers of propylene and 1‐hexene had random sequence distributions and showed significant comonomer incorporation. Because of the presence of regioerrors, a modified method for determining the monomer composition and sequence distribution was developed from the direct measurement of the monomer content from the number of methylene and methine carbons per polymer chain, regardless of propylene inversion. An estimate of the error in the copolymerization reactivity ratio determination for regioirregular ethylene/α‐olefin copolymers was obtained by the calculation of the reactivity ratios from monomer dyad sequences, with consideration given to the contribution of major regioirregular sequences. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3840–3851, 2005     

Hydrogen effects in propylene polymerization reactions with titanium‐based Ziegler–Natta catalysts. I. Chemical mechanism of catalyst activation

The hydrogen activation effect in propylene polymerization reactions with Ti‐based Ziegler–Natta catalysts is usually explained by hydrogenolysis of dormant active centers formed after secondary insertion of a propylene molecule into the growing polymer chain. This article proposes a different mechanism for the hydrogen activation effect due to hydrogenolysis of the Ti? iso‐C₃H₇ group. This group can be formed in two reactions: (1) after secondary propylene insertion into the Ti? H bond (which is generated after β‐hydrogen elimination in the growing polymer chain or after chain transfer with hydrogen), and (2) in the chain transfer with propylene if a propylene molecule is coordinated to the Ti atom in the secondary orientation. The Ti? CH(CH₃)₂ species is relatively stable, possibly because of the β‐agostic interaction between the H atom of one of its CH₃ groups and the Ti atom. The validity of this mechanism was demonstrated in a gas chromatography study of oligomers formed in ethylene/α‐olefin copolymerization reactions with δ‐TiCl₃/AlEt₃ and TiCl₄/dibutyl phthalate/MgCl₂–AlEt₃ catalysts. A quantitative analysis of gas chromatography data for ethylene/propylene co‐oligomers showed that the probability of secondary propylene insertion into the Ti? H bond was only 3–4 times lower than the probability of primary insertion. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1353–1365, 2002     

Thermoresponsive brush copolymers with poly(propylene oxide‐ran‐ethylene oxide) side chains via metal‐free anionic polymerization “grafting from” technique

Thermoresponsive brush copolymers with poly(propylene oxide‐ran‐ethylene oxide) side chains were synthesized via a “grafting from” technique. Poly(p‐hydroxystyrene) was used as the backbone, and the brush copolymers were prepared by random copolymerization of mixtures of oxyalkylene monomers, using metal‐free anionic ring‐opening polymerization, with the phosphazene base (t‐BuP₄) being the polymerization promoter. By controlling the monomer feed ratios in the graft copolymerization, two samples with the same side‐chain length and different compositions were prepared, both of which possessed high molecular weights and low molecular weight distributions. The results from light scattering and fluorescence spectroscopy indicated that the brush copolymers in their dilute aqueous solutions were near completely solvated at low temperature and underwent slight intramolecular chain contraction/association and much more profound intermolecular aggregation at different stages of the step‐by‐step heating process. Above 50 °C, very turbid solutions, followed by macrophase separation, were observed for both of the samples, which implied that it was difficult for the brush copolymers to form stable nanoscopic aggregates at high temperature. All these observations were attributed, at least partly, to the distribution of the oxyalkylene monomers along the side chains and the overall brush‐like molecular architecture. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2320–2328, 2010     

Kinetics and mechanism of metallocene‐catalyzed olefin polymerization: Comparison of ethylene,propylene homopolymerizations,and their copolymerization

A series of ethylene, propylene homopolymerizations, and ethylene/propylene copolymerization catalyzed with rac‐Et(Ind)₂ZrCl₂/modified methylaluminoxane (MMAO) were conducted under the same conditions for different duration ranging from 2.5 to 30 min, and quenched with 2‐thiophenecarbonyl chloride to label a 2‐thiophenecarbonyl on each propagation chain end. The change of active center ratio ([C^*]/[Zr]) with polymerization time in each polymerization system was determined. Changes of polymerization rate, molecular weight, isotacticity (for propylene homopolymerization) and copolymer composition with time were also studied. [C^*]/[Zr] strongly depended on type of monomer, with the propylene homopolymerization system presented much lower [C^*]/[Zr] (ca. 25%) than the ethylene homopolymerization and ethylene–propylene copolymerization systems. In the copolymerization system, [C^*]/[Zr] increased continuously in the reaction process until a maximum value of 98.7% was reached, which was much higher than the maximum [C^*]/[Zr] of ethylene homopolymerization (ca. 70%). The chain propagation rate constant (k_p) of propylene polymerization is very close to that of ethylene polymerization, but the propylene insertion rate constant is much smaller than the ethylene insertion rate constant in the copolymerization system, meaning that the active centers in the homopolymerization system are different from those in the copolymerization system. Ethylene insertion rate constant in the copolymerization system was much higher than that in the ethylene homopolymerization in the first 10 min of reaction. A mechanistic model was proposed to explain the observed activation of ethylene polymerization by propylene addition. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 867–875     

Copolymerization of ethylene with cycloolefins or cyclodiolefins by a constrained‐geometry catalyst

The copolymerization of ethylene and cycloolefins [cyclopentene (CPE), cyclohexene (CHX), cycloheptene (CHP), cyclooctene (COT), cyclododecene (CDO), norbornene (NB), and 5,6‐dihydrodicyclopentadiene HDCPD] and cyclodiolefins [1,3‐cyclopentadiene (CPD), 1,4‐cyclohexadiene (CHD), 1,5‐cyclooctadiene (COD), 2,5‐norbornadiene (NBD), and dicyclopentadiene (DCPD)] was investigated with a constrained‐geometry catalyst, dimethylsilylene(tetramethylcyclopentadienyl)(N‐tert‐butyl)titanium dichloride, with methyl isobutyl aluminoxane as a cocatalyst. In the copolymerization with cycloolefins, the olefins, except for CHX, CDO, and HDCPD, were copolymerized via the 1,2‐insertion mode with the following reactivity: NB > CHP > COT > CPE. In the copolymerization with cyclodiolefins, corresponding copolymers, except for copolymerization with CHD, were obtained. A crosslinking fraction was detected in the copolymers with COD and NBD. The reactivity of the cyclodiolefins, except for COD, was higher than that of the cycloolefins. CPD was copolymerized via 1,2‐insertion, 1,4‐insertion or 1,2‐insertion of dimerized DCPD. The copolymerization with COD showed peculiar behavior under the copolymerization condition of a high COD concentration in the feed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1285–1291, 2005     

Kinetics of ethylene polymerization reactions with chromium oxide catalysts

Principal kinetic data are presented for ethylene homopolymerization and ethylene/1‐hexene copolymerization reactions with two types of chromium oxide catalyst. The reaction rate of the homopolymerization reaction is first order with respect to ethylene concentration (both for gas‐phase and slurry reactions); its effective activation energy is 10.2 kcal/mol (42.8 kJ/mol). The r₁ value for ethylene/1‐hexene copolymerization reactions with the catalysts is ～30, which places these catalysts in terms of efficiency of α‐olefin copolymerization with ethylene between metallocene catalysts (r₁ ～ 20) and Ti‐based Ziegler‐Natta catalysts (r₁ in the 80–120 range). GPC, DSC, and Crystaf data for ethylene/1‐hexene copolymers of different compositions produced with the catalysts show that the reaction products have broad molecular weight and compositional distributions. A combination of kinetic data and structural data for the copolymers provided detailed information about the frequency of chain transfer reactions for several types of active centers present in the catalysts, their copolymerization efficiency, and stability. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5315–5329, 2008     

A theoretical study of the comonomer effect in the ethylene polymerization with zirconocene catalytic systems

The PM3(tm) semiempirical method has been used to optimize the structures for the reactants and transition states of the first and second ethylene insertion processes into zirconocene catalytic systems. The results obtained for these reactions are compared with calculations published in the literature performed at different ab-initio theoretical levels. The agreement between our calculations and those reported in the literature is satisfactory. Taking advantage of the reduced computational effort required in semiempirical calculations two additional processes related with the so-called comonomer effect were also studied: ethylene/1-hexene copolymerization, and chain termination reaction, both in the homopolymerization and in copolymerization of ethylene with 1-hexene comonomer. The calculated activation energies support some experimental findings such as the higher polymerization activities in the presence of comonomers and also the molecular weight reduction of the copolymers due to the more favorable β-elimination reactions. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1157–1167, 1998     

Copolymerization of ethylene with linear α‐olefins by 2‐phosphinophenolate nickel catalysts

2‐Dicyclohexyl‐ and 2‐diphenylphosphinophenol, CCHH and PPHH , react with Ni(1,5‐COD)₂ to form catalysts for polymerization of ethylene in or copolymerization with α‐olefins. The more P‐basic CCHH/Ni catalyst allows concentration‐dependent incorporation of olefins to give copolymers with isolated side groups and higher molecular weights, whereas the PPHH/Ni catalyst undergoes mainly stabilizing interactions with the olefins and leads to ethylene oligomers with no or marginal olefin incorporation. Pressure–time plots of the batch reactions show that the ethylene conversion is usually slower by catalysis with CCHH/Ni than by PPHH/Ni . The microstructure of the copolymers was determined by ¹³C NMR spectra, the number of side groups per main chain was estimated by ¹H NMR analyses. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 258–266, 2009     

Copolymerization of 3‐buten‐1‐ol and propylene with an isospecific zirconocene/methylaluminoxane catalyst

The copolymerization of propylene and 3‐buten‐1‐ol protected with alkylaluminum [trimethylaluminum (TMA) or triisobutylaluminum] was conducted with an isospecific zirconocene catalyst [rac‐dimethylsilylbis(1‐indenyl)zirconium dichloride], combined with methylaluminoxane as a cocatalyst, in the presence of additional TMA or H₂ as the chain‐transfer reagent if necessary. The results indicated that end‐hydroxylated polypropylene was obtained in the presence of the chain‐transfer reagents because of the formation of dormant species after the insertion of the 3‐buten‐1‐ol‐based monomer followed by chain‐transfer reactions. The selectivity of the chain‐transfer reactions was influenced by the alkylaluminum protecting the comonomer and the catalyst structure. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5600–5607, 2004     

Effect of 1‐hexene comonomer on polyethylene particle growth and copolymer chemical composition distribution

An investigation of the polymer particle growth characteristics and polymer molecular weight and composition distributions in ethylene homopolymerization and ethylene/1‐hexene copolymerization has been carried out with a catalyst comprising a zirconocene and methylaluminoxane immobilized on a silica support. The presence of 1‐hexene leads to higher productivity and easier fragmentation of the support during particle growth. Crystallization analysis fractionation and gel permeation chromatography analysis of ethylene/1‐hexene copolymers prepared at different polymerization times reveals a broadening of the chemical composition distribution with increasing polymerization time as a result of the gradual formation of a relatively high‐molecular‐weight, ethylene‐rich fraction. The results are indicative of significant monomer diffusion effects in both homopolymerization and copolymerization. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2883–2890, 2006