Akihiro Yano

Homo‐ and copolymerization of ethylene by cationic hafnocene catalysts based on tetrakis(pentafluorophenyl)borate

Ethylene homopolymerization and ethylene/1-hexene copolymerization were conducted at different temperature and ethylene pressure using several hafnocenes activated with dimethylanilinium tetrakis-(pentafluorophenyl))borate (Me 2 PhNH. B(C 6 F 5 ) 4 ). rac-Ethylene(bisindenyl)hafnium dichloride (rac-Et(Ind) 2 -HfCl 2 ) activated with Me 2 PhNH. B(C 6 F 5 ) 4 shows ten times higher activity than methylaluminoxane(MAO)-activated catalyst for ethylene polymerization at 40°C, and produces high molecular weight polyethylene with high activity even at 150 C independent of ethylene pressure. The molecular weight of ethylene/1-hexene copolymers synthesized at high temperature is influenced by the ligand structure, and a rac-(dimethylsilyl)bis(2,4-dimethylcyclopentadienyl)hafnium dichloride (rac-Me 2 Si(2,4-Me 2 Cp) 2 HfCl 2 )-based catalyst exceptionally produces only low molecular weight copolymers. These copolymers contain high amount of vinylidene end groups, indicating that β-H transfer from propagating chains containing primary inserted 1-hexene as terminal unit occurs frequently. At high ethylene pressure, the rac-Et(Ind) 2 HfCl 2 .-based catalyst produces high molecular weight ethylene/1-hexene copolymers with high activity, but this activity is slightly lower than that of zirconium analogs.

Ethylene/1-hexene copolymerization with Ph2C(Cp)(Flu)ZrCl2 derivatives : correlation between ligand structure and copolymerization behavior at high temperature

Ethylene homo- and copolymerization with 1-hexene were performed in the presence of diphenylmethylidene(cyclopentadienyl)(fluorenyl)zirconium dichloride (Ph 2 C(Cp)(Flu)ZrCl 2 ) derivatives activated with dimethylanilinium tetrakis(pentafluorophenyl)borate (Me 2 PhNH.(C 6 F 5 )4)/triisobutylaluminium (i-Bu 3 Al) or methylaluminoxane (MAO) to study the role of the substituent on activity, comonomer incorporation and molecular weight. C 1 symmetric metallocenes which have several substituents in β-position of the cyclopentadienyl ligand produce lower molecular weight copolymers than the Ph 2 C(Cp)(Flu)ZrCl 2 catalyst at 200 °C, whereas the copolymerization reactivity is significantly influenced by the volume of the substituent: the trimethylsilyl substituted derivative produces ethylene/1-hexene copolymers with a broad chemical composition distribution. Polyethylene obtained with the diphenylmethylidene(cyclopentadienyl)(indenyl)zirconium dichloride (Ph 2 C(Cp)(Ind)ZrCl 2 ) based catalyst is branched, and the molecular weight distribution and the chemical composition distribution are significantly affected by the cocatalyst. C s symmetric metallocenes which have alkyl substituents in 2,7 position of the fluorenyl ligand produce higher molecular weight copolymers than the Ph 2 C(Cp)(Flu)ZrCl 2 catalyst with equal copolymerization reactivity.

Homo- and copolymerization of ethylene at high temperature with cationic zirconocene catalysts

Homo- and copolymerization of ethylene with 1-hexene were conducted at different temperature and ethylene pressure with several zirconocenes activated with dimethylanilinium tetrakis(pentafluorophenyl)borate (Me 2 PhNH. B(C 6 F 5 ) 4 )/triisobutylaluminium (i-Bu 3 Al) to study the effect of ligand structure and polymerization conditions on catalytic activity, molecular weight and chain transfer reactions. At high temperature and low ethylene pressure, rac-ethylene(bisindenyl)zirconiumdichloride (rac-Et(Ind) 2 ZrCl 2 ) activated with Me 2 PhNH. B(C 6 F 5 ) 4 /i-Bu 3 Al initially gives a highly active catalyst that is rapidly deactivated. trans-Vinylene double bonds, which were not formed at low temperature, were detected in polyethylene synthesized at high temperature and low ethylene pressure. They reasonably arise from β-H transfer after isomerization reaction. The molecular weight of ethylene/1-hexene copolymers decreases with increasing 1-hexene feed, followed by the formation of vinylidene end groups. This reveals that β-H transfer from propagating chains containing primary inserted 1-hexene as a terminal unit is predominant. This reaction is influenced by the ligand structure. At high temperature and high ethylene pressure, trans-vinylene and vinylidene contents decrease and the vinyl content increases, indicating that the high ethylene pressure controls β-H transfer after isomerization reaction.

Novel zirconocene catalysts for the production of high molecular weight LLDPE in high‐temperature polymerization

Ethylene polymerization and ethylene/α-olefin copolymerization were conducted using diphenylmethylidene(cyclopentadienyl)(fluorenyl)zirconium dichloride (Ph 2 C(Cp)(Flu)ZrCl 2 ) as a catalyst activated with dimethylanilinium tetrakis(pentafluorophenyl)borate (Me 2 PhNH. B(C6F5) 4 )/triisobutylaluminium (i-Bu 3 Al) at high temperature and different ethylene pressure. This catalyst produces high molecular weight polyethylene with high activity. The molecular weight of the copolymers hardly decreases with increasing amount of comonomer in the feed. This is attributed to the control of β-H transfer from the propagating chain containing primary inserted comonomer. The occurrence of inner trisubstituted double bonds was confirmed. These bonds are probably formed by dehydrogenation reactions after β-H transfer from the propagating chain followed by ethylene insertion. Therefore, this reaction might play an important role in the production of high molecular weight ethylene/1-hexene copolymers at high temperature. At high ethylene pressure, isomerization reactions from inserted ethylene or primary inserted α-olefin as terminal units, which were observed under low ethylene pressure, can be controlled at low level.

Influence of activators on ethylene polymerization with diphenylmethylidene-(cyclopentadienyl)(fluorenyl)zirconium dichloride catalysts at high temperature

Abstract Ethylene polymerization was carried out with diphenylmethylidene-(cyclopentadienyl)(fluorenyl)zirconium dichloride (Ph2C(Cp)(Flu)ZrCl2) activated with various activators such as methylaluminoxane (MAO), tetrakis(pentafluorophenyl)borates (R·B(C6F5)4, R=Me2PhNH, Ph3C, C7H7, H(Et2O)n), dimethylanilinium tetrakis(pentafluorophenyl)aluminate (Me2PhNH·Al(C6F5)4) and tris(pentafluorophenyl)borane (B(C6F5)3) to study the correlation between catalyst performance for ethylene polymerization and cocatalysts at high temperature. R·B(C6F5)4-activated catalysts showed relatively high activity but Al(C6F5)4-activated catalyst showed very low activity, presumably due to the low thermal stability. B(C6F5)3-activated catalyst also indicated low activity. This activity difference reflected the relative coordinative abilities of the anions and tightness of the ion-pairing. MAO-activated catalyst was comparable in activity and copolymerization reactivity with Me2PhNH·B(C6F5)4-activated catalyst and these two catalyst produced high molecular weight ethylene/1-hexene copolymers in a high pressure process.

Propylene polymerization with Ph2C(3-RCp)(Flu)ZrCl2 [R = Me, i-Pr, PhCH2, Me3Si] catalysts activated with MAO and Me2PhNH.B(C6F5)4/i-Bu3Al

Propylene polymerization was conducted with Ph 2 C(R-Cp)(Flu)ZrCl 2 [R = Me, i-Pr, PhCH 2 , Me 3 Si] catalysts in combination with methylaluminoxane (MAO) and dimethylanilinium tetrakis(pentafluorophenyl)borate (Me 2 PhNH. B(C 6 F 5 ) 4 ) as cocatalyst; the dependence of the stereoregularity of poly(propylene) on cocatalysts and bulkiness of the substituents in β-position of the cyclopentadienyl ligand was studied. Methyl and i-propyl substituted metallocene catalysts produce hemi-isotactic poly(propylene). These results are in good agreement with the results of the isopropylidene bridged metallocene analogue. The benzyl substituted metallocene catalyst produces syndiotactic poly(propylene) regardless of the cocatalyst. This means that this substituent group does not affect migration insertion of propylene. Stereoregularity of poly(propylene) obtained with diphenylmethylidene(3-trimethylsilylcyclopentadienyl)(fluorenyl)zirconium dichloride (Ph 2 C(Me 3 SiCp)(Flu)ZrCl 2 ) as a catalyst was significantly influenced by the cocatalyst. Me 2 PhNH. B(C 6 F 5 ) 4 /triisobutylaluminium(i-Bu 3 Al) produces poly(propylene) with 65% racemic and 23% meso pentads at 40°C, whereas the MAO activated catalyst produces isotactic rich poly(propylene). Fractionation experiments indicated that Me 2 PhNH. B(C 6 F 5 ) 4 /i-Bu 3 Al forms two active sites, one of them being the same as that of the MAO activated catalyst, the other one producing syndiotactic rich poly(propylene).

Propylene polymerization with dimethylsilylbis(3-methylcyclo-pentadienyl)MCl2 [M = Ti, Zr, Hf] in combination with methylaluminoxane

Propylene polymerizations with rac-dimethylsilylbis(3-methylcyclopentadienyl)MCl (M = Ti, Zr, Hf) in combination with methylaluminoxane (MAO) were carried out to study the effect of the metal species on catalytic activity, stereoregularity, regioregularity, and molecular weight of poly(propylene). The rac-Me2Si(3-MeCp) 2 TiCl 2 /MA catalyst showed lowest activity among the three catalysts. The stereospecificity of the titanium based catalyst is very high and the portion of the mmmm pentads is roughly as high as for the zirconium and hafnium analogue. On the other hand, the regiospecificity of the titanium based catalyst is low and only the 1,3-regioirregular structure was observed, whereas the 2,1-regioirregular structure was detected in poly(propylene)s obtained with the zirconium and hafnium analogue. As a result, the melting point of poly(propylene) obtained with the titanium based catalyst is lower than that of poly(propylene) obtained with the zirconium or hafnium analogue. Addition of hydrogen with the titanium based catalyst gave rise to an increase in activity; but this accelerating effect was not observed in ethylene polymerization.

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.

Effect of ligand structures on high temperature homo- and copolymerization of ethylene by cationic hafnocene catalysts based on tetrakis(pentafluorophenyl)borate

Abstract Ethylene (Et) polymerization and Et/α-olefin copolymerization were carried out with various hafnocenes activated with dimethylanilinium tetrakis(pentafluorophenyl)borate (Me 2 PhNH·B(C 6 F 5 ) 4 /triisobutylaluminum ( i -Bu 3 Al) to study the relationship between ligand structures and catalyst performance at high temperature. Dimethylsilylene(bisindenyl)hafnium dichloride (Me 2 Si(Ind) 2 HfCl 2 )-based catalyst produced highest molecular weight polyethylene among indenyl-based catalysts. Hydrogenation of the indenyl ligand resulted in the decrease in activity and copolymerization reactivity, presumably due to the increased mobility of the ligand framework at high temperature. Diphenylmethylidene(cyclopentadienyl)(fluorenyl)hafnium dichloride (Ph 2 C(Cp)(Flu)HfCl 2 )-based catalyst produced higher molecular weight polyethylene than zirconium analog and indenyl-based hafnocene catalysts, but the activity was drastically dependent upon the alkylaluminum compound. This phenomenon was not observed in the corresponding zirconium catalyst. A broad chemical composition distribution, which was observed in Et/1-hexene copolymers obtained with Ph 2 C(Cp)(Flu)HfCl 2 -based catalyst, was attributed to the small amount of zirconium contamination.

Effect of topotactic reduction product of molybdenum disulfide on catalytic activity of metallocene catalyst for olefin polymerization

Abstract N,N-Dimethylanilinium (Ph(Me)2NH+) salt of tungsten disulfide (WS2) was developed as a novel cocatalyst for metallocene catalysts. The cocatalyst is composed of N,N-dimethylanilinium ion as a cationic part and “topotactic” reduction product of WS2, obtained by acquisition of an electron by the neutral host lattice of WS2 without structural alteration, as an anionic part. Notable improvement of the catalytic activity for ethylene polymerization using the bis(indenyl)zirconium dichloride (Ind2ZrCl2)/triethylaluminum (Et3Al) catalyst was observed upon the addition of the Ph(Me)2NH+ salt of WS2. The addition of the corresponding molybdenum disulfide (MoS2) one that had smaller crystallite size than the Ph(Me)2NH+ salt of WS2 showed the lower catalytic activity. The resultant poly(ethylene) prepared by the Ind2ZrCl2/Et3Al/Ph(Me)2NH+ salt of WS2 possessed similar properties like narrow polydispersity to that prepared by conventional metallocene type catalysts. The Zr loadings on the precipitate of the Ind2ZrCl2/Et3Al catalyst activated by the Ph(Me)2NH+ salt of WS2 increased with a decrease in the crystallite size of the Ph(Me)2NH+ salt of WS2. However, the catalytic activities in ethylene polymerization decreased drastically, indicating that the decrease of the crystallite size led to the significant increase of inactive species for ethylene polymerization.