Branched polyethylene prepared byin situ copolymerization of ethylene with monotitanocene and modified methylaluminoxane catalyst

Abstract

Branched polyethylene was synthesized in heptane used as a polymerization medium with monotitanocene catalyst composed of η5‐pentamethylcyclopentadienyl tribenzyloxy titanium and modified methylaluminoxane (mMAO) that contained different amounts of residual trimethylaluminum (TMA). The residual TMA more strongly reduced Ti(IV) complexes to Ti(III) and Ti(II) ones, and Ti(IV) active species were suggested to be more effective for ethylene polymerization. Influences of the polymerization temperature and Al/Ti molar ratio on the catalytic activity and the degree of branching, branch length, and molecular weight of polyethylene were investigated. The obtained polymers were confirmed by 13C NMR to be higher molecular weight polyethylene containing significant amounts of isolated ethyl branches, butyl branches, or both. Branched polyethylene was prepared by the in situ copolymerization of ethylene with 1‐butene and 1‐hexene, which were formed through a proposed mechanism including metallcycloheptane and metallcyclopentane intermediates of Ti(II) species that were produced by the reaction of Ti(IV) complexes with TMA coexisting in mMAO. There was a remarkable increase in the chance of 1‐butene being produced from metallcyclopentane of Ti(II) intermediates with an increase in the polymerization temperature. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4258–4263, 2000

Catalytic Trimerization of Ethene with Highly Active Cyclopentadienyl−Arene Titanium Catalysts

“…Zhu and co-workers reported recently that the catalyst system ( η 5 -C 5 Me 5 )Ti(OCH 2 Ph) 3 /MAO in heptane produces short chain (ethyl and butyl) branched polyethene in the homopolymerization of ethene, and they proposed a reduced titanium species as being responsible for in situ dimerization and trimerization of ethene . They suggest that free AlMe 3 , present in MAO, is essential in the reduction of titanium(IV) and the subsequent oligomerization of ethene.…”

Catalytic Trimerization of Ethene with Highly Active Cyclopentadienyl−Arene Titanium Catalysts

“…Zhu and co-workers reported recently that the catalyst system ( η 5 -C 5 Me 5 )Ti(OCH 2 Ph) 3 /MAO in heptane produces short chain (ethyl and butyl) branched polyethene in the homopolymerization of ethene, and they proposed a reduced titanium species as being responsible for in situ dimerization and trimerization of ethene . They suggest that free AlMe 3 , present in MAO, is essential in the reduction of titanium(IV) and the subsequent oligomerization of ethene.…”

Synthesis and Ethylene Polymerization Capability of Metallocene-like Imido Titanium Dialkyl Compounds and Their Reactions with AliBu3

“…The adverse effects of aluminum alkyls on group 4 catalyst systems and their precursors are well known and involve the trapping of active species as well as (pre)catalyst decomposition and other detrimental pathways. ,− ,− Therefore, in the catalyst systems reported here, the imido group appears to have two roles: (i) to stabilize the dialkyl precatalyst to degradation by the TIBA itself and (ii) to inhibit the formation of catalytically inactive heterobimetallic or homobimetallic complexes.…”

Dinuclear titanium complexes with methylphenylsilylene bridge between cyclopentadienyl rings. Synthesis, characterization and reactivity towards ethylene

“…Furthermore, MWD was dramatically broadened with increase of ethylene pressure from 1 to 5 bar to extreme MWD values MWD = 570 at 3 bars (run 5) and MWD = 620 at 5 bars (run 6). Although MWD of polyethylenes prepared by monocylopentadienyl titanium/MAO catalysts varies from relatively narrow with MWD = 2.2 for [(g 5 -C 5 H 5 )TiCl 3 ]/MAO [22], MWD = 2.3-2.5 for [(g 5 -C 5 H 5 )Ti(OBz) 3 ]/ MAO (Bz = benzyl) [10], to broad one with MWD ca. 40 for [{(g 5 -C 5 H 4 (cyclohex-1,1-diyl)Ar}TiCl 3 ]/MAO) [26], extra-high MWD values similar to those obtained from runs 5 and 6 are unexpected for HDPE polymer prepared by metallocene/MAO system.…”

“…monocationic dinuclear species) arising from a mutual interaction of both metals forced to a close proximity by a short silicone bridge cannot be ruled out. Although Ti(IV) species are more beneficial for ethylene polymerization [10], the paramagnetic Ti(III) species formed (vide infra) could also contribute to the activity of studied systems. DFT calculations published recently showed that the polymerization of ethylene on CpTi(III)Et + A À (A À denote counteranionts CH 3 B(C 6 F 5 ) 3 À or B(C 6 F 5 ) 4 À ) is thermodynamically allowed although with a low polymerization degree only [27].…”

Catalytic Trimerization of Ethene with Highly Active Cyclopentadienyl−Arene Titanium Catalysts

“…Zhu and co-workers reported recently that the catalyst system ( η 5 -C 5 Me 5 )Ti(OCH 2 Ph) 3 /MAO in heptane produces short chain (ethyl and butyl) branched polyethene in the homopolymerization of ethene, and they proposed a reduced titanium species as being responsible for in situ dimerization and trimerization of ethene . They suggest that free AlMe 3 , present in MAO, is essential in the reduction of titanium(IV) and the subsequent oligomerization of ethene.…”

Synthesis and Ethylene Polymerization Capability of Metallocene-like Imido Titanium Dialkyl Compounds and Their Reactions with AliBu3

“…The adverse effects of aluminum alkyls on group 4 catalyst systems and their precursors are well known and involve the trapping of active species as well as (pre)catalyst decomposition and other detrimental pathways. ,− ,− Therefore, in the catalyst systems reported here, the imido group appears to have two roles: (i) to stabilize the dialkyl precatalyst to degradation by the TIBA itself and (ii) to inhibit the formation of catalytically inactive heterobimetallic or homobimetallic complexes.…”

Dinuclear titanium complexes with methylphenylsilylene bridge between cyclopentadienyl rings. Synthesis, characterization and reactivity towards ethylene

“…Furthermore, MWD was dramatically broadened with increase of ethylene pressure from 1 to 5 bar to extreme MWD values MWD = 570 at 3 bars (run 5) and MWD = 620 at 5 bars (run 6). Although MWD of polyethylenes prepared by monocylopentadienyl titanium/MAO catalysts varies from relatively narrow with MWD = 2.2 for [(g 5 -C 5 H 5 )TiCl 3 ]/MAO [22], MWD = 2.3-2.5 for [(g 5 -C 5 H 5 )Ti(OBz) 3 ]/ MAO (Bz = benzyl) [10], to broad one with MWD ca. 40 for [{(g 5 -C 5 H 4 (cyclohex-1,1-diyl)Ar}TiCl 3 ]/MAO) [26], extra-high MWD values similar to those obtained from runs 5 and 6 are unexpected for HDPE polymer prepared by metallocene/MAO system.…”

“…monocationic dinuclear species) arising from a mutual interaction of both metals forced to a close proximity by a short silicone bridge cannot be ruled out. Although Ti(IV) species are more beneficial for ethylene polymerization [10], the paramagnetic Ti(III) species formed (vide infra) could also contribute to the activity of studied systems. DFT calculations published recently showed that the polymerization of ethylene on CpTi(III)Et + A À (A À denote counteranionts CH 3 B(C 6 F 5 ) 3 À or B(C 6 F 5 ) 4 À ) is thermodynamically allowed although with a low polymerization degree only [27].…”

Catalytic Trimerization of Ethene with Highly Active Cyclopentadienyl−Arene Titanium Catalysts

“…Zhu and co-workers reported recently that the catalyst system ( η 5 -C 5 Me 5 )Ti(OCH 2 Ph) 3 /MAO in heptane produces short chain (ethyl and butyl) branched polyethene in the homopolymerization of ethene, and they proposed a reduced titanium species as being responsible for in situ dimerization and trimerization of ethene . They suggest that free AlMe 3 , present in MAO, is essential in the reduction of titanium(IV) and the subsequent oligomerization of ethene.…”

Synthesis and Ethylene Polymerization Capability of Metallocene-like Imido Titanium Dialkyl Compounds and Their Reactions with AliBu3

“…The adverse effects of aluminum alkyls on group 4 catalyst systems and their precursors are well known and involve the trapping of active species as well as (pre)catalyst decomposition and other detrimental pathways. ,− ,− Therefore, in the catalyst systems reported here, the imido group appears to have two roles: (i) to stabilize the dialkyl precatalyst to degradation by the TIBA itself and (ii) to inhibit the formation of catalytically inactive heterobimetallic or homobimetallic complexes.…”

Dinuclear titanium complexes with methylphenylsilylene bridge between cyclopentadienyl rings. Synthesis, characterization and reactivity towards ethylene

“…Furthermore, MWD was dramatically broadened with increase of ethylene pressure from 1 to 5 bar to extreme MWD values MWD = 570 at 3 bars (run 5) and MWD = 620 at 5 bars (run 6). Although MWD of polyethylenes prepared by monocylopentadienyl titanium/MAO catalysts varies from relatively narrow with MWD = 2.2 for [(g 5 -C 5 H 5 )TiCl 3 ]/MAO [22], MWD = 2.3-2.5 for [(g 5 -C 5 H 5 )Ti(OBz) 3 ]/ MAO (Bz = benzyl) [10], to broad one with MWD ca. 40 for [{(g 5 -C 5 H 4 (cyclohex-1,1-diyl)Ar}TiCl 3 ]/MAO) [26], extra-high MWD values similar to those obtained from runs 5 and 6 are unexpected for HDPE polymer prepared by metallocene/MAO system.…”

“…monocationic dinuclear species) arising from a mutual interaction of both metals forced to a close proximity by a short silicone bridge cannot be ruled out. Although Ti(IV) species are more beneficial for ethylene polymerization [10], the paramagnetic Ti(III) species formed (vide infra) could also contribute to the activity of studied systems. DFT calculations published recently showed that the polymerization of ethylene on CpTi(III)Et + A À (A À denote counteranionts CH 3 B(C 6 F 5 ) 3 À or B(C 6 F 5 ) 4 À ) is thermodynamically allowed although with a low polymerization degree only [27].…”