Remarkable Effects of Aluminum Cocatalyst and Comonomer in Ethylene Copolymerizations Catalyzed by (Arylimido)(aryloxo)vanadium Complexes:  Efficient Synthesis of High Molecular Weight Ethylene/Norbornene Copolymer

Abstract

Copolymerizations of ethylene with norbornene (NBE), cyclopentene (CPE) and 1-hexene by (arylimido)(aryloxo)vanadium(V) complexes of the type VCl 2(N-2,6-Me2C6H3)(OAr) [Ar ) 2,6-Me2C6H3 (1), 2,6-i Pr2C6H3 (2), 2,6-Ph2C6H3 (3)] with cocatalyst [methylaluminoxane (MAO) or Et2AlCl] catalyst systems have been explored. These complexes exhibited remarkable catalytic activities for ethylene polymerization in the presence of Et 2AlCl cocatalyst; in particular, the resultant polyethylene prepared by 1 possessed narrow molecular weight distributions and the Mn value increased linearly upon increasing the polymer yields (TON values). Notable effects of Al cocatalyst have been observed in the copolymerization of ethylene with NBE: the catalytic activities, the NBE incorporation, dominant chain transfer reactions, and the M n values for resultant copolymers were highly dependent upon the Al cocatalyst employed (MAO or Et2AlCl). The 1-Et2AlCl catalyst system exhibited remarkable catalytic activities, affording ultrahigh molecular weight poly(ethylene-co-NBE)s with narrow molecular weight distributions (Mn ) 2.12-2.70 × 10 6 , Mw/Mn ) 1.29-1.53), and the Mn values were independent upon the NBE contents but were dependent upon the Al/V molar ratios. In contrast, 1-MAO catalyst exhibited better NBE incorporation than the 1-Et2AlCl catalyst, and the Mn value was independent of the Al/V molar ratio but was dependent upon the NBE contents. Modification of the aryloxide ligand affected the catalytic activity, but it did not strongly affect the NBE incorporation, the M n values, and microstructure in the resultant copolymers. However, 1 exhibited a negligible amount of CPE incorporation in the ethylene/ CPE copolymerization and also exhibited inefficient 1-hexene incorporation in the ethylene/1-hexene copolymerization. Since the resultant polymer obtained by the attempted copolymerization of ethylene with styrene was polyethylene, the effect of comonomer toward both the catalytic activity and the comonomer incorporation has been demonstrated.

Ethylene/1-olefin copolymerization behaviour of vanadium and titanium complexes bearing salen-type ligand

“…Heterogeneous Ziegler-Natta catalysts usually give copolymers with both broad comonomer distribution and wide molecular weight distribution, while homogeneous metallocene catalysts produce much more uniform copolymers [2,3]. Recently copolymerization in the presence of postmetallocene catalysts also became an interesting and important field of research [4][5][6][7][8][9][10][11]. Very efficient copolymerization postmetallocene catalysts are titanium complexes of the general formula [N-(3,5-di-tert-butylsalicylidene)-2-alkylsulfanylanilinato]Ti(IV)Cl 3 .…”

“…Hence, much interest was attracted by postmetallocene complexes which had vanadium as the central metal, both for homoand copolymerization of olefins [5][6][7][15][16][17][18][19][20][21]. Nomura and Wang [7] used (arylimino)(aryloxo)vanadium(V) complexes in ethylene/1-hexene copolymerization. However, poor 1-hexene incorporation was observed (0.8 mol%).…”

Ethylene Polymerization Using (Imino)vanadium(V) Dichloride Complexes Containing (Anilido)methyl-pyridine, -quinoline Ligands–Halogenated Al Alkyls Catalyst Systems

“…We previously reported that (arylimido)vanadium(V) complexes, containing anionic donor ligands (L), V(N-2,6-Me 2 C 6 H 3 )Cl 2 (L) (L = aryloxo, ketimide, phenoxyimine etc. ), exhibited remarkable catalytic activities for ethylene polymerization in the presence of Al cocatalysts [3][4][5][6][7][8][9][10]. The activity by the aryloxo analogue was strongly affected by the Al cocatalyst; the activities in the presence of halogenated Al alkyls ( i Bu 2 AlCl, EtAlCl 2 , Me 2 AlCl, Et 2 AlCl) were higher than those in the presence of methylaluminoxane (MAO) [7,8].…”

“…), exhibited remarkable catalytic activities for ethylene polymerization in the presence of Al cocatalysts [3][4][5][6][7][8][9][10]. The activity by the aryloxo analogue was strongly affected by the Al cocatalyst; the activities in the presence of halogenated Al alkyls ( i Bu 2 AlCl, EtAlCl 2 , Me 2 AlCl, Et 2 AlCl) were higher than those in the presence of methylaluminoxane (MAO) [7,8]. Both the activity, and the norbornene incorporation, in the ethylene/norbornene copolymerization were also affected by the Al cocatalyst employed [7,8].…”

“…The activity by the aryloxo analogue was strongly affected by the Al cocatalyst; the activities in the presence of halogenated Al alkyls ( i Bu 2 AlCl, EtAlCl 2 , Me 2 AlCl, Et 2 AlCl) were higher than those in the presence of methylaluminoxane (MAO) [7,8]. Both the activity, and the norbornene incorporation, in the ethylene/norbornene copolymerization were also affected by the Al cocatalyst employed [7,8]. We thus speculated that a reason for the observed difference would be due to a formation of the different catalytically-active species, catalyst/cocatalyst nuclearity effect (assumed in Scheme 1) [5,[11][12][13].…”