Cyclohexene (CHE) has been incorporated into the polymer chain in ethylene/CHE copolymerization by nonbridged half-titanocenes containing aryloxo ligands of the type, Cp'TiCl2(O-2,6-iPr2C6H3), in the presence of methylaluminoxane (MAO) cocatalyst. The effect of the substituent in the cyclopentadienyl fragment was found to be very important for CHE incorporation; both the tert-BuCp (3) and 1,2,4-Me3Cp analogues (4) showed efficient CHE incorporation, whereas a negligible amount of CHE incorporation was observed by both the indenyl (1) and the Cp* analogue (2) under the same conditions. Cp-ketimide analogue, CpTiCl2(N=CtBu2) (5), zirconocene-like Cp2ZrCl2 (6), and linked half-titanocene-like [Me2Si(C5Me4)(NtBu)]TiCl2 (7) did not show any CHE incorporation under the same conditions; unique characteristics for using this type of catalyst precursor for the present copolymerization have thus been emphasized.

The effects of both Al cocatalyst and solvent on catalytic activity in the ethylene polymerization by the (arylmido)(aryloxo)vanadium

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.

CpTiCl2(N=CtBu2) exhibits both remarkable catalytic activity and efficient norbornene (NBE) incorporation for ethylene-NBE copolymerization: the NBE incorporation by Cp'TiCl2(X) (X = N=CtBu2, O-2,6-iPr2C6H3; Cp' = Cp, C5Me5, indenyl) was related to the calculated coordination energy after ethylene insertion.

The mechanism for the formation and sustainment of a self-organized global profile and the 'E × B staircase' are investigated through simulations of a flux-driven ion temperature gradient (ITG) turbulence based on GKNET, a 5D global gyrokinetic code. The staircase is found to be initiated from the radially extended ITG mode structures with nearly up-down symmetry during the saturation phase, and is established as it evolves into a quasi-steady turbulence, leading to a self-organized global temperature profile and to meso-scale isomorphic profiles of the radial electric field and the temperature gradient. It is found that the quasi-regular E × B shear flow pattern is primarily originated from an even-symmetrical zonal flow produced by the extended ITG mode, which flow pattern exhibits an in-phase relation with the mean flow variation induced by the temperature relaxation. Consequently, the staircase is initiated through the profiles of total electric field and temperature gradient with a self-organized manner. Since the sign of E × B shear flow at the central part are opposite to that at both edges, it disintegrates the ITG mode into smaller scale eddies. Meanwhile, smaller scale eddies tend to be aligned radially by spontaneous phase matching, which can provide the growth of mode amplitude and the formation of radially extended mode structures, leading to the bursty heat transport. This process is repeated quasi-periodically, sustaining self-organized structures and the E × B staircase. Moreover, the equilibrium mean field is found to be of specific importance in causing the structures and dynamics from meso-to macro scales in toroidal plasmas.

Dedicated in honor to Prof. Richard R. Schrock on the occasion of his 60th birthday.Abstract: The effect of the cyclopentadienyl fragment in the copolymerization of ethylene with norbornene (NBE) by various non-bridged (aryloxo)(cyclopentadienyl)titanium(IV) complexes of the type, Cp'TiCl 2 -(OAr) [Cp' ¼ indenyl (1), C 5 Me 5 (Cp*, 2), t-BuC 5 H 4 (3), 1,2,4-Me 3 C 5 H 2 (4); OAr ¼ O-2,6-i-Pr 2 C 6 H 3 ], À MAO catalyst systems has been explored. The catalytic activity and the NBE incorporation were highly dependent upon substituent on Cp' employed, and 1 exhibited both a remarkable catalytic activity and an efficient NBE incorporation, affording high molecular weight polymers with unimodal molecular weight distributions. NBE repeat units were observed in the resultant poly(ethylene-co-NBE)s prepared by 1, 3, and 4, and the degree of NBE dyads as well as alternating sequences was strongly influenced by the Cp' employed. These complexes (1,3,4) also exhibited high catalytic activities for ethylene/cyclopentene (CPE) copolymerization, but the CPE incorporation by 1 was less efficient than the NBE incorporation under the same conditions. The ab initio density functional (DF) molecular orbital (MO) methods were utilized to explore the effect of substituents on Cp' toward the catalytic activity, the NBE incorporation and the monomer sequence distribution. Good correlations between the DE coord Et (coordination energy of ethylene) after NBE insertion and the activity, and between DE coord NBE (coordination energy of NBE) after ethylene (or NBE insertion) and NBE content were observed, strongly suggesting that the capability producing NBE repeat units was dependent upon DE coord NBE after NBE insertion.

No abstract

No abstract