Synthesis, structure and behavior of vanadium(III) diphosphine complexes in the homo- and co-polymerization of ethylene with norbornene: the ligand donor strength and bite angle make the difference

Thermally stable vanadium complexes supported by the iminophenyl oxazolinylphenylamine ligands: synthesis, characterization and application for ethylene (co-)polymerization

In this work, a series of oxovanadium complexes bearing the ligands (S,E)-(+)-2, 6-dialkyl-N-(2-((2-(4-isopropyl-4,5-dihydrooxazole-2-yl)phenyl)amino)benzylidene)aniline (dialkyl = dimethyl (V1), diethyl (V2), and isopropyl (V3)) have been synthesized and characterized by FTIR spectroscopy and elemental analysis. Moreover, the molecular structures of complexes V2 and V3 were defined by X-ray diffraction. On activation with ethylaluminium sesquichloride (Al₂Et₃Cl₃), these complexes exhibited high activity towards ethylene polymerization (up to 1.39 × 10⁷ g mol_v^-1 h^-1) and showed excellent thermal stability (up to 60 °C). The obtained polyethylene had a moderate molecular weight (21.9 × 10⁴ to 66.4 × 10⁴ g mol^-1) and exhibited narrow distribution (1.91 to 2.86) and unimodal features. The effect of the substituents on the ligands was also investigated in detail. The compound bearing the diisopropyl group showed the highest activity toward ethylene polymerization as the bimolecular deactivation of the catalyst can be effectively inhibited by the steric hindrance of the ortho-substituent on aniline. The complex V2 with moderate steric hindrance was also evaluated as a catalyst for the copolymerization of ethylene with norbornene and showed moderate to high activity.

Structural and Thermal Properties of Ethylene-Norbornene Copolymers Obtained Using Vanadium Homogeneous and SIL Catalysts

The series of ethylene-norbornene (E-NB) copolymers was obtained using different vanadium homogeneous and supported ionic liquid (SIL) catalyst systems. The ¹³C and ¹H NMR (carbon and proton nuclear magnetic resonance spectroscopy) together with differential scanning calorimetry (DSC) were applied to determine the composition of copolymers such as comonomer incorporation (C_NB), monomer dispersity (MD), monomer reactivity ratio (r_e), sequence length of ethylene (l_e) and tetrad microblock distributions. The relation between the type of catalyst, reaction conditions and on the other hand, the copolymer microstructure, chain termination reaction analyzed by the type of unsaturation are discussed. In addition, the thermal properties of E-NB copolymers such as the melting and crystallization behavior, like also the heterogeneity of composition described by successive the self-nucleation and annealing (SSA) and the dispersity index (DI) were determined.

Titanium and Vanadium Catalysts with 2-Hydroxyphenyloxazoline and Oxazine Ligands for Ethylene-Norbornene (co)Polymerization

A series of titanium and vanadium complexes with oxazoline 2-(4,5-dihydro-1,3-oxazol-2-yl)phenol (L1), 2-(4-methyl-4,5-dihydro-1,3-oxazol-2-yl)phenol (L2), and oxazine 2-(5,6-dihydro-4H-1,3-oxazin-2-yl)phenol (L3) ligands were synthesized, and their structures were determined by NMR and MS methods as (L)2MtCl2. The vanadium complexes were found to be highly active in ethylene (7300 kgPE/(molV·h)) and ethylene/norbornene (5300 kgCop/(molV·h)) (co)polymerization. The polyethylene characteristics were melting temperature (123–142 °C), crystallinity degree (49–75%), molecular weight (5.7–8.5 × 105 g/mol), molecular weight distribution (1.5–2.4). The ethylene-norbornene (E-NB) copolymer characteristics were molecular weight (2.6–0.9 × 105 g/mol), molecular weight distribution (1.6–2.2), glass transition temperature (4–62 °C), norbornene incorporation (12.3–30.1 mol%) at initial concentration (0.5–1.5 mol/L). The microstructure of E-NB copolymers depends on the catalyst applied with the highest diads content for the (L3)2VCl2 and triads for the (L2)2VCl2 complexes.

Homo- and Copolymerization of Ethylene with Norbornene Catalyzed by Vanadium(III) Phosphine Complexes

Herein, we report the homo- and co-polymerization of ethylene (E) with norbornene (NB) catalyzed by vanadium(III) phosphine complexes of the type VCl₃(PMe_nPh_3-n)₂ [n = 2 (1a), 1 (1b)] and VCl₃(PR₃)₂ [R = phenyl (Ph, 1c), cyclohexyl (Cy, 1d), tert-butyl (tBu, 1e)]. In the presence of Et₂AlCl and Cl₃CCOOEt (ETA), 1a-1e exhibit good activities for the polymerization of ethylene, affording linear, semicrystalline PEs with a melting temperature of approximately 130 °C. Mainly alternating copolymers with high comonomer incorporation were obtained in the E/NB copolymerization. A relationship was found between the electronic and steric properties of the phosphine ligands and the catalytic performance. Overall, the presence of electron-withdrawing ligand substituents increases the productivity, complexes with aryl phosphine (weaker σ-donor character) exhibiting a higher (co)polymerization initiation rate than those with alkyl phosphines (stronger σ-donor character). Steric effects also seem to play a key role since 1d and 1e, having large size phosphines (PCy₃ θ = 170° and PtBu₃ θ = 182°, respectively) are more active than 1a (PMe₂Ph θ = 122°). In this case, the larger size of PtBu₃ and PCy₃ likely compensates for their higher donor strength compared to PMe₂Ph.

Copolymerization of ethylene with propylene and higher α-olefins catalyzed by (imido)vanadium(iv) dichloride complexes

We have synthesized and characterized a series of (imido)V(iv) complexes bearing different imido groups and coligands, to be used, in combination with an aluminum alkyl, as catalysts for the (co)polymerization of ethylene with propylene.