Synthesis of low to high molecular weight poly(1-hexene); rigid/flexible structures in a di- and mononuclear Ni-based catalyst series

Khoshsefat, Mostafa; Ahmadjo, Saeid; Mortazavi, Seyed Mohammad Mahdi; Zohuri, Gholamhossein; Soares, João B. P.

doi:10.1039/c8nj01678j

Cited by 22 publications

(33 citation statements)

References 33 publications

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“…D r is the dead polymer and C d is the deactivated site. [51] Polymerization at higher temperature (45 and 65°C) showed a moderate thermal stability of catalyst C 2 . As the first step in the ethylene insertion process is formation of a π-Comp.…”

Section: Ethylene Polymerization Catalyzed By Mononuclear and Dinucmentioning

confidence: 96%

“…As the first step in the ethylene insertion process is formation of a π-Comp. [43,51] 3.2 | Microstructural properties Molecular weight and MWD of mononuclear catalysts (M 1 and M 2 ) correspond to their single-site feature of the center, while for dinuclear catalysts, the presence of stereoisomers afforded different trends in polymerization pathway and products as can be observed in the GPC and short-chain branching (SCB) curves (Figure 4). [45] Although the narrow energy interval (Figure 3) between the precatalyst and catalyst (lower activation energy) led to faster activation (K a ) and coordination for catalyst M 2 having lower steric and electronic effects, catalyst C 2 through optimum bulkiness, synergistic effect and higher stability showed higher K p /K tr and K p /K d rates.…”

Section: Ethylene Polymerization Catalyzed By Mononuclear and Dinucmentioning

confidence: 97%

“…Molecular weight distributions (MWDs) were determined with a Polymer Char high-temperature gel permeation chromatography (GPC) instrument, run at 145°C under a flow of 1,2,4-trichlorobenzene at a rate of 1 ml min −1 . [51,52] The catalysts studied were mononuclear (M 1 and M 2 ) and dinuclear (C 1 -C 6 ) Ni α-diimine-based catalysts. [49] 13 C NMR spectra of polyethylene were recorded with a Bruker AC-400 MHz instrument at 115°C in deuterated tetrachloroethane with tetramethylsilane as an internal standard.…”

Section: Characterizationmentioning

confidence: 99%

“…Since the reactions were carried out under similar conditions, the effects of structure on polymerization kinetics revealed that optimum bulkiness in architecture of catalyst leads to efficient shielding of axial sites of active centers against deactivation and chain transfer reactions (Equations (4) and (5)). [43,51,53] Higher monomer pressure at high temperature of polymerization (run 11) afforded a higher yield of polyethylene with higher molecular weight and degree of crystallinity. and the most stable structure is found, the ethylene monomer is oriented in a direction perpendicular to the MCC.…”

Section: Ethylene Polymerization Catalyzed By Mononuclear and Dinucmentioning

confidence: 99%

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Cooperative effect through different bridges in nickel catalysts for polymerization of ethylene

Khoshsefat

Dechal

Ahmadjo

et al. 2019

Applied Organom Chemis

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A series of mononuclear (M 1 and M 2 ) and dinuclear (C 1 -C 6 ) Ni α-diimine catalysts activated by modified methylaluminoxane were used in polymerization of ethylene. Catalyst C 2 bearing the optimum bulkiness showed the highest activity (1.6 × 10 6 g PE (mol Ni) −1 h −1 ) and the lowest short-chain branching (32.5/1000 C) in comparison to the dinuclear and mononuclear analogues.Although the mononuclear catalysts M 1 and M 2 polymerized ethylene to a branched amorphous polymer, the dinuclear catalysts led to different branched semicrystalline polyethylenes. Homogeneity and heterogeneity in the microstructure of the polyethylene samples was observed. Different trends for each catalyst were assigned to syn and anti stereoisomers. In addition, thermal behavior of the samples in the successive self-nucleation and annealing technique exhibited different orders and intensities from methylene sequences and lamellae thickness in respect of each stereoisomer behavior. Higher selectivity of hexyl branches obtained by catalyst C 2 showed a cooperative effect between the centers. The results also revealed that for catalysts C 5 and C 6 , selectivity of methyl branches led to very high endotherms and crystalline sequences with melting temperatures higher than that of 100% crystalline polyethylene indicating ethylene/propylene copolymer analogues. For catalysts C 3 and C 4 , more vinyl end groups were a result of the long distance between the Ni centers. Kinetic profiles of polymerization along with a computational study of the precatalysts and catalysts demonstrated that there is a direct relation between rate constant, energy interval of catalyst and precatalyst, and interaction energy of Et···methyl cationic active center (Et···MCC or π-Comp.). Based on this, narrow energy interval (activation energy) of precatalyst and catalyst leads to fast and higher activation rate (catalyst M 2 ), and strong interaction of ethylene and catalyst leads to high monomer uptake and productivity (catalyst C 2 ). Moreover, theoretical parameters including electron affinity, Mulliken charge on Ni, chemical potential and hardness, and global electrophilicity showed optimum values for C 2 .

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Section: Ethylene Polymerization Catalyzed By Mononuclear and Dinucmentioning

confidence: 96%

Section: Ethylene Polymerization Catalyzed By Mononuclear and Dinucmentioning

confidence: 97%

Section: Characterizationmentioning

confidence: 99%

Section: Ethylene Polymerization Catalyzed By Mononuclear and Dinucmentioning

confidence: 99%

See 2 more Smart Citations

Cooperative effect through different bridges in nickel catalysts for polymerization of ethylene

Khoshsefat

Dechal

Ahmadjo

et al. 2019

Applied Organom Chemis

Self Cite

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“…18) with alkyl-and 1,4-phenyl-linked based ligands. 116,117 The ethylene polymerization results using C37b-f suggested that these steric and electronic substituent effects of α-diimine ligands have significant influences on polymerization behaviors. 116 C37a and C37f polymerized 1-hexene to obtain low to high molecular weight poly(1hexene) with M w of up to 1.7 × 10 6 g mol −1 .…”

Section: Dinuclear α-Diimine Nickel and Palladium Catalystsmentioning

confidence: 99%

A continuing legend: the Brookhart-type α-diimine nickel and palladium catalysts

2019

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Microstructural study on MMA/1‐hexene copolymers made by mononuclear and dinuclear α‐diimine nickel (II) catalysts

Bagherabadi

Zohuri

Ramezanian

et al. 2020

Applied Organom Chemis

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Homogenous catalytic homopolymerization and copolymerization of 1-hexene (H) with methyl methacrylate (MMA) were carried out in presence of two different types of mononuclear (MNC1 and MNC2) and dinuclear Ni-based catalysts (BNC1 and BNC2). Modified methylaluminoxane was used as cocatalyst due to good reactivity in MMA/H copolymerization. Among the structures, BNC1 showed the highest catalyst activity (6.9 × 10 4 g P. mol −1 Ni. h −1). Although M w of the copolymer made by BNC1 was higher than its mononuclear, molecular weight distribution was broader. The optimum molar ratios for mononuclear and dinuclear were obtained at [Al]/[Ni] = 1,000:1 and [Al]/[Ni] = 1,500:1, respectively. Surprisingly, introduction of MMA (up to [MMA]/[H] = 50:50 molar ratio) into the polymerization solution increased the activity of all catalysts. 1 H NMR analysis study revealed that increasing of MMA in the feed composition raised incorporation of the comonomer into the obtained copolymers. The result was consistent on the calculated reactivity ratio of monomers, using Kelen-Tudos method. In addition, BNC1 (at [MMA]/[H] = 70:30 molar ratio) demonstrated more incorporation of MMA to the main copolymer chain (95.2% mol). On the other side, study on tacticity of the PMMA sample was investigated that showed a distribution of stereoregularity in the order of atactic > > syndiotatic > isotactic (53.2 > 26.7 > 20.1). In addition, for copolymers made by BNC1, an unusual pattern was observed as lower concentration of MMA in the feed (i.e., 30%) led to high isotactic blocks of MMA. The highest branching density of the polymer, however, was obtained by BNC1 (217/1000C) and the lowest by BNC2 (80/1000C). Higher extent of the polar comonomer (MMA) in the copolymer backbone led to increasing of T g for the copolymer samples (from 74.4 to 98.9 C). The structural properties of the obtained copolymers were investigated using both Fourier transform infrared spectroscopy and Raman spectroscopies, as well.

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Synthesis of low to high molecular weight poly(1-hexene); rigid/flexible structures in a di- and mononuclear Ni-based catalyst series

Abstract: Poly(1-hexene)s with a wide range of Mw and MWD using mono- and dinuclear rigid/flexible bridged Ni catalysts; structure–property relation.

Cited by 22 publications

References 33 publications

Cooperative effect through different bridges in nickel catalysts for polymerization of ethylene

Cooperative effect through different bridges in nickel catalysts for polymerization of ethylene

A continuing legend: the Brookhart-type α-diimine nickel and palladium catalysts

Microstructural study on MMA/1‐hexene copolymers made by mononuclear and dinuclear α‐diimine nickel (II) catalysts

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