Modified Methylaluminoxane Research Articles

Synthesis, structural characterization and MMA polymerization studies of dimeric 5-coordinate copper(II), cadmium(II), and monomeric 4-coordinate zinc(II) complexes supported by N-methyl-N-((pyridine-2-yl)methyl)benzeneamine

Copper(II), cadmium(II) and zinc(II) complexes containing N-methyl-N-((pyridine-2-yl)methyl)benzeneamine (npmb) ligand have been synthesized and characterized by X-ray crystallography. Molecular structures of Cu(II) and Cd(II) complexes revealed dimeric structures with square pyramidal and distorted trigonal bipyramidal geometries, respectively, involving two nitrogen atoms, two bridged and one terminal halogen ligands. However, the monomeric Zn(II) complex showed a distorted tetrahedral geometry around the Zn centre. [(npmb)ZnCl2] exhibited the higher catalytic activity (2.88 × 104 g PMMA/molZn·h) for the polymerization of methyl methacrylate (MMA) in the presence of modified methylaluminoxane (MMAO) at 60 °C and yielded high molecular weight (11.1 g/mol × 105) syndiotactic-enriched poly(methylmethacrylate) (PMMA) compared to its Cu(II) and Cd(II) analogues.

Synthesis, characterization and polymerisation studies of cadmium(II) complexes containing N,N′,X-tridentate X-substituted (X = N, O) 2-iminomethylpyridines

The reaction of [CdBr2·4H2O] with N1,N1-dimethyl-N2-(pyridin-2-ylmethylene)ethane-1,2-diamine) (LA), 2-methoxy-N-(pyridin-2-ylmethylene)ethanamine (LB), 2-(piperidin-1-yl)-N-(pyridin-2-ylmethylene)ethanamine (LC), 2-morpholino-N-(pyridin-2-ylmethylene)ethanamine (LD), N1,N1-dimethyl-N3-(pyridin-2-ylmethylene)propane-1,3-diamine (LE) and 3-methoxy-N-(pyridin-2-ylmethylene)propan-1-amine (LF) in methanol produced the tridentate [(NN′X)CdBr2] complexes, namely [LACdBr2], [LBCdBr2], [LCCdBr2], [LDCdBr2], [LECdBr2] and [LFCdBr2], respectively. The molecular structures of the Cd(II) complexes revealed that the cadmium atom in [LnCdBr2] (Ln = LA, LC-LE) has a distorted square pyramidal geometry involving two nitrogen atoms and one nitrogen or oxygen atom of the N,N′,X-tridentate ligands and two bromo ligands. The dimethyl derivatives, generated in situ, [LnCdMe2] (LA-LF) initiated the polymerisation of rac-Lactide (rac-LA) and yielded heterotactic PLA. Notably, the substituent attached to ligand architecture affects the activities towards the rac-LA polymerisation, whereas the stereoselectivities remained unchanged. Moderate activities towards the polymerisation of methylmethacrylate (MMA) polymerisation in the presence of modified methylaluminoxane (MMAO) at 60 °C were observed for [LnCdBr2] (LA-LF). The preliminary results showed that these complexes yielded syndio-rich poly(methylmethacrylate) (PMMA) ([rr] = 0.66).

A comparative kinetic study of ethylene polymerization mediated by iron, cobalt and chromium catalysts bearing the same N,N,N-bis(imino)trihydroquinoline

The iron(II), cobalt(II) and chromium(III) chlorides, [2-{(2,4,6-Me3C6H2)NCMe}-8-{N(2,4,6-Me3C6H2)}C9H8N]MCln (n = 2, M = Fe LFeCl2, Co LCoCl2; n = 3, M = Cr LCrCl3), each bearing the same N,N,N-bis(imino)trihydroquinoline chelating ligand, have been employed as precatalysts for ethylene polymerization with modified methylaluminoxane (MMAO) as the co-catalyst. The kinetic profiles for these homogeneous polymerizations are reported in addition to the properties of the resultant polymers under comparable reaction conditions. All the experimental data indicate that the active metal center plays a key role on the catalytic performances of the complexes, especially the polymerization activity, thermal stability and lifetime of the active species. Under optimized conditions the iron catalyst displays the highest rate of polymerization but displays this for only a short period, while the chromium catalyst shows a lower maximum polymerization rate but sustains its performance over a longer period and at a higher temperature. In terms of the polymer properties, all three metal catalysts afford highly linear polymers with the metal center influencing the molecular weight and type of end group. Specifically, the cobalt and chromium catalysts produce narrowly dispersed low molecular weight polymers incorporating vinyl end groups, while the iron catalyst affords polymers of higher molecular weight displaying broad molecular weight distributions, with both fully saturated and unsaturated chain ends.

Ethylene polymerization and ethylene/1-octene copolymerization with a titanium complex supported by a bis(indolyl) ligand

The synthesis of bis(diethylamido){di(3-methylindol-2-yl)phenylmethane}titanium (1) was achieved in high yield (85%) by the treatment of 2,2′-di(3-methylindolyl)phenylmethane with Ti(NEt2)4 in toluene at reflux for 18 h. The ethylene polymerization activity of the 1/modified methylaluminoxane (MMAO) catalyst system was low (16.3 kg of polyethylene (PE)/mol of Ti•h), but pretreatment of 1 with ClSiMe3 followed by activation with MMAO improved the activity up to 154 kg of PE/mol of Ti•h. An NMR-scale reaction of 1 with ClSiMe3 in C6D6 at 80 °C for 22 h indicated the generation of an amido chlorido complex together with the formation of Et2N–SiMe3. Partial chlorination would facilitate methylation by MMAO. The polyethylenes obtained in this study are all monomodal by size exclusion chromatography and have linear structures by NMR spectroscopy. The catalyst system was also found to be active for ethylene/1-octene copolymerization (90 kg of copolymer/mol of Ti•h). Ethylene polymerization with bis(diethylamido){di(3-methylindol-2-yl)phenylmethane}titanium (1) was examined using modified methylaluminoxane (MMAO) as an activator. The activity of the 1/MMAO catalyst system was low (16.3 kg of polyethylene (PE)/mol of Ti•h), but pretreatment of 1 with ClSiMe3 followed by activation with MMAO improved the activity up to 154 kg of PE/mol of Ti•h. The obtained PEs are all monomodal by size exclusion chromatography and have linear structures by NMR spectroscopy. The 1/ClSiMe3/MMAO catalyst system was also active for ethylene/1-octene copolymerization (90 kg of copolymer/mol of Ti•h).

Strictly linear polyethylene using Co-catalysts chelated by fused bis(arylimino)pyridines: Probing ortho-cycloalkyl ring-size effects on molecular weight

Six examples of α,α′-bis(arylimino)-2,3:5,6-bis(pentamethylene)pyridine-cobalt(II) chlorides, [2,3:5,6-{C4H8C(NAr)}2C5HN]CoCl2 (Ar = 2-(C5H9)-6-MeC6H3Co1, 2-(C6H11)-6-MeC6H3Co2, 2-(C8H15)-6-MeC6H3Co3, 2-(C5H9)-4,6-Me2C6H2Co4, 2-(C6H11)-4,6-Me2C6H2Co5, 2-(C8H15)-4,6-Me2C6H2Co6), containing N-aryl groups that differ in either the ring size of the ortho-cycloalkyl substituents or the para-R group (R = H, Me), have been synthesized using a one-pot template approach. The molecular structure of Co1 highlights the ring puckering of both the ortho-cyclopentyl substituents and the two pyridine-fused seven-membered rings; a square-based pyramidal geometry is conferred about the metal center. On activation with either methylaluminoxane (MAO) or modified MAO (MMAO), all six complexes afforded strictly linear polyethylene (all Tm's > 130 °C) with high molecular weight (Mw up to 64.3 kg mol−1). Furthermore, all precatalysts displayed high activities (up to 2 × 106 g PE mol-1 (Co) h−1) at temperatures between 20 and 60 °C with the catalytic activities correlating with the type of ortho-cycloalkyl substituent: cyclohexyl (Co2, Co5) > cyclopentyl (Co1, Co4) > cyclooctyl (Co6, Co3) for either R = H or Me. The narrow unimodal distributions of the resulting polymers are consistent with single-site active species for the catalysts.

Mechanistic Insights into Chromium-Catalyzed Ethylene Trimerization

The kinetics of ethylene trimerization by a chromium N-phosphinoamidine (Cr-(P,N)) precatalyst activated by modified methylaluminoxane (MMAO) has been investigated by high-pressure NMR techniques. An in-depth kinetic analysis of this metallacyclic mechanism has been conducted. It was found that an intermediate in the trimerization catalytic cycle, proposed in this study as the chromium alkenyl hydride species, degrades into a polymer active site where this degradation step is independent of ethylene concentration and is first order in catalyst. Additionally, we report that at least one of the first two ethylene coordination steps must be reversible in order to predict the features of the monomer consumption profiles. The reaction order in ethylene is dependent on the reversibility of the ethylene coordination steps. The observation of these details of the mechanism explains many of the challenges inherent in the examination of this and similar catalyst systems and emphasizes the usefulness of operando hig...

Palladium(II) complexes containing N,N′-bidentate imine ligands derived from picolinaldehyde and substituted anilines: Synthesis, structure and polymerisation of methyl methacrylate

Palladium(II) complexes, LnPdCl2 (Ln = LA–LI), with N,N′-bidentate imine ligands derived from picolinaldehyde and substituted anilines have been synthesized and structurally characterized. Molecular structures revealed a distorted square plane geometry around Pd(II) centre in LnPdCl2 (Ln = LA–LC) obtained via coordination with pyridine and imine nitrogens and two chloro ligands. Pd(II) complexes LnPdCl2 (Ln = LA–LI) initiate polymerisation of methylmethacrylate (MMA) in the presence of modified methylaluminoxane (MMAO). The complex LIPdCl2 (of which the ligand was N-furfuryl substituted) showed the highest catalytic activity for the polymerisation of MMA with an activity of 7.08 × 104 g PMMA/mol·Pd·h at 60 °C. All the complexes yielded syndio-rich poly(methyl methacrylate) (PMMA) ([rr] = 0.70). Notably, the substituents on the imine moiety of the iminopyridine fragments affects the activities towards MMA polymerization, whereas the stereoselectivities remained unchanged.

Chain-Walking Polymerization of Linear Internal Octenes Catalyzed by α-Diimine Nickel Complexes

The chain-walking polymerization of linear internal alkenes (i.e., trans-2-, 3-, and 4-octenes) using α-diimine nickel catalysts activated with modified methylaluminoxane (MMAO) was studied in comparison with the corresponding terminal alkene polymerization. The rates of polymerization were found to decrease in the following order: 1-octene > 4-octene ≥ 2-octene ≫ 3-octene. The obtained branched poly(2-octene)s and poly(4-octene)s with high molecular weight and Mw/Mn less than 2 were amorphous polymers with low glass transition temperature (Tg) of approximately −66 °C. At 0 °C, 4-octene polymerized in a living/controlled manner. The NMR analyses of the polymers showed that the chain-walking polymerization of 4-octene gave periodically branched polymers with the constant branching density, while that of 2-octene gave the polymer possessing fewer branches than the expected value due to monomer-isomerization. The (n+2),(n+3)- and (n+3),(n+2)-insertions of the internal (n+2)-alkene [CH3(CH2)nCH═CH(CH2)mCH3] f...

Vinyl/Vinylene functionalized highly branched polyethylene waxes obtained using electronically controlled cyclohexyl‐fused pyridinylimine‐nickel precatalysts

ABSTRACTA series of 8‐(2,6‐dibenzhydryl‐4‐R‐phenylimino)‐5,6,7‐trihydroquinoline ligands have been prepared in which the nature of 4‐R substitutions vary from electron withdrawing to electron donating. The treatment with NiCl2.6H2O or (DME)NiBr2 afforded the corresponding complexes of nickel chloride (4‐R = Me Ni1, Et Ni2, tBu Ni3, CHPh2 Ni4, Cl Ni5, and F Ni6) and nickel bromide (4‐R = Me Ni7, Et Ni8, tBu Ni9, CHPh2 Ni10, Cl Ni11, and F Ni12). X‐ray diffraction study of complexes Ni3, Ni6, and Ni10, revealed that Ni3.1/2H2O and Ni6.H2O adopted unsymmetrical and symmetrical chloride‐bridged dinuclear structures respectively, while Ni10.H2O is found as mononuclear specie forming distorted‐square planer geometry. In the presence of either diethylaluminum chloride (Et2AlCl) or modified methylaluminoxane (MMAO), all the nickel complexes (Ni1–Ni12) displayed high activities (up to 1.91 × 106 g(PE) mol (Ni)−1h−1. Highly branched polyethylene waxes with low molecular weights (Mw ≤ 2.6 kg/mol) and narrow molecular weights distributions (Mw/Mn ≤ 1.96) incorporated with vinylene and vinyl groups were obtained. The effects of 4‐R substitutions to the nickel chloride and bromide pre‐catalysts and reaction conditions on the catalytic performance and the properties of the resulting polyethylene were the subject of a detail investigation. The positive influences of using electron‐withdrawing 4‐R substitutions and bromides were observed. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 1269–1281

Zinc(II) complexes containing N′-aromatic group substituted N,N′,N-bis((1H-pyrazol-1-yl)methyl)amines: Synthesis, characterization, and polymerizations of methyl methacrylate and rac-lactide

A novel series of Zn(II) complexes [LnZnCl2] (Ln = LA − LF) based on N,N′,N-bis((1H-pyrazol-1-yl)methyl)amine bidentate ligands, N,N-bis((1H-pyrazol-1-yl)methyl)-3,5-dimethylaniline [LA], N,N-bis((1H-pyrazol-1-yl)methyl)-2,6-dimethylaniline [LB], N,N-bis((1H-pyrazol-1-yl)methyl)-2,6-diethylaniline [LC], N,N-bis((1H-pyrazol-1-yl)methyl)-2,6-diisopropylaniline [LD], N,N-bis((1H-pyrazol-1-yl)methyl)-4-bromoaniline [LE] and N,N-bis((1H-pyrazol-1-yl)methyl)benzhydrylamine [LF], has been synthesized and characterized. X-ray structures of these Zn(II) complexes showed a distorted tetrahedral geometry. No interaction exists between the Namine and the Zn(II) center in the [LnZnCl2] (Ln = LA − LF) complexes, resulting in formation of an eight-membered chelate ring. [LFZnCl2] exhibited the highest catalytic activity (3.95 × 104 g PMMA/mol·Zn·h) for the polymerization of methyl methacrylate (MMA) in the presence of modified methylaluminoxane (MMAO) at 60 °C and yielded high molecular weight (Mw) (11.0 × 105 g/mol) of poly(methylmethacrylate) (PMMA). All the complexes resulted in syndiotactic enriched PMMA with high Tg (125–131 °C). The steric bulk of ligand architecture plays an influential role in controlling the catalytic activity and stereoregularity of the resultant PMMA. Further, alkyl derivatives [LnZnMe2] (Ln = LA − LF) of synthesized Zn(II) complexes, generated in situ, showed moderate to high activities toward ring opening polymerization (ROP) of rac-lactide (rac-LA) and yielded heterotactic polylactide (PLA) with Pr up to 0.95 at −50 °C. The activity and stereoselectivity toward ROP of rac-LA by these dimethyl Zn(II) complexes should be considered as a combined effect of steric hindrance and electronic density around the metal center.

New type of highly active chromium(III) catalysts containing both organic cations and anions designed for polymerization of beta-olefin derivatives

The new type of catalysts designed for the olefin derivatives polymerization has been synthetized. The novel catalysts are chromium(III) salt type complexes composed of both organic cation and anion, i.e. [Cr(dipic)2][Cr(bipy)(dipic)H2O]∙2H2O and [Cr(dipic)2]Hdmbipy∙2.5 H2O. The compositions of these complexes have been confirmed by a number of instrumental methods including NMR, IR, UV-Vis, MS and elemental analysis ones. Moreover, the crystal structures of these novel catalysts were determined and reported. Furthermore, the [Cr(dipic)2][Cr(bipy)(dipic)H2O]∙2H2O and [Cr(dipic)2]Hdmbipy∙2.5H2O complexes have been studied towards their catalytic activity, after the activation by MMAO (modified methylaluminoxane), in the case of 2-chloro-2-propen-1-ol polymerization at 21 °C and atmospheric pressure. It has been found that novel catalysts, [Cr(dipic)2][Cr(bipy)(dipic)H2O]∙2H2O and [Cr(dipic)2]Hdmbipy∙2.5 H2O, exhibit a very high catalytic activity in the process of the polymerization of the beta-olefin derivatives. The products of a such catalyzed polymerization are the poly(allyl alcohol) derivatives.

Bis(imino)pyridines Incorporating Doubly Fused Eight-Membered Rings as Conformationally Flexible Supports for Cobalt Ethylene Polymerization Catalysts

Five distinct α,α′-bis(arylimino)-2,3:5,6-bis(hexamethylene)pyridine-cobalt(II) chloride complexes, [2,3:5,6-{C5H10C(NAr)}2C5HN]CoCl2 (Ar = 2,6-Me2C6H3, Co1; 2,6-Et2C6H3, Co2; 2,6-i-Pr2C6H3, Co3; 2,4,6-Me3C6H2, Co4; 2,6-Et2-4-MeC6H2, Co5), have been synthesized by one-pot template reaction of α,α′-dioxo-2,3:5,6-bis(hexamethylene)pyridine with the corresponding aniline and cobalt(II) chloride in acetic acid. The molecular structures of Co2 and Co3 reveal distorted square pyramidal geometries with two conformationally flexible eight-membered rings, a feature of the ligand manifold. On activation with either methylaluminoxane (MAO) or modified MAO (MMAO), all five complexes displayed high catalytic activities for ethylene polymerization (up to 3.62 × 106 g PE mol–1 (Co) h–1) generating strictly linear polyethylenes with the activity decreasing in the orders: Co4 > Co5 > Co1 > Co2 > Co3 (MAO) and Co1 > Co4 > Co2 > Co5 > Co3 (MMAO). Moreover, the nature of the aluminoxane cocatalyst employed had a marked effec...

Synthesis and self-assembly of a novel amphiphilic diblock copolymer consisting of isotactic polystyrene and 1,4-trans-polybutadiene-graft-poly(ethylene oxide).

Herein, a novel amphiphilic diblock copolymer consisting of isotactic polystyrene (iPS) and 1,4-trans-polybutadiene-graft-poly(ethylene oxide) (1,4-trans-PBD-g-PEO), iPS-b-(1,4-trans-PBD-g-PEO), was synthesized by the combination of living coordination copolymerization and graft copolymerization. iPS-b-1,4-trans-PBD was firstly synthesized via sequential monomer addition in the presence of 1,4-dithiabutandiyl-2,2′-bis(6-cumenyl-4-methylphenoxy) titanium dichloride (complex 1) activated by triisobutyl aluminum modified methylaluminoxane (MMAO). Moreover, hydroboration of double bonds in the 1,4-trans-PBD blocks were performed with 9-borabicyclo[3.3.1]nonane (9-BBN) and subsequent oxidation by NaOH/H2O2 to form hydroxyls. Consequently, PEO was grafted into the hydroxylated 1,4-trans-PBD block in terms of ring-opening polymerization of ethylene oxide with potassium/naphthalide as initiatior. We also described solvent-evaporation-induced self-assembly of iPS-b-1,4-trans-PBD in n-dodecane and iPS-b-1,4-trans-PBD-g-PEO in aqueous solution, which were selective solvent for 1,4-trans-PBD and for 1,4-trans-PBD-g-PEO blocks, respectively. In these cases, tetrahydrofuran (THF) was used as good and volatile solvent. These resultant iPS-containing diblock copolymers could self-assemble into spherical nano-micelles with an iPS core as amorphous agglomeration or a very low degree of crystallinity resulting from slow crystallization rate and nanoconfinement. In addition, after isothermal crystallization of iPS in the micellar cores self-assembled in n-dodecane at 120 °C for 3 hours, the micellar morphology changed from sphere-like to platelet-like. It was believed that isothermal crystallization of iPS induced the deformation of the micelles.

A novel tridentate [ONS] binuclear titanium complex bearing oxo-bridged macrocyclic structure for ethylene polymerization

A novel xanthene-bridged bissalicylaldiminato tridentate [ONS] ligand ligated binuclear titanium complex Ti2L bearing oxo-bridged macrocyclic structure were synthesized and characterized by 1H NMR, IR and elemental analysis. This binuclear complex Ti2L was also investigated by single-crystal X-ray diffraction, which demonstrated C2 symmetric structure with each titanium coordinated with six atoms and formed a distorted octahedral configuration. The two titanium centers were also bridged by an oxygen atom to form a relatively stable macrocyclic structure. The binuclear complex exhibited excellent activity up to 1.99 × 106 g/molTi·h for ethylene polymerization upon activation with modified methylaluminoxane (MMAO), producing high molecular weight polyethylene with bimodal distribution. The reaction conditions, such as ethylene pressure, Al/Ti molar ratios and reaction temperatures, were found to have great influence on catalytic activity and polymer properties. Compared with the corresponding mononuclear analogue TiL′, Ti2L showed similar catalytic activity towards ethylene polymerization but produced polymer with lower molecular weight and much wider polydispersities (6.74–20.88), suggesting that two different active centers were present in this binuclear complex.

Polymerizations of methyl methacrylate and rac-lactide by 4-coordinate cobalt(II) complexes supported by N′-substituted N,N′,N-bis((1H-pyrazol-1-yl)methyl)amine derivatives

The novel complexes [LnCoCl2] (Ln = LA − LH), containing the N,N-chelating ligands N,N-bis((1H-pyrazol-1-yl)methyl)aniline (LA), N,N-bis((3,5-dimethyl-1H-pyrazol-1-yl)-3,5-dimethylaniline (LB), N,N-bis((1H-pyrazol-1-yl)methyl)-3,5-dimethylaniline (LC), N,N-bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-3,5-dimethylaniline (LD), N,N-bis((1H-pyrazol-1-yl)methyl)-4-methoxyaniline (LE), N,N-bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-4-methoxyaniline (LF), N,N-bis((1H-pyrazol-1-yl)methyl)-4-fluoroaniline (LG) and N,N-bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-4-fluoroaniline (LH), have been synthesized and structurally characterized. The molecular structures of these Co(II) complexes showed a distorted tetrahedral geometry. No interaction exists between the Namine atom and the Co(II) centre in the [LnCoCl2] complexes, thus resulting in the formation of an eight membered chelate ring. [LDCoCl2] exhibited the highest catalytic activity (4.02 × 104 g PMMA/molCo h) for the polymerization of methyl methacrylate (MMA) in the presence of modified methylaluminoxane (MMAO) at 60 °C and yielded poly(methylmethacrylate) (PMMA) with high molecular weight (Mw) (10.5 × 105 g/mol). Syndiotactic enriched PMMA was obtained with Tg in range 123–130 °C. The MMA polymerization activity of the complexes in the current study should not be solely considered as a function of the total steric hindrance from the ligands around the metal center. The dimethyl derivatives [LnCoMe2] (Ln = LA − LH), generated in situ, effectively polymerized rac-lactide (rac-LA) and yielded polylactide (PLA) with good number-average molecular weights and narrower polydispersity indices (PDIs). The electronic density around the metal center in these dimethyl cobalt initiators seemed to enhance the activity, while the stereoselectivity is negatively affected. Thus, the presence or absence of a methyl group in the pyrazole ring moiety influences not only the activity of the Co(II) complexes in the MMA polymerization, but also the stereoselectivity of the Co(II) initiators in the ROP of rac-LA.

Polymerizations of methyl methacrylate and rac-lactide by zinc(II) precatalyst containing N-substituted 2-iminomethylpyridine and 2-iminomethylquinoline

The reaction of [ZnCl2] with N-cyclopentyl-1-(quinolin-2-yl)methanimine (LA), N-cyclohexyl-1-(quinolin-2-yl)methanimine (LB), N-cyclohexyl-1-(pyridin-2-yl)methanimine (LC), 2,6-diethyl-N-(pyridin-2-ylmethylene)aniline (LD), N-cyclopentyl-1-(pyridin-2-yl)methanimine (LE), and N-phenyl-(pyridin-2-yl)methanimine (LF) in ethanol produced the bidentate [(NN′)ZnCl2] complexes, [LAZnCl2], [LBZnCl2], [LCZnCl2], [LDZnCl2], [LEZnCl2] and [LFZnCl2], respectively. The molecular structures revealed that the zinc in [LnZnCl2] (Ln = LA − LD) showed a distorted tetrahedral geometry involving two nitrogens of N,N’-bidentate ligands and two chloride ligands. Most of these initiators were effective for polymerization of methyl methacrylate (MMA) and polymerization of rac-lactide (rac-LA). [LCZnCl2] (with N-cyclohexyl substituted at imine-pyridine moiety) exhibited the highest catalytic activity for MMA polymerization in the presence of modified methylaluminoxane (MMAO) with an activity of 3.33 × 104 g PMMA/mol·Zn·h at 60 °C, giving moderate syndiotactic poly methyl methacrylate (PMMA) with high molecular weight (9.62 × 105 g/mol). The dimethyl derivatives [LnZnMe2] (Ln = LA − LF), generated in situ, polymerized rac-LA with moderate activity and yielded a polylactide (PLA) with good number-average molecular weights and narrower polydispersity indices (PDIs). [LAZnMe2] effectively initiates the ring-opening polymerization (ROP) of rac-LA to attain heterotactic PLA (Pr = 0.91).

Ligand steric effects on naphthyl-α-diimine nickel catalyzed α-olefin polymerization

Naphthyl-a-diimine nickel complexes with systematically varied ligand sterics, activated by modified methylaluminoxane (MMAO), were tested in the polymerization of higher a-olefin (1-hexene, 1-decene and 1-hexadecene) under suitable conditions. The polymerization results indicated the possibility of precise microstructure control, depending on catalyst structure, polymerization temperature, monomer concentration and types of monomers, which in turn strongly affects the resultant polymer properties. Naphthyl-a-diimine nickel complex bearing chiral bulky sec-phenethyl groups in the o-naphthyl position showed good catalytic activity, and resulted in branched polymers (42-88/1000C) with high molecular weights (Mn: (4.3-15.2) × 104 g·mol-1) and narrow molecular weight distribution (Mw/Mn = 1.13-1.29, RT), which suggested a living polymerization. The increasing steric hindrance of catalyst leads to enhance insertion for 2,1-insertion of a-olefin and the chain-walking reaction.

Living polymerization of higher 2-alkene with α-diimine nickel catalysts: Synthesis and characterization of high molecular weight poly(2-alkene)s

A series of higher 2-alkenes, i.e., 2-pentene, 2-hexene and 2-octene were polymerized with phenyl substituted α-diimine nickel complexes in combination with modified methylaluminoxane (MMAO) to produce branched poly(2-alkene)s with high molecular weight and narrow molecular weight distribution (Mw/Mn < 1.8). At 0 °C, these 2-alkenes polymerized in a living manner to produce amorphous polymers with glass transition temperature of –70 ∼ –65 °C. The microstructures of the produced polymers indicated the 2,3- and 3,2-insertion followed by chain-walking and the incorporation of a small amount of 1-alkene formed by isomerization. The branch structures were significantly depended on the polymerization temperature, and the ratio of methyl branch predominantly derived from 3,2-insertion was increased with increasing the polymerization temperature.

Synthesis of isotactic polystyrene-block-polyethylene by the combination of sequential monomer addition and hydrogenation of 1,4-trans-polybutadiene block

Herein, we demonstrate the synthesis of a well-defined diblock copolymer consisting of isotactic polystyrene (iPS) and linear polyethylene, isotactic polystyrene-block-polyethylene (iPS-b-PE), by the combination of sequential monomer addition and hydrogenation. Isospecific living polymerization of styrene and living trans-1,4-polymerization of 1,3-butadiene were catalyzed by 1,4-dithiabutandiyl-2,2′-bis(6-cumenyl-4-methylphenoxy) titanium dichloride (complex 1) activated by triisobutyl aluminum modified methylaluminoxane (MMAO) at room temperature to provide highly isotactic polystyrene (iPS) and 1,4-trans-polybutadiene (1,4-trans-PBD) with narrow molecular weight distribution. Furthermore, the iPS-b-1,4-trans-PBD was synthesized via sequential monomer addition in the presence of complex 1 and MMAO. The hydrogenation of the 1,4-trans-PBD block was promoted by RuCl2(PPh3)3 used as a catalyst to produce iPS-b-PE.

N-(2,2-Dimethyl-1-(quinolin-2-yl)propylidene) arylaminonickel Complexes and Their Ethylene Oligomerization.

A series of N-(2,2-dimethyl-1-(quinolin-2-yl)propylidene) arylamines was sophisticatedly synthesized and reacted with nickel(II) bromine for the formation of the corresponding nickel complexes. All the organic compounds were characterized by IR, NMR spectra and elemental analysis, while all the nickel complexes were characterized by IR spectra and elemental analysis. On activation with ethylaluminium sesquichloride (EASC) and modified methylaluminoxane (MMAO), all nickel precatalysts exhibited good activities toward ethylene oligomerization, indicating the positive efficiency of gem-dimethyl substitutents; in which major hexenes were obtained with MMAO. The catalytic parameters were verified, and the steric and electronic influences of substituents with ligands were observed, with a slight change of activities under different ethylene pressures.