Ethylene polymerization by sterically and electronically modulated Ni(II) α‐diimine complexes

A series of highly active ethylene polymerization catalysts based on bidendate α‐diimine ligands coordinated to nickel are reported. The ligands are prepared via the condensation of bulky ortho‐substituted anilines bearing remote push–pull substituents with acenaphthenequinone, and the precatalysts are prepared via coordination of these ligands to (DME)NiBr₂ (DME = 1,2‐dimethoxyethane) to form complexes having general formula [ZN = C(An)‐C(An) = NZ]NiBr₂ [Z = (4‐NH₂‐3,5‐C₆H₂R₂)₂CH(4‐C₆H₄Y); An, acenaphthene quinone; R, Me, Et, iPr; Y = H, NO₂, OCH₃]. When activated with methylaluminoxane (MAO) or common alkyl aluminiums such as ethyl aluminium sesquichloride (EAS) all catalysts polymerize ethylene with activities exceeding 10⁷ g‐PE/ mol‐Ni h atm at 30 °C and atmospheric pressure. Among the cocatalysts used EAS records the best activity. Effects of remote substituents on ethylene polymerization activity are also investigated. The change in potential of metal center induced by remote substituents, as evidenced by cyclic voltammetric measurements, influences the polymerization activity. UV–visible spectroscopic data have specified the important role of cocatalyst in the stabilization of nickel‐based active species. A tentative interpretation based on the formation of active and dormant species has been discussed. The resulting polyethylene was characterized by high molecular weight and relatively broad molecular weight distribution, and their microstructure varied with the structure of catalyst and cocatalyst. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1066–1082, 2008     

Polymerization of 1,3‐dienes and styrene catalyzed by cationic allyl Ni(II) complexes

Polymerizations of 1,3‐dienes using in situ generated catalyst [(2‐methallyl)Ni][B(Ar_F)₄], 6 , (Ar_F = 3,5‐bis(trifluoromethyl)phenyl) as well as [(2‐methallyl)Ni(mes)][B(Ar_F)₄], 14 , (mes = mesitylene) are reported. Highly sensitive complex 6 polymerizes butadiene (BD) at –30 °C to yield polybutadiene with a M_n of ca. 10 K and 94% cis‐1,4‐enchainment while less reactive isoprene (IP) was polymerized at 23 °C to yield polyisoprene with M_n ca. 7 K. Complex 6 was also shown to polymerize a functionalized diene, 2,3‐bis(4‐trifluoroethoxy‐4‐oxobutyl)‐1,3‐BD, to polymer with M_n = 113 K. The stable and readily isolated arene complex 14 initiates BD and IP polymerizations at somewhat higher temperatures relative to 6 and delivers polymers with higher molecular weights. Complex [(allyl)Ni(mes)][B(Ar_F)₄], 13 , catalyzes polymerization of styrene to yield polystyrene with high conversion, M_n's = ca. 6 K and MWD = 2. The π‐benzyl complex [(η³‐1‐methylbenzyl)Ni(mes)] [B(Ar_F)₄], 19 , was detected as an intermediate following chain transfer by in situ NMR studies. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1901–1912, 2010     

Addition polymerization of norbornene using bis(β‐ketoamino)nickel(II)/tris(pentafluorophenyl)borane catalytic systems

Norbornene polymerizations proceeded in toluene with bis(β‐ketoamino)nickel(II) {Ni[CH₃C(O)CHC(NR)CH₃]₂ [R = phenyl ( 1 ) or naphthyl ( 2 )]} complexes as the catalyst precursors and the organo‐Lewis compound tris(pentafluorophenyl)borane [B(C₆F₅)₃] as a unique cocatalyst. The polymerization conditions, such as the cocatalyst/catalyst ratio (B/Ni), catalyst concentration, monomer/catalyst ratio (norbornene/Ni), polymerization temperature, and polymerization time, were studied in detail. Both bis(β‐ketoamino)nickel(II)/B(C₆F₅)₃ catalytic systems showed noticeably high conversions and activities. The polymerization activities were up to 3.64 × 10⁷ g of polymer/mol of Ni h for complex 1 /(B(C₆F₅)₃ and 3.80 × 10⁷ g of polymer/mol of Ni h for complex 2 /B(C₆F₅)₃, and very high conversions of 90–95% were maintained; both polymerizations provided high‐molecular‐weight polynorbornenes with molecular weight distributions (weight‐average molecular weight/number‐average molecular weight) of 2.5–3.0. The achieved polynorbornenes were confirmed to be vinyl‐addition and atactic polymers through the analysis of Fourier transform infrared, ¹H NMR, and ¹³C NMR spectra, and the thermogravimetric analysis results showed that the polynorbornenes exhibited good thermal stability (decomposition temperature > 410 °C). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4733–4743, 2007     

Copolymerization of norbornene and 5‐norbornene‐2‐yl acetate using novel bis(β‐ketonaphthylamino)Ni(II)/B(C6F5)3/AlEt3 catalytic system

Vinyl‐type copolymerization of norbornene (NBE) and 5‐NBE‐2‐yl‐acetate (NBE‐OCOMe) in toluene were investigated using a novel homogeneous catalyst system based on bis(β‐ketonaphthylamino)Ni(II)/B(C₆F₅)₃/AlEt₃. The copolymerization behavior as well as the copolymerization conditions, such as the levels of B(C₆F₅)₃ and AlEt₃, temperature, and monomer feed ratios, which influence on the copolymerization were examined. Without combination of AlEt₃, the catalytic bis(β‐ketonaphthylamino)Ni(II)/B(C₆F₅)₃ exhibited very high catalyst activity for polymerization of NBE. Combination of AlEt₃ in catalyst system resulted in low conversion for polymerization of NBE. For copolymerization of NBE and NBE‐OCOMe, involvement of AlEt₃ in catalyst is necessary. Slight addition of NBE‐OCOMe in copolymerization of NBE and NBE‐OCOMe gives rise to significant increase of catalyst activity for catalytic system bis(β‐ketonaphthylamino)Ni(II)/B(C₆F₅)₃/AlEt₃. Nevertheless, excess increase of the NBE‐OCOMe content in the comonomer feed ratios results in decrease of conversion as well as activity of catalyst. The achieved copolymers were confirmed to be vinyl‐addition copolymers through the analysis of FTIR, ¹H NMR, and ¹³C NMR spectra. ¹³C NMR studies further revealed the composition of the copolymer and the incorporation rate was 7.6–54.1 mol % ester units at a content of 30–90 mol % of the NBE‐OCOMe in the monomer feeds ratios. TGA analysis results showed that the copolymer exhibited good thermal stability (T_d > 410 °C) and failed to observe the glass transitions temperature over 300 °C. The copolymers are confirmed to be noncrystalline by WAXD analysis results and show good solubility in common organic solvents. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3990–4000, 2009     

Nonconjugated diene homopolymerization and copolymerization with ethylene catalyzed by α‐diimine Ni(II) complex/Et2AlCl

Four nonconjugated diene comonomers 1,9‐decadiene (19DD), 6‐ethylundeca‐1,10‐diene (EUD), 1,5‐cyclooctadiene (COD) and cinene (1‐methyl‐4‐(prop‐1‐en‐2‐yl) cyclohex‐1‐ene) (CE) were used in copolymerization with ethylene catalyzed by α‐diimine Ni(II) complex ([2,6‐(iPr)₂C₆H₃N = C(CH₃)?(CH₃)C = N2,6‐(iPr)₂C₆H₃)]NiBr₂ ( 1 )) activated by Et₂AlCl. These dienes showed quite distinct copolymerization behaviors. Ethylene‐19DD copolymerization formed highly branched polyethylene with cyclic units and pendent vinyls, and a large part of crosslinked polymer when the 19DD concentration was relatively high. Using EUD as comonomer lead to evidently reduced gel formation and increased content of pendent vinyl. COD can be incorporated in the copolymer with evidently lower catalyst efficiency than the ethylene homopolymerization, and CE behaves like an inert compound as it was not incorporated in the copolymer. Homopolymerization of 19DD with the same catalyst produced polymer containing both cyclic units and pendent vinyls. The cyclic units were formed by cyclopolymerization of the inserted 19DD after several steps of chain walking. Crosslinking through the pendent vinyl took place when the initial 19DD concentration was relatively high, forming large amount of gel in the product. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 1900–1909     

Molecular structure determination of Ni(II) diimine complex and DMA analysis of Ni(II) diimine‐based polyethenes

Dynamic mechanical thermoanalysis showed that polyethene, prepared under suitable polymerization conditions with the Brookhart‐type catalyst dibromo‐N,N′‐1,2‐acenaphthylenediylidenebis[2,6‐bis(1‐methylethyl)benzeneamine]Ni(II)/methylaluminoxane (MAO), behaved like an elastomer, even though no comonomer was added. A structural characterization showed that the polymers contained methyl to hexyl branches and some longer branches. The effect of the polymerization conditions on branching was investigated through variations in the pressure and temperature of the polymerization. Depending on the degree and type of branching, polyethene was either quite amorphous or highly crystalline with a high melting temperature. The solid‐state structure of the catalyst dibromo‐N,N′‐1,2‐acenaphthylenediylidenebis[2,6‐bis(1‐methylethyl)benzeneamine]Ni(II) consisted of two centrosymmetrically related monomeric moieties, where Ni atoms were bridged by two bromide ligands. The Ni atom was five‐coordinated, with a square pyramidal coordination polyhedron. The sixth coordination site of the octahedral geometry was effectively blocked by the isopropyl groups of the 2,6‐C₆H₃(i‐Pr) substituents of the diimine ligand. In solution in the presence of MAO, the longer bridging Ni? Br bonds broke, and the complex dissociated to a monomeric species. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1426–1434, 2001     

Ni(II) and Pd(II) complexes bearing benzocyclohexane–ketoarylimine for copolymerization of norbornene with 5‐norbornene‐2‐carboxylic ester

A serial of late transition metal complexes, which bearing Benzocyclohexane–ketoarylimine ligand and named as Mt(benzocyclohexane–ketoarylimino)₂ {Mt(bchkai)₂: Mt=Ni or Pd; bchkai=C₁₀H₈(O)CN(Ar)CH₃; Ar=naphthyl or fluoryl}, have been synthesized and characterized. The molecular structures of the ligands and nickel complex have been confirmed by X‐ray single‐crystal analyses. The nickel complexes exhibited very high activity up to 2.7 × 10⁵ g_polymer/mol_Ni·h and palladium complexes showed high activity up to 2.3 × 10⁵ g_polymer/mol_Pd·h for norbornene (NB) homo‐polymerization with tris(pentafluorophenyl)borane as cocatalyst. The four complexes were effective for copolymerization of NB and 5‐norbornene‐2‐carboxylic acid methyl ester (NB‐COOCH₃) in relatively high activities (0.1–2.4 × 10⁵ g_polymer/mol_Mt·h) and produced the addition‐type copolymers with relatively high molecular weights (0.5 × 10⁵–1.2 × 10⁵ g/mol) as well as narrow molecular weight distributions (PDI < 2 for all polymers). Influences of the metals and comonomer feed content on the polymerization activity as well as on the incorporation rates (20.9–42.6%) were investigated. The achieved NB/NB‐COOCH₃ copolymers were confirmed to be noncrystalline, exhibited good thermal stability (T_d > 400°C) and showed good solubility in common organic solvents. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis of long‐chain‐branched polyethylene by ethylene homopolymerization with a novel nickel(II) α‐diimine catalyst

Long‐chain‐branched polyethylene with a broad or bimodal molecular weight distribution was synthesized by ethylene homopolymerization via a novel nickel(II) α‐diimine complex of 2,3‐bis(2‐phenylphenyl)butane diimine nickel dibromide ({[2‐C₆H₄(C₆H₅)]? N?C? (CH₃)C(CH₃)?N? [2‐C₆H₄(C₆H₅)]}NiBr₂) that possessed two stereoisomers in the presence of modified methylaluminoxane. The influences of the polymerization conditions, including the temperature and Al/Ni molar ratio, on the catalytic activity, molecular weight and molecular weight distribution, degree of branching, and branch length of polyethylene, were investigated. The resultant products were confirmed by gel permeation chromatography, gas chromatography/mass spectrometry, and ¹³C NMR characterization to be composed of higher molecular weight polyethylene with only isolated long‐branched chains (longer than six carbons) or with methyl pendant groups and oligomers of linear α‐olefins. The long‐chain‐branched polyethylene was formed mainly through the copolymerization of ethylene growing chains and macromonomers of α‐olefins. The presence of methyl pendant groups in the polyethylene main chain implied a 2,1‐insertion of the macromonomers into [Ni]? H active species. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1325–1330, 2005     

Cyclometalated 2‐phenylpyridine complex [RuII(o‐C6H4‐py)(MeCN)4]PF6 as a tunable catalyst for living radical polymerization

The cyclometalated complex [Ru^II(o‐C₆H₄‐py)(MeCN)₄]PF₆ ( 1 ) with a σ‐Ru? C bond and four substitutionally labile acetonitrile ligands mediates radical polymerization of different vinyl monomers, viz. n‐butyl acrylate, methyl methacrylate, and styrene, initiated by three alkyl bromides: ethyl 2‐bromoisobutyrate, methyl 2‐bromopropionate, and 1‐phenylethyl bromide. The polymerization requires the presence of Al(OiPr)₃ and occurs uncontrollably as a conventional radical process. The variation of the molar ratio of the components of the reaction mixture, such as initiator, Al(OiPr)₃ and catalyst, affected the polymerization rates and the molecular weights but did not improve the control. A certain level of control has been achieved by adding 0.5 eq of SnCl₂ as a reducing agent. Tin(II) chloride decreased the rate of polymerization and simultaneously the molecular weights became conversion‐dependent and the polydispersities were also narrowed. Remarkably, the level of control was radically improved in the presence of excess of the poorly soluble catalyst ( 1 ), when the added amount of ( 1 ) was not soluble any more, i.e., under heterogeneous conditions, the system became adjustable and the living polymerization of all three monomers was finally achieved. Possible mechanisms of the ( 1 )‐catalyzed polymerization are discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4193–4204, 2008     

Poly(1‐hexene) with long methylene sequences and controlled branches obtained by a thermostable α‐diimine nickel catalyst with bulky camphyl backbone

1‐Hexene polymerizations catalyzed by α‐diimine nickel complexes after activation with modified methylaluminoxane were performed at various reaction temperatures. Effects of catalyst structure and polymerization temperature on activity and polymer microstructure were evaluated in detail. Bulky catalyst 1b with camphyl backbone exhibited good control ability and greatly enhanced thermal stability to be capable of polymerizing 1‐hexene at 80°C. The poly(1‐hexene)s with long methylene sequences and dominate branches (methyl and butyl) were synthesized using catalyst 1b . Differential scanning calorimetry analysis further confirmed that long polymethylene block (? (CH₂)_n? , n > 20) was formed in the poly(1‐hexene)s with melting point of 64°C obtained by catalyst 1b on the basis of initial branched model polyethylene. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Efficient ethylene/norbornene copolymerization by half‐titanocenes containing imidazolin‐2‐iminato ligands and MAO catalyst systems

Ethylene copolymerizations with norbornene (NBE) using half‐titanocenes containing imidazolin‐2‐iminato ligands, Cp′TiCl₂[1,3‐R₂(CHN)₂C?N] [Cp′ = Cp ( 1 ), ^tBuC₅H₄ ( 2 ); R = ^tBu ( a ), 2,6‐ⁱPr₂C₆H₃ ( b )], have been explored in the presence of methylaluminoxane (MAO) cocatalyst. Complex 1a exhibited remarkable catalytic activity with better NBE incorporation, affording high‐molecular‐weight copolymers with uniform molecular weight distributions, whereas the tert‐BuC₅H₄ analog ( 2a ) showed low activity, and the resultant polymer prepared by the Cp‐2,6‐diisopropylphenyl analog ( 1b ) possessed broad molecular weight distribution. The microstructure analysis of the poly(ethylene‐co‐NBE)s prepared by 1a suggests the formation of random copolymers including two and three NBE repeating units. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2575–2580     

New chiral α‐diimine nickel(II) complexes bearing ortho‐sec‐phenethyl groups for ethylene polymerization

A series of new α‐diimine nickel(II) catalysts bearing bulky chiral sec‐phenethyl groups have been synthesized and characterized. The molecular structure of representative chiral ligand, bis[N,N′‐(4‐methyl‐2,6‐di‐sec‐phenethylphenyl)imino]‐1,2‐dimethylethane rac‐1c and chiral complexes, {bis[N,N′‐(4‐methyl‐2‐sec‐phenethylphenyl)imino]‐2,3‐butadiene}dibromidonickel rac‐2a and bis{bis[N,N′‐(4‐methyl‐2‐sec‐phenethylphenyl)imino]‐2,3‐butadiene}dibromidonickel rac‐2b, were confirmed by X‐ray crystallographic analysis. Complex rac‐2c bearing two chiral sec‐phenethyl groups in the ortho‐aryl position and a methyl group in the para‐aryl position, activated by diethylaluminum chloride (DEAC), showed highly catalytic activity for the polymerization of ethylene [4.12 × 10⁶ g PE (mol Ni.h.bar)^?1], and produced highly branched polyethylenes under low ethylene pressure (branching degree: 104, 118 and 126 branches/1000 C at 20, 40 and 60°C, respectively). Chiral 20‐electron bis‐α‐diimine Ni(II) complex rac‐2b also exhibited high activity toward ethylene polymerization [1.71 × 10⁶ g PE (mol Ni · h · bar)^?1]. The type and amount of branches of the polyethylenes obtained were determined by ¹H and ¹³C NMR. Copyright © 2013 John Wiley & Sons, Ltd.     

Highly symmetric single nickel catalysts bearing bulky bis(α‐diimine) ligand: Synthesis,characterization, and electron‐effects on copolymerization of norbornene with 1‐alkene at elevated temperarure

Three new three‐dimensional geometry bulky α‐diimine ligands ( L ) containing electron‐donating and electron‐withdrawing groups, 9,10‐dihydro‐9,10‐ethanoanthracene‐11,12‐di(Ar)imine (Ar = p‐PhCH₃, L1 ; Ar=p‐PhCl, L2 ; Ar=p‐PhCF₃, L3 .), and their corresponding single Ni(II) catalysts, NiL₂Br₂ ( Ni(L1)₂Br₂ , Ni(L2)₂Br₂ , and Ni(L3)₂Br₂ , were synthesized and the molecular structure were determined by X‐ray crystallography. All NiL₂Br₂ catalysts were tested for norbornene polymerization and copolymerization of norbornene with 1‐alkene after activation with B(C₆F₅)₃. The results that the polymerization catalytic activities for norbornene up to 10⁵ g_polymer/mol_Ni·h even at 140 °C, shown that NiL₂Br₂ catalysts have high thermal stability. Meanwhile, catalysts with electron‐withdrawing groups could achieve higher reactivity. The obtained poly(NB‐co‐1‐alkene)s were confirmed to be vinyl‐addition copolymers and noncrystalline. All copolymers exhibited high 1‐alkenes insertion ratio, good thermal stability (T_d > 375 °C), high molecular weight (up to 10⁵ g/mol), good solubility in common organic solvents and could be processed into films with good transparency in the visible region. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3495–3505     

Homo‐ and copolymerization of norbornene and 5‐norbornene‐2‐yl acetate with bis‐(β‐ketonaphthylamino)palladium(II)/B(C6F5)3 catalytic system

The polymerization of norbornene with bis(β‐ketonaphthylamino) palladium(II), Pd{CH₃C(O)CHC[N(naphthyl)]CH₃}₂, in combination with tris(pentafluorophenyl)borane (B(C₆F₅)₃), was investigated by varying the B:Pd(II) molar ratio, monomer concentration, reaction temperature, and time. The catalytic activity was found to reach 2.8 × 10⁴ gPolymer/(molPd^?h) and the obtained polynorbornene (PNBE) was confirmed to be vinyl addition polymer and showed good thermo‐stability (T_dec > 350°C), but exhibited poor solubility in organic solvents due to the relative higher stereo regularity. Pd{CH₃C(O)CHC[N(naphthyl)]CH₃}₂/B(C₆F₅)₃ system is also an active catalyst for copolymerization of norbornene and 5‐norbornene‐2‐yl acetate (NBE‐OCOCH₃) in toluene with moderate yields (in 9.2–36.5% yields) and produces the addition‐type copolymer with relatively high molecular weights (0.96 × 10⁴–2.13 × 10⁴ g/mol). The incorporation of functional group in the copolymer can be controlled up to 0.9–23.5 mol% by varying the NBE‐OCOCH₃ monomer feed ratios from 10 to 90%. The copolymers are proved to be noncrystalline and show good solubility in common organic solvents and excellent thermal stability up to 350°C. Copyright © 2011 John Wiley & Sons, Ltd.     

Vinyl polymerization of norbornene by bis(nitro‐substituted‐salicylaldiminate)nickel(II)/methylaluminoxane catalysts

The polymerization of norbornene has been investigated in the presence of different bis(salicylaldiminate)nickel(II) precursors activated by methylaluminoxane. These systems are highly active in affording nonstereoregular vinyl‐type polynorbornenes (PNBs) with high molecular weights. The productivity of the catalytic systems is strongly enhanced (up to 35,000 kg of PNB/mol of Ni × h) when electron‐withdrawing nitro groups are introduced on the phenol moiety. On the contrary, the presence of bulky alkyl groups on the N‐aryl moiety of the ligand does not substantially affect the activity or characteristics of the resulting PNBs. The catalytic performances are also markedly influenced by the reaction parameters, such as the nature of the solvent, the reaction time, and the monomer/Ni and Al/Ni molar ratios. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1514–1521, 2006     

Ethylene/α‐olefin copolymerization with bis(β‐enaminoketonato) titanium complexes activated with modified methylaluminoxane

Copolymerizations of ethylene with α‐olefins (i.e., 1‐hexene, 1‐octene, allylbenzene, and 4‐phenyl‐1‐butene) using the bis(β‐enaminoketonato) titanium complexes [(Ph)NC(R₂)CHC(R₁)O]₂TiCl₂ ( 1a : R₁ = CF₃, R₂ = CH₃; 1b : R₁ = Ph, R₂ = CF₃; and 1c : R₁ = t‐Bu, R₂ = CF₃), activated with modified methylaluminoxane as a cocatalyst, have been investigated. The catalyst activity, comonomer incorporation, and molecular weight, and molecular weight distribution of the polymers produced can be controlled over a wide range by the variation of the catalyst structure, α‐olefin, and reaction parameters such as the comonomer feed concentration. The substituents R₁ and R₂ of the ligands affect considerably both the catalyst activity and comonomer incorporation. Precatalyst 1a exhibits high catalytic activity and produces high‐molecular‐weight copolymers with high α‐olefin insertion. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6323–6330, 2005     

Titanium complexes based on aminodiol ligands for the ring‐opening polymerization of ε‐caprolactone,rac‐β‐butyrolactone,and trimethylene carbonate

Several titanium complexes based on aminodiol ligands were tested as initiators for the ring‐opening polymerization (ROP) of ε‐caprolactone under solution and bulk conditions. All complexes were found to be efficient under both conditions. For bulk polymerization at 70 °C, high activities were observed (113.3–156.2 g_poly mmol_cat^?1 h^?1) together with controlled molar mass distribution. Kinetic studies revealed controlled polymerization, and the chain propagation was first order with respect to monomer conversion. One complex was also tested for the ROP of rac‐β‐butyrolactone and the end‐group analysis suggested that ring opening occurs through acyl‐oxygen bond cleavage via coordination–insertion mechanism. The microstructure analysis of polymer by ¹³C NMR indicates atactic polymer. Another complex was also found to be efficient initiator for the ROP of trimethylene carbonate under solution and bulk conditions. Again, end‐group analysis suggests coordination–insertion mechanism. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Functional syndiotactic poly(β‐hydroxyalkanoate)s via stereoselective ring‐opening copolymerization of rac‐β‐butyrolactone and rac‐allyl‐β‐butyrolactone

The copolymerization of racemic β‐butyrolactone (rac‐BL^Me) with racemic “allyl‐β‐butyrolactone” (rac‐BL^allyl) in toluene, catalyzed by the discrete amino‐alkoxy‐bis(phenolate) yttrium‐amido complex 1 , gave new poly(β‐hydroxyalkanoate)s with unsaturated side chains. The poly(BL^Me‐co‐BL^allyl) copolymers produced have a highly syndiotactic backbone structure (P_r = 0.80–0.84) with a random enchainment of monomer units, as evidenced by ¹³C NMR, and high molecular weight (M_n up to 58,000 g mol^?1) with a narrow polydispersity (M_w/M_n = 1.07–1.37), as determined by GPC. The comonomer incorporation (5–50 mol % rac‐BL^allyl) was a linear function of the feed ratio. The pendant vinyl bond of the side‐chains in those poly(BL^Me‐co‐BL^allyl) copolymers allowed the effective introduction of hydroxy or epoxy groups via dihydroxylation, hydroboration‐oxidation or epoxidation reactions. NMR studies indicated that all of these transformations proceed in an essentially quantitative conversion and do not affect the macromolecular architecture. Some thermal properties (T_m, ΔH_m, T_g) of the prepared polymers have been also evaluated. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3177–3189, 2009     

Synthesis,characterization, and ethylene (Co)polymerization behavior of trichlorotitanium 2‐(1‐(arylimino)propyl)quinolin‐8‐olates

A series of trichlorotitanium complexes containing 2‐(1‐(arylimino)propyl)quinolin‐8‐olates was synthesized by stoichiometric reaction of titanium tetrachloride with the corresponding potassium 2‐(1‐(arylimino)propyl)quinolin‐8‐olates and was fully characterized by elemental analysis, nuclear magnetic resonance spectroscopy, and by single‐crystal X‐ray diffraction study of representative complexes. All titanium complexes, when activated with methylaluminoxane, exhibited high catalytic activity toward ethylene polymerization [up to 1.15 × 10⁶ g mol^?1(Ti) h^?1] and ethylene/α‐olefin copolymerization [up to 1.54 × 10⁶ g mol^?1 (Ti) h^?1]. The incorporation of comonomer was confirmed to amount up to 2.82 mol % of 1‐hexene or 1.94 mol % of 1‐octene, respectively. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and reactivity of allyl nickel(II) N‐heterocyclic carbene enolate complexes

Two new N‐heterocyclic carbene enolate nickel(II) allyl complexes have been prepared and their activity towards ethylene polymerization was investigated. It was found that in the presence of diethyl zinc, the carbene enolate complex bearing a nitro substituent produces highly linear polyethylene of modest molecular weight and high polydispersity. The influence of the reaction parameters on catalytic activity and the characteristics of the resulting polymer were investigated through systematic variation of the time, temperature, and diethyl zinc concentration. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45:3637–3647, 2007