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     

Well‐controlled ring‐opening polymerization of cyclic esters catalyzed by aluminum amido complexes: Kinetics and mechanism

A series of aluminum dimethyl complexes 1 – 6 bearing N‐[2‐(pyrrolidinyl)benzyl]anilido ligands were synthesized and well characterized. The molecular structure of complex 1 determined by an X‐ray diffraction study indicates the bidentate chelating mode of the pyrrolidinyl‐anilido ligand. In the absence of a coinitiator, these complexes exhibited excellent control toward the polymerizations of ε‐caprolactone and rac‐lactide, affording polyesters with quite narrow molecular weight distributions (M_w/M_n = 1.04–1.26). The end group analysis of ε?CL oligomer via ¹H NMR and ESI‐TOF MS methods gave strong support to the hypothesis that the polymerization catalyzed by these aluminum complexes proceeds via a coordination‐insertion mechanism involving a unique Al? N (amido) bond initiation. Via ¹H NMR scale oligomerization studies, it is suggested that the insertion of the first lactide monomer into Al? N bond of the complex is much easier than the insertion of lactide monomer into the newly formed Al? O (lactate) bond and might also be easier than the insertion of the first ε?CL monomer into Al? N bond. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3096–3106     

Highly branched and high‐molecular‐weight polyethylenes produced by 1‐[2,6‐bis(bis(4‐fluorophenyl)methyl)‐4‐MeOC6H2N]‐2‐aryliminoacenaphthylnickel(II) halides

A series of unsymmetrical 1‐[2,6‐bis(bis(4‐fluorophenyl)methyl)‐4‐MeOC₆H₂N]‐2‐aryliminoacenaphthene‐nickel(II) halides has been synthesized and fully characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance (¹H NMR), ¹³C NMR, and ¹⁹F NMR spectroscopy as well as elemental analysis. The structures of Ni1 and Ni6 have been confirmed by the single‐crystal X‐ray diffraction. On activation with cocatalysts either ethylaluminum sesquichloride or methylaluminoxane, all the title nickel complexes display high activities toward ethylene polymerization up to 16.14 × 10⁶ g polyethylene (PE) mol^?1(Ni) h^?1 at 30 °C, affording PEs with both high branches (up to 103 branches/1000 carbons) and molecular weight (1.12 × 10⁶ g mol^?1) as well as narrow molecular weight distribution. High branching content of PE can be confirmed by high temperature ¹³C NMR spectroscopy and differential scanning calorimetry. In addition, the PE exhibited remarkable property of thermoplastic elastomers (TPEs) with high tensile strength (σ_b = 21.7 MPa) and elongation at break (ε_b = 937%) as well as elastic recovery (up to 85%), indicating a better alternative to commercial TPEs. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 130–145     

Synthesis of branched polyethylenes by the tandem catalysis of silica‐supported linked cyclopentadienyl‐amido titanium catalysts and a homogeneous dibromo nickel catalyst having a pyridylimine ligand

The synthesis of branched polyethylenes by ethylene polymerization with new tandem catalyst systems consisting of methylaluminoxane‐preactivated linked cyclopentadienyl‐amido titanium catalysts [Ti(η⁵:η¹‐C₅Me₄SiMe₂NR)Cl₂ (R = Me or ^tBu)] supported on pyridylethylsilane‐modified silica (PySTiNMe and PySTiN^tBu) and homogeneous dibromo nickel catalyst having a pyridyl‐2,6‐diisopropylphenylimine ligand (PyminNiBr₂) in the presence of modified methylaluminoxane was investigated. Ethylene polymerization with only PyminNiBr₂ yielded a mixture of 1‐ and 2‐olefin oligomers with methyl branches [weight‐average molecular weight (M_w) ～ 460)] with a ratio of about 1:7. By the combination of this nickel catalyst with PySTiN^tBu, polyethylenes with long‐chain branches (M_w = 15,000–50,000) were produced. No incorporation of 2‐olefin oligomers was observed in the ¹³C NMR spectra. Unexpectedly, the combination of the nickel catalyst with PySTiNMe produced lower molecular weight polyethylenes with only methyl branches. The molecular weight distributions of branched polyethylenes obtained with both PySTiNMe and PySTiN^tBu combined with the nickel catalyst were broad (weight‐average molecular weight/number‐average molecular weight < 9). Bimodal gel permeation chromatography (GPC) curves were clearly observed in the PySTiNMe system, whereas GPC curves with small shoulders in low molecular weight areas were observed for PySTiN^tBu. The synthesis of branched polyethylenes with tandem catalyst systems of corresponding homogeneous titanium catalysts and the nickel catalyst was also investigated for comparison. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 528–544, 2003     

Stereoselective synthesis and polymerization of Exo‐5‐trimethylsilylnorbornene

Herein the stereoselective two‐step synthesis of pure exo‐5‐trimethylsilylnorbornene is reported. The monomer proved to be highly reactive in both metathesis and addition polymerization. ROMP polymerization was catalyzed by the first‐generation Grubbs catalyst. High‐molecular‐weight saturated addition polymers were prepared using nickel or palladium complexes as precatalysts and Na⁺[B(3,5‐(CF₃)₂C₆H₃)₄]⁻ and/or MAO as cocatalysts. The obtained addition polynorbornenes are highly gas permeable and microporous materials possessing large free volume and BET surface area (up to 540 m²/g). The influence of the substituent orientation (exo‐ vs. exo‐/endo‐mixture) on polymer properties was established. The metathesis polymer based on exo‐isomer exhibits 1.5‐ to 2‐fold increase of permeability coefficients for all gases in comparison to the similar polymer based on the mixture of exo‐ and endo‐isomers. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1234–1248     

Phosphido‐diphosphine pincer aluminum complexes as catalysts for ring opening polymerization of cyclic esters

New aluminum alkyl complexes, supported by o‐phenylene‐derived phosphido diphosphine pro‐ligands [Ph‐PPP]‐H and [ⁱPr‐PPP]‐H ([Ph‐PPP]‐H = bis(2‐diphenylphosphinophenyl)phosphine; [ⁱPr‐PPP]‐H = bis(2‐diisopropylphosphinophenyl)phosphine) are reported. Compounds [Ph‐PPP]AlMe₂ ( 1 ), [ⁱPr‐PPP]AlMe₂ ( 2 ), and [Ph‐PPP]AlⁱBu₂ ( 3 ) have been synthesized by reaction of the pro‐ligand with the appropriate trialkyl aluminum precursor and have been characterized by ¹H, ¹³C and ³¹P NMR spectroscopy. The solution NMR data and theoretical calculations suggest for all complexes trigonal bipyramidal structures with C_2v symmetry in which the phosphido diphosphine ligand acts as a κ³ coordinated ligand. All complexes promote the ring‐opening polymerization of ε‐caprolactone, L‐ and rac‐lactide. Polyesters with controlled molecular parameters (M_n, end groups) and low polydispersities are obtained. Upon addition of isopropanol, efficient binary catalytic systems for the immortal ring‐opening polymerization of the cyclic esters are produced. Preliminary investigations show the ability of these complexes to promote copolymerization of l ‐lactide and ?‐caprolactone to achieve copolymers whose microstructures are depending on the structure of the catalyst. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 49–60     

Vinylic and ring‐opening metathesis polymerization of norbornene with bis(β‐ketoamine) cobalt complexes

Cobalt complexes 1 – 4 bearing N,O‐chelate ligands based on condensation products of 1‐phenyl‐3‐methyl‐4‐benzoyl‐5‐pyrazolone with aniline, o‐methylaniline, α‐naphthylamine, and p‐nitroaniline, respectively, were synthesized, and the structures of 1 and 4 were characterized by single‐crystal X‐ray diffraction analyses. The bis(β‐ketoamine) cobalt complexes could act as moderately active catalyst precursors for norbornene polymerization with the activation of methylaluminoxane. This catalytic reaction proceeded mainly through a vinyl‐type polymerization mechanism. ¹H NMR and IR showed that in all cases, a small amount of double bonds raised from ring‐opening metathesis polymerization (ROMP) was present in the polymerization products. The variation of the polymerization conditions affected the ROMP unit ratio in the polynorbornenes. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5535–5544, 2005     

Vinyl polymerizations of norbornene catalyzed by nickel complexes with acetoacetamide ligands

On the basis of a remote effect, a series of acetoacetamide ligands and corresponding nickel complexes N‐(R‐phenyl) acetoacetamide Ni(CH₂Ph) (PMe₃) (R = H, 1 ; R = 2‐methyl, 2 ; R = 2,6‐dimethyl, 3 ; R = 2,6‐diisopropyl, 4 ; R = 4‐NO₂, 5 ) were synthesized and characterized. The solid structure of complex 3 was confirmed by X‐ray single‐crystal analysis to be of cis form. ¹H and ³¹P NMR spectroscopy confirmed that cis and trans isomers of nickel complexes were present in solution. Norbornene polymerizations with acetoacetamide nickel complexes activated with modified methylaluminoxane (MMAO) were investigated in detail. Remote steric and electronic effects of acetoacetamide ligand on catalytic activity and molecular weight of polynorbornenes (PNBs) were observed. Characterizations of the obtained PNBs show that the obtained polymer products are non‐crystalline vinylic‐addition polynorbornenes. Copyright © 2013 John Wiley & Sons, Ltd.     

Controlled/living copolymerization of styrene and acrylamide in DMF with Fe/TMEDA complex as catalyst

In this work, Fe(0)‐mediated single electron‐living radical copolymerization of styrene (St) and acrylamide (AM) was investigated at ambient temperature in N,N‐dimethylformamide using carbon tetrachloride as initiator and tetramethylethylenediamine as ligand. Kinetic studies showed that the copolymerization followed the first‐order kinetics model. The resulting copolymers of St and AM possessed predetermined molecular weights and narrow molecular weight distribution, which agreed with the character of controlled/living polymerization. On the basis of Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (NMR), the monomer reactivity ratios were calculated. The amount of ligand played an important role in copolymerization. The obtained polymer was characterized by FTIR, ¹H NMR, ¹³C NMR, and gel permeation chromatography. The living characteristics were demonstrated by chain extension experiment. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2919–2924     

Achieving branched polyethylene waxes by aryliminocycloocta[b]pyridylnickel precatalysts: Synthesis,characterization, and ethylene polymerization

Cycloocta[b ]pyridin‐10‐one was prepared to form the corresponding imino derivatives, which then reacted with (DME)NiBr₂ to form 10‐aryliminocycloocta[b ]pyridylnickel bromides ( Ni1 – Ni5 ). The new compounds were characterized by means of FT‐IR spectroscopy as well as elemental analysis and the organic ligands were also analyzed by the NMR measurements. Furthermore, the molecular structure of a representative complex Ni3 was determined by the single crystal X‐ray diffraction, indicating the distorted tetrahedral geometry around the nickel atom. Upon the activation with either methylaluminoxane (MAO) or diethylaluminium chloride (Et₂AlCl), the title nickel complexes exhibited high activity in ethylene polymerization and produced polyethylene of low molecular weight (1.43–6.78 kg mol^?1) and low dispersity (1.7–2.4), which suggests a single‐site catalytic system. More importantly, the microstructure of the resultant polyethylene (especially degree of branching) and certain physical properties, such as T _m values, can easily be modulated by selecting the proper substituents within the ligands and adjusting the polymerization conditions. This finding demonstrates that it is plausible to use a single catalyst for synthesizing different types of polyethylene on demand.10‐Aryliminocycloocta[b ]pyridylnickel bromides ( Ni1–Ni5 ), upon activation with either MAO or Et₂AlCl, exhibited high activity towards ethylene polymerization and produced polyethylenes with low molecular weight (1.43–6.78 kg mol^?1) and low dispersity (1.7–2.4). © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 2601–2610     

Novel miktofunctional initiator for the preparation of an ABC‐type miktoarm star polymer via a combination of controlled polymerization techniques

An ABC‐type miktoarm star polymer was prepared with a core‐out method via a combination of ring‐opening polymerization (ROP), stable free‐radical polymerization (SFRP), and atom transfer radical polymerization (ATRP). First, ROP of ϵ‐caprolactone was carried out with a miktofunctional initiator, 2‐(2‐bromo‐2‐methyl‐propionyloxymethyl)‐3‐hydroxy‐2‐methyl‐propionic acid 2‐phenyl‐2‐(2,2,6,6‐tetramethyl‐piperidin‐1‐yl oxy)‐ethyl ester, at 110 °C. Second, previously obtained poly(ϵ‐caprolactone) (PCL) was used as a macroinitiator for SFRP of styrene at 125 °C. As a third step, this PCL–polystyrene (PSt) precursor with a bromine functionality in the core was used as a macroinitiator for ATRP of tert‐butyl acrylate in the presence of Cu(I)Br and pentamethyldiethylenetriamine at 100 °C. This produced an ABC‐type miktoarm star polymer [PCL–PSt–poly(tert‐butyl acrylate)] with a controlled molecular weight and a moderate polydispersity (weight‐average molecular weight/number‐average molecular weight < 1.37). The obtained polymers were characterized with gel permeation chromatography and ¹H NMR. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4228–4236, 2004     

Nickel(II) complexes bearing pyrazolylimine ligand: synthesis,structure, and catalytic properties for vinyl‐type polymerization of norbornene

Two nickel(II) complexes of {2‐[C₃HN₂(R₁)₂‐3,5]}[C(R₂)?N(C₆H₃ⁱPr₂‐2,6)]NiBr₂ (complex 1 : R₁ = CH₃, R₂ = 2,4,6‐trimethylphenyl; complex 2 : R₁ = R₂ = Ph) were synthesized and characterized. The solid‐state structure of complex 1 has been confirmed by X‐ray single‐crystal analysis. Activated by methylaluminoxane (MAO), complexes 1 and 2 are capable of catalyzing the polymerization of norbornene with moderate activities [up to 10.56 × 10⁵ gPNBE (mol Ni h)^?1] with high molecular weights (M_w?13.56 × 10⁵ g mol^?1) and molecular weight distributions were around 2. The influences of polymerization parameters such as reaction temperature and Al–Ni molar ratio on catalytic activity and molecular weight of the polynorbornene were investigated in detail. The obtained polynorbornenes were characterized by means of ¹H‐NMR and FTIR techniques. The analytical results of polymer structures indicated that the norbornene polymerization is vinyl‐type polymerization rather than ROMP. Copyright © 2009 John Wiley & Sons, Ltd.     

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     

Methyl branching in polyethylene from homopolymerization of ethylene with N‐arylcyano‐β‐diketiminate methallyl nickel‐B(C6F5)3

N‐Arylcyano‐β‐diketiminate methallyl nickel complexes activated with B(C₆F₅)₃ were used in the polymerization of ethylene. The microstructure analysis of obtained polyethylene (PE) was done by differential scanning calorimetry and ¹³C nuclear magnetic resonance (NMR). The branched polymer structures produced by these catalysts were attributed to one step isomerization mechanism of the catalyst along the polymer chain. The ortho or para position of the cyano group with co‐ordinated B(C₆F₅)₃ in both methallyl nickel catalysts influenced the polymer molecular weight, branching, and consequently melting and crystallization temperatures. NMR spectroscopic studies showed predominantly the formation of methyl branches in the obtained PE. Catalysts under study gave linear low‐density PEs with good crystallinities at temperatures of reaction between 50 °C and 70 °C at moderate pressures (12.3 atm). A propylene–ethylene copolymer produced by the metallocene catalyst had the same concentration of branches as the PE synthesized from methallyl nickel/B(C₆F₅)₃. Comparing the two polyolefins with the same degree of branching, it was observed that the polymer obtained with the nickel catalyst proved to be twice more crystalline and had greater T_m. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 452–458     

Polymeric nanocomposite comprising gold nanoparticles and bilaterally sulfur‐functionalized polystyrene

Anionic polymerization technique has been utilized to synthesize a bilaterally sulfur‐functionalized polystyrene, SCH3‐polystyrene‐SH. The synthesis scheme consists of (1) initiation of 4‐vinylbenzylmethyl sulfide with sec‐butyllithium to form a living sulfur‐containing initiator, (2) polymerization of styrene, and (3) termination of growing polystyrene chain with ethylene sulfide. The resulting bilaterally sulfur‐functionalized polystyrene is used to make polystyrene/gold nanoparticles (AuNPs) nanocomposite with AuNPs formed in situ in polymer solution through reduction of AuClO₄. The effects of the polymer/Au molar ratio as well as the molecular weight of polymer on the size and dispersion of formed AuNPs have been studied, and the superiority of bilaterally functionalized polymer to unilaterally functionalized polymer has been demonstrated. The polystyrene/AuNPs composite has been characterized by GPC, ¹H‐NMR, ¹³C‐NMR, EDS, TEM, UV‐Vis, and DSC. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1268–1277     

Polymerization of β‐pinene with Schiff‐base nickel complexes catalyst: Synthesis of relatively high molecular weight poly(β‐pinene) at high temperature with high productivity

A series of easily accessible and stable Schiff‐base nickel complexes (complex 1 – 4 ) in conjunction with methylaluminoxane (MAO) were employed for the synthesis of relatively high molecular weight β‐pinene polymers at high temperature with high productivity. The ligand structure of the complex had a substantial effect on the polymerization in terms of the productivity and the molecular weight. With complex 4 in the presence of MAO, high molecular weight polymers of β‐pinene (M_n ～ 10,900) were obtained at 40 °C with an extremely high productivity up to 1.25 × 10⁷ g polyβ‐pinene/mol of Ni. ¹H NMR analyses showed that the obtained β‐pinene polymer was structurally identical to that formed by conventional cationic Lewis acid initiators. The polymerization was presumably initiated by the nickel cation formed by the reaction of the schiff‐base nickel complex and MAO, while the propagation proceeded in a manner typical for a conventional carbocationic polymerization process. Direct evidence for the carbocationic polymerization was offered by the fact that quenching of the polymerization with methanol at a low monomer conversion resulted in incorporation of a methoxyl end group into the polymer chain. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3739–3746, 2007     

1‐(2,6‐dibenzhydryl‐4‐fluorophenylimino)‐2‐aryliminoacenaphthylylnickel halides highly polymerizing ethylene for the polyethylenes with high branches and molecular weights

A series of 1‐(2,6‐dibenzhydryl‐4‐fluorophenylimino)‐ 2‐aryliminoacenaphthylene derivatives ( L1–L5 ) and their halonickel complexes LNiX₂ (X = Br, Ni1–Ni5 ; X = Cl, Ni6–Ni10 ) are synthesized and well characterized. The molecular structures of representative complexes Ni2 and Ni4 are confirmed as the distorted tetrahedron geometry around nickel atom by the single crystal X‐ray diffraction. Upon activation with methylaluminoxane, all nickel complexes show high activities up to 1.49 × 10⁷ g of PE (mol of Ni)^?1 h^?1 toward ethylene polymerization, producing polyethylenes with high branches and molecular weights up to 1.62 × 10⁶ g mol^?1 as well as narrow polydispersity. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1369–1378     

Synthesis of norbornenes containing cationic mono‐ and di(cyclopentadienyliron)arene complexes and their ring‐opening metathesis polymerization

A number of classes of polynorbornenes containing cationic iron moieties within their side chains were prepared via ring‐opening metathesis polymerization with a ruthenium‐based catalyst. The iron‐containing polymers displayed excellent solubility in polar organic solvents. The weight‐average molecular weights of these polymeric materials were estimated to be in the range of 18,000–48,000. Thermogravimetric analysis of these polymers showed two distinct weight losses. The first weight loss was in the range of 204–260 °C and was due to the loss of the metallic moieties, whereas the second weight loss was observed at 368–512 °C and was due to the degradation of the polymer backbone. Cyclic voltammetry studies of the iron‐containing polymers showed that the 18 e^? cationic iron centers underwent a reduction to give the neutral 19 e^? complexes at half‐wave potential (E_1/2) = ?1.105 V. Photolysis of the metallated polymers led to the isolation of the norbornene polymers in very good yields. Differential scanning calorimetry studies showed a sharp increase in the glass‐transition temperatures up to 91 °C when rigid aromatic side chains were incorporated into the norbornene polymers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3053–3070, 2006     

Tailoring polymers through interplay of ligands within precatalysts: 8‐(Nitro/benzhydryl‐arylimino)‐7,7‐dimethyl‐5,6‐dihydroquinolylnickel halides in ethylene polymerization

A series of 8‐(nitro/benzhydryl‐substituted arylimino)‐7,7‐dimethyl‐5,6‐dihydroquinolines and the corresponding nickel halide complexes were synthesized and characterized. Molecular structures of representative nickel complexes were determined by single crystal X‐ray diffraction, showing the dinuclear dimers with distorted square‐pyramidal geometry around the nickel center. The binding energies determined by X‐ray photoelectron spectroscopy (XPS) indicate the effective coordination between the sp²‐nitrogen and nickel atoms as well as the influence of both the halogen ligands and the substituents within dihydroquinolines on the strength of the Ni? N bond. Ethylene polymerization with the nickel precatalysts in presence of either methylaluminoxane or diethylaluminum chloride was explored in detail. For the complexes containing the nitro substituent within the organic ligand, the catalytic activity is inversely proportional to the electron density around the nickel core determined by XPS; such phenomenon is consistent with the conclusion of the computational study stating that the activity of precatalysts is correlated with the net charge on the metal center. In the polymerization process, unimodal and branched polyethylenes containing vinyl or vinylene groups were obtained. The nickel precatalysts bearing bulky benzhydryl within the organic ligand as well as bromide rather than chloride attached to the nickel atom produce polymers with relatively large amount of vinylene groups. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 2071–2083     

Synthesis and properties of functional aliphatic polycarbonates

Two, functional, cyclic carbonate monomers, 5‐methyl‐5‐methoxycarbonyl‐1,3‐dioxan‐2‐one and 5‐methyl‐5‐ethoxy carbonyl‐1,3‐dioxan‐2‐one, were synthesized starting from 2,2‐bis(hydroxymethyl) propionic acid. The ring‐opening polymerization of the cyclic carbonate monomers in bulk with stannous 2‐ethylhexanoate as a catalyst under different conditions was examined. The results showed that the yield and molecular weight of polycarbonates were significantly influenced by the reaction conditions. The polycarbonates obtained were characterized by IR, ¹H NMR, and differential scanning calorimetry. Their molecular weight was measured by gel permeation chromatography. The in vitro biodegradation and controlled drug‐release properties of the polycarbonates were also investigated. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 4001–4006, 2003