Synthesis and crystallization behavior of rigid copolyesters with biphenyl‐4,4′‐dicarboxylate and 2,6‐naphthalenedicarboxylate in the main chain

Structurally rigid copolyester thermoplastics were synthesized from 1,4‐cyclohexanedimethanol and the diesters dimethyl biphenyl‐4,4′‐dicarboxylate and dimethyl 2,6‐naphthalenedicarboxylate (DMN) via conventional melt transesterification. Conventional differential scanning calorimetry (CDSC) showed all compositions to exhibit multiple endotherms upon heating. Wide‐angle X‐ray diffraction analysis showed copolyester compositions to exhibit the crystalline structure of either the homopolyester Poly(1,4‐cyclohexylenedimethylene 2,6‐naphthalate) (PCN) or the homopolyester Poly(1,4‐cyclohexylenedimethylene 4,4′‐bibenzoate) (PCB), but not both simultaneously. Further thermal analysis using CDSC and fast DSC investigated the origin of the multiple endotherm behavior. While three endotherms are observed for low heating rates, the upper two endotherms appear to merge at heating rates about 1–5 °C s^?1 and a single endotherm remains above heating rates about 10–50 °C s^?1. While the behavior of the upper two endotherms is undeniably consistent with the mechanism of melting–recrystallization–remelting (MRR), we suggest that the low endotherm is likely associated with the melting of constrained secondary crystals, although MRR effects cannot be ruled out. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 973–980     

Synthesis and properties of alternating copolyamide‐imides based on 2,6‐bis(4‐aminophenoxy)naphthalene and comparison with its related isomeric polymers

A series of novel polyamide‐imides III containing 2,6‐bis(phenoxy)naphthalene units were synthesized by 2,6‐bis(4‐aminophenoxy)naphthalene and various bis(trimellitimide)s in N‐methyl‐2‐pyrrolidone (NMP) using triphenyl phosphite and pyridine as condensing agents through direct polycondensation. The polymers were obtained in quantitative yield with inherent viscosities up to 1.53 dL/g. Most of the polymers showed good solubility in NMP, N,N‐dimethylacetamide, N,N‐dimethylformamide, and dimethyl sulfoxide and could be solution‐cast into transparent, flexible, and tough films. The films had tensile strengths of 84–111 MPa, elongations at break of 8–33%, and initial moduli of 2.2–2.8 GPa. Wide‐angle X‐ray diffraction revealed that most polymers III were amorphous. The glass‐transition temperatures of some of the polymers could be determined by differential scanning calorimetry traces, recorded at 247–290 °C. The polyamide‐imides exhibited excellent thermal stabilities and had 10% weight loss at temperatures in the range of 501–575 °C under nitrogen atmosphere. They left more than 57% residue even at 800 °C in nitrogen. A comparative study of some corresponding polyamide‐imides is also presented. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2591–2601, 2001     

Transesterification kinetics of poly(ethylene terephthalate) and poly(ethylene 2,6‐naphthalate) blends with the addition of 2,2′‐bis(1,3‐oxazoline)

The kinetics of the transesterification reaction between poly(ethylene terephthalate) (PET) and poly(ethylene 2,6‐naphthalate) (PEN) with and without the addition of a chain extender were studied with ¹H NMR. Different kinetic approaches were considered, and a second‐order, reversible reaction was accepted for the PET/PEN reactive blend system. The addition of 2,2′‐bis(1,3‐oxazoline) (BOZ) promoted the transesterification reaction between PET and PEN in the molten state. The activation energy of the transesterification reaction for the PET/PEN reactive blend with BOZ (94.0 kJ/mol) was lower than that without BOZ (168.9KJ/mol). The rate constant k took an almost constant value for blend samples with different compositions mixed at 275 °C. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2607–2614, 2001     

Synthesis of three new 1‐(2,6‐diisopropylphenyl)‐2,5‐di(2‐thienyl) pyrrole‐based donor polymers and their bulk heterojunction solar cell applications

A series of three new 1‐(2,6‐diisopropylphenyl)‐2,5‐di(2‐thienyl)pyrrole‐based polymers such as poly[1‐(2,6‐diisopropylphenyl)‐2,5‐di(2‐thienyl)pyrrole] ( PTPT ), poly[1,4‐(2,5‐bis(octyloxy)phenylene)‐alt‐5,5'‐(1‐(2,6‐diisopropylphenyl)‐2,5‐di(2‐thienyl)pyrrole)] ( PPTPT ), and poly[2,5‐(3‐octylthiophene)‐alt‐5,5'‐(1‐(2,6‐diisopropylphenyl)‐2,5‐di(2‐thienyl)pyrrole)] ( PTTPT ) were synthesized and characterized. The new polymers were readily soluble in common organic solvents and the thermogravimetric analysis showed that the three polymers are thermally stable with the 5% degradation temperature >379 °C. The absorption maxima of the polymers were 478, 483, and 485 nm in thin film and the optical band gaps calculated from the onset wavelength of the optical absorption were 2.15, 2.20, and 2.13 eV, respectively. Each of the polymers was investigated as an electron donor blending with PC₇₀BM as an electron acceptor in bulk heterojunction (BHJ) solar cells. BHJ solar cells were fabricated in ITO/PEDOT:PSS/polymer:PC₇₀BM/TiO_x/Al configurations. The BHJ solar cell with PPTPT :PC₇₀BM (1:5 wt %) showed the power conversion efficiency (PCE) of 1.35% (J_sc = 7.41 mA/cm², V_oc = 0.56 V, FF = 33%), measured using AM 1.5G solar simulator at 100 mW/cm² light illumination. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Glass‐formation kinetics of miscible blends of atactic polystyrene and poly(2,6‐dimethyl‐1,4‐phenylene oxide)

We present a detailed investigation of the kinetics associated with the glass transitions of miscible blends composed of atactic polystyrene (a‐PS) and poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO). According to both dynamic mechanical analysis and differential scanning calorimetry, relaxation times displayed an enhanced temperature dependence (i.e., more fragile or more cooperative behavior) for the blends compared with additive behavior based on the responses of neat a‐PS and PPO. This is consistent with the notion that specific interactions between the blend components heighten the intermolecular cooperativity. The compositional dependence of fragility provided insight into physical aging results for the properties of volume and enthalpy. The combination of our research and a previously reported pressure–volume–temperature study by Zoller and Hoehn (J Polym Sci Polym Phys Ed 1982, 20, 1385) provided evidence that the observation of increased glassy densities for the blends compared with those of the pure polymers was kinetic in origin and was not a feature of the thermodynamics of miscibility. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2118–2129, 2001     

Reverse atom transfer radical polymerization of vinyl monomers with Fe[SC(S)NEt2]3 alone as the catalyst

The living radical polymerization of methyl methacrylate and styrene was successfully carried out with diethyl 2,3‐dicyano‐2,3‐diphenylsuccinate (DCDPS)/ferric tri(diethyldithiocarbamate) as a novel reverse atom transfer radical polymerization initiation system in which DCDPS was a hexa‐substituted ethane‐type thermal iniferter, DC was a diethyldithiocarbamate group, and no additional ligands such as nitrogen‐ or phosphine‐based compounds were required. The bulk polymerization of methyl methacrylate was carried out at 95 °C, and that of styrene was carried out at 120 °C. Poly(methyl methacrylate) and polystyrene (PSt) with high molecular weights and quite narrow molecular weight distributions (as low as 1.09 for PSt) were obtained. ¹H NMR spectroscopy revealed the presence of an α‐(carbethoxycyanophenyl)methyl group from the initiator and an ω‐DC group from the catalyst in the obtained polymers. Various chain‐extension reactions under UV light or thermal treatments were successfully conducted to prove the presence and efficient reinitiating of the ω‐DC group. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3464–3473, 2001     

Mitigating chain‐transfer and enhancing the thermal stability of co‐based olefin polymerization catalysts through sterically demanding ligands

Sterically demanding Fe‐ and Co‐based olefin polymerization catalysts 2‐Fe and 2‐Co bearing 2,6‐bis(biphenylmethyl)‐4‐methylaniline substituted bis(imino)pyridine ligands were synthesized and evaluated for ethylene polymerization. The late‐transition metal complexes were characterized by X‐ray diffraction, NMR spectroscopy, and HRMS, while their resultant polymers were characterized by size‐exclusion chromatography and ¹H NMR spectroscopy. While catalyst 2‐Fe was inactive, catalyst 2‐Co was found to polymerize ethylene and avoid any detectable chain‐transfer to aluminum events that are known to plague other Fe‐ and Co‐based catalyst systems and to limit molecular weight. Furthermore, 2‐Co displays virtually perfect thermal stability up to 80 °C and shows greatly enhanced thermal stability at 90 °C as compared to previously reported analogues. These observations are attributed to the extreme steric demand imposed by the ligand which mitigates catalyst transfer, deactivation, and decomposition reactions. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3990–3995     

Cu(0)/2,6‐bis(imino)pyridines catalyzed single‐electron transfer‐living radical polymerization of methyl methacrylate initiated with poly(vinylidene fluoride‐co‐chlorotrifluoroethylene)

A series of 2,6‐bis(imino)pyridines, as common ligands for late transition metal catalyst in ethylene coordination polymerization, were successfully employed in single‐electron transfer‐living radical polymerization (SET‐LRP) of methyl methacrylate (MMA) by using poly(vinylidene fluoride‐co‐chlorotrifluoroethylene) (P(VDF‐co‐CTFE)) as macroinitiator with low concentration of copper catalyst under relative mild‐reaction conditions. Well‐controlled polymerization features were observed under varied reaction conditions including reaction temperature, catalyst concentration, as well as monomer amount in feed. The typical side reactions including the chain‐transfer reaction and dehydrochlorination reaction happened on P(VDF‐co‐CTFE) in atom‐transfer radical polymerization process were avoided in current system. The relationship between the catalytic activity and the chemical structure of 2,6‐bis(imino)pyridine ligands was investigated by comparing both the electrochemical properties of Cu(II)/2,6‐bis(imino)pyridine and the kinetic results of SET‐LRP of MMA catalyzed with different ligands. The substitute groups onto N‐binding sites with proper steric bulk and electron donating are desirable for both high‐propagation reaction rate and C? Cl bonds activation capability on P(VDF‐co‐CTFE). The catalytic activity of Cu(0)/2,6‐bis(imino)pyridines is comparable with Cu(0)/2,2′‐bipyridine under the consistent reaction conditions. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4378–4388     

Copolymerization of propylene with higher α‐olefins in the presence of the syndiospecific catalyst i‐Pr(Cp)(9‐Flu)ZrCl2/MAO

The catalyst system i‐Pr(Cp)(9‐Flu)ZrCl₂/methylaluminoxane was used for the synthesis of random syndiotactic copolymers of propylene with 1‐hexene, 1‐dodecene, and 1‐octadecene as comonomers. An investigation of the microstructure by ¹³C NMR spectroscopy revealed that the stereoregularity of the copolymers decreased because of an increase in skipped insertions in the presence of the higher 1‐olefin. The melting temperature of the copolymers, as measured by differential scanning calorimetry (DSC), decreased linearly with increasing comonomer content independently of the comonomer nature. During the DSC heating cycle, an exothermic peak indicating a crystallization process was observed. The decrease in the crystallization temperature with higher 1‐olefin content, measured by crystallization analysis fractionation, indicated a small but significant dependence on the nature of the comonomer. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 128–140, 2002     

Synthesis and properties of new polyarylates from 1,4‐bis(4‐carboxyphenoxy)naphthyl or 2,6‐bis(4‐carboxyphenoxy)naphthyl and various bisphenols

New 1,4‐naphthyl and 2,6‐naphthyl‐containing polyarylates having inherent viscosities up to 1.28 dL/g were synthesized by the high‐temperature solution polycondensation from the acid chloride of 1,4‐bis(4‐carboxyphenoxy)naphthyl or 2,6‐bis(4‐carboxyphenoxy)naphthyl and various bisphenols. Most of the resulting polyarylates showed amorphous characteristics and were readily soluble in common organic solvents such as N,N‐dimethylacetamide (DMAc), N‐methyl‐2‐pyrrolidone (NMP), o‐chlorophenol, and chloroform. Transparent, flexible, and colorless films of these polymers could be cast from the DMAc solutions. Their cast films had tensile strengths ranging from 54.9 to 84.2 MPa, elongations at break from 5.3% to 19.0%, and initial modulus from 2.0 to 2.8 GPa. These polymers had glass transition temperatures in the range of 172–280°C and began to lose weight around 400°C, with 10% weight loss being recorded at about 450°C in air. Dynamic mechanical analysis (DMA) reveals that the polyarylates containing isopropylidene linkages have three transitions on the temperature scale between −100 and 300°C. However, only two transitions were observed in the other polyarylates without isoproylidene linkage. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 645–652, 1999     

Kinetics for the catalyzed formation of poly(ethylene 2,6-naphthalate) (PEN) by various metal compounds

The catalyzed transesterification between dimethyl 2,6-naphthalate and ethylene glycol and polycondensation of bis (2-hydroxyethyl) naphthalate have been investigated in the presence of various metal compounds as catalysts. The effect of the nature and concentration of these catalysts on both reactions has been studied. The observed overall rate of the transesterification was third order; first order with respect to dimethyl 2,6-naphthalate, ethylene glycol, and the catalyst including initial concentration of catalyst, respectively. The decreasing order in catalytic activity on the transesterification was the order of Pb(II) > Zn(II) > Mn(II) > Co(II) > Ti(IV) > Sn(II) > Mg(II) > Ca(II) > Na(I) > Sb(III). And also, the decreasing order in catalytic activity on the polycondensation was found to be Ti(IV) > mixtures of Ti(IV) and Sb(III) > Sn(II) > Sb(III) > Co(II) > Zn(II) > Pb(II) > Mn(II) > Mg(II). © 1994 John Wiley & Sons, Inc.     

High‐performance poly(ethylene‐2,6‐naphthalate) fiber prepared by high‐tension annealing

A high‐tension annealing (HTA) method has been applied to zone‐annealed poly(ethylene‐2,6‐naphthalate) (PEN) fibers in order to further improve their mechanical properties. The HTA treatment was carried out under an applied tension of 428 MPa at a treating temperature of 175 °C. The applied tension was close to the tensile strength at 175 °C. The resulting HTA fiber had a birefringence of 0.492 and degree of crystallinity of 57%. Wide‐angle X‐ray diffraction (WAXD) photographs of the HTA fibers showed three reflections (010, 100, and 1 10) attributed to an α form crystal, but no (020) reflection attributed to a β form was observed in the equator. The tensile modulus and tensile strength increased with processing, and the HTA fiber had a maximum modulus of 33 GPa, a tensile strength of 1.1 GPa, and a storage modulus of 33 GPa at 25 °C. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 61–67, 2000     

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     

Branched polyethylene prepared by in situ copolymerization of ethylene with monotitanocene and modified methylaluminoxane catalyst

Branched polyethylene was synthesized in heptane used as a polymerization medium with monotitanocene catalyst composed of η⁵‐pentamethylcyclopentadienyl tribenzyloxy titanium and modified methylaluminoxane (mMAO) that contained different amounts of residual trimethylaluminum (TMA). The residual TMA more strongly reduced Ti(IV) complexes to Ti(III) and Ti(II) ones, and Ti(IV) active species were suggested to be more effective for ethylene polymerization. Influences of the polymerization temperature and Al/Ti molar ratio on the catalytic activity and the degree of branching, branch length, and molecular weight of polyethylene were investigated. The obtained polymers were confirmed by ¹³C NMR to be higher molecular weight polyethylene containing significant amounts of isolated ethyl branches, butyl branches, or both. Branched polyethylene was prepared by the in situ copolymerization of ethylene with 1‐butene and 1‐hexene, which were formed through a proposed mechanism including metallcycloheptane and metallcyclopentane intermediates of Ti(II) species that were produced by the reaction of Ti(IV) complexes with TMA coexisting in mMAO. There was a remarkable increase in the chance of 1‐butene being produced from metallcyclopentane of Ti(II) intermediates with an increase in the polymerization temperature. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4258–4263, 2000     

Temperature‐dependent desorption of surfactants in LLDPE blend films

The temperature‐dependent desorption behavior of surfactants in linear low‐density polyethylene (LLDPE) blend films was studied with Fourier transform infrared spectroscopy at 25, 40, and 50 °C. The LLDPE/low‐density polyethylene blend was 70/30. Three different specimens (labeled II, III, and IV) were prepared with various compositions of the surfactant, sorbitan palmitate (SPAN‐40), and the migration controller, poly(ethylene acrylic acid) (EAA). The calculated diffusion coefficients of SPAN‐40 in specimens II, III, and IV at 25, 40, and 50 °C varied from 9.6 × 10⁻¹² to 17.4 × 10⁻¹² cm²/s, from 5.5 × 10⁻¹² to 11.0 × 10⁻¹² cm²/s, and from 3.1 × 10⁻¹² to 5.8 × 10⁻¹² cm²/s, respectively. In addition, the activation energies of specimens II, III, and IV measured between 25 and 50 °C were 18.74, 19.42, and 20.14, respectively. Hence, the desorption rate of the surfactant increased with the temperature and decreased with an addition of EAA, but the activation energy increased with EAA. The diffusion kinetics, analyzed with a plot of the integrated intensity ratio as a function of time, log(I_t/I_∞) versus log t, at 25, 40, and 50 °C obeyed Fickian diffusion behavior. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 218–227, 2001     

Synthesis of new thermosetting poly(2,6‐dimethyl‐1,4‐phenylene oxide)s containing epoxide pendant groups

A new class of thermosetting poly(2,6‐dimethyl‐1,4‐phenylene oxide)s containing pendant epoxide groups were synthesized and characterized. These new epoxy polymers were prepared through the bromination of poly(2,6‐dimethyl‐1,4‐phenylene oxide) in halogenated aromatic hydrocarbons followed by a Wittig reaction to yield vinyl‐substituted polymer derivatives. The treatment of the vinyl‐substituted polymers with m‐chloroperbenzoic acid led to the formation of epoxidized poly(2,6‐dimethyl‐1,4‐phenylene oxide) with variable pendant ratios, and the structures and properties were studied with nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and gel permeation chromatography. The ratios of pendant functional groups were tailored for the polymer properties, and the results showed that the glass‐transition temperatures increased as the benzylic protons were replaced by bromo‐, vinyl‐, or epoxide‐functional groups, whereas the thermal stability decreased in comparison with the original polymer. Within a molar fraction of 20–50%, the degree of functionalization had little effect on the glass‐transition temperature; however, it correlated inversely with the thermal stability of each functionalized polymer. The thermal curing behavior of the epoxide‐functionalized polymer was enhanced by the increment of the pendant functionality, which resulted in a significant increase in the glass‐transition temperature as well as the thermal stability after the curing reaction. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5875–5886, 2006     

The synthesis,characterization and polycondensation of metal‐containing diols: crystal structure of [(η5‐C5H5)(CO)2Fe(CH2)3O‐{2,6‐(CH2OH)2‐4‐CH3?C6H2}]

The synthesis of two new transition‐metal‐containing polyesters is described. The precursors are bifunctional organometallic monomers that were synthesized using 2,6‐bis(hydroxymethyl)‐p‐cresol as the key reagent. This was achieved by simple coupling reactions between the appropriate organometallic alkyl halide and the cresol reagent. Polycondensation reactions were carried out with terephthaloyl chloride using ambient temperature solution techniques. The new low molecular weight oligomeric polyesters were characterized using Fourier transform infrared and ¹HNMR spectroscopy, differential scanning calorimetry, thermogravimetric analysis and size‐exclusion chromatography analyses. Copyright © 2002 John Wiley & Sons, Ltd.     

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     

Oxidative polymerization of 2,6‐dimethylphenol to form poly(2,6‐dimethyl‐1,4‐phenylene oxide) in water through one water‐soluble copper(II) complex of a zwitterionic calix[4]arene

In the presence of excess NaOH, reaction of Cu(OAc)₂·H₂O with equimolar ammonium calix[4]arene [H₄L]I₄ ( 1 , H₄L = [5,11,17,23‐tetrakis(trimethylammonium)‐25,26,27,28‐tetrahydroxycalix[4]arene]) resulted in the formation of a mononuclear cationic Cu(II) complex [Cu(II)L(H₂O)]I₂ ( 2 ) in 43% yield. Complex 2 was characterized by elemental analysis, infrared (IR), and single crystal X‐ray diffraction. The Cu(II) atom in 2 is coordinated by four oxygen atoms of one L^4? ligand and one O atom from one water molecule, forming a square pyramidal geometry. Complex 2 exhibited high catalytic activity in the oxidative polymerization of 2,6‐dimethylphenol using O₂ as oxidizing agent in water under mild conditions. The selective polymerization produced poly(2,6‐dimethyl‐1,4‐phenylene oxide) in high yields with almost no diphenoquinone. The influence of the polymerization temperature, the time interval, the molar ratio of 2,6‐dimethylphenol/ 2 , the concentrations of sodium hydroxide, and sodium n‐dodecyl sulfate were examined. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Ethylene polymerization by bis(salicylaldiminate)nickel(II)/aluminoxane catalysts

The homopolymerization of ethylene by using different catalytic systems based on dinitro‐substituted bis(salicylaldiminate)nickel(II) precursors such as bis[3,5‐dinitro‐N(2,6‐diisopropylphenyl)]nickel(II) and bis[3,5‐dinitro‐N(phenyl)]nickel(II) in combination with organoaluminum compounds was investigated. In particular, the catalytic performances were studied as a function of the main reaction parameters, such as temperature, pressure, Al/Ni molar ratio, and duration. Methylaluminoxane resulted in the best co‐catalyst. Activities up to 200 kg polyethylene/(mol Ni × h) to give a linear high‐molecular‐weight polymer were achieved. The influence of the bulkiness of the substituents on the N‐aryl group of the aldimine ligand was also checked; it resulted in a determinant for catalytic activity rather than for polymer characteristics. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2534–2542, 2004