High Molecular Weight Polymers Research Articles

Vanadium chlorides supported by BIAN (BIAN = bis(arylimo)-acenaphthene) ligands: Synthesis, characterization, and catalysis on ethylene polymerization

Several vanadium chlorides bearing bis(arylimino)-acenaphthene (BIAN) ligands, (2,6-Me2C6H3-BIAN)V(THF)Cl3 (1), (2,6-Et2C6H3-BIAN)V(THF)Cl3 (2), (2,6-iPr2C6H3-BIAN)V(THF)Cl3 (3), [3,5-(CF3)2C6H3-BIAN]V(THF)Cl3 (4), [4-OMe-C6H4-BIAN]V(THF)Cl3 (5), and [2,6-(Ph2CH)2-4-OMeC6H2-BIAN]V.(THF)Cl3 (6) were synthesized by direct reaction of VCl3(THF)3 with corresponding BIAN ligands. All these complexes were characterized by elemental analyses, and FT-IR spectroscopy. The molecular structures of 1, 2, and 4 were identified by X-ray crystallography, in which the six-coordinated vanadium metal centers were in distorted octahedral geometry with the oxygen atom of the coordinated THF, two nitrogen atoms of the diimine ligand and one chlorine atom in the same plane. When activated with AlEt2Cl these vanadium complexes showed high catalytic activities for ethylene polymerization affording linear polyethylene with high molecular weight. However, when MAO was used as co-catalyst, ultra high molecular-weight polymers were obtained albeit with decreased activity.

Supramolecular Architecture of Molecular-Level-Ordered 1,1′-Ferrocenedicarboxylic Acid with Poly(4-vinylpyridine) for Bulk Magnetic Coupling

Molecular-level ordering provides a powerful approach to enhancing the properties of materials. However, the precise arrangement of molecules in a bulk material is a considerable challenge. To overcome such limitations, hydrogen bonding-directed self-assembly has drawn a lot of attention due to its facile nature in controlling molecular-level order. In this study, we report ordering of the magnetic Fe centers achieved through hydrogen bonding between poly(4-vinylpyridine) (P4VP, MW 60 kDa) and 1,1′-ferrocenedicarboxylic acid (FDA). Co-dissolving P4VP and FDA in dry methanol leads to P4VP–FDA showing an unprecedented degree of order for both FDA and the polymer chain. Such an event of mutual assistance between a dicarboxylic acid and a high molecular weight polymer chain in building the ordered supramolecular architecture is rare. FDA is uniformly distributed in an ordered polymer matrix, with each Fe center in P4VP–FDA linked at the molecular-level through polymeric bridges in a face-centered cubic struct...

Bisphenol A based carbon-carbon coupled poly(arylene)s from dibenzoyl-dichlorobenzene via Ni(II) catalyzed and condensation polymerization for PEMFC

The major challenges experienced by the researchers till now are to synthesis the chemically and mechanically stable proton exchange membranes. However, Ni catalyzed CC coupling polymerization together with condensation reaction assist to get the high molecular weight polymer membranes as well as thermally and chemically stable PEMs. In this study, bisphenol A-based sulfonated poly (arylene)s copolymers (bis A-SPAs) have been successfully synthesized by the carbon-carbon coupling polymerization using Ni (0) catalyst from sulfonated 1,4-dibenzoyl-2,5-dichlorobenzene (SDBDCB) monomer and subsequently condensation reaction with bisphenol A. The (bis A-SPAs) membranes were flexible in nature and attained high molecular weight. The synthesized (bis A-SPAs) membranes exhibited water uptake from 7.42 to 56.4%, ion exchange capacity ranging from 0.73 to 1.67 meq/g, and proton conductivity from 48.8 to 96.4 mS/cm (at 90 °C) with maximum power density of 0.48–0.60 W/cm2. Membrane with high-sulfonated degree (bis A-SPAs-50) showed almost analogous conductivity (96.4 mS/cm) to Nafion® 117 membrane (98.92 mS/cm) at 90 °C and 90% humidity. The synthesized sulfonated polymer membranes displayed well phase separation that increased the proton conductivity. The TGA and Fenton's test results confirmed that the synthesized membranes possessed admirable thermal stability and mechanical stability. Therefore, the new synthesized (bis A-SPAs) membranes have the promising suitable properties as a proton exchange membrane in the fuel cell applications.

Aromatic polyesters containing cardo perhydrocumyl cyclohexylidene groups: Synthesis, characterization and gas permeation study

Three bisphenols containing cardo perhydrocumyl cyclohexylidene group, namely; 1,1-bis(4-hydroxyphenyl)-4-perhydrocumylcyclohexane, 1,1-bis(4-hydroxy-3-methylphenyl)-4-perhydrocumylcyclohexane and 1,1-bis(4-hydroxy-3,5-dimethylphenyl)-4-perhydrocumylcyclohexane were synthesized starting from p-cumyl phenol. Each of these bisphenols was polycondensed with both terephthaloyl chloride and isophthaloyl chloride by phase transfer-catalyzed interfacial polymerization to obtain a series of new aromatic polyesters. Inherent viscosities and number average molecular weights of polyesters were in the range 0.51-0.64 dL/g and 17390-41430 g/mol, respectively which indicated the formation of reasonably high molecular weight polymers. The detailed NMR studies revealed that axial and equatorial identity of the phenyl rings of bisphenols was retained in polyesters resulting in constitutional isomerism. Polyesters containing perhydrocumyl cyclohexylidene groups showed excellent solubility in organic solvents viz, chloroform, dichloromethane, 1,1,2,2-tetrachloroethane and tetrahydrofuran. The self-standing films of polyesters could be cast from their chloroform solution. The 10% weight loss temperatures and glass transition temperatures of polyesters were in the range 453–485 °C and 201–267 °C, respectively demonstrating their excellent thermal characteristics. The gas permeability study of polyesters was carried out for He, H2 and N2 by variable-volume method. An improvement in permeability and decrease in selectivity was observed due to symmetric methyl substituents while reverse trend was observed in case of polyesters with asymmetric methyl substituents.

Detailed Structural Analysis of the Hyperbranched Polymers Formed in Self‐Condensing Vinyl Polymerization

AbstractMonte Carlo simulation is applied to investigate the effect of reactor types on the formed hyperbranched architecture. When a continuous stirred‐tank reactor (CSTR) is used for the synthesis, the number of units incorporated into the largest cluster of dendritic units inside the hyperbranched polymer increases with molecular weight, while it does not increase in batch polymerization. The largest dendritic cluster formed in a CSTR consists of the monomeric units whose average residence time is large, while the average residence time of the singly connected peripheral units is small. The maximum span length as well as the mean‐square radius of gyration of the high molecular weight polymer is much smaller for the polymers synthesized in a CSTR, compared with batch polymerization. A universal relationship between the mean‐square radius of gyration and the maximum span length is found, which is valid for both batch and CSTR.

A MAPbBr3:poly(ethylene oxide) composite perovskite quantum dot emission layer: enhanced film stability, coverage and device performance.

Metal halide perovskite quantum dots (PQDs) have become the most promising optoelectronic material in new generation displays and lighting devices due to their excellent optical properties. However, their stability and surface defects have affected their large-scale applications. We demonstrate enhanced stability of high-surface-area colloidal PQDs encapsulated with long-chain organic polymer poly(ethylene oxide) (PEO) via simply mixing the PQDs with this high molecular-weight polymer. The introduction of the polymer deactivates the surface defects of PQDs and sufficiently protects the organic ligands on the surfaces of PQDs with obviously improved ambient stability and photoluminescence quantum yield. Moreover, the use of PEO efficiently confines electrons within the PQD emission layer and generates extremely stable green electroluminescence spectra in MAPbBr3 light-emitting diodes (LEDs) over a wide voltage operation range of 5-12 V, accompanied by significant improvements in external quantum efficiencies with enhancement factors of 18.3 times. Our work provides a robust platform for the fabrication of stable PQDs, high-quality PQD films and efficient PQD-based LEDs.

Exploring Novel Functions of the Small GTPase Ypt1p under Heat-Shock by Characterizing a Temperature-Sensitive Mutant Yeast Strain, ypt1-G80D.

In our previous study, we found that Ypt1p, a Rab family small GTPase protein, exhibits a stress-driven structural and functional switch from a GTPase to a molecular chaperone, and mediates thermo tolerance in Saccharomyces cerevisiae. In the current study, we focused on the temperature-sensitive ypt1-G80D mutant, and found that the mutant cells are highly sensitive to heat-shock, due to a deficiency in the chaperone function of Ypt1pG80D. This defect results from an inability of the protein to form high molecular weight polymers, even though it retains almost normal GTPase function. The heat-stress sensitivity of ypt1-G80D cells was partially recovered by treatment with 4-phenylbutyric acid, a chemical chaperone. These findings indicate that loss of the chaperone function of Ypt1pG80D underlies the heat sensitivity of ypt1-G80D cells. We also compared the proteomes of YPT1 (wild-type) and ypt1-G80D cells to investigate Ypt1p-controlled proteins under heat-stress conditions. Our findings suggest that Ypt1p controls an abundance of proteins involved in metabolism, protein synthesis, cellular energy generation, stress response, and DNA regulation. Finally, we suggest that Ypt1p essentially regulates fundamental cellular processes under heat-stress conditions by acting as a molecular chaperone.

Catalyst-free, aza-Michael polymerization of hydrazides: polymerizability, kinetics, and mechanistic origin of an α-effect.

Despite the powerful nature of the aza-Michael reaction for generating C-N linkages and bioactive moieties, the bis-Michael addition of 1° amines remains ineffective for the synthesis of functional, step-growth polymers due to the drastic reduction in reactivity of the resulting 2° amine mono-addition adduct. In this study, a wide range of commercial hydrazides are shown to effectively undergo the bis-Michael reaction with divinyl sulfone (DVS) and 1,6-hexanediol diacrylate (HDA) under catalyst-free, thermal conditions to afford moderate to high molecular weight polymers with M n = 3.8-34.5 kg mol-1. The hydrazide-Michael reactions exhibit two distinctive, conversion-dependent kinetic regimes that are 2nd-order overall, in contrast to the 3rd-order nature of amines previously reported. The mono-addition rate constant was found to be 37-fold greater than that of the bis-addition at 80 °C for the reaction between benzhydrazide and DVS. A significant majority (12 of 15) of the hydrazide derivatives used here show excellent bis-Michael reactivity and achieve >97% conversions after 5 days. This behavior is consistent with calculations that show minimal variance of electron density on the N-nucleophile among the derivatives studied. Reactivity differences between hydrazides and hexylamine are also explored. Overall, the difference in reactivity between hydrazides and amines is attributed to the adjacent nitrogen atom in hydrazides that acts as an efficient hydrogen-bond donor that facilitates intramolecular proton-transfer following the formation of the zwitterion intermediate. This effect not only activates the Michael acceptor but also coordinates with additional Michael acceptors to form an intermolecular reactant complex.

Effects of particle stiffness on the extensional rheology of model rod-like nanoparticle suspensions.

The linear and nonlinear rheological behavior of two rod-like particle suspensions as a function of concentration is studied using small amplitude oscillatory shear, steady shear and capillary breakup extensional rheometry. The rod-like suspensions are composed of fd virus and its mutant fdY21M, which are perfectly monodisperse, with a length on the order of 900 nm. The particles are semiflexible yet differ in their persistence length. The effect of stiffness on the rheological behavior in both, shear and extensional flow, is investigated experimentally. The linear viscoelastic shear data is compared in detail with theoretical predictions for worm-like chains. The extensional properties are compared to Batchelor's theory, generalized for the shear thinning nature of the suspensions. Theoretical predictions agree well with the measured complex moduli at low concentrations as well as the nonlinear shear and elongational viscosities at high flow rates. The results in this work provide guidelines for enhancing the elongational viscosity based on purely frictional effects in the absence of strong normal forces which are characteristic for high molecular weight polymers.

Exploring Extracellular Matrix Degradomes by TMT-TAILS N-Terminomics.

Global characterization of protein N termini provides valuable information on proteome dynamics and diversity in health and disease. Driven by the progress in mass spectrometry-based proteomics, novel approaches for the dedicated investigation of protein N termini and protease substrates have been recently developed. Terminal amine isotopic labeling of substrates (TAILS) is a quantitative proteomics approach suitable for high-throughput and system-wide profiling of protein N termini in complex biological matrices. TAILS employs isotopic labeling of primary amines of intact proteins in combination with an amine-reactive high molecular weight polymer (HPG-ALD) for depletion of internal tryptic peptides and high enrichment of protein N termini by negative selection. Thereby, TAILS allows simultaneous identification of the natural N termini, protease-generated neo-N termini, and endogenously modified (e.g., acetylated) N termini. In this chapter, we provide a protocol for tandem mass tag (TMT)-TAILS analysis and further discuss specific considerations regarding N-terminome data interpretation using Proteome Discoverer™ software.

Synthesis of new polyesters by acyclic diene metathesis polymerization of bio-based α,ω-dienes prepared from eugenol and castor oil (undecenoate).

Synthesis of new polyesters by acyclic diene metathesis (ADMET) polymerization of α,ω-diene, 4-allyl-2-methoxyphenyl 10-undecenoate (M1), prepared from bio-renewable eugenol and castor oil (undecenoate), have been demonstrated. Ruthenium-carbene (called second generation Grubbs) catalyst afforded polymers with unimodal molecular weight distributions (Mn = 12 700, Mw/Mn = 1.85). The polymerization in the presence of a triarm cross-linker, 5-formylbenzene-1,2,3-triyl tris(undec-10-enoate), also afforded polymers with certain uniform network structures.

Изучение низкоэнергетических процессов в полиметилметакрилате и его короткоцепочечных олигомерах методом терагерцовой ИК и рамановской спектроскопии

Based on the data of low-frequency (terahertz) IR and Raman spectroscopy, it was found that low-energy vibrational excitations in PMMA and its oligomers with polymerization degrees n = 2, 7, 9, and 50 are due to small-angle correlated torsion-vibrational dynamics, which prepares the relaxation mobility of macromolecules. The minimum size of the chain segment ("torsion-vibrational segment"), the spectrum of which is identical to the spectrum of a high molecular weight polymer, is determined.

PREPARATION OF NEW POLYETHERPHTHALIMIDES BASED ON CHLORAL DERIVATIVES USING NUCLEOPHILIC POLYNITRO SUBSTITUTION REACTIONS

Non-previously described new bis (3-nitropthalimide) arylenes activated with two carbonyls and containing flexible “bridging” groups, in particular dichloroethylene and ketones between the phthalimide fragments of the dinitrocompounds were obtained. The reactivity of the dinitrophthalimides used is determined, first of all, by the position of (3 or 4) nitro groups, and not by the nature of the Ar residue; monomers containing nitro groups in position 3 are more reactive than systems containing nitro groups in position 4. The interaction of synthesized bis (nitropthalimide) arylenes containing central dichloroethylene and ketone groups between phthalimide fragments and bis-phenolate derivatives of chloral was carried out. Synthesis of polyetherphthalimides using the process of polynitro substitution was carried out under modified conditions with complete absence of moisture. In general, the reactions of polynitro substitution proceed rapidly under relatively mild conditions; when dipolar aprotic solvents or a mixture of them with toluene are used, relatively high molecular weight polymers are formed. It has been established that the rate of dissolution of monomers is an important factor affecting the reaction rate; this determines the possibility of the formation of relatively high-molecular polymers, even with some deviation from the equimolarity of the monomers. As the general conditions for the synthesis of polyetherphthalimides based on synthesized bis (3-nitropthalimide) arylenes and bis-phenols, the optimal conditions were: reaction temperature -60 °C, reaction time -1 h with equimolar monomer ratio and concentration of each of them 0.25 mol/l. The influence of moisture on the synthesis of polyetherimides using the reaction of nucleophilic polynitro substitution was studied. It is shown that the process in the maximally dry system in the DMSO medium or (DMSO / toluene) leads to the formation of polymers with hr at least 0.63 dl/g. All the polymers obtained are readily soluble in dipolar and aprotic solvents. The structure of all the obtained intermediates and monomers was confirmed by elemental analysis and IR spectroscopy. An analysis of the primary thermal characteristics of the polymers obtained showed that they are characterized by relatively high and near destruction temperatures was found that the largest oxygen index (CI) in polymers, where more macromolecules contain more dichloroethylene fragments, and the lowest CI in polymers with a high oxygen content. It is shown that the polymers obtained have satisfactory deformation-strength characteristics. A feature of synthesized polyetherphthalimides is a significant difference between the temperatures of intensive destruction and softening temperatures, which determines the possibility of their processing into products by injection molding.

Targeted Reinforcement of Macrophage Reprogramming Toward M2 Polarization by IL-4-Loaded Hyaluronic Acid Particles.

Alteration of macrophage polarization from inflammatory (M1) to anti-inflammatory (M2) phenotype can have striking implications for the regeneration of injured tissues, treatment of inflammatory diseases, and relief of autoimmune disorders. Although certain cytokines like interleukin (IL)-4 and IL-13 are capable of inducing M2 macrophage polarization, their therapeutic potential in vivo is suffering from low efficacy due to their instability and poor access to target cells. Here, we report the synthesis of IL-4-loaded hyaluronic acid (HA) particle for the targeted delivery of cytokines through the high affinity of HA to CD44 receptors of macrophages. HA carriers composed of low, middle, and high molecular weight (MW) polymers were synthesized using divinyl sulfone (DVS) cross-linking. The MW of HA had a negligible effect on the physicochemical properties and biocompatibility of the macrophages, but as an indicative of M2 polarization, a significant change in the arginase-1 (Arg-1) activity, TNF-α release, and IL-10 secretion was observed for the HA particles prepared with high MW polymers. Therefore, these particles were loaded with IL-4 for simultaneous macrophage targeting and M1 to M2 reprogramming, evidenced by a remarkable increase in the Arg-1 to iNOS ratio, as well as CD163 and CD206 upregulation in the M1 macrophages, which were initially triggered by lipopolysaccharide and interferon-γ.

ASP flooding in tight carbonate rocks

Alkaline-Surfactant-Polymer (ASP) floods can mobilize oil left behind by waterfloods by lowering the interfacial tension. However, conducting such floods in tight carbonate rocks presents several challenges, e.g., polymer transport in low permeability carbonates, presence of divalent ions, geochemical interactions with chemicals and rock surface, pore-scale heterogeneity, and oil-/mixed-wettability. This paper addresses the first three challenges. A systematic study of polymer transport in low permeability carbonate cores was performed. Shearing of high molecular weight polymers and successive filtration treatment were performed to improve polymer size distribution. Single phase polymer transport experiments were performed in low permeability carbonate rocks, and optimum pretreatment method was developed. Surfactant phase behavior and aqueous stability experiments were performed to develop ultralow tension ASP and SP formulations with a reservoir crude oil. ASP and SP corefloods were performed in oil-wet low permeability limestone rocks. The oil recovery, pressure drop, effluent ionic composition, effluent viscosity and effluent surfactant concentrations were measured. PHREEQC simulations were performed to understand geochemical reactions during ASP floods. The polymer treatment procedure was able to successfully transport polymer through low permeability Edwards Yellow limestone cores, but not through Texas Cream limestone due to differences in their pore structures. It was found that polymer hydrodynamic radius must be smaller than the pore throat radii of the rock for successful polymer transport. Therefore, mercury porosimetry data of the porous medium is critical for polymer selection, especially in case of low permeability rocks. Tertiary ASP floods resulted in improving the cumulative oil recovery to 77–87% OOIP, whereas SP flood improved the cumulative oil recovery to 85% in an outcrop core. Surfactant retentions during ASP and SP corefloods were found to be 0.4 mg/g-rock and 0.3 mg/g-rock, respectively, in outcrop cores.

Synthesis of Soluble Star-Shaped Polymers via In and Out Approach by Ring-Opening Metathesis Polymerization (ROMP) of Norbornene: Factors Affecting the Synthesis

The methods for one-pot synthesis of ‘soluble’ star-shaped polymers by sequential living ring-opening metathesis polymerization (ROMP) of norbornene (NBE) and cross-linking (CL) reagent using Mo(CHCMe2Ph)(N-2,6-iPr2C6H3)(OtBu)2 have been explored. The method (called the “in and out” or core-first approach) basically consists of (i) the living ROMP of NBE (formation of arm), (ii) reaction with CL (formation of core), (iii) additional living ROMP of NBE (propagating arms from the core, formation of star), (iv) end-modification via Wittig-type cleavage of metal–carbon double bonds containing polymer chain with aldehyde. Two different approaches in the core formation step (reaction with CL mixed with/without NBE) for synthesis of the high molecular weight star-shaped ROMP polymers with more branching, unimodal molecular weight distributions have been explored in detail. The method (reacting CL with NBE in the core formation step) under highly diluted conditions afforded the high molecular weight polymers with unimodal molecular weight distributions.

Linear and Hyperbranched Copolymers of PEG-Based Acrylates and Methacrylic Acid as pH-Responsive Hydrophobic Drug Carriers

The oral administration of pharmaceuticals is typically preferred over other methods due to its non-intrusiveness and convenience of administration. However, the varying chemical environments of the gastro-intestinal tract pose a challenge in ensuring the stability and inertness of a drug compound until it reaches its target. Polymers that are responsive to pH changes have potential as smart materials for the controlled oral administration of pharmaceuticals. In this study, linear and hyperbranched copolymers of methacrylic acid (MAA) and poly (ethylene glycol) methyl ether methacrylate (PEGMEMA) were synthesized by RAFT polymerization. High molecular weight polymers were produced with PDI values close to 1.0. These smart materials underwent phase changes at pH 5.15-5.6. This property enabled the amphiphilicity of the copolymers to be switched on or off. By doing so inin vitrodrug release studies with ibuprofen as the model hydrophobic drug, the copolymers were able to inhibit drug release in simulated stomach conditions to up to 13% while enhancing drug release in simulated intestinal conditions to up to 75% within 6 hours. These indicate that copolymers based on MAA and PEGMEMA have potential as smart materials for drug delivery applications.

Responses of biological soil crusts to rehabilitation strategies

Biological soil crusts (biocrusts) are common to dryland ecosystems and can influence a broad suite of soil ecological functions including stability and surface hydrology. Due to long recovery times following disturbance, there is a clear need for rehabilitation strategies to enhance the recovery of biocrust communities. Essential to biocrust recovery are exopolysaccharides (EPS): secretions comprised mainly of high molecular weight polymers that protect cyanobacteria and other biocrust organisms from harsh environmental conditions. We examined whether biocrust rehabilitation strategies (combinations of inoculation with surface shading and artificial soil stabilization) promote EPS production. To test if responses varied by soil texture, we measured biocrust recovery on two fine-textured soils (clay and sandy clay loam) in a cool desert ecosystem. Shade coupled with inoculum addition resulted in the highest biocrust recovery, especially on clay soils. Independent of rehabilitation strategies, natural recovery of biocrusts occurred more rapidly on clay soils, reflected by greater increases in chlorophyll a (chl a). Chl a, a proxy for cyanobacterial biomass, was correlated to EPS amounts, suggesting that cyanobacteria are significant contributors to EPS production in biocrust development. Despite the role of EPS in biocrust establishment, EPS amounts had negligible effects on soil stability on the fine soil texture.

Effect of acid treatment on extraction yield and gel strength of gelatin from whiptail stingray (Dasyatis brevis) skin.

Chemical properties of fish gelatins differ from those of conventional mammalian sources, representing an attractive technological alternative for the food industry. Ray filleting generates a considerable amount of skin waste that can be used as a collagen source for gelatin extraction. Thus, this research evaluated the HCl and CH3COOH effect, at 0.01, 0.025, 0.05, 0.075, 0.1, 0.15, and 0.2M, on extraction yield, molecular weight distribution, and gel strength (GS) of whiptail stingray (Dasyatis brevis) skin gelatins. Results showed differences (P < 0.05) between acid type and concentration used. CH3COOH (0.15M) gave the highest extraction yield (7.0% vs. 5.5% at 0.15M HCl) and GS (653 ± 71g vs. 619.5 ± 82g at 0.2M HCl). Gelatin electrophoretic profile from CH3COOH revealed α-/β-components and high molecular weight (> 200kDa) polymers. Ray gelatin GS was higher than commercial bovine gelatin, suggesting its possible use for technological food applications.

Sterics versus electronics: Imine/phosphine-oxide-based nickel catalysts for ethylene polymerization and copolymerization

A series of imine/phosphine-oxide ligands was synthesized and characterized. These ligands are easily prepared in a modular fashion, with positions that are independently tunable. The corresponding nickel allyl complexes were synthesized and serve as single-component catalysts for the homopolymerization of ethylene. It is generally believed that sterically bulky substituents lead to high polymer molecular weights during olefin polymerization. In this system, however, catalysts bearing the sterically bulky dibenzhydryl substituent afforded polyethylenes with much lower molecular weights than those bearing the sterically unhindered isopropyl substituent. Based on control experiments, theoretical calculations, and literature evidence, we propose that electronic effects override steric effects and play dominant roles in this nickel system. Efficient copolymerizations of ethylene with methyl 10-undecenoate and 6-chloro-1-hexene were also facilitated by this system without the need for any cocatalyst or protecting agent.