Vinyl Chains Research Articles

Early bird gets the network: The relative importance of reactivity ratios, Ψ parameter, and crosslinker level on gel formation in FRP

AbstractNetwork topology is manipulated in free‐radical copolymerization via proper selection of crosslinker type and its respective properties when paired with specific monomers. Our prior work has focused on the impact of the reduced reactivity parameter Ψ applied to a pendent vinyl, characteristic for each monomer/crosslinker pair, yet here we assess the relative importance of the comonomer reactivity ratios to see whether one factor can counterbalance the other. The traditional reactivity ratio determines when the crosslinker molecule is incorporated into the polymer backbone, while the reduced reactivity Ψ parameter relates to the efficiency of the resulting pendent side chain vinyl being utilized to form a crosslink node at some later point during the polymerization. Both factors are then contrasted with simply the overall loading of crosslinker. Either n‐butyl methacrylate (n‐BMA) or styrene (STY) was chosen as a primary backbone monomer to copolymerize with one of three crosslinkers: 1,4‐butanediol dimethacylate (BDDMA), 1,4‐butanediol diacrylate (BDDA), or divinylbenzene (DVB). Both kinetics and gel can be most dramatically boosted when a crosslinker is applied having a reactivity ratio favouring early insertion. This in turn leads to an earlier onset of gel formation, which ultimately results in greater final gel content. This amplification of both kinetics and gel can overcome an otherwise small Ψ due to crosslinker or main monomer choice. This reactivity ratio effect was further confirmed by Monte Carlo simulations. By whatever mechanism (higher Ψ, lower rA, or higher crosslinker level), earlier onset of gelation produces more gel overall and a tighter network topology.

Ion-Specific Water–Macromolecule Interactions at the Air/Aqueous Interface: An Insight into Hofmeister Effect

The specificity of ions in inducing conformational changes in macromolecules is introduced as the Hofmeister series; however, the detailed underlying mechanism is not comprehensible yet. We utilized surface-specific sum frequency generation (SFG) vibrational spectroscopy to explore the Hofmeister effect at the air/polyvinylpyrrolidone (PVP)/water interface. The spectral signature observed from the ssp polarization scheme reveals ion-specific ordering of water molecules following the Hofmeister series attributed to the ion-macromolecule interactions. Along with this, the presence of ions does not reflect any significant influence on the structure of the PVP macromolecule. However, the ppp-SFG spectra in the CH-stretch region reveal the impact of ions on the orientation angle of vinyl chain CH2-groups, which follows the Hofmeister series: SO42- > Cl- > NO3- > Br- > ClO4- > SCN-. The minimal orientation angle of CH2-groups indicates significant reordering in PVP vinyl chains in the presence of chaotropic anions ClO4-, and SCN-. The observation is attributed to the ion-specific water-macromolecule interactions at the air/aqueous interface. It is compelling to observe the signature of spectral blue shifts in the OH-stretch region in the ppp configuration in the presence of chaotropic anions. The origin of spectral blue shifts has been ascribed to the existence of weaker interactions between the interfacial water molecules and the backbone CH- and CH2-moieties of the PVP macromolecules. The ion-specific modulation in water-macromolecule interactions is endorsed by the relative propensity of anion's adsorption toward the air/aqueous interface. The experimental findings highlight the existence and cooperative participation of ion-specific water-macromolecule interactions in the mechanism of the Hofmeister effect, along with the illustrious ion-water and ion-macromolecule interactions.

Impact of Raw Phenyl Silicone Rubber Parameters on ethod Vulcanized Phenyl Silicone Rubber

Based on the structure of raw phenyl silicone rubber and performance of vulcanized rubber, the properties of raw and vulcanized phenyl silicone rubber are tested in this study. The relationship between raw rubber parameters and the influence of raw rubber properties on the performance of vulcanized rubber are also analyzed. Conclusions are as follows: (1) The viscosity average molecular weight of the raw silicone rubber measured by Ubbelohde viscometer and gel permeation chromatography (GPC) mdiffers relatively greatly, with the result of Ubbelohde viscometer higher than that of GPC. (2) The glass transition temperature of raw silicone rubber is significantly affected by the molar content of phenyl chain (phenyl content) in its structure. In a good linear relationship with phenyl content, it increases as the phenyl content increases. (3) The static glass transition temperature of raw rubber measured by differential scanning calorimetry (DSC) is 0-15 °C lower than the dynamic glass transition temperature measured by dynamic thermo-mechanical analyzer (DMA). (4) Mooney viscosity increases with the increase of the viscosity average molecular weight of raw rubber. (5) As phenyl content rises from 20 % to 40 %, the damping peak loss factor of vulcanized rubber increases from 0.4 to 0.7 and the damping peak temperature increases from -90 °C to -40 °C. (6) As the molar content of vinyl chain (vinyl content) is raised from 0.1 % to 0.6 %, the hardness of vulcanized rubber is boosted from 45 to 65, and the tensile strength decreases from 12 MPa to 6 MPa. (7) With the increase of vinyl content from 0.1 % to 0.4 %, the tear strength of vulcanized rubber decreases from 45 kN/m to 25 kN/m. (8) The vinyl content has an obvious impact on the damping performance of vulcanized rubber at high temperatures. When vinyl content increases from 0.1 % to 0.5 %, the damping property of the vulcanized rubber under high temperature drops from 0.25 to 0.1. (9) The compression set of vulcanized rubber decreases with the increase of vinyl content of raw rubber.

Substrate Specificity of the Highly Thermostable Esterase EstDZ3.

Esterases are among the most studied enzymes, and their applications expand into several branches of industrial biotechnology. Yet, despite the fact that information on their substrate specificity is crucial for selecting or designing the best fitted biocatalyst for the desired application, it cannot be predicted from their amino acid sequence. In this work, we studied the substrate scope of the newly discovered hydrolytic extremozyme, EstDZ3, against a library of esters with variable carbon chain lengths in an effort to understand the crucial amino acids for the substrate selectivity of this enzyme. EstDZ3 appears to be active against a wide range of esters with high selectivity towards medium- to long-carbon chain vinyl esters. In-silico studies of its 3D structure revealed that the selectivity might arise from the mainly hydrophobic nature of the active site's environment.

Synthesis, characterization, and functionalization of superadhesive melamine formaldehyde polyvinylpyrrolidone resins doped with metallic and graphene oxide nanoparticles for better industrial applications

AbstractStructure of melamine‐formaldehyde‐polyvinylpyrrolidone (MFP) polymer resin prepared with melamine, formaldehyde, polyvinyl pyrrolidone (PVP) at was determined using FTIR, 1H NMR, and 13C NMR spectroscopy. Physicochemical properties and thermal stability were analyzed with dynamic light scattering (DLS) and thermogravimetric analysis (TGA) respectively. 1H NMR spectra showed doublet at 3.13 and 3.17 ppm due to neighboring electron‐deficient nitrogen and electron density of bridged carbon atoms. The 13C NMR have infrared vinyl chain, melamine, and pyrrolidone peak for , 48.72 ppm depicts C atom of between O and C atoms. Peak at 17.50 ppm inferred terminal of vinyl chain. FTIR stretching frequencies at 3426.38 and 2915.5 cm−1 vibrations depicted (tertiary amine), and group of vinyl chain of PVP, respectively. New band at 2350 cm−1 inferred –CH2 of formaldehyde attached with O atoms of PVP. MFP was doped with Fe3O4 (magnetic nanoparticles = MNPs), CaS (calcium sulfide), CaO, and graphene nanoparticles for reinforcement. Encapsulated Fe3O4–MFPR, CaS–MFPR, graphene oxide–MFPR are compared with MFPR alone. TGA inferred higher stability of Fe3O4–MFPR, CaS–MFPR.

Improvement of physical and mechanical properties of poplar wood via immobilization of rosin by grafting of vinyl chains

Rosin is renewable biomass with the potential to enhance wood properties. However, its high leaching rate restricts the durability of rosin impregnation. To immobilize rosin in wood structure, polymeric rosin (R-GMA) with vinyl chains was synthesized by the chemical reaction between rosin and glycidyl methacrylate (GMA) in the present work. Poplar wood was impregnated by different concentrations of the R-GMA. Due to the initiator and high temperature, R-GMA polymerized both in wood cell lumens and cell walls through radical polymerization. The polymer loading gradually increased with the concentration increased. As a result, the ASE can reach 50% with a WPG of 54%. Compared with the control sample, the 7-day water uptake of treated wood (WPG was 54%) was reduced by 55%. At 20% R-GMA concentration, the MOR, MOE, and CS of wood were increased by 23.5%, 46.6%, and 66%, respectively. The dynamic wettability of wood was remarkably reduced by the R-GMA impregnation. The lightness of the wood surface was reduced and the surface color became reddish and yellowish after modification. Additionally, the thermal stability of wood was marginally improved by the filling of R-GMA polymers.

Preparation and characterization of composites using blends of divinylbenzene‐based hyperbranched and linear functionalized polymers

AbstractIn this study, hyperbranched polymers were explored as matrix modifiers to create E‐glass fiber (GF) reinforced polymer composites with enhanced mechanical properties. Hyperbranched polymers have lower viscosities than their linear equivalents, potentially providing enhanced fiber wet out leading to improved stress transfer. Hyperbranched (HB), hydrogenated hyperbranched (H‐HB), and linear functional (LF) divinyl benzene were blended with linear polystyrene (LP) to form a range of composite matrix formulations. Blends of the HB and LP polymers were used since the neat hyperbranched polymers alone proved to be highly brittle when formed into a film. A neat LP‐GF composite was also prepared as control. Of the three matrix modifiers considered, only the H‐HB provided an improvement in mechanical properties in comparison to LP‐GF. With the addition of 10 and 20 wt% H‐HB, respectively, the flexural modulus increased by 25% (p < 0.05) and 36% (p < 0.05) and flexural strength increased by 15% (p < 0.05) and 31% (p < 0.005). The enhanced mechanical properties were attributed to better fiber wetting along with crystallization observed with the addition of 20 wt% H‐HB. The non‐reactive ethyl (CH2CH3) chain end group of the macromolecular H‐HB resulted in a plasticizing effect, which in turn improved its wettability. The LP:HB polymer blends, on the other hand, underwent crosslinking due to the presence of the vinyl (CHCH2) chain ends leading to poor wettability in comparison to the LP:H‐HB and LP:LF blended films and hence lower mechanical properties.

Enhancing Performance of a Bis(arylimino)pyridine‐Iron Precatalyst for Ethylene Polymerization by Substitution with a 2,4‐Bis(4,4′‐dimethoxybenzhydryl)‐6‐methylphenyl Group

AbstractA series of unsymmetrical 2‐(2,4‐bis(bis(4‐methoxyphenyl)methyl)‐6‐MeC6H2N)‐6‐(1‐(arylimino)ethyl)pyridine‐iron halides has been synthesized and characterized. The molecular structure of two representative species was determined by the single‐crystal X‐ray diffraction. Activated with either MAO or MMAO, the precatalysts displayed high activity, reaching 2.19×107 g PE (mol Fe)−1 h−1at 60 °C in ethylene polymerization. The microstructural analysis of the polymers obtained indicates highly linear polyethylene containing a vinyl chain end.

Synthesis of vinyl polymers substituted with 2-propanol and acetone and investigation of their reversible hydrogen storage capabilities

Developing a safe hydrogen carrier without the risks of high pressures and toxicities is an issue of significant urgency. In this study, we prepared a polymeric hydrogen carrier with high thermal stability by incorporating 2-propanol and acetone units into polymers. Poly(methyl vinyl ketone) with a high molecular weight (~105) was synthesized via bulk polymerization of methyl vinyl ketone and then dehydrogenated in one step to give poly(3-buten-2-ol) in high yield. Reversible hydrogen fixation and release by these polymers were achieved with full conversion under mild conditions (80–180 °C, ≦3 atm hydrogen pressure). A simple temperature-dependent hydrogenation/dehydrogenation cycle that operated at temperatures higher than the boiling points of 2-propanol and acetone in the presence of an iridium complex catalyst was established by virtue of having these groups as pendants of the vinyl chain, with a compact repeating unit to maximize the mass hydrogen storage density of 2.8 wt%. Polymeric hydrogen carrier with high thermal stability was prepared by incorporating isopropanol and acetone units into polymers via a facile reaction process. Reversible hydrogen fixing and releasing were achieved with full conversion under mild conditions. Temperature-dependent facile hydrogenation and dehydrogenation cycle that operated at temperatures higher than the boiling points of isopropanol and acetone, in the presence of an iridium complex catalyst, was established by virtue of having these groups as pendants of the vinyl chain, with a compact repeating unit to maximize the mass hydrogen storage density of 2.8 wt%.

Umbelliferone esters with antibacterial activity produced by lipase-mediated biocatalytic pathway.

The present report describes the enzymatic acylation of umbelliferone with different vinyl esters as acyl donors biocatalyzed by the commercial lipase Novozym® 435, and the investigation for their antibacterial activity against ATCC and clinical strains isolated from hospital infection sites. The umbelliferone esters (1-5) were synthesized through the acylation reaction of 7-hydroxy-2H-chromen-2-one with different long chain vinyl esters catalyzed by the lipase Novozym 435. The reaction conditions were: 10% Novozym 435; tetrahydrofuran:acetone (3:1) for the reactions with acetate, propionate and butyrate vinyl esters 50-90% conversion, and (9:1) for decanoate and laurate vinyl esters 10-15% conversion; acyl donor/umbelliferone molar ratio of 10:1 and 60°C. All the umbelliferone esters were characterized NMR and (HRMS). The antibacterial activity of the products were tested using the broth microdilution method in order to determine the minimum inhibitory concentration (MIC). The results displayed by 7-laurate and 7-decanoate-umbelliferone esters showed the highest antibacterial potential, with 1mM inhibitory activity for ATCC 33591, a methicillin and oxacillin resistant Staphylococcus aureus strain. They were also able to inhibit gram-negative bacterial strains, such as Pseudomonas aeruginosa (MIC 0.5mM) and Klebsiella pneumoniae (MIC 1mM). In addition, 7-laurate- and 7-decanoate-umbelliferone esters were able to inhibit all clinical strains (MIC 1mM; except 7-laurate-umbelliferone in which MIC 0.5mM against 55a). This is the first study performing the biocatalysis of umbelliferone followed by the purification of the products and the antibacterial evaluation.

Synthesis of ABC Miktoarm Star Copolymers via Organocatalyzed Living Radical Polymerization

ABC-type miktoarm star copolymers are synthesized using a single living radical polymerization (organocatalyzed living radical polymerization) via a "combinatorial" approach. The arm A is poly(butyl acrylate), the arm B is poly(methyl methacrylate), and the arm C encompasses hydrophobic and hydrophilic polyacrylates. A poly(butyl acrylate) with a vinyl chain end (macromonomer) is synthesized. A poly(methyl methacrylate) is subsequently connected to the reactive vinyl group to generate diblock copolymer. From the junction of the diblock copolymer, polymer C grew to yield star copolymers. An amphiphilic star copolymer is also synthesized, and its self-assembly structure is studied in an aqueous solution.

Intramolecular Photocycloaddition of 2(5 H)-Furanones to Temporarily Tethered Terminal Alkenes as a Stereoselective Source of Enantiomerically Pure Polyfunctionalyzed Cyclobutanes.

Allyloxymethyloxymethyl and 4-pentenoyloxymethyl substituents have been used as tethering groups to study the intramolecular [2 + 2] photocycloaddition of chiral 5-substituted 2(5 H)-furanones. The photoreactions proceed in good yield and provide the expected regio- and diastereoselective tricyclic compounds with complementary regioselectivity, which depends on whether the vinyl chain is attached to the furanone by an acetal or an ester linkage. Computational simulations agree with experimental observations and indicate that the origin of the different observed regioselectivity in the intramolecular photochemical reaction of lactones 5 and 6 arises from the relative stability of the initial conformers. The synthetic potential of the enantiomerically pure photoadducts is illustrated by preparing an all- cis 1,2,3-trisubstituted cyclobutane bearing fully orthogonally protected hydroxyl groups.

Structural Elucidation and Bioinspired Total Syntheses of Ascorbylated Diterpenoid Hongkonoids A-D.

Hongkonoids A-D (1-4), the first example of ascorbylated terpenoids featuring a unique 5,5,5-fused tricyclic spiroketal butyrolactone moiety and diterpenoid-derived long chain, were isolated from Dysoxylum hongkongense. Their structures were unambiguously assigned by a combination of spectroscopic data, chemical degradation, X-ray crystallography, CD analysis, and total synthesis. The total syntheses of compounds 1-4 were effectively accomplished by a convergent strategy with the longest linear sequences of 12-14 steps and overall yields of 5.4-9.6%. Notably, we exploited a bioinspired one-pot method to construct the key intermediate 14 from an easily made compound 12 by involving the cascade reactions of an elaborate Claisen rearrangement, deprotections, and a 5-exo-trig cyclization. The desired major epimer 14a was then transformed to the main building block 21. Assembly of 21 and the long chain vinyl iodide 7 was made by an NHK coupling reaction to furnish the framework of 1-4. Some of the hongkonoids and/or synthetic analogs showed significant to moderate inhibitory activities against NF-κB, 11β-HSD1, and sterol synthesis. The most active NF-κB inhibitor 34 exhibited distinct inhibition on the LPS-induced inflammatory responses in RAW 246.7 and primary BMDM cells.

Incorporation of Kojic Acid-Azo Dyes on TiO2 Thin Films for Dye Sensitized Solar Cells Applications

Sensitization of heavy metal free organic dyes onto TiO2 thin films has gained much attention in dye sensitized solar cells (DSSCs). A series of new kojic acid based organic dyes KA1–4 were synthesized via nucleophilic substitution of azobenzene bearing different vinyl chains A1–4 with kojyl chloride 4. Azo dyes KA1–4 were characterized for photophysical properties employing absorption spectrometry and photovoltaic characteristic in TiO2 thin film. The presence of vinyl chain in A1–4 improved the photovoltaic performance from 0.20 to 0.60%. The introduction of kojic acid obtained from sago waste further increases the efficiency to 0.82–1.54%. Based on photovoltaic performance, KA4 achieved the highest solar to electrical energy conversion efficiency (η = 1.54%) in the series.

Synthesis, radiolabeling and preclinical evaluation of a [11C]GMOM derivative as PET radiotracer for the ion channel of the N-methyl-D-aspartate receptor

IntroductionPresently available PET ligands for the NMDAr ion channel generally suffer from fast metabolism. The purpose of this study was to develop a metabolically more stable ligand for the NMDAr ion channel, taking [11C]GMOM ([11C]1) as the lead compound. Methods[11C]1, its fluoralkyl analogue [18F]PK209 ([18F]2) and the newly synthesized fluorovinyloxy analogue [11C]7b were evaluated ex vivo in male Wistar rats for metabolic stability. In addition, [11C]7b was subjected to a biodistribution study and its affinity (Ki) and lipophilicity (logD7.4) values were determined. ResultsThe addition of a vinyl chain in the fluoromethoxy moiety did not negatively alter the affinity of [11C]7b for the NMDAr, while lipophilicity was increased. Biodistribution studies showed higher uptake of [11C]7b in forebrain regions compared with cerebellum. Pre-treatment with MK-801 decreased the overall brain uptake significantly, but not in a region-specific manner. 45min after injection 78, 90 and 87% of activity in the brain was due to parent compound for [11C]1, [18F]2 and [11C]7b, respectively. In plasma, 26–31% of activity was due to parent compound. ConclusionComplete substitution of the alpha-carbon increased lipophilicity to more favorable values. Substitution of one or more hydrogens of the alpha-carbon atom in the methoxy moiety improved metabolic stability. In plasma, more parent compound was found for [18F]2 and [11C]7b then for [11C]1, although differences were not significant. At 45min, significantly more parent [18F]2 and [11C]7b was measured in the brain compared with [11C]1.

Effects of End-Groups on Photophysical Properties of Poly(9,9-di-n-octylfluorene-2,7-vinylene)s Linked with Metalloporphyrins: Synthesis and Time-Resolved Fluorescence Spectroscopy

A series of poly(9,9-di-n-octyl-fluorene-2,7-vinylene)s (PFVs) containing metalloporphyrins at the chain ends with different conjugation lengths (ca. average 8 or 24 FV repeat units), PFV-[Por(M)]2, have been prepared by olefin metathesis of the vinyl chain ends in PFVs (prepared by acyclic diene metathesis polymerization by ruthenium–carbene catalysts) using molybdenum–alkylidene catalyst (reagent) followed by Wittig-type cleavage with formyl porphyrin containing different metal ions [Zn(II), Cu(II), Ni(II), and Pt(II)]. Effects of the metalloporphyrins on photophysical properties of PFVs were studied by means of time-resolved fluorescence spectroscopy. The fluorescence spectral profile from PFV moiety in all the polymers with end-porphyrins was almost identical to that of the reference PFV. However, fluorescence quantum yields were remarkably lower, depending upon the central metal ion and the chain length. The observed reduction of the quantum yields is ascribed to intramolecular energy transfer to the...

Kinetic Studies on Bulk Atom Transfer Radical Polymerization of Styrene

The long chain vinyl end-functional polystyrene has been synthesized in bulk polymerization method using atom transfer radical polymerization (ATRP) with Undecenyl-2-Bromopropionate (UnBP) and CuCl/bypyridine catalytic system. The polymerizations demonstrate an increase in molecular weight and conversion in direct proportion to the polymerization time by consumed monomer which exhibited first-order kinetics. This study concludes the simple kinetics of polystyrene synthesized by ATRP using initiator and ligand-to-copper(I) halide was found to be 1:2:1, which tentatively indicates that the coordination sphere of the active copper(I) center contains two bipyridine ligands. The propagation rate has been investigated for long range of time for ensuring that the rate of radical combination or disproportionation is sufficiently less.

Cumulative effect of hydrophobic PLMA and surface epoxide groups in composite polymer particles on adsorption behavior of congo red and direct red-75

Industrial application of hydrophobic materials is numerous particularly as adsorption beads to remove organic pollutants. In this research combined effect of hydrophobicity and reactive epoxide group on the adsorption behavior of dye molecules by composite polymer particles was investigated. Lauryl methacrylate (LMA) a poor water soluble long chain vinyl monomer is commercially available. Polystyrene/poly(LMA-divinyl benzene) or PS/P(LMA-DVB) composite seed particles were first prepared by slightly modified activated swelling of micron-sized PS seed particles utilizing either water or water-ethanol dispersion medium. The influence of poly(vinyl alcohol) (PVA) as steric stabilizer on the size and size distribution was evaluated. The poor solubility of LMA in the continuous phase hindered the homogeneous swelling of PS particles even in the presence of ethanol (5% w/w) and resulted in fairly polydispersed PS/P(LMA-DVB) composite seed particles. The composite seed particles were then functionalized with epoxide group by seeded polymerization of glycidyl methacrylate (GMA) to produce PS/P(LMA-DVB)/PGMA composite polymer particles. The epoxide functionalized PS/P(LMA-DVB)/PGMA composite polymer particles were used to adsorb two kinds of azo dyes, congo red (CR) and direct red-75 (DR-75). The effects of initial dye concentration at 303 and 323K on adsorption behavior were investigated and the adsorption was explained by adsorption isotherms. Temperature dependent adsorption measurements were also carried out at identical initial dye concentration. The adsorption results showed that inclusion of reactive epoxide group on/near the surface of hydrophobic PS/P(LMA-DVB) composite seed particles improved the adsorption capacity of dye molecules.

One-pot Synthesis of End-functionalized Conjugated Polymers by Combined Acyclic Diene Metathesis (ADMET) Polymerization Using Molybdenum Catalyst with Wittig-type Coupling

Precise, one-pot synthesis of end-functionalized conjugated polymers, poly(9,9-di-n-octyl-fluorene vinylene)s (PFVs), have been prepared by acyclic diene metathesis (ADMET) polymerization followed by Wittig-type coupling with aldehyde in the presence of molybdenum-alkylidene catalyst, Mo(CHMe2Ph)(N-2,6-Me2C6H3)[OC(CH3)(CF3)2]2 (Mo cat.). Further addition of Mo cat. after the ADMET polymerization was necessary for completion of olefin metathesis (with the vinyl chain end) and for exclusive end-functionalization by the subsequent coupling. Various end-functionalities could be introduced without purification or isolation by this one-pot methodology.

Termination Events in Sterically Hindered Metallocene-Catalyzed Olefin Oligomerizations: Vinyl Chain Ends in Oligooctenes

Sterically hindered rac-dimethylsilylbis(2-methyl-3-propylindenyl)hafnium dimethyl (1) activated with dimethylanilinium tetrakis(perfluoronaphthylborate) (2) gave high levels of allylic chain ends in the oligomerization of higher α-olefins such as 1-octene. Solution oligomerization of 1-octene in hexanes yielded atactic macromers with roughly 60 mol % vinyl termination and lesser amounts of trisubstituted (25%) and vinylidene (20%) termination. To further probe the mechanism of elimination, oligomerization with 1-octene (1-13C) was performed and the label distribution determined by 13C NMR spectroscopy. Enhancement of the methylene (H2C═C−) vinyl resonance was observed, supporting β-hexyl elimination as a possible mechanistic step and ruling out allylic formation by a chain-walking mechanism prevalent in late-transition-metal systems.