Monomer-isomerization polymerization. V. Effects of transition metal compounds on monomer-isomerization polymerizations of butene-2 and pentene-2

In order to clarify the correlation between polymerization and monomer isomerization in the monomer-isomerization polymerization of β-olefins, the effects of some transition metal compounds which have been known to catalyze olefin isomerizations on the polymerizations of butene-2 and pentene-2 with Al(C₂H₅)₃–TiCl₃ or Al(C₂H₅)₃–VCl₃ catalyst have been investigated. It was found that some transition metal compounds such as acetylacetonates of Fe(III), Co(II), and Cr(III) or nickel dimethylglyoxime remarkably accelerate these polymerizations with Al(C₂H₅)₃–TiCl₃ catalyst at 80°C. All the polymers from butene-2 were high molecular weight polybutene-1. With Al(C₂H₅)₃–VCl₃ catalyst, which polymerizes α-olefins but does not catalyze polymerization of β-olefins, no monomer-isomerization polymerizations of butene-2 and pentene-2 were observed. When Fe(III) acetylacetonate was added to this catalyst system, however, polymerization occurred. These results strongly indicate that two independent active centers for the olefin isomerization and the polymerizations of α-olefins were necessary for the monomer-isomerization polymerizations of β-olefins.     

Effect of central spacer chain structure on cationic cyclopolymerization tendency of divinyl ethers

To clarify the effects of the central spacer chain structure of divinyl ethers on their cationic cyclopolymerization tendencies, 1,4‐bis[(2‐vinyloxy)ethoxy]benzene ( 1 ), 1,4‐bis[(2‐vinyloxy)ethoxy]butane ( 2 ), 1,6‐bis[(2‐vinyloxy)ethoxy]hexane ( 3 ), 1,8‐bis[(2‐vinyloxy)ethoxy]octane ( 4 ), and 1,4‐bis[(4‐vinyloxy)butoxy]butane ( 5 ) were polymerized with the hydrogen chloride/zinc chloride (HCl/ZnCl₂) initiating system in methylene chloride (CH₂Cl₂) at 0 °C at low initial monomer concentration ([M]₀ = 0.15 M). The polymerizations of divinyl ethers 2 and 3 gave soluble polymers quantitatively. In contrast, the polymerizations of divinyl ethers 1 , 4 , and 5 underwent gel formation at high monomer conversion. The content of the unreacted vinyl groups of the obtained soluble polymers was measured by ¹H NMR spectroscopy. Judging from the relatively low vinyl contents of the polymers produced even in the early stage of the polymerization (monomer conversion < ～20%), the cyclopolymerization occurred to some extent for 2 , 3 , and 4 . On the contrary, the polymers produced from 1 and 5 exhibited the relatively high vinyl content, indicating that the cyclopolymerization tendencies of 1 and 5 were lower than those of 2 , 3 , and 4 . These results are discussed in terms of the structural variety of the spacer chains: (1) the presence of benzene ring ( 1 vs 2 ), (2) their length ( 2 vs 3 and 4 ), and (3) the position of ether oxygen ( 4 vs 5 ). © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4002–4012, 2002     

Gel formation in cationic polymerization of divinyl ethers. III. Effect of oligooxyethylene chain versus oligomethylene chain as central spacer units

Cationic polymerizations of two series of divinyl ethers were carried out to clarify the effects of their central spacer chain structure on their crosslinking polymerization behavior. One series of the monomers involves divinyl ethers with an oligooxyethylene central spacer chain: diethylene glycol divinyl ether ( O‐3 ), triethylene glycol divinyl ether ( O‐4 ), tetraethylene glycol divinyl ether ( O‐5 ), pentaethylene glycol divinyl ether ( O‐6 ), and heptaethylene glycol divinyl ether ( O‐8 ) (see Scheme 1 ). The other series includes divinyl ethers with an oligomethylene central spacer chain: 1,4‐butanediol divinyl ether ( C‐4 ), 1,6‐hexanediol divinyl ether ( C‐6 ), and 1,8‐octanediol divinyl ether ( C‐8 ). Cationic polymerizations of these monomers were carried out with the hydrogen chloride/zinc chloride (HCl/ZnCl₂) initiating system in methylene chloride (CH₂Cl₂) at ?30 °C ([Monomer]₀ = 0.15 M; [HCl]₀ = 5.0 mM; [ZnCl₂]₀ = 0.5 mM). The polymerizations of the oligomethylene‐based divinyl ethers C‐6 and C‐8 caused gel formation at high monomer conversions (～90%), whereas C‐4 formed soluble polymers even at almost 100% monomer conversion. The oligooxyethylene‐based divinyl ethers O‐3 , O‐4 , O‐5 , and O‐6 underwent gel‐free polymerizations up to 100% monomer conversion and O‐8 did so at least up to ～80% conversion. The content of unreacted pendant vinyl groups of the obtained soluble polymers was measured by ¹H NMR spectroscopy. In the polymerizations of the oligomethylene‐based divinyl ethers ( C‐4 , C‐6 , and C‐8 ), the vinyl contents of the polymers decreased monotonously with increasing monomer conversion, and their number‐average molecular weights (M_n's) and polydispersity ratios (M_w/M_n's) increased considerably just before the gelation occurred. On the contrary, the vinyl contents of the polymers obtained from the oligooxyethylene‐based divinyl ethers ( O‐3 , O‐4 , O‐5 , O‐6 , and O‐8 ) decreased steeply even in the early stage of the polymerizations and almost all the pendant vinyl ether groups were consumed in the soluble polymers at the final stage of the polymerizations. The oligooxyethylene spacer units adjacent to the pendant unreacted vinyl ether groups may solvate intramolecularly with the carbocationic active center to accelerate frequent occurrence of intramolecular crosslinking reactions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3729–3738, 2004     

A method for the prediction of metallocene-type catalyst activity in olefin (co)polymerisation reactions

The use of ultraviolet/visible spectroscopy (UV-Vis) for the prediction of metallocene catalyst potential for the polymerisation of olefins is described. Upon addition of methylaluminoxane (MAO) to rac-[C₂H₄(1-indenyl)₂ZrCl₂] ([Al]/[Zr] = 200) the ligand-to-metal charge transfer band shows a hypsochromic shift while a bathochromic shift is observed when more MAO is added ([Al]/[Zr] = 2000). These shifts can be explained by assuming that methylation of the zirconocene by MAO occurs in the case of [Al]/[Zr] = 200 while a cationic complex, the active catalytic system, is formed upon addition of more MAO, e.g., [Al]/[Zr] = 2000.     

Hydrolytic selenoxide elimination reaction for the preparation of 2-chloro-1-olefins

2-Chloro-1-olefins were synthesized in a regiocontrolled way from terminal olefins by a sequence involving Markownikoff-addition of PhSeCl, chlorination of the resulting β-chloroalkyl phenyl selenides with SO₂Cl₂ and, after recrystallization, hydrolysis/selenoxide elimination in a two-phase system.     

Polymerization of phenylacetylene catalysed by RhTp(cod) and RhBp(cod) in ionic liquids: effect of alcohols and of tetraammonium halides

RhTp(cod) ( 1 ) and RhBp(cod) ( 2 ), almost inactive in CH₂Cl₂, became good catalysts of phenylacetylene polymerization in ionic liquids ([bmim]Cl, [bmim]BF₄: bmim = 1‐butyl‐3‐methylimidazolium, [mokt]BF₄: mokt = 1‐methyl‐3‐oktylimidazolium, [bumepy]BF₄: 1‐butyl‐4‐methylpyridinium) and in CH₂Cl₂ in the presence of tetraammonium halides ([R₄N]X, R = Bu, Et; X = Cl, Br). The highest yields of polyphenylacetylene with catalyst 1 were obtained in [bmim]Cl at 65°C (64% after 2 h) and in [mokt]BF₄ at 20°C (56% after 24 h). In alcohols (CH₃OH, (CH₃)₂CHOH, (CH₃)₃COH) as solvents, up to 100% of the polymer was produced. When a mixture of an ionic liquid and CH₃OH was used as the reaction medium, the polymer yield was similar to the yield achieved in an ionic liquid only, but the molecular weight increased remarkably. Tetraammonium salts, [R₄N]X, are co‐catalysts for 1 , and the yield of the polymer increased in the order [Et₄N]Br < [Bu₄N]Br < [Et₄N]Cl < [Bu₄N]Cl. Polymers with molecular weights from 6900 to 38 800 Da were obtained with catalyst 2 in [R₄N]Br or [R₄N]Cl, whereas in ionic liquids ([bmim]Cl, [bmim]BF₄) the corresponding molecular weights were higher, from 51 300 to 60 300 Da. Copyright © 2004 John Wiley & Sons, Ltd.     

High-Field 1H-NMR Study of Poly(Vinyl Chloride) Defects

Radical poly(vinyl chlorides), (PVC), obtained in bulk and in suspension polymerizations, and their low molecular weight extracts have been thoroughly studied by high-field NMR to obtain better qualitative and quantitative analyses of their structural defects. Assignments have been achieved by ¹H-¹H decoupling experiments and hyperfine spectral structure analysis of model compounds and low molecular weight extracts. Strong effects of the nature of the solvents used in ¹H-NMR analysis were observed. Most of the defects of these radical PVC's have been quantitatively estimated in terms of average number values in correlation with their [Mbar]_n. End-groups of type [I'] (= ?CH₂?CH[dbnd]CH[sbnd]CH₂C1) are about 0.5 per chain; internal double bonds can only be estimated by difference, and their amount increases with increasing conversion. A very low quantity of vinyl chain end [I'] ([dbnd] [sbnd]CHC1[sbnd]CH[dbnd]CH₂) has been found only in low molecular weight extracts. For the three probable saturated chloromethyl ends [II] ([dbnd][sbnd]CHCl[sbnd]CH₂Cl), [III] ([dbnd] [sbnd]CH₂[sbnd]CH₂Cl), and [IV] ([dbnd] >CH[sbnd]CH₂C1), only [II] and [III] were definitely identified. Finally, in taking into account all the endgroups, it has been concluded that branches would be grafted throughout the process. On the average, 4 to 5 branches have been found per chain of high molecular weight PVC.     

Construction of Cyclobutanes by Multicomponent Cascade Reactions in Homogeneous Solution through Visible-Light Catalysis

[2+2] Photocycloaddition of two olefins is a general method to assemble the core scaffold, cyclobutane, found in numerous bioactive molecules. A new approach to synthesize cyclobutanes through multicomponent cascade reactions by merging aldol reaction and Witting reaction with visible-light-induced [2+2] cycloaddition is reported. An array of cyclobutanes with high selectivity has been achieved from commercially available aldehydes, ketones (or phosphorus ylide), and olefins with visible-light irradiation of a catalytic amount of (fac-tris(2-phenylpyridinato-C₂,N)iridium) ([Ir(ppy)₃]) at room temperature. Control experiments and spectroscopic studies revealed that the triplet–triplet energy transfer from the excited [Ir(ppy)₃]* to enones, generated in situ from aldehyde and ketone or aldehyde and phosphorus ylide, is responsible for these simple and efficient muticomponent transformations.     

Use of water in aiding olefin/paraffin (liquid + liquid) extraction via complexation with a silver bis(trifluoromethylsulfonyl)imide salt

This paper describes the extraction of C₅–C₈ linear α-olefins from olefin/paraffin mixtures of the same carbon number via a reversible complexation with a silver salt (silver bis(trifluoromethylsulfonyl)imide, Ag[Tf₂N]) to form room temperature ionic liquids [Ag(olefin)_x][Tf₂N]. From the experimental (liquid + liquid) equilibrium data for the olefin/paraffin mixtures and Ag[Tf₂N], 1-pentene showed the best separation performance while C₇ and C₈ olefins could only be separated from the corresponding mixtures on addition of water which also improves the selectivity at lower carbon numbers like the C₅ and C₆, for example. Using infrared and Raman spectroscopy of the complex and Ag[Tf₂N] saturated by olefin, the mechanism of the extraction was found to be based on both chemical complexation and the physical solubility of the olefin in the ionic liquid ([Ag(olefin)_x][Tf₂N]). These experiments further support the use of such extraction techniques for the separation of olefins from paraffins.     

Further Evidence for ‘Extended’ Cumulene Complexes: Derivatives from Reactions with Halide Anions and Water

Reactions of [Ru{C=C(H)-1,4-C₆H₄C≡CH}(PPh₃)₂Cp]BF₄ ([ 1 a ]BF₄) with hydrohalic acids, HX, results in the formation of [Ru{C≡C-1,4-C₆H₄-C(X)=CH₂}(PPh₃)₂Cp] [X=Cl ( 2 a-Cl ), Br ( 2 a-Br )], arising from facile Markovnikov addition of halide anions to the putative quinoidal cumulene cation [Ru(=C=C=C₆H₄=C=CH₂)(PPh₃)₂Cp]⁺. Similarly, [M{C=C(H)-1,4-C₆H₄-C≡CH}(LL)Cp ]BF₄ [M(LL)Cp’=Ru(PPh₃)₂Cp ([ 1 a ]BF₄); Ru(dppe)Cp* ([ 1 b ]BF₄); Fe(dppe)Cp ([ 1 c ]BF₄); Fe(dppe)Cp* ([ 1 d ]BF₄)] react with H⁺/H₂O to give the acyl-functionalised phenylacetylide complexes [M{C≡C-1,4-C₆H₄-C(=O)CH₃}(LL)Cp’] ( 3 a – d ) after workup. The Markovnikov addition of the nucleophile to the remote alkyne in the cations [ 1 a–d ]⁺ is difficult to rationalise from the vinylidene form of the precursor and is much more satisfactorily explained from initial isomerisation to the quinoidal cumulene complexes [M(=C=C=C₆H₄=C=CH₂)(LL)Cp’]⁺ prior to attack at the more exposed, remote quaternary carbon. Thus, whilst representative acetylide complexes [Ru(C≡C-1,4-C₆H₄-C≡CH)(PPh₃)₂Cp] ( 4 a ) and [Ru(C≡C-1,4-C₆H₄-C≡CH)(dppe)Cp*] ( 4 b ) reacted with the relatively small electrophiles [CN]⁺ and [C₇H₇]⁺ at the β-carbon to give the expected vinylidene complexes, the bulky trityl ([CPh₃]⁺) electrophile reacted with [M(C≡C-1,4-C₆H₄-C≡CH)(LL)Cp’] [M(LL)Cp’=Ru(PPh₃)₂Cp ( 4 a ); Ru(dppe)Cp* ( 4 b ); Fe(dppe)Cp ( 4 c ); Fe(dppe)Cp* ( 4 d )] at the more exposed remote end of the carbon-rich ligand to give the putative quinoidal cumulene complexes [M{C=C=C₆H₄=C=C(H)CPh₃}(LL)Cp’]⁺, which were isolated as the water adducts [M{C≡C-1,4-C₆H₄-C(=O)CH₂CPh₃}(LL)Cp’] ( 6 a–d ). Evincing the scope of the formation of such extended cumulenes from ethynyl-substituted arylvinylene precursors, the rather reactive half-sandwich (5-ethynyl-2-thienyl)vinylidene complexes [M{C=C(H)-2,5-^cC₄H₂S-C≡CH}(LL)Cp’]BF₄ ([ 7 a – d ]BF₄ add water readily to give [M{C≡C-2,5-^cC₄H₂S-C(=O)CH₃}(LL)Cp’] ( 8 a – d )].     

Utilization of α-olefins obtained by pyrolysis of waste high density polyethylene to synthesize α-olefin-succinic-anhydride based cold flow improvers

A new route of utilization of α-olefin rich hydrocarbon fractions obtained by waste polymer pyrolysis was investigated. α-olefin-succinic-anhydride intermediate-based pour point depressant additives for diesel fuel were synthesized, in which reactions needed α-olefins were obtained by pyrolysis of waste high-density polyethylene (HDPE). Fraction of α-olefins was produced by the de-polymerization of plastic waste in a tube reactor at 500℃ in the absence of catalysts and air. C_17~22 range of mixtures of olefins and paraffins were separated for synthesis and then, these hydrocarbons were reacted with maleic-anhydride (MA) for formation of α-olefin-succinic-anhydride intermediates. The olefin-rich hydrocarbon fraction contained approximately 60% of olefins, including 90%~95% α-olefins. Other intermediates were produced in the same way by using commercial C₂₀ α-olefin instead of C_17~22 olefin mixture. The two different experimental intermediates with number average molecular weights of 1850g/mol and 1760g/mol were reacted with different alcohols: 1-butanol, 1-hexanol, 1-octanol, i-butanol, and c-hexanol to produce their ester derivatives. The synthesized ten experimental pour point depressants were added in different concentrations to conventional diesel fuel, which had no other additive content before. The structure and efficiency of experimental additives were followed by different standardized and non-standardized methods. Results showed that the experimental additives on the basis of the product of waste pyrolysis were able to decrease not only the pour but also the cloud point and cold filter plugging point (CFPP) of diesel fuel, whose effects could be observed even if the concentration of additives was low. Furthermore, all additives had anti-wear and anti-friction effects in diesel fuel.     

Acetone chemical ionization studies: Olefins

Acyclic, cyclic and bicyclic olefins have been found to undergo acetylation in the gas phase under acetone chemical ionization, giving rise to diagnostic ions. Terminal olefins show enhanced loss of water from the [M + 43]⁺ adduct. The [M + 43]⁺ ion of Δ³? Δ⁴? and Δ⁵-olefins give characteristic collision-induced dissociation spectra.     

Magnesium chloride supported high mileage catalysts for olefin (decene-1) polymerization XV. Termination and energetics

Polymerizations of decene-1 were carried out from 0° to 70° at A/T = 167 and [M] = 0.75 M initiated by 0.17, 0.34, and 0.69 mM of Ti contained in the MgCl₂/ethylbenzoate/p-cresol/AlEt₃/TiCl₄-AlEt₃/methyl-p-toluate catalyst. The rate of polymerization is directly proportional to the catalyst concentration. About 12% of the Ti in the catalyst is initially active at 50°; they are 1.4%, 8.8%, and 9.4% at 0°, 25°, and 70°, respectively. The changes of R_p with temperature parallels the variations in the active site concentration. The decline of R_p with time has second-order plots with slopes which are inversely proportional to the catalyst concentration, but the rate constants for these deactivations are nearly the same for decene and propylene polymerizations. These results strongly support a mechanism of deactivation involving two adjacent sites in the catalyst particle surfaces. The rate constants of propagation and of chain transfer to AlEt₃, the energetics for these processes, and MW and MW distribution data have been obtained.     

New organic supports for metallocene catalysts applied in olefin polymerizations

Nano-sized latex particles as organic supports for metallocenes applied in olefin polymerizations are introduced. The particles are functionalized with nucleophilic surfaces such as polyethylenoxide (PEO), polypropyleneoxide (PPO) or pyridine units allowing an immobilization of the metallocene catalysts via a non-covalent immobilization process. The latices are obtained by emulsion or miniemulsion polymerization with styrene, divinylbenzene as the crosslinker, and either PEO or PPO functionalized styrene or 4-vinylpyridine for surface functionalization. The supported catalysts, e.g. [Me₂Si(2MeBenzInd)₂ZrCl₂/MAO] on PPO containing latices or Cp₂ZrMe₂/([Ph₃C][B(C₆F₅)₄]) on pyridine functionalized materials were tested in ethylene polymerizations. Remarkably, high activities and excellent product morphologies were obtained. The influence of the degree of surface functionalization on activity and productivity was investigated. Furthermore, the fragmentation of the catalyst was studied by electron microscopy using bismuth-labeled latex particles or by fluorescence and confocal fluorescence microscopy using dye-labeled supports. Finally, a self-immobilizing catalyst/monomer system is presented. It is demonstrated that by using PEO-functionalized olefins, the metallocenes were immobilized on the monomers. Subjecting these mixtures to an ethylene copolymerization, again high activities and productivities as well as polyolefin beads with high bulk densities are observed, indicating that an extra supporting process for controlling the product size and shape of the polyolefins is not necessary for these monomers.     

Conventional radical polymerization and iodine‐transfer polymerization of 4′‐nonafluorobutyl styrene: Surface and thermal characterizations of the resulting poly(fluorostyrene)s

4′‐Nonafluorobutylstyrene (3) was synthesized and polymerized by conventional and controlled radical polymerization (iodine transfer polymerization (ITP)). Such an aromatic fluoromonomer was prepared from Ullmann coupling between 1‐iodoperfluorobutane and 4‐bromoacetophenone followed by a reduction and a dehydration in 50% overall yield. Two radical polymerizations of (3) were initiated by AIBN either under conventional or controlled conditions, with 1‐iodoperfluorohexane in 84% monomer conversion and in 50% yield. ITP of (3) featured a fast monomer conversion and a linear evolution of the ln([M]₀/[M]) versus time. The kinetics of radical homopolymerization of (3) enabled one to assess its square of the propagation rate to the termination rate (k_p²/k_t) in ITP conditions (36.2·10^?2 l·mol^?2·sec^?2 at 80 °C) from the Tobolsky's kinetic law. Polydispersity index (?) of the fluoropolymer achieved by conventional polymerization was 1.30 while it worthed 1.15 when synthesized by ITP. Thermal stabilities of these oligomers were satisfactory (10% weight loss under air occurred from 305 °C) whereas the melting point was 47 °C. Contact angles and surface energies assessed from spin‐coated poly(3) films obtained by conventional (hysteresis = 18°, surface energy 18 mN.m^?1) and ITP (hysteresis = 47°, surface energy 15 mN.m^?1) evidenced ? values' influence onto surface properties of the synthesized polymers. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3202–3212     

Electrochemical Ammonia Gas Sensing in Nonaqueous Systems: A Comparison of Propylene Carbonate with Room Temperature Ionic Liquids

First, the direct and indirect electrochemical oxidation of ammonia has been studied by cyclic voltammetry at glassy carbon electrodes in propylene carbonate. In the case of the indirect oxidation of ammonia, its analytical utility of indirect for ammonia sensing was examined in the range from 10 and 100 ppm by measuring the peak current of new wave resulting from reaction between ammonia and hydroquinone, as function of ammonia concentration, giving a sensitivity 1.29×10^?7 A ppm^?1 (r²=0.999) and limit‐of‐detection 5 ppm ammonia. Further, the direct oxidation of ammonia has been investigated in several room temperature ionic liquids (RTILs), namely 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([C₄mim] [BF₄]), 1‐butyl‐3‐methylimidazolium trifluoromethylsulfonate ([C₄mim] [OTf]), 1‐Ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([C₂mim] [NTf₂]), 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([C₄mim] [NTf₂]) and 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([C₄mim] [PF₆]) on a 10 μm diameter Pt microdisk electrode. In four of the RTILs studied, the cyclic voltammetric analysis suggests that ammonia is initially oxidized to nitrogen, N₂, and protons, which are transferred to an ammonia molecule, forming NH via the protonation of the anion(s) (A^?). However, in [C₄mim] [PF₆], the protonated anion was formed first, followed by NH . In all five RTILs, both HA and NH are reduced at the electrode surface, forming hydrogen gas, which is then oxidized. The analytical ability of this work has also been explored further, giving a limit‐of‐detection close to 50 ppm in [C₂mim] [NTf₂], [C₄mim] [OTf], [C₄mim] [BF₄], with a sensitivity of ca. 6×10^?7 A ppm^?1 (r²=0.999) for all three ionic liquids, showing that the limit of detection was ca. ten times larger than that in propylene carbonate since ammonia in propylene carbonate might be more soluble in comparison with RTILs when considering the higher viscosity of RTILs.     

Oligomerization and co-oligomerization of α-olefins catalyzed by nickel(II)/alkylaluminum systems

This work describes α-olefins oligomerization/co-oligomerization of 1-butene, 1-hexene, 1-octene to linear oligomers (C₈---C₁₆ range) promoted by catalytic systems based on nickel(II) salts/alkylaluminum compounds. Conversion, selectivity (isomerization or oligomerization) and linearity are determined by mass distribution calculation of the substrates (α-olefins) in the products. The best results are obtained with Ni(acac)₂/AlEt₂OEt working at 60°C, Al/Ni ratio between 0.8–1.4 and using toluene as a solvent. Under these conditions, the conversion is higher than 90% giving 40% of oligomerization selectivity. The linearity varies from 65% (C₁₆ fraction) to 98% (C₈ fraction).     

Ionic Liquids - New Solvents in the Free Radical Polymerization

Summary: The analysis of the influence of ionic liquids (ILs) in polymer synthesis as an alternative for common organic solvents is still an active field of research. 1 Using ILs as solvents for free radical polymerizations implies a significant increase in polymerization rates and molecular weights which can be observed. In this work we examined the copolymerization behaviour of styrene (S) and methyl methacrylate (MMA), glycidyl methacrylate (GMA) and 2-hydroxypropyl methacrylate (HPMA) with acrylonitrile (AN) in 1-etyhl-3-methylimidazolium ethylsulfate ([EMIM]EtSO₄). ILs are liquids with comparable high polarities and viscosities. These two characteristic properties are strongly correlated with the rate coefficients of propagation k_p and termination k_t. 2 - 4 The rate constant of termination k_t decreases when the IL concentration and therefore the viscosity of the reaction mixture is increased, whereas the propagation rate coefficient k_p increases with increasing IL content. The viscosity of the IL can be varied by either working with mixtures of IL with conventional organic solvents – here the IL [EMIM]EtSO₄ was mixed with DMF – or by variation of the temperature. The influence of the viscosity of the IL ([EMIM]EtSO₄) on polymerization kinetics of methyl methacrylate (MMA) and styrene/acrylonitrile (S/AN) was investigated.     

Co-oligomerization of ethylene and higher linear alpha olefins. I. Co-oligomerization with the sulfonated nickel ylide-based catalytic system

Co-oligomers of ethylene and a series of linear α-olefins (propylene, 1-butene, 1-hexene, 1-heptene, 1-octene, and 1-decene) were synthesized with a homogeneous catalyst consisting of sulfonated nickel ylide and diethylaluminum ethoxide at 90°C. GC analysis of the co-oligomerization products allowed complete structural identification of all reaction products, α-olefins with linear and branched chains, vinylidene olefins, and linear olefins with internal double bonds. The article describes the reaction scheme of ethylene–olefin co-oligomerization. The scheme includes chain initiation reactions (insertion of ethylene or an olefin into the Ni? H bond), chain propagation reactions, and chain termination reactions via β-hydride elimination. Primary and secondary inertions of α-olefins into the Ni? H bond in the initiation stage proceed with nearly equal probabilities. Higher olefins participate in the chain growth reactions (insertion into the Ni? C bond) also both in primary and secondary insertion modes. The primary insertion of an α-olefin molecule into the Ni? C bond produces the β-branched Ni? CH₂? CR₁R₂ group. This group is susceptible to β-hydride elimination with the formation of vinylidene olefins. However, the Ni? CH₂? CR₁R₂ groups can participate in further ethylene insertion reactions and thus form vinyl oligomerization products with branched alkyl groups. On the other hand, the secondary insertion of an α-olefin molecule into the Ni? C bond produces the α-branched Ni? CR₁R₂ bond which does not participate in further chain growth reactions and undergoes the β-hydride elimination reaction with the formation of linear reaction products with internal double bonds. Most co-oligomer molecules contain only one α-olefin fragment. However, the analysis of ethylene-propylene and ethylene-1-heptene co-oligomers allowed identification of products with two olefinic fragments which are also formed in the copolymerization reactions with small yields.     

Redox non-innocence of thioether crowns: spectroelectrochemistry and electronic structure of formal nickel(III) complexes of aza-thioether macrocycles

The Ni^II complexes [Ni([9]aneNS₂‐CH₃)₂]²⁺ ([9]aneNS₂‐CH₃=N‐methyl‐1‐aza‐4,7‐dithiacyclononane), [Ni(bis[9]aneNS₂‐C₂H₄)]²⁺ (bis[9]aneNS₂‐C₂H₄=1,2‐bis‐(1‐aza‐4,7‐dithiacyclononylethane) and [Ni([9]aneS₃)₂]²⁺ ([9]aneS₃=1,4,7‐trithiacyclononane) have been prepared and can be electrochemically and chemically oxidized to give the formal Ni^III products, which have been characterized by X‐ray crystallography, UV/Vis and multi‐frequency EPR spectroscopy. The single‐crystal X‐ray structure of [Ni^III([9]aneNS₂‐CH₃)₂](ClO₄)₆?(H₅O₂)₃ reveals an octahedral co‐ordination at the Ni centre, while the crystal structure of [Ni^III(bis[9]aneNS₂‐C₂H₄)](ClO₄)₆?(H₃O)₃? 3H₂O exhibits a more distorted co‐ordination. In the homoleptic analogue, [Ni^III([9]aneS₃)₂](ClO₄)₃, structurally characterized at 30 K, the Ni? S distances [2.249(6), 2.251(5) and 2.437(2) Å] are consistent with a Jahn–Teller distorted octahedral stereochemistry. [Ni([9]aneNS₂‐CH₃)₂](PF₆)₂ shows a one‐electron oxidation process in MeCN (0.2 M NBu₄PF₆, 293 K) at E_1/2=+1.10 V versus Fc⁺/Fc assigned to a formal Ni^III/Ni^II couple. [Ni(bis[9]aneNS₂‐C₂H₄)](PF₆)₂ exhibits a one‐electron oxidation process at E_1/2=+0.98 V and a reduction process at E_1/2=?1.25 V assigned to Ni^II/Ni^III and Ni^II/Ni^I couples, respectively. The multi‐frequency X‐, L‐, S‐, K‐band EPR spectra of the 3+ cations and their 86.2 % ⁶¹Ni‐enriched analogues were simulated. Treatment of the spin Hamiltonian parameters by perturbation theory reveals that the SOMO has 50.6 %, 42.8 % and 37.2 % Ni character in [Ni([9]aneNS₂‐CH₃)₂]³⁺, [Ni(bis[9]aneNS₂‐C₂H₄)]³⁺ and [Ni([9]aneS₃)₂]³⁺, respectively, consistent with DFT calculations, and reflecting delocalisation of charge onto the S‐thioether centres. EPR spectra for [⁶¹Ni([9]aneS₃)₂]³⁺ are consistent with a dynamic Jahn–Teller distortion in this compound.