Effect of a cocatalyst modifier in the synthesis of ultrahigh molecular weight polyethylene having reduced number of entanglements

The use of a hindered phenol to trap free trimethylaluminum (TMA) in methylaluminoxane (MAO) solutions has been reported to improve the performance of single‐site, homogeneous catalysts for olefin polymerization. In the present study, with the help of rheological analyses, we have investigated and compared the molecular weight, molecular weight distribution and entanglement density of ultrahigh molecular weight polyethylene synthesized with a single‐site catalyst activated by MAO and phenol‐modified MAO. While the number average molecular weight (M_n) of the obtained polymers remains the same for both activations, a higher yield and a higher entanglement density are found in the initial stages of polymerization on using phenol‐modified MAO as the cocatalyst. These results suggest that on using the phenol‐modified MAO as activator, a higher number of active sites are obtained. Surprisingly in the presence of untreated MAO, a tail in the higher molecular mass region is produced. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013     

Palladium‐catalyzed carbonylative cyclization of 3‐bromoallyl alcohols leading to furan‐2(5H)‐ones

3‐Bromoallyl alcohols are carbonylatively cyclized under carbon monoxide pressure in toluene in the presence of a catalytic amount of Pd(OAc)₂ and PPh₃ along with Na₂CO₃ to give furan‐2(5H)‐ones in good yields. Copyright © 2012 John Wiley & Sons, Ltd.     

Dimeric ortho‐palladated homoveratrylamine as an efficient homogeneous catalyst for copper‐free Sonogashira cross‐coupling reaction

The catalytic activity of ortho‐palladated [Pd{C6H2(CH2CH2NH2)‐(OMe)2,3,4}(m‐Br)]2, a complex of homoveratrylamine in the copper‐free Sonogashira coupling reaction has been investigated. This complex is a catalyst that is efficient, stable and non‐sensitive to air and moisture in the Sonogashira reaction. In this homogeneous catalytic system, various aryl halides were efficiently coupled with phenylacetylene in mostly moderate to good yields in N‐methylpyrrolidone at 100 °C under copper‐free conditions. Copyright © 2012 John Wiley & Sons, Ltd.     

Hydroformylation of Oct‐1‐ene in Novel Ionic Liquid Crystals

Hydroformylation of oct‐1‐ene leading to nonanal (denoted by n) and 2‐methyloctanal (denoted by iso), in a novel series of caprolactam‐based and common imidazolium‐based ionic liquid crystals (ILCs; see Fig. 1) carried out for the first time (caprolactam=hexahydro‐2H‐azepin‐2‐one) (Scheme). Variation of the chain length (n) of the alkyl substituent (C_n) at the caprolactam cation (CP⁺) from n=12 to 18 caused the n/iso ratios to vary from 1.7 to 2.9. Meanwhile, the TOF (turnover frequency) decreased from 148 to 122 mol mol⁻¹ h⁻¹. Hydroformylation in the imidazolium‐based ILCs revealed that [C₁₆MIm]⋅BF₄ (n/iso 5.2, TOF 969 mol mol⁻¹ h⁻¹) was more favorable than [C₁₆MIm]⋅MsO (n/iso 3.7, TOF 969 mol mol⁻¹ h⁻¹) for the formation of the unbranched aldehyde. Although the n/iso ratio in caprolactam‐based ILCs was lower than that in imidazolium‐based ILCs, the conversions are higher in the former ILCs on the whole. It should be noted that the lamellar mesophase has a strong effect on the regioselectivity and TOF of the hydroformylation. Also, it is evident that the influences of different ILCs on the hydroformylation under the various reaction conditions are greatly different. The identification of the reaction products was established by GC and GC/MS analyses.     

Air‐tolerantly surface‐initiated AGET ATRP mediated by iron catalyst from silica nanoparticles

Well‐defined polymer‐nanoparticle hybrids were prepared by a newly reported method: atom transfer radical polymerization using activators generated by electron transfer (AGET ATRP) mediated by iron catalyst. The kinetics of the surface‐initiated AGET ATRP of methyl methacrylate from the silica nanoparticles, which was mediated by FeCl₃/triphenylphosphine as a catalyst complex, ascorbic acid as a reducing agent, N,N‐dimethylformamide as the solvent in the presence of a “sacrificial” (free) initiator, was studied. Both the free and grafted polymers were grown in a control manner. The chemical composition of the nanocomposites was characterized by Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and ¹H nuclear magnetic resonance spectroscopy. Thermogravimetric analysis was used to estimate the content of the grafted organic compound, and transmission electron micrographs was used to observe the core‐shell structure of the hybrid nanoparticles. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2006–2015, 2010     

Use of ionic liquid for the enzyme‐catalyzed polymerization of phenols

Ionic liquid and buffer mixture media are first reported in the peroxidase‐catalyzed polymerization of phenol. Yield of 100% with molecular weights of 7000 KDa, as assessed by size‐exclusion chromatography (SEC), were attained using 1‐butyl‐3‐methylimidazolium tetrafluoroborate–buffer mixtures with added hydrogen peroxide. The simplicity of the process and the low vapor pressure of the solvent media allow an eco‐friendly alternative to the general synthesis of polyphenolic‐type biopolymers. Evidence for the consequent polyphenol (PPO) was obtained from solid‐state ¹³C cross‐polarization magic angle spinning (CP‐MAS) NMR spectroscopy and FT‐IR. Copyright © 2009 John Wiley & Sons, Ltd.     

Novel organotin‐containing shell‐cross‐linked knedel and core‐cross‐linked knedel: Synthesis and application in catalysis

A series of novel organotin‐containing core‐cross‐linked knedels and shell‐cross‐linked knedels were first synthesized facilely from poly(styrene)‐b‐poly(acrylate acid) nanoparticles in different selective solvents [Tetrahydrofuran (THF)/H₂O or THF/n‐octane] by using organotin compound 1,3‐dichloro‐tetra‐n‐butyl‐distannoxane as a new cross‐linker. The formation of the 1‐chloro‐3‐carboxylato‐tetra‐n‐butyl‐distannoxane layer in our cross‐linking reaction was supported by Fourier transform infrared (FT‐IR) and inductive coupled plasma emission spectrometer (ICP) analysis of the resulting shell‐cross‐linked knedels and core‐cross‐linked knedels. Transmission electron microscopy (TEM) study showed the spherical morphology and the size of the core‐cross‐linked knedels and shell‐cross‐linked knedel. Especially, the layer structure of the core‐cross‐linked knedels was clearly displayed in TEM image. The increase of extent of cross‐linking lead to the increasing of diameter for the shell‐cross‐linked knedels, whereas there was no significant effect on the core‐cross‐linked knedels. Dynamic light scattering (DLS) measurements gave hydrodynamic diameters of the core‐cross‐linked knedels that were in agreement with the TEM diameters. Moreover, the wall thickness of the shell layer of the core‐cross‐linked knedels could be easily modified by varying the block copolymer composition. Notably, the organotin‐containing core‐cross‐linked knedel exhibited highly efficient catalytic activity for the aqueous esterification reaction under nearly neutral conditions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Copper(II) tetrafluroborate-promoted Meinwald rearrangement reactions of epoxides

Epoxides undergo a highly efficient Meinwald rearrangement in the presence of catalytic quantities of copper(II) tetrafluoroborate to give carbonyl compounds in high yields and with excellent selectivity. The low toxicity and ease of handling of this reagent make it an attractive alternative to the more corrosive or costly Lewis acids frequently employed.     

Iron-catalyzed selective reduction of nitro compounds to amines

An efficient reduction of the nitro group with a catalytic amount of Fe(acac)₃ and TMDS in THF at 60 °C affording the corresponding amine is described.