Polymerization Catalysis in Liquid Propylene: High Activities and Molecular Weights in Propylene/CO Copolymerization Reactions

Summary: The dicationic [(dppp)Pd(NCCH₃)₂](BF₄)₂ catalyst (dppp = 1,3‐bis(diphenylphosphino)propane) was applied in a liquid monomer, two phase process for the CO/propene copolymerization reaction. For the first time it was possible to synthesize propene/CO copolymers with an activity up to 7 500 g/(mol · h) and molecular weights of 500 000 g/mol. Activities up to 40 000 g/(mol · h) could be obtained with the use of the unsymmetric catalyst [(CF₃‐dppp)Pd(NCCH₃)](BF₄)₂ (CF₃‐dppp = 1‐diphenylphosphino‐3‐bis[3,5‐di(trifluormethyl)phenyl]phosphinopropane) in homogeneous liquid propene solution.

Granules found after copolymerization.     

Structure Studies on 6a-Thiathiophthenes and Related Compounds

The results from structure studies on 6a-thiathiophthenes show that different substituent groups perturb the bonding in the three-sulphur sequence to different degrees. Both equal and unequal S? S bonds occur in symmetrically as well as in unsymmetrically substituted derivatives. The specific effect of methyl and phenyl substituents on the sulphur-sulphur bonding may be described by the results from CNDO/2 calculations on mono-methyl and mono-phenyl substituted 6a-thiathiophthenes. Molecular packing and intermolecular close contacts also seem to affect the S? S bonding. The structures of equally substituted 6a-thiathiophthene analogues with and show, when compared with the equivalent 6a-thiathiophthene, that and cause a pronounced change in the S? S bonding, while the perturbation caused by is negligible. In symmetrical 6a-thiathiophthene analogues with and , the average bond length in the linear three-atom sequence is 9 – 12% longer than the respective single bond.     

Segmented Block Copolymers with Monodisperse Hard Segments: The Influence of H‐Bonding on Various Properties

The properties of segmented‐copolymer‐based H‐bonding and non‐H‐bonding crystallisable segments and poly(tetramethylene oxide) segments were studied. The crystallisable segments were monodisperse in length and the non‐hydrogen‐bonding segments were made of tetraamidepiperazineterephthalamide (TPTPT). The polymers were characterised by DSC, FT‐IR, SAXS and DMTA. The mechanical properties were studied by tensile, compression set and tensile set measurements. The TPTPT segmented copolymers displayed low glass transition temperatures (T_g, ?70 °C), good low‐temperature properties, moderate moduli (G′ ≈ 10–33 MPa) and high melting temperatures (185–220 °C). However, as compared to H‐bonded segments, both the modulus and the yield stress were relatively low.

     

The Crystal and Molecular Structures of Overcrowded Halogenated Compounds VII. 1:10-Dichloro-3:8-Dimethyl4:7-Phenanthroline

1,10-dichloro-3,8-dimethyl-4,7-phenanthroline crystallizes in the triclinic system with a = 7.651(3), b = 7.792(3), c = 12.301(3)Å, α = 108.48(6), β = 82.74(2), γ = 116.53(4)° space group , D_m = 1.479 g cm^?3, D_c = 1.480(5) g cm^?3 for two formula units per cell. The intensities of about 2000 reflections were measured by semi-automatic Weissenberg diffractometer and supplemented by precession diffractometer measurements. The crystal structure was solved by the SEARCH method (Rabinovich and Schmidt, Nature, 211: 1391 (1968)) and refined by full-matrix least squares methods, using anisotropic temperature factors for non-hydrogen atoms. The final R-factor was 0.067 and the “goodness of fit” 0.94. The molecule has an approximate two-fold axis of symmetry and is appreciably distorted from planarity, the two chlorines being displaced by +1.12Å and ?1.15Å from the mean molecular plane; the non-bonded Cl? Cl distance is 3.082(3)Å. Bond lengths are close to standard values but there are appreciable distortions in bond angles, torsion angles and fold angles. There is hexagonal close packing of stacks of molecules, with van der Waals binding between stacks. Anti-parallelism of adjacent molecules in a stack suggests that dipole-dipole forces are important in the intrastack binding. Comparison of the present molecular structure with that of 2,7-dibromo-4,5-bis-(2-pyridyl)phenanthrene-3,6-diol (Smith and Barrett, Acta Crystallogr., B27 : 419 (1971)) shows that the present molecule is the more highly overcrowded.     

Reactive Species Mutually Isolated on Insoluble Polymeric Carriers. II. The Alkylation of Esters

Polymer esters of the type have been alkylated by the use of trityllithium and an alkyl halide. The sole product obtained was that of monoalkylation. No self condensation occurred due to the immobilizing effect of the polymeric carrier.     

Comparison of Olefin Polymerization Processes with Metallocene Catalysts

Summary: Solution and gas phase processes of the polymerization of ethene are compared using new types of pentalenyl bridged ansa‐metallocenes such as [Me₃Pen(Flu)]ZrCl₂. As of the bridge, the catalyst system is remarkable thermostable up to 105 °C and a deactivation of the metallocene on the silica support can be suppressed. Compared to the non‐supported catalyst in a solution process, the application of the heterogenized system in a gas phase process leads to a decrease in activities while molar masses of the polyethenes are similar. Due to a higher degree of short chain branches of 20–30 per 1 000 carbon atoms instead of 10–17, the melting temperatures are 10 °C lower than those for polymers obtained in the solution process.

Basic structure of the here used pentalenyl bridged ansa‐metallocenes.     

Aluminum‐Catalyzed Formation of Functional 1,3,2‐Dioxathiolane 2‐Oxides from Sulfur Dioxide: An Easy Entry towards N‐Substituted Aziridines

Aluminum(III) complexes derived from aminotriphenolate ligands are shown to be excellent catalysts for the formation of cyclic sulfites from a range of (functionalized) terminal and internal epoxides, and ex situ generated sulfur dioxide. The developed catalytic protocol is characterized by its operational simplicity, wide scope in epoxide reaction partners, good to excellent isolated yields and mild reaction conditions [50–70 °C, p(SO₂) <1 bar]. The synthetic potential of these cyclic sulfites in organic synthesis is demonstrated in the preparation of N‐substituted aziridines through a three‐step protocol.

     

Strongly Photosensitive and Fluorescent F8T2 Electrospun Fibers

Electrospun fibers of poly[(9,9‐dioctylfluorenyl‐2,7‐diyl)‐co‐bithiophene] (F8T2) with exceptional electro‐optical performance are obtained. The I/T characteristics measured in fibers with 7–15 µm diameter and 1 mm length show a semiconductor behavior; their thermal activation energy is 0.5 eV and the dark conductivity at RT is 5 × 10^?9 (Ω cm)^?1. Besides exhibiting a photosensitivity of about 60 under white light illumination with a light power intensity of 25 mW · cm^?2, the fibers also attain RT photoluminescence in the cyan, yellow, and red wavelength range under ultraviolet, blue, and green light excitation, respectively. Optical microscope images of F8T2 reveal homogeneous electrospun fibers, which are in good agreement with the uniformly radial fluorescence observed.

     

Kinetics and mechanism of the vapour-phase ammoxidation of 4-picoline

The kinetics of the heterogeneous vapour phase ammoxidation of 4-picoline was studied over V₂O₅-Cr₂O₃-Al₂O₃ catalysts in a differential flow reactor between 548 and 598 K and under atmospheric pressure. The rate equation for the conversion of 4-picoline to isonicotinonitrile and the rate equation for the overall conversion of 4-picoline, represented the rate data satisfactorily. The overall conversion of 4-picoline was also tested by the Langmuir-Hinshelwood mechanism.     

Copper‐Catalyzed Domino Synthesis of Benzo[4,5]imidazo[1,2‐a]pyrimidin‐4(10H)‐ones using Cyanamide as a Building Block

An efficient and practical copper‐catalyzed domino synthesis of benzo[4,5]imidazo[1,2‐a]pyrimidin‐4(10H)‐ones has been developed. The protocol uses N‐(2‐halophenyl)‐3‐alkylpropiolamides and cyanamide as the starting materials, inexpensive copper(I) iodide and pipecolinic acid as the catalyst and ligand, and the corresponding products were obtained in moderate to good yields.

     

PTFE Micropowder Functionalized with Carboxylic Acid Groups

PTFE powder irradiated in air at room temperature was studied by infrared spectroscopy, potentiometric titration with sodium hydroxide, and polyelectrolyte titration with poly(diallyl dimethylammonium chloride). Through the radiation‐induced degradation ? COF groups are formed in the material, which can be hydrolyzed to ? COOH groups. About 10–20% of the ? COOH groups are located at the surface of the PTFE particle. The ? COOH groups start to decompose under oxidizing conditions at temperatures above 200 °C. The decarboxylation results in the formation of ? CF?CF₂ groups, which are oxidized to ? COF groups in the presence of air.

     

Intercalated Polycarbonate/Clay Nanocomposites: Nanostructure Control and Foam Processing

Intercalated polycarbonate (PC)/clay nanocomposites (PCCN)s have been prepared successfully through the melt intercalation method in the presence of a compatibilizer. The internal structure and morphology of the PCCNs has been established by using wide‐angle X‐ray diffraction (WAXD) analyses and transmission electron microscopic (TEM) observations. The morphology of these nanocomposites and degradation of the PC matrix after nanocomposites preparation can be controlled by varying surfactants used for the modification of clay and compatibilizer. The intercalated PCCNs exhibited remarkable improvements of mechanical properties when compared with PC without clay. We also discuss foam processing of one representative PCCN using supercritical CO₂ as a foaming agent.

TEM bright field image of intercalated polycarbonate/synthetic fluorohectorite nanocomposite.     

Copper‐Catalyzed Monoborylation of Silylalkynes; Regio‐ and Stereoselective Synthesis of (Z)‐β‐(Borylvinyl)silanes

The selective copper‐catalyzed borylation of silylalkynes in the presence of a diboron reagent and methanol produced a variety of (Z)‐β‐(borylvinyl)silanes. The appropriate use of a selective ligand for copper allows the chemo‐, regio‐, and stereoselective monoborylation of silylalkynes. The β‐regioselectivity of an N‐heterocyclic carbene (NHC)‐copper catalyst was investigated by DFT calculations.

     

Long‐Aliphatic‐Segment Polyamides: Salt Preparation and Subsequent Anhydrous Polymerization

Long‐aliphatic‐segment polyamides were prepared based on hexamethylenediamine and α,ω‐(CH₂)_x biosynthetic diacids (x = 10, 11, 12). The pertinent monomers (salts) were isolated as solids, thoroughly characterized for the first time, and then submitted to an anhydrous melt prepolymerization technique. The obtained prepolymers exhibited in the range of 5 100–11 800 g · mol^?1, and the molecular weight was further increased by up to 55% through solid‐state finishing. The suggested overall polyamidation cycle was conducted at short melt‐reaction times, so as to avoid any thermal degradation, and was proved efficient, indicating similar reactants polymerizability independently of the methylene content.

     

Constant Selectivity in Proton Exchange Reactions Between Aqueous Sulphuric Acid and Acetylenes

Linear Pfluger plots of unit slope are obtained from logarithmic rate constants for acid–catalysed hydration of phenylacetylene and its substituted derivatives p-OCH₃, p-CH₃, m-CH₃, p-Br, m-Cl, m-NO₂, p-NO₂ in aqueous sulphuric acid solution. This direct experimental observation of absence of any dependence on selectivity gives evidence for the applicability of the kinetic acidity function in these systems.