Catalysts for the living insertion polymerization of alkenes: access to new polyolefin architectures using Ziegler-Natta chemistry

Coordination-insertion polymerization systems have long been superior to their anionic, cationic, and radical polymerization counterparts with regard to stereochemical control. However, until five years ago, these metal-based insertion methods were inferior to ionic and radical mechanisms in the category of living polymerization, which is simply a polymerization that occurs with rapid initiation and negligible chain termination or transfer. In the last half decade, the living insertion polymerization of unactivated olefins has emerged as a powerful tool for the synthesis of new polymer architectures. Materials available today by this route range from simple homopolymers such as linear and branched polyethylene, to atactic or tactic poly(alpha-olefins), to end-functionalized polymers and block copolymers. This review article summarizes recent developments in this rapidly growing research area at the interface of synthetic and mechanistic organometallic chemistry, polymer chemistry, and materials science. While special emphasis is placed on polymer properties and novel polymeric architectures, most of which were inaccessible just a decade ago, important achievements with respect to ligand and catalyst design are also highlighted.     

Ethylenediaminetetraacetato-monoperoxo complexes of vanadium(V)

Summary The monoperoxo complexes, M₂[VO(HEDTA)(O₂)]· 4H₂O, where M is K⁺ or NH ₄ ⁺ and H₄EDTA is ethylene-diaminetetraacetic acid, were prepared and characterized by Raman and i.r. spectra in the solid state and in aqueous solution. The single crystal X-ray study revealed a pentagonal bipyramidal anion structure with a tetradentate HEDTA(3—) ligand. The decomposition of complexes in aqueous solution to blue vanadium(IV) complexes as end products proceeds via a nonperoxo complex of vanadium.     

Insertion/isomerization polymerization of 1,5-hexadiene: synthesis of functional propylene copolymers and block copolymers

Polymerization of 1,5-hexadiene with a bis(phenoxyimine) titanium catalyst system is reported. The microstructure of the polymer contains the expected methylene-1,3-cyclopentane units as well as the unexpected 3-vinyl tetramethylene units. A mechanism for formation of this polymer is proposed. This unusual reaction is also employed in the synthesis of vinyl-functional polypropylene copolymers and block copolymers with low polydispersity indices.     

Studies on pectin coating of liposomes for drug delivery

The present study investigated the surface coating of charged liposomes by three different types of pectin (LM, HM and amidated pectin) by particle size determinations and zeta potential measurements. The pectins and the pectin coated liposomes were visualized by atomic force microscopy. The adsorption of pectin onto positive liposomes yielded a reproducible increase in particle size and a shift of the zeta potential from positive to negative side for all three pectin types, whereas the adsorption of pectin onto negative liposomes did not render any significant changes probably due to electrostatic repulsion. The positive liposomes coated with HM-pectin gave the largest pectin coated particles with the least negative zeta potential, while the opposite was observed for the LM-pectin coated positive liposomes. Furthermore, results from dynamic light scattering revealed narrow size distributions, indicating that the degree of aggregation was low for the pectin coated liposomes. As liposomes are able to encapsulate drugs and pectin has been found to be mucoadhesive, these pectin coated liposomes may be potential drug delivery systems.     

Mean amplitudes of vibration for cyclobutane and cyclobutane-d8 from spectroscopic data

Mean amplitudes of vibration for cyclobutane and cyclobutane-d₈ are calculated on the basis of spectroscopic data. Results for the bonded distances are compared with data from electron diffraction, and a good agreement is found.     

Validation of a simple HPLC method for assay of haplamine and its metabolites in plasma suitable for pharmacokinetic application in rats

A simple HPLC method with ultraviolet detection has been developed and validated for the simultaneous determination of haplamine and its metabolites (trans/cis-3,4-dihydroxyhaplamine) in rat. A liquid-liquid extraction was used to extract the compounds from rat plasma. The analysis was performed on a C(18) Nucleosil Nautilus column. The mobile phase consisted of water (A) and a mixture of methanol and acetonitrile (85:15; v/v) (B) used in gradient mode (38-40% B for 10 min, 40-58% B for 49 min, 58-38% B for 1 min, and 38% for 5 min) pumped at 1 mL/min. The calibration curves showed good linearity with correlation coefficients greater than 0.999 for the analytes in the investigated concentration range. The lower limit of detection was 0.007, 0.008 and 0.009 microg/mL and the lower limit of quantification was 0.014, 0.017 and 0.018 microg/mL for haplamine, and trans/cis-3,4-dihydroxyhaplamine, respectively. The method was applied to a preliminary pharmacokinetic study in rats. This method proved to meet fully the standards required of experimental pharmacokinetic studies and should be used in further preclinical investigation.     

Composite hollow fiber membranes for CO2 capture

Composite hollow fibers membranes were prepared by coating poly(phenylene oxide) (PPO) and polysulfone (PSf) hollow fibers with high molecular polyvinylamine (PVAm). Two procedures of coating hollow fibers outside and respective inside were investigated with respect to intrinsic PVAm solution properties and hollow fibers geometry and material.The influence of operating mode (sweep or vacuum) on the performances of membranes was investigated. Vacuum operating mode gave better results than using sweep because part of the sweep gas permeated into feed and induced an extra resistance to the most permeable gas the CO₂. The composite PVAm/PSf HF membranes having a 0.7–1.5 μm PVAm selective layer, showed CO₂/N₂ selectivity between 100 and 230. The selectivity was attributed to the CO₂ facilitated transport imposed by PVAm selective layer. The CO₂ permeance changed from 0.006 to 0.022 m³(STP)/(m² bar h) in direct correlation with CO₂ permeance and separation mechanism of the individual porous supports used for membrane fabrication. The multilayer PVAm/PPO membrane using as support PPO hollow fibers with a 40 nm PPO dense skin layer, surprisingly presented an increase in selectivity with the increase in CO₂ partial pressure. This trend was opposite to the facilitated transport characteristic behaviour of PVAm/porous PSf. This indicated that PVAm/PPO membrane represents a new membrane, with new properties and a hybrid mechanism, extremely stable at high pressure ratios. The CO₂/N₂ selectivity ranged between 20 and 500 and the CO₂ permeance from 0.11 to 2.3 m³(STP)/(m² bar h) depending on the operating conditions.For both PVAm/PSf and PVAm/PPO membranes, the CO₂ permeance was similar with the CO₂ permeance of uncoated hollow fiber supports, confirming that the CO₂ diffusion rate limiting step resides in the properties of the relatively thick support, not at the level of 1.2 μm thin and water swollen PVAm selective layer. A dynamic transfer of the CO₂ diffusion rate limiting step between PVAm top layer and PPO support was observed by changing the feed relative humidity (RH%). The CO₂ diffusion rate was controlled by the PPO support when using humid feed. At low feed humidity the 1.2 μm PVAm top layer becomes the CO₂ diffusion rate limiting step.     

Metavanadates and dihydrogendecavanadates with cations of macrocyclic tetraamines

Summary From the reaction systemsCyclam/Mecyclam-KVO₃-H₂O-HCl-EtOH (Cyclam=1,4,8,11-tetraazacyclotetradecane; Mecyclam=5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane), the first polyvanadates with cations of macrocyclic amines were isolated: (CyclamH₂)₂-H₂V₁₀O₂₈·2H₂O, (MecyclamH₂)₂H₂V₁₀O₂₈·6H₂O, (CyclamH₂)(VO₃)₂·3H₂O, (CyclamH₂)(VO₃)₂·2H₂O, and (MecyclamH₂)(VO₃)₂·H₂O. The metavanadates with theCyclamH ₂ ²⁺ cation differ markedly in their IR spectra, obviously due to the different structure of the polyanion. The interruption of dynamic heating at the thermal analysis of the crystallohydrates of dihydrogendecavanadates resulted in the formation of corresponding anhydrous dihydrogendecavanadates.

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Metavanadate und Dihydrogendecavanadate mit Kationen aus makrocyclischen Tetraaminen

Zusammenfassung Aus demCyclam/Mecyclam-KVO₃-H₂O-HCl-EtOH Reaktionssystem (Cyclam=1,4,8,11-tetraazacyclotetradecane;Mecyclam=5,5,7,12,12,14-hexamethyl-1,4,8,11-tetrazacyclotetradecane) wurden die ersten Polyvanadate mit cyclischen Aminen als Kationen isoliert: (CyclamH₂)₂V₁₀O₂₈·H₂O, (MecyclamH₂)₂H₂V₁₀O₂₈·6H₂O, (CyclamH₂)(VO₃)₂·3H₂O, (CyclamH₂)(VO₃)₂·2H₂O und (MecyclamH₂)(VO₃)₂·H₂O. Die zwei Metavanadate mit dem KationCyclamH ₂ ²⁺ unterscheiden sich wesentlich in ihren Infrarotspektren, was auf unterschiedliche Polyanionstruktur der Metavanadate hinweist. Durch Unterbrechen der dynamischen Erhitzung bei der thermischen Analyse von Kristallhydraten der Dihydrogendekavanadate wurden entsprechende Verbindungen ohne Kristallwasser gewonnen.

     

Synthèse et étude physico-chimique de sulfures,sulfoxydes et sulfones en série thiazolique

The alkylation of Δ⁴-thiazoline-2-thiones under phase transfer catalysis conditions leads to the corresponding thioethers in good yields. The oxidation of 2-alkylthiazoles with m-chloroperbenzoic acid leads to the corresponding sulfines or sulfones depending on experimental conditions in yields of about 80-90%. The characteristic gle, tlc, ir, ¹H nmr and ms data are reported for most of the compounds studied.