Polymer Brushes by Nitroxide‐Mediated Polymerization

This review article describes the preparation of polymer brushes by nitroxide‐mediated radical polymerization using either the ‘grafting to’ or the ‘grafting from’ approach. The use of TEMPO as a classical initiator is intensively described. More sophisticated nitroxides are also included in the discussion. Brush formation on flat surfaces such as wafers and also on particles is reported. Finally, some applications of polymer brushes are presented.

     

Tools to Simulate Distributive Mixing in Twin‐Screw Extruders

The application of the mapping method in finite element modeling is extended to quantitatively compare mixing in different twin‐screw extruder layouts. The mapping method provides volumetric quantities, which are crucial for the analysis and optimization of mixing based on the tracking of particles in the velocity field. A new approach to the mapping method is developed to analyze mixing in complex, dynamic open geometries. Several screw configurations and different types of conveying screws are compared, changing the pitch and gap widths. The volume‐weighted intensity of segregation is used as a mixing measure.

     

The pyrolyses of tri- and tetramethylethylene in the presence of nitric oxide

The pyrolyses of trimethylethylene and tetramethylethylene have been investigated in the presence and absence of nitric oxide. It appears that apart from a unimolecular split, e.g., a disproportionation reaction such as may play an important role in initiation. Nitric oxide had no effect on H₂ production, which is probably a molecular process. There was similar behavior of both compounds in the presence of NO, indicating that the olefinic hydrogen atom does not play a decisive role. Other aspects of the mechanisms are discussed.     

Practical Microwave Synthesis for Organic Chemists.Strategies,Instruments, and Protocols. Herausgegeben von C. Oliver Kappe,Doris Dallinger und Shaun Murphree.

Wiley‐VCH, Weinheim 2008. 300 S., geb., 59.00 €.—ISBN 978‐3527320974

     

Electron impact studies. CVII—Negative ion mass spectra of the oxime group. Monoximes derived from α-dicarbonyl systems

Specific losses of water are observed from the molecular anions of monoximes of α-diketones. Labelling studies, kinetic energy release values and the +E spectra of ions have been used to aid in the elucidation of the fragmentation pathways. It is proposed that the majority of ions have α-keto nitrile structures.     

Synthesis and psychotropic properties of furyl- and thienyl-germatranes

Trihalogermyl-furans and -thiophenes were prepared by inserting germanium dibromide (GeBr₂) generated from the dibromogermane(II) dioxanate complex into the carbon-halogen bond of halo-furans and -thiophenes. Their ethanolysis and transesterification by triethanolamine yielded the germatranes which were subjected to psychotropic activity assays. The psychotropic properties of germatranes were found to depend on the type of the heterocycle and on the position of the germatrane moiety.     

Reactivity of the A-CH=N=NR-CX-B System. 1,3,4-thiadiazoles and Δ2 -thiadiazolines

The reactivity of the - system towards ferric chloride has been investigated. The cyclo-oxidation reaction led to the formation of 2-amino-5-thenoyl-1,3,4-thiadiazoles and 4-methyl-5-imino-2-thenoyl-Δ²-1,3,4-thiadiazolines. Their structures were proven spectro-scopically and chemically (nucleophilic attack and formation of the related 2-amino-1,3,4-thiadiazoles and 4-methyl-5-imino-Δ²-1,3,4-thiadiazolines).     

Effect of Chain‐Length Dependence of Interaction Parameter on Spinodals for Polydisperse Polymer Blends

Summary: The chain‐length dependence of the Flory‐Huggins (FH) interaction parameter is introduced into the FH lattice theory for polydisperse polymer‐blend systems. The spinodals are calculated for the model polymer blends with different chain lengths and distributions. It is found that all the related variables, r_n, r_w, r_z, and chain‐length distribution, have effects on the spinodals for polydisperse polymer blends.

The spinodals at different chain lengths.     

Cellulose Derivatives Carrying Triphenylamine (TPA) Moieties: Synthesis and Electro‐Optical Properties

A novel ethyl cellulose derivative [poly( 1 )] that carries triphenylamine moieties is synthesized with a moderate number‐average molecular weight up to 78 200 in 85% yield by the reaction of 4‐(diphenylamino)benzoic acid with the residual hydroxy group of ethyl cellulose. Poly( 1 ) is soluble in common organic solvents including toluene, CHCl₃, CH₂Cl₂, and tetrahydrofuran while insoluble in hexane, diethyl ether, and methanol. The polymer emits blue–green fluorescence with quantum yields up to 65% in CHCl₃ and displays unique solvatochromism. The cyclic voltammograms of poly( 1 ) indicate that the polymer carrying TPA moieties is electrochemically redox active. The onset temperature of weight loss of the poly( 1 ) is about 177 °C according to thermogravimetric analysis in air.

     

Dipolmomente 1, 6-überbrückter [10]- Annulene

The dipole moments of 1, 6-bridged [10]-annulenes of type I (X = CH₂, O, NH) and of bromo derivatives with X = CH₂, O are in agreement with the previously established structure of these compounds if a partial moment of approximately 0,8 D is assigned to the non-planar π-electron system.     

Horseradish Peroxidase as a Catalyst for Atom Transfer Radical Polymerization

The hemoprotein horseradish peroxidase (HRP) catalyzes the polymerization of N‐isopropylacrylamide with an alkyl bromide initiator under conditions of activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) in the absence of any peroxide. This is a novel activity of HRP, which we propose to name ATRPase activity. Bromine‐terminated polymers with polydispersity indices (PDIs) as low as 1.44 are obtained. The polymerization follows first order kinetics, but the evolution of molecular weight and the PDI upon increasing conversion deviate from the results expected for an ATRP mechanism. Conversion, and PDI depend on the pH and on the concentration of the reducing agent, sodium ascorbate. HRP is stable during the polymerization and does not unfold or form conjugates.

     

Microphase‐Separated Brushes on Square Platelets in PS‐b‐PEO Thin Films

In polystyrene‐block‐poly(ethylene oxide) thin films, microphase‐separated brushes on the square platelets can be obtained via fast solvent evaporation by controlling the tethering density (0.08 < σ < 0.11). The tethering density of the brushes is proportional to the thickness of the PEO crystal and increases with increasing initial solution heating temperature (T_i). When T_i < T_m, where T_m is the melting point of PEO, brushes with microphase‐separated structures are observed. The formation of microphase‐separated brushes depends on two factors: the strong incompatibility between PS and noncrystalline PEO chains (attached to the crystalline PEO) and the weak interaction between PS‐PS brushes.

     

Novel C‐acylated triazole derivatives of ravuconazole,an azole antifungal agent

Novel C‐acylated triazoles were synthesized from ravuconazole via bicyclic triazole lactone. The synthesis and antifungal activity of these C‐acylated derivatives are described.     

Synthesis of Optically Active Polymer with P‐Stereogenic Phosphine Units

Optically active polymer containing P‐stereogenic bisphosphine as a repeating unit in the main was successfully synthesized. A coordinated borane on the phosphorus atom could be completely removed by an organic base under mild condition, and the successive reaction with Pd afforded the corresponding polymer complex. The chirality of P‐stereogenic centers was transferred to the m‐phenylene‐ethynylene linkers by complexation because of the prohibition of the rotary motion of the bisphosphine‐Pd unit.

     

Alkyne‐Linked Poly(1,8‐carbazole)s: A Novel Class of Conjugated Carbazole Polymers

Novel conjugated carbazole polymers based on the alkyne‐linked 1,8‐carbazole structure are synthesized in high yield by the Sonogashira cross‐coupling reaction and acetylenic oxidative coupling reaction. The polymers are thermally stable and highly soluble in common organic solvents such as CHCl₃, CH₂Cl₂, and THF. As compared to ethynylene‐linked polymer, the butadiynylene‐linked polymer display a bathochromic shift in the absorption maximum and end absorption position. In addition, the fluorescence behaviors in CH₂Cl₂ are almost identical for both polymers. Electrochemical measurements indicate that the ethynylene‐linked polymer possesses a lower first oxidation potential than the butadiynylene‐linked one.

     

Poly(diindenonaphthalene) and Poly(indenofluorene) – Tuning the Absorption Properties of Low Bandgap Cross‐Conjugated Polymers

Summary: Semiconducting polymers with moderate HOMO–LUMO energy gaps between 1.5 and 2.0 eV are of increasing attraction as donor components of bulk heterojunction‐type organic solar cells. The synthesis and characterization of a novel cross‐conjugated, aromatic polymer, poly(diindenonaphthalene) PDIN, with a HOMO‐LUMO gap of ca. 1.6 eV (λ_max: 724 nm) in comparison to poly(indenofluorene) PIF, a previously described, structurally related polymer, is presented. The replacement of the central benzene ring of PIF by a naphthalene moiety in PDIN leads to an increase of the optical bandgap energy of ca. 0.16 eV.

Chemical structure of PIF and PDIN.     

Patterning Proteins on Surfaces of Cross‐Sectioned Multilayer Polymer Films

Summary: A new approach is introduced to create submicrometer patterned surfaces using multilayer polymer films that contain alternating layers of two polymers, linear low‐density polyethylene (LLDPE) and ethylene‐co‐(acrylic acid) copolymer (EAA). Patterned templates have been prepared by microtoming the multilayer molded sheets. Regionally confined chemical functionality is confirmed by grafting an amine‐terminated biotin and adsorbing streptavidin specifically on the alternating layers of EAA.

Fluorescence micrograph of the Alexa488‐streptadivin patterned polymer surface.     

Synthesis and Characterization of Novel Ethene‐graft‐Ethene/Propene Copolymers

The synthesis of ethene/propene macromers with a high amount of sterically unhindered vinyl groups is described. These macromers are incorporated as long‐chain branches into polyethylene (PE). The remaining low molecular fractions were removed by Soxhlet extraction. Up to 60 wt.‐% macromer was included, which leads to comb‐like molecular topographies that distinctly affect the rheological behavior. The thermal activation energy increased significantly and the zero shear‐rate viscosity enhancement factor η ₀ / η was also changed noticeably.

     

Instrumentation for Combinatorial and High‐Throughput Polymer Research: A Short Overview

Starting in biochemistry and pharmaceutical chemistry, combinatorial methods, automated synthesis and high‐throughput characterization are being further developed for organic synthesis and polymer research. The development is strongly driven by the achievements in biochemistry and pharmaceutical chemistry and the need to minimize the time‐to‐market for novel polymeric products. The success of high‐throughput methodologies in polymer science is partially limited by the commercially available hardware (synthesizers, workstations, robots, online‐characterization instruments, etc.) and software. A short overview of commercially available equipment for polymer research is provided in this Review.

     

Insertion of Copper(II)/Schiff‐Base Complexes with NLO Properties into Commercial Polycarbonates by Thermal Processes

The preparation of a bisphenol‐A carbonate copolymer, containing Cu‐diimine units with nonlinear optical (NLO) properties, and its MALDI‐TOF mass spectrometric characterization are reported. Contrary to the usual synthetic method, NLO groups were inserted directly into a commercial polycarbonate by prolonged heating at 250 °C. This innovative procedure allows to obtain a Cu/diimine‐containing polymer of high molecular weight.