Aziridine Termination of Living Anionic Polymerization

A switch from carbanions to aza‐anions is performed by the addition of N‐tosylaziridine (TAz) to living poly(styryl) (PS) chains. This is the first example of carbanionic aziridine ring‐opening which was previously activated by amidation with a tosyl group to enable nucleophilic ring‐opening by the living chain end. Poly(styrene)‐tosylaziridines (PS‐TAz) with narrow molecular weight distributions and variable molecular weights are synthesized. The removal of the tosyl group and subsequent functionalization is shown, evidencing quantitative transfer to azaanionic species. All polymers are characterized in detail by ¹H NMR spectroscopy, DOSY ¹H NMR spectroscopy, and size exclusion chromatography (SEC). This strategy allows the introduction of amine groups via anionic polymerization in analogy to the well‐established epoxide termination.

     

From an Epoxide Monomer Toolkit to Functional PEG Copolymers With Adjustable LCST Behavior

The lower critical solution temperature (LCST) behavior of novel poly(ethylene glycol) (PEG)‐based copolymers bearing multiple functional groups, obtained by anionic ring‐opening (co)polymerization (AROP), has been investigated. Variable comonomer ratios of ethylene oxide (EO) and the corresponding oxiranes isopropylidene glyceryl glycidyl ether (IGG), ethoxyl vinyl glycidyl ether (EVGE), allyl glycidyl ether (AGE), or N,N‐dibenzyl amino glycidyl (DBAG), particularly designed to implement functional groups at the PEG backbone, were found to influence the LCST behavior. Sharp transitions from translucent to opaque solutions, comparable to other well‐established stimuli‐responsive polymers, were observed at temperatures ranging from 9 to 82 °C. The influence of the side group hydrophobicity could be quantified by the comparison of the different copolymer systems observed.     

Degradation patterns in water and oxygen of an inverted polymer solar cell

The spatial distribution of reaction products in multilayer polymer solar cells induced by water and oxygen atmospheres was mapped and used to elucidate the degradation patterns and failure mechanisms in an inverted polymer solar cell. The active material comprised a bulk heterojunction formed by poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) sandwiched between a layer of zinc oxide and a layer of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) that acted as, respectively, electron and hole transporting layers between the active material and the two electrodes indium-tin-oxide (ITO) and printed silver. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) in conjunction with isotopic labeling using H(2)(18)O and (18)O(2) enabled detailed information on where and to what extent uptake took place. A comparison was made between the use of a humid (oxygen-free) atmosphere and a dry oxygen atmosphere during testing of devices that were kept in the dark and devices that were subjected to illumination under simulated sunlight. It was found that the reactions taking place at the interface between the active layer and the PEDOT:PSS were the major cause of device failure in the case of these inverted devices, which are compatible with full roll-to-roll (R2R) coating and industrial manufacture. The PEDOT:PSS was found to phase separate, with the PEDOT-rich phase being responsible for most of the interface degradation in oxygen atmospheres. In water atmospheres, little chemically induced degradation was observed, whereas a large partially reversible dependence of the open circuit voltage on the relative humidity was observed. In addition, temporal aspects are discussed in regard to degradation mechanisms. Finally, analytical aspects in regard to storing devices are discussed.     

Carbon Fibre Prepregs: Simulation of a Thermo-Mechanical-Chemical Coupled Problem

In automotive industry research is done to replace high strength steel by combinations of steel and carbon-fibre prepregs (pre-impregnated fibres). It is planned to form both steel and uncured prepregs in one step followed by the curing process under pressure in the forming die. The ability to simulate the mechanical behaviour during forming and curing would allow more economical processes. The simulation of prepregs must regard highly anisotropic, viscoelastic and thermal- chemical properties. For this the model is split into an anisotropic elastic part, which represents the fibre fraction and an isotropic, viscoelastic part, representing the matrix. This part also contains curing, causing a dependency on time and temperature. During deep-drawing large deformations are occurring, so a large strain model regarding anisotropy, viscoelasticity and curing has been developed. Also experiments were made to validate this model. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the stability of a variety of organic photovoltaic devices by IPCE and in situ IPCE analyses - the ISOS-3 inter-laboratory collaboration

This work is part of the inter-laboratory collaboration to study the stability of seven distinct sets of state-of-the-art organic photovoltaic (OPV) devices prepared by leading research laboratories. All devices have been shipped to and degraded at RIS?-DTU up to 1830 hours in accordance with established ISOS-3 protocols under defined illumination conditions. In this work, we apply the Incident Photon-to-Electron Conversion Efficiency (IPCE) and the in situ IPCE techniques to determine the relation between solar cell performance and solar cell stability. Different ageing conditions were considered: accelerated full sun simulation, low level indoor fluorescent lighting and dark storage. The devices were also monitored under conditions of ambient and inert (N(2)) atmospheres, which allows for the identification of the solar cell materials more susceptible to degradation by ambient air (oxygen and moisture). The different OPVs configurations permitted the study of the intrinsic stability of the devices depending on: two different ITO-replacement alternatives, two different hole extraction layers (PEDOT:PSS and MoO(3)), and two different P3HT-based polymers. The response of un-encapsulated devices to ambient atmosphere offered insight into the importance of moisture in solar cell performance. Our results demonstrate that the IPCE and the in situ IPCE techniques are valuable analytical methods to understand device degradation and solar cell lifetime.     

Synthesis and reactivity of solid-supported organotrifluoroborates in Suzuki cross-coupling

Solid-supported organotrifluoroborates were prepared in high yields by ion exchange with Amberlyst resins. The reactivity of solid supported aryltrifluoroborates was evaluated in Suzuki-Miyaura couplings with numerous aryl bromide partners. Electron-rich and -poor substituents were tolerated on both substrates, providing yields up to 90%. Examples of alkyl-, alkenyl-, alkynyl-, and heteroaryltrifluoborates were also successfully cross-coupled to aryl halides.     

Adsorption behavior of iron phthalocyanine at the initial stage on Cu(100) surface

The adsorption behavior of iron phthalocyanine (FePc) on the Cu(100) surface at the initial stage has been investigated by combining scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. At low coverage, FePc molecules deposited on the sample surface at room temperature tend to adsorb dispersedly with their molecular planes parallel to the crystallographic directions of the substrate. Another interesting STM observation for the sub-monolayer coverage is that the molecular axes of FePc are aligned along [037] (as well as $\left[0\overline{3}7\right]$) azimuth. At the monolayer coverage and elevated temperature, two types of ordered structures are observed. The FePc adsorption sites for the experimentally observed two distinct ordered domains have been revealed through DFT calculations. With further increasing the coverage, molecular clusters are formed particularly near the step edges.     

Electronic effects of linker substitution on Lewis acid catalysis with metal-organic frameworks

Functionalized linkers can greatly increase the activity of metal-organic framework (MOF) catalysts with coordinatively unsaturated sites. A clear linear free-energy relationship (LFER) was found between Hammett σ(m) values of the linker substituents X and the rate k(X) of a carbonyl-ene reaction. This is the first LFER ever observed for MOF catalysts. A 56-fold increase in rate was found when the substituent is a nitro group.