Macromol. Rapid Commun. 19/2011Lee, Yeonju; Geckeler, Kurt E.
doi: 10.1002/marc.201190051pmid: N/A
Front Cover: Biocompatible single‐walled carbon nanotubes wrapped by the water‐soluble, synthetic polyampholyte, poly(2‐(dimethylamino)ethyl methacrylate‐co‐methacrylic acid), are internalized by mouse embryonic fibroblast NIH‐3T3 cells without any significant cytotoxicity. Further details can be found in the article by Y. Lee and K. E. Geckeler* on page 1518.
Kumada Catalyst‐Transfer Polycondensation: Mechanism, Opportunities, and ChallengesKiriy, Anton; Senkovskyy, Volodymyr; Sommer, Michael
doi: 10.1002/marc.201100316pmid: 21800394
Kumada catalyst‐transfer polycondensation (KCTP) is a new but rapidly developing method with great potential for the preparation of well‐defined conjugated polymers (CPs). The recently discovered chain‐growth mechanism is unique among the various transition metal‐catalyzed polycondensations, and has thus attracted much attention among researchers. Most progress is found in the areas of mechanism and external initiation via new initiators, but also the number of monomers other than thiophene that can be polymerized is steadily increasing. Accordingly, the variety of CP chain architectures is increasing as well, and a considerable contribution of KCTP toward more efficient materials can be expected in the future. This review critically focuses on very recent progress in the synthesis of CPs and the mechanism of KCTP, and is finally aimed at providing a comprehensive picture of this exciting polymerization method.
Polyampholyte‐Wrapped Carbon Nanotubes: Preparation and Internalization by Embryonic Fibroblast CellsLee, Yeonju; Geckeler, Kurt E.
doi: 10.1002/marc.201100226pmid: 21751277
The cytotoxicity and cellular uptake of carbon nanotubes (CNTs) has recently attracted considerable interest because of the issue of biosphere‐nanomaterial interactions. The biocompatibility of CNTs is determined by the metal impurities in the CNTs, the size of the CNTs and the CNT dispersion states; in particular, the type of surface modifications on the CNTs affects how they interact with cells and determines their cytotoxicity and cellular uptake. In this study, biocompatible single‐walled carbon nanotubes (SWNTs) wrapped with a water‐soluble copolymer, poly(2‐(dimethylamino)ethyl methacrylate‐co‐methacrylic acid) (PDM), were prepared. We report that these SWNTs have enhanced water dispersibility and cellular internalization but no significant cytotoxic activity against mouse embryonic fibroblast NIH‐3T3 cells.
Mechanics of Homeotropically Ordered Smectic‐A Elastomers with Global Oblate Chain ConformationKramer, Dominic; Finkelmann, Heino
doi: 10.1002/marc.201100259pmid: 21786356
Smectic‐A elastomers combine one‐dimensional translational order of rod‐like segments with the rubber elasticity of a polymer network. In recent years, detailed investigations were carried out on elastomers showing a global prolate chain conformation. In this communication, the first experiments on fluorinated SA elastomers exhibiting a global oblate chain conformation are presented, where the polymer chains are on average compressed along the layer normal of the lamellar phase structure. The mechanical anisotropy is studied by means of thermoelastic experiments and stress–strain measurements. For the first time, the layer compression modulus B of smectic elastomers is directly measured. B is significantly larger as compared to conventional low molar mass liquid crystals and decreases significantly with increasing local disorder introduced by the isotropic crosslinker.
Reversible Photoinduced Switching of Permeability in a Cast Non‐Porous Film Comprising Azobenzene Liquid Crystalline PolymerLiu, Jian; Wang, Mingle; Dong, Mingling; Gao, Liude; Tian, Jingjing
doi: 10.1002/marc.201100370pmid: 21786360
Permeation characteristics of an azobenzene‐containing liquid crystalline (LC) non‐porous film are investigated using a metallic corrosion method. Thin films (300 nm) are fabricated by the solution casting of an azobenzene side‐chain LC polymer on freshly polished carbon steel coupons. Coated coupons are treated under the following conditions: a) gradual annealing at a cooling rate lower than 1 °C · min−1 from 150 °C (above its Tg) to room temperature, and b) irradiation at 465 nm (20 mW · cm−2) with either circularly polarized light (CPL) or non‐polarized light (NPL). The morphology of these films is characterized using X‐ray diffraction, polarized optical microscopy, and transmission measurements. The results suggest that the annealing treatment resulted in the formation of a polydomain structure consisting of locally ordered small smectic domains that lack mutual orientation. Ordered micro domains are surrounded by disordered phases. CPL and NPL irradiation generates a monodomain orientated structure and an isotropic liquid crystal glass, respectively. The permeability of these non‐porous films treated by CPL, NPL, and annealing are found to be 6.14 × 10−4, 1.92 × 10−2, and 1.56 × 10−3 cm3 · m−2 · d−1. An orientation‐dependent structure model is constructed to explain the permeation phenomenon, considering the ordered phase is impermeable, only the disordered phase is accessible to penetrating molecules. Fast switching of gas permeation is demonstrated by alternative irradiation of the film with CPL and NPL, which results in an approximately 30‐fold difference in the permeability of the non‐porous film.