Copolymerization of hepta‐1,6‐diene with ethylene using a cobalt–bis(imino)pyridine complex affords a polymer that contains trans‐1,2‐five‐membered rings in the repeating unit from hepta‐1,6‐diene. The ratio of the repeating units of diene to those of ethylene is controlled from 3: 97 to 50:50, depending on the reaction conditions. Isotope‐labeling reactions reveal that the major chain transfer pathway involves β‐hydrogen elimination of the polymer end formed after ethylene insertion.
Future advances in designing bioactive materials, such as antithrombotic coatings for cardiovascular stents, will require widely applicable and robust methods of surface modification. In this paper, we report on the development of multifunctional polymer coatings made by chemical vapor deposition (CVD) copolymerization. Polymer coatings of various [2.2]paracyclophane derivatives were co‐deposited in controlled ratios and their chemical composition verified by FT‐IR and X‐ray photoelectron spectroscopy. Furthermore, preliminary biocompatibility of these coatings was assessed using human umbilical vein endothelial cells and 3T3 murine fibroblasts. The parallel immobilization of two different antithrombotic biomolecules onto a CVD‐based copolymer is also demonstrated by orthogonal immobilization strategies.
Summary: A simple compounding technique for the fabrication of polymer nanocomposites with single‐walled carbon nanotubes having exceptional alignment and improved mechanical properties is described. The aligned‐nanotube composite was prepared by dissolving single‐walled carbon nanotubes in a solution of thermoplastic polyurethane and tetrahydrofuran. Solvent‐polymer interactions that induce the orientation of soft chain segments during the swelling and moisture curing stage are believed to serve as a driving force for the macroscopic alignment of the carbon nanotubes.
Alignment of single‐walled carbon nanotubes in thermoplastic polyurethane during polar solvent exposure. 相似文献
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.
Self‐assembly of two‐dimensional (2D) structures from functional molecules is of great scientific importance. Herein, using a typical linear conducting polymer, polyaniline as building blocks, 2D single crystalline microplates are successively produced. The structure of 2D microplates is clearly defined by selected area electron diffraction, X‐ray diffraction, and Raman spectroscopy. Owing to the anisotropic arrangement of linear conjugated PANI molecules, the microplate shows a typical anisotropic electrical transport property.
A compositional graded film of poly(ε‐caprolactone) (PCL) with 4,4′‐thiodiphenol (TDP), in the film thickness direction, was fabricated by self‐diffusing of TDP in the PCL melt. We found out the self‐bending deformation of the gradient film, which bent into a rolled‐up shape by itself. The initial shape of the film was flat when the sample was quenched from the melt. Upon the fast crystallization of PCL, the gradient film bent to the side with low TDP content. Then, after PCL crystallized the film bent to the opposite direction, that is, to the side with high TDP content. This bending to the TDP rich region was induced by not only the crystallization of PCL but also mass transfer due to the diffusion of TDP from TDP rich region to poor region.
Summary: We show in this communication that large‐scale necklace‐like single‐crystalline tetragonal perovskite PbTiO3 nanowires can be obtained via a simple electrospinning method. The morphology and the crystal structure are investigated by SEM, XRD, and HRTEM. The length of the necklace‐like PbTiO3 nanowires is from tens to several tens of micrometers, the wider the diameter of it is between 100 and 200 nm and the thinner the part is between 20 and 50 nm. The necklace‐like PbTiO3 nanowires exhibit high surface photovoltage under the action of external electric field, which is probably applicable in displaying photoelectric devices of heterojunction structure.
SEM image of the electrospinning necklace‐like PbTiO3 nanowires. 相似文献
Summary: The ring‐opening cationic polymerization of 2‐ethyl‐2‐oxazoline was performed in a single‐mode microwave reactor as the first example of a microwave‐assisted living polymerization. The observed increase in reaction rates by a factor of 350 (6 h → 1 min) in the range from 80 to 190 °C could be attributed solely to a temperature effect as was clearly shown by control experiments and the determined activation energy. Because of the homogenous microwave irradiation, the polymerization could be performed in bulk or with drastically reduced solvent ratios (green chemistry).
Monomer conversion, represented by the ratio ln{[M0]/[Mt]}, plotted against time for six temperatures in the range from 80 to 180 °C, and polymerization reaction vials, showing an increase in yellow color for those reactions performed (well) above and below 140 °C, indicating side reactions. 相似文献
We report for the first time the preparation of single polypyrrole (PPy) molecule chains using a “metal‐organic framework” with 1 nm channels as a template. The obtained one‐dimensional (1‐D) PPy has highly structure order and excellent conductivity, which has improved by as much as five orders of magnitude in comparison with that of 2‐D PPy.
The kinetics of microemulsion polymerization depend on the structure of the initial microemulsion and the transport of species between the aqueous domain, the micelles, and the polymer particles. The water solubility of the monomer and the proximity of the initial microemulsion composition to a phase boundary are key considerations for studying microemulsion polymerization kinetics and producing the desired products. Complications frequently arise in the synthesis of copolymers or the incorporation of controlled polymerization mechanisms because of the compartmentalized nature of microemulsion polymerizations.
Summary: Four constitutionally isomeric copoly(amide acid)s (coPAAs), two alternating and two random, have been successfully obtained from the same combination of one non‐symmetrical alicyclic tetracarboxylic dianhydride (1.0 molar equivalents) and two symmetric aromatic diamines (0.5 molar equivalents each) by only slightly changing the reaction procedures. When the reaction mixture is subjected to chemical imidization conditions without isolation of coPAAs, the corresponding copolyimides (coPIs) are obtained in one pot. All of the coPIs are slightly yellow amorphous powders and the solubility of them is similar to each other. The glass transition temperatures of the alternating coPIs are lower in comparison to those of the random coPIs.
Schematic of the possible arrangement of monomers in the copoly(amide acid)s/copolyimides synthesized here. 相似文献
New multifunctional copoly(2‐oxazoline) nanoparticles were prepared for cell studies. The polymer contains double‐bond side chains as potential reaction sites for “thio”‐click reactions as well as a fluorescein label covalently bound to the polymer backbone. Using the nanoprecipitation technique, spherical nanoparticles of 200–800 nm were obtained. Confocal laser scanning microscopy measurements revealed the cellular uptake of the nanoparticles.
Well‐defined PEO‐b‐PMMA was prepared, initiated by macroinitiator PEO‐Br, by means of ATRP, where esterification of the terminal hydroxyl group of PEO with 2‐bromoisobutyryl bromide yielded a macroinitiator PEO‐Br. Highly ordered microporous films (hexagonal pattern) were constructed by emulsion micelles of such amphiphilic diblock copolymer formed from a solution with CHCl3/H2O/THF = 100:5:10 (v/v). We also constructed the microporous films using diblock copolymer by the current water‐assisted method.
