1,721,051 research outputs found
Synthesis of microspheres as versatile functional scaffolds for materials science applications
No full textFunctional polymeric microspheres are of great interest as they have high potential as functional scaffolds in material science applications. Highly cross-linked poly(divinyl benzene) (pDVB) microspheres can be synthesized via the precipitation polymerization technique. Recently, various methods of controlled polymerization techniques (e.g., atom transfer radical polymerization (ATRP), reversible addition fragmentation chain transfer (RAFT), and anionic ring-opening polymerization (AROP)) and highly orthogonal conjugation methods (e.g., copper-catalyzed Huisgen 1,3-dipolar cycloaddition of azides and terminal alkynes (CuAAc), thiol-ene addition and RAFT hetero Diels-Alder cycloaddition (RAFT-HDA)) have been applied to functionalize microspheres via the “grafting from” and “grafting to” approaches. The synthesis of pDVB microspheres, their susbsequent modification via grafting of polymer strands to the surface, and the characterization of the obtained functional particles are reviewed
Surface grafting via the reversible addition–fragmentation chain-transfer (RAFT) process: From polypropylene beads to core–shell microspheres
No full textLeonie Barner studied chemistry at the Universities of Kassel and Gottingen ( Germany). She joined Michael Buback's group and received her Ph. D. in 1998. From 1998 to 2001 she held a senior research position at Sartorius ( Gottingen), developing microfiltration membranes for biotechnology applications. She then joined the Centre for Advanced Macromolecular Design, where she currently holds a senior research associate position. Her prime research interests are controlled/ living radical polymerization methods and the development of novel polymeric surfaces for biotechnology and combinatorial chemistry applications
Polymers with well-defined end groups via RAFT - synthesis, applications and postmodification
No full textThe control over the chain-end functionality of a polymeric chain produced by\ud
controlled/‘living’ radical polymerization is inherent to the mechanism of the re- action. Indeed, \ud
the final product contains a majority of polymeric chains showing an ω-functional end group which is \ud
used to control the molecular weight growth. The growth of the molecular weight can be mediated \ud
either via the reversible homolytic cleavage of the covalent bond between the terminal carbon and \ud
the chain-end group (e.g. halogen for transition-metal-mediated living radical poly- \ud
merization/atom transfer radical polymerization (ATRP), nitroxide for nitroxide- mediated \ud
polymerization (NMP)) or via the degenerative transfer of chain-end groups between propagating \ud
radicals and dormant species (e.g. thiocarbonylthio groups for reversible addition–fragmentation \ud
chain transfer (RAFT)). Furthermore, α-functional end groups can also be introduced via the \ud
initiator/mediator of the polymerization, for example, halogen alkyls (ATRP), alkyl nitroxides \ud
(NMP) or\ud
dithioesters (RAFT)..
Applications of Lawesson's reagent in organic and organometallic syntheses
No full textThis review, including 245 references, describes the application of Lawesson's reagent [2,4-bis(p-methoxyphenyl)-1,3-dithiaphosphetane-2,4-disulfide] LR in organic and organometallic syntheses. Thionations of carbonyl-containing compounds as well as unexpected reactions are shown for different applications (e.g. cyclizations, rerrangements, syntheses of heterocyclic compounds etc.). Syntheses of novel organometallic compounds by LR are also discussed
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Thermally responsive core-shell microparticles and cross-linked networks based on nitrone chemistry
No full textComplex cross-linked soluble architectures with molecular weights ranging from 25 000 to 71 000 g mol(-1) and polydispersities (PDIs) ranging from 2.5 to 8.1 are generated using nitrone mediated chemistry. These cross-linked architectures are subsequently cleaved into their constituting fragments, i.e. linear chains with molecular weights ranging from 36 000 to 40 000 g mol(-1) and a PDI of 2.0 or network fragments with molecular weights ranging from 28 000 to 30 000 g mol(-1) and PDIs from 2.5 to 3.7, respectively. The cleavage into linear chains or network fragments depends on the pathway of network formation. Nitrone mediated reactions are also applied for the synthesis of microspheres. Conventional distillation precipitation polymerization was performed in the presence of a nitrone, leading to uniform microspheres with diameters ranging from 2.2 to 2.4 mu m. These microspheres feature alkoxyamine functionalities throughout their interior and on their surface. The alkoxyamine functionality on the surface is employed in a subsequent nitroxide mediated polymerization (NMP) with N-isopropylacrylamide (NiPAAm) in a ‘grafting from' approach to generate pNiPAAm on the surface of the microspheres. The resulting stimuli-responsive core-shell microspheres are characterized via SEM, XPS, elemental analysis as well as turbidity measurements. The characterization methods confirm the presence of a stimuli-responsive layer of pNiPAAm on the microspheres' surface
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Controlled growth of protein resistant PHEMA brushes via S-RAFT polymerization
No full textThe reversible addition-fragmentation chain transfer polymerization of 2-hydroxyethyl methacrylate (HEMA) from surfaces (S-RAFT) using an R-group-attached chain transfer agent (CTA) is presented. The approach was exploited for the efficient preparation of well-defined PHEMA brushes of up to 50 nm thickness in a controlled fashion without using any cytotoxic catalyst. The chemical composition, morphology and wettability of the samples were assessed by X-ray photoelectron spectroscopy, atomic force microscopy and water contact angle measurements, while the growth kinetics were studied by monitoring the dry thickness via spectroscopic ellipsometry. The mechanism and kinetics of the RAFT polymerization on the surface-in the presence of a sacrificial CTA and of solvent mixtures with different polarities-were investigated. A marked effect of the concentration of the sacrificial CTA on the kinetics was observed. Importantly -and for the first time -the living PHEMA brushes were exploited as macroRAFT agents for chain extension, and thicknesses up to 70 nm were achieved. The prepared PHEMA brushes were challenged with protein solutions demonstrating their resistance to fouling
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