1,721,140 research outputs found
Kinetics of Amine-Bis(phenolate) Iron-Mediated ATRP Up to High Pressure
No full textAtom-transfer radical polymerization (ATRP) of styrene catalyzed by chloro-substituted amine-bis(phenolate)iron complexes was investigated via online vis/NIR spectroscopy up to 6000 bar. Pressure significantly increases the rate of ATRP by enhancing both the equilibrium constant, K-ATRP, and the propagation rate coefficient, k(p). The observed negative reaction volume, Delta V-r(K-ATRP), is due to a stronger contraction of the ligand sphere for the Lewis-acidic Fe-III complex compared to the Fe-II complex. Despite the enormous rate enhancement of ATRP, narrow molar mass distributions may be obtained even at very high pressure and thus very high rates
Data supporting "Iron(II) b-ketiminate complexes as mediators of controlled radical polymerisation" (2016) in Dalton Transactions - EPSRC EP/M000842/1
No full textA series of tridentate, ONO- and ONN-chelating β-ketiminate ligands were synthesised via condensation
reactions, and complexed with iron(II) using [Fe(N(SiMe3)2)2THF]. The complexation reactions proceeded
in high yields to generate novel, monomeric, tetracoordinate iron(II) complexes, each bearing a bis(trimethylsilyl)
amide ligand, as confirmed by X-ray crystallography. These complexes were amenable to
further reaction (protonolysis) with alcohols and phenols, generating alkoxide/phenolate-containing
complexes that were dimeric in the solid state. All complexes synthesised were screened as potential
mediators of the controlled radical polymerisation (CRP) of styrene and methyl methacrylate under both
atom transfer radical polymerisation (ATRP) and organometallic mediated radical polymerisation (OMRP)
conditions. Whilst all of the complexes were relatively poor ATRP mediators under the conditions used here,
regardless of monomer choice, dispersities (Đ) as low as 1.58 for styrene and 1.23 for methyl methacylate
polymerisation under OMRP conditions could be achieved. The better performance in methacrylate polymerisation
suggests the formation of a stronger metal–carbon bond in these systems. In particular, the use
of a β-ketiminate ligand functionalised with an N,N-dimethylethylene pendant arm and a 2,6-diphenylphenolate
ligand affords a potential Fe-based mediator of methyl methacrylate OMRP.Raw data files for X-ray crystallography, NMR spectroscopy and Gel-permeation Chromatography measurements
Tacticity Control in the Synthesis of Poly(lactic acid) Polymer Stars with Dipentaerythritol Cores
Full text linkThe synthesis of a family of polymer stars with arms of varied tacticities is discussed. The effect of polymer tacticity on the physical properties of these polymer stars is presented. Dipentaerythritol cores support six poly(lactic acid) (PLA) arms. Lewis acidic tin and aluminum catalysts control the polymerization to afford polymer stars of variable tacticity. The analysis of these polymers by NMR spectroscopy, thermogravimetric analysis, powder X-ray diffraction, and differential scanning calorimetry reveals the effects of tacticity control on the physical properties of the polymer stars. Preliminary decomposition studies suggest that the biodegradation profile of a polymer star may also be tuned by stereochemical control. This is the first systematic altering of tacticity in PLA polymer stars, showing that polymer tacticity can have a great impact on star properties.</p
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
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
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