1,720,958 research outputs found
From terpenes to sustainable and functional polymers
No full textOur dependence on fossil-fuel based raw materials and alarming plastics accumulation in the environment has inspired many scientists to design and implement more sustainable approaches for polymer synthesis. The identification and assessment of new and renewable biobased monomers has become a major topic of interesten routeto a circular economy. In this respect, terpenes and terpenoid scaffolds have attracted much attention due to their ubiquitous nature and high functionality. This minireview uncovers recent advancements in the synthesis of terpene-based polymers, and specifically discusses the formation of terpene-derived polycarbonates, polyesters, polyurethanes and polyamides. The potential of these polymers in post-synthetic curing and modifications is also highlighted to illustrate the opportunities that exist to develop new polymer formulations beyond bench scale
Synthesis and Characterization of Biobased Polyesters with Tunable T-g by ROCOP of Beta-Elemene Oxides and Phthalic Anhydride
Get PDFThe use of terpene-based oxides derived from beta-elemene is reported in the context of new functional semiaromatic polyester development. In particular, poly(beta-elemene monoxide-alt-phthalic anhydride) featuring two double bonds per repeating unit having distinct reactivity is conveniently prepared by iron- and aluminum-mediated ring-opening polymerization (ROCOP). Sequential and selective transformation of each of these double bonds is addressed by epoxidation allowing one to precisely manipulate the degree and nature of the functionality in the polymer backbone while modulating the T-g from 68 to 121 degrees C. Direct access to cross-linked polyesters is demonstrated by ROCOP of bifunctional beta-elemene dioxide and phthalic anhydride furnishing a material with a Tg of 125 degrees C
Mechanistic guidelines in nonreductive conversion of CO2: the case of cyclic carbonates
No full textNonreductive conversion of carbon dioxide has received wide attention in the area of homogeneous catalysis, especially in the context of cyclic organic carbonate formation processes. Whereas the synthesis of such carbonates has been central in the majority of the scientific contributions with a crucial role for catalyst design, much less attention has been paid to the mechanistic requisites that allow for more challenging transformations to occur. In this perspective article, a detailed summary of the efforts leading to a better understanding of the manifolds providing efficient preparative routes for cyclic organic carbonates is presented, considering primarily experimental and theoretical breakthrough results
Unlocking the Potential of Substrate-Directed CO(2)Activation and Conversion: Pushing the Boundaries of Catalytic Cyclic Carbonate and Carbamate Formation
No full textThe unparalleled potential of substrate-induced reactivity modes in the catalytic conversion of carbon dioxide and alcohol or amine functionalized epoxides is discussed in relation to more conventional epoxide/CO(2)coupling strategies. This conceptually new approach allows for a substantial extension of the substitution degree and functionality of cyclic carbonate/carbamate products, which are predominant products in the area of nonreductive CO(2)transformations. Apart from the creation of an advanced library of CO2-based heterocyclic products and intermediates, also the underlying mechanistic reasons for this novel reactivity profile are debated with a prominent role for the design and structure of the involved catalysts
Photocatalytic synthesis of substituted cyclic carbonate monomers for ring-opening polymerization
No full textAn operationally mild, ruthenium-based photocatalytic protocol has been developed for the conversion of gamma-mono- and gamma,gamma-disubstituted allyl carbonates in the presence of Umemoto's reagent to afford substituted six-membered cyclic carbonates. Variation and diversification of the carbonate ring substitution provides access to new monomers useful in ring-opening polymerization leading to polycarbonates with potentially tailored properties, as illustrated by comparative experiments using monomers with different pi-stacking capabilities
Recent progress in the catalytic transformation of carbon dioxide into biosourced organic carbonates
No full textCyclic organic carbonates are among the most widely studied targets in the nonreductive conversion of carbon dioxide using oxiranes as the common reaction partners. Apart from using fossil fuel based precursors, recent developments have shown that biomass related feedstock can also serve as coupling partner for CO2 allowing the preparation of more functional and complex types of carbonate architectures. This tutorial review places this latter development in the current context of new and more sustainable material designs, and highlights the main types of biomass that have been examined using primarily homogeneous catalysis approaches
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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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