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showing 10 items of 3963 documents
Natural Anti-oxidants for Bio-polymeric Materials
2017
In this work, three different bio-polymers, i.e. a commercial starch-based polymer (Mater-Bi®) a bio-polyester (PLA), and a bio-polyether (PEO) were additivated with quercetin, a natural flavonoid antioxidants, in order to formulate biobased films for eco-sustainable packaging and outdoor applications. The photo-oxidation behavior of unstabilized and quercetin stabilized films has been evaluated and compared with that of films additivated with a commercial synthetic light stabilizer. Obtained results show that quercetin molecules are able to slow down the photodegradation rate of all investigated bio-polymeric films, opening new avenues in the formulation of fully renewable polymer-based sy…
Nonlinear Macromolecules by Ring-Opening Polymerization
2012
Ring-opening polymerization (ROP) is a well-established method for the controlled synthesis of linear polymers, which can be found in various everyday applications. However, during the past decades, there has been an increasing interest in the generation of nonlinear highly branched polymers, profiting from the fascination created by the structurally perfect dendrimers. The applicability of various heterocyclic monomers renders the ring-opening multibranching polymerization (ROMBP), a versatile tool for the generation of multifunctional hyperbranched polymers. First, the historical key steps leading to the development of ROMBP are described, which is the basis for the controlled synthesis o…
ortho-Metalation of aromatic ethers by yttrium alkyl complexes that contain a linked amido-cyclopentadienyl ligand
2003
Abstract The reaction of the half-sandwich alkyl complex [Y(η5:η1-C5Me4CH2SiMe2NtBu)(CH2SiMe3)(THF)] (1) with anisole smoothly gives the ortho-metalation product [Y(η5:η1-C5Me4CH2SiMe2NtBu)(2-C6H4OMe)(THF)] (2). 3- and 4-Methylanisole as well as phenetole analogously undergo ortho-metalation, whereas thioanisole, N,N′-dimethylaniline, fluorobenzene, and trifluorobenzene do not react with yttrium complex 1. 2-Methylanisole reacts with 1 under activation of the ring methyl group to give the 2-methoxybenzyl complex [Y(η5:η1-C5Me4CH2SiMe2NtBu)(CH2C6H4OMe-2)(THF)] (6). A single-crystal X-ray structure analysis of the 2-anisyl complex 2 revealed a four-legged piano-stool configuration with the me…
Hyperbranched aliphatic polyether polyols
2012
Hyperbranched polymers, dendritic macromolecules with branch-on-branch structures, have become an important polymer class since the early 1990s. They combine several advantages of the perfectly branched dendrimers with easy accessibility, typically in a one-step synthesis. Hyperbranched polyethers are a particularly interesting class of chemically stable and often biocompatible materials. Multifunctional hyperbranched polyethers with controllable molar mass and comparably low polydispersities can been prepared using hydroxyl-functional epoxides or oxetanes for polymerization via anionic and cationic polymerization mechanisms. Here, we review the progress in the preparation, characterization…
Functional end groups for polymers prepared using ring-opening metathesis polymerization.
2011
The precise placement of functional groups on the chain-ends of macromolecules is a major focus of polymer research. Most common living polymerization techniques offer specific methods of end-functionalization governed by the active propagating species and the kinetics of the polymerization reaction. Ring-opening metathesis polymerization has established itself as one of the most functional-group-tolerant living polymerization techniques known, but this tolerance has limited the number of available functionalization reactions. Metathesis chemists have therefore been required to develop a variety of end-functionalizations, adapting each of them to the reactivity scheme of the particular cata…
Synthesis of novel isoxazoline-fused cispentacin stereoisomers
2009
Abstract New isoxazoline-fused cispentacins were prepared by the 1,3-dipolar cycloaddition of nitrile oxides to β-amino esters containing a cyclopentene skeleton. This synthetic procedure gave regio- and diastereoisomers of the cispentacins. The synthetic route was extended to the synthesis of these compounds in enantiomerically pure form.
A pea nuclear protein that is induced by dehydration belongs to the vicilin superfamily
2000
The purification to homogeneity of p16, a protein with an electrophoretic mobility compatible with an apparent molecular mass of 16 kDa, from nuclei of ungerminated pea embryonic axes is described. A cDNA clone of its gene, which was designated psp54, was also isolated. The psp54 cDNA contains an open reading frame coding for a 54.4-kDa polypeptide (p54). p16 corresponds to the C-terminal third of p54, although the mechanisms by which the primary polypeptide could be processed are not yet known. The sequence of p54 is 60% identical with that of the precursor of a sucrose-binding soybean protein, and, to a lesser extent (31-34%), it shares homology with some storage proteins. p16 is also 30%…
Investigation of α-amino acid N-carboxyanhydrides by X-ray diffraction for controlled ring-opening polymerization
2019
Abstract The need for a scalable synthesis of not sequence defined polypeptides as biomaterials is met by the ring-opening polymerization of α-amino acid N-carboxyanhydrides (NCAs). Even though this polymerization technique appears straight forward, it holds pitfalls in terms of reproducibility and overall control over the polymerization conditions, which depends, beside choice of solvent or initiator, significantly on reagent purity. In addition, the synthesis of monomers can lead to the formation of racemic amino acids. Thus, in this work, we describe the benefits of highly pure monomers in order to control nucleophilic ring-opening polymerization NCAs. Hereby, monomer purity is investiga…
Non-linear effect of 18-crown-6 in propylene oxide polymerization with potassium glycidoxide used as the inimer
2004
A new initiating system containing potassium glycidoxide as the inimer and 18-crown-6 as the activator was used for propylene oxide polymerization. It was found that the rate of the reaction increased together with the crown ether concentration in a rather unexpected way. Two maxima of that parameter were found in the case of crown ether : inimer molar ratio equal to 3:1 and 6:1. On the other hand, the molecular weight of polymers showed two minima in those conditions. The heterogeneity of the reaction mixture and interactions between species present in the system could be responsible for the phenomena observed. The polydispersity of the polymers obtained was equal to about 1.2 and it was i…
Cyclodextrins in polymer synthesis: Free radical polymerization of cyclodextrin complexes withN-methacryloyl-11-aminoundecanoic acid orN-methacryloyl…
1998
The hydrophobic monomers N-methacryloyl-11 -aminoundecanoic acid (1) or N-methacryloyl-1-aminononane (2) were incorporated as guests into the cavity of heptakis(2,6-di-O-methyl)-β-cyclodextrin (Me 2 -β-CD) as a host, yielding the water compatible monomers N-methacryloyl-l 11-aminoundecanoic acid/ Me 2 -β-CD-complex (1a) and N-methacryloyl-1 -aminononane/Me 2 -β-Cl complex (2a). These complexes were polymerized radically in aqueous medium. The resulting polymers 1b and 2b which were obtained from the complexes 1a and 2a, are insoluble in water because of the unthreading of the cyclodextrin during the polymerization. The polymerization rate of 1a and 2a is high in comparison to the rate of th…