Search results for " Fiber"

Organolanthanides, catalysts for specific olefin-diene copolymerization: access to new materials

2001

Abstract Non-hindered ansa dicyclopentadienylallyl complexes of samarium, [(CMe2C5H4)2Sm(allyl)]n, and (CMe2C5H4)2Sm(allyl)L (L=THF or allylLi) polymerize isoprene without an aluminum cocatalyst. The polymerizations are highly stereospecific, affording nearly quantitatively 1–4 trans polyisoprene. In the presence of linear 1-olefins, copolymers are formed, with 6–10% of olefin inserted; the 1–4 trans structure of the polyisoprene chain is not altered, and only one olefin molecule is inserted between two polyisoprene fragments. In the common initiator of these three catalytic systems, the (CMe2C5H4)2Sm(allyl) moiety, only one vacant site would be available. As a consequence of the presence o…

Revisiting the photochemical synthesis of [FeFe]-hydrogenase mimics: reaction optimization, mechanistic study and electrochemical behaviour

2020

The photoreaction of [(μ-S)2Fe2(CO)6] and alkenes or alkynes has been optimized to readily obtain functionalized [FeFe]-hydrogenase mimics. Irradiation under low CO pressure in THF produces the corresponding photo-adducts in good/acceptable (alkenes/alkynes) yields, with retention of the starting olefin stereochemistry. DFT-calculations provide plausible reaction pathways in both, singlet and triplet states. The DFT-calculation based in the singlet state is energetically more favorable. The electrochemical behavior of the synthesized compounds is also presented, including studies in acidic media. The electrochemical properties of the products vary in the presence of a double bond (cycloaddi…

Enantioselective epoxidation of olefins with molecular oxygen catalyzed by gold(III): A dual pathway for oxygen transfer

2009

Abstract A chiral gold(III) complex has been prepared that performs the epoxidation of olefins in the presence of O 2 , PhIO, or bleach. Catalytic experiments with 18 O show that O 2 is activated on the catalyst and can be directly incorporated into the epoxide through a non-radical mechanism that probably involves formation of gold, oxo, or peroxo species. In addition to this, there is a parallel radical mechanism operating that yields α , β -unsaturated ketones and alcohols as subproducts. Electrochemical and UV–Vis experiments confirmed the occurrence of a Au(III)/Au(I) redox cycle during the catalytic epoxidation in a mechanism sustained by molecular oxygen.

Diene/olefin/polar monomer copolymerisation: unprecedented functional polymers from a rare earth catalyst

2002

An ansasamarocene allyl system is an efficient initiator which polymerises 1,3-dienes, copolymerises dienes and long-chain α-olefins or α,ω-dienes to give functionalisable polymers. It also polymerises caprolactone and allows the controlled diblock copolymerisation of isoprene or isoprene/ α-olefin copolymer and caprolactone.

Olefin Polymerisation Catalysts

2002

Polyolefins, which are products of polymerisation of unsaturated hydrocarbons of the olefin series, have a molecular weight in the range from several thousands to several millions. Depending on the type of monomer and method and mechanism of polymerisation the resulting polyolefins may differ in their structure and molecular weight. They can be used in many applications, for example as constructional plastics and in packaging, fibres, rubbers, and also as additives to control the viscosity of motor oils(1). As regards their scale of production polyolefins occupy the top position among mass-produced polymers(2).

New Viscoelastic Materials Obtained by Insertion of anα-Olefin in atrans-Polyisoprene Chain with a Single-Component Organolanthanide Catalyst

2001

Copolymerisation of isoprene with C 6 -C 18 a-olefins by a single component organolanthanide catalyst affords poly(trans-1,4-isoprene) containing 6-10% of inserted olefin. The mechanical properties of highly crystalline transpolyisoprene are dratically modified after insertion of the alkyl chains, leading to quasi-amorphous viscoelastic materials.

Chemodiscrimination of Olefin Bonds Through Cross‐Metathesis Reactions – Synthesis of Functionalized β‐Lactam and β‐Amino Acid Derivatives

2019

Atmospheric aging and surface degradation in As2S3 fibers in relation with suspended-core profile

2015

Abstract Microstructured optical fibers (MOF) can be seen as next generation fiber of significance in advancing the compact optics because of its excellent compatibility in integrated optics. However, the degradation of their physicochemical properties limits their efficiency and lifetime. Atmospheric moisture is responsible for the degradation of amorphous systems especially chalcogenide glasses. In the light of previously reported studies, in order to clarify the aging process continuously evolving in sulfide microstructured optical fiber over time, a detailed investigation of this phenomenon has been conducted. The time-dependent transmission and glass chemical deterioration have been st…

Chalcogenide Fibers for Mid-IR Light Generation: Potentialities and Drawbacks of the Microstructured Design in Sulfide Waveguides

2014

We study optical and structural aging in As2S3 microstructured optical fibers, submitted to room atmosphere that may have, among others, an impact on mid-infrared supercontinuum generation.

Improving the properties of polypropylene–wood flour composites by utilization of maleated adhesion promoters

2007

Polymer composites filled with natural organic fillers have gained a significant interest during the last few years, because of several advantages they can offer compared with properties of inorganic-mineral fillers. However, these composites (based, in most cases, on polyolefins) often show a reduction in some mechanical properties. This is mainly due to the problems regarding dispersion of the polar filler particles in the non-polar polymer matrix and their interfacial adhesion with polymer chains. In this work, polypropylene-wood flour composites were prepared and the effect of the addition of a maleated polypropylene was investigated. The two materials were compounded by an industrial c…