Lithiation of toluene by organolithium compounds activated by lithium polyether alkoxides

peer reviewedThe catalytic effect of polyether alkoxides (PEAs) on the activity of organolithium. compounds as metallating agent has been investigated. Toluene has been lithiated by using different organolithiums activated by various PEAs. It has been found that n-BuLi, yields higher conversion with 100% benzylic position metallation, whereas sec-BuLi gives some metallation at ring positions with the most reactive ligand, lithium 2-methoxy ethoxide (LiOEM). Optimum PEA to organolithium molar ratio for both sec- and n-BuLi activated by LiOEM where the amount of toluene being kept constant, was found to be as 3:1 with highest yield and regioselectivity. Substantial increment in yield was observed when the amount of substrate increased whereas regioselectivity stayed almost constant. It was also found that, for a constant reactant molar ratio (3:1:15) for which the optimum results were achieved, reaction began early and then yield values increased with time whereas upon increase in reaction temperature from -78 to 20degreesC, the benzylic metallation yield increased drastically while keeping the same regioselectivity high

A competency-based model to bridge the gap between academic trainings and industrial trades

Within today's European socioeconomic context, supporting careers choices and occupational integration has become a major challenge. Education has to fit the changes of industry and job market, but this process requires a unified representation of professions and training programs. The competency concept appears to be a common vector, since it has turned to be a pervasive idea. Although industry has started specifying trades through competencies, similar attempts are not initiated for education yet. In this paper, we present a unifying model for training programs, professions and learners, built around competencies. Based on this model, several tools have been developed to help (1) educational teams to make sure that conceptions of curriculum fit the targeted learning objectives, (2) learners to make their careers choices through life easier, (3) industrial actors to identify training programs matching with their needs

Macromolecular engineering of polylactones and polylactides: 13. Synthesis of telechelic polyesters by coupling reactions

Aromatic diisocyanates, such as phenylene-1,4-diisocyanate have proved to be very effective coupling agents of α-X functional ω-hydroxy poly-ε-caprolactone (PCL). Very high yields (> 98%) have been observed in the presence of triethylamine, in tetrahydrofuran. Accordingly α,ω-X functional PCL of a two-fold molecular weight have been obtained and characterized by size exclusion chromatography and nuclear magnetic resonance spectroscopy. More interestingly, the same coupling reactions have been successfully carried out when applied to the precursor living polyester (XCH2OPCLOAlEt2) rather than to the chains recovered after hydrolysis of the living propagating sites. Terephthalic acid chloride has been the most efficient coupling agent and, in the presence of pyridine, has yielded quantitatively the expected α,ω-functional polyesters. © 1994

The in situ formation of a new initiator system for the syndiotactic anionic polymerization of methyl methacrylate in toluene at 0°C

This paper reports on an efficient 'in-situ' one pot synthesis of an initiatior/ligand adduct, which can be used to initiate the anionic polymerization of methyl methacrylate in toluene at 0 °C. Predominantly syndiotactic PMMA is formed

Polymer blends: From molecular structure through morphology to controlled bulk properties

peer reviewedIt is shown how the morphology and the bulk physico‐mechanical properties of polymer blends and alloys may be tailored, by using proper physical and processing conditions for homogeneous systems, and molecular engineering of the interfaces for heterophase ones. That approach, which has been substantiated by a physical study of the miscibility situations at molecular level, has been applied successfully to commodity and engineering polymer‐polymer blends, but also to polymer‐filler and polymer‐liquid heterophase systems. Copyright © 1988 Hüthig & Wepf Verla

Triblock copolymer based thermoreversible gels. 1. Self-association of sPMMA end-blocks in o-xylene and viscoelasticity of the gels

Syndiotactic poly(methyl methacrylate) (sPMMA)-polybutadiene (PBD)-sPMMA triblock copolymers, or MBM, have been studied in the presence of o-xylene which is a selective solvent for the central PBD block. Syndiotactic PMMA is known to self associate in o-xylene. The central PBD sequence does not prevent the self-association of sPMMA from occurring. Actually, this phenomenon contributes to the stability of the gels formed at room temperature. An endotherm is observed at 35°C, which is responsible for a gel-sol transition. The original solutions have been heated up to 80°C and then rapidly cooled down below 35°C and maintained at 10, 20 and 25°C respectively. The self-association of the sPMMA outer blocks, and thus the liquid-solid transition, have been studied at each of these temperatures. Dependence of the gel viscosity on frequency and temperature effects on viscoelasticity has also been investigated

A new family of "ligated" anionic initiators for the "living" polymerization of (meth)acrylic esters

A new family of ligands (dual sigma - pi ligand), i.e. chelating lithium alkoxides, Li-O-(CH2-CH2O)nCH3, is shown to be very effective in promoting the living anionic Polymerization of methacrylic and acrylic esters, including a number of primary alkyl acrylates such as n-butyl acrylate and 2-ethylhexylacrylate

Microencapsulation by coacervation of poly(lactide-co-glycolide). IV. Effect of the processing parameters on coacervation and encapsulation

Attention has been paid to phase separation of poly (lactide-co-glycolide) solutions in CH2Cl2 induced by the addition of a silicone oil in order to promote protein microencapsulation. Since the process is very fast, the system is anytime out of equilibrium. The effect of the main processing parameters on the microencapsulation process has been analyzed and has highlighted that kinetics of the main encapsulation steps has a great effect on the characteristics of the final microspheres. These results have been discussed on the basis of a physico-chemical study of coacervation reported in previous papers of this series

Polydiolefines equibinaires-IV. Catalyse homogene de polymerisation stereospecifique en presence de monoethoxydiethylaluminium et de sels de cobalt

[No abstract available

THEORY OF COORDINATION CATALYSIS.

peer reviewedThis bibliography-based review paper is concerned with mechanisms of coordination polymerization reactions in light of existing theories, beginning with the discovery by Ziegler of coordination catalysts by transition-metal complexes. the discussion is presented in the following parts - introduction; the determinant role of transition metal complexes in stereo specific polymerization of unsaturated hydrocarbons; the evolution of ideas on the mechanism of olefin coordination polymerization; advances in deolefin coordination polymerization; current progress in related areas; trends and directions of research