206 research outputs found
Design and Synthesis of Bio-Based Benzoxazines
Polybenzoxazine (PBz) resins are a new type of high-performance synthetic resins that are attractive alternatives to traditional resins. Their properties include near-zero shrinkage upon polymerization, fast evolution of mechanical properties with the conversion, glass transition temperatures much higher than curing temperatures, low water absorption, and excellent dielectrical and mechanical properties. The development of polybenzoxazines has always been linked to petro-based feedstocks, but for the last 5 years, the number of studies related to bio-based benzoxazines is exploding as a consequence of the versatility of the design of the chemical structure of their monomers. Benzoxazine (Bz) monomers are subjected to cationic ring-opening polymerization (ROP), activated by a thermal treatment in the range of 160â250°C. In addition, Bz synthesis promotes the use of naturally occurring phenolic compounds instead of petroleum-based ones to develop high-performance materials from renewable resources and to fit to REACH restrictions. For this purpose, vanillin, eugenol, and cardanol are examples of bio-phenols bridged with several kinds of aromatic and aliphatic diamines. In this chapter, the synthesis and the properties of di-functional benzoxazine monomers prepared from naturally occurring phenolic compounds are reviewed. Symmetric and asymmetric monomers will be detailed. The last part of the chapter is dedicated to the use of bio-phenols to functionalize polymers and to provide benzoxazine functional groups
Switching the stereochemical outcome of 6-endo-trig cyclizations; Synthesis of 2,6-Cis-6-substituted 4-oxopipecolic acids
A base-mediated 6-endo-trig cyclization of
readily accessible enone-derived α-amino acids has been
developed for the direct synthesis of novel 2,6-cis-6-
substituted-4-oxo-L-pipecolic acids. A range of aliphatic and
aryl side chains were tolerated by this mild procedure to give
the target compounds in good overall yields. Molecular
modeling of the 6-endo-trig cyclization allowed some insight as
to how these compounds were formed, with the enolate
intermediate generated via an equilibrium process, followed by irreversible tautomerization/neutralization providing the driving force for product formation. Stereoselective reduction and deprotection of the resulting 2,6-cis-6-substituted 4-oxo-L-pipecolic acids to the corresponding 4-hydroxy-L-pipecolic acids was also performed
Cardanol : un intermédiaire chimique bio-sourcé pour l'éléboration de nouveaux matériaux durables et fonctionnels
Recently, considerable interest of the chemistry of renewable ressources and their resulting materials has grown with a view to reduce the use of finite petroleum-based resources. The present thesis entitled « Cardanol: a bio-based building block for new sustainable and functional materials » is dealing with the chemical modification of cardanol and its use for various applications. Cardanol is a naturally occurring phenolic compound issued from cashew nutshell liquid. Its chemical structure is interesting because cardanol is bearing a phenolic hydroxyl function and an unsaturated alkyl chain in meta. Numerous chemical reactions can thus be considered for its chemical modification.The first part of this study is dealing with the synthesis and the characterization of three cardanol-based ammonium surfactants differing by their amine functionalities content. Their effectiveness on the exfoliation of silicate clay within an epoxy matrix was investigated with the aim to elaborate composit materials.The second chapter is describing a novel method for the synthesis of bio-based benzoxazine monomers and the elaboration of polybenzoxazine networks issued from cardanol. A new generation of benzoxazine monomers issued from cardanol or from lignin derivatives such as vanillin were recently developed. However, up to now, the majority of the synthetised benzoxazine monomers are mainly mono-functionnal or display too high melting temperatures. The elaboration of valuable self-standing materials is thus strongly impeded. To solve this problem, an innovative synthesis of asymmetric benzoxazine monomers by combination of cardanol and lignin derivatives is described. The resulting self-standing materials display improved properties in comparison to materials issued from symmetric bio-based monomers.Finally, the third chapter realtes to the use of a cardanol-based epoxy pre-polymer for the elaboration of bio-based epoxy materials. Nevertheless, this new material displays low Tg and high water uptake due to the alkyle side chain of cardanol. In order to reinforce the thermo-mechanical properties of the material and to reduce its water uptake, a chemical modification was achieved at the macromolecular scale by the elaboration of interpenetrating polymer networks with polybenzoxazine networks.These various studies allowed to highlight the easy and versatile modification of cardanol, resulting thus in a diversity of bio-based synthons and their resulting materials. This work paves the way to the elaboration of other chemical structures and molecular architectures for various applications.RĂ©cemment, la chimie des ressources renouvelables et les matĂ©riaux qui en dĂ©coulent ont suscitĂ©s un intĂ©rĂȘt considĂ©rable dans le but de limiter lâutilisation des ressources fossiles. La prĂ©sente thĂšse intitulĂ©e « Cardanol : a bio-based building block for new sustainable and functional materials » traite de la modification chimique du cardanol et de son utilisation dans diverses applications. Le cardanol est un dĂ©rivĂ© phĂ©nolique naturel extrait de lâhuile de coque de noix de cajou. Sa structure chimique est intĂ©ressante : il est substituĂ© dâune chaĂźne alkyle en C15, partiellement insaturĂ©e, et il est porteur dâune fonction phĂ©nol, permettant dâenvisager de nombreuses rĂ©actions chimiques.La premiĂšre partie de cette Ă©tude traite de la synthĂšse et de la caractĂ©risation de trois surfactants ammoniums issus du cardanol se diffĂ©renciant par le degrĂ© de substitution de leurs amines. Leur capacitĂ© Ă favoriser lâexfoliation dâune argile lamellaire dans une matrice de type Ă©poxy a Ă©tĂ© Ă©tudiĂ©e dans le but de concevoir des matĂ©riaux composites.Le second chapitre dĂ©crit une nouvelle mĂ©thode de synthĂšse de monomĂšres benzoxazines bio-basĂ©s et lâĂ©laboration de rĂ©seaux polybenzoxazines Ă partir du cardanol. Une nouvelle gĂ©nĂ©ration de monomĂšres benzoxazine, issus du cardanol ou de dĂ©rivĂ©s de la lignine tels que la vanilline, a rĂ©cemment Ă©tĂ© dĂ©veloppĂ©e. Cependant lâessentiel des benzoxazines bio-basĂ©es synthĂ©tisĂ©es jusquâĂ prĂ©sent sont monofonctionnelles ou prĂ©sentent des tempĂ©ratures de fusion trop Ă©levĂ©es. Elles ne permettent donc pas lâĂ©laboration de matĂ©riaux autosupportĂ©s valorisables. Afin de pallier ce problĂšme, une synthĂšse originale de monomĂšres benzoxazines asymĂ©triques, reposant sur la combinaison de cardanol et de dĂ©rivĂ©s de la lignine, est dĂ©crite. Les matĂ©riaux autosupportĂ©s rĂ©sultants prĂ©sentent des propriĂ©tĂ©s amĂ©liorĂ©es par rapport Ă celles que ne pourraient atteindre les monomĂšres symĂ©triques issus de ces phĂ©nols bio-sourcĂ©s.Finalement, le troisiĂšme chapitre concerne lâutilisation dâun prĂ©-polymĂšre Ă©poxy issu du cardanol pour lâĂ©laboration de matĂ©riaux Ă©poxy bio-basĂ©s. Cependant, en raison de la chaĂźne alkyle du cardanol, ce nouveau matĂ©riau prĂ©sente une faible Tg et une forte prise en eau. Afin de renforcer ses propriĂ©tĂ©s thermo-mĂ©caniques et de diminuer sa prise en eau, une modification chimique a Ă©tĂ© rĂ©alisĂ© Ă lâĂ©chelle macromolĂ©culaire par lâĂ©laboration de rĂ©seaux interpĂ©nĂ©trĂ©s de polymĂšres Ă base de rĂ©seaux polybenzoxazines.Ces diffĂ©rents travaux ont permis de mettre en avant la modification aisĂ©e et versatile du cardanol, pouvant ainsi rĂ©sulter en une large variĂ©tĂ© de synthons bio-basĂ©s et des matĂ©riaux qui en dĂ©coulent. Ces travaux ouvrent la voie vers dâautres structures et architectures molĂ©culaires aux applications nombreuses
Cardanol : un intermédiaire chimique bio-sourcé pour l'éléboration de nouveaux matériaux durables et fonctionnels
RĂ©cemment, la chimie des ressources renouvelables et les matĂ©riaux qui en dĂ©coulent ont suscitĂ©s un intĂ©rĂȘt considĂ©rable dans le but de limiter lâutilisation des ressources fossiles. La prĂ©sente thĂšse intitulĂ©e « Cardanol : a bio-based building block for new sustainable and functional materials » traite de la modification chimique du cardanol et de son utilisation dans diverses applications. Le cardanol est un dĂ©rivĂ© phĂ©nolique naturel extrait de lâhuile de coque de noix de cajou. Sa structure chimique est intĂ©ressante : il est substituĂ© dâune chaĂźne alkyle en C15, partiellement insaturĂ©e, et il est porteur dâune fonction phĂ©nol, permettant dâenvisager de nombreuses rĂ©actions chimiques.La premiĂšre partie de cette Ă©tude traite de la synthĂšse et de la caractĂ©risation de trois surfactants ammoniums issus du cardanol se diffĂ©renciant par le degrĂ© de substitution de leurs amines. Leur capacitĂ© Ă favoriser lâexfoliation dâune argile lamellaire dans une matrice de type Ă©poxy a Ă©tĂ© Ă©tudiĂ©e dans le but de concevoir des matĂ©riaux composites.Le second chapitre dĂ©crit une nouvelle mĂ©thode de synthĂšse de monomĂšres benzoxazines bio-basĂ©s et lâĂ©laboration de rĂ©seaux polybenzoxazines Ă partir du cardanol. Une nouvelle gĂ©nĂ©ration de monomĂšres benzoxazine, issus du cardanol ou de dĂ©rivĂ©s de la lignine tels que la vanilline, a rĂ©cemment Ă©tĂ© dĂ©veloppĂ©e. Cependant lâessentiel des benzoxazines bio-basĂ©es synthĂ©tisĂ©es jusquâĂ prĂ©sent sont monofonctionnelles ou prĂ©sentent des tempĂ©ratures de fusion trop Ă©levĂ©es. Elles ne permettent donc pas lâĂ©laboration de matĂ©riaux autosupportĂ©s valorisables. Afin de pallier ce problĂšme, une synthĂšse originale de monomĂšres benzoxazines asymĂ©triques, reposant sur la combinaison de cardanol et de dĂ©rivĂ©s de la lignine, est dĂ©crite. Les matĂ©riaux autosupportĂ©s rĂ©sultants prĂ©sentent des propriĂ©tĂ©s amĂ©liorĂ©es par rapport Ă celles que ne pourraient atteindre les monomĂšres symĂ©triques issus de ces phĂ©nols bio-sourcĂ©s.Finalement, le troisiĂšme chapitre concerne lâutilisation dâun prĂ©-polymĂšre Ă©poxy issu du cardanol pour lâĂ©laboration de matĂ©riaux Ă©poxy bio-basĂ©s. Cependant, en raison de la chaĂźne alkyle du cardanol, ce nouveau matĂ©riau prĂ©sente une faible Tg et une forte prise en eau. Afin de renforcer ses propriĂ©tĂ©s thermo-mĂ©caniques et de diminuer sa prise en eau, une modification chimique a Ă©tĂ© rĂ©alisĂ© Ă lâĂ©chelle macromolĂ©culaire par lâĂ©laboration de rĂ©seaux interpĂ©nĂ©trĂ©s de polymĂšres Ă base de rĂ©seaux polybenzoxazines.Ces diffĂ©rents travaux ont permis de mettre en avant la modification aisĂ©e et versatile du cardanol, pouvant ainsi rĂ©sulter en une large variĂ©tĂ© de synthons bio-basĂ©s et des matĂ©riaux qui en dĂ©coulent. Ces travaux ouvrent la voie vers dâautres structures et architectures molĂ©culaires aux applications nombreuses.Recently, considerable interest of the chemistry of renewable ressources and their resulting materials has grown with a view to reduce the use of finite petroleum-based resources. The present thesis entitled « Cardanol: a bio-based building block for new sustainable and functional materials » is dealing with the chemical modification of cardanol and its use for various applications. Cardanol is a naturally occurring phenolic compound issued from cashew nutshell liquid. Its chemical structure is interesting because cardanol is bearing a phenolic hydroxyl function and an unsaturated alkyl chain in meta. Numerous chemical reactions can thus be considered for its chemical modification.The first part of this study is dealing with the synthesis and the characterization of three cardanol-based ammonium surfactants differing by their amine functionalities content. Their effectiveness on the exfoliation of silicate clay within an epoxy matrix was investigated with the aim to elaborate composit materials.The second chapter is describing a novel method for the synthesis of bio-based benzoxazine monomers and the elaboration of polybenzoxazine networks issued from cardanol. A new generation of benzoxazine monomers issued from cardanol or from lignin derivatives such as vanillin were recently developed. However, up to now, the majority of the synthetised benzoxazine monomers are mainly mono-functionnal or display too high melting temperatures. The elaboration of valuable self-standing materials is thus strongly impeded. To solve this problem, an innovative synthesis of asymmetric benzoxazine monomers by combination of cardanol and lignin derivatives is described. The resulting self-standing materials display improved properties in comparison to materials issued from symmetric bio-based monomers.Finally, the third chapter realtes to the use of a cardanol-based epoxy pre-polymer for the elaboration of bio-based epoxy materials. Nevertheless, this new material displays low Tg and high water uptake due to the alkyle side chain of cardanol. In order to reinforce the thermo-mechanical properties of the material and to reduce its water uptake, a chemical modification was achieved at the macromolecular scale by the elaboration of interpenetrating polymer networks with polybenzoxazine networks.These various studies allowed to highlight the easy and versatile modification of cardanol, resulting thus in a diversity of bio-based synthons and their resulting materials. This work paves the way to the elaboration of other chemical structures and molecular architectures for various applications
Printemps arabe : des racines des mouvements révolutionnaires aux développements actuels
Du printemps arabe, il fut beaucoup question en 2011. Et puis, peu aÌ peu, lâinteÌreÌt du monde sâest quelque peu essouffleÌ. Pourtant, le feu eÌmancipateur couve toujours, le profond processus de transformation sociale demeure en cours, ainsi que nous le deÌmontrent les mouvements reÌcents en AlgeÌrie, en Irak, au Liban. Quelle filiation entre les reÌvolutions tunisiennes, eÌgyptiennes, et les deÌveloppements actuels ? Quelles perspectives pour les processus de contestations et dâeÌmancipation en cours autour de la MeÌditerraneÌe
- âŠ