48 research outputs found
(co)polymérisation par ouverture de cycle stéréosélective catalysée par l'yttrium de β-lactones fonctionnelles racémiques et de ε-caprolactones substituées
No full textLe paradigme actuel sur la gestion des déchets plastiques met l'accent sur leur minimisation et la prévention, parallèlement à l'exploration de substituts (bio)dégradables tels que les polyesters qui sont largement utilisés dans divers domaines. La capacité à contrôler précisément la microstructure de ces polymères reste cependant un défi important pour exploiter leurs propriétés potentielles. La (co)polymérisation stéréosélective par ouverture de cycle (RO(CO)P) d'esters cycliques est la stratégie privilégiée pour accéder aux polyesters stéréoréguliers. Dans ce travail, de nouveaux monomères de β-propiolactones substituées BPLFG (FG = CH2OiPr, CH2OtBu, CH2OSitBuMe2, CH2OCF2CHF2) ont été synthétisés, et leur ROP a été étudiée en utilisant des complexes phénolate diamino-bis(ortho,para-R1, R2-substitués) d'yttrium Y{ONNOR1R2}/iPrOH (avec R1 = R2= tBu, Me, cumyl, Cl, respectivement 1a-d/iPrOH), en vue de la préparation de polyhydroxyalcanoates (PHAs) synthétiques. L'influence de l'encombrement stérique du groupe pendant et des interactions non covalentes (NCI) impliquant les substituants du ligand, sur la stéréosélectivité du catalyseur, a été étudiée et comparée à celle des BPLFGs (FG = CH2OAll, CH2OMe, CH2OBn), similaires mais moins encombrés, précédemment établis. Nos observations ont révélé le rôle crucial des facteurs stériques et électroniques du substituant latéral du monomère et du ligand ancillaire du catalyseur, dans le contrôle de l’isotacticité du PHA. Afin d'introduire les fonctionnalités souhaitées sur les PHAs et d'ajuster leurs propriétés, une stratégie de ROCOP efficace a été mise en œuvre avec succès pour incorporer des groupes phosphinates dans le PHB. L'interaction entre la teneur en comonomère phosphinate et le contrôle de la masse molaire et de la tacticité des PHBs résultants a été systématiquement étudiée, révélant leur impact significatif sur les caractéristiques thermiques des PHAs produits. Alors que le stéréocontrôle des lactones à quatre, six et huit chaînons portant un ou deux centres chiraux est largement développé dans la littérature, le ROP stéréosélective des caprolactones substituées à sept chaînons portant un centre chiral (CLMe et CLnBu) est resté inexploitée. L'évaluation typique par RMN de la stéréosélectivité des complexes d'yttrium sur l'homopolymérisation de CLMe et CLnBu s'est révélée inappropriée. Une évaluation indirecte du stéréocontrôle a été obtenue par ROCOP de mélanges équimolaires de (R)-CLnBu avec (S)-CLMe, où le degré d'incorporation de comonomères alternatifs reflète la capacité de syndio-contrôle du catalyseur. La distribution aléatoire des deux monomères, établie à partir d'analyses détaillées de spectrométrie de masse, indique l'absence de stéréocontrôle du catalyseur d'yttrium sur la ROP de ces larges caprolactones.The current paradigm of plastic waste management emphasizes minimization and prevention, alongside exploration of (bio)degradable substitutes like polyesters that are widely applied in various domains. The ability to precisely control the microstructure of these polymers, however, remains a significant challenge in unlocking their full potential for desired properties. Stereoselective ring-opening (co)polymerization (RO(CO)P) of cyclic esters is the privileged strategy to access stereoregular polyesters. In this work, new substituted β-propiolactones BPLFG monomers (FG = CH2OiPr, CH2OtBu, CH2OSitBuMe2, CH2OCF2CHF2) were synthesized, and their ROP was investigated using diamino-bis(ortho,para-R1,R2-substituted)phenolate yttrium catalyst systems Y{ONNOR1R2}/iPrOH (with R1 = R2 = tBu, Me, cumyl, Cl, namely 1a-d/iPrOH, respectively), towards the preparation of synthetic polyhydroxyalkanoates (PHAs). The influence of the pendant group steric hindrance and of non-covalent interactions involving ligand substituents (NCIs) on the catalyst stereoselectivity was studied and compared to that of the previously reported similar but less hindered BPLFGs (FG = CH2OAll, CH2OMe, CH2OBn). Our insights unveiled the crucial role of steric and electronic factors at the level of the monomer side-substituent and catalyst ancillary ligand, in achieving isotactic stereocontrol. In an approach to introduce desired functionalities on PHAs and to tune their properties, an effective ROCOP strategy was successfully implemented to incorporate phosphinate groups into PHB. The interplay between phosphinate comonomer content, and control of PHB molar mass and tacticity was systematically investigated, revealing their significant impact on the thermal characteristics of the resulting PHAs. While stereocontrol over four, six, and eight-membered lactones bearing one or two chiral centers is largely developed in the literature, the stereoselective ROP of larger seven-membered substituted caprolactones bearing one chiral center (CLMe and CLnBu) remained elusive. Typical NMR assessment of the stereoselectivity of yttrium complexes on the homopolymerization of CLMe and CLnBu revealed unsuitable. Rewardingly, indirect stereocontrol evaluation was gained by ROCOP of equimolar mixtures of (R)-CLnBu with (S)-CLMe, where the degree of alternating comonomer incorporation reflects the catalyst’s syndio-control ability. The random distribution of both monomers, as established from detailed mass spectrometry analyses, indicated the lack of stereocontrol by the yttrium catalyst over the ROP of these large caprolactones
Complexes organométalliques des groupes 3 et 13 (applications en chimie fine et catalyse de polymérisation)
No full textDans un premier temps, nous avons étudié des systèmes organométalliques formés in situ à partir de différents précurseurs d aluminium AlX et de pro-ligands {salen}H . Les études à l état solide et en solution indiquent, dans certains cas, la formation, outre des complexes attendus AlX{Salen}, de complexes secondaires de type bimétalliques [AlX ] {Salen}. Les différentes espèces qui résultent de ces combinaisons in situ ont été isolées, caractérisées et testées individuellement en cyanosilylation asymétrique de l acétophénone. Plusieurs fois, une amélioration de l activité et de l énantiosélectivité par rapport aux systèmes catalytiques générés in situ a été constatée. L influence des ligands chiraux (Salen) et achiraux (X) sur l activité et la sélectivité de la réaction a pu être mise en évidence. Notamment, le système hexafluoro-2-propylate d aluminium-Salen présente une activité sans précédent pour un catalyseur aluminique. Dans un second temps, des familles de complexes bis(oxazoline) (Box) de métaux du groupe 3 ont été synthétisés. Ces complexes ont démontré une activité et une productivité sans précédent pour la polymérisation du rac-lactide. Cependant, quelle que soit la nature achirale ou chirale du ligand BOX, tous les PLA(s) obtenus présentent une microstructure atactique. Des familles de nouveaux complexes diimino-dialcoxy fluorés d aluminium et d yttrium ont également été synthétisés. Les études structurales par RMN et par diffraction des rayons X montrent clairement que ces complexes adoptent des structures comparables à leurs homologues dérivés de ligands Salen. Un complexe d aluminium a démontré un bon contrôle et une haute sélectivité pour la production de PLA isotactique (80%).For the first time, we have studied the organometallic outcome of the catalyst systems generated in situ from an aluminum precursor AlX and a diprotio {Salen}H pro-ligand. The different species that result from these binary combinations have been isolated, characterized and individually evaluated in the asymmetric cyanosilylation of acetophenone. It is shown that, in some cases, those discrete catalysts display dramatically different performances than the binary systems which are assumed to generate them. The influence of the achiral ligand on both the enantioselectivity and activity of the reaction has been investigated, resulting in the definition of a highly active hexafluoro-2-propoxide-based catalyst. For the second time, the family of bis[bis(oxazolinato)]lanthanide complexes have been synthesized. These complexes show a high activity and productivity for the rac-lactide polymerization. However, such complexes based on well-known chiral Box ligands appear unable to control the microstructure of the polymer: only atactic PLAs. New families of diimines-dialcooxy fluorinated aluminium and yttrium complexes have been synthesized. These complexes were caracterized by NMR-spectroscopy and X-ray diffraction analysis and it was shown that they are the familiar structure Salen-complexes. Alumnium complexes show high control and selectivity for production of isotactic PLA (80%).RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF
Reduction of aromatic nitriles into aldehydes using calcium hypophosphite and a nickel precursor
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Kinetic and mechanistic aspects of the iodine transfer copolymerization of vinylidene fluoride with 2,3,3,3-tetrafluoro-1-propene and functionalization into ω-hydroxy fluorinated copolymers
No full textInternational audienceThe synthesis of functional poly(VDF-co-1234yf) copolymers bearing –OH end groups was achieved via iodine transfer copolymerizations of vinylidene fluoride (VDF) with 2,3,3,3-tetrafluoro-1-propene (1234yf) followed by selective post-functionalization. First, free radical copolymerization (FRP) (in absence of any chain transfer agent, CTA) of VDF with 1234yf was investigated in different experimental conditions: varying the comonomer feed ([VDF]0/[1234yf]0) ratio led to several poly(VDF-co-1234yf) copolymers with molecular weights (Mns) ranging between 4600 and 12400 g·mol-1 and dispersities (Ð) of ca. 2.05, and fair to good conversions (45-77%). Thermoplastic crystalline powders were obtained when mol % VDF in the copolymers was higher than 85 %, while amorphous copolymers contained a lower mol % VDF. This study also reports for the first time the determination of reactivity ratios (rVDF= 0.76 ± 0.34 and r1234yf = 1.23 ± 0.17 at 74 °C). Subsequently, iodine transfer polymerization (ITP) of VDF and 1234yf in the presence of 1-iodoperfluorohexane as the CTA in 1,1,1,3,3-pentafluorobutane and even in water using potassium persulfate as the initiator without any surfactant led to satisfactory yields (ca. 80%), Mn up to 4100 g·mol-1 and narrow Ð (ca. 1.35). Detailed kinetics study of ITP enabled to assess the chain transfer constant of C6F13I, CTr = 7.4 at 74 °C. The compositions and microstructures of all the obtained copolymers were determined by 1H and 19F NMR spectroscopies. Finally, chemical modification of the iodide end functionality of the poly(VDF-co-1234yf)-I copolymer into a primary hydroxyl end group was achieved by radical addition of these iodinated poly(VDF-co-1234yf) copolymers onto allyl alcohol, followed by selective reduction of iodine atoms
Synthesis of methallylic monomers bearing ammonium side-groups and their radical copolymerization with chlorotrifluoroethylene
No full textInternational audienceMethallylic monomers bearing triethyl or 4-diazabicyclo[ 2.2.2]octane (DABCO) ammonium side-groups are prepared and copolymerized with chlorotrifluoroethylene (CTFE). First, three different monomers are synthesized from chloro-2- methylprop-1-ene or 3-chloro-2-chloromethylprop-1-ene in fair to good yields (57-95%). Then, several parameters (initiators, aqueous or solution processes, temperature) of the radical copolymerization of these monomers with chlorotrifluoroethylene are investigated. Various initiators are tested in the presence of ammonium perfluorooctanoate (APFO) as watersoluble surfactant, and tert-butyl peroxypivalate/APFO leads to the best results in a mixed solvent (H2O/CH3CN/C4F5H5). In all experiments, the radical copolymerization shows that CTFE is more reactive than the methallylic monomer as evidenced by the characterization of poly(CTFE-co-M) copolymer by nuclear magnetic resonance spectroscopy and elemental analysis. Thermal degradation of these copolymers by thermogravimetric analyses indicates that the copolymers are stable up to 180 C without any degradation and have a Td,10% above 300 C. Finally, their ionic exchange capacities range between 0.94 and 1.69 meq g-1
Recent Advances on New Fluorinated Copolymers Based on Carbonate and Oligo(ethylene oxide) by Radical Copolymerization
No full textThe synthesis and characterizations of original poly[CTFEalt-VEoligo(EO)] and poly(F-alkene-alt-GCVE) alternated copolymers (where CTFE, VEoligo(EO), and F-alkene stand for chlorotrifluoroethylene, oligo(ethylene oxide) vinyl ether, hexafluoropropylene (HFP) or perfluoromethyl vinyl ether (PMVE), and glycerol carbonate vinyl ether, respectively) are presented. First, vinyl ethers bearing oligo(ethylene oxide) or carbonate side-group (i.e. 2-oxo-1,3-dioxolan-4-yl-methyl vinyl ether, GCVE) were synthesized by transetherification of ω-hydroxyl oligo(EO) (of different molecular weights (3 and 10 EO units) or glycerol carbonate with ethyl vinyl ether catalyzed by a palladium complex were obtained in 45-74% yields. Although HFP, PMVE, and vinyl ethers do not homopolymerize under radical conditions, they copolymerized readily yielding alternated poly(F-alkene-alt-VE) copolymers that bore carbonate group or oligo(EO) side-chains. The alternated structures of these original poly(F-alkenes-alt-VE) copolymers were confirmed by elemental analysis and by 1H, 19F and 13C NMR spectroscopy. All copolymers were obtained in good yield (61-85 %). Their molecular weights varied depending on the [initiator]o/[monomers]o intial molar ratios, reaching either 3,900-4,600 g mol-1 or 19,000 g.mol-1 with polydispersities below 2.0
Synthesis and characterization of novel functional vinyl ethers that bear various groups
No full textThe synthesis of new functionalized vinyl ethers (VEs) by transetherification reaction between ethyl vinyl ether (EVE) and different alcohols is presented. An air-stable palladium catalyst generated in situ efficiently catalyzed the reaction leading to various VEs in a single step with good alcohol conversion (50–82%) and good VE yields (up to 75%). The reaction conditions were optimized in terms of the initial EVE/alcohol molar ratio, alcohol concentration, solvent, presence and nature of the ligand, amount of the catalyst, and choice of the metal precursor. All VEs were characterized using H and C NMR spectroscopy
Synthesis and characterization of original alternated fluorinated copolymers bearing glycidyl carbonate side groups
No full textInternational audienceA vinyl ether bearing a carbonate side group (2- oxo-1,3-dioxolan-4-yl-methyl vinyl ether, GCVE) was synthesized and copolymerized with various commercially available fluoroolefins [chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), and perfluoromethyl vinyl ether (PMVE)] by radical copolymerization initiated by tert-butyl peroxypivalate. Although HFP, PMVE, and vinyl ether do not homopolymerize under radical conditions, they copolymerized easily yielding alternating poly(GCVE-alt-F-alkene) copolymers. These alternating structures were confirmed by elemental analysis as well as 1H, 19F, and 13C NMR spectroscopy. All copolymers were obtained in good yield (73-85%), with molecular weights ranging from 3900 to 4600 g mol 1 and polydispersities below 2.0. Their thermogravimetric analyses under air showed decomposition temperatures at 10% weight loss (Td,10%) in the 284-330 C range. The HFP-based copolymer exhibited a better thermal stability than those based on CTFE and PMVE. The glass transition temperatures were in the 15-65 C range. These original copolymers may find potential interest as polymer electrolytes in lithium ions batteries
Polymeric materials as anion-exchange membranes for alkaline fuel cells
No full textInternational audienceAfter summarizing the different fuel cells systems, including advantages and drawbacks, this review focuses on the preparation of copolymers and polymeric materials as starting materials for solid alkaline fuel cells membranes. The requirements for such membranes are also summarized. Then, different strategies are given to synthesize anion-exchange polymeric materials containing cationic (especially ammonium) groups. The first pathway focuses on heterogeneous membranes that consist in: (i) polymer blends and composites based on poly(alkene oxide)s and hydroxide salts or polybenzimidazole doped with potassium hydroxide, (ii) organic-inorganic hybrid membranes especially those synthesized via a sol-gel process, and (iii) (semi)interpenetrated networks based on poly(epichlorhydrine), poly(acrylonitrile) and polyvinyl alcohol for example, that have led to new polymeric materials for anion-exchange membranes. The second and main part concerns the homogeneous membranes divided into three categories. The first one consists in materials synthesized from (co)polymers obtained via direct (co)polymerization, for example membranes based on poly(diallyldimethylammonium chloride). The second pathway concerns the modification of polymeric materials via radiografting or chemical reactions. These polymeric materials can be hydrogenated or halogenated. The radiografting of membranes means the irradiation via various sources - electron beam, X and gamma rays, 60Co and 137Cs - that lead to trapped radicals or macromolecular peroxides or hydroperoxides, followed by the radical graft polymerization of specific monomers such as chloromethyl styrene. The third route deals with the chemical modifications of commercially available hydrogenated aliphatic and aromatic (co)polymers, and the syntheses of fluorinated (co)polymers such as carboxylic and sulfonic perfluoropolymers. In addition, several approaches for the crosslinking of above-mentioned polymeric materials are also reported as this process enhances the properties of the resulting membranes. Moreover, electrochemical and thermal properties of various above ionomers are given and discussed
Kinetics of radical copolymerization of vinylidene fluoride with tert -butyl 2-trifluoromethyl acrylate: a suitable pair for the synthesis of alternating fluorinated copolymers
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