Synthèse et étude de nouveaux nitroxydes et alcoxyamines (application en polymerisation radicalaire contrôlée)

Le contrôle d'une polymérisation radicalaire en présence de nitroxydes est basé sur le piégeage réversible des radicaux en croissance par les nitroxydes, formant des alcoxyamines. Des travaux précédents ont montré que le nitroxyde b-phophoré SG1 est un contrôleur efficace des polymérisations du styrène et des acrylates. Nous avons préparé un nouveau nitroxyde, aussi performant que le SG1, mais offrant une synthèse plus avantageuse au niveau industriel. Ensuite, nous avons abaissé la température de polymérisation du styrène en augmentant l'encombrement stérique ou en introduisant des fonctions alcools sur le nitroxyde. L'utilisation de nitroxydes encombrés diminue la qualité du contrôle, et la masse molaire des polystyrènes n'excède pas 800000 g.mol-1. Enfin, nous avons testé sans succès différents nitroxydes afin de contrôler la polymérisation du méthacrylate de méthyle. Nous sommes revenus au cas du SG1 et, avec des conditions opératoires adaptées, le contrôle devient possible.The control of a free radical polymerization mediated by nitroxides relies on the reversible trapping of the polymer radicals by the nitroxides to form N-alcoxyamines. Earlier works showed that the b-phophonylated nitroxide SG1 was very efficient in the radical polymerization of styrene and acrylates monomers. We have prepared a new nitroxide, as efficient as SG1, which synthesis is more attractive from the view of industry. Then, we have reduced the temperature of the polymerization in increasing the steric strain of the nitroxide, or in introducing hydroxyl functions in the nitroxide. The use of steric hindred nitroxides gives a less efficient control, and it is not possible to obtain polystyrenes with a molecular mass higher than 80000 g.mol-1. Lastly, we have unsuccessfully tried several nitroxides in order to control the polymerization of methylmethacrylate. We have gone back over the use of SG1, and under suitable conditions, the control of the polymerization can be effective.AIX-MARSEILLE1-BU Sci.St Charles (130552104) / SudocSudocFranceF

Transfer and propagation reactions in free-radical copolymerization

The contribution of entropic factors to the penultimate unit effect in free-radical copolymerizations is discussed and exemplified. In addition, significant penultimate unit effects on radical selectivity in transfer reactions are demonstrated and are shown to have a significant polar component. Further, ring-opening copolymerization studies are presented and describe surprising results that seem to originate from strong solvent effects in copolymerization. These results could not have been predicted with current knowledge, prior to the experiment. The present contribution demonstrates in detail that radical reactions are highly complex and there are significant dangers and drawbacks in employing simplified kinetic models when in search of fundamental understanding