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Contribution à la compréhension des mécanismes d’agglomération de mélanges de systèmes macromoléculaires PMMA/PEO en solution diluée : Rôle de la tacticité du PMMA et de la masse molaire du PEO sur le contrôle de la structure des nanoagrégats

Abstract : Use of NMR pulse sequences to measure diffusion permits to study the dynamic exchange of PEO as a small molecule that diffuses through hollow PMMA nanocapsules walls in order to control its release according to the environment. These nanostructured objects being composed of stereocomplex between isotactic and syndiotactic PMMA in acetonitrile, a preliminary study was devoted to the influence of PMMA/PEO interactions on the morphology of hollow nanocapsules.Firstly, we studied stereospecific interactions in binary systems stereoregular PMMA/PEO in chloroform, non-complexing solvent, and acetonitrile. The use of the DOSY NMR method allowed us to demonstrate the formation of a double distribution of nanoaggregates of controlled size and composition. PEO is present in a population of nanoaggregates inducing and stabilizing the PMMA aggregates. PMMA/PEO interactions dependent of tacticity PMMA are responsible for these nanostructures. They are not only controlled by PMMA tacticity but also by concentration and molecular weight of PEO. In chloroform, an interaction model in three stages depending on PEO concentration has been deducted highlighting predominant effect of polymer conformation on these interactions. In addition, a generalization of this stereospecific interactions model in several solvents has highlighted the correlation between the length of isotactic or syndiotactic sequences, their conformations and PEO molecular weight. In a second step, we were able to deduce a correlation with the decrease of stereocomplexation phenomenon in the systems PMMA stereocomplex/PEO/CD3CN based on interactions observed between the two polymers in solution in acetonitrile. PEO partly disrupts stereocomplex formation, thus highlighting the influence of PEO presence on hollow PMMA nanocapsules structure and its disintegrating effect. These studies have shown that diffusion mechanisms through the walls used in controlled release systems cannot ignore preliminary analysis of potential interactions between probe molecules and polymer walls structure. Indeed, these interactions can significantly change the structure of these containers and delivery mechanisms must take these effects into account quantitatively to be efficient.These studies suggest scientific approach to follow the development of controlled release model of active molecules through nanocapsules membranes, which are included in polymeric systems.
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Zomalala Ramananarivo. Contribution à la compréhension des mécanismes d’agglomération de mélanges de systèmes macromoléculaires PMMA/PEO en solution diluée : Rôle de la tacticité du PMMA et de la masse molaire du PEO sur le contrôle de la structure des nanoagrégats. Autre. Université de Toulon, 2011. Français. ⟨NNT : 2011TOUL0018⟩. ⟨tel-00919432⟩

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