Literatura académica sobre el tema "Flower-like micelles"

Rifampicin-loaded poly( ε -caprolactone)– b -poly(ethylene glycol)–poly( ε -caprolactone) flower-like polymeric micelles display low aqueous physical stability over time and undergo substantial secondary aggregation. To improve their physical stability, the lyoprotection–lyophilization process was thoroughly characterized. The preliminary cryoprotectant performance of mono- and disaccharides (e.g. maltose, glucose), hydroxypropyl-β-cyclodextrin (HPβCD) and poly(ethylene glycol) (PEG) of different molecular weights was assessed in freeze–thawing assays at −20°C, −80°C and −196°C. The size and size distribution of the micelles at the different stages were measured by dynamic light scattering (DLS). A cryoprotectant factor ( f c ) was determined by taking the ratio between the size immediately after the addition of the cryoprotectant and the size after the preliminary freeze–thawing assay. The benefit of a synergistic cryoprotection by means of saccharide/PEG mixtures was also assessed. Glucose (1 : 20), maltose (1 : 20), HPβCD (1 : 5) and glucose or maltose mixtures with PEG3350 (1 : 20) (copolymer:cryoprotectant weight ratio) were the most effective systems to protect 1 per cent micellar systems. Conversely, only HPβCD (1 : 5) cryoprotected more concentrated drug-loaded micelles (4% and 6%). Then, those micelle/cryoprotectant systems that displayed f c values smaller than 2 were freeze-dried. The morphology of freeze-dried powders was characterized by scanning electron microscopy and atomic force microscopy and the residual water content analysed by the Karl Fisher method. The HPβCD-added lyophilisates were brittle porous cakes (residual water was between 0.8% and 3%), easily redispersable in water to form transparent systems with a minimal increase in the micellar size, as determined by DLS.

Reversible addition fragmentation chain transfer (RAFT) synthesis and self-assembly of free-base porphyrin cored star polymers are reported. The polymerization, in the presence of a free-base porphyrin cored chain transfer agent (CTA-FBP), produced porphyrin star polymers with controlled molecular weights and narrow polydispersities for a number of monomers includingN,N-dimethylacrylamide (DMA) and styrene (St). Well-defined amphiphilic star block copolymers, P-(PS-PDMA)4and P-(PDMA-PS)4(P: porphyrin), were also prepared and used for self-assembly studies. In methanol, a selective solvent for PDMA, spherical micelles were observed for both block copolymers as characterized by TEM. UV-vis studies suggested star-like micelles were formed from P-(PS-PDMA)4, while P-(PDMA-PS)4aggregated into flower-like micelles. Spectrophotometric titrations indicated that the optical response of these two micelles to external ions was a function of micellar structures. These structure-related properties will be used for micelle studies and functional material development in the future.

Well controlled ABA triblock copolymer with pendent boronic acid groups is prepared using RAFT chemistry. The resulting flower like micelles in mixture of H₂O/NMP forms stimuli responsive porous network.

Depuis une dizaine d’années, l’auto-assemblage induit par polymérisation (PISA) s’est révélé être un outil efficace pour la préparation de nanoparticules à base de copolymères amphiphiles à des taux de solide élevés, aussi bien dans des solvants organiques que dans l’eau. Jusqu’à présent, la plupart des systèmes étudiés concernaient les copolymères diblocs AB (dans lesquels A = bloc solvophile stabilisant, et B = bloc solvophobe). Un autre type de copolymères à blocs intéressant est le tribloc associatif BAB. Peu d’études décrivent leur synthèse par PISA et les polymérisations sont réalisées dans des mélanges alcool/eau. Dans ce travail de thèse, et pour la première fois, la synthèse par voie radicalaire contrôlée de copolymères triblocs BAB par PISA a été réalisée dans l’eau pure et une étude approfondie du système a été menée. Un macro-agent RAFT hydrophile symétrique à base de poly(acrylamide de N,N-diméthyle) possédant une unité acide benzoïque au centre, et le diacétone acrylamide (blocs B) ont été sélectionnés pour étudier ce système. Des particules de différentes morphologies (sphères, fibres et vésicules) ont pu être obtenues avec de bons contrôles des polymérisations. Nous avons montré que le degré d’ionisation de l’unité centrale acide benzoïque du bloc stabilisant jouait un rôle crucial dans la stabilité du système et la morphologie obtenue. Le mécanisme de formation de ces copolymères triblocs au cours de la PISA a également été étudié. Enfin, nous avons montré qu’il était possible de former des réseaux dynamiques de copolymères BAB – via un procédé one-pot entièrement dans l’eau – menant à la formation de systèmes thermosensibles avec une viscosité modulable
Over the past decade, the polymerization-induced self-assembly (PISA) has become an efficient tool for the preparation of block-copolymer nanoparticles at high solid contents, in both organic solvents and water. Nonetheless, most of the studied systems are currently based on simple AB diblock copolymers (where A = solvophilic, stabilizer block and B = solvophobic block). Another interesting class of block copolymers are associative BAB triblocks. To the best of our knowledge, very few studies report their synthesis by PISA and the polymerizations are performed in mixtures of alcohol and water. In this work, for the first time, a straightforward strategy to synthesize, in pure water, BAB triblock copolymers through the use of reversible deactivation radical polymerization is developed and studied in details. To this end, an hydrophilic, bifunctional macroRAFT agent of poly(N,N-dimethylacrylamide) with a central benzoic acid group was used in the aqueous dispersion polymerization of diacetone acrylamide. Various morphologies (spheres, fibers and vesicles) could be obtained with good polymerization controls. Moreover, we showed that the particle morphology and colloidal stability strongly depend on the degree of ionization of the central charge in the stabilizer loop. Then, the mechanism of formation of these triblock copolymers during PISA was investigated. Finally, we showed the possibility to form dynamic networks of BAB copolymers – using a one-pot process entirely in water – leading to the formation of thermoresponsive copolymer networks with tunable viscosity