9 research outputs found
Synthesis of New lonic Functional Polymers by Free Radical Polymerization via the RAFT Process
Within the emerging methods of controlled free radical polymerization, the Reversible Addition-Fragmentation chain Transfer (RAFT) process has been recently established as a powerful technique to synthesize standard polymers with controlled characteristics (narrow polydispersity and predictable molar masses). This method is now employed to synthesize well-defined, reactive precursor polymers that are subsequently converted into speciality polymers such as fluorescent-labeled polycations. Those are suitable for Electrostatic Self-Assembly (ESA). The observation of the Förster Resonance Energy Transfer (FRET) in such films is established, contributing to the understanding of the self-organization during thin film growth.
The RAFT process using Benzyl Dithiobenzoate (BDTB) is shown to enable the control of the free radical polymerization of vinylbenzyl chloride (VBC). The high tolerance of the method to functional groups allows the preparation of such reactive polymers with narrow polydispersities and predictable molar masses. The well-defined precursors are easily converted, for instance, to polycations. Also they are easily functionalized by fluorophores, here derived from coumarin and perylene. The fluorophores, as pendent side chains, served as label to investigate the alternating deposition process, while the influence of molecular variations on the self-assembly can be systematized. Furthermore, when using complementary fluorophores, Fluorescence Resonance Energy Transfer (FRET) studies in organized media become possible.
The alternating deposition cycles are followed by UV-Vis spectroscopy, ellipsometry, and X-Ray reflectivity. Regular growth is observed for three complementarily labeled polycations. Noteworthy, fluorescence and UV-Vis studies reveal the formation of large fluorescent dye aggregates for one coumarin and for the perylene derivative in the ESA multilayers. When these polycations are used in mixed thin films, Forster Resonance Energy Transfer (FRET) between fluorophores is observed. The non-radiative nature of the different energy transfer was confirmed by fluorescence decay time measurements.Parmi les rĂ©centes mĂ©thodes pour contrĂŽler la polymĂ©risation radicalaire, le procĂ©dĂ© RAFT (Reversible Addition-Fragmentation chain Transfer) a Ă©tĂ© rĂ©cemment Ă©tabli et s'impose comme une mĂ©thode performante pour la synthĂšse de polymĂšres standards possĂ©dant des caractĂ©ristiques contrĂŽlĂ©es (faibles polydispersitĂ©s et masses molaires prĂ©dictibles). Cette mĂ©thode est dĂ©sormais utilisĂ©e pour la synthĂšse de prĂ©curseurs rĂ©actifs bien dĂ©finis qui sont par la suite convertis en polymĂšres spĂ©cialisĂ©s, par exemple en polycations marquĂ©s a l'aide de sondes fluorescentes. Ces polycations peuvent ĂȘtre ensuite auto-assemblĂ©s Ă©lectrostatiquement afin d'Ă©laborer des films minces. Le phĂ©nomĂšne de transfert de fluorescence (Förster Resonance Energy Transfer -FRET-) dans de tels films a Ă©tĂ© Ă©tabli, contribuant par lĂ -mĂȘme Ă une meilleure comprĂ©hension du phĂ©nomĂšne d'auto-organisation durant la croissance des films.
Le procĂ©dĂ© RAFT, utilisant le dithiobenzoate de benzyle (BDTB), a dĂ©montrĂ© sa capacitĂ© Ă contrĂŽler la polymĂ©risation radicalaire du chloromĂ©thlstyrĂšne (VBC). La tolĂ©rance de cette mĂ©thode vis Ă vis des groupes fonctionnels permet la synthĂšse de polymĂšres rĂ©actifs possĂ©dant de faibles polydispersitĂ©s et des masses molaires prĂ©dictibles. Les prĂ©curseurs ainsi dĂ©finis sont facilement convertis, en polycations par exemple. Ils sont tout aussi facilement fonctionnalisĂ©s par des fluorophores dĂ©rivĂ©s de la coumarine ou du pĂ©rylĂšne. Les fluorophores en tant que chaĂźnes pendantes servent de marqueurs pour Ă©tudier le processus de dĂ©pĂŽts alternĂ©s, alors que l'influence des variations au niveau molĂ©culaire peut ĂȘtre systĂ©matisĂ©e. De plus, en utilisant des fluorophores complĂ©mentaires, il devient possible de mener des Ă©tudes sur le transfert de fluorescence (FRET) au sein de milieux organisĂ©s.
Les cycles de dépÎts alternés ont été suivis par spectroscopie UV-Vis, éllipsométrie et reflexion des rayons X. Une croissance réguliÚre est observée dans le cas des trois polycations marqués. Il convient de noter que les études UV-Vis et de fluorescence révÚlent la formation de larges aggrégats de fluorophores au sein des multicouches, dans le cas d'une coumarine et du dérivé de pérylÚne. Lorsque les polycations complémentaires sont utilisés dans des films minces mixtes, le FRET est observé. La nature radiative ou non-radiative du processus de transfert d'énergie a été confirmée par des mesures de déclin de fluorescence.(CHIM 3)--UCL, 200
Enhanced Förster Resonance Energy Transfer in Electrostatically Self-Assembled Multilayer Films Made from New Fluorescently Labeled Polycations
Funktionelle und reactive polymerfilme durch schicht-fĂŒr-Shicht dsorption von polyelektrolyten
Nanoaggregates of a random amphiphilic polyanion to carry water-insoluble clofazimine in neutral aqueous media.
International audienceClofazimine, an antibiotic drug active against mycobacteria and used for the treatment of leprosy, is a very weak base insoluble in neutral aqueous media. It may cause rather severe secondary effects. Basically, these two shortcomings can be minimized by combination with a drug carrier. The potential of a polymeric carrier composed of nanosized aggregates formed by hydrophobized poly(methyl vinyl ether-alt-maleic acid) to solubilize clofazimine in neutral aqueous media and to administer it to mice was investigated. This amphiphilic polyanion was synthesized by partial esterification of commercial poly(methyl vinyl ether-alt-maleic anhydride) by dodecanol. An aggregate-forming analog bearing mannose residues aimed at targeting mannose receptors born by macrophages was also synthesized and characterized. In the presence of the aggregates, rather large amounts of clofazimine were compatibilized with neutral aqueous media. Comparison with a water-insoluble neutral dye, namely yellow OB, showed that the apparent solubilization of clofazimine was due to a synergistic combination of electrostatic and hydrophobic interactions and not only to the latter as in the case of yellow OB. Despite its favorable in vitro characteristics, clofazimine entrapped within the lipophilic pockets born by the amphiphilic aggregates exhibited no antibiotic activity after administration to mice infected with Mycobacterium bovis BCG
Water soluble polymeric nanogels by xanthate-mediated radical crosslinking copolymerisation
Branched water-soluble copolymers were obtained by direct radical crosslinking copolymerisation of acrylic acid or acrylamide and N,N'-methylenebisacrylamide at high solid content in the presence of an O-ethylxanthate as a reversible chain transfer agent
Aggregation phenomena in polyelectrolyte multilayers made from polyelectrolytes bearing bulky functional, hydrophobic fragments
The functionalization of polyelectrolyte multilayers often implies the use of bulky functional fragments, attached to a standard polyelectrolyte matrix. Despite of the high density of non-charged, often hydrophobic substituents, regular film growth by sequential adsorption proceeds easily when an appropriate polyelectrolyte counter ion is chosen. However, the functional fragments may cluster or aggregate. This complication is particularly evident when using chromophores and fluorophores as bulky pendant groups. Attention has to be paid to this phenomenon for the design of functional polyelectrolyte films, as aggregation may modify crucially the properties. The use of charged spacer groups does not necessarily suppress the aggregation of functional side groups. Still, clustering and aggregation depend on the detailed system employed, and are not obligatory. In the case of cationic poly(acrylamide)s labeled with naphthalene and pyrene fluorophores, for instance, the polymers form intramolecular hydrophobic associates in solution, as indicated by strong excimer formation. But the polymers can undergo a conformational rearrangement upon adsorption so that they are decoiled in the adsorbed films. Analogous observations are made for polyanions bearing mesogenic biphenyls fragments. In contrast, polycations functionalized with the dye coumarin 343 show little aggregation in solution, but a marked aggregation in the ESA films