|Title||Etude des poly(2-alkyl-2-oxazoline)s munis d’extremites hydrophobes en solution aqueuse et a l’interface eau/air|
The overall objective of this work was to synthetize and to characterize polymers that are able to self-assemble in aqueous solution in response to an external trigger. To achieve this goal, we concentrated our efforts on two polymers, poly2-isopropyl-2-oxazoline) PiPrOx and poly2-ethyl-2-oxazoline) PEtOx derivatives. Hydrophobically end-modified HM) poly2-alkyl-2-oxazoline)s HM-PAkOx), AkOx ï¼ 2-ethyl-2-oxazoline and 2-isopropyl-2-oxazoline, bearing an n-C18H37 chain on both termini telechelic HM-PiPrOx) or on one chain end only semitelechelic HM-PiPrOx) were prepared by cationic ring-opening polymerization CROP) of 2-alkyl-2-oxazoline and subsequent end-group modification. The polymers had a molar mass Mn) ranging from 7,000 to 13,000 g mol-1. Most of them formed nanostructures RH &simï¼ 7 — 12 nm) in cold water, as demonstrated by SLS, DLS, SAXS, 1 H NMR spectroscopy and fluorescence spectroscopy measurements carried out with aqueous solutions of telechelic and semitelechelic HM-PAkOx. As HM-PiPrOx aqueous solutions are heated near their cloud point, intermicellar bridging takes place leading to the formation of large assemblies or hydrated microgels. Further heating of the solutions to the lower critical solution temperature LCST) of PAkOx caused the dehydration of the polymer chains and collapse of the microgels, leading to mesoglogule formation. The thermodynamic properties of polymers in water have been studied by microcalorimetry DSC and PPC) in order to assess the influence of the molecular weight of the polymers, and of their self-assemblies into micelles star or flower micelles). Transition temperatures, enthalpy of transition, thermal expansion coefficient, changes in the volume of the hydration layer of the polymer in H2O and D2O were determined for all polymers. Moreover, it was shown that semitelechelic HM-PiPrOx crystallized upon incubation in hot water, whereas telechelic HM-PiPrOx do not exhibit this property. Furthermore, the self-assembly of the HM-polymers at the A/W interface was studied by the Langmuir film method. The influence of the molecular weight, the spreading solution concentration and the water subphase temperature on the interfacial properties of HM-polymers was evaluated. By Brewster angle microscopy BAM) and by atomic force microscopy AFM) observation, it was established that HM-PiPrOx polymers form large domains 400 nm — 1 mum in diameter) at the interface rather than homogenous films. Keywords: Poly2-isopropyl-2-oxazoline), poly2-ethyl-2-oxazoline), Lower critical solution temperature LCST), amphiphilic polymers, telechelic polymers, micelles, microcalorimetry, light scattering, air/water interface.
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