Hydrogen-bonded complexes in block copolymers


In order to broaden the range of micellar structures and functionalities, specific non-covalent interactions have been recently considered as driving force for micellization. In this respect, non-covalent interactions between mutually interacting polymer blocks or between a polymer block and low molecular weight functional molecules such as surfactants have been used. The complexes resulting from these non-covalent interactions may be insoluble and further aggregate into a micellar core. These micellar cores are surrounded by a corona formed by the polymer blocks which were not involved in the complexation process.
We use this strategy to prepare micelles in organic solvents from poly(styrene)-block-poly(4-vinylpyridine) (PS-b-P4VP) diblock copolymers mixed with either fluorinated surfactants bearing a carboxylic acid group or poly(acrylic acid) (PAA). In both cases, hydrogen-bonding between the P4VP blocks and carboxylic acid groups is the driving force for aggregation.
Spherical micellar aggregates have been obtained in chloroform by mixing PS-b-P4VP diblock copolymers with perfluorinated surfactants (FS) bearing a carboxylic acid head. These micellar aggregates are resulting from the self-assembly of the insoluble P4VP/fluorinated complexes into a core surrounded by the soluble PS coronal chains. Their characteristic features have been studied as a function of various parameters including the composition of the PS-b-P4VP copolymer, the tail length of the fluorinated surfactant, the 4VP/FS molar ratio, the number of carboxylic acid group (1 or 2) on the surfactant, the presence of the PS block and of the fluorine atoms on the surfactant. Dilution of these initial micellar aggregates triggers a morphological reorganization resulting in the formation of more stable vesicles. The extent of this morphological transition is related to the solubility of the P4VP/fluorinated complexes during the dilution process. This transition is complete for short P4VP/FS complexes, incomplete for long P4VP/FS complexes and is not observed whenever an α,ω-difunctional FS is used in P4VP/FS complexes, leading to a crosslinked core. This spheres-to-vesicles transition has been advantageously used in order to encapsulate molecules, as demonstrated by confocal fluorescence microscopy.

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Micellar aggregates initially formed at a concentration of 1 g/L by (a) PS192-b-P4VP179/PFPA and (b) PS327-b-P4VP27/PFPA and vesicles observed after dilution at 0.1 g/L by (c) PS192-b-P4VP179/PFPA and (d) PS327-b-P4VP27/PFPA (4VP/PFPA molar ratio of 4/1 in all cases; a and b: AFM height contrast pictures; c and d: TEM pictures).


Micelles have been prepared by mixing poly(styrene)-block-poly(4-vinylpyridine) (PS-b-P4VP) copolymers and poly(acrylic acid) (PAA) homopolymers in organic solvents. Complexation via hydrogen bonding occurs between the P4VP and PAA blocks. Further aggregation of the accordingly formed complexes results in micelles stabilized by a corona of PS blocks. The influence of the relative lengths of the different blocks and of the quality of the solvent towards the complexes on the micellar characteristic features is studied. Soluble complexes have been observed in DMF, provided that the complexes are sufficiently small. In all other cases, micelles have been obtained. The size of the those micelles depends strongly on the length of the P4VP blocks but only weakly on the PAA length. Reorganization of these structures occurs upon addition of acidic or basic water, which results in the breaking of the hydrogen bonds between the P4VP and PAA blocks. After transfer of the initial complexes in acidic water, micelles consisting of a PS core and a protonated P4VP corona are observed. In basic water, well-defined nanoparticles formed by the PS-b-P4VP copolymers are obtained. It is demonstrated that these nanoparticles are stabilized by the negatively charged PAA chains. Finally, thermally-induced disintegration of the micelles is investigated in organic solvents.

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Reorganization of the micellar structure due to the addition of acidic or basic water in PS-b-P4VP/PAA mixtures.


Researchers involved: Zhijun Hu, Nathalie Lefèvre

Collaborations: Alain Jonas (UCL), Johan Hofkens (KUL)

Relevant papers:

"Dilution-induced spheres-to-vesicles morphological transition in micelles from block copolymer/surfactant complexes"
Z. Hu, S. Varshney, A. M. Jonas, J.-F. Gohy,
J. Am. Chem. Soc. 2005, 127, 6526-6527

"Formation of vesicles in block copolymer-fluorinated surfactant complexes"
Z. Hu, W. Verheijen, J. Hofkens, A. M. Jonas, J.-F. Gohy
Langmuir 2007, 23, 116-122

"Reorganization of hydrogen bonded block copolymer complexes"
N. Lefèvre, C.-A. Fustin, J.-F. Gohy
Langmuir 2007, 23, 4618-4622