Chemically induced supramolecular reorganization of triblock copolymer assemblies: Trapping of intermediate states via a shell-crosslinking methodology

doi:10.1073/pnas.052653099

Chemically induced supramolecular reorganization of triblock copolymer assemblies: Trapping of intermediate states via a shell-crosslinking methodology

^*Department of Chemistry, Washington University, One Brookings Drive, St. Louis, MO 63130; and ^†Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, PA 15213

Edited by Jack Halpern, University of Chicago, Chicago, IL, and approved January 3, 2002 (received for review December 6, 2001)

Abstract

The mechanism of morphological phase transitions was studied for rod-shaped supramolecular assemblies comprised of a poly(acrylic acid)-block-poly(methyl acrylate)-block-polystyrene (PAA₉₀-b-PMA₈₀-b-PS₁₀₀) triblock copolymer in 33% tetrahydrofuran/water after perturbation by reaction with a positively charged water-soluble carbodiimide. Tetrahydrofuran solvation of the hydrophobic core domain provided the dynamic nature required for the rod-to-sphere phase transition to be complete within 30 min. The intermediate morphologies such as fragmenting rods and pearl-necklace structures were trapped kinetically by the subsequent addition of a diamino crosslinking agent, which underwent covalent crosslinking of the shell layer. Alternatively, shell-crosslinked rod-shaped nanostructures with preserved morphology were obtained by the addition of the crosslinking agent before the addition of the carbodiimide, which allowed for the shell crosslinking to be performed at a faster rate than the morphological reorganization. The formation of robust shell-crosslinked nanostructures provides a methodology by which the morphological evolution processes can be observed, and it allows access to otherwise thermodynamically unstable nanostructures.

Footnotes

↵ ‡ To whom reprint requests should be addressed at: Department of Chemistry, Washington University, One Brookings Drive, CB 1134, St. Louis, MO 63130-4899. E-mail: klwooley{at}artsci.wustl.edu.
This paper was submitted directly (Track II) to the PNAS office.
↵ § Victor Luaña's tessel2 (www.uniovi.es/∼quimica.fisica/qcg/tessel/tessel.html), John VanSickle's reorient matrix macro (enphilistor.users4.50megs.com/macs.htm), and pov-ray (www.povray.org/) were used in the generation and rendition of the three-dimensional tesselations. Inference of specific length-scale differences between assemblies caused by changes in morphology should not be drawn from the illustrations.
Abbreviations:

TEM,

transmission electron microscopy;

THF,

tetrahydrofuran;

ETC,

1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide methiodide;

PAA,

poly(acrylic acid);

PMA,

poly(methyl acrylate);

PS,

polystyrene;

AFM,

atomic force microscopy