Block copolymer vesicles
J. A. Opsteen, J. J. L. M. Cornelissen, and J. C. M. van Hest
Department of Organic Chemistry, NSRIM Institute,
University of Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands
Abstract: Amphiphilic block copolymers have the ability to assemble
into multiple morphologies in solution. Depending on the length of the
hydrophilic block, the morphology can vary from spherical micelles,
rods, and vesicles to large compound micelles (LCMs). Vesicle formation
is favored upon an increase in total molecular weight of the block copolymer,
that is, an increasing bending modulus (K). Owing to the polymeric
character of this type of vesicle (also called polymersomes), they possess
remarkable properties. The diffusion of (polymeric) amphiphiles in these
vesicles is very low compared to liposomes and for high-molecular-weight
chain entanglements even lead to reptation-type motions, which make
it possible to trap near-equilibrium and metastable morphologies. Additionally,
in contrast to liposomes, membrane thicknesses can exceed 200 nm. As
a consequence, this increased membrane thickness, in combination with
the conformational freedom of the polymer chains, leads to a much lower
permeability for water of block copolymer vesicles compared to liposomes.
The enhanced toughness and reduced permeability of polymersomes makes
them, therefore, very suitable as stable nanocontainers, which can be
used, for example, as reactors or drug delivery vehicles.
*Lecture presented at the symposium "Controlling the self assembly in macromolecular systems: From nature to chemistry to functional properties", as part of the 39th IUPAC Congress and 86th Conference of the Canadian Society for Chemistry: Chemistry at the Interfaces, Ottawa, Canada, 10-15 August 2003. Other Congress presentations are published in this issue, pp. 1295-1603.
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