University CrestOne-Pot Synthesis and Self-assembly of Amphiphilic Block CopolymersArmes Research Group
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  4 September 2005

Amphiphilic diblock copolymers composed of two covalently linked, chemically distinct chains can be considered to be biological mimics of cell membrane-forming lipid molecules, but with typically more than an order of magnitude increase in molecular weight. These macromolecular amphiphiles are known to form a wide range of nanostructures (spheres, worms, vesicles, etc.) in solvents that are selective for one of the blocks. However, such self-assembly is usually limited to dilute copolymer solutions (<1%), which is a significant disadvantage for potential commercial applications such as drug delivery and coatings. In principle, this problem can be circumvented by polymerization-induced block copolymer self-assembly.

Detailed phase diagram constructed for the M25Hx-Y formulation (where M denotes MPC and H denotes HPMA) by systematic variation of the mean target degree of polymerization of PHPMA (x) and the total solids concentration (Y) used for each synthesis.

Detailed phase diagram constructed for the M25Hx-Y formulation (where M denotes MPC and H denotes HPMA) by systematic variation of the mean target degree of polymerization of PHPMA (x) and the total solids concentration (Y) used for each synthesis.

Reversible addition–fragmentation chain transfer polymerization has been utilized to polymerize 2-hydroxypropyl methacrylate (HPMA) using a water-soluble macromolecular chain transfer agent based on either poly(2-(methacryloyloxy)ethylphosphorylcholine) (PMPC) [S. Sugihara et al., JACS, 2011] or poly(glycerol monomethacrylate) [Y. Li and S. P. Armes, Angew. Chemie., 2010 and A. Blanazs et al., JACS, 2011]. Detailed phase diagrams have been elucidated for these aqueous dispersion polymerization formulations that reliably predict the precise block compositions associated with well-defined particle morphologies (i.e., pure phases).

JACS front cover October 19th 2011: intermediate nanostructures observed during the worm-to-vesicle transition.

JACS front cover October 19th 2011: intermediate nanostructures observed during the worm-to-vesicle transition.

Careful monitoring of these in situ polymerization reactions by transmission electron microscopy reveals various novel intermediate structures (including branched worms, partially coalesced worms, nascent bilayers, “octopi”, “jellyfish”, and finally pure vesicles) that provide important mechanistic insights regarding the evolution of the particle morphology during the sphere-to-worm and worm-to-vesicle transitions. This environmentally benign approach (which involves no toxic solvents, is conducted at relatively high solids, and requires no additional processing) is readily amenable to industrial scale-up, since it is based on commercially available starting materials.

Selected Publications
"Mechanistic Insights for Block Copolymer Morphologies: How Do Worms Form Vesicles?"
A. Blanazs, J. Madsen, A. J. Ryan, G. Battaglia and S. P. Armes
Journal of the American Chemical Society 2011, 133, 16581
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"Aqueous dispersion polymerisation: a new paradigm for in situ block copolymer self-assembly in concentrated solution"
S. Sugihara, A. Blanazs, A. J. Ryan, S. P. Armes and A. L. Lewis
Journal of the American Chemical Society 2011, 133, 15707
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"RAFT synthesis of sterically-stabilized methacrylic nanolatexes and vesicles by aqueous dispersion polymerization"
Y. T. Li and S. P. Armes
Angewandte Chemie 2010, 49, 4042
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