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Highly-ordered onion micelles made from amphiphilic highly-branched copolymers
Canning, S.L. Ferner, J.M.F. Mangham, N.M. Wear, T.J. Reynolds, S.W. Morgan, J. Fairclough, J.P.A. King, S.M. Geoghegan, M.
Canning, S.L.
Ferner, J.M.F.
Mangham, N.M.
Wear, T.J.
Reynolds, S.W.
Morgan, J.
Fairclough, J.P.A.
King, S.M.
Geoghegan, M.
Publication Date
2018
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© 2018 The Royal Society of Chemistry. This work is licensed under a Creative Commons Attribution 4.0 International License. http://creativecommons.org/licenses/by/4.0/
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openAccess
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08/10/2018
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Abstract
Uniform onion micelles formed from up to ten nano-structured polymer layers were produced by the
aqueous self-assembly of highly-branched copolymers. Highly-branched poly(alkyl methacrylate)s were
chain extended with poly(acrylic acid) in a two-step reversible addition–fragmentation chain transfer-self-condensing
vinyl polymerization (RAFT-SCVP) in solution. The resulting polymers were dispersed into
water from oxolane (THF) using a self-organized precipitation-like method and the self-assembled particles
were studied by phase-analysis light scattering, small-angle neutron scattering, and electron
microscopy techniques. The relative hydrophobicity of the blocks was varied by changing the alkyl methacrylate
(methyl, butyl, or lauryl) and this was found to affect the morphology of the particles. Only the
poly(butyl methacrylate)-containing macromolecule formed an onion micelle structure. The formation of
this morphology was observed to depend on: the evaporation of the good solvent (THF) during the self assembly
process causing kinetic trapping of structures; the pH of the aqueous phase; and also on the
ratio of hydrophobic to hydrophilic segments within the copolymer. The lamellar structure could be
removed by annealing the dispersion above the glass transition temperature of the poly(butyl methacrylate).
To exemplify how these onion micelles can be used to encapsulate and release an active compound,
a dye, rhodamine B (Rh B), was encapsulated and released. The release behaviour was dependent
on the morphology of the particles. Particles formed containing the poly(methyl methacrylate) or poly
(lauryl methacrylate) core did not form onions and although these materials absorbed Rh B, it was continuously
released at room temperature. On the other hand, the lamellar structure formed from branchpoly(
butyl methacrylate)-[poly(butyl methacrylate)-block-poly(acrylic acid)] allowed for encapsulation of
approximately 45% of the dye, without release, until heating disrupted the lamellar structure.
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Citation
Canning SL, Ferner JMF, Mangham NM et al (2018) Highly-ordered onion micelles made from amphiphilic highly-branched copolymers. Polymer Chemistry. 9: 5617-5639.
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