Fielding, L.A., Lane, J.A., Derry, M.J. et al. (2 more authors) (2014) Thermo-responsive Diblock Copolymer Worm Gels in Non-polar Solvents. Journal of the American Chemical Society, 136 (15). pp. 5790-5798.
Abstract
Benzyl methacrylate (BzMA) is polymerized using a poly(lauryl methacrylate) macromolecular chain transfer agent (PLMA macro-CTA) using reversible addition-fragmentation chain transfer (RAFT) polymerization at 70 °C in n-dodecane. This choice of solvent leads to an efficient dispersion polymerization, with polymerization-induced self-assembly (PISA) occurring via the growing PBzMA block to produce a range of PLMA-PBzMA diblock copolymer nano-objects, including spheres, worms, and vesicles. In the present study, particular attention is paid to the worm phase, which forms soft free-standing gels at 20 °C due to multiple inter-worm contacts. Such worm gels exhibit thermo-responsive behavior: heating above 50 °C causes degelation due to the onset of a worm-to-sphere transition. Degelation occurs because isotropic spheres interact with each other much less efficiently than the highly anisotropic worms. This worm-to-sphere thermal transition is essentially irreversible on heating a dilute solution (0.10% w/w) but is more or less reversible on heating a more concentrated dispersion (20% w/w). The relatively low volatility of n-dodecane facilitates variable-temperature rheological studies, which are consistent with eventual reconstitution of the worm phase on cooling to 20 °C. Variable-temperature (1)H NMR studies conducted in d26-dodecane confirm partial solvation of the PBzMA block at elevated temperature: surface plasticization of the worm cores is invoked to account for the observed change in morphology, because this is sufficient to increase the copolymer curvature and hence induce a worm-to-sphere transition. Small-angle X-ray scattering and TEM are used to investigate the structural changes that occur during the worm-to-sphere-to-worm thermal cycle; experiments conducted at 1.0 and 5.0% w/w demonstrate the concentration-dependent (ir)reversibility of these morphological transitions.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2014 The Author(s). This is an Open Access article distributed under the terms of the Creative Commons Attribution Licence (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. |
Dates: |
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Institution: | The University of Sheffield |
Academic Units: | The University of Sheffield > Faculty of Science (Sheffield) > Department of Chemistry (Sheffield) |
Funding Information: | Funder Grant number EPSRC EP/J007846/1 |
Depositing User: | Symplectic Sheffield |
Date Deposited: | 19 May 2014 13:20 |
Last Modified: | 19 May 2014 13:20 |
Published Version: | http://dx.doi.org/10.1021/ja501756h |
Status: | Published |
Publisher: | American Chemical Society |
Refereed: | Yes |
Identification Number: | 10.1021/ja501756h |
Related URLs: | |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:79027 |