Thermoresponsive Poly(2-oxazine) Block Copolymers Exhibiting two Cloud Points: Complex Multistep Assembly Behaviour
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Trinh, Loan T. T.; Lambermont-Thijs, Hanneke M. L.; Schubert, Ulrich S.; Hoogenboom, Richard; Kjøniksen, Anna-Lena
- Abstract:
- Aqueous solutions of poly(2-oxazoline) block
copolymers consisting of a 2-ethyl-2-oxazoline block and a
block consisting of a random copolymer of 2-ethyl-2-oxazoline
and 2-n-propyl-2-oxazoline (PEtOx-block-P(EtOx-stat-PropOx))
have been studied by dynamic light scattering (DLS),
static light scattering (SLS), and turbidimetry. Even at
temperatures significantly below the lower critical solution
temperature (LCST), polymer unimers are found to coexist
with a few large aggregates with an open structure. When heated, the systems exhibit an intricate transmittance behavior whereby
the samples becomes visually clear again after an initial cloud point and then exhibit a second cloud point at even higher
temperatures. The DLS data indicate that the aggregates formed around the first cloud point restructure and fragment into
smaller micelle-like structures ascribed to further dehydration of the more hydrophobic PPropOx containing block, causing the
samples to become optically clear again. The observed fragmentation is confirmed by the SLS experiments. At even higher
temperatures, both blocks become hydrophobic, causing the formation of large, compact aggregates, resulting in a second cloud
point.
- Year:
- 2012
- Type of Publication:
- Article
- Journal:
- Macromolecules
- Volume:
- 45
- Pages:
- 4337 - 4345