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Synthesis and Self-Assembly of Thiophene-Based All-Conjugated Amphiphilic Diblock Copolymers with a Narrow Molecular Weight Distribution
journal contribution
posted on 2016-02-20, 18:38 authored by In Young Song, Jinseck Kim, Min Jeong Im, Byung Joon Moon, Taiho ParkA series of amphiphilic poly(3-hexylthiophene-b-3-(2-(2-{2-[2-(2-methoxy–ethoxy)-ethoxy]-ethoxy}-ethyl))thiophene)
(P(3HT-b-3EGT)) polymers was synthesized via a nickel-catalyzed
quasi-living polymerization. Size exclusion chromatograms (SEC) revealed
that the molecular weight distributions of the P3HT blocks
in the block copolymers were comparable with those of the polystyrene
standard (monodisperse). 1H NMR spectra revealed that the P3HT and PEGT units in the block copolymers were
well-defined and did not form compositionally mixed regions at the
boundary between the blocks and the highly regioregular P3HT units. The correlations among the block ratio, the amphiphilicity,
and the self-assembled nanostructures of the block copolymers in thin
films and in solution were examined. Differential scanning calorimetry
(DSC) and X-ray diffraction (XRD) studies revealed that the crystallinity
of the BP93 composed of 93 mol % P3HT blocks
was higher than the crystallinity of the P3HT alone due
to the packing effects caused by repulsion among the hydrophobic hexyl
and hydrophilic ethylene glycol oligomer side chains. A long relaxation
time was required to observe the ordering among P3HT blocks
in the BP26 composed of 26 mol % P3HT blocks, suggesting
that self-assembly could occur if induced on the molecular level.
We demonstrated that the molecular-level self-assembly of BP26 (at dilute concentrations) via a slow dialysis method produced highly
ordered polymer vesicles 200–250 nm in size under thermodynamic
control. The size could be tuned via competitive hydrophobic interactions
using polystyrene. In contrast, kinetic control via a rapid precipitation
method yielded 5–20 nm micelles.