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Rational Design of Poly(fluorene)‑b‑poly(thiophene) Block Copolymers to Obtain a Unique Aggregation Behavior
journal contribution
posted on 2019-08-23, 12:34 authored by Lize Verheyen, Kwinten Janssens, Martina Marinelli, Elisabetta Salatelli, Guy KoeckelberghsIn poly(thiophene)
(PT) block copolymers, aggregation features
can be transferred from one block to the other. In this paper, it
is investigated whether this is also possible in block copolymers
consisting of blocks with different electronic properties, i.e. PT
and poly(fluorene) (PF), in order to obtain a polymer with a unique
combination of aggregation properties. By combining a PT block with
chiral side chains with a PF block with linear octyl side chains,
it is probed to obtain a polymer in which chiral expression (arising
from the PT with chiral side chains) and β-phase aggregation
(arising from the PF with linear octyl side chains) are brought together.
This combination is not possible in homopolymers, since chiral aggregation
implies chiral, branched side chains and β-phase aggregation
is only possible for PF with linear side chains. In a stepwise approach,
the right conditions are elucidated to obtain both characteristics
in one polymer. For this purpose, three block copolymers were synthesized
via Suzuki catalyst transfer condensative polymerization (SCTCP),
i.e. , poly(9,9-dioctylfluorene)-b-poly(3-((S)-3,7-dimethyloctyl)thiophene) (POF-b-P3OT*), poly(9,9-dihexylfluorene)-b-poly(3-((S)-3,7-dimethyloctyl)thiophene)
(PHF-b-P3OT*), and poly(9,9-dioctylfluorene)-b-poly(3-((S)-2-methylbutyl)thiophene)
(POF-b-P3BT*), and their
aggregation behavior was studied via solvatochromism experiments.
It is concluded that the side chains of the PF block should be 8 C
atoms long to ensure maximal β-phase aggregation and that the
side chains of the PT block should be short to ensure this block aggregates
first in a chiral way. In this way, the PT block can transfer its
chirality to the PF block and a polymer is obtained in which β-phase
aggregation and expression of chirality are combined in one PF, something
which is impossible for homopolymers.