Crystallization-Driven Self-Assembly of Amphiphilic
Triblock Terpolymers With Two Corona-Forming Blocks of Distinct Hydrophilicities
Posted on 2020-07-20 - 18:40
We
report the synthesis and studies of self-assembly in solution
of two related polyferrocenyldimethylsilane (PFS) ABC triblock terpolymers
(TTPs), in which the BC blocks are amphiphilic comb diblock copolymers,
PFS27-b-POEGMA180-b-PTDMA178 and PFS27-b-PTDMA181-b-POEGMA166. The subscripts
refer to the mean degrees of polymerization. Crystallization-driven
self-assembly of these TTPs was studied in four alcohol solvents of
decreasing polarity. Poly(tetradecyl methacrylate) (PTDMA) has limited
solubility in 1-butanol below 45 °C, whereas POEGMA exhibits
upper critical solution temperature (UCST) behavior in 1-hexanol (27
°C), 1-octanol (38 °C), and 1-decanol (42 °C). Consequently,
the corona component below its UCST would be in a collapsed or microphase-separated
state. PFS27-b-POEGMA180-b-PTDMA178 dissolved in hot 1-hexanol, 1-octanol,
and 1-decanol and formed long rodlike micelles upon cooling. Micelle
fragments generated by sonication served as seeds for both seeded
growth and self-seeding experiments, leading to rodlike micelles of
uniform length. PFS27-b-PTDMA181-b-POEGMA166 exhibited similar behavior
in 1-butanol. The characteristic that these experiments have in common
is that the outer block of the corona exhibits good solubility in
the medium. PFS27-b-PTDMA181-b-POEGMA166 in the more hydrophobic
alcohols behaved differently. Seeded growth experiments led to raftlike
objects made up of 5–10 rodlike micelles of similar length,
lined up side-by-side. The length of the rods, and hence the length
of the rafts, increased linearly with the unimer-to-seed ratio. Self-seeding
experiments with these micelle fragments, particularly in 1-octanol
and 1-decanol, also led to raftlike objects built up from uniform
rodlike micelle building block. We propose a model for raft formation
based on the idea that at T < UCST for the outer POEGMA block,
there is an attractive interaction between the corona blocks of the
micelles. This attraction is strong enough to promote association
but not strong enough to lead to precipitation. Parallel alignment
of the adjacent micelles of similar length maximizes the interaction
between them.
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Song, Shaofei; Puzhitsky, Matthew; Ye, Shuyang; Abtahi, Mahtab; Rastogi, Chandresh Kumar; Lu, Elsa; et al. (2020). Crystallization-Driven Self-Assembly of Amphiphilic
Triblock Terpolymers With Two Corona-Forming Blocks of Distinct Hydrophilicities. ACS Publications. Collection. https://doi.org/10.1021/acs.macromol.0c01414