Branched
Micelles by Living Crystallization-Driven
Block Copolymer Self-Assembly under Kinetic Control
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Abstract
We have found that
the width and shape (from rectangular to elliptical,
to almost circular in cross-section) of the crystalline core of fiberlike
micelles of polyferrocenyldimethylsilane (PFDMS) diblock copolymers
can be varied by altering the degree of polymerization of PFDMS, and
also the chemistry of the complementary corona-forming block. This
enabled detailed studies of living crystallization-driven self-assembly
(CDSA) processes that involved the addition of unimers with a short,
crystallizable core-forming PFDMS block to a seed solution of short
micelles with a large diameter crystalline core, derived from block
copolymers with a longer PFDMS block. The morphology of resultant
micelles was found to be highly dependent on the polarity of the solvent
and temperature. For example, linear micelles were formed in less
polar solvents (which are moderately poor solvents for PFDMS) and/or
at higher temperatures. In contrast, the formation of branched structures
could be “switched on” when the opposite conditions
were used. Thus, the use of more polar solvents (which are very poor
solvents for PFDMS) and ambient or subambient temperatures allowed
the formation of branched micelles and block comicelles with variable
and spatially distinct corona chemistries, including amphiphilic nanostructures.
Rapid crystallization of added unimers at the seed micelle termini
under nonequilibrium self-assembly conditions appears to facilitate
the formation of the branched micellar structures as a kinetically
trapped morphology. This is evidenced by the transformation of the
branched micelles into linear micelles on heating at elevated temperatures