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Developing novel polymer architectures for applications In magnetic resonance imaging and self-assembly

Macromolecular scaffolds for drug delivery,
self-assembly, and imaging applications have attracted significant
attention over the last several decades. As polymerization
techniques become more sophisticated, it becomes possible to create
polymeric architectures with increasing control over structure,
molecular weight, and mass dispersity. Herein, ring-opening
metathesis polymerization (ROMP) is paired with highly efficient
synthetic methods to create functional bottle-brush polymers for
MRI imaging and self-assembly applications. In this "graft-through"
approach, bivalent macromonomers bearing a terminal exo-norbornene
group were synthesized and polymerized to yield bottle-brush
polymers with controlled molar masses and low dispersities. This
approach is first utilized in the development of organic radical
contrast agents (ORCAs) for magnetic resonance imaging (MRI). These
ORCAs are composed of macromonomers bearing long polyethylene
glycol chains and sterically hindered bis(spirocyclohexyl)
nitroxide free radicals. This approach enables facile tuning of
nitroxide loading percentages and molecular size. Bottle-brush
ORCAs displayed high r₁ and r₂ relaxivities suggesting that they
have potential for further in vivo MRI studies. Next, bottle-brush
copolymers composed of multiple polymeric domains are synthesized
by ROMP. We propose that these multi-block bottle-brush polymers
will self-assemble into interesting solution and bulk
architectures. Several approaches to synthesizing tetrablock
bottle-brush polymers were explored by combining "graft-through"
and "graft-from" polymerization methods.