Using EPR To Compare PEG-<i>branch</i>-nitroxide “Bivalent-Brush Polymers” and Traditional PEG Bottle–Brush Polymers: Branching Makes a Difference
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Abstract
Attachment of poly(ethylene glycol) (PEG) to polymeric
nanostructures
is a general strategy for sterically shielding and imparting water
solubility to hydrophobic payloads. In this report, we describe direct
graft-through polymerization of branched, multifunctional macromonomers
that possess a PEG domain and a hydrophobic nitroxide domain. Electron
paramagnetic resonance (EPR) spectroscopy was used to characterize
microenvironments within these novel nanostructures. Comparisons were
made to nitroxide-labeled, traditional bottle-brush random and block
copolymers. Our results demonstrate that bivalent bottle-brush polymers
have greater microstructural homogeneity compared to random copolymers
of similar composition. Furthermore, we found that compared to a traditional
brush polymer, the branched-brush, “pseudo-alternating”
microstructure provided more rotational freedom to core-bound nitroxides,
and greater steric shielding from external reagents. The results will
impact further development of multivalent bottle-brush materials as
nanoscaffolds for biological applications