Sequential Nucleophilic Substitutions Permit Orthogonal
Click Functionalization of Multicomponent PEG Brushes
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Abstract
Multicomponent
poly(ethylene glycol) (PEG) brushes (i.e., ≥2
adjacent PEG brushes) can be used to engineer culture substrates with
microscale, nonfouling regions decorated with covalently immobilized
ligands that mediate biospecific interactions. However, synthesizing
such brushes with orthogonal immobilization chemistries to permit
differential biofunctionalization is nontrivial and often requires
synthesis of PEG-<i>co</i>-polymers. To simplify synthesis
and enhance the versatility of such substrates, we developed a protocol
for generating orthogonal click-functionalized multicomponent PEG
brushes using sequential nucleophilic substitutions by sodium azide,
ethanolamine, and propargylamine. The novel application of propargylamine-mediated
substitution functionalizes PEG brushes with acetylene groups, and
for the first time, ethanolamine-mediated substitution is shown to
be sufficient for passivating the “living” polymer chain
ends between brush synthesis steps. Thus, our multicomponent PEG brushes
present dual orthogonal chemistries (i.e., azido and acetylene groups)
for ligand immobilization via versatile copper-free click reactions,
which are useful for in situ surface modifications during cell culture