Amphiphilic block copolymers with aldehyde and ferrocene-functionalized hydrophobic block and their redox-responsive micelles

Abstract

Well-defined amphiphilic block copolymers consisting of a hydrophilic poly(ethylene oxide) (PEO) block linked to a hydrophobic block with reactive aldehyde and redox-active ferrocene groups was synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization of 2-formal-4-vinylphenyl ferrocenecarboxylate (FVFC) using a monomethoxy-terminated PEO-based macro-chain transfer agent. These amphiphilic block copolymers self-assembled into spherical micelles in aqueous solution, and their size clearly depended on the molecular weight of the PFVFC hydrophobic block, which could be controlled directly via the aforementioned RAFT polymerization. The availability of the synthesized amphiphilic block copolymer to conjugate bioactive molecules was confirmed via the reaction with an aminooxy model drug O-benzylhydroxylamine (BHA). The oxidation peak potential of the conjugates in cyclic voltammetry depended on the amount of the conjugated BHA, allowing one to quantify the degree of the conjugation simply by electrochemical measurement. Also, water-soluble (NH₄)Ce(NO₃)₆ and NaHSO₃ were used as the oxidizing and reducing agents, respectively, to explore the redox-controlled responsive behaviors of BHA conjugated PEO-b-PFVFC micelles using UV-vis spectroscopy, scanning electron microscopy and dynamic light scattering. This redox-responsive behavior would provide a prerequisite for redox-controlled release of encapsulants.