Polyvinylferrocene-Based Amphiphilic Block Copolymers Featuring Functional Junction Points for Cross-Linked Micelles

Abstract

The synthesis of high-molecular-weight, well-defined poly(vinylferrocene)-block-poly(ethylene glycol) (PVFc-b-PEG) diblock copolymers (Mn = 13 000–44 000 g mol–1; Đ = 1.29–1.34) with precisely one allyl group at the junction point is introduced. Allyl glycidyl ether (AGE) was used to end-functionalize PVFc, resulting in hydroxyl functional macroinitiators for the oxyanionic polymerization of ethylene oxide. The self-assembly behavior of the amphiphilic PVFc-b-PEG copolymers in water has been investigated in a detailed manner, using dynamic light scattering (DLS) and transmission electron microscopy (TEM). The redox activity of the PVFc block was confirmed by UV/vis spectroscopy, while cyclovoltammetry (CV) measurements were carried out to support the stability and full reversibility of the ferrocene/ferrocenium redox couple. Both formation and dissociation of the macromolecular self-assemblies in aqueous solution via oxidation and reduction of the PVFc segments were evidenced by TEM and DLS. The dye Nile Red was used as model compound to investigate the stabilization of a water-insoluble molecule in aqueous solution by the block copolymers via encapsulation inside micellar structures. Oxidation of the PVFc segments lead to instantaneous and quantitative release of the dye. Furthermore, incorporation of the allyl moiety at the block junction point was used to cross-link the shell of the compartments. By this strategy a stable incorporation of the dye was achieved while triggered release via oxidation led to quantitative liberation.