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

The synthesis of high-molecular-weight, well-defined poly­(vinylferrocene)-<i>block</i>-poly­(ethylene glycol) (PVFc-<i>b</i>-PEG) diblock copolymers (<i>M</i>_n = 13 000–44 000 g mol^–1; <i>Đ</i> = 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-<i>b</i>-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

Ferrocene Polymers for Switchable Surface Wettability

The changes in surface wettability induced by immobilized polyvinylferrocene (PVFc) and poly­(2-(methacryloyloxy)­ethyl ferrocenecarboxylate) (PFcMA) on silica wafers were studied after oxidation with two different oxidation reagents. Surface-attached PFcMA was accessible by applying a surface-initiated atom transfer radical polymerization (SI-ATRP) protocol, while end-functionalized PVFc was immobilized by using a grafting onto approach. In the case of PFcMA, a remarkable contact angle (CA) drop for water of approximately 70° after oxidation could be observed, while the effect for immobilized PVFc after oxidation was less pronounced (CA drop of approximately 30°). In the case of PFcMA, the effect of chain length was additionally studied, showing a more significant CA drop for PFcMA chains with higher molar masses

Dynamic Nuclear Polarization Signal Amplification as a Sensitive Probe for Specific Functionalization of Complex Paper Substrates

In this work, it is shown how solid-state NMR combined with dynamic nuclear polarization (DNP) can be employed as a powerful tool to selectively enhance the spectral intensity of functional groups on the surface of cellulose fibers in paper materials. As a model system, a poly­(benzyl methacrylate) (PBEMA)-functionalized paper material is chosen that contains hydrophobic and hydrophilic domains. Detailed analysis of the DNP NMR data and of <i>T</i>_1ρ data suggests that inhomogeneous ¹H–¹H spin diffusion is responsible for the observed differences in signal enhancement. These findings are fundamental for structural understanding of complex paper substrates for fluid transport or sensor materials

Structure Formation of Metallopolymer-Grafted Block Copolymers

Microphase separation drives the structure formation in block copolymers. Here, functional metallopolymer-grafted diblock copolymers consisting of polystyrene-<i>block</i>-polyisoprene (PS-<i>b</i>-PI) as polymer backbone featuring low molar mass poly­ferrocenyl­dimethyl­silane (PFS) and polyvinyl­ferrocene (PVFc) are synthesized via an iterative anionic grafting-to polymerization strategy. PS-<i>b</i>-PI block copolymers having about 30 mol % 1,2-polyisoprene moieties are subjected to platinum-catalyzed hydrosilylation reaction for the introduction of chlorosilane groups. The Si–Cl moieties are shown to efficiently react with the active metallopolymers yielding block-selective metallopolymer-grafted copolymers with 34 vol % PVFc and 43 vol % PFS as evidenced by ¹H NMR spectroscopy as well as size exclusion chromatography. The microphase separation of the functional metallopolymer-grafted block copolymers is evidenced via TEM measurements revealing fascinating morphologies. The structure formation of the PVFc-grafted block copolymers is studied in more detail by TEM, small-angle X-ray scattering, wide-angle X-ray scattering, and atomic force microscopy measurements evidencing a lamellar morphology featuring a spherical substructure for the PVFc segments inside the polyisoprene lamellae

Metallopolymer-Based Block Copolymers for the Preparation of Porous and Redox-Responsive Materials

Metallopolymers are a unique class of functional materials because of their redox-mediated optoelectronic and catalytic switching capabilities and, as recently shown, their outstanding structure formation and separation capabilities. Within the present study, (tri)­block copolymers of poly­(isoprene) (PI) and poly­(ferrocenylmethyl methacrylate) having different block compositions and overall molar masses up to 328 kg mol^–1 are synthesized by anionic polymerization. The composition and thermal properties of the metallopolymers are investigated by state-of-the-art polymer analytical methods comprising size exclusion chromatography, ¹H NMR spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. As a focus of this work, excellent microphase separation of the synthesized (tri)­block copolymers is proven by transmission electron microscopy, scanning electron microcopy, energy-dispersive X-ray spectroscopy, small-angle X-ray scattering measurements showing spherical, cylindrical, and lamellae morphologies. As a highlight, the PI domains are subjected to ozonolysis for selective domain removal while maintaining the block copolymer morphology. In addition, the novel metalloblock copolymers can undergo microphase separation on cellulose-based substrates, again preserving the domain order after ozonolysis. The resulting nanoporous structures reveal an intriguing switching capability after oxidation, which is of interest for controlling the size and polarity of the nanoporous architecture

Fluid Flow Programming in Paper-Derived Silica–Polymer Hybrids

In paper-based devices, capillary fluid flow is based on length-scale selective functional control within a hierarchical porous system. The fluid flow can be tuned by altering the paper preparation process, which controls parameters such as the paper grammage. Interestingly, the fiber morphology and nanoporosity are often neglected. In this work, porous voids are incorporated into paper by the combination of dense or mesoporous ceramic silica coatings with hierarchically porous cotton linter paper. Varying the silica coating leads to significant changes in the fluid flow characteristics, up to the complete water exclusion without any further fiber surface hydrophobization, providing new approaches to control fluid flow. Additionally, functionalization with redox-responsive polymers leads to reversible, dynamic gating of fluid flow in these hybrid paper materials, demonstrating the potential of length scale specific, dynamic, and external transport control