Markus Gallei

Patchy Nanocapsules of Poly(vinylferrocene)-Based Block Copolymers for Redox-Responsive Release

Nanocapsules composed of a poly(vinylferrocene)-block-poly(methyl methacrylate) shell and a hydrophobic liquid core are prepared in water. The nanocapsule shells display a patchy structure with poly(vinylferrocene) patches with sizes of 25 ± 3 nm surrounded by poly(methyl methacrylate). The functional nanopatches can be selectively oxidized, thereby influencing the colloidal morphology and introducing polar domains in the nanocapsule shell. The hydrophobic to hydrophilic transition in the redox-responsive nanopatches can be advantageously used to release a hydrophobic payload encapsulated in the core by an oxidation reaction.

Redox Responsive Release of Hydrophobic Self-Healing Agents from Polyaniline Capsules

Redox-responsive nanocapsules consisting of conductive polyaniline and polypyrrole shells were successfully synthesized by using the interface of miniemulsion droplets as a template for oxidative polymerizations. The redox properties of the capsules were investigated by optical spectroscopies, electron microscopy, and cyclic voltammetry. Self-healing (SH) chemicals such as diglycidyl ether or dicarboxylic acid terminated polydimethylsiloxane (PDMS-DE or PDMS-DC) were encapsulated into the nanocapsules during the miniemulsion process and their redox-responsive release was monitored by (1)H NMR spectroscopy. The polyaniline capsules exhibited delayed release under oxidation and rapid release under reduction, which make them promising candidates for anticorrosion applications.

Ceramic Nanocomposites from Tailor-Made Preceramic Polymers

The present Review addresses current developments related to polymer-derived ceramic nanocomposites (PDC-NCs). Different classes of preceramic polymers are briefly introduced and their conversion into ceramic materials with adjustable phase compositions and microstructures is presented. Emphasis is set on discussing the intimate relationship between the chemistry and structural architecture of the precursor and the structural features and properties of the resulting ceramic nanocomposites. Various structural and functional properties of silicon-containing ceramic nanocomposites as well as different preparative strategies to achieve nano-scaled PDC-NC-based ordered structures are highlighted, based on selected ceramic nanocomposite systems. Furthermore, prospective applications of the PDC-NCs such as high-temperature stable materials for thermal protection systems, membranes for hot gas separation purposes, materials for heterogeneous catalysis, nano-confinement materials for hydrogen storage applications as well as anode materials for secondary ion batteries are introduced and discussed in detail.

Redox- and mechano-chromic response of metallopolymer-based elastomeric colloidal crystal films

A novel and convenient route for the preparation of monodisperse ferrocene-containing core-interlayer-shell particles using emulsion polymerisation protocols is described. These metallopolymer-based particles can be used to produce highly ordered elastomeric opal films with fascinating distinct reflection colours. The present work additionally describes the combined addressability of both stimuli, redox-chemistry and mechanical stress. The obtained materials are interesting since application of the melt-shear process followed by crosslinking of the matrix provides access to large-area, mechano-responsive elastomeric opal films featuring an additional redox response. Both, basic synthesis aspects and first steps towards application in the field of stimuli-responsive sensing of respective materials are discussed.

Fully Reversible Shape Transition of Soft Spheres in Elastomeric Polymer Opal Films

Core-interlayer-shell (CIS) beads featuring noncross-linked hard cores were used to prepare large and well-defined elastomeric opal films with remarkably distinct iridescent reflection colors. The matrix of the opal films was cross-linked by UV-irradiation after compression molding of the CIS beads mixed with a bifunctional monomer. Stress-induced deformation of the embedded PS cores lead to hexagonally arranged spheroid oblates with an aspect ratio of 2.5. Optical characterization shows that bead deformation provokes a tremendous photonic band gap shift of about 160 nm. Fully reversible shape transition from the spheroid oblates back to the spherical beads and hence full recovery of the original photonic band gap can be achieved.

Smart polymer inverse-opal photonic crystal films by melt-shear organization for hybrid core–shell architectures

A feasible strategy to achieve large-area mechano-, thermo- and solvatochromic hybrid opal (OPC) and inverse opal photonic crystal (IOPC) films based on polymer hydrogels is described. Silica core particles featuring surface-anchored stimuli-responsive polymers are prepared and advantageously used for the melt-shear organization technique. By this approach hybrid OPC films with adjustable periodicities for photonic applications can be prepared. The large-area OPC films can be furthermore converted into IOPC structures simply by etching the silica particles while maintaining the excellent order of the entire opal film. This herein developed new process seems to be universal and is successfully applied to two thermo-responsive polymers, poly(N-isopropylacrylamide) (PNIPAM) and poly(diethylene glycol methylether methacrylate) (PDEGMEMA) as particle shell materials. Besides the remarkable mechanical robustness of the hybrid OPC and IOPC films, optical properties upon changes of temperature, mechanical stress and different solvents as external triggers are successfully confirmed. The herein described novel strategy for the preparation of inorganic/organic OPC and IOPC polymer films is feasible for a wide range of applications in fields of sensing and photonic band gap materials.

Individually Addressable Thermo‐ and Redox‐Responsive Block Copolymers by Combining Anionic Polymerization and RAFT Protocols

A novel diblock copolymer consisting of poly(vinylferrocene) (PVFc) and poly(N,N-diethylacrylamide) (PDEA) is synthesized via a combination of anionic and RAFT polymerization. The use of a novel route to hydroxyl-end-functionalized metallopolymers in anionic polymerization and subsequent esterification with a RAFT agent leads to a PVFc macro-CTA (M¯n = 3800 g mol(-1) ; Đ = 1.17). RAFT polymerization with DEA affords block copolymers as evidenced by (1) H NMR spectroscopy as well as size exclusion chromatography (6400 ≤ M¯n≤ 33700 g mol(-1) ; 1.31 ≤ Đ 1.28). Self-assembly of the amphiphilic block copolymers in aqueous solution leads to micelles as shown via TEM. Importantly, the distinct thermo-responsive and redox-responsive character of the blocks is probed via dynamic light scattering and found to be individually and repeatedly addressable.

Thermo-cross-linked Elastomeric Opal Films

An efficient and convenient thermal cross-linking protocol in elastomeric opal films leading to fully reversible and stretch-tunable optical materials is reported. In this study, functional monodisperse core-shell particles were arranged in a face-centered cubic (fcc) lattice structure by a melt flow process. A problem up to now was that un-cross-linked films could not be drawn fully reversibly and hence lost their optical and mechanical performance. After thermal cross-linking reaction, the obtained films can be drawn like rubbers and the color of their Bragg reflection changes because of controlled lattice deformation, which makes the cross-linked films mechanochromic sensors. Different techniques were developed for the cross-linking of the films a posteriori, after their preparation in the melt flow process. A photo-cross-linking approach was reported earlier. This study now deals with a very efficient thermo-cross-linking approach based on the chemistry of hydroxyl- and isocyanate-functionalities that form urethane bridges. The focus of the present work is the mechanism and efficiency of this cross-linking process for elastomeric opal films with excellent mechanical and optical properties.

Utilizing Stretch‐Tunable Thermochromic Elastomeric Opal Films as Novel Reversible Switchable Photonic Materials

In this work, the preparation of highly thermoresponsive and fully reversible stretch-tunable elastomeric opal films featuring switchable structural colors is reported. Novel particle architectures based on poly(diethylene glycol methylether methacrylate-co-ethyl acrylate) (PDEGMEMA-co-PEA) as shell polymer are synthesized via seeded and stepwise emulsion polymerization protocols. The use of DEGMEMA as comonomer and herein established synthetic strategies leads to monodisperse soft shell particles, which can be directly processed to opal films by using the feasible melt-shear organization technique. Subsequent UV crosslinking strategies open access to mechanically stable and homogeneous elastomeric opal films. The structural colors of the opal films feature mechano- and thermoresponsiveness, which is found to be fully reversible. Optical characterization shows that the combination of both stimuli provokes a photonic bandgap shift of more than 50 nm from 560 nm in the stretched state to 611 nm in the fully swollen state. In addition, versatile colorful patterns onto the colloidal crystal structure are produced by spatial UV-induced crosslinking by using a photomask. This facile approach enables the generation of spatially cross-linked switchable opal films with fascinating optical properties. Herein described strategies for the preparation of PDEGMEMA-containing colloidal architectures, application of the melt-shear ordering technique, and patterned crosslinking of the final opal films open access to novel stimuli-responsive colloidal crystal films, which are expected to be promising materials in the field of security and sensing applications.

Silacyclobutane-Based Diblock Copolymers with Vinylferrocene, Ferrocenylmethyl Methacrylate, and [1]Dimethylsilaferrocenophane

Well-defined diblock copolymers have been prepared in which three different ferrocene-based monomers are combined with 1,1-dimethylsilacyclobutane (DMSB) and 1-methylsilacyclobutane, respectively, as their carbosilane counterparts. Optimized procedures are reported for the living anionic chain growth following sequential monomer addition protocols, ensuring narrow polydispersities and high blocking efficiencies. The DMSB-containing copolymers show phase segregation in the bulk state, leading to micromorphologies composed of crystalline DMSB phases and amorphous polymetallocene phases.