A Modular Route for the Synthesis of ABC Miktoarm Star Terpolymers via a New Alkyne-Substituted Diphenylethylene Derivative

We introduce a modular route for the synthesis of well-defined ABC miktoarm star terpolymers. To this aim, the synthesis of a 1,1-diphenylethylene derivative bearing a protected alkyne function (1-[(4-(<i>tert</i>-butyldimethylsilyl)­ethynyl)­phenyl]-1-phenylethylene) was developed. This compound was for the first time employed in sequential anionic polymerization to readily prepare alkyne mid-functionalized diblock copolymers with polybutadiene as first and a poly­(alkyl methacrylate) (poly­(<i>tert</i>-butyl methacrylate), poly­(<i><i>N,N</i></i>-dimethylaminoethyl methacrylate)) as second block. For the third arm controlled radical polymerization methods (polystyrene, poly­(<i>tert</i>-butyl methacrylate), poly­(<i><i>N,N</i></i>-dimethylaminoethyl methacrylate)) and anionic ring-opening polymerization (poly­(ethylene oxide)) were used to separately prepare homopolymers with an azido function. Afterward, azide–alkyne Huisgen cycloaddition was successfully employed to synthesize a library of ABC miktoarm star terpolymers with different molecular weights and chemical compositions via modular combination of the functionalized diblock copolymers and homopolymers. The resulting new ABC miktoarm star terpolymers showed narrow, monomodal molecular weight distributions with dispersities typically below 1.10, as determined by size exclusion chromatography

Influence of the Polymeric Interphase Design on the Interfacial Properties of (Fiber-Reinforced) Composites

In fiber-reinforced composites, the interphase nanostructure (i.e., the extended region between two phases in contact) has a pronounced influence on their interfacial adhesion. This work aims at establishing a link between the interphase design of PS-based polymeric fiber coatings and their influence on the micromechanical performance of epoxy-based composite materials. Thiol–ene photochemistry was utilized to introduce a polymeric gradient on silica-like surfaces following a two-step approach without additional photoinitiator. Two complementary grafting-techniques were adapted to modify glass fibers: “Grafting-onto” deposition of PB-<i>b</i>-PS diblock copolymers for thin-film coatings (thickness <20 nm) at low grafting density (<0.1 chains/nm²) - and “grafting-from” polymerization for brush-like PS homopolymer coatings of higher thickness (up to 225 nm) and higher density. Polymer-coated glass fibers were characterized for polymer content using thermogravimetric analysis (TGA) and their nanostructural morphologies by scanning electron microscopy (SEM). Model substrates of flat glass and silicon were studied by atomic force microscopy (AFM) and spectroscopic ellipsometry (SE). The change in interfacial shear strength (IFSS) due to fiber modification was determined by a single fiber pull-out experiment. Thick coatings (>40 nm) resulted in a 50% decrease in IFSS. Higher shear strength occurred for thinner coatings of homopolymer and for lower grafting densities of copolymer. Increased IFSS (10%) was found upon dilution of the surface chain density by mixing copolymers. We show that the interfacial shear strength can be increased by tailoring of the interphase design, even for systems with inherently poor adhesion. Perspectives of polymeric fiber coatings for tailored matrix–fiber compatibility and interfacial adhesion are discussed

Micellar Interpolyelectrolyte Complexes with a Compartmentalized Shell

We investigate the formation of micellar interpolyelectrolyte complexes (IPECs) from multicompartment micelles (MCMs) of polybutadiene-<i>block</i>-poly­(1-methyl-2-vinylpyridinium methylsulfate)-<i>block</i>-poly­(methacrylic acid) (BVqMAA) triblock terpolymers and polycations of opposite charge. As cationic material, predominantly a polymer with a high charge density is used: quaternized poly­(2-((2-(dimethylamino)­ethyl)­methylamino)­ethyl methacrylate) (PDAMAq), which carries two positive net charges per monomer unit. Upon IPEC formation at different charge stoichiometries, particles with a compartmentalized IPEC shell are formed. These rather unusual structures even form when both BVqMAA micelles and PDAMAq are mixed at high salinity, followed by dialysis, indicating that the structures formed are not kinetically trapped. Whereas the nature of the polycation seems to play a minor role, our studies suggest that the length of the PMAA corona is the key factor for the formation of a compartmentalized IPEC shell

Hidden Structural Features of Multicompartment Micelles Revealed by Cryogenic Transmission Electron Tomography

The demand for ever more complex nanostructures in materials and soft matter nanoscience also requires sophisticated characterization tools for reliable visualization and interpretation of internal morphological features. Here, we address both aspects and present synthetic concepts for the compartmentalization of nanoparticle peripheries as well as their <i>in situ</i> tomographic characterization. We first form negatively charged spherical multicompartment micelles from ampholytic triblock terpolymers in aqueous media, followed by interpolyelectrolyte complex (IPEC) formation of the anionic corona with bis-hydrophilic cationic/neutral diblock copolymers. At a 1:1 stoichiometric ratio of anionic and cationic charges, the so-formed IPECs are charge neutral and thus phase separate from solution (water). The high chain density of the ionic grafts provides steric stabilization through the neutral PEO corona of the grafted diblock copolymer and suppresses collapse of the IPEC; instead, the dense grafting results in defined nanodomains oriented perpendicular to the micellar core. We analyze the 3D arrangements of the complex and purely organic compartments, <i>in situ</i>, by means of cryogenic transmission electron microscopy (cryo-TEM) and tomography (cryo-ET). We study the effect of block lengths of the cationic and nonionic block on IPEC morphology, and while 2D cryo-TEM projections suggest similar morphologies, cryo-ET and computational 3D reconstruction reveal otherwise hidden structural features, <i>e.g.</i>, planar IPEC brushes emanating from the micellar core

Counterion-Mediated Hierarchical Self-Assembly of an ABC Miktoarm Star Terpolymer

Directed self-assembly processes of polymeric systems represent a powerful approach for the generation of structural hierarchy in analogy to biological systems. Herein, we utilize triiodide as a strongly polarizable counterion to induce hierarchical self-assembly of an ABC miktoarm star terpolymer comprising a polybutadiene (PB), a poly(<i>tert</i>-butyl methacrylate) (P<i>t</i>BMA), and a poly(<i>N</i>-methyl-2-vinylpyridinium) (P2VPq) segment. Hereby, the miktoarm architecture in conjunction with an increasing ratio of triiodide <i>versus</i> iodide counterions allows for a stepwise assembly of spherical micelles as initial building blocks into cylindrical structures and superstructures thereof. Finally, micrometer-sized multicompartment particles with a periodic lamellar fine structure are observed, for which we introduce the term “woodlouse”. The counterion-mediated decrease in hydrophilicity of the corona-forming P2VPq block is the underlying trigger to induce this hierarchical structure formation. All individual steps and the corresponding intermediates toward these well-defined superstructures were intensively studied by scattering and electron microscopic techniques, including transmission electron microtomography

Counterion-Mediated Hierarchical Self-Assembly of an ABC Miktoarm Star Terpolymer

Directed self-assembly processes of polymeric systems represent a powerful approach for the generation of structural hierarchy in analogy to biological systems. Herein, we utilize triiodide as a strongly polarizable counterion to induce hierarchical self-assembly of an ABC miktoarm star terpolymer comprising a polybutadiene (PB), a poly(<i>tert</i>-butyl methacrylate) (P<i>t</i>BMA), and a poly(<i>N</i>-methyl-2-vinylpyridinium) (P2VPq) segment. Hereby, the miktoarm architecture in conjunction with an increasing ratio of triiodide <i>versus</i> iodide counterions allows for a stepwise assembly of spherical micelles as initial building blocks into cylindrical structures and superstructures thereof. Finally, micrometer-sized multicompartment particles with a periodic lamellar fine structure are observed, for which we introduce the term “woodlouse”. The counterion-mediated decrease in hydrophilicity of the corona-forming P2VPq block is the underlying trigger to induce this hierarchical structure formation. All individual steps and the corresponding intermediates toward these well-defined superstructures were intensively studied by scattering and electron microscopic techniques, including transmission electron microtomography

Counterion-Mediated Hierarchical Self-Assembly of an ABC Miktoarm Star Terpolymer

Directed self-assembly processes of polymeric systems represent a powerful approach for the generation of structural hierarchy in analogy to biological systems. Herein, we utilize triiodide as a strongly polarizable counterion to induce hierarchical self-assembly of an ABC miktoarm star terpolymer comprising a polybutadiene (PB), a poly(<i>tert</i>-butyl methacrylate) (P<i>t</i>BMA), and a poly(<i>N</i>-methyl-2-vinylpyridinium) (P2VPq) segment. Hereby, the miktoarm architecture in conjunction with an increasing ratio of triiodide <i>versus</i> iodide counterions allows for a stepwise assembly of spherical micelles as initial building blocks into cylindrical structures and superstructures thereof. Finally, micrometer-sized multicompartment particles with a periodic lamellar fine structure are observed, for which we introduce the term “woodlouse”. The counterion-mediated decrease in hydrophilicity of the corona-forming P2VPq block is the underlying trigger to induce this hierarchical structure formation. All individual steps and the corresponding intermediates toward these well-defined superstructures were intensively studied by scattering and electron microscopic techniques, including transmission electron microtomography

Multicompartment Micelles with Adjustable Poly(ethylene glycol) Shell for Efficient <i>in Vivo</i> Photodynamic Therapy

We describe the preparation of well-defined multicompartment micelles from polybutadiene-<i>block</i>-poly(1-methyl-2-vinyl pyridinium methyl sulfate)-<i>block</i>-poly(methacrylic acid) (BVqMAA) triblock terpolymers and their use as advanced drug delivery systems for photodynamic therapy (PDT). A porphyrazine derivative was incorporated into the hydrophobic core during self-assembly and served as a model drug and fluorescent probe at the same time. The initial micellar corona is formed by negatively charged PMAA and could be gradually changed to poly(ethylene glycol) (PEG) in a controlled fashion through interpolyelectrolyte complex formation of PMAA with positively charged poly(ethylene glycol)-<i>block</i>-poly(l-lysine) (PLL-<i>b</i>-PEG) diblock copolymers. At high degrees of PEGylation, a compartmentalized micellar corona was observed, with a stable bottlebrush-on-sphere morphology as demonstrated by cryo-TEM measurements. By <i>in vitro</i> cellular experiments, we confirmed that the porphyrazine-loaded micelles were PDT-active against A549 cells. The corona composition strongly influenced their <i>in vitro</i> PDT activity, which decreased with increasing PEGylation, correlating with the cellular uptake of the micelles. Also, a PEGylation-dependent influence on the <i>in vivo</i> blood circulation and tumor accumulation was found. Fully PEGylated micelles were detected for up to 24 h in the bloodstream and accumulated in solid subcutaneous A549 tumors, while non- or only partially PEGylated micelles were rapidly cleared and did not accumulate in tumor tissue. Efficient tumor growth suppression was shown for fully PEGylated micelles up to 20 days, demonstrating PDT efficacy <i>in vivo</i>