ATRP of <i>tert</i>-Butoxycarbonylaminomethyl acrylate (<i>t</i>BAMA): Well-Defined Precursors for Polyelectrolytes of Tunable Charge

We present the controlled radical polymerization of homo and block copolymers containing <i>tert</i>-butoxycarbonylaminomethyl acrylate (<i>t</i>BAMA) via ATRP. By varying monomer concentration, solvent, reaction temperature, and ligand (PMDETA, HMTETA, TPMA, Me₆TREN and d<i>N</i>bpy), suitable reaction conditions could be established. Moderate control over the polymerization was achieved when using Me₆TREN as ligand, whereas this could be drastically improved in case of d<i>N</i>bpy. For block copolymerization, a variety of macroinitiators (polystyrene, poly­(<i>n</i>-butyl acrylate), poly­(ethylene oxide)) were prepared via ATRP or end group modification. Block extensions resulted in well-defined block copolymers with moderately low dispersity indices (<i>M</i>_w/<i>M</i>_n = 1.12–1.36). In addition, the use of a bromine-functionalized porp core as multifunctional initiator (<i>n</i> = 4) resulted in monomodal star-shaped P<i>t</i>BAMA. The applied homopolymers, macroinitiators, and diblock copolymers were characterized by ¹H NMR, ¹³C NMR and SECas well as MALDI–ToF for one P<i>t</i>BAMA homopolymer. We have already shown for materials prepared using free radical polymerization that the presence of orthogonal protective groups for either −NH₂ or −COOH moiety of P<i>t</i>BAMA allows for selective deprotection, thereby generating polyelectrolytes of different charge and charge density. The herein presented P<i>t</i>BAMA of moderate dispersity and different architecture will enable the preparation of similar albeit better defined materials in the near future

Reversible Electrostatic Adsorption of Polyelectrolytes and Bovine Serum Albumin onto Polyzwitterion-Coated Magnetic Multicore Nanoparticles: Implications for Sensing and Drug Delivery

We herein present the reversible formation of hybrid nanoparticles featuring a magnetic core and two consecutive polyzwitterion/polyelectrolyte (or protein) layers. Starting from multicore iron oxide nanoparticles, a first coating with zwitterionic poly­(dehydroalanine) is realized, and the resulting PDha@MCNP [PDha = poly­(dehydroalanine) and MCNP = multicore nanoparticle] shows pH-dependent (invertible) surface charge and dispersion stability. In a second step, this can be used as a versatile platform to adsorb either polycations {[poly­(<i>N</i>,<i>N</i>-dimethylamino)­ethyl methacrylate] (PDMAEMA) or poly­(aminomethyl acrylate)}, a polyanion [poly­(styrenesulfonic acid) (PSS)], or a model protein in a quasi layer-by-layer approach. The size, surface charge, and aggregation behavior of the resulting double-layer-coated particles are investigated via dynamic light scattering, transmission electron microscopy, ζ-potential, and turbidity measurements. In contrast to typical layer-by-layer coatings, the use of polyzwitterionic PDha as the first layer allows the pH-dependent release of the second polyelectrolyte shell (PDMAEMA and PSS) upon charge inversion. This turns such reversible multilayer coatings into interesting candidates for applications where controlled swelling or release is in focus and where it is important to control which part of a segmented or nanostructured system responds to changes in the surrounding medium

Controlling Electronic Transitions in Fullerene van der Waals Aggregates via Supramolecular Assembly

Morphologies crucially determine the optoelectronic properties of organic semiconductors. Therefore, hierarchical and supramolecular approaches have been developed for targeted design of supramolecular ensembles of organic semiconducting molecules and performance improvement of, <i>e.g</i>., organic solar cells (OSCs), organic light emitting diodes (OLEDs), and organic field-effect transistors (OFETs). We demonstrate how the photonic properties of fullerenes change with the formation of van der Waals aggregates. We identified supramolecular structures with broadly tunable absorption in the visible spectral range and demonstrated how to form aggregates with targeted visible (vis) absorption. To control supramolecular structure formation, we functionalized the C60-backbone with polar (bis-polyethylene glycol malonate-MPEG) tails, thus yielding an amphiphilic fullerene derivative that self-assembles at interfaces. Aggregates of systematically tuned size were obtained from concentrating MPEGC60 in stearic acid matrices, while different supramolecular geometries were provoked via different thin film preparation methods, namely spin-casting and Langmuir–Blodgett (LB) deposition from an air–water interface. We demonstrated that differences in molecular orientation in LB films (<i>C</i>_2<i>v</i> type point group aggregates) and spin-casting (stochastic aggregates) lead to huge changes in electronic absorption spectra due to symmetry and orientation reasons. These differences in the supramolecular structures, causing the different photonic properties of spin-cast and LB films, could be identified by means of quantum chemical calculations. Employing supramolecular assembly, we propounded that molecular symmetry in fullerene aggregates is extremely important in controlling vis absorption to harvest photons efficiently, when mixed with a donor molecule, thus improving active layer design and performance of OSCs

Formation of Lenticular Platelet Micelles via the Interplay of Crystallization and Chain Stretching: Solution Self-Assembly of Poly(ferrocenyldimethylsilane)-<i>block</i>-poly(2-vinylpyridine) with a Crystallizable Core-Forming Metalloblock

The influence of solvent composition on micelle morphology has been investigated for two crystalline-coil poly­(ferrocenyldimethylsilane-<i>block</i>-2-vinylpyridine) (PFS-<i>b</i>-P2VP) diblock copolymers with different block ratios (5:1 and 1:1). The solution self-assembly of these materials was explored in solvent mixtures containing different ratios of a good solvent for both blocks (THF) and a selective solvent for the P2VP block (isopropanol). Various micellar morphologies such as spheres and platelets were characterized using transmission electron microscopy (TEM), selected area electron diffraction (SAED), dynamic light scattering (DLS), wide-angle X-ray scattering (WAXS), and atomic force microscopy (AFM). The results showed that the solution self-assembly of PFS-<i>b</i>-P2VP block copolymers (5:1, 1:1) gave spherical micelles with an amorphous PFS core at low THF content (10 vol %). Subsequently, the amorphous spheres were slowly transformed into platelet micelles with a lenticular shape that consisted of a crystalline PFS core sandwiched by two coronal P2VP layers. This indicated that the amorphous spherical micelles were in a metastable state. The transformation of spheres into platelets was significantly slower for the 5:1 block copolymer with the longer PFS core-forming segment presumably due to a lower rate of crystallization of the metalloblock. Platelets were found to be dominant for both block copolymers at higher THF content (THF ≥ 30 vol %). The formation of lenticular rather than regular platelets was attributed to a poisoning effect whereby interference of the P2VP corona-forming blocks in the growth of the crystalline PFS core leads to the creation of defects in the crystal growth fronts

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

A Paradigm Change: Efficient Transfection of Human Leukemia Cells by Stimuli-Responsive Multicompartment Micelles

The controlled nonviral delivery of genetic material using cationic polymers into cells has been of interest during the past three decades, yet the ideal delivery agent featuring utmost transfection efficiency and low cytotoxicity still has to be developed. Here, we demonstrate that multicompartment micelles from stimuli-responsive triblock terpolymers, polybutadiene-<i>block</i>-poly(methacrylic acid)-<i>block</i>-poly(2-(dimethylamino)ethyl methacrylate) (BMAAD), are promising candidates. The structures exhibit a patchy shell, consisting of amphiphilic (interpolyelectrolyte complexes, MAA and D) and cationic patches (excess D), generating a surface reminiscent to those of certain viruses and capable of undergoing pH-dependent changes in charge stoichiometry. After polyplex formation with plasmid DNA, superior transfection efficiencies can be reached for both adherent cells and human leukemia cells. Compared to the gold standard PEI, remarkable improvements and a number of advantages were identified for this system, including increased cellular uptake and an improved release of the genetic material, accompanied by fast and efficient endosomal escape. Furthermore, high sedimentation rates might be beneficial regarding <i>in vitro</i> applications

Self-Assembly of Amphiphilic Triblock Terpolymers Mediated by Multifunctional Organic Acids: Vesicles, Toroids, and (Undulated) Ribbons

The self-assembly of block copolymers in the presence of additives represents an elegant strategy to adjust micellar morphologies in solution and to design complex structures that are not accessible otherwise. Herein, we use linear ABC triblock terpolymers comprising a polyamine block: polybutadiene-<i>block</i>-poly­(<i>tert</i>-butyl methacrylate)-<i>block</i>-poly­(2-(dimethylamino)­ethyl methacrylate) (PB-<i>b</i>-P<i>t</i>BMA-<i>b</i>-PDMAEMA) terpolymers coassembled with organic di- or triacids in mixtures of THF and water. The interactions between the organic multiacids and the hydrophilic PDMAEMA block can be adjusted via the chain architecture, amount, and functionality of added acid, the solvent quality, and the PDMAEMA block length. Consequently, these parameters allow a certain level of control over the resulting micellar morphology. Characterization by (cryogenic) transmission electron microscopy and atomic force microscopy revealed the formation of spherical, disk-shaped, and toroidal structures, alongside ribbons featuring enlarged end-caps. In the latter case, changing the solvent composition or the amount/type of organic diacid induced the formation of undulated ribbons and, eventually, partition into spherical particles

Toward Anisotropic Hybrid Materials: Directional Crystallization of Amphiphilic Polyoxazoline-Based Triblock Terpolymers

We present the design and synthesis of a linear ABC triblock terpolymer for the bottom-up synthesis of anisotropic organic/inorganic hybrid materials: polyethylene-<i>block</i>-poly(2-(4-(<i>tert</i>-butoxycarbonyl)amino)butyl-2-oxazoline)-<i>block</i>-poly(2-<i>iso</i>-propyl-2-oxazoline) (PE-<i>b</i>-PBocAmOx-<i>b</i>-P<i>i</i>PrOx). The synthesis was realized <i>via</i> the covalent linkage of azide-functionalized polyethylene and alkyne functionalized poly(2-alkyl-2-oxazoline) (POx)-based diblock copolymers exploiting copper-catalyzed azide–alkyne cycloaddition (CuAAC) chemistry. After purification of the resulting triblock terpolymer, the middle block was deprotected, resulting in a primary amine in the side chain. In the next step, solution self-assembly into core–shell-corona micelles in aqueous solution was investigated by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Subsequent directional crystallization of the corona-forming block, poly(2-<i>iso</i>-propyl-2-oxazoline), led to the formation of anisotropic superstructures as demonstrated by electron microscopy (SEM and TEM). We present hypotheses concerning the aggregation mechanism as well as first promising results regarding the selective loading of individual domains within such anisotropic nanostructures with metal nanoparticles (Au, Fe₃O₄)

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

Core–Shell–Corona Micelles from a Polyether-Based Triblock Terpolymer: Investigation of the pH-Dependent Micellar Structure

Core–shell-corona micelles featuring a pH-responsive shell have been characterized in dilute aqueous solution at different pH values (4–8) by using dynamic light scattering (DLS), field-flow fractionation coupled with multiangle light scattering detector (FFF-MALS), steady-state fluorescence, small-angle X-ray scattering (SAXS), and cryogenic transmission electron microscopy (cryo-TEM). The micelles are formed by self-assembly of a polyether-based triblock terpolymer consisting of a hydrophobic poly­(<i>tert</i>-butyl glycidyl ether) block (P<i>t</i>BGE), a pH-responsive modified poly­(allyl glycidyl ether) segment (PAGE_COOH), and a neutral hydrophilic poly­(ethylene oxide) block (PEO). Because of the side-chain carboxylic acids in the middle block, the micellar structure and size depends on the solution pH. Hereby, we show that an increase in pH induces a decrease in the aggregation number (<i>N</i>_agg). In addition, the combination of the above measurements revealed an unexpected morphological change from spherical to ellipsoidal micelles by increasing pH