Easy Synthetic Access to High-Melting Sulfurated Copolymers and their Self-Assembling Diblock Copolymers from Phenylisothiocyanate and Oxetane.

Although sulfurated polymers promise unique properties, their controlled synthesis, particularly when it comes to complex and functional architectures, remains challenging. Here, we show that the copolymerization of oxetane and phenyl isothiocyanate selectively yields polythioimidocarbonates as a new class of sulfur containing polymers, with narrow molecular weight distributions (Mn=5-80 kg/mol with D≤1.2; Mn,max=124 kg/mol) and high melting points of up to 181 °C. The method tolerates different substituent patterns on both the oxetane and the isothiocyanate. Self-nucleation experiments reveal that π-stacking of phenyl substituents, the presence of unsubstituted polymer backbones, and the kinetically controlled linkage selectivity are key factors in maximising melting points. The increased tolerance to macro-chain transfer agents and the controlled propagation allows the synthesis of double crystalline and amphiphilic diblock copolymers, which can be assembled into micellar- and worm-like structures with amorphous cores in water. In contrast, crystallization driven self-assembly in ethanol gives cylindrical micelles or platelets.

Surface-Compartmentalized Micelles by Stereocomplex-Driven Self-Assembly.

The unique corona structure of surface-compartmentalized micelles (Janus micelles, patchy micelles) opens highly relevant applications, e.g. as efficient particulate surfactants for emulsion stabilization or compatibilization of polymer blends. Here, stereocomplex-driven self-assembly (SCDSA) as a facile route to micelles with a semicrystalline stereocomplex (SC) core and a patch-like microphase separated corona, employing diblock copolymers with enantiomeric poly(L-lactide)/poly(D-lactide) blocks and highly incompatible corona-forming blocks (polystyrene (PS), poly(tert-butyl methacrylate)) is introduced. The spherical patchy SC micelles feature a narrow size distribution and show a compartmentalized, shamrock-like corona structure. Compared to SC micelles with a homogeneous PS corona the patchy micelles have a significantly higher interfacial activity attributable to the synergistic combination of an amphiphilic corona with the Pickering effect of nanoparticles. The patchy micelles are successfully employed in the stabilization of emulsions, underlining their application potential.

Functional Mesostructured Electrospun Polymer Nonwovens with Supramolecular Nanofibers.

Functional, hierarchically mesostructured nonwovens are of fundamental importance because complex fiber morphologies increase the active surface area and functionality allowing for the effective immobilization of metal nanoparticles. Such complex functional fiber morphologies clearly widen the property profile and enable the preparation of more efficient and selective filter media. Here, the realization of hierarchically mesostructured nonwovens with barbed wire-like morphology is demonstrated by combining electrospun polystyrene fibers, decorated with patchy worm-like micelles, with solution-processed supramolecular short fibers composed of 1,3,5-benzenetricarboxamides with peripheral N,N-diisopropylaminoethyl substituents. The worm-like micelles with a patchy microphase-separated corona are prepared by crystallization-driven self-assembly of a polyethylene based triblock terpolymer and deposited on top of the polystyrene fibers by coaxial electrospinning. The micelles are designed in a way that their patches promote the directed self-assembly of the 1,3,5-benzenetricarboxamide and the fixation of the supramolecular nanofibers on the supporting polystyrene fibers. Functionality of the mesostructured nonwoven is provided by the peripheral N,N-diisopropylaminoethyl substituents of the 1,3,5-benzenetricarboxamide and proven by the effective immobilization of individual palladium nanoparticles on the supramolecular nanofibers. The preparation of hierarchically mesostructured nonwovens and their shown functionality demonstrate that such systems are attractive candidates to be used for example in filtration, selective separation and heterogenous catalysis.

Self-Assembled Fluorescent Block Copolymer Micelles with Responsive Emission.

Responsive fluorescent materials offer a high potential for sensing and (bio-)imaging applications. To investigate new concepts for such materials and to broaden their applicability, the previously reported non-fluorescent zinc(II) complex [Zn(L)] that shows coordination-induced turn-on emission was encapsulated into a family of non-fluorescent polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) diblock copolymer micelles leading to brightly emissive materials. Coordination-induced turn-on emission upon incorporation and ligation of the [Zn(L)] in the P4VP core outperform parent [Zn(L)] in pyridine solution with respect to lifetimes, quantum yields, and temperature resistance. The quantum yield can be easily tuned by tailoring the selectivity of the employed solvent or solvent mixture and, thus, the tendency of the PS-b-P4VP diblock copolymers to self-assemble into micelles. A medium-dependent off-on sensor upon micelle formation could be established by suppression of non-micelle-borne emission background pertinent to chloroform through controlled acidification indicating an additional pH-dependent process.

Janus Micelles by Crystallization-Driven Self-Assembly of an Amphiphilic, Double-Crystalline Triblock Terpolymer.

Surface-compartmentalized micellar nanostructures (Janus and patchy micelles) have gained increasing interest due to their unique properties opening highly relevant applications, e.g., as efficient particulate surfactants, compatibilizers in polymer blends, or templates for catalytically active nanoparticles. We present a facile method for the production of worm-like Janus micelles based on crystallization-driven self-assembly of a double-crystalline triblock terpolymer with a crystallizable polyethylene middle block and two highly incompatible corona blocks, polystyrene and poly(ethylene oxide). This approach enables the production of amphiphilic Janus micelles with excellent interfacial activity by a comparably simple heating and cooling protocol directly in solution.

Hierarchical Superstructures by Combining Crystallization-Driven and Molecular Self-Assembly.

Combining the unique corona structure of worm-like patchy micelles immobilized on a polymer fiber with the molecular self-assembly of 1,3,5-benzenetricarboxamides (BTAs) leads to hierarchical superstructures with a fir-tree-like morphology. For this purpose, worm-like patchy micelles bearing pendant, functional tertiary amino groups in one of the corona patches were prepared by crystallization-driven self-assembly and immobilized on a supporting polystyrene fiber by coaxial electrospinning. The obtained patchy fibers were then immersed in an aqueous solution of a tertiary amino-functionalized BTA to induce patch-mediated molecular self-assembly to well-defined fir-tree-like superstructures upon solvent evaporation. Interestingly, defined superstructures are obtained only if the pendant functional groups in the surface patches match with the peripheral substituents of the BTA, which is attributed to a local increase in BTA concentration at the polymer fibers' surface.

Converting Poly(Methyl Methacrylate) into a Triple-Responsive Polymer.

Multiresponsive polymers that can respond to several external stimuli are promising materials for a manifold of applications. Herein, a facile method for the synthesis of triple-responsive (pH, temperature, CO2 ) poly(N,N-diethylaminoethyl methacrylamide) by a post-polymerization amidation of poly(methyl methacrylate) (PMMA) is presented. Combined with trivalent counterions ([Fe(CN)6 ]3- ) both an upper and lower critical solution temperature (UCST/LCST)-type phase behavior can be realized at pH 8 and 9. PMMA and PMMA-based block copolymers are readily accessible by living anionic and controlled radical polymerization techniques, which opens access to various responsive polymer architectures based on the developed functionalization method. This method can also be applied on melt-processed bulk PMMA samples to introduce functional, responsive moieties at the PMMA surface.

"Dumb" pH-Independent and Biocompatible Hydrogels Formed by Copolymers of Long-Chain Alkyl Glycidyl Ethers and Ethylene Oxide.

The formation and rheological properties of hydrogels based on amphiphilic ABA triblock polyether copolymers are described, relying solely on the hydrophobic interaction of long-chain alkyl glycidyl ether (AlkGE)- based A-blocks that are combined with a hydrophilic poly(ethylene glycol) (PEG) midblock. Via anionic ring-opening copolymerization (AROP), ethylene oxide (EO) and long-chain alkyl glycidyl ethers (AlkGEs) were copolymerized, using deprotonated poly(ethylene glycol) (PEG) macroinitiators (Mn of 10, 20 kg mol-1). The polymerization afforded amphiphilic ABA triblock copolymers with molar masses in the range of 21-32 kg mol-1 and dispersities (D) of D = 1.07-1.17. Kinetic studies revealed random copolymerization of EO and AlkGE, indicating random spacing of the hydrophobic AlkGE units by polar EO units. Following this approach, the hydrophobicity of the apolar blocks of amphiphilic ABA triblock polyethers can be tailored. Detailed rheological measurements confirmed the successful formation of hydrogels at different pH values as a consequence of nonpolar interactions and alkyl chain crystallization. Hydrogel formation was also observed at different ionic strengths (i.e., varied salt concentration), based on the hydrophobic aggregates. This behavior is in contrast to other often-used supramolecular cross-linking strategies, such as Coulomb interactions, complexation, or hydrogen bonding. Micro-differential scanning calorimetry (µ-DSC) measurements of the hydrogels revealed crystalline hydrophobic domains with melting temperatures in the physiological temperature range. In 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazoliumbromide (MTT) assays, diblock copolymers possessing structural analogy to the triblock copolymers were studied to assess the general cytotoxicity of amphiphilic polyethers bearing long alkyl chains at the polyether backbone, using splenic immune cells. At intermediate polymer concentrations, no cytotoxic effects were observed. This indicates that long-chain alkyl glycidyl ethers are promising for the introduction of highly hydrophobic as well as crystalline motifs at the polyether backbone in hydrogels for biomedical purposes.

Confined Crystallization of Spin-Crossover Nanoparticles in Block-Copolymer Micelles.

Nanoparticles of the spin-crossover coordination polymer [FeL(bipy)]n were synthesized by confined crystallization within the core of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) diblock copolymer micelles. The 4VP units in the micellar core act as coordination sites for the Fe complex. In the bulk material, the spin-crossover nanoparticles in the core are well isolated from each other allowing thermal treatment without disintegration of their structure. During annealing above the glass transition temperature of the PS block, the transition temperature is shifted gradually to higher temperatures from the as-synthesized product (T1/2 ↓=163 K and T1/2 ↑=170 K) to the annealed product (T1/2 ↓=203 K and T1/2 ↑=217 K) along with an increase in hysteresis width from 6 K to 14 K. Thus, the spin-crossover properties can be shifted towards the properties of the related bulk material. The stability of the nanocomposite allows further processing, such as electrospinning from solution.

Guided hierarchical co-assembly of soft patchy nanoparticles.

The concept of hierarchical bottom-up structuring commonly encountered in natural materials provides inspiration for the design of complex artificial materials with advanced functionalities. Natural processes have achieved the orchestration of multicomponent systems across many length scales with very high precision, but man-made self-assemblies still face obstacles in realizing well-defined hierarchical structures. In particle-based self-assembly, the challenge is to program symmetries and periodicities of superstructures by providing monodisperse building blocks with suitable shape anisotropy or anisotropic interaction patterns ('patches'). Irregularities in particle architecture are intolerable because they generate defects that amplify throughout the hierarchical levels. For patchy microscopic hard colloids, this challenge has been approached by using top-down methods (such as metal shading or microcontact printing), enabling molecule-like directionality during aggregation. However, both top-down procedures and particulate systems based on molecular assembly struggle to fabricate patchy particles controllably in the desired size regime (10-100 nm). Here we introduce the co-assembly of dynamic patchy nanoparticles--that is, soft patchy nanoparticles that are intrinsically self-assembled and monodisperse--as a modular approach for producing well-ordered binary and ternary supracolloidal hierarchical assemblies. We bridge up to three hierarchical levels by guiding triblock terpolymers (length scale ∼10 nm) to form soft patchy nanoparticles (20-50 nm) of different symmetries that, in combination, co-assemble into substructured, compartmentalized materials (>10 µm) with predictable and tunable nanoscale periodicities. We establish how molecular control over polymer composition programs the building block symmetries and regulates particle positioning, offering a route to well-ordered mixed mesostructures of high complexity.

pH-Responsive Biohybrid Carrier Material for Phenol Decontamination in Wastewater.

Smart polymers are a valuable platform to protect and control the activity of biological agents over a wide range of conditions, such as low pH, by proper encapsulation. Such conditions are present in olive oil mill wastewater with phenol as one of the most problematic constituents. We show that elastic and pH-responsive diblock copolymer fibers are a suitable carrier for Corynebacterium glutamicum, i.e., bacteria which are known for their ability to degrade phenol. Free C. glutamicum does not survive low pH conditions and fails to degrade phenol at low pH conditions. Our tea-bag like biohybrid system, where the pH-responsive diblock copolymer acts as a protecting outer shell for the embedded bacteria, allows phenol degradation even at low pH. Utilizing a two-step encapsulation process, planktonic cells were first encapsulated in poly(vinyl alcohol) to protect the bacteria against the organic solvents used in the second step employing coaxial electrospinning.

Composite Polymeric Membranes with Directionally Embedded Fibers for Controlled Dual Actuation.

In this paper, preparation method and actuation properties of an innovative composite membrane composed of thermo- and pH-responsive poly(N-isopropylacrylamide-co-acrylic acid) fibers (average diameter ≈ 905 nm) embedded within a passive thermoplastic polyurethane (TPU) matrix at different angles with degree of alignment as high as 98% are presented. The composite membrane has a gradient of TPU along the thickness. It has the capability of temperature- and pH-dependent direction-, and size-controlled actuation in few minutes. The stresses generated at the responsive fiber and nonresponsive matrix provide actuation, whereas the angle at which fibers are embedded in the matrix controls the actuation direction and size. The temperature has no effect on actuation and actuated forms at pH 7 and above, whereas the size of the actuated forms can be controlled by the temperature at lower pH. The membranes are strong enough to reversibly lift and release ≈426 times weight of their own mass (2.47 g metal ring is lifted by a 5.8 mg membrane). Soft actuators are of interest as smart scaffolds, robotics, catalysis, drug release, energy storage, electrodes, and metamaterials.

Template Removal via Boudouard Equilibrium Allows for Synthesis of Mesostructured Molybdenum Compounds.

Oxidative thermal removal of the polymeric templates is not trivial for molybdenum oxides and hampers mesostructuring of this material. At ambient oxygen fugacity, MoVI is the thermodynamically stable oxidation state and sublimation of MoO3 leads to a quick loss of the mesostructure through Oswald ripening. Taking advantage of the Boudouard equilibrium allows to fix the oxygen fugacity at a level where non-volatile MoO2-x is stable while carbonaceous material may be oxidized by CO2 . Mesostructured MoO2-x can be chemically converted into MoO3 or MoN under retention of the mesostructure.

Bottom-Up Meets Top-Down: Patchy Hybrid Nonwovens as an Efficient Catalysis Platform.

Heterogeneous catalysis with supported nanoparticles (NPs) is a highly active field of research. However, the efficient stabilization of NPs without deteriorating their catalytic activity is challenging. By combining top-down (coaxial electrospinning) and bottom-up (crystallization-driven self-assembly) approaches, we prepared patchy nonwovens with functional, nanometer-sized patches on the surface. These patches can selectively bind and efficiently stabilize gold nanoparticles (AuNPs). The use of these AuNP-loaded patchy nonwovens in the alcoholysis of dimethylphenylsilane led to full conversion under comparably mild conditions and in short reaction times. The absence of gold leaching or a slowing down of the reaction even after ten subsequent cycles manifests the excellent reusability of this catalyst system. The flexibility of the presented approach allows for easy transfer to other nonwoven supports and catalytically active NPs, which promises broad applicability.

Self-Organization of Gold Nanoparticle Assemblies with 3D Spatial Order and Their External Stimuli Responsiveness.

Gold nanoparticles (AuNP) with pyridyl end-capped polystyrenes (PS-4VP) as "quasi-monodentate" ligands self-assemble into ordered PS-4VP/AuNP nanostructures with 3D hexagonal spatial order in the dried solid state. The key for the formation of these ordered structures is the modulation of the ratio AuNP versus ligands, which proves the importance of ligand design and quantity for the preparation of novel ordered polymer/metal nanoparticle conjugates. Although the assemblies of PS-4VP/AuNP in dispersion lack in high dimensional order, strong plasmonic interactions are observed due to close contact of AuNP. Applying temperature as an external stimulus allows the reversible distortion of plasmonic interactions within the AuNP nanocomposite structures, which can be observed directly by naked eye. The modulation of the macroscopic optical properties accompanied by this structural distortion of plasmonic interaction opens up very interesting sensoric applications.

The Influence of the Chain Length of Polycations on their Complexation with Anionic Liposomes.

A series of strong polycations is synthesized through the anionic polymerization of 2-vinylpyridine, followed by subsequent quaternization of the resulting polymer. Polycations based on quaternized 2-vinylpyridine (PVPQs) with degrees of polymerization (DP) from 20 to 440 are adsorbed on the surface of small anionic liposomes. Liposome/PVPQ complexes are characterized by using a number of physicochemical methods. All PVPQs are totally adsorbed onto the liposome surface up to a certain concentration at which saturation is reached (which is specific for each PVPQ). The integrity of the adsorbed liposomes remains intact. Short PVPQs interact with anionic lipids localized on the outer membrane leaflet, whereas long PVPQs extract anionic lipids from the inner to outer leaflet. Complexes tend to aggregate, and the largest aggregates are formed when the initial charge of the liposomes is fully neutralized by the charge of the PVPQ. PVPQs with intermediate DPs demonstrate behavioral features of both short and long PVPQs. These results are important for the interpretation of the biological effects of cationic polymers and the selection of cationic polymers for biomedical applications.

Polymer Cages as Universal Tools for the Precise Bottom-Up Synthesis of Metal Nanoparticles.

A template synthesis allows the preparation of monodisperse nanoparticles with high reproducibility and independent from self-assembly requirements. Tailor-made polymer cages were used for the preparation of nanoparticles, which were made of cross-linked macromolecules with pendant thiol groups. Gold nanoparticles (AuNPs) were prepared in the polymer cages in situ, by using different amounts of cages versus gold. The polymer cages exhibited a certain capacity, below which the AuNPs could be grown with excellent control over the size and shape. Control experiments with a linear diblock copolymer showed a continuous increase in the AuNP size as the gold feed increased. This completely different behavior regarding the AuNP size evolution was attributed to the flexibility of the polymer chain depending on cross-linking. Moreover, the polymer cages were suitable for the encapsulation of AgNPs, PdNPs, and PtNPs by the in situ method.

Tea-bag-like polymer nanoreactors filled with gold nanoparticles.

Gold-containing polymer nanotubes, which showed both catalytic activity and resistance to leaching, were prepared by the "tubes by fiber templates" (TUFT) process. For this purpose, electrospun polymer nonwovens with incorporated poly(L-lactide)-stabilized gold nanoparticles were coated with poly(p-xylylene) by the chemical vapor deposition process, and then the inner fiber templates were removed. The resulting polymer tubes carried encapsulated gold nanoparticles which were shown to be immobilized and featured pronounced catalytic activity towards the hydrolytic oxidation of dimethylphenylsilane and the alcoholysis of dimethylphenylsilane with n-butanol. The macroscopic nonwovens could be used as tea-bag-like catalyst systems and showed excellent reusability.

A Closed-Loop Recyclable Low-Density Polyethylene.

Low-density polyethylene (LDPE) is one of the most important plastics, which is produced unfortunately under extreme conditions. In addition, it consists of robust aliphatic C─C bonds which are challenging to cleave for plastic recycling. A low-pressure and -temperature (pethylene = 2 bara, T = 70 °C) macromonomer-based synthesis of long chain branched polyethylene is reported. The introduction of recycle points permits the polymerization (grafting to) of the macromonomers to form the long chain branched polyethylene and its depolymerization (branch cleavage). Coordinative chain transfer polymerization employing ethylene and co-monomers is used for the synthesis of the macromonomers, permitting a high flexibility of their precise structure and efficient synthesis. The long chain branched polyethylene material matches key properties of low-density polyethylene.

PDMAEMA-grafted core-shell-corona particles for nonviral gene delivery and magnetic cell separation.

Monodisperse, magnetic nanoparticles as vectors for gene delivery were successfully synthesized via the grafting-from approach. First, oleic acid stabilized maghemite nanoparticles (γ-Fe2O3) were encapsulated with silica utilizing a reverse microemulsion process with simultaneous functionalization with initiating sites for atom transfer radical polymerization (ATRP). Polymerization of 2-(dimethylamino)ethyl methacrylate (DMAEMA) from the core-shell nanoparticles led to core-shell-corona hybrid nanoparticles (γ-Fe2O3@silica@PDMAEMA) with an average grafting density of 91 polymer chains of DP(n) = 540 (PDMAEMA540) per particle. The permanent attachment of the arms was verified by field-flow fractionation. The dual-responsive behavior (pH and temperature) was confirmed by dynamic light scattering (DLS) and turbidity measurements. The interaction of the hybrid nanoparticles with plasmid DNA at various N/P ratios (polymer nitrogen/DNA phosphorus) was investigated by DLS and zeta-potential measurements, indicating that for N/P ≥ 7.5 the complexes bear a positive net charge and do not undergo secondary aggregation. The hybrids were tested as transfection agents under standard conditions in CHO-K1 and L929 cells, revealing transfection efficiencies >50% and low cytotoxicity at N/P ratios of 10 and 15, respectively. Due to the magnetic properties of the hybrid gene vector, it is possible to collect most of the cells that have incorporated a sufficient amount of magnetic material by using a magnetic activated cell sorting system (MACS). Afterward, cells were further cultivated and displayed a transfection efficiency of ca. 60% together with a high viability.