Felix H. Schacher

Functional Block Copolymers: Nanostructured Materials with Emerging Applications

Recent advances in polymer synthesis have significantly enhanced the ability to rationally design block copolymers with tailored functionality. The self-assembly of these macromolecules in the solid state or in solution allows the formation of nanostructured materials with a variety of properties and potential functions. This Review illustrates recent progress in the field of block copolymer materials by highlighting selected emerging applications.

Precise hierarchical self-assembly of multicompartment micelles

Hierarchical self-assembly offers elegant and energy-efficient bottom-up strategies for the structuring of complex materials. For block copolymers, the last decade witnessed great progress in diversifying the structural complexity of solution-based assemblies into multicompartment micelles. However, a general understanding of what governs multicompartment micelle morphologies and polydispersity, and how to manipulate their hierarchical superstructures using straightforward concepts and readily accessible polymers remains unreached. Here we demonstrate how to create homogeneous multicompartment micelles with unprecedented structural control via the intermediate pre-assembly of subunits. This directed self-assembly leads to a step-wise reduction of the degree of conformational freedom and dynamics and avoids undesirable kinetic obstacles during the structure build-up. It yields a general concept for homogeneous populations of well-defined multicompartment micelles with precisely tunable patchiness, while using simple linear ABC triblock terpolymers. We further demonstrate control over the hierarchical step-growth polymerization of multicompartment micelles into micron-scale segmented supracolloidal polymers as an example of programmable mesoscale colloidal hierarchies via well-defined patchy nanoobjects.

Self‐Healing Polymer Coatings Based on Crosslinked Metallosupramolecular Copolymers

Self-healing coating based on metallopolymers are prepared and fully characterized. Iron bisterpyridine complexes are incorporated into a polymer network based on methacrylates, resulting in self-healing properties of these materials. Moreover, the influence of the comonomers on the thermal properties is studied in detail.

Self-healing metallopolymers based on cadmium bis(terpyridine) complex containing polymer networks

The utilization of metal–ligand interactions within polymers generates materials which are of interest for several applications, including self-healing materials. In this work we use methacrylate copolymers containing terpyridine moieties in the side chain for the formation of self-healing metallopolymer networks. The materials were synthesized using the reversible addition–fragmentation chain transfer (RAFT) polymerization technique and subsequent crosslinking by the addition of a metal salt, here cadmium(II) salts, with different counter-ions. The influence of the counter-ions on the self-healing process within these structures was analyzed. The research resulted in a new polymeric material featuring a high (intrinsic) healing efficiency at relatively low temperatures (<75 °C).

Dual stimuli-responsive multicompartment micelles from triblock terpolymers with tunable hydrophilicity

A plethora of stimuli-responsive micellar aggregates with a compartmentalized shell can be formed in aqueous solution from ABC triblock terpolymers with tunable hydrophilicity. Polybutadiene-block-poly(tert-butyl methacrylate)-block-poly(2-(dimethylamino)ethyl methacrylate) (PB-b-PtBMA-b-PDMAEMA) and, after modifications by hydrolysis to poly(methacrylic acid) (PMAA) or quaternization to PDMAEMAq, PB-b-PMAA-b-PDMAEMAq terpolymers self-assemble in water, depending on pH and temperature. We demonstrate control over micellar shape, size, and charge via three different preparation pathways. Even more, the micelles are capable of undergoing rearrangements in both the shell and the corona in response to external stimuli like pH or salinity. In that way, different structures such as multicompartment, core–shell–corona or flower-like micelles were identified and characterized viacryogenic transmission electron microscopy (cryo-TEM) and dynamic light scattering (DLS). The presence of two oppositely charged polyelectrolyte blocks within the structures leads to the formation of intramicellar interpolyelectrolyte complexes (im-IPECs) in the shell of the particles. Surprisingly, the im-IPEC formed between PMAA and PDMAEMAq can be redissolved by changes in pH, even in the absence of additional salt.

Cylindrical crystalline-core micelles: pushing the limits of solution self-assembly

Within the last few years, crystallisation-induced self-assembly of block copolymers (BCs) in solution has become more and more attractive for the production of well-defined cylindrical crystalline-core micelles (cCCMs). The “livingness” of this process has been shown for a number of crystallisable blocks and allows fine tuning of the length as well as the length distribution of such structures. This unprecedented control is hardly achievable in the self-assembly of purely amorphous BCs. Furthermore, in an analogy to living/controlled polymerisation methods, the epitaxial growth of different BCs onto preformed cCCMs allows for the preparation of complex micellar architectures, e.g., cylindrical block co-micelles. This highlight tries to provide an overview over recent developments in crystallisation-induced self-assembly of BCs with a particular focus on one-dimensional (1D) micellar nanostructures.

Multicompartment micelles with adjustable poly(ethylene glycol) shell for efficient in vivo photodynamic therapy

We describe the preparation of well-defined multicompartment micelles from polybutadiene-block-poly(1-methyl-2-vinyl pyridinium methyl sulfate)-block-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)-block-poly(L-lysine) (PLL-b-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 in vitro cellular experiments, we confirmed that the porphyrazine-loaded micelles were PDT-active against A549 cells. The corona composition strongly influenced their in vitro PDT activity, which decreased with increasing PEGylation, correlating with the cellular uptake of the micelles. Also, a PEGylation-dependent influence on the in vivo 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 in vivo.

Calcium Phosphate Mineralization beneath a Polycationic Monolayer at the Air-Water Interface

The self-assembly of the amphiphilic block copolymer poly(n-butyl methacrylate)-block-poly[2-(dimethylamino)ethyl methacrylate] at the air-water interface has been investigated at different pH values. Similar to Rehfeldt et al. (J. Phys. Chem. B 2006, 110, 9171), the subphase pH strongly affects the monolayer properties. The formation of calcium phosphate beneath the monolayer can be tuned by the subphase pH and hence the monolayer charge. After 12 h of mineralization at pH 5, the polymer monolayers are still transparent, but transmission electron microscopy (TEM) shows that very thin calcium phosphate fibers form, which aggregate into cotton ball-like features with diameters of 20 to 50 nm. In contrast, after 12 h of mineralization at pH 8, the polymer film is very slightly turbid and TEM shows dense aggregates with sizes between 200 and 700 nm. The formation of calcium phosphate is further confirmed by Raman and energy dispersive X-ray spectroscopy. The calcium phosphate architectures can be assigned to the monolayer charge, which is high at low pH and low at high pH. The study demonstrates that the effects of polycations should not be ignored if attempting to understand the colloid chemistry of biomimetic mineralization. It also shows that basic block copolymers are useful complementary systems to the much more commonly studied acidic block copolymer templates.

Correlation between scratch healing and rheological behavior for terpyridine complex based metallopolymers

Certain metallopolymers possess the ability to close scratches by a simple thermal treatment. The present study comprehensively explores the structure–property relationship of these materials by variation of the corresponding metal salts. The scratch-healing properties are studied in detail and correlated to the rheological behavior. Rheological measurements are utilized to determine the supramolecular bond life time (τb). A crossover of G′ and G′′ is found for the scratch healing metallopolymers, whereas this is absent in materials displaying no healing under the investigated conditions. Thus, this study provides a first step for the fundamental understanding of the dynamic behavior of metallopolymers and the impact on the self-healing properties. Furthermore, the effect of the chosen cation and anion on the self-healing behavior is illustrated and studied in detail.

Poly(ethylene oxide) (PEO)-based ABC triblock terpolymers – synthetic complexity vs. application benefits

During the last few decades considerable scientific effort has been devoted to the synthesis, self-assembly, and application of ABC triblock terpolymers with various building blocks. Such materials show high potential in the fields of materials science and life sciences. In particular, poly(ethylene oxide) (PEO) is a versatile building block and related materials featuring PEO segments are often exploited due to its solubility in a wide range of solvents, its non-toxicity, biocompatibility, and the so called “stealth effect”. This review presents a short summary of possible synthetic routes for the synthesis of PEO-containing triblock terpolymers, as well as different applications in the bulk and in solution – including the preparation of porous materials, hybrid systems, and carriers for controlled drug delivery.