Nopadiene: A Pinene-Derived Cyclic Diene as a Styrene Substitute for Fully Biobased Thermoplastic Elastomers.

The bicyclic 1,2-substituted, 1,3-diene monomer nopadiene (1R,5S)-2-ethenyl-6,6-dimethylbicyclo[3.1.1]hept-2-ene was successfully polymerized by anionic and catalytic polymerization. Nopadiene is produced either through a facile one-step synthesis from myrtenal via Wittig-olefination or via a scalable two-step reaction from nopol (10-hydroxymethylene-2-pinene). Both terpenoids originate from the renewable ß-pinene. The living anionic polymerization of nopadiene in apolar and polar solvents at 25 °C using organolithium initiators resulted in homopolymers with well-controlled molar masses in the range of 5.6-103.4 kg·mol-1 (SEC, PS calibration) and low dispersities (D) between 1.06 and 1.18. By means of catalytic polymerization with Me4CpSi(Me)2NtBuTiCl2 and (Flu)(Pyr)CH2Lu(CH2TMS)2(THF), the 1,4 and 3,4- microstructures of nopadiene are accessible in excellent selectivity. In pronounced contrast to other 1,3-dienes, the rigid polymers of the sterically demanding nopadiene showed an elevated glass temperature, Tg,∞ = 160 °C (in the limit of very high molar mass, Mn). ABA triblock copolymers with a central polymyrcene block and myrcene content of 60-75 mol %, with molar masses of 100-200 kg/mol were prepared by living anionic polymerization of the pinene-derivable monomers nopadiene and myrcene. This diene copolymerization resulted in thermoplastic elastomers displaying nanophase separation at different molar ratios (DSC, SAXS) and an upper service temperature about 30 K higher than that for traditional petroleum-derived styrenic thermoplastic elastomers due to the high glass temperature of polynopadiene. The materials showed good thermal stability at elevated temperatures under nitrogen (TGA), promising tensile strength and ultimate elongation of up to 1600%.

Anionic Copolymerization Enables the Scalable Synthesis of Alternating (AB)n Multiblock Copolymers with High Molecular Weight in n/2 Steps.

Based on the highly disparate reactivities of isoprene (I, rI = 25.4) and 4-methylstyrene (4MS, r4MS = 0.007) in the anionic copolymerization in nonpolar media, a general strategy for the rapid and scalable synthesis of tapered multiblock copolymers with an extremely steep gradient has been developed. A repetitive addition strategy of a mixture of isoprene and 4MS leads to a tapered diblock in each case, giving access to linear alternating multiblock copolymers of the (AB)n type with up to 10 blocks. All multiblock copolymers showed narrow molecular weight distributions (dispersity D = 1.04-1.12). High molecular weights in the range of 80 to 400 kg mol-1 were achieved. Due to the incompatibility of PI and P4MS segments, the multiblock copolymers exhibit nanophase separation, manifested by separate glass transitions for both constituents. Stress-strain measurements revealed extraordinary toughness and elongations up to 1150% strain at break, even at a 50/50 molar ratio I/4MS (i.e., 37 wt% isoprene). Our synthesis permits access to a wide range of tapered multiblock copolymer architectures with rigid (P4MS, high glass transition, Tg) and flexible (low Tg) chains, in n/2 steps, while keeping overall dispersity low.

Interfacial Assembly and Jamming Behavior of Polymeric Janus Particles at Liquid Interfaces.

The self-assembly and interfacial jamming of spherical Janus nanoparticles (JNPs) at the water/oil interface were investigated. Polymeric JNPs, made by cross-linking polystyrene-block-polybutadiene-block-poly(methyl methacrylate) (PS-PB-PMMA), with a high interfacial activity assemble at the water/oil interface. During the self-assembly at the interface, the interfacial energy was reduced and a dynamic interlayer was observed that is responsive to the pH of the aqueous phase. Unlike hard particles, the JNPs are composed of polymer chains that can spread at the liquid-liquid interface to maximize coverage at relatively low areal densities. In a pendant drop geometry, the interfacial area of a water droplet in oil was significantly decreased and the JNPs were forced to pack more closely. Entangling of the polymer chains causes the JNPs to form a solid-like interfacial assembly, resulting in the formation of wrinkles when the interfacial area is decreased. The wrinkling behavior, the retention of the wrinkles, or the slow relaxation of the liquid drop back to its original equilibrium shape was found to depend upon the pH.

Compaction and Transmembrane Delivery of pDNA: Differences between l-PEI and Two Types of Amphiphilic Block Copolymers.

Polycations are popular agents for nonviral delivery of DNA to mammalian cells. Adding hydrophobic, biodegradable, or cell-penetrating functions could help to improve their performance, which at present is below that of viral agents. A crucial first step in gene delivery is the complexation of the DNA. The characteristics of these "polyplexes" presumably influence or even determine the subsequent steps of membrane passage, intracellular traveling/DNA release, and nuclear uptake. Herein, polyplexes formed with linear poly(ethylenimine) (l-PEI) are compared to complexes generated with functionalized diblock copolymers. While l-PEI interacts only electrostatically with the DNA, interaction in the case of the diblock polymers may be mixed-mode. In certain cases, transfection efficiency improved when the polyplexes were formed in hypertonic solution. Moreover, whereas conventional PEI-based polyplexes enter the cells via endocytosis, at least one of the diblock agents seemed to promote entry via transient destabilization of the plasma membrane.

Systematic Study of a Library of PDMAEMA-Based, Superparamagnetic Nano-Stars for the Transfection of CHO-K1 Cells.

The introduction of the DNA into mammalian cells remains a challenge in gene delivery, particularly in vivo. Viral vectors are unmatched in their efficiency for gene delivery, but may trigger immune responses and cause severe side-reactions. Non-viral vectors are much less efficient. Recently, our group has suggested that a star-shaped structure improves and even transforms the gene delivery capability of synthetic polycations. In this contribution, this effect was systematically studied using a library of highly homogeneous, paramagnetic nano-star polycations with varied arm lengths and grafting densities. Gene delivery was conducted in CHO-K1 cells, using a plasmid encoding a green fluorescent reporter protein. Transfection efficiencies and cytotoxicities varied systematically with the nano-star architecture. The arm density was particularly important, with values of approximately 0.06 arms/nm² yielding the best results. In addition, a certain fraction of the cells became magnetic during transfection. The gene delivery potential of a nano-star and its ability to render the cells magnetic did not have any correlations. End-capping the polycation arms with di(ethylene glycol) methyl ether methacrylate (PDEGMA) significantly improved serum compatibility under transfection conditions; such nano-stars are potential candidates for future in vivo testing.

A block copolymer-templated construction approach for the creation of nano-patterned polyelectrolyte multilayers and nanoscale objects.

A block copolymer-based assembly approach for the creation of nano-patterned polyelectrolyte multilayers over cm2-scale areas is presented. Up to 5 bi-layers were selectively assembled on top of specific nano-domains featuring different morphologies. The successful isolation of nanoscale objects corresponding in shape to the template features is also demonstrated. This methodology is applicable to different types of polyelectrolytes, and opens up a new dimension for layer-by-layer construction.

Rational design of ABC triblock terpolymer solution nanostructures with controlled patch morphology.

Block copolymers self-assemble into a variety of nanostructures that are relevant for science and technology. While the assembly of diblock copolymers is largely understood, predicting the solution assembly of triblock terpolymers remains challenging due to complex interplay of block/block and block/solvent interactions. Here we provide guidelines for the self-assembly of linear ABC triblock terpolymers into a large variety of multicompartment nanostructures with C corona and A/B cores. The ratio of block lengths NC/NA thereby controls micelle geometry to spheres, cylinders, bilayer sheets and vesicles. The insoluble blocks then microphase separate to core A and surface patch B, where NB controls the patch morphology to spherical, cylindrical, bicontinuous and lamellar. The independent control over both parameters allows constructing combinatorial libraries of unprecedented solution nanostructures, including spheres-on-cylinders/sheets/vesicles, cylinders-on-sheets/vesicles, and sheets/vesicles with bicontinuous or lamellar membrane morphology (patchy polymersomes). The derived parameters provide a logical toolbox towards complex self-assemblies for soft matter nanotechnologies.

Periodic nanoscale patterning of polyelectrolytes over square centimeter areas using block copolymer templates.

Nano-patterned materials are beneficial for applications such as solar cells, opto-electronics, and sensing owing to their periodic structure and high interfacial area. Here, we present a non-lithographic approach for assembling polyelectrolytes into periodic nanoscale patterns over cm(2)-scale areas. Chemically modified block copolymer thin films featuring alternating charged and neutral domains are used as patterned substrates for electrostatic self-assembly. In-depth characterization of the deposition process using spectroscopy and microscopy techniques, including the state-of-the-art scanning transmission X-ray microscopy (STXM), reveals both the selective deposition of the polyelectrolyte on the charged copolymer domains as well as gradual changes in the film topography that arise from further penetration of the solvent molecules and possibly also the polyelectrolyte into these domains. Our results demonstrate the feasibility of creating nano-patterned polyelectrolyte layers, which opens up new opportunities for structured functional coating fabrication.

Splitting of Surface-Immobilized Multicompartment Micelles into Clusters upon Charge Inversion.

We investigate a morphological transition of surface-immobilized triblock terpolymer micelles: the splitting into well-defined clusters of satellite micelles upon pH changes. The multicompartment micelles are formed in aqueous solution of ABC triblock terpolymers consisting of a hydrophobic polybutadiene block, a weak polyanionic poly(methacrylic acid) block, and a weak polycationic poly(2-(dimethylamino)ethyl methacrylate) block. They are subsequently immobilized on silicon wafer surfaces by dip-coating. The splitting process is triggered by a pH change to strongly basic pH, which goes along with a charge reversal of the micelles. We find that the aggregation number of the submicelles is well-defined and that larger micelles have a tendency to split into a larger number of submicelles. Furthermore, there is a clear preference for clusters consisting of doublets and triplets of submicelles. The morphology of surface-immobilized clusters can be "quenched" by returning to the original pH. Thus, such well-defined micellar clusters can be stabilized and are available as colloidal building blocks for the formation of hierarchical surface structures. We discuss the underlying physicochemical principles of the splitting process considering changes in charge and total free energy of the micelles upon pH change.

Promoter, transgene, and cell line effects in the transfection of mammalian cells using PDMAEMA-based nano-stars.

Non-viral transfection protocols are typically optimized using standard cells and reporter proteins, potentially underestimating cellular or transgene effects. Here such effects were studied for two human (Jurkat, HEK-293) and two rodent (CHO-K1, L929) cell lines and three fluorescent reporter proteins. Expression of the enhanced green fluorescent protein (EGFP) was studied under the control of the human elongation factor 1 alpha promoter and three viral promoters (SV40, SV40/enhancer, CMV), that of ZsYellow1 (yellow fluorescence) and mCherry (red fluorescence) for the CMV promoter. Results varied with the cell line, in particular for the Jurkat cells. Pair-wise co-transfection of the CMV controlled transgenes resulted in a significant fraction of monochromatic cells (EGFP for EGFP/YFP and EGFP/RFP co-transfections, YFP in case of YFP/RFP co-transfections). Only Jurkat cells were almost incapable of expressing YFP. Dilution of the plasmid DNA with a non-expressed plasmid showed cell line dependent effects on transfection efficiency and/or expression levels.

Influence of Polyplex Formation on the Performance of Star-Shaped Polycationic Transfection Agents for Mammalian Cells.

Genetic modification ("transfection") of mammalian cells using non-viral, synthetic agents such as polycations, is still a challenge. Polyplex formation between the DNA and the polycation is a decisive step in such experiments. Star-shaped polycations have been proposed as superior transfection agents, yet have never before been compared side-by-side, e.g., in view of structural effects. Herein four star-shaped polycationic structures, all based on (2-dimethylamino) ethyl methacrylate (DMAEMA) building blocks, were investigated for their potential to deliver DNA to adherent (CHO, L929, HEK-293) and non-adherent (Jurkat, primary human T lymphocytes) mammalian cells. The investigated vectors included three structures where the PDMAEMA arms (different arm length and grafting densities) had been grown from a center silsesquioxane or silica-coated γ-Fe2O3-core and one micellar structure self-assembled from poly(1,2-butadiene)-block PDMAEMA polymers. All nano-stars combined high transfection potential with excellent biocompatibility. The micelles slightly outperformed the covalently linked agents. For method development and optimization, the absolute amount of polycation added to the cells was more important than the N/P-ratio (ratio between polycation nitrogen and DNA phosphate), provided a lower limit was passed and enough polycation was present to overcompensate the negative charge of the plasmid DNA. Finally, the matrix (NaCl vs. HEPES-buffered glucose solution), but also the concentrations adjusted during polyplex formation, affected the results.

Controlling Multicompartment Morphologies Using Solvent Conditions and Chemical Modification.

The solution self-assembly of amphiphilic diblock copolymers into spheres, cylinders, and vesicles (polymersomes) has been intensely studied over the past two decades, and their morphological behavior is well understood. Linear ABC triblock terpolymers with two insoluble blocks A/B, on the other hand, display a richer and more complex morphological spectrum that has been recently explored by synthetic block length variations. Here, we describe facile postpolymerization routes to tailor ABC triblock terpolymer solution morphologies by altering block solubility (solvent mixtures), blending with homopolymers, and block-selective chemical reactions. The feasibility of these processes is demonstrated on polystyrene-block-polybutadiene-block-poly(methyl methacrylate) (SBM) that assembles to patchy spherical micelles, which can be modified to evolve into double and triple helices or patchy and striped vesicles. These results demonstrate that postpolymerization treatments give access to a broad range of morphologies from single triblock terpolymers without the need for multiple polymer syntheses.

Self-assembly concepts for multicompartment nanostructures.

Compartmentalization is ubiquitous to many biological and artificial systems, be it for the separate storage of incompatible matter or to isolate transport processes. Advancements in the synthesis of sequential block copolymers offer a variety of tools to replicate natural design principles with tailor-made soft matter for the precise spatial separation of functionalities on multiple length scales. Here, we review recent trends in the self-assembly of amphiphilic block copolymers to multicompartment nanostructures (MCNs) under (semi-)dilute conditions, with special emphasis on ABC triblock terpolymers. The intrinsic immiscibility of connected blocks induces short-range repulsion into discrete nano-domains stabilized by a third, soluble block or molecular additive. Polymer blocks can be synthesized from an arsenal of functional monomers directing self-assembly through packing frustration or response to various fields. The mobility in solution further allows the manipulation of self-assembly processes into specific directions by clever choice of environmental conditions. This review focuses on practical concepts that direct self-assembly into predictable nanostructures, while narrowing particle dispersity with respect to size, shape and internal morphology. The growing understanding of underlying self-assembly mechanisms expands the number of experimental concepts providing the means to target and manipulate progressively complex superstructures.

Efficient size control of copper nanoparticles generated in irradiated aqueous solutions of star-shaped polyelectrolyte containers.

The formation of copper nanoparticles (Cu-NPs) in irradiated aqueous solutions of star-shaped poly(acrylic acid) (PAA) were studied at two pH values. Transmission electron microscopy (TEM) demonstrates that the star-shaped macromolecules loaded with Cu(2+) ions can act as individual nanosized containers providing a perfect control over the size and size distribution of Cu-NPs. Electron paramagnetic resonance (EPR) and optical spectroscopy show a transformation of mechanisms controlling the reduction of Cu(2+) ions and the further formation of Cu-NPs. At pH 2.9, Cu-NPs are formed from the aquacomplexes of Cu(2+) ions through homogeneous nucleation. At pH 4.3, the formation of Cu-NPs occurs inside macromolecular containers loaded with Cu(2+) ions, which are bound to carboxylic groups of the polyelectrolyte. In the latter case, Cu-NPs apparently ripen from preformed hydrated Cu2O seeds, which are thought to result from the ultrasmall (Cu(2+))m(OH(-))k(COO(-))n species, thus implying a heterogeneous nucleation.

The impact of Janus nanoparticles on the compatibilization of immiscible polymer blends under technologically relevant conditions.

Several hundred grams of Janus nanoparticles (d ≈ 40 nm) were synthesized from triblock terpolymers as compatibilizers for blending of technologically relevant polymers, PPE and SAN, on industry-scale extruders. The Janus nanoparticles (JPs) demonstrate superior compatibilization capabilities compared to the corresponding triblock terpolymer, attributed to the combined intrinsic properties, amphiphilicity and the Pickering effect. Straightforward mixing and extrusion protocols yield multiscale blend morphologies with "raspberry-like" structures of JPs-covered PPE phases in a SAN matrix. The JPs densely pack at the blend interface providing the necessary steric repulsion to suppress droplet coagulation during processing. We determine the efficiency of JP-compatibilization by droplet size evaluation and find the smallest average droplet size of d ≈ 300 nm at 10 wt % of added compatibilizer, whereas at 2 wt %, use of JPs is most economic with reasonable small droplets and narrow dispersity. In case of excess JPs, rheological properties of the system is changed by a droplet network formation. The large-scale synthesis of JPs, the low required weight fractions and their exceptional stability against extensive shear and temperature profiles during industrial extrusion process make JP promising next generation compatibilizers.

Control of morphology and corona composition in aggregates of mixtures of PS-b-PAA and PS-b-P4VP diblock copolymers: effects of solvent, water content, and mixture composition.

The morphologies and corona compositions in aggregates of mixtures of PS-b-PAA and PS-b-P4VP diblock copolymers are influenced by controllable assembly parameters such as water content, block copolymer molar ratios, and solvent effects as well as the hydrophilic block lengths and block length ratios. All these factors can affect the morphology of the aggregates as well as their corona composition, the latter especially in vesicles, where two interfaces are involved. The morphologies and corona compositions of the aggregates were investigated by transmission electron microscopy and electrophoretic mobility, respectively. They depend, to a large extent, on the solubility of P4VP and PAA in the given organic solvent (e.g., DMF, THF, or dioxane), which influences the coil dimensions of the hydrophilic chains. The water content affects both the size and the shape of the block copolymer aggregates as well as the corona composition. Water acts as a precipitant for the hydrophobic block in the common solvent and, therefore, its progressive addition to the solution changes the interaction parameter with the hydrophobic block. The block copolymer molar ratio has an effect on both the morphology and the corona composition of the aggregates. With increasing PS-b-P4VP content in the mixture, the morphology transforms gradually from large compound micelles (LCMs), through coexistence of LCMs and small spherical micelles (SSMs), and eventually to vesicles. As expected, the corona composition of the aggregates is also affected by the block copolymer molar ratio, and changes progressively from pure PAA to a mixture of PAA and P4VP and to pure P4VP with increasing PS-b-P4VP content. It is clear that the use of mixtures of the soluble chains offers the opportunity of fine-tuning the corona composition in block copolymer aggregates under assembly conditions.

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 in situ 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, in situ, 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, e.g., planar IPEC brushes emanating from the micellar core.

Glycopolymer functionalization of engineered spider silk protein-based materials for improved cell adhesion.

Silk protein-based materials are promising biomaterials for application as tissue scaffolds, due to their processability, biocompatibility, and biodegradability. The preparation of films composed of an engineered spider silk protein (eADF4(C16)) and their functionalization with glycopolymers are described. The glycopolymers bind proteins found in the extracellular matrix, providing a biomimetic coating on the films that improves cell adhesion to the surfaces of engineered spider silk films. Such silk-based materials have potential as coatings for degradable implantable devices.

Towards completely miscible PMMA nanocomposites reinforced by shear-stiff, nano-mica.

Optimizing the reinforcement of polymers with nanoplatelets requires optimization of the aspect ratio and the moduli of the filler while providing a complete stress transfer. Employing a novel shear-stiff, nano-mica with large aspect ratio, we focus on maximizing the interfacial interaction between filler and matrix. External surfaces of the nano-mica were selectively modified by a polycationic macro-initiator and two PMMA-polymer brushes of length below and above critical entanglement length, respectively, and the mechanical properties of the three PMMA nanocomposites were measured. The multiple electrostatic anchoring groups of the macro-initiator not only provide reliable adhesion but at the same time allow the variation of the degree of protonation providing a local match between the charge densities of the clay surface and the adsorbed macro-initiator. PMMA coating of the nano-mica via surface initiated polymerization yielded long-term stable suspensions in THF that showed birefringence of a nematic phase. Solution blending of the PMMA coated nano-mica allows for dispersing single clay tactoids in the translucent PMMA nanocomposites at 5 wt% clay loading as determined by transmission electron microscopy (TEM). Although significantly improved mechanical properties could be achieved as compared to nanocomposites made with conventional clay fillers, the full potential - as expressed by Halpin-Tsai equations - of the PMMA coated nano-mica can still not be completely utilized. This is attributed to the non-wetting character of the densely packed PMMA brushes attached to planar nanoplatelets.

Control of corona composition and morphology in aggregates of mixtures of PS-b-PAA and PS-b-P4VP diblock copolymers: effects of pH and block length.

The corona compositions and morphologies in aggregates of mixtures of amphiphilic polystyrene-block-poly(acrylic acid) (PS-b-PAA) and polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) diblock copolymers are influenced by controllable assembly parameters such as the hydrophilic block length and solution pH. The morphologies and corona compositions of the aggregates were investigated by transmission electron microscopy and electrophoretic mobility, respectively. When mineral acids or bases are present during aggregate formation, they can exert a strong influence on the corona composition. Morphology changes were also seen with changing pH, as well as changes in corona composition, specifically for vesicles. Because of complications introduced by the presence of ions, the general hypothesis that the external corona of the vesicles is composed of the longer chains, while the shorter chains form the inner corona, which is valid only in mixtures containing only nonionic chains without any additives (no acids or bases) or within a well-defined narrow pH range. In addition to the numerical block lengths and the pH, the solubility of the hydrophilic blocks can also influence the morphology and as well as the interfacial composition of vesicles; as the numerically longer chains become less soluble, they can contract and move to the interior, while the numerically shorter but more soluble chains go to the external corona. A remarkable morphological feature of the pH continuum is that for some compositions vesicles are observed in four distinct pH regions, separated by pH ranges in which other morphologies dominate. The effect of pH and microion content on coil dimensions of the PVP and PAA chains in the block copolymers is most likely responsible for the observed behavior.