High-Resolution Tracking of Multiple Distributions in Metallic Nanostructures: Advanced Analysis Was Carried Out with Novel 3D Correlation Thermal Field-Flow Fractionation

Multifunctional metallic nanostructures are essential in the architecture of modern technology. However, their characterization remains challenging due to their hybrid nature. In this study, we present a novel photoreduction-based protocol for augmenting the inherent properties of imidazolium-containing ionic polymers (IIP)­s through orthogonal functionalization with gold nanoparticles (Au NPs) to produce IIP_Au NPs, as well as novel and advanced characterization via three-dimensional correlation thermal field-flow fractionation (3DCoThFFF). Coordination chemistry is applied to anchor Au3+ onto the nitrogen atom of the imidazolium rings, for subsequent photoreduction to Au NPs using UV irradiation. Thermal field-flow fractionation (ThFFF) and the localized surface plasmon resonance (LSPR) of Au NPs are both dependent on size, shape, and composition, thus synergistically co-opted herein to develop mutual correlation for the advanced analysis of 3D spectral data. With 3DCoThFFF, multiple sizes, shapes, compositions, and their respective distributions are synchronously correlated using time-resolved LSPR, as derived from multiple two-dimensional UV–vis spectra per unit ThFFF retention time. As such, higher resolutions and sensitivities are observed relative to those of regular ThFFF and batch UV–vis. In addition, 3DCoThFFF is shown to be highly suitable for monitoring and evaluating the thermostability and dynamics of the metallic nanostructures through the sequential correlation of UV–vis spectra measured under incremental ThFFF temperature gradients. Comparable sizes are measured for IIP and IIP_Au NPs. However, distinct elution profiles and UV–vis absorbances are recorded, thereby reaffirming the versatility of ThFFF as a robust tool for validating the successful functionalization of IIP with Au to produce IIP_Au NPs

Nonlinear Ziegler–Natta-Homopolyethylene with Enhanced Crystallinity: Physical and Macromolecular Characteristics

Polyolefin engineering and design are at the forefront of a significant number of research and development laboratories, helping to bring about new and highly specific materials for tailored uses. Tailoring the chain architecture of polyolefins improves their performance and physical properties. Four unique polyethylene (PE) materials with long-chain branches (LCBPE) are studied using advanced chromatographic fractionation techniques alongside linear high-density PE (HDPE) and typical commercial low-density PE (LDPE). The absence of short-chain branching in the analyzed LCBPEs allows for a defined correlation of long-chain branching (LCB) with specific physical properties. Possible effects of side-chain crystallization on melt behavior and crystallinity clearly show that the nonlinearity in architecture positively affects crystallinity while simultaneously lowering melting temperature. The separation of polyolefins according to the LCB content is demonstrated for the first time by high-temperature interaction chromatography and thermal analysis, in addition to size exclusion chromatography coupled to differential viscometer and light scattering detectors. This study is pioneering in applying solvent gradient interaction chromatography and stationary-phase-assisted crystallization to the separation of PE regarding long-chain branching

Alkoxide-Initiated Regioselective Coupling of Carbon Disulfide and Terminal Epoxides for the Synthesis of Strongly Alternating Copolymers

The synthesis of highly regioregular and alternating polythiocarbonates from carbon disulfide and terminal epoxides has been achieved. The copolymerizations were performed under ambient and solvent-free conditions in the presence of LiO^<i>t</i>Bu (0.125–0.5 mol %) as initiator. At higher loadings the reaction pathway switched in favor to the catalytic formation of cyclic dithiocarbonates. Under optimized reaction conditions polymers with molecular weights up to 109 kg mol^–1 were isolated. The NMR spectroscopic analysis of the polythiocarbonates revealed that 94% of backbone structure is formed by strongly alternating head-to-head arrangement of epoxypropane and 1,2-epoxybutane monomers, respectively, at a thiocarbonate group −CHR–OC­(S)­O–CHR– and tail-to-tail arrangement at a trithiocarbonate group −CH₂–SC­(S)­S–CH₂–. Atactic polymers were obtained using racemic mixtures of the epoxides, but an isotactic polymer was obtained when chiral (<i>R</i>)-epoxy­propane was converted. A mechanism is proposed which rationalizes the regio- and stereochemistry observed for the alkoxide-initiated copolymerization of CS₂ and terminal epoxides

From 1D Rods to 3D Networks: A Biohybrid Topological Diversity Investigated by Asymmetrical Flow Field-Flow Fractionation

Biohybrid structures formed by noncovalent interaction between avidin as a bridging unit and biotinylated glycodendrimers based on poly­(propyleneimine) (GD-B) have potential for biomedical application. Therefore, an exact knowledge about molar mass, dispersity, size, shape, and molecular structure is required. Asymmetrical flow field-flow fractionation (AF4) was applied to separate pure and assembled macromolecules according to their diffusion coefficients. The complex biohybrid structures consist of single components (avidin, differently valent GD-B) and nanostructures. These nanostructures were systematically studied depending on the degree of biotinylation and ligand–receptor stoichiometry by AF4 in combination with dynamic and static light scattering detection. This enables the quantification of composition and calculation of molar masses and radii, which were used to analyze scaling properties and apparent density of the formed structures. These data are compared to hydrodynamic radii obtained by applying the retention theory to the AF4 data. It is shown that depending on their architecture the molecular shape of biohybrid structures is changed from rod-like to spherical toward network-like behavior

High Temperature Quadruple-Detector Size Exclusion Chromatography for Topological Characterization of Polyethylene

Modifying material properties in simple macromolecules such as polyethylene (PE) is achieved by different connection modes of ethylene monomers resulting in a plurality of possible topologies–from highly linear to dendritic species. However, the challenge still lies within the experimental identification of the topology and conformation of the isolated macromolecules because of their low solubility, which demands methods with specific solvents and high operating temperatures. Additionally, a separation technique has to be coupled to different detection methods to meet the specific demands of the respective characterization goal. In this work, we report a quadruple-detector high temperature size exclusion chromatography (HT-SEC) system which contains online multiangle laser light scattering, dynamic light scattering, differential viscometry, and differential refractometry detectors. Quadruple-detector HT-SEC was successfully applied to explore the full range of physical parameters of various PE samples with different branching topologies ranging from highly linear macromolecules, polymers with moderate level of branching, to highly branched PEs with hyperbranched structure. This method is a useful tool not only to investigate molecular weight, mass distribution, and size but also to enable access to important factors which describe the conformation in dilute solution and branching density

Effect of Connectivity on the Structure and the Liquid–Solid Transition of Dense Suspensions of Soft Colloids

Aqueous solutions of multiarm flower-like poly­(ethylene oxide) (PEO) were formed and connected to various degrees by self-assembly. The structure was rendered permanent by <i>in situ</i> UV-irradiation. Dense suspensions of these single and connected soft colloids were studied by static and dynamic light scattering and viscosity measurements. The concentration dependence of the osmotic compressibility, the dynamic correlation length, and the viscosity of single flowers was shown to be close to that of equivalent PEO star-like polymers demonstrating that the effect of forming loops on the interaction is small. It was found that the osmotic compressibility and the dynamic correlation length of dense suspensions are not influenced by the bridging. However, when flower polymers are connected into clusters, motion in dense suspensions needs to be collective over larger length scales. This causes a much stronger increase of the viscosity for dense suspensions of interpenetrated clusters compared to single-flower polymers

Coil-like Enzymatic Biohybrid Structures Fabricated by Rational Design: Controlling Size and Enzyme Activity over Sequential Nanoparticle Bioconjugation and Filtration Steps

Well-defined enzymatic biohybrid structures (BHS) composed of avidin, biotinylated poly­(propyleneimine) glycodendrimers, and biotinylated horseradish peroxidase were fabricated by a sequential polyassociation reaction to adopt directed enzyme prodrug therapy to protein–glycopolymer BHS for potential biomedical applications. To tailor and gain fundamental insight into pivotal properties such as size and molar mass of these BHS, the dependence on the fabrication sequence was probed and thoroughly investigated by several complementary methods (e.g., UV/vis, DLS, cryoTEM, AF4-LS). Subsequent purification by hollow fiber filtration allowed us to obtain highly pure and well-defined BHS. Overall, by rational design and control of preparation parameters, e.g., fabrication sequence, ligand–receptor stoichiometry, and degree of biotinylation, well-defined BHS with stable and even strongly enhanced enzymatic activities can be achieved. Open coil-like structures of BHS with few branches are available by the sequential bioconjugation approach between synthetic and biological macromolecules possessing similar size dimensions