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

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

Sphere-Like Protein–Glycopolymer Nanostructures Tailored by Polyassociation

Key parameters allow a reproducible polyassociation between avidin and biotinylated glycopolymers in order to fabricate defined supramolecular nanostructures for future (bio)­medical and biotechnological applications. Thus, the polymerization efficiency of biotinylated glycopolymers in the fabrication of biohybrid structures (BHS) was investigated with regard to the influence of (i) the degree of biotinylation of the dendritic glycoarchitectures, (ii) two biotin linkers, (iii) the dendritic scaffold (perfectly branched vs hyperbranched), and (iv) the ligand–receptor stoichiometry. The adjustment of all these parameters opens the way to fabricate defined sizes of the final biohybrid structures as a multifunctional platform ready for their use in different applications. Various analytical techniques, including purification of BHS, were used to gain fundamental insights into the structural properties of the resulting protein–glycopolymer BHS. Finally, the elucidation of pivotal conformational properties of isolated BHS with defined sizes by asymmetrical flow field flow fractionation study revealed that they mainly possess spherical-/star-like properties. From this study, the fundamental knowledge can be likely transferred to other assemblies formed by molecular recognition processes (e.g., adamantane-β-cyclodextrin)

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

One-Pot Synthesis of All-Conjugated Block-Like Bisthiophene–Naphthalenediimide/Fluorene Copolymer

A copolymerization of electron-rich and electron-deficient monomers via the chain-growth catalyst-transfer polycondensation route is highly challenging and has never been accomplished thus far, to the best of our knowledge. Herein, we report a simple method to copolymerize two monomers of a significantly different nature: anion-radical naphthalene diimide–dithiophene-based and zinc-organic AB-type fluorenic ones. We found that the copolymerization proceeds rapidly in the presence of Pd catalyst having the bulky and electron-rich tri<i>-tert</i>-butylphosphine ligand. Despite the fact that the two monomers are simultaneously added to the copolymerization (batch polymerization), the polymerization leads to a gradient or even block-like copolymer rather than to a random copolymer or to a mixture of homopolymers, as evident from NMR, GPC, AFM, and fluorescence quenching experiments. The block-like copolymer is formed because the fluorenic monomer polymerizes much faster, yet because the resulting PF2/6 homopolymer is able to initiate polymerization of the second monomer, presumably acting as macroinitiator. Although the investigated copolymerization does not involve a living propagation mechanism and the resulting product is not a well-defined block copolymer, this result is an important step toward a general protocol for preparation of all-conjugated donor–acceptor block copolymers for optoelectronic applications

Supracolloidal Multivalent Interactions and Wrapping of Dendronized Glycopolymers on Native Cellulose Nanocrystals

Cellulose nanocrystals (CNCs) are high aspect ratio colloidal rods with nanoscale dimensions, attracting considerable interest recently due to their high mechanical properties, chirality, sustainability, and availability. In order to exploit them for advanced functions in new materials, novel supracolloidal concepts are needed to manipulate their self-assemblies. We report on exploring multivalent interactions to CNC surface and show that dendronized polymers (DenPols) with maltose-based sugar groups on the periphery of lysine dendrons and poly­(ethylene-<i>alt</i>-maleimide) polymer backbone interact with CNCs. The interactions can be manipulated by the dendron generation suggesting multivalent interactions. The complexation of the third generation DenPol (G3) with CNCs allows aqueous colloidal stability and shows wrapping around CNCs, as directly visualized by cryo high-resolution transmission electron microscopy and electron tomography. More generally, as the dimensions of G3 are in the colloidal range due to their ∼6 nm lateral size and mesoscale length, the concept also suggests supracolloidal multivalent interactions between other colloidal objects mediated by sugar-functionalized dendrons giving rise to novel colloidal level assemblies

Poly(ethylene oxide)‑<i>b</i>‑poly(3-sulfopropyl methacrylate) Block Copolymers for Calcium Phosphate Mineralization and Biofilm Inhibition

Poly­(ethylene oxide) (PEO) has long been used as an additive in toothpaste, partly because it reduces biofilm formation on teeth. It does not, however, reduce the formation of dental calculus or support the remineralization of dental enamel or dentine. The present article describes the synthesis of new block copolymers on the basis of PEO and poly­(3-sulfopropyl methacrylate) blocks using atom transfer radical polymerization. The polymers have very large molecular weights (over 10⁶ g/mol) and are highly water-soluble. They delay the precipitation of calcium phosphate from aqueous solution but, upon precipitation, lead to relatively monodisperse hydroxyapatite (HAP) spheres. Moreover, the polymers inhibit the bacterial colonization of human enamel by <i>Streptococcus gordonii</i>, a pioneer bacterium in oral biofilm formation, in vitro. The formation of well-defined HAP spheres suggests that a polymer-induced liquid precursor phase could be involved in the precipitation process. Moreover, the inhibition of bacterial adhesion suggests that the polymers could be utilized in caries prevention

Efficient Tin-Free Route to a Donor–Acceptor Semiconducting Copolymer with Variable Molecular Weights

For the fabrication of efficient photovoltaic devices and thin-film transistors, π-conjugated polymers with high molecular weight are desirable as they frequently show superior charge transport, morphological, and film-forming properties. Herein, we present an extremely fast tin-free method to polymerize a naphthalene diimide-dithiophene-based anion-radical monomer in the presence of Pd catalyst having bulky and electron-rich tritert-butylphosphine ligands (Pd/P^<i>t</i>Bu₃). With this method, the corresponding semiconducting polymer, PNDIT2 (also known as P­(NDI2OD-T2 or N2200) with a molecular weight in excess of 1000 kg/mol can be obtained quickly at room temperature and at rather low catalyst concentrations. In general, molecular weights of resulting polymer can be regulated by reaction conditions (e.g., catalyst concentration and reaction time). Besides high molecular weight PNDIT2 (e.g., with <i>M</i>_N ∼ 350 kg/mol, <i>Đ</i>_M =2.9), PNDIT2 with moderate molecular weight (e.g., <i>M</i>_N ∼ 110 kg/mol, <i>Đ</i>_M = 2.3) and low molecular weight (e.g., <i>M</i>_W ∼ 12 kg/mol, <i>Đ</i>_M = 1.9), can also be obtained. It was found that thus-prepared PNDIT2 exhibits field-effect electron mobilities of up to ∼0.31 cm²/(V s), similar to the Stille-derived N2200 control polymer (up to ∼0.33 cm²/(V s)). Preliminary studies demonstrated that Pd/P^<i>t</i>Bu₃ catalyst is remarkably efficient in polymerizing of other anion-radical monomers, such as isoindigo-, and diketopyrrolopyrrole-based ones, although conventional Ni and Pd catalysts (e.g., Ni­(dppp)­Cl₂, Ni­(dppp)­Cl₂, Pd­(PPh₃)₄) failed to polymerize these monomers