Thiol-Bromo Click Reaction for One-Pot Synthesis of Star-Shaped Polymers.

Star-shaped polymers have unique physical properties and they are sought after materials in industry. However, the ease of synthesis is essential for translation of these materials into large-scale applications. Herein, a highly efficient synthetic method to prepare star-shaped polymers by combination of Cu-mediated reversible deactivation radical polymerization (Cu-RDRP) and thiol-bromo click reaction is described. Well-defined linear and block polymers with a very high bromine chain end fidelity are obtained via Cu-RDRP and subsequently react with multi-functional thiol compounds. High coupling efficiencies of larger than 90% are obtained owing to the quick and efficient reaction between thiols and alkyl bromides. Moreover, the arms of the obtained star-shaped polymers are linked via thioether bonds to the core, making them susceptible for oxidative degradation.

Fluorinated Polymers via Para-Fluoro-Thiol and Thiol-Bromo Click Step Growth Polymerization.

Click reactions are utilized widely to modify chain ends and side groups of polymers while click polymerizations based on step-growth polymerization of bifunctional monomers have recently attracted increased attention of polymer chemists. Herein, the combination of two highly efficient click reactions, namely para-fluoro-thiol click and thiol-bromo substitution reactions, is demonstrated to form fluorinated polymers with tuned hydrophobicity owing to the nature of the dithiol linker compound. The key compound in this study is 2,3,4,5,6-pentafluoro benzyl bromide that provides the combination of thiol click reactions. The thiols used here are 4,4-thiobisbenzenthiol, 2,2'-(ethylenedioxy) diethanethiol, and 1,2-ethanedithiol that allow tuning of the properties of obtained polymers. The step-growth click reaction conditions are optimized by screening the effect of reaction temperature, base, solvent, and stochiometric ratio of the compounds. Thermal properties and hydrophobicity of synthesized polymers are determined via water contact angle, thermogravimetric analysis and differential scanning calorimetry measurements, showing thermal stability up to 300 °C, glass transition temperatures ranging from -25 to 82 °C and water contact angles ranging from 55 to 90 °C.

Synthesis of Brush-Like Glycopolymers with Monodisperse, Sequence-Defined Side Chains and Their Interactions with Plant and Animal Lectins.

The synthesis of brush glycopolymers mimicking the architecture of proteoglycans is achieved by grafting sequence-defined glycooligomers derived from solid-phase polymer synthesis onto a poly(active ester) scaffold. This approach gives access to a first library of brush glycopolymers with controlled variations in the degree of branching and number of carbohydrate ligands per branch. When studying lectin binding of linear and brush glycopolymers to lectins Concanavalin A (ConA), dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN), and mannose-binding lectin (MBL), different preferences are observed with MBL showing higher binding to linear glycopolymer and ConA and DC-SIGN favoring brush glycopolymers. This finding suggests that the architecture of polymeric glycan mimetics affects binding to lectins not only in terms of creating higher avidity but potentially also selectivity ligands.

Transformation of Thioester-Initiated Star Polymers into Linear Arms via Native Chemical Ligation.

The synthesis of a new class of Cu-mediated polymerization initiators with thioester functionality is demonstrated and their polymerization kinetics via single-electron transfer living radical polymerization is reported. From periodic sampling, it is found that thioester- or ester-based initiators can be employed interchangeably, resulting in very similar polymerization rates. Furthermore, a multifunctional thioester initiator is employed for the preparation of a well-defined four-arm star-shaped polymer. It is further shown that the full dissociation of the star polymer into linear arms via native chemical ligation can easily be followed via size exclusion chromatography, as a result of the change in hydrodynamic volume. Finally, the obtained linear polymers are characterized via matrix-assisted laser desorption/ionization-time of flight mass spectrometry and found to be in good agreement with the expected molecular weight distribution that confirms the successful transformation.

Guided Cell Attachment via Aligned Electrospinning of Glycopolymers.

The creation of biomaterials with aligned fibers offers broad applications in tissue regeneration, guiding cell organization and physiological cues, and providing appropriate mechanical properties for many biomedical applications. Herein, for the first time, highly aligned electrospun membranes are designed and developed using glycopolymers. The membranes retain the strong mechanical properties of polycaprolactone, and fiber alignment facilitates the creation of anisotropic mechanical properties, enabling failure stress to be manipulated by an order of magnitude relative to randomly ordered fibers. Biocompatibility and cell attachment in these materials are characterized using tenocytes as a cell model. Both random and aligned fiber glycopolymers show promising biocompatibility, but aligned glycopolymer fibers additionally offer patterning to guide cell organization. These materials potentially provide a novel platform for tissue regeneration studies, demonstrating that the sugar-lectin interaction can produce materials capable of managing cell guidance.

RAFT Polymerization Meets Coordination Chemistry: Synthesis of a Polymer-Based Iridium(III) Emitter.

A synthetic approach toward the synthesis of well-defined copolymers with attached phosphorescent iridium(III) emitters is presented. A reactive µ-hydroxy-bridged precursor complex has been utilized to coordinate suitable ligand sites of a methacrylate-based copolymer. The starting copolymer has been synthesized via the reversible addition fragmentation chain transfer (RAFT) polymerization technique. Using a reactive complex species, the coordination reaction at the copolymer could be performed under very mild conditions in the absence of any supporting additives.