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

Copolymerization Involving Sulfur-Containing Monomers

Incorporating sulfur (S) atoms into polymer main chains endows these materials with many attractive features, including a high refractive index, mechanical properties, electrochemical properties, and adhesive ability to heavy metal ions. The copolymerization involving S-containing monomers constitutes a facile method for effectively constructing S-containing polymers with diverse structures, readily tunable sequences, and topological structures. In this review, we describe the recent advances in the synthesis of S-containing polymers via copolymerization or multicomponent polymerization techniques concerning a variety of S-containing monomers, such as dithiols, carbon disulfide, carbonyl sulfide, cyclic thioanhydrides, episulfides and elemental sulfur (S8). Particularly, significant focus is paid to precise control of the main-chain sequence, stereochemistry, and topological structure for achieving high-value applications.

Synthesis, Characterization, and Environmental Applications of Novel Per-Fluorinated Organic Polymers with Azo- and Azomethine-Based Linkers via Nucleophilic Aromatic Substitution

This study reports on the synthesis and characterization of novel perfluorinated organic polymers with azo- and azomethine-based linkers using nucleophilic aromatic substitution. The polymers were synthesized via the incorporation of decafluorobiphenyl and hexafluorobenzene linkers with diphenols in the basic medium. The variation in the linkers allowed the synthesis of polymers with different fluorine and nitrogen contents. The rich fluorine polymers were slightly soluble in THF and have shown molecular weights ranging from 4886 to 11,948 g/mol. All polymers exhibit thermal stability in the range of 350-500 °C, which can be attributed to their structural geometry, elemental contents, branching, and cross-linking. For instance, the cross-linked polymers with high nitrogen content, DAB-Z-1h and DAB-Z-1O, are more stable than azomethine-based polymers. The cross-linking was characterized by porosity measurements. The azo-based polymer exhibited the highest surface area of 770 m2/g with a pore volume of 0.35 cm3/g, while the open-chain azomethine-based polymer revealed the lowest surface area of 285 m2/g with a pore volume of 0.0872 cm3/g. Porous structures with varied hydrophobicities were investigated as adsorbents for separating water-benzene and water-phenol mixtures and selectively binding methane/carbon dioxide gases from the air. The most hydrophobic polymers containing the decafluorbiphenyl linker were suitable for benzene separation, while the best methane uptake values were 6.14 and 3.46 mg/g for DAB-Z-1O and DAB-A-1O, respectively. On the other hand, DAB-Z-1h, with the highest surface area and being rich in nitrogen sites, has recorded the highest CO2 uptake at 298 K (17.25 mg/g).

Accessing the Thiol Toolbox: Synthesis and Structure-Activity Studies on Fluoro-Thiol Conjugated Antimicrobial Peptides

The para-fluoro-thiol reaction (PFTR) is a modern name for the much older concept of a nucleophilic aromatic substitution reaction in which the para-position fluorine of a perfluorinated benzene moiety is substituted by a thiol. As a rapid and mild reaction, the PFTR is a useful technique for the post-synthetic modification of macromolecules like peptides on the solid phase. This reaction is of great potential since it allows for peptide chemists to access the vast catalogue of commercially available thiols with diverse structures to conjugate to peptides, which may impart favorable biological activity, particularly in antimicrobial sequences. This work covers the generation of a library of antimicrobial peptides by modifying a relatively inactive tetrapeptide with thiols of various structures using the PFTR to grant antimicrobial potency to the core sequence. In general, nucleophilic substitution of the peptide scaffold by hydrophobic thiols like cyclohexanethiol and octanethiol imparted the greatest antimicrobial activity over that of hydrophilic thiols bearing carboxylic acid or sugar moieties, which were ineffectual at improving the antimicrobial activity. The general trend here follows expected structure-activity relationship outcomes like that of changing the acyl group of lipopeptide antibiotics and is encouraging for the use of this reaction for structural modifications of antimicrobial sequences further.

Click Step-Growth Polymerization and E/Z Stereochemistry Using Nucleophilic Thiol-yne/-ene Reactions: Applying Old Concepts for Practical Sustainable (Bio)Materials

Polymer sustainability is synonymous with "bioderived polymers" and the zeitgeist of "using renewable feedstocks". However, this sentiment does not adequately encompass the requirements of sustainability in polymers. In addition to recycling considerations and mechanical performance, following green chemistry principles also needs to be maximized to improve the sustainability of polymer synthesis. The synthetic cost (i.e., maximizing atom economy, reducing chemical hazards, and lowering energy requirements) of producing polymers should be viewed as equally important to the monomer source (biomass vs petrol platform chemicals). Therefore, combining the use of renewable feedstocks with efficient syntheses and green chemistry principles is imperative to delivering truly sustainable polymers. The high efficiency, atom economy, and single reaction trajectories that define click chemistry reactions position them as ideal chemical approaches to synthesize polymers in a sustainable manner while simultaneously expanding the structural scope of accessible polymers from sustainably sourced chemicals.Click step-growth polymerization using the thiol-yne Michael addition, a reaction first reported over a century ago, has emerged as an extremely mild and atom-efficient pathway to yield high-performance polymers with controllable E/Z stereochemistry along the polymer backbone. Building on studies of aromatic thiol-yne polymers, around 10 years ago our group began investigating the thiol-yne reaction for the stereocontrolled synthesis of alkene-containing aliphatic polyesters. Our early studies established a convenient path to high-molecular-weight (>100 kDa) E-rich or Z-rich step-growth polymers by judiciously changing the catalyst and/or reaction solvent. This method has since been adapted to synthesize fast-degrading polyesters, high-performance polyamides, and resilient hydrogel biomaterials. Across several systems, we have observed dramatic differences in material properties among polymers with different alkene stereochemistry.We have also explored the analogous thiol-ene Michael reaction to create high-performance poly(ester-urethanes) with precise E/Z stereochemistry. In contrast to the stereoselective thiol-yne polymerization, here the use of monomers with predefined E/Z (geometric) isomerism (arising from either alkenes or the planar rigidity of ring units) affords polymers with total control over stereochemistry. This advancement has enabled the synthesis of tough, degradable materials that are derived from sustainable monomer feedstocks. Employing isomers of sugar-derived isohexides, bicyclic rigid-rings possessing geometric isomerism, led to degradable polymers with fundamentally opposing mechanical behavior (i.e., plastic vs elastic) simply by adjusting the stereochemistry of the isohexide.In this Account, we feature our investigation of thiol-yne/-ene click step-growth polymers and efforts to establish structure-property relationships toward degradable materials with practical mechanical performance in the context of sustainable polymers and/or biomaterials. We have paid attention to installing and controlling geometric isomerism by using these click reactions, an overarching objective of our work in this research area. The exquisite control of geometric isomerism that is possible within polymer backbones, as enabled by convenient click chemistry reactions, showcases a powerful approach to creating multipurpose degradable polymers.

One-pot synthesis of amphiphilic multiblock poly(2-oxazoline)s via para-fluoro-thiol click reactions

A clickable initiator, pentafluoro benzyl bromide, has been investigated for the cationic ring opening polymerization of poly(2-oxazolines).

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.