Multi-Functional Hyperbranched Poly(vinylene sulfide)s Constructed via Spontaneous Thiol–Yne Click Polymerization

Catalyst-free synthesis of diverse fluorescent polyoxadiazoles for the facile formation and morphology visualization of microporous films and cell imaging

The development of facile polymerizations toward functional heterocyclic polymers is of great significance for chemistry and materials science. As an important class of heterocyclic polymers, polyoxadiazoles (PODs) have found applications in various fields. However, the synthetic difficulties of PODs greatly restrict their structural diversity and property investigation. Herein, we report a series of catalyst-free multicomponent polymerizations (MCPs) that can facilely synthesize functional PODs with well-defined and diversified topological structures from commercially available or readily accessible aldehydes, carboxylic acids, secondary amines, and (N-isocyanimino)triphenylphosphorane at room temperature. Unlike conventional Ugi polycondensations, the present Ugi-type MCPs can in situ generate oxadiazole moieties in polymer backbones. The obtained PODs possess good solubility, high thermal and morphological stability, and excellent film-forming ability. The introduction of aggregation-induced emission (AIE) moieties together with the inherent structural features of PODs endow these polymers with multiple functionalities. The AIE-active linear PODs can form fluorescent microporous films with stable and ordered structures based on the simple breath figure patterning method, and the self-assembly morphologies can be directly visualized by fluorescence microscopy in a high-contrast and sensitive manner. Moreover, both the linear and hyperbranched AIE-active PODs possess excellent biocompatibility, good lysosome specificity, and excellent photobleaching resistance, which enable them to serve as promising lysosome-specific fluorescent probes in biological imaging.

Thiol-yne chemistry of diferrocenylacetylene: from synthesis and electrochemistry to theoretical studies

The thiol-yne coupling chemistry of diferrocenylacetylene (FcCCFc) 1, bearing two electron rich and redox-active ferrocenyl units (Fc = Fe(η⁵-C₅H₄)(η⁵-C₅H₅)) and an internal triple bond, has been investigated for the first time. In order to determine whether steric limitations might affect hydrothiolation, a model reaction using a functionalized monothiol was tested, namely 2-mercaptoethanol I. The thiol-diferrocenylacetylene reactions were initiated either thermally (in toluene with AIBN) or by UV light irradiation (in THF and in the presence of DMPA as the photoinitiator). The outcomes of these thiol-yne reactions showed a strong dependence on the initiation method used, with the thermally initiated one being the most efficient. These thiol-diferrocenylacetylene reactions mainly afforded the (Z)-stereoisomer of the newly obtained vinyl thioether sulfide FcCHC(Fc)S-(CH₂)₂OH (2), unlike the more common (E)-vinyl sulfides found in other additions to alkynes. The hydrothiolation of the internal -CC- bond in 1 was successfully extended to dithiol 2,2'-(ethylenedioxy)diethanethiol II, leading to the formation of the (ZZ)-isomer, with four ferrocenyl units, as the major product. According to the electrochemical studies, the new asymmetrical ferrocenyl-vinyl sulfides show iron-iron electronic and electrostatic interactions. Theoretical results for the (Z)-stereoisomer (2) suggest that adiabatic oxidation would lead to the loss of almost one electron on the ferrocenyl subunit closer to the thioether chain. Furthermore, the thiol-yne chemistry of the internal -CC- bond in diferrocenylacetylene has been compared to the external triple bond in ethynylferrocene, the theoretical results of which helped us to rationalize the very different reactivities observed in both metallocenes.

Selective removal of toxic organic dyes using Trӧger base-containing sulfone copolymers made from a metal-free thiol-yne click reaction followed by oxidation

Three copolymers TCP1–3 bearing Trӧger's base (TB) units intercalated with various thioether groups were synthesized using a catalyst-free thiol-yne click reaction. TCP1–3 display excellent solubility in common organic solvents allowing for their structural, and photophysical characterization. The thioether groups in TCP1–3 were selectively oxidized into their respective sulfone derivatives under mild oxidation reaction conditions affording the postmodified copolymers TCP4–6. Investigation of organic dye uptake from water by TCP1–6 proved their efficiency as selective adsorbents removing up to 100% of the cationic dye methylene blue (MEB) when compared to anionic dyes, such as Congo red (CR), methyl orange (MO) and methyl blue (MB). The sulfone-containing copolymers TCP4–6 display superior and faster MEB removal efficiencies with respect to their corresponding synthons TCP1–3.

Copolymers TCP1–3 with Trӧger's base units and aryl thioether groups were made via a click reaction. Selective oxidation of the thioethers into sulfone groups afforded TCP4–6 which display up to 100% removal efficiency of methylene blue from water.

Chromic and Fluorescence-Responsive Metal-Organic Frameworks Afforded by N-Amination Modification

Sensory materials that show color and/or fluorescence changes in response to specific gases or vapors have important applications in many fields. Here, we report the postsynthetic preparation of novel sensory metal-organic frameworks (MOFs) and their multiple responsive properties. Through postsynthetic N-amination, the 2,2'-bipyridyl spacers in a Zr(IV) MOF are partially transformed into N-aminobipyridinium. The new MOF (Zr-bpy-A) shows chromic behavior toward ammonia and amines because the electron-deficient pyridinium groups form charge-transfer complexes with amino moieties. It also shows a unique chromic response to formaldehyde owing to the Schiff-base condensation with the N-amino groups. Furthermore, the N-amino group can be used to graft different polycyclic aromatic hydrocarbons, which endow the MOF with strong fluorescence of variable colors and afford a high-contrast fluorescence response to ammonia/amines and formaldehyde associated with the chromic response. The presence of the unquaternized bipyridyl group also leads to a fluorescence response to HCl. The multiple responsive behaviors hold appeal for applications in sensing, switching, and antifake marking, which are illustrated with a test paper and writing ink.

Metal-Free Catalysts for the Polymerization of Alkynyl-Based Monomers

Novel polymerizations based on alkyne monomers are becoming a powerful tool to construct polymers with unique structures and advanced functions in the areas of polymer and material sciences, and scientists have been attracted to develop a variety of novel polymerizations in recent decades. Therein, catalytic systems play an indispensable role in the influence of polymerization efficiencies and the performances of the resultant polymers. Concerning the shortcomings of metallic catalysts, much of the recent research focus has been on metal-free polymerization systems. In this paper, metal-free catalysts are classified and the corresponding polymerizations are reviewed, including organobase-catalyzed polymerizations, Lewis-acid-catalyzed polymerizations, as well as catalyst-free polymerizations. Moreover, the challenges and perspectives in this area are also briefly discussed.

Hyperbranched Poly(ester-enamine) from Spontaneous Amino-yne Click Reaction for Stabilization of Gold Nanoparticle Catalysts

Hyperbranched polymers have garnered much attention due to attractive properties and wide applications, such as drug-controlled release, stimuli-responsive nano-objects, photosensitive materials and catalysts. Herein, two types of novel hyperbranched poly(ester-enamine) (hb-PEEa) were designed and synthesized via the spontaneous amino-yne click reaction of A₂ monomer (1, 3-bis(4-piperidyl)-propane (A_2a ) or piperazine (A_2b )) and B₃ monomer (trimethylolpropanetripropiolate). According to Flory's hypothesis, gelation is an intrinsic problem in an ideal A₂ +B₃ polymerization system. By controlling the polymerization conditions, such as monomer concentration, molar ratio and rate of addition, a non-ideal A₂ +B₃ polymerization system can be established to avoid gelation and to synthesize soluble hb-PEEa. Due to abundant unreacted alkynyl groups in periphery, the hb-PEEa can be further functionalized by different amino compounds or their derivates. The as-prepared amphiphilic PEG-hb-PEEa copolymer can readily self-assemble into micelles in water, which can be used as surfactant to stabilize Au nanoparticles (AuNPs) during reduction of NaBH₄ in aqueous solution. As a demonstration, the as-prepared PEG-hb-PEEa-supported AuNPs demonstrate good dispersion in water, solvent stability and remarkable catalytic activity for reduction of nitrobenzene compounds.

Development of Novel Triazine-Based Poly(phenylene sulfide)s with High Refractive Index and Low Birefringence

High-refractive-index (high-n) polymers with a high optical transparency and low birefringence (Δn) have been desired in progressive optoelectronic devices. However, the trade-off between high-n and low-Δn remains a challenge at present. Here, the development of a novel array of high-n, high-sulfur-containing, highly transparent, colorless poly(phenylene sulfide) (PPS) polymers bearing triazine units in the main chains is reported. Six new triazine monomers T1-T6 with various pendant groups via different linkers (-O- and -NH-) could be prepared for developing PPSs with high-n and low Δn values. These PPSs (P1-P6) were obtained by the polycondensation of T1-T6 with commercial aromatic dithiol, 4,4'-thiobisbenzenethiol, respectively, which showed very high-n values (n av: 1.6902-1.7169 at 633 nm), high optical transparency (T % > 90% @ 400 nm), and low birefringence (Δn = 0.0015-0.0042). All the PPSs displayed high n ∞ values (1.6340-1.6654), providing valuable information for the development of high-n triazine-based PPS materials for application not only in the visible region but also in the near-infrared region.

Organobase-catalysed hydroxyl–yne click polymerization

An efficient organobase (DABCO)-catalysed hydroxyl–yne click polymerization is successfully developed under mild conditions.

Synthesis and direct assembly of linear–dendritic copolymers via CuAAC click polymerization-induced self-assembly (CPISA)

A one-pot method was developed for in situ preparation of linear–dendritic copolymer assemblies via click polymerization-induced self-assembly (CPISA).

Interfacial Synthesis of Conjugated Crystalline 2D Fluorescent Polymer Film Containing Aggregation-Induced Emission Unit

A fully conjugated 2D fluorescent film containing a tetraphenylethene (TPE) unit is constructed by Glaser-Hay coupling reaction on the surface of copper foil. A large-area, freestanding fluorescent films with an average thickness 4.5 nm can be obtained through the strategy of solid-liquid interfacial synthesis. The film and the pore structure are characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS). High-resulution TEM and selected area electron diffraction (SAED) further confirm the dual pores structure with triangular- and hexagonal-shaped pores. The as-prepared 2D films exhibit excellent solid-state fluorescence emission arising from the confinement of TPE units.

Aggregation-induced emission (AIE)-active polymers for explosive detection

This review is to summarize the latest progress on aggregation-induced-emission (AIE)-active polymers for explosive detection.

Transition metal-free thiol–yne click polymerization toward Z-stereoregular poly(vinylene sulfide)s

An efficient K₃PO₄-mediated thiol–yne click polymerization was established, and regio- and stereoregular poly(vinylene sulfide)s with Z-isomers were produced.

A Simple Approach to Bioconjugation at Diverse Levels: Metal-Free Click Reactions of Activated Alkynes with Native Groups of Biotargets without Prefunctionalization

The efficient bioconjugation of functional groups/molecules to targeted matrix and bio-related species drives the great development of material science and biomedicine, while the dilemma of metal catalysis, uneasy premodification, and limited reaction efficiency in traditional bioconjugation has restricted the booming development to some extent. Here, we provide a strategy for metal-free click bioconjugation at diverse levels based on activated alkynes. As a proof-of-concept, the abundant native groups including amine, thiol, and hydroxyl groups can directly react with activated alkynes without any modification in the absence of metal catalysis. Through this strategy, high-efficient modification and potential functionalization can be achieved for natural polysaccharide, biocompatible polyethylene glycol (PEG), synthetic polymers, cell penetrating peptide, protein, fast whole-cell mapping, and even quick differentiation and staining of Gram-positive bacteria, etc. Therefore, current metal-free click bioconjugation strategy based on activated alkynes is promising for the development of quick fluorescence labeling and functional modification of many targets and can be widely applied towards the fabrication of complex biomaterials and future in vivo labeling and detection.

Thiol-yne Click Polymerization

Thiol-yne click polymerization (TYCP) is one of the most significant synthetic techniques for artificial polymers, due to its simplicity, efficiency, and functionality tolerance. In nature, it is a classic nucleophilic addition reaction and a step-growth polymerization, which can be initiated or accelerated in the presence of free-radicals, amines, and transition metals, respectively. Its rate is greatly influenced by the structures (i.e., their electrophilicity and steric hindrance) of the used thiols and/or alkynes. With aliphatic monomers being used as feeding materials, the topological architectures (such as linear, branching, and cross-linked network, etc.) and available functional groups (such as hydroxyl, carboxyl, amino, and epoxy groups, and so on) can be facilely tailored via altering the chemical structure and feeding order. In contrast, for aromatic monomers, mono-addition occurs only during the process of thiol-yne click reaction, leading exclusively to linear poly(vinyl thioether)s. These sulfur-containing polymers synthesized by TYCP are promising to be widely utilized as high refractive index materials, photovoltaic materials, drug-delivery vehicles, biomaterials, and hybrid materials, etc.

Lignin Nanosphere-Supported Cuprous Oxide as an Efficient Catalyst for Huisgen [3+2] Cycloadditions under Relatively Mild Conditions

In this work, low-cost lignin nanospheres were fabricated and further applied as an efficient and sustainable support for preparing cuprous oxide (Cu₂O) "green" catalyst by using electrospraying technology. The unalloyed lignin, a special three-dimensional molecular structure, was successfully processed into uniform nanospheres under an electrospraying condition. The synthesized lignin-supported Cu₂O catalyst had a well-defined nanosphere structure, and Cu₂O nanoparticles with sizes less than 30 nm were supported by exposed layers of lignin nanospheres. There were C⁻O⁻Cu bonds formed between the lignin nanospheres and the metallic nanoparticles. The lignin nanospheres and the lignin nanosphere-supported catalyst werfe characterized by utilizing XRD, SEM, TEM, XPS, EDS, and TGA. The immobilization of Cu₂O nanoparticles on the lignin nanospheres was beneficial for dispersion of the Cu₂O nanoparticles and preventing their aggregation, which could cause catalyst deactivation, which favored the Huisgen [3+2] cycloaddition reaction. The triazole synthesis results indicated that the lignin nanosphere-supported Cu₂O catalyst had a high catalytic performance with 99% yield under solvent-free conditions. Furthermore, the as-synthesized catalyst could be recycled for four times without significantly losing its catalytic activity.

Progress on Catalytic Systems Used in Click Polymerization

Click polymerization, a powerful synthetic technique to construct polymers with unique structures and advanced functions, is of crucial importance in the areas of polymer and material sciences. A variety of click polymerizations such as azide-alkyne, thiol-yne, amino-yne, and hydroxyl-yne reactions have been established, wherein the catalytic systems play an indispensable role in realizing these highly practical reactions based on triple-bond building blocks, as they directly influence the efficiencies of the click polymerizations and the performances of the resultant polymers. The vital employment of catalysts is reviewed and their developments from innovative discoveries to the eminent position are outlined. Moreover, the challenges and perspectives in this area are also briefly discussed.

Recent advances in alkyne-based click polymerizations

The recent progress in alkyne-based click polymerizations and their application in the preparation of new functional polymers are summarized. The challenges and opportunities in this area are also briefly discussed.

Vinylidene-based polymers by Rh(i)-NHC catalyzed thiol–yne click polymerization: synthesis, characterization and post-polymerization modification

High molecular weight polymers by rhodium-catalyzed Markovnikov-selective alkyne polyhydrothiolation.

Ultrafast and efficient aza- and thiol-Michael reactions on a polyester scaffold with internal electron deficient triple bonds

A polyester scaffold possessing electron deficient triple bonds in the main chain was prepared and utilized as a precursor for aza- and thiol-Michael addition reactions.

Superbase catalyzed regio-selective polyhydroalkoxylation of alkynes: a facile route towards functional poly(vinyl ether)s

A superbase of t-BuP₄ catalysed polyhydroxylation of aromatic diynes was established, and regio-regular poly(vinyl ether)s with versatile properties were produced.

Postsynthetic N-methylation making a metal–organic framework responsive to alkylamines

The postsynthetically created electron-deficient bipyridinium moieties in a Zr-MOF provide charge-transfer sites for selectively recognizing and capturing alkylamines with fast and reversible vapochromism and luminescence quenching.

A novel post-polymerization modification route to functional poly(disubstituted acetylenes) through phenol–yne click reaction

This work not only enriches the precursor species for the synthesis of functional poly(disubstituted acetylenes) but also adds a powerful tool to the tool box for the preparation of other functional polymers through the post-polymerization modification route.

A Facile Strategy to Prepare Hyperbranched Hydroxyl-Rich Polycations for Effective Gene Therapy

For effective gene therapy, nonviral gene carriers with low toxicity and high transfection efficiency are of much importance. In this work, we developed a facile strategy to prepare hyperbranched hydroxyl-rich polycations (denoted by TE) by the one-pot method involving ring-opening reactions between two commonly used reagents, ethylenediamine (ED) with two amino groups and 1,3,5-triglycidyl isocyanurate (TGIC) with three epoxy groups. The hyperbranched TEs with different molecular weights were investigated on their DNA condensation ability, protein absorption property, biocompatibility, transfection efficiency, and in vivo cancer therapy and toxicity. TE exhibited low cytotoxicity and protein absorption property due to the plentiful hydroxyl groups. The optimal transfection efficiency of TE was significantly higher than that of the gold standard polycationic gene carrier branched polyethylenimine (PEI, 25 kDa). Furthermore, TE was applied for in vivo tumor inhibition by the delivery of antioncogene p53, which showed good antitumor efficiency with low adverse effects. The present work provides a new concept for the facile preparation of hyperbranched hydroxyl-rich polycationic carriers with good transfection performances.

Click-chemistry approaches to π-conjugated polymers for organic electronics applications

Given the wide utility of click-chemistry reactions for the preparation of simple moieties within large architecturally complex materials, this minireview article aims at surveying papers exploring their scope in the area of π-conjugated polymers for application in organic electronics to enable advanced functional properties.

Facile synthesis of functional poly(vinylene sulfide)s containing donor–acceptor chromophores by a double click reaction

The new electronically active poly(vinylene sulfide)s containing dialkylaniline-substituted electron-rich alkynes in the side chains were designed and synthesized by the ‘thiol-click’ polymerization.

High porosity microspheres with functional groups synthesized by thiol–yne click suspension polymerization

We employed a combination of thiol–yne click polymerization and suspension polymerization for the synthesis of porous epoxy-functionalized polymeric microspheres.