Efficient Conversion of Inert Nitriles to Multifunctional Poly(5-amino-1,2,3-triazole)s via Regioselective Click Polymerization with Azide Monomers under Ambient Conditions

Nitrile compounds are abundant, stable, cheap, and readily available natural and chemical industrial sources. However, the efficient conversion of nitrile monomers to functional polymers is mostly limited due to their inert reactivity, and developing efficient polymerizations based on nitrile monomers under very mild conditions is still a big challenge. In this work, a facile and powerful base-catalyzed acetonitrile-azide click polymerization was successfully established under ambient conditions. This polymerization also enjoys the merits of short reaction time (15 min), 100% atom economy, transition-metal-free catalyst system, and regioselectivity. A series of poly(5-amino-1,2,3-triazole)s (PATAs) with high weight-average molecular weights (Mw, up to 204,000) were produced in excellent yields (up to 99%). The PATAs containing tetraphenylethene (TPE) moieties exhibit unique aggregation-induced emission (AIE) characteristics, which could be used to sensitively detect Fe(III) ions with a low limit of detection (1.205 × 10-7 M) and to specifically image lysosomes of living cells. Notably, PATAs could be facilely post-modified due to their containing primary amino groups in the polymer chains even through a one-pot tandem reaction. Thus, this work not only establishes a new powerful click polymerization to convert stable nitriles but also generates a series of PATAs with versatile properties for diverse applications.

Facile conversion of water to functional molecules and cross-linked polymeric films with efficient clusteroluminescence

Exploring approaches to utilize abundant water to synthesize functional molecules and polymers with efficient clusteroluminescence properties is highly significant but has yet to be reported. Herein, a chemistry of water and alkyne is developed. The synthesized products are proven as nonaromatic clusteroluminogens that could emit visible light. Their emission colors and luminescent efficiency could be adjusted by manipulating through-space interaction using different starting materials. Besides, the free-standing polymeric films with much high photoluminescence quantum yields (up to 45.7%) are in situ generated via a water-involved interfacial polymerization. The interfacial polymerization-enhanced emission of the polymeric films is observed, where the emission red-shifts and efficiency increases when the polymerization time is prolonged. The synthesized polymeric film is also verified as a Janus film. It exhibits a vapor-triggered reversible mechanical response which could be applied as a smart actuator. Thus, this work develops a method to synthesize clusteroluminogens using water, builds a clear structure-property relationship of clusteroluminogens, and provides a strategy to in situ construct functional water-based polymeric films.

Poly(ether)s derived from oxa-Michael polymerization: a comprehensive review

Poly(ether)s represent an important class of polymers and are typically formed by ring-opening polymerization, Williamson ether synthesis, or self-condensation of alcohols. The oxa-Michael reaction presents another method to form poly(ether)s with additional functional groups in the polymer backbone starting from di- or triols and electron deficient olefins such as acrylates, sulfones, or acrylamides. However, research on oxa-Michael polymerization is still limited. Herein, we outline the principles of the oxa-Michael polymerization and focus on the synthesis and preparation of poly(ether-sulfone)s, poly(ether-ester)s, poly(ether)s, and poly(ether-amide)s. Further, challenges as well as future perspectives of the oxa-Michael polymerization are discussed.

Graphical abstract

Highly Efficient Darzens Reactions Mediated by Phosphazene Bases under Mild Conditions

The highly basic and poorly nucleophilic phosphazene base P₁‐t‐Bu promotes the Darzens condensation of α‐halo esters with aromatic aldehydes affording α,β‐epoxy esters in nearly quantitative yields under mild conditions and in short reaction times. The more basic P₄‐t‐Bu phosphazene was found useful with low reactivity aldehydes. These reactions can be performed in aprotic organic solvents of low polarity, thus minimizing the hydrolysis of α,β‐epoxy esters which often accompanies the base‐promoted Darzens condensations.

Fluorene-Based Fluorometric and Colorimetric Conjugated Polymers for Sensitive Detection of 2,4,6-Trinitrophenol Explosive in Aqueous Medium

Nitroaromatic explosives are a class of compounds that are responsible for various health hazards and terrorist outrages. Among these, sensitive detection of 2,4,6-trinitrophenol (TNP) explosive has always been highly desirable considering public health and national security. In this regard, three fluorene-based conjugated polymers (CP 1, CP 2, and CP 3) were synthesized through the Suzuki-Miyaura coupling reaction and were found to be highly sensitive for fluorescence detection of TNP with detection limits of 3.2, 5.7, and 6.1 pM, respectively. Excellent selectivity of CPs toward TNP was attributed to their unique π-π interactions based on fluorescence studies and density functional theory (DFT) calculations. The high sensitivity of CPs to TNP was attributed to the static quenching mechanism based on the photoinduced electron transfer process and was evaluated by fluorescence, UV-visible absorption, dynamic light scattering, Job's plots, the Benesi-Hildebrand plots, and DFT calculations. CPs were also used for colorimetric and real-water sample analysis for the detection of TNP explosive. Meanwhile, sensor-coated test strips were fabricated for on-site detection of TNP, which makes them convenient solid-supported sensors.

Click Nucleophilic Conjugate Additions to Activated Alkynes: Exploring Thiol-yne, Amino-yne, and Hydroxyl-yne Reactions from (Bio)Organic to Polymer Chemistry

The 1,4-conjugate addition reaction between activated alkynes or acetylenic Michael acceptors and nucleophiles (i.e., the nucleophilic Michael reaction) is a historically useful organic transformation. Despite its general utility, the efficiency and outcomes can vary widely and are often closely dependent upon specific reaction conditions. Nevertheless, with improvements in reaction design, including catalyst development and an expansion of the substrate scope to feature more electrophilic alkynes, many examples now present with features that are congruent with Click chemistry. Although several nucleophilic species can participate in these conjugate additions, ubiquitous nucleophiles such as thiols, amines, and alcohols are commonly employed and, consequently, among the most well developed. For many years, these conjugate additions were largely relegated to organic chemistry, but in the last few decades their use has expanded into other spheres such as bioorganic chemistry and polymer chemistry. Within these fields, they have been particularly useful for bioconjugation reactions and step-growth polymerizations, respectively, due to their excellent efficiency, orthogonality, and ambient reactivity. The reaction is expected to feature in increasingly divergent application settings as it continues to emerge as a Click reaction.

Construction of hyperbranched and pH-responsive polymeric nanocarriers by yne-phenol click-reaction for tumor synergistic chemotherapy

In past decades, to improve the chemotherapeutic efficiency and reduce the systemic toxicity of small molecule anti-cancer drugs, polymer-based drug delivery systems (DDSs) have attracted great attention for tumor treatment due to their remarkable biocompatibility and responsive degradation in tumor microenvironment (TME). Herein, we developed a kind of pH-responsive and degradable hyperbranched polymeric nanocarriers via yne-phenol click-reaction of resveratrol (RSV) with bifunctional n-butyl dipropiolate (BDP) for efficient doxorubicin (DOX) delivery. The natural product RSV with three phenol groups has excellent antioxidant activity and synergetic enhancement for some anticancer drugs such as DOX. RSV tends to attack the alkynyl groups on BDP by nucleophilic addition in the presence of base as catalyst to afford hyperbranched polyprodrug (denoted as RB). PEGylated RB (termed as RBP) were further synthesized to improve the water solubility and prolong blood circulation by the click reaction of propiolate-terminated RB with amino terminated poly(ethylene glycol) (PEG-NH₂). Interestingly, the RBP have high DOX loading ratio (∼58.6 %) at neutral pH, but the vinyl-ether bonds in RB could break down at low pH conditions such as acidic TME (extracellular pH∼6.8, endosomes and lysosomes pH∼5.0) that leading to the targeting release of DOX and RSV. Therefore, the developed RBP@DOX nanoparticles exhibited high kill efficiency to tumor cells and slight damage to normal cells due to the effective delivery and release of DOX and RSV in tumor sites and the synergistic enhancement effect of two drugs.

Sulfur Conversion to Multifunctional Poly(O-thiocarbamate)s through Multicomponent Polymerizations of Sulfur, Diols, and Diisocyanides

Sulfur, which is generated from the waste byproducts in the oil and gas refinery industry, is an abundant, cheap, stable, and readily available source in the world. However, the utilization of excessive amounts of sulfur is mostly limited, and developing novel methods for sulfur conversion is still a global concern. Here, we report a facile one-step conversion from elemental sulfur to functional poly(O-thiocarbamate)s through a multicomponent polymerization of sulfur, diols, and diisocyanides, which possesses a series of advantages such as mild condition (55 °C), short reaction time (1 h), 100% atom economy, and transition-metal free in the catalyst system. Seven poly(O-thiocarbamate)s are constructed with high yields (up to 95%), large molecular weight (up to 53100 of M_w), good solubility in organic solvents, and completely new polymer structures. The poly(O-thiocarbamate)s possess a high refractive index above 1.7 from 600 to 1700 nm by adjusting the sulfur content. By incorporating tetraphenylethene (TPE) moieties into the polymer structure, the poly(O-thiocarbamate)s can also be designed as fluorescent sensors to detect harmful metal cation of Hg²⁺ in a turn-on mode with high sensitivity (LOD = 32 nM) and excellent selectivity (over interference cations of Pb²⁺, Au³⁺, Ag⁺). Different from the previous reports, the exact coordination structure is first identified by single-crystal X-ray diffraction, which is revealed in a tetracoordination fashion (two sulfur and two chloride) using a model coordination compound.

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.

Isocyanoacetate-Aldehyde Polymerization: A Facile Tool toward Functional Oxazoline-Containing Polymers

As an important nitrogen source, isocyanides have been involved in numerous organic reactions. As a result, many complicated compounds have been successfully synthesized through isocyanide chemistry. However, compared with its popular research in organic reactions, the application of isocyanides in polymerization is less investigated. In this work, a new polymerization based on isocyanide monomers is established. By simply mixing diisocyanoacetates and dialdehydes in the presence of a catalytic system of CuCl/PPh₃ /organobase in dichloromethane at room temperature readily produces soluble and thermally stable oxazoline-containing polymers with moderate weight-averaged molecular weights (M_w up to 11 200) in excellent yields (up to 97%) after 6 h. Furthermore, introducing the tetraphenylethene moiety into the main chains endows the resultant polymers with aggregation-induced emission, which can function as fluorescent probes for Fe³⁺ ion detection with high sensitivity and selectivity. This work not only enriches the family of isocyanide-based polymerizations but also provides an efficient tool for the preparation of functional heterocycle-containing polymers.

Organobase-catalysed hydroxyl–yne click polymerization

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

Preparation of hyperbranched polymers by oxa-Michael addition polymerization

Hyperbranched polymers with high molecular weights were synthesized by t-BuP₂-catalyzed oxa-Michael addition polymerization of trifunctional hydroxyl and diacrylate monomers.

Palladium/Benzoic Acid-Catalyzed Regio- and Stereoselective Polymerization of Internal Diynes and Diols through C(sp3)-H Activation

The C-H activation has been a hot research area in organic chemistry, and the most difficult one is the C(sp³)-H activation. Although the C-H activation has been introduced to the research of synthetic polymer chemistry, the polymerization developed based on C(sp³)-H activation is rarely reported, which will enrich the tools for the preparation of functional polymers. In this work, palladium/benzoic acid catalyzed polymerization of internal diynes and diols through C(sp³)-H activation was successfully established. Regio- and stereoregular functional poly(allylic ether)s with 100% E-isomers and high weight average molecular weights (M_w up to 33200) were prepared in excellent yield (98%). The reaction mechanism was unveiled with the assistance of density functional theory calculations. Furthermore, the thin films of polymers display high refractive indices and low optical dispersions. The polymer containing tetraphenylethene moiety displays the aggregation-enhanced emission feature and could be used to generate 2D fluorescent photopattern. Thus, this work not only establishes a powerful polymerization based on C(sp³)-H activation, but also furnishes functional polymers for diverse applications.

Multicomponent Polymerizations of Alkynes, Sulfonyl Azides, and 2-Hydroxybenzonitrile/2-Aminobenzonitrile toward Multifunctional Iminocoumarin/Quinoline-Containing Poly(N-sulfonylimine)s

Multicomponent polymerizations (MCPs) provide a powerful synthetic tool for the construction of polymers with complex structures and multifunctionalities, owing to their great structural diversity, mild condition, high efficiency, simple procedure, and environmental benefit. They possess significant advantages in synthesizing heteroatom-rich or heterocycle-containing functional polymers through directly constructing fused heterocycles from the MCP. In this work, the MCPs of diynes, disulfonyl azides, and 2-hydroxybenzonitrile or 2-aminobenzonitrile were reported under the catalysis of CuCl and Et₃N, generating iminocoumarin/quinoline-containing poly(N-sulfonylimine)s with high molecular weights (up to 37700 g/mol) and high yields (up to 96%). The MCPs enjoy a wide monomer scope and high atom economy, releasing N₂ as the only byproduct. The fluorescent poly(N-sulfonylimine) can be utilized for sensitive and selective detection of Ru³⁺, which also possesses antibacterial properties. The efficient MCPs could produce polymers with unique structures and functionalities, thereby accelerating the development of polymer materials.

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.

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.

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.

Room temperature multicomponent polymerizations of alkynes, sulfonyl azides, and N-protected isatins toward oxindole-containing poly(N-acylsulfonamide)s

The development of a new polymerization methodology affords polymer materials with new structures and functionalities.

Phosphazene-catalyzed oxa-Michael addition click polymerization

This paper reports a new type of click chemistry via a phosphazene bases-catalyzed oxa-Michael addition of an alcohol to an acrylate.