Thiol-ene Click Reaction Research Articles

Room-temperature fast-curing polybenzoxazine hybrid thermosets via UV irradiation

Room-temperature fast-curing polybenzoxazine hybrid thermosets were synthesized by crosslinking allyl-containing benzoxazine oligomer (O-ABZ) and thiol-containing siloxane oligomer (O-TS) under UV irradiation via thiol-ene click reaction. The O-ABZ was synthesized through the thermally-activated ring-opening polymerization of mono-functional benzoxazine (ABZ) obtained via Mannich reaction of the p-cresol, allylamine, and paraformaldehyde. The O-TS was synthesized by the co-hydrolysis and condensation of 3-mercaptopropylmethyldimethoxysilane with dimethyldimethoxysilane. The structures and molecular weights of O-ABZ and O-TS were characterized by FT-IR, 1H NMR, and SEC. The kinetics of thiol-ene click reaction were studied by FT-IR spectroscopy. The results showed that the curing reaction of polybenzoxazine/polysiloxane hybrid resin proceeded rapidly at room temperature under UV irradiation. The conversions of thiol and allyl groups were 56.6% and 58.3% in the first 30 s, respectively. Nearly complete curing was obtained after 3 min of UV irradiation. Meanwhile, the gel contents of the resulting resin were greater than 95%. On the other hand, the crosslinking density of the hybrids could be tuned by adjusting the thiol content of the siloxane oligomers. Their physical states transformed from rubber to plastic.

Ultrafine and well-dispersed Pd-Ni bimetallic catalyst stabilized by dendrimer-grafted magnetic graphene oxide for selective reduction of toxic nitroarenes under mild conditions

A facile and efficient strategy is introduced for growing a dendrimer structure on the surface of magnetic graphene oxide by using thiol-ene click reaction. The as-synthesized dendrimer-grafted magnetic graphene oxide was used as a suitable support for bimetallic Pd-Ni nanoparticles. The prepared nanocomposite was utilized for the reduction of toxic nitroarenes to aminoarenes by using sodium borohydride in aqueous medium at room temperature. Various nitroarenes with functional groups like nitrile, halogen, carbonyl, hydroxyl, acid, and heterocycles were converted to their corresponding anilines with good to excellent yields. The enhanced performance of the catalyst could be attributed to the synergistic effect between Ni and Pd which causes the reaction to proceed more efficiently. Moreover, the catalyst could be readily isolated from the reaction mixture by utilizing an external magnet and reused till 5th cycles with marginal loss of activity.

Thiolene- and Polycaprolactone Methacrylate-Based Polymerized High Internal Phase Emulsion (PolyHIPE) Scaffolds for Tissue Engineering.

Highly porous emulsion templated polymers (PolyHIPEs) provide a number of potential advantages in the fabrication of scaffolds for tissue engineering and regenerative medicine. Porosity enables cell ingrowth and nutrient diffusion within, as well as waste removal from, the scaffold. The properties offered by emulsion templating alone include the provision of high interconnected porosity, and, in combination with additive manufacturing, the opportunity to introduce controlled multiscale porosity to complex or custom structures. However, the majority of monomer systems reported for PolyHIPE preparation are unsuitable for clinical applications as they are nondegradable. Thiol-ene chemistry is a promising route to produce biodegradable photocurable PolyHIPEs for the fabrication of scaffolds using conventional or additive manufacturing methods; however, relatively little research has been reported on this approach. This study reports the groundwork to fabricate thiol- and polycaprolactone (PCL)-based PolyHIPE materials via a photoinitiated thiolene click reaction. Two different formulations, either three-arm PCL methacrylate (3PCLMA) or four-arm PCL methacrylate (4PCLMA) moieties, were used in the PolyHIPE formulation. Biocompatibility of the PolyHIPEs was investigated using human dermal fibroblasts (HDFs) and human osteosarcoma cell line (MG-63) by DNA quantification assay, and developed PolyHIPEs were shown to be capable of supporting cell attachment and viability.

Bio-based self-healing coating material derived from renewable castor oil and multifunctional alamine

Bio-based self-healing coating materials have attracted considerable interest owing to the advantages of extended life cycle, renewable raw materials, and performance comparable to petroleum-based coatings. A bio-based self-healing coating material was prepared using multifunctional alamine and bio-based modified acetoacetylated castor oil (MACO) containing acetoacetate moieties as well as acid groups. The MACO was synthesized using a transesterification reaction and thiol-ene click reaction (allowing control of the ratio of acid groups). Based on the different ratios of acid groups of MACO, three coating materials were prepared from an amine-acetoacetate reaction (or amine-carboxylic acid condensation reaction) using multifunctional alamine. The Young’s modulus, crosslinking density (ve), and glass transition temperature (Tg) of our prepared coating materials were improved with higher ratio of acid groups from the MACO. Hence, the ratio of acid groups in the bio-based coating can be employed to readily adjust the mechanical properties. For the bio-based coating of a representative film containing 50 % acid groups of -C = C in castor oil, the elongation strength and tensile strength were as high as 52 % and 5.53 MPa, respectively. The stress-relaxation and mechanical performance recovery experiments revealed that the film had a low activation energy (Ea) of 69 kJ/mol, and a self-healing efficiency of 80 % at 120 °C for 6 h. These results showed that the bio-based self-healing coating material exhibits good self-healing performance.

Fabrication of highly crosslinked and monodispersed silicon-containing polymeric microspheres via photo-initiated polymerization and their application in capillary liquid chromatography

Although inorganic silica-based and polymeric micron-sized spheres have widely been explored as column packing materials in high performance liquid chromatography (HPLC), they are still suffering the problems of either alkali corrosion of silica or polymer swelling. It is still necessary to search simple approaches for fabrication of monodisperse micron-sized hybrid particles as packing materials in HPLC. A novel kind of silicon-containing polyacrylate microspheres was designed and fabricated via two-step swelling and photo-initiated polymerization approach using 3-(allylpropylsilane) propyl acrylate (TAPA) containing both acrylate and vinyl groups and trimethylolpropane triacrylate (TRIM) as precursors. After carefully optimizing the fabrication conditions, the monodisperse micron-sized microspheres could be acquired as chromatographic packing, exhibiting excellent mechanical stability and reproducibility. Due to existence of electron-rich vinyl groups, three kinds of thiols such as octadecanethiol (ODT), dithiothreitol (DTT) and trimethylolpropane tris(3-mercaptopropionate) (TTMP) were facilely anchored onto the surface of microsphere via photo-initiated thiol-ene click reaction. They were applied in the separation of small molecules by cLC-UV and complex biosamples by cLC-MS/MS. A total of 6691 unique peptides from 1771 unique proteins was identified by ODT-modified microsphere, which was higher than those by unmodified and DTT/TTMP-modified poly(TAPA-co-TRIM) microspheres. It was expected this kind of hybrid microspheres can be further modified and widely applied in chromatographic field, offering great potential in commercialization.

Design of self-cleaning molecularly imprinted membrane with antibacterial ability for high-selectively separation of ribavirin

Powerful drivers exist for the exploitation of high natural life materials to selectively separate valuable substances or pollutants. Molecularly imprinted membranes (MIMs) possessing high selectivity and stability are highly desirable. Carefully designed Ribavirin (RBV)-imprinted membranes (RBVMIMs) with remarkable self-cleaning ability as well as anti-fouling and antibacterial surfaces enable selective separation of RBV from industrial effluent produced by the RBV process. (i) Self-cleaning ability was achieved by the photo-Fenton catalytic activity of RBVMIMs based on Fe2O3 nanoparticles. (ii) Anti-fouling and antibacterial performance were provided by a multifunction hybrid coating of polydopamine (pDA)-quaternary ammonium compounds (QAC). (iii) Satisfactory selectivity was stemmed from the uniform presence of RBV-imprinted sites which synthesized by “thiol-ene click reaction” on the membrane surface. Nfioteworthily, the employment of two functional monomers (methacrylic acid and acrylamide) synergistically promoted selective recognition of RBV-imprinted sites. The results indicated that satisfactory rebinding selectivity (αRBV/ACV = 9.87, αRBV/AZT = 9.21, αRBV/LAM = 6.63 and αRBV/G = 13.59) and permselectivity (βAZT/RBV = 11.361, βLAM/RBV = 12.518, βACV/RBV = 30.918 and βG/RBV = 18.732) with negligible permselectivity fluctuation (<10%) of RBVMIMs suggested the potential of RBVMIMs in practical applications, which was further confirmed by superior performance in semi-practical experiments. Importantly, the development and modification strategies developed in this work not only guided selective separation of valuable constituents from complex environments but also provided the reference for the development of membrane with high natural life.

Cross-linking fluorene copolymers via thiol-ene click chemistry

A series of 9,9-bis(allyl)fluorene copolymers (PFAF) with allyl groups on the side chain were synthesized by Suzuki coupling reaction. The cross-linked fluorene copolymers were realized via thiol-ene click reaction between allyl groups and thiol groups from crosslinker under ultraviolet light. Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV), UV–Vis absorption spectroscopy and photoluminescence spectroscopy (PL) were used to investigate the crosslinking efficiency of the thiol-ene click reaction and the impacts of crosslinking on the performances of fluorene copolymers. The results showed that allyl fluorene copolymers with high molecular weight and different content of 9,9-bis(allyl) fluorene units were successfully synthesized. Fluorene copolymers containing allyl fluorene structural units can be effectively crosslinked by the thiol-ene click reaction. The crosslinking conditions and the factors which influence the crosslinking were investigated in detail. The fluorene copolymer films which were composed of a fluorene copolymer with 10 mol% allyl fluorene structural units (PF10AF) and 39 wt% pentaerythritol tetra(3-mercaptopropionate) (PETMP) can be crosslinked to 85% crosslinking degree under irradiation of 1.8 mW/cm2 LED UV light at 390 nm for 50 s in air. It was found that the thiol-ene click cross-linking had little effects on the photoluminescence spectra of the fluorene copolymers. The thiol-ene click crosslinking showed a much faster crosslinking rate and higher crosslinking efficiency for fluorene copolymers than those of conventional free radical polymerization crosslinking. The results of this study provide a feasible method for cross-linking conjugated polymers in various applications.

Exploiting styrene-maleic acid copolymer grafting chromatographic stationary phase materials for separation of membrane lipids

High performance liquid chromatography-mass spectrometry is one of the most commonly used strategies for lipid analysis. The development of versatile chromatographic stationary phases to meet the increasing demands for separation of complex lipids is very important. Styrene-maleic acid (SMA) copolymer is an amphiphilic polymer, which has been proven to have the ability to solubilize lipid molecules of various structures. In this study, styrene-maleic anhydride copolymer coated silica was first prepared by the thiol-ene click reaction. With l-cysteine hydrochloride or dodecanol as the post-modification reagents, Sil-SMA-amino acid and Sil-SMA-dodecanol stationary phase materials were further successfully fabricated via nucleophilic ring-opening reaction. The Fourier-transform infrared, thermogravimetric analysis, and elemental analysis results confirmed the two stationary phase materials were successfully prepared. Furthermore, both the Sil-SMA-dodecanol column and the Sil-SMA-amino acid column possessed reversed-phase/hydrophilic interaction/ion exchange mixed-mode retention mechanisms. The column efficiency of the Sil-SMA-derivatives columns reached 77,300 N/m. Based on the mixed-mode retention characteristics, the Sil-SMA-derivatives columns achieved both the lipid classes and species separation via a single column. The Sil-SMA-amino acid column was further successfully used to separate lipid extract from gastric cancer cell membrane. All these results demonstrated that the SMA-based stationary phase materials have a good potential for use in lipid separation.

Injectable Micelle-Incorporated Hydrogels for the Localized Chemo-Immunotherapy of Breast Tumors.

Although immune checkpoint blockade (ICB) holds potential for the treatment of various tumors, a considerable proportion of patients show a limited response to ICB therapy due to the low immunogenicity of a variety of tumors. It has been shown that some chemotherapeutics can turn low-immunogenic tumors into immunogenic phenotypes by inducing a cascade of immune responses. In this paper, we synthesized an injectable micelle-incorporated hydrogel, which was able to sequentially release the chemotherapeutic gemcitabine (GEM) and the hydrophobic indoleamine 2, 3-dioxygenase inhibitor, d-1-methyltryptophan (d-1MT) at tumor sites. The hydrogel was formed via the thiol-ene click reaction between the thiolated chondroitin sulfate and the micelle formed by amphiphilic methacrylated Pluronic F127, in which hydrophobic d-1MT was encapsulated in the core of the F127 micelles and the hydrophilic GEM was dispersed in the hydrogel network. The successive release of chemotherapeutics and immune checkpoint inhibitors at tumor tissues will first promote the infiltration of cytotoxic T lymphocytes and subsequently induce a robust antitumor immune response, ultimately exerting a synergetic therapeutic efficacy. In a 4T1 tumor-bearing mice model, our results showed that the combination of chemotherapy and immunotherapy through the micelle-incorporated hydrogel triggered an effective antitumor immune response and inhibited tumor metastasis to the lung. Our results highlight the potential of the injectable micelle-incorporated hydrogel for the localized chemo-immunotherapy in the treatment of breast tumors.

In situ implantation of cross-linked functional POSS blocks in Nafion® for high performance direct methanol fuel cells

Polyhedral oligomeric silsesquioxane (POSS) has attracted increasing attention because of its organic/inorganic, nanosize, easily functional nature, especially in the applications of direct methanol fuel cells (DMFCs). In this work, we have successfully synthesized a novel bifunctional POSS (Vi-POSS-SO3Na) with vinyl and sulfonic acid groups by thiol-ene click reaction. Vi-POSS-SO3Na was introduced into Nafion® matrix and cross-linked by in-situ simply thermal treatment. The implantation of the bifunctional POSS filler gives significant improvements in the performance of such proton exchange membranes (PEMs). The cross-linked hybrid membrane with 12 wt% of Vi-POSS-SO3Na (X-Nafion@POSS-12) has a high proton conductivity (121 mS cm−1) at 80 °C, excellent dimensional stability and the lowest methanol permeability (5.4 × 10−8 cm2 s−1). The highest power density of the DMFCs was obtained by using the X-Nafion@POSS-12 as PEM in DMFC at 80 °C, and its value (34.93 mW cm−2) is twice higher than that of Nafion 212 membrane (14.90 mW cm−2). The novel in-situ fabrication method gives a simple and potential approach for the preparation of PEMs used in DMFCs.

Nonflammable highly-fluorinated polymer electrolytes with enhanced interfacial compatibility for dendrite-free lithium metal batteries

Conventional liquid electrolytes applied in lithium-ion batteries suffer from high flammability, lithium dendrites and leakage. Gel polymer electrolytes (GPEs) are promising alternative electrolytes owing to their high ionic conductivities and enhanced safeties. Nevertheless, the flammable plasticizers of GPEs still bring safety hazards for the batteries. To address these issues, nonflammable highly-fluorinated quasi-solid-state polymer electrolytes (ED@PVDF) with ultrahigh ionic conductivities, excellent flame-retardant properties and superior cycling stability are developed. ED@PVDF possesses three-dimensional polymeric network within the framework of electrospun PVDF fibers, which is fabricated by thiol-ene click reaction. Highly-fluorinated carbonates (fluoroethylene carbonate and methyl 2,2,2-trifluoroethyl carbonate) are employed as plasticizers for ED@PVDF to improve flame-retardant property and enhance compatibility with anodes. Nonflammable ED@PVDF exhibits remarkable flame resistance, the highest ionic conductivity (4.41 mS cm−1 at 30 °C) among the nonflammable polymer electrolytes and wide electrochemical windows (5.6 V). ED@PVDF can promote the generation of LiF-rich solid electrolyte interphase and effectively restrain dendrite growth on Li metal anodes. ED@PVDF endows LiFePO4 cells with outstanding rate capability (specific capacity of 123.8 mAh g−1 at 5C rate) and superior cycling stability (capacity retention of 81.4% over 1000 cycles).

Novel eugenol-based allyl-terminated precursors and their bio-based polymer networks through thiol-ene click reaction

The design of biobased allyl-terminated precursors with high renewable carbon content for the construction of the thiol-ene polymer networks is essential for sustainable development and green society. In this work, a series of allyl-terminated precursors were synthesized from renewable eugenol and aliphatic diols through a two-step procedure. Then, the alternating aliphatic-aromatic thiol-ene polymer networks with tunable flexibility, thermal and mechanical properties were constructed via solvent-free thiol-ene click photopolymerization. The results showed that the thermal-physical and mechanical properties of the resulting polymers improved with the decrease of the carbon length of the aliphatic diols and the increase of thiol functionality. The thiol-ene polymers exhibited high tensile strength of 22.12 MPa and elongation at break of 126 %. All the polymer networks are thermally stable without obvious weight loss (T5%) up to 270 °C. All the polymers exhibited excellent solvent resistance in alkaline solution, acid solution natural solution brine, water and ethanol solvent. This work successfully provided a facile and simple method to develop biobased ally compounds from eugenol and high-performance polymer networks with tunable performance.

Degradable cationic polyesters via ring-opening copolymerization of valerolactones as nanocarriers for the gene delivery

The development of cationic polymers as non-viral gene vectors has been hurdled by their high toxicity, thus degradable and biocompatible polymers are urgently demanded. Herein, five polyesters (B3a-B3e) were synthesized based on the ring-opening copolymerization between α-allyl-δ-valerolactone and δ-valerolactone derivatives decorated with alkyl or alkoxyl chains of different lengths, followed by the modification with 1,5,9-triazacyclododecyl ([12]aneN3) through thiol-ene click reactions. The five polyesters effectively condensed DNA into nanoparticles. Of them, B3a with a shorter alkyl chain and B3d with more positive charged units showed stronger DNA condensing performance and can completely retard the migration of DNA at N/P = 1.6 in the presence of DOPE. B3b/DOPE with a longer alkyl chain exhibited the highest transfection efficiency in HeLa cells with 1.8 times of 25 kDa PEI, while B3d/DOPE with more positive charged units exhibited highest transfection efficiency in A549 cells with 2.3 times of 25 kDa PEI. B3b/DOPE and B3d/DOPE successfully delivered pEGFP into zebrafish, which was superior to 25 kDa PEI (1.5 folds and 1.1 folds, respectively). The cytotoxicity measurements proved that the biocompatibility of these polyesters was better than 25 kDa PEI, due to their degradable property in acid environment. The results indicated that these cationic polyesters can be developed as potential non-viral gene vectors for DNA delivery.

Two-component waterborne polyurethane modified with terpene derivative-based polysiloxane for coatings via a thiol-ene click reaction

Waterborne polyurethane has gradually become a focus among researchers due to its low volatile organic emissions and low pollution. However, some problems exist with waterborne polyurethane, such as poor mechanical properties, obvious hydrophilicity and poor heat resistance. Herein, a terpene-modified polysiloxane-based polyurethane was designed to solve the abovementioned problems. 3-Mercaptopropylmethyldimethoxysilane and octamethylcyclotetrasiloxane were used as raw materials to prepare hydroxyl-terminated polysiloxane (PMMS). As a derivative of camphene, biomass resources, isobornyl acrylate was grafted to the prepared polysiloxane side chain through the thiol-ene click reaction under ultraviolet light irradiation conditions. Terpene-based polysiloxane (PMMS-I) was used as one of the polyol components to modify two-component waterborne polyurethane. Due to the combination of low surface energy polysiloxane and a hydrophobic terpene derivative, the hydrophobicity of the modified waterborne polyurethane was significantly improved, where the static water contact angle was increased from 70.7 ° to 101.2 ° and the water absorption was reduced from 16.0% to 6.9%. In addition, because of the unique rigidity of the terpene ring, the tensile strength of the modified polyurethane was significantly improved from 4.70 MPa to 8.82 MPa. In addition, the thermogravimetric analysis results showed that the thermal stability of the modified polyurethane was ameliorated. In terms of improving the properties of polymer materials, terpene bio-based compounds have broad potential.

Anodic reduction of electrodeposited polymethacrylates containing pendent sulfones

Anionic polymerization of a non-conjugated polar alkene, allyl methacrylate (AMA) was initiated by tert-BuLi (t-BuLi) in toluene at −20 °C for 2 h in the presence of a bulky aluminum Lewis acid, methylaluminum bis(2,6-di-tert-butyl-4-methylphenoxide) (MAD). Quantitative monomer consumption was confirmed and >99% of the expected poly(AMA) was obtained after reprecipitation using chloroform and methanol as good and poor solvents, respectively [Mn of 12.2 × 103 -21.6 × 103with a molecular dispersity index (Mw/Mn = 1.70-1.83)]. A thiol-ene click reaction of the pendent ally groups with 1-butanethiol and subsequent Oxone-oxidation gave the poly(AMA) with pendent ternary units of sulfone, sulfoxide, and sulfide [Mn of 11.3 × 103 -26.0 × 103 with a molecular dispersity index (Mw/Mn = 1.43-1.79)]. Electrophoretic deposition (EPD) was performed as detailed in our previous report dealing with electrophoretic sulfone-containing non-ionic polymers, using a dispersion consisting of tetrahydrofuran (THF) and methanol (1/50, v/v). As we expected, the obtained poly(AMA) derivatives were deposited on an iron plate. However, 1H NMR results surprisingly supported the simultaneous reduction of the pendent sulfone to sulfide after the deposition, which indicated that anodic reduction of sulfone-containing electrophoretic polymer had been demonstrated without the need for expensive commercially available reagents.

Preparation of bactericidal PDMS surfaces by benzophenone photo-initiated grafting of polynorbornenes functionalized with quaternary phosphonium or pyridinium groups

Cationic ROMP-polymers bearing ammonium or phosphonium groups were photo-grafted onto a PDMS surface via the thiol-ene click reaction, in the presence of benzophenone. The PDMS surface was first thiolated using pentaerythritol tetrakis (3-mercaptopropionate) (PTTMP) under UV, in the presence of benzophenone. The obtained cationic surfaces exhibited charge densities above 1014 charge/cm2 and a higher degree of hydrophilicity compared to non-grafted surfaces. The live and dead tests performed by fluorescence microscopy revealed an effective contact bactericidal effect of these surfaces against Escherichia coli and Staphylococcus epidermidis.

Controllable organosilane monolayer density of surface bonding using silatranes for thiol functionalization of silica particles for liquid chromatography and validation of microanalytical method for elemental composition determination

The present work systematically investigates a new strategy for the functionalization of silica gel using alkyl silatrane chemistry instead of alkylsilanes for synthesis of chromatographic stationary phases. In this work, silica was chemically modified for further functionalization by a thiol-ene click reaction. Thus, 3-mercaptopropylsilatrane (MPS) was used which is capable to form self-assembled monolayers (SAM) on top of silanol surfaces in a controlled manner as previously shown for silicon wafers. The utility of this chemistry for stationary phase synthesis in liquid chromatography was not evaluated yet. Hence, silica surface modifications using MPS were studied in comparison to established 3-mercaptopropyltrimethoxysilane (MPTMS) chemistry. First, the employed elemental analysis method was validated and it showed excellent intra-day and inter-day precisions (typically less than 5% RSD). It could be shown that the reaction kinetics of MPS was roughly 35-times faster than with MPTMS. After 30 min reaction time with MPS, the thiol content reached 74% of the maximal coverage. Due to controlled chemistry with MPS, which does not lead to oligomeric siloxane network at the silica surface, the ligand coverage was lower. However, multiple silanization cycles with MPS led to a dense surface coverage (around 4 µmol m−2). 29Si cross polarization/magic angle spinning (CP/MAS) solid-state NMR revealed distinct T1/T2/T3 ratios for MPS and MPTMS materials with up to 80% T3 (indicative for trifunctional siloxane linkage) for MPS and around 20% T3 for MPTMS. This indicates a more homogeneous, thinner monolayer film of MPS on the silica surface, as compared to an irregular thick oligomeric siloxane network with MPTMS. Bonding of quinine carbamate as chiral selector afforded an efficient chiral stationary phase (CSP) for chromatographic enantiomer separation. Separation factors were comparable to MPTMS-bonded CSP, however, chromatographic efficiency was much better for the MPS-bonded CSP. H/u curves indicated a reduced mass transfer resistance by roughly factor 3 for MPS- compared to MPTMS-bonded CSP. This confirms better chromatographic performance of surfaces with homogeneous monolayer compared to network structures on the silica surface which suffer from poor stationary phase mass transfer.

Fabrication of Two-Dimensional Functional Covalent Organic Frameworks via the Thiol-Ene "Click" Reaction as Lubricant Additives for Antiwear and Friction Reduction.

To address the energy wastage problem caused by friction, novel lubricant additives other than the traditional and basic used additives with outstanding performance are urgently needed. A facile and efficient postsynthetic strategy for modification of two-dimensional (2D) covalent organic frameworks (COFs) was proposed to obtain dialkyl dithiophosphate (DDP)-functionalized COFs (DDP@TD-COF) as lubricant additives. The DDP@TD-COF was prepared by amine-aldehyde condensation reaction of the triazine compound and vinyl-functionalized monomers through a solvothermal process to form a vinyl-functionalized 2D COF (TD-COF), followed by covalent bonding of commercial lubricating molecules (DDP) via the UV-induced thiol-ene "click" reaction. The as-obtained DDP@TD-COF with homogeneous distribution of N, P, and S elements exhibits exceptional dispersion stability in the 500SN base oil, which remains stable for over 6 days. With a trace amount addition of 0.05 wt %, superior friction and wear reduction of DDP@TD-COF are observed with the friction coefficient lessened to 0.096 from 0.19, wear volume loss declined by 94.9%, and load carrying ability increased from 150 to 650 N simultaneously. The mechanism studies show that the shear force can induce interlayer slipping during the friction process, and the stripped DDP@TD-COF can get involved in the contacting interface inducing tribo-chemical reactions via N, P, and S elements forming a protective layer on the surfaces. Consequently, the DDP@TD-COF demonstrated remarkable friction diminution and abrasion resistance abilities even with a trace amount addition, and this work provides a dependable and valid route for the design and preparation of functional COF-based nanoadditives.

Covalent-bond-forming method to reinforce rubber with cellulose nanocrystal based on the thiol-ene click reaction

Cellulose nanocrystals (CNCs) have been widely used in reinforcing polymers due to their excellent mechanical properties, whereas the poor compatibility between CNCs and hydrophobic rubber matrices limits their applications in elastomers and flexible devices. Moreover, hydrophobically modified CNCs cannot offer enough increment in mechanical properties because it lowers the interaction related to CNC. We thus introduced thiol-functionalized CNCs (mCNCs) into a nitrile butadiene rubber (NBR) matrix to form covalent linkage between CNC and NBR via thiol-ene click reaction, which was fast, simple, byproduct-little, and controllable. The results from element analysis and Fourier transform infrared spectroscopy showed the thiol substitution degree could be controlled from 0.33% to 0.98%. The obtained nanocomposites showed increased tensile strength (from 0.48 MPa to 2.28 MPa) and elongation at break (from 244% to 526%) as mCNC (0.98%) content increased. The increase in glass-transition temperature (from −30.01 °C to −22.73 °C) proved that the interaction between CNC and NBR was much higher than the interaction between NBR polymer chains. The result also indicated that the increment in mechanical properties was proportional to the thiol substitution degree. This highly efficient method is environmentally friendly and renewable, which can also be used for reinforcing other rubbers.

Lower Critical Solution Temperature Phase Transition of Poly(PEGMA) Hydrogel Thin Films.

Surface-attached hydrogel films with well-controlled chemistry are a new approach of polymer thin layers and an actual alternative to polymer brushes and layer-by-layer assemblies. The advantage is that the thickness of hydrogel films can widely range from a few nanometers to several micrometers. Hydrogel films can also remarkably respond to stimuli such as temperature: (i) the thickness change is of great amplitude, fourfold and more, which could not be reached with the geometry of polymer brushes or layer-by-layer assemblies, (ii) the time response is very short (less than 1 s), and (iii) the swelling-to-collapse transition is narrow (a small temperature change of a few degrees may be enough). Poly(N-isopropylacrylamide) (PNIPAM) is the most temperature-responsive polymer investigated with a lower critical solution temperature (LCST) of around 32 °C. However, it is relevant to have the available polymers responding to various transition temperatures with the advantage of keeping the same chemistry. Poly[oligo(ethylene glycol) methacrylate] (PEGMA) meets these specifications since its transition temperature can be finely tuned with the number of oligo ethylene glycol units, while it attractively combines biocompatibility with PEG side chains. Here, we report the synthesis and the temperature-responsive properties of poly(PEGMA) hydrogel thin films. We used a simple, versatile, and well-controlled approach through thiol-ene click reaction, the so-called cross-linking and grafting, to synthesize surface-attached poly(PEGMA) hydrogel films with various thickness. We show that the transition temperature of poly(PEGMA) hydrogel films ranges from 15 to 60 °C if the number of PEG units is from 2 to 5. This transition temperature can also be finely adjusted for hydrogel films containing copolymers or mixing homopolymers of PEGMA with a suitable ratio. Moreover, the LCST properties, swelling-to-collapse amplitude and transition temperature, are not sensitive to salt. In particular, there is no effect on the LCST properties of surface-attached poly(PEGMA) hydrogel films in phosphate saline buffer, which is promising for applications in biology such as injectable hydrogels, drug delivery systems, hydrogel-based microfluidic valves, and flow switches for biotechnologies.