UV-initiated Thiol-ene Click Reaction Research Articles

UV-Curable Optical-Silicone-Modified Coatings Prepared from CO2-Based Non-Isocyanate Polyurethane Diol

Though polyurethanes (PUs) are widely used in people’s daily lives, traditional PUs are generally fabricated from toxic (poly)isocyanates. Furthermore, (poly)isocyanates are commonly industrially prepared from a seriously toxic and injurious chemical compound named phosgene, which is a dangerous gas that can cause lung irritation and eventually death. As is known to all, the consumption of carbon dioxide (CO2)-based raw materials in chemical reactions and productions will be conducive to reducing the greenhouse effect. In this paper, non-isocyanate polyurethane (NIPU) diol was fabricated through a polyaddition reaction from ethylenediamine and CO2-based ethylene carbonate, and then NIPU-based silicone-containing thiol hyperbranched polymers (NIPU-SiHPs) were synthesized from the NIPU diol. Finally, UV-curable optical-silicone-modified CO2-based coatings (UV-NIPUs) were fabricated from NIPU-SiHPs and pentaerythritol triacrylate by a UV-initiated thiol-ene click reaction without a UV initiator. The UV-NIPUs demonstrated high transparency over 90% (400–800 nm), good mechanical performance with tensile strength reaching 3.49 MPa, superior thermal stability with an initial decomposition temperature (Td5) in the range of 239.7–265.6 °C, moderate hydrophilicity with a water contact angle in the range of 42.6–62.1°, a high pencil hardness in the range of 5–9H, and good adhesive performance of grade 0. The results indicate that it is a promising green chemical strategy to fabricate CO2-based high-performance materials.

UV-curable Schiff base-containing polymeric adsorbent for selective and efficient removal of Au(III) from aqueous solutions

UV-curable Schiff base-containing polymeric adsorbent for selective and efficient removal of Au(III) from aqueous solutions

Fabrication and performance of UV–curable Schiff base–containing antibacterial silicone modified materials

There are numerous noxious bacteria, fungi and parasites in environment for human survival, so antibacterial materials are significant for medical devices, food packaging, and personal care. UV–curable silicone modified antibacterial materials were prepared from Schiff base–containing silicone modified hyperbranched thiol and castor oil based polyurethane acrylates (PUAs) by UV initiated thiol–ene click reaction. It exhibited that these UV–curable materials show fairly good antimicrobial activity of Escherichia coli ( E. coli ) and Neurospora crassa. A contact–kill antibacterial mechanism was proposed according to the antibacterial behavior of these UV–curable materials. These materials also exhibit a fairly high transparency over 92 % and pencil hardness can reach 4H. It need to be pointed out that the surface water contact angle of these materials is in the range of 84.1°–74.7°, which means these materials exhibit a certain degree of hydrophilicity, which can overcome the shortcoming of traditional polydimethylsiloxane(PDMS) to some content. These UV–curable materials show quite good mechanical performance because the tensile strength of them can reach 11.6 MPa. It denotes that the UV–curable Schiff base–containing antibacterial silicone modified materials may be a good candidate of antibacterial materials. • UV–curable Schiff base–containing silicone modified materials exhibit fairly good antimicrobial activity follow a contact–kill antibacterial mechanism. • The materials show quite good mechanical performance with the tensile strength of 11.6 MPa. • The materials are with fairly high transparency over 92 %. • The materials have fairly high Pencil hardness of 4 H.

Preparation and performance of nitrogen–phosphorus–silicone-containing flame retardant UV–curable coatings with high transparency

UV-curable transparent silicone-modified flame retardant materials are highly desired because they usually serve as protecting polymer matrix from moisture, ionic contaminants and particulates in vast fields such as coatings, electronic devices attributed to their merits such as high flame-retardant efficiency, high curing efficiency and low volatile organic chemical emissions. In this paper, nitrogen–phosphorus–silicone-containing flame retardant UV-curable coatings were prepared from nitrogen–phosphorus–silicone-containing acrylate and thiol-containing silicone hyperbranched polymers by UV initiated thiol-ene click reaction. It shows that these coatings were with fairly high transmittance, pencil hardness and initial decomposition temperature (Td5) of 80.7–96.9 % (400–800 nm), 9H, and 159–185 °C, respectively. Vertical burning behavior of the UV-curable coatings prepared with different acrylate derivatives was investigated and the self-extinguish time for the coatings prepared from POPHA was about 9 s. To make clear of the flame retardant mechanism, cone calorimetric test and XPS spectra of UV-curable coatings, and SEM images for the surface morphology of the chars were carried out. SEM images of the chars show that there is fine and dense white SiO 2 “in-situ” generated during the course of combustion spreading on the surface. It also shows that honeycombed-like structures attributed by nitrogen and phosphorus form a quite good barrier to heat, oxygen and other flammable gas. Therefore, a ternary synergistic flame retardant mechanism of phosphorus, nitrogen and silicone elements in the UV-curable coatings was proposed. This work denotes that it is a good method to develop nitrogen–phosphorus–silicone-containing flame retardant transparent UV-curable materials. • Transparent coatings did not be ignited until they were exposed to fire for 12–13 s and the self-extinguish time was 2–5 s. • Transmittance, pencil hardness and initial decomposition temperature is 96 % (400–800 nm), 9H, and 159–185C, respectively. • A ternary synergistic flame retardant mechanism of phosphorus, nitrogen and silicone elements in the UV–curable coatings was proposed.

High specific surface area hybrid silica aerogel containing POSS

A UV-initiated thiol-ene click reaction was utilized to synthesize the multifunctional POSS-based silane coupling agent (OTS) from Octavinyl silsesquioxane (OVS) and 3-mercaptopropyltrimethoxysilane (MPTMS). Through supercritical drying, a series of hybrid aerogels with different OTS contents were successfully prepared by two-step sol-gel method using OTS and tetraethyl orthosilicate (TEOS) as the main precursors. In the formation of hybrid aerogels, the nucleation of OTS with flexible side chains had a significant effect on the size of the secondary particles and pore structure of aerogels. Compared with silica aerogels prepared from single TEOS, the hybrid aerogels had more uniform mesoporous and higher specific surface area. The result revealed all hybrid aerogels owned mesoporous structure (3–4 nm), low thermal conductivity (0.038–0.044 W m −1 K −1 ) and remarkable high specific surface area (945–1283 m 2 g −1 ). The outstanding properties made hybrid aerogels promising as adsorbents or thermal insulation materials. • A multifunctional POSS-based silane coupling agent (OTS) was successfully synthesized. • The addition of OTS with flexible side chains as nucleating agents had a significant effect on the pore structure of aerogels. • A series of hybrid silica aerogels with high specific surface area were successfully prepared, which the maximum reached to 1283 m 2 g −1 .

An Easy Fabrication Method to Prepare Inexpensive UV–Cured Transparent Silicone Modified Polyacrylate Coatings with Good Adhesion and UV Resistance

UV–curable polyacrylate is widely used in free–radical type UV–cure coating systems, the disadvantages of which including poor thermal stability and UV resistance can be overcome through chemical modification by silicone. However, it is a remarkable fact that the strategies for fabrication UV–cured silicone modified polyacrylates are somewhat complicated and the price of the products may be much expensive than pure UV–cured polyacrylates. In this work, an easy fabrication method to prepare inexpensive UV–cured transparent silicone modified polyacrylate coatings with good adhesion and UV resistance performance was developed from copolymers of acylates and thiol silicone resin by UV initiated thiol–ene click reaction without UV initiator. The striking results with a high application value should be emphasized that when the amount of thiol silicone resin is only one wt.% of the copolymer of acrylates, the UV–cured coatings obtained exhibit fairly good performance. These coatings prepared exhibit transparency higher than 96% (800 nm), adhesion property to glass slides can reach grade 0, pencil hardness can reach 6H, water absorption is less than 0.16%. In particular, it is observed obviously that the silicone modified polyacrylate coatings exhibit better UV resistance performance than the coating prepared with only copolymers of acrylates initiated by UV initiator 1173. It is proved that it is actually an easy fabrication method to prepare inexpensive UV–cured transparent silicone modified polyacrylate coatings with high performance by UV initiated thiol–ene click reaction of copolymers of acylates and thiol silicone resin.

Rapid Buildup Arrays with Orthogonal Biochemistry Gradients via Light-Induced Thiol-Ene "Click" Chemistry for High-Throughput Screening of Peptide Combinations.

The concept of high-throughput screening sheds new light on fabrication and analysis of materials. Herein, a combinatorial surface-modified platform with biochemical gradients was developed through thiol-ene "click" chemistry by adjusting the intensity of ultraviolet (UV) irradiation. Contact angle, X-ray photoelectron spectroscopy, and ellipsometry measurement results demonstrated that the sulfhydryl molecules including polyethylene glycol and RGD (arginine-glycine-aspartic acid) and REDV (arginine-glutamic acid-aspartic acid-valine) peptides can be directly attached onto alkene-modified substrates, in which the graft density can be well controlled by the intensity of UV irradiation. The multistep attachment of different molecules onto substrates is archived via the multistep UV-initiated thiol-ene "click" reaction. The high-throughput arrays with the gradient density of single ligand and the orthogonal gradient density of two ligands were rapidly fabricated via the one-step UV gradient irradiation and the two-step orthogonal UV gradient-initiated thiol-ene "click" reaction. Endothelial cells (ECs) and smooth muscle cells (SMCs) were cocultured on the array with the orthogonal gradient density of RGD and REDV to screen the peptide combination with high EC selectivity, which is essential for in situ endothelialization during stent implant. From 64, 8 × 8, combinations investigated, a special combinatorial surface representing the really high competitiveness of ECs over SMCs was screened. This platform puts forward a facile, high-throughput method to study the combinatorial variation of biochemical signals to cell behavior.

Highly Efficient Fluorescent Material Based on Rare-Earth-Modified Polyhydroxyalkanoates.

Fluorescent materials play an important role in biomedical fields. However, the main types of fluorescent materials suffer from several disadvantages especially the biotoxicity, which largely restrict its wider applications in biological fields. In this study, a highly efficient rare-earth-modified fluorescent material was successfully designed and fabricated based on polyhydroxyalkanoates, which are known as biodegradable and biocompatible materials. A new Functional-PHA polymer was microbially synthesized by engineered Halomonas bluephagenesis and was used as a basal matrix to generate the rare-earth-modified PHA. N-Acetyl-l-cysteine-grafted PHA (NAL-grafted-PHA) was first produced via a UV-initiated thiol-ene click reaction and the rare earth metal ions (Eu3+ and Tb3+) were subsequently chelated onto the NAL-grafted-PHA through the coordination effect. The composite material exhibited intense photoluminescence properties under UV laser excitation, indicating the excellent features as fluorescent material. The enhanced hydrophilicity and superior biocompatibility of rare-earth-chelated PHA were confirmed, suggesting its great potential application value in biomedical fields.

Hydrogels from norbornene-functionalized carboxymethyl cellulose using a UV-initiated thiol-ene click reaction

Chemically crosslinked cellulose hydrogels have wide applications in agriculture and biomedicine, but most crosslinking methods involve potentially toxic crosslinking chemistries or lack significant control over the final modulus of the material. To overcome these challenges, carboxymethyl cellulose (CMC) hydrogels were synthesized utilizing thiol-ene click chemistry. CMC was functionalized with norbornene groups through a base catalyzed, water-borne functionalization reaction with carbic anhydride, yielding a reactive norbornene group. Both reaction pH and anhydride concentration could be used to control the degree of norbornene functionalization of CMC up to 45% norbornene functionalization per CMC repeat unit. This new norbornene functionalized CMC (cCMC) was crosslinked though a UV-light initiated thiol-ene reaction with a 2,2′-(ethylenedioxy)diethanethiol (DEG) crosslinker. Both the ratio of thiols to norbornenes and the irradiation time could be varied at a constant polymer concentration to control the modulus over an order of magnitude. Interestingly, thiol to norbornene ratios of 1:2 and 1:1 yielded the same modulus values, which was attributed to the crosslinking limiting chain mobility early in the reaction and preventing increased crosslink density as the reaction progressed. Hydrolytic degradation of the hydrogels yielded two degradation regimes of initial burst release and continuous daily release. Burst release behavior was tied to the thiol to norbornene ratio used to fabricate the hydrogel, while the daily degradation rate could be correlated to the crosslinking density. Due to its straightforward synthesis and significant control over modulus and degradation rates, cCMC offers high utility for future applications where cellulose derived hydrogels are needed.

Thiol–Ene Synthesis of Cysteine-Functionalized Lignin for the Enhanced Adsorption of Cu(II) and Pb(II)

N-Acetyl-l-cysteine-functionalized lignin (CFL) was synthesized via UV-initiated thiol–ene click reaction. The structure and morphology of CFL were characterized by FT-IR, 1H NMR, and SEM. Influenc...

Influence of vinyl-terminated hyperbranched polyester on performance of films obtained by UV-initiated thiol–ene click reaction of A2 + B3 system

UV curing technology has become an efficient method to fabricate films with desirable properties, although it is susceptible to oxygen inhibition, resulting in low conversion of double bonds and poor mechanical performance. Thiol–ene click reaction can overcome the shortcomings of common UV curing techniques. In this paper, the vinyl-terminated hyperbranched polyester (VTDP) was incorporated into the curing system of di-ene (A2) and trithiol (B3). Trithiols, including 1,3,5-tris(2-hydroxyethyl)isocyanurate tris(3-mercaptopropionate) (THMP) and trimethylolpropane tris(3-mercaptopropionate) (TMMP), were synthesized by an esterification between 3-mercaptopropionic acid and 1,3,5-tris(2-hydroxyethyl) isocyanurate, and tri(hydroxymethyl)propane, respectively. The UV-initiated thiol–ene click reaction between 1,4-butanediol diacrylate (BDDA) and trithiols (TMMP and THMP) was researched by adjusting different VTDP content. FTIR spectral analysis showed that the thiol–ene reactions proceeded smoothly and the conversion degree of acrylic groups was higher than that of thiol groups. The pencil hardness and abrasion resistance of the cured film increased first and then decreased with the increase in VTDP content, but both their flexibility and adhesion had little change. Their glass transition temperatures increased slightly with the increase in VTDP content. THMP has better positive effect than TMMP on the pencil hardness, abrasion resistance and thermal performance of the cured film.

Highly efficient preparation of hyperbranched epoxy resins by UV-initiated thiol-ene click reaction

Hyperbranched epoxy resins (HEPs) attract an increasingly interest due to their remarkably reinforcing and toughening properties on thermoset. A major challenge for HEPs is the serious environmental pollution resulted from the large amount of organic solvents used during tedious synthetic procedure. Another challenge is low yield and low epoxy content of HEPs, resulting in low crosslinking density and impairing mechanical strength and compatibility with matrix. Here we report a fast and environmentally friendly approach to addressing these challenges using a UV-initiated thiol-ene click reaction. The new synthesis process has been used to prepare not only hyperbranched epoxides with high epoxy content, and also many kinds of glycidyl ether epoxy resins (mono-epoxide, di-epoxides, tri-epoxides) based on thiols precursors and allylglycidyl ether. Their chemical structures and molecular weights were characterized by FT-IR, 1H NMR, electrospray ionization mass spectrometry (ESI–MS) and GPC spectra. All the click reactions took only 5–10 min of UV radiation at room temperature and show very high yields between 98.1 and 99.8%, and epoxy equivalent weight of all the epoxy resins is very close to its theoretical value. This fast and environmentally friendly process may open a new avenue for the design and synthesis of HEPs as well as common epoxy resins.

Modification of microbial polymers by thiol-ene click reaction: Nanoparticle formation and drug encapsulation

Comb-like amphiphilic polymers were obtained by grafting long paraffinic chains on microbial poly(?,dl-glutamic acid) and poly(s,l-malic acid) through two steps, i.e. allylation of the carboxylic side groups followed by UV-initiated thiol-ene click reaction with 1-alkanethiols bearing 8, 12 and 16 carbon atoms, and their characterization was accomplished by 1H NMR, GPC and DSC. The grafted polymers were capable of self-assembling in nanoparticles with diameters in the 80–240 nm range. Incubation in water under physiological conditions led to hydrolysis of the lateral ester bonds followed by scission of the polyamide or polyester main chain. The model drugs, Theophylline and Carbamazepine, were efficiently encapsulated in these systems with much better results attained for the later. Drug release from nanoparticles incubated under physiological conditions occurred with a burst effect and were completely discharged in 24 h. Release profiles recorded from drug-loaded films suggested that the drug was delivered in both cases through a diffusion process.

Advanced functionalization of polyhydroxyalkanoate via the UV-initiated thiol-ene click reaction.

Polyhydroxyalkanoates (PHAs) incorporating vinyl-bearing 3-hydroxyalkanoates were prepared in 8.5-12.9gL(-1) yield. The molar ratios (0-16mol%) of the vinyl-bearing 3-hydroxyalkanoate derivatives were controlled by the continuous feeding of undecylenate at various concentrations. Subsequently, the PHAs were functionalized by UV-initiated thiol-ene click reaction and chemical modification. (1)H NMR spectra suggested that 3-mercaptopropionic acid and 2-aminoethanethiol were successfully introduced into the vinyl-bearing PHA. Subsequently, chemical modification using fluorescein or a fibronectin active fragment (GRGDS) was attempted. The former yielded a PHA derivative capable of emitting fluorescence under UV irradiation, which was useful for determining the miscibility of PHA in a composite film comprising poly-ʟ-lactic acid (PLLA) and PHA. In the latter case, PHA bearing GRGDS peptides exhibited cell adhesiveness, suggesting that its biocompatibility was improved upon peptide introduction. Taken together, the UV-initiated thiol-ene click reaction was demonstrated to be useful in PHA modification.

Preparation of stimuli-responsive hydrogel networks with threaded β-cyclodextrin end-capped chains via combination of controlled radical polymerization and click chemistry

Hydrogel networks of poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEG-b-PPG-b-PEG primary network), with threaded sliding β-cyclodextrin-capped poly(2-(methacryloyloxy)ethyl succinate) (βCD-capped-PMES) chains, are described. The hydrogels were prepared by UV-initiated thiol–ene click reaction of the PEG-b-PPG-b-PEG diacrylate polymer with a crosslink agent, pentaerythritol tetrakis(3-mercaptopropionate) (PETMP), in the presence of βCD end-capped chains, βCD-capped-PMES. The latter was prepared a priori by reversible addition–fragmentation chain transfer (RAFT) polymerization. Due to the controlled character of RAFT polymerization and the quantitative yield of thiol–ene click reaction, the as-synthesized PEG-b-PPG-b-PEG-thread-βCD-capped-PMES hydrogels have a well-defined PEG-b-PPG-b-PEG network and tunable PMES chain length. The length of PMES chains can be regulated by varying the molar ratio of 2-(methacryloyloxy)ethyl succinate (MES) monomer to RAFT agent. The molecular structures and thermal properties of the PEG-b-PPG-b-PEG-thread-βCD-capped-PMES hydrogels were studied by 1H NMR, XPS, TGA and DSC measurements. The polymer hydrogels with threaded sliding rings exhibit both pH- and temperature-dependent equilibrium swelling ratios in aqueous media and have potential applications as biomaterials and biomedical materials.

Functional poly(vinylidene fluoride) copolymer membranes via surface-initiated thiol–ene click reactions

Thermally induced graft copolymerization of allyl methacrylate (AMA) from ozone-preactivated poly(vinylidene fluoride) (PVDF) chains was first carried out in N-methyl-2-pyrrolidone (NMP) solution to produce the PVDF-g-PAMA copolymers. The PVDF-g-PAMA copolymers were cast, by phase inversion in an aqueous medium, into microporous membranes with enriched allyl groups on the membrane and pore surfaces. The pendant allyl groups in the PAMA side chains allowed the thiol–ene click grafting of thiol-functionalized moieties on the membrane surface. Thermally initiated thiol–ene click reaction with 3-mercaptopropionic acid (MPA) produced the PVDF-g-P[AMA-comb-MPA] membrane which exhibited a pH-responsive permeation behavior, with the most drastic change in permeation rate of the aqueous media being observed between pH 2 and 4. The PVDF-g-P[AMA-comb-DMAPS] membrane was synthesized via UV-initiated thiol–ene click reaction of 1,6-hexanedithiol (HDT) with the PVDF-g-PAMA membranes, using 2,2-dimethoxy-2-phenylacetophenone (DMPA) as the photoinitiator, followed by thiol-Michael addition reaction of the zwitterionic molecules, N,N′-dimethyl-(methylmethacryloyl ethyl) ammonium propanesulfonate (DMAPS). A significant reduction in microbial adhesion was observed on the PVDF-g-P[AMA-comb-DMAPS] membrane in a flow chamber, in comparison to the pristine hydrophobic PVDF membrane.