Thiol Ene Research Articles

Synthesis of Thiomorpholine via a Telescoped Photochemical Thiol-Ene/Cyclization Sequence in Continuous Flow.

A procedure for the continuous flow generation of thiomorpholine in a two-step telescoped format was developed. The key step was the photochemical thiol–ene reaction of cysteamine hydrochloride and vinyl chloride as low-cost starting materials. This reaction could be conducted under highly concentrated (4 M) conditions using a low amount (0.1–0.5 mol %) of 9-fluorenone as the photocatalyst, leading to the corresponding half-mustard intermediate in quantitative yield. Thiomorpholine was subsequently obtained by base-mediated cyclization. The robustness of the process was demonstrated by performing the reaction for 7 h (40 min overall residence time), isolating the desired thiomorpholine via distillation.

Polymerization of Myrcene in Both Conventional and Renewable Solvents: Postpolymerization Modification via Regioselective Photoinduced Thiol-Ene Chemistry for Use as Carbon Renewable Dispersants.

Polymeric dispersants are useful materials used in many different industries and often derived from oil-based chemicals, for example, in automotive fluids so as to prevent particulates from precipitation and causing potential damage. These are very often polyisobutene derivatives, and there is a growing need to replace these using chemicals using renewable resources such as the use of naturally occurring myrcene. Polymyrcene (PMy), with an ordered microstructure, has been successfully synthesized via both anionic and radical polymerization in different solvents and subsequently subjected to functionalization via photoinduced thiol–ene click reactions with a number of thiols, methyl thioglycolate, 3-mercaptopropionic acid, 3-mercapto-1-hexanol, 2-mercaptoethanol, and 1-thioglycerol, using 2,2-dimethoxy-2-phenylacetophenone as a photoinitiator under UV irradiation (λ = 365 nm) at ambient temperature. The polarity of the solvent has an important impact on the microstructure of the produced polymyrcene and, in particular, 1,2-unit (∼4%), 3,4-unit (∼41%), and 1,4-unit (∼51%) PMy were obtained via anionic polymerization in a polar solvent (THF) at ambient temperature, while 3,4-unit (∼6%) and 1,4-unit (∼94%, including cis and trans) PMy were obtained with cyclohexane as the solvent. Subsequently, photochemical thiol–ene reactions were carried out on the resulting PMy with different isomers exhibiting different reactivities of the double bonds. This strategy allows for the introduction of functional/polar groups (−COOH, −OH) into hydrophobic PMy in a controlled process. Hydrogenation of PMy and derivatized PMy was carried out to investigate any effects on the stabilities of the products which are desirable for many applications.

Thermally Stable, Solvent Resistant, and Multifunctional Thermosetting Polymer Networks with High Mechanical Properties Prepared from Renewable Plant Phenols via Thiol–Ene Photo Click Chemistry

Thermally Stable, Solvent Resistant, and Multifunctional Thermosetting Polymer Networks with High Mechanical Properties Prepared from Renewable Plant Phenols via Thiol–Ene Photo Click Chemistry

Synthetic Polypeptide–Polyester PolyHIPEs Prepared by Thiol–Ene Photopolymerization

Synthetic polypeptides and aliphatic polyesters represent promising materials in biomedical applications due to their degradability and biocompatibility. In this work, we investigated the preparation and properties of porous synthetic polypeptide–polyester materials prepared by thiol–ene photopolymerization of allyl-functionalized star macromonomers based on poly(γ-benzyl-l-glutamate) (PBLG) and poly(ε-caprolactone) (PCL). We copolymerized the macromonomers in the continuous phase of high internal phase emulsions (HIPEs) to obtain highly porous polyHIPEs. We demonstrated that the PBLG polyHIPE is a stiffer material compared to the softer PCL polyHIPE, while the copolyHIPEs composed of both components have a combination of thermomechanical properties that can be tuned by varying the chemical composition. Moreover, using a thiol–ene HIPE-templating approach, we were able to prepare a bilayered PBLG–PCL polyHIPE consisting of two chemically and mechanically distinct layers covalently bonded with a thin and robust interface while maintaining the typical polyHIPE morphology throughout the material.

Zwitterionic Polypeptoids: A Promising Class of Antifouling Bioinspired Materials.

Biofouling caused by protein adsorption and microbial colonization remains a great challenge in many applications. In this work, we synthesized a new type of zwitterionic polypeptoid containing carboxybetaine (CB) moieties (PeptoidCB) through thiol–ene chemistry of poly(N-allylglycine) (PNAG). The zwitterionic antifouling hydrogel was subsequently prepared by co-mixing PeptoidCB with agarose, which exhibited excellent resistance to non-specific protein adsorption and bacterial adhesion. Further, PeptoidCB-modified block copolypeptoids with amphiphilic structure were synthesized to form nanoparticles in an aqueous solution with neglected protein adsorption. The ability of PeptoidCB to resist non-specific protein adsorption and bacterial adhesion makes it a promising candidate for biomedical and industrial applications.

Magnolol-derived thiol-ene photo-polymerized membranes with intrinsic anti-flammability and high transparency

In this study, a phosphorus-containing bio-based monomer (MBDPP) was first synthesized from renewable magnolol, and subsequently photo-cured with tri-thiol (TPTMP) or tetra-thiol (PETMP) monomers via thiol–ene polymerization. The synthesized MBDPP/TPTMP and MBDPP/PETMP membranes exhibited high char residues at 700 °C in the TGA tests, which were 19.8 wt% and 24.2 wt% for nitrogen while 16.5 wt% and 20.2 wt% for air, respectively, indicating superior charring capacity of both membranes. DMA results indicated that both the higher stiffness and the Tg of the cured MBDPP/PETMP membrane was ascribed to its higher cross-linking density than that of the cured MBDPP/TPTMP owing to the tetra-functional groups of PETMP. In the open flame test, both MBDPP/TPTMP and MBDPP/PETMP membranes self-extinguished immediately when removing the flame source, manifesting excellent intrinsic anti-flammability. The cone calorimeter results further demonstrated that MBDPP/TPTMP and MBDPP/PETMP membranes showed lower PHRR (419 and 388 kW/m2, respectively) and THR (41.38 and 38.98 MJ/m2, respectively) values than most of the thiol-ene photo-polymerized counterparts previously reported. The excellent anti-flammability of MBDPP/TPTMP and MBDPP/PETMP membranes originated from the formation of expandable char residues that played an efficient role in hampering the transfer of flammable pyrolysis products to flame zone as well as insulating the heat irradiation during combustion. Additionally, both MBDPP/TPTMP and MBDPP/PETMP membranes showed excellent transparency (transmittance >85% in the visible region) and flexibility (breaking elongation around 40%). Taking the intrinsic anti-flammability, exceptional transparency and high flexibility into account, the MBDPP/TPTMP and MBDPP/PETMP systems are suitable as intumescent flame retardant coating materials.

Gel Polymer Electrolytes with Mixture of Triazolium Ionic Liquids and Propylene Carbonate.

This study is focused on the structural influence of 1,2,4-triazolium ionic liquid (IL), that is, the effect of the length of the substituent and the type of substitution (1-methyl-4-alkyl or 1-alkyl-4-methyl) used in the mixture with propylene carbonate (PC) on the properties of thiol–ene polymer ionogels and on the preparation of an ionogel with satisfactory mechanical and conductive properties. PC allows for higher conductivity but also causes electrolyte leakage from the gel. When using triazolium IL (instead of the imidazolium one), because of the stronger interactions between components of the system, the ionogels do not leak. In this study, 1,4-dialkyl-1,2,4-triazolium ILs were successfully synthesized by the alkylation of 1,2,4-triazole. Subsequently, gel polymer electrolytes were obtained by one-pot thiol–ene photopolymerization reactions of tetrafunctional thiols with different chemical structures: pentaerythritol tetra(3-mercaptopropionate) (PETMP) or pentaerythritol tetra(3-mercaptobutyrate) (PETMB) and trifunctional ene (TATT) in the presence of a mixture of 1,4-dialkyl-1,2,4-triazolium IL with PC. Measurements made by electrochemical impedance spectroscopy showed that all ionogels with TATT+PETMB as a polymer matrix presented smaller relative ionic conductivity compared to ionogels containing TATT+PETMP. The puncture resistance and elongation at puncture, measured by the puncture resistance method, were higher for ionogels with poly(TATT+PETMB) than for those with poly(TATT+PETMP). Moreover, ILs containing a methyl group in position N1 of the 1,2,4-triazole ring presented lower puncture resistance than ionogels with ILs containing a methyl group in position N4, especially for shorter alkyl chains. Additionally, the photo-differential scanning calorimetry method was employed to characterize the course of photopolymerization. The compositions and their constituents were characterized by UV and IR spectroscopy.

Development and Characterization of Oxidatively Responsive Thiol–Ene Networks for Bone Graft Applications

First metatarsophalangeal joint (MPJ) arthroplasty procedures are a common podiatric procedure. However, almost one-third of cases require revision surgeries because of nonunions. Revision or salvage surgery requires more extensive hardware and bone grafts to recreate the first metatarsal. Unfortunately, salvage surgeries have a similar rate of failure attributed to delayed healing, bone graft dissolution, and the lack of bone ingrowth. Furthermore, patients who suffer from neuropathic comorbidities such as diabetes suffer from a diminished healing capacity. An increase in proinflammatory factors and the high presence of reactive oxygen species (ROS) present in diabetics are linked to lower fusion rates. To this end, there is a need for a clinically relevant bone graft to promote bone fusions in patients with neuropathic comorbidities. Incorporating thiol-ene networks for bone scaffolds has demonstrated increased osteogenic biomarkers over traditional polymeric materials. Furthermore, thiol-ene networks can act as antioxidants. Sulfide linkages within the network have an inherent ability to consume radical oxygen to create sulfoxide and sulfone groups. These unique properties of thiol-ene networks make them a promising candidate as bone grafts for diabetic patients. In this work, we propose a thiol-ene biomaterial to address the current limitations of MPJ fusion in diabetics by characterizing mechanical properties, degradation rates under accelerated conditions, and oxidative responsiveness under pathophysiologic conditions. We also demonstrated that thiol-ene-based materials could reduce the number of hydroxyl radicals associated with neuropathic comorbidities.

Chemically Recyclable Poly(β-thioether ester)s Based on Rigid Spirocyclic Ketal Diols Derived from Citric Acid.

Incorporating rigid cyclic acetal and ketal units into polymer structures is an important strategy toward recyclable high-performance materials from renewable resources. In the present work, citric acid, a widely used platform chemical derived from biomass, has been efficiently converted into di- and tricyclic diketones. Ketalization with glycerol or trimethylolpropane afforded rigid spirodiols, which were obtained as complex mixtures of isomers. After a comprehensive NMR analysis, the spirodiols were converted into the respective di(meth)acrylates and utilized in thiol–ene polymerizations in combination with different dithiols. The resulting poly(β-thioether ester ketal)s were thermally stable up to 300 °C and showed glass-transition temperatures in a range of −7 to 40 °C, depending on monomer composition. The polymers were stable in aqueous acids and bases, but in a mixture of 1 M aqueous HCl and acetone, the ketal functional groups were cleanly hydrolyzed, opening the pathway for potential chemical recycling of these materials. We envision that these novel bioderived spirodiols have a great potential to become valuable and versatile bio-based building blocks for several different kinds of polymer materials.

Actuation of Liquid Crystalline Elastomers at or Below Ambient Temperature

AbstractLiquid crystal elastomers (LCE) are an emerging class of material actuators. LCE undergo macroscopic dimensional changes when subjected to a stimulus. The large stimuli‐response of LCE is associated with thermotropic disruption of order. Historically, comparatively high temperatures are required to disrupt orientation in LCE to achieve meaningful work output. Here, we introduce an approach to prepare LCE via thiol‐Michael/thiol–ene reactions that actuate at or below ambient temperature. Alignment was imparted to the LCE by mechanical alignment and 3D printing. The LCE materials detailed here achieve strains of 40 % with a maximum deformation rate of 6.5 % °C−1. The functional utility of the tunability of the thermotropic response of these materials is illustrated in reconfiguration triggered via body heat and sequential actuation of a multi‐material element.

Preparation of Stable POSS-Based Superhydrophobic Textiles Using Thiol-Ene Click Chemistry.

In this study, a superhydrophobic fabric was synthesized by modifying the fiber’s surface with dopamine-containing hydroxyl functional groups. Furthermore, we introduced mercapto-based functional groups by the hydrolysis of mercaptopropylmethyldimethoxysilane (MPMDS) and finally grafted POSS and mercaptans using a thiol–ene click reaction. These processes generated a superhydrophobic fabric with a static contact and a sliding angle of 162° and 8°, respectively. The superhydrophobic fabric’s compact and regular micro-nano rough structure based on POSS and mercaptans provides stable fastness and durability, as well as high resistance to organic solvents, acid–base environments, mechanical abrasion, UV rays, and washing. Moreover, it can be used for self-cleaning and oil–water separation, and it has a wide range of applications in the coating industry.

Study on Fire Behavior, Thermal Stability and Degradation Kinetics of Thiol-Ene with Poly(aminopropyl/phenyl)silsesquioxane.

In this article, the flame retardant poly(aminopropyl/phenyl)silsesquioxane (PA) was incorporated into thiol-ene (TE), to obtain a flame-retardant thiol-ene (FRTE) composite. The cone calorimeter (CONE) measurement results showed that, compared with neat TE, the peak of heat release rate (PHRR) and total heat release (THR) of FRTE have decreased by almost 23.7% and 14.5%, respectively. Thermogravimetric analysis (TGA) results further confirmed that the flame retardant PA could induce the initial thermal degradation of TE, and increased the amounts of residual char. Moreover, the activation energies of FRTE were calculated through the Kissinger and Flynn–Wall–Ozawa methods. Compared with the neat TE, the activation energies of FRTE were raised by the addition of PA. It indicated that the flame retardant PA promoted cross-linking reactions of TE, to form a compact char layer and retarded further the thermal degradation of the polymer matrix.

Photosensitive thiol–ene composition for DLP 3D printing of thermally stable polymer materials

N-allylated derivatives with a modification degree of 80% were obtained by reacting poly[N,N′-(1,3-phenylene)isophthalamide] with allyl bromide in the presence of a strong base. Using the obtained functionalized polyamide and pentaerythritol tetrakis(3-mercaptopropionate), we formulated new photo- sensitive compositions capable of forming crosslinked structures due to UV-initiated thiol–ene polymerization. High-resolution 3D objects that are heat resistant up to 380 °C were formed using digital light processing (DLP) 3D printing

Manipulating the Relative Rates of Reaction and Diffusion in a Holographic Photopolymer Based on Thiol–Ene Chemistry

Properly balanced reaction and diffusion kinetics are crucial for achieving optimal performance in holographic photopolymers. However, a comprehensive study on the effect of reaction and diffusion on the performance of thiol–ene-based holographic photopolymers has not been performed previously. To determine the relationship between reaction and diffusion, the refractive index modulation (Δn) of holographic gratings recorded in a model thiol–ene photopolymer system was evaluated with controlling the rates of reaction and diffusion processes. By changing the molecular weight of the polymer binder, the diffusion rate was varied over orders of magnitudes with the highest Δn of 0.026 achieved at a molecular weight of 2.9 × 104 Da. Meanwhile, the haze was significantly reduced in binders of higher molecular weight. Similarly, as the reaction rate was reduced in accordance with lowering the light intensity, the Δn reached a peak value of 0.023 at 7 mW/cm2 and was found to decrease at both higher (2500 lines/mm) and lower (1000 lines/mm) spatial frequencies. In particular, Δn approaching 0 was observed at a very low intensity (2 mW/cm2) and when the binder with a molecular weight as low as 0.5 × 104 Da was used. An analogous formulation incorporating a secondary thiol, which has slower reaction kinetics and a more stable thiyl radical relative to the primary thiol, exhibited a lower Δn , especially at higher spatial frequencies. Through one-step thiol-Michael addition, the functionality of a tetrathiol monomer was reduced to various extents to obtain a series of thiol–ene photopolymers with precise control over gel point conversions, among which the thiol with an average functionality of 3.5 realized the highest Δn of 0.028. An enhanced reactive binder with norbornene pendant groups was also synthesized, and holographic gratings recorded in it showed notably higher Δn at low light intensities compared to those recorded in non-reactive or less reactive binders.

Flame Retardancy and Thermal Degradation Behaviors of Thiol-Ene Composites Containing a Novel Phosphorus and Silicon-Containing Flame Retardant.

In this article, a novel phosphorus and silicon-containing flame retardant (DOPO-V-PA) was synthesized via condensation reaction and then added into thiol-ene (TE) to prepare a flame-retardant composite. The results of cone calorimeter measurement demonstrated that, compared with pure TE, 22.7% and 53.2% reduction of TE/DOPO-V-PA (thiol-ene/9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide-vinyltrimethoxysilane-phenyltrimethoxysilane-(3-aminopropyl)trimethoxysilane copolymer) was found for the peak heat release rate (PHRR) and total heat release (THR), respectively. The thermal degradation of TE composites was investigated by the TGA measurement under non-isothermal conditions, and kinetic parameters were both calculated by the Kissinger and Flynn-Wall-Ozawa methods. It was indicated that the activation energies of TE at conversions exceeding 50% were enhanced by the incorporation of DOPO-V-PA for the whole conversion range.

Spatial and Temporal Control of Photomediated Disulfide–Ene and Thiol–Ene Chemistries for Two-Stage Polymerizations

Spatial and Temporal Control of Photomediated Disulfide–Ene and Thiol–Ene Chemistries for Two-Stage Polymerizations

Highly transparent acrylate epoxidized soybean oil based UV–curable silicone–modified coatings with good thermal stability and flame retardancy

Thermal stability, flame retardancy and transparency are essential for UV–curable materials serving as package materials for some optical or electronics devices. In this paper, acrylate epoxidized soybean oil (AESO) based UV–curable silicone modified coatings with good thermal stability, good flame retardancy, transmittance above 97% were fabricated by UV initiated thiol–ene reaction of AESO and thiol silicone resin. The thermal stability of AESO–based UV–curable silicone–modified coatings is better than that of neat AESO–based UV–curable coatings reported previously, because the thermal initial decomposition temperature (Td5) of the former is in the range of 313–322 °C while that of the latter is only in the range of 214–283 °C. Cone calorimetry test denotes AESO–based UV–curable silicone–modified coatings possess good flame retardancy because the maximum value of the heat release rate (HRR) and CO release (CO Yield) for AESO–based UV–curable silicone–modified coatings are 450–550 kW/m2 and 0.02%–0.33%, respectively. The mechanism for the improvement of flame retardancy was studied by scanning electron microscope (SEM) analysis of the surface morphology of the chars after being burned.

Engineering a covalently constructed superomniphobic membrane for robust membrane distillation

Wetting, scaling, and functionality loss of the active layer are critical challenges facing membrane distillation (MD) technology that substantially hinder its practical applications. Herein, we propose an effective strategy to fabricate a superomniphobic MD membrane with excellent wetting/scaling resistance and mechanical robustness. Specifically, a hierarchical re-entrant architecture was created by immobilizing spherical silica nanoparticles onto a poly(vinylidene fluoride) membrane surface via covalent bonds, followed by fluorination via thiol–ene click chemistry. An ultrahigh water contact angle (166.5 ± 1.4°) and low sliding angle (5.0 ± 1.1°) confirmed the superhydrophobicity and slippery characteristics of the modified membrane, which were further illustrated by its excellent wetting resistance toward various liquids with low surface tension. The membrane sustained a long-duration MD for the treatment of a highly saline brine, with a surfactant content of approximately 2.0 mM, outperforming all the MD membranes reported in the exiting literature. In addition, the membrane exhibited excellent desalination performance for synthetic multi-component hypersaline wastewater, achieving a high water recovery ratio of approximately 60% without a significant decline in water flux. Overall, this study provides a novel and effective approach to fabricate high-performance MD membranes with robust functionality for operations under harsh environments. • A superomniphobic PVDF membrane was constructed via entire covalent bonding. • The membrane exhibited excellent wetting/scaling resistance for membrane distillation. • The membrane demonstrated a robust desalination performance for hypersaline wastewater treatment.

Integration of a Hydrophilic Hyperbranched Polymer and a Quaternary Ammonium Compound to Mitigate Membrane Biofouling

Membrane biofouling, adhesion of microorganisms on the surface and the subsequent formation of a biofilm, remains a persistent and inevitable issue, which results in a dramatic reduction of permeability and lifespan. Constructing a membrane with active bacteria-killing and passive anti-adhesion properties is still a challenge to mitigate membrane biofouling. Herein, an active–passive anti-biofouling membrane was originally fabricated by integration of hydrophilic hyperbranched poly(N-acryloylmorpholine) (HPA) and the dimethylaminoethyl acrylate–dodecylammonium bromide (DD) quaternary ammonium compound. Inspired by modern dopamine biomimetic adhesion chemistry, thiolated HPA was first immobilized on the polydopamine (PD)-modified poly(vinylidene fluoride) membrane surface through Michael addition, followed by conjugation of DD via a thiol–ene click reaction. The membrane surface changes of the chemical structure, hydrophilicity, and zeta potential proved that bacteria-killing DD and the anti-adhesion HPA layer were successively conjugated. The initial contact angle of the M-PD/HPA/DD membrane was reduced from 120.5° for the pure membrane to 52.3°. Furthermore, the water flux of the M-PD/HPA/DD membrane increased from 318.9 L m–2 h–1 (0.02 MPa) for the pure membrane to 854.4 L m–2 h–1. In addition, the M-PD/HPA/DD membrane exhibited excellent active bacteria-killing property with inhibition rates of ∼90% for Escherichia coli and ∼95% for Staphylococcus aureus, respectively. Meanwhile, in the filtration of artificial bacteria wastewater, the M-PD/HPA/DD membrane showed a higher water flux recovery rate of 86.9% than 43.3% for the pure membrane, indicating an excellent anti-biofouling property. Therefore, this molecular-level design approach for the modification of the membrane surface could significantly enhance permeability and mitigate membrane biofouling, which provides a promising dimension for the preparation of the anti-biofouling membrane.

L-Cysteine modified metal-organic framework as a chiral stationary phase for enantioseparation by capillary electrochromatography.

A new kind of chiral zirconium based metal–organic framework, l-Cys-PCN-222, was synthesized using l-cysteine (l-Cys) as a chiral modifier by a solvent-assisted ligand incorporation approach and utilized as the chiral stationary phase in the capillary electrochromatography system. l-Cys-PCN-222 was characterized by X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, Fourier-transform infrared spectra, nitrogen adsorption/desorption, circular dichroism spectrum, zeta-potential and so on. The results revealed that l-Cys-PCN-222 had the advantages of good crystallinity, high specific surface area (1818 m2 g−1), thermal stability and chiral recognition performance. Meanwhile, the l-Cys-PCN-222-bonded open-tubular column was prepared using l-Cys-PCN-222 particles as the solid phase by ‘thiol–ene’ click chemistry reaction and characterized by scanning electron microscopy, which proved the successful bonding of l-Cys-PCN-222 to the column inner wall. Finally, the stability, reproducibility and chiral separation performance of the l-Cys-PCN-222-bonded OT column were measured. Relative standard deviations (RSD) of the column efficiencies for run-to-run, day-to-day, column-to-column and runs were 1.39–6.62%, and did not obviously change after 200 runs. The enantiomeric separation of 17 kinds of chiral compounds including acidic, neutral and basic amino acids, imidazolinone and aryloxyphenoxypropionic pesticides, and fluoroquinolones were achieved in the l-Cys-PCN-222-bonded OT column. These results demonstrated that the chiral separation system of the chiral metal–organic frameworks (CMOFs) coupled with capillary electrochromatography has good application prospects.