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A scalable synthesis of high refractive index, optically transparent photopolymers from a family of low-viscosity multifunctional thiol and alkyne monomers via thiol-yne "click" is described herein. The monomers designed to incorporate high refractive index cores consisting of aryl and sulfide groups with high intrinsic molar refraction were synthesized starting from commercially available low-cost raw materials. The low-viscosity (

Thermoplastics encompass the majority of commercial plastics but are limited to manufacturing techniques that require heat and/or solvent to enable material reprocessing and reshaping. Photopolymer...

Diarylethene-functionalized liquid-crystalline elastomers (DAE-LCEs) containing thiol-anhydride bonds were prepared and shown to undergo reversible, reprogrammable photoinduced actuation. Upon exposure to UV light, a monodomain DAE-LCE generated 5.5 % strain. This photogenerated strain was demonstrated to be optically reversible over five cycles of alternating UV/Visible light exposure with minimal photochrome fatigue. The incorporation of thiol-anhydride dynamic bonds allowed for retention of actuated states. Further, re-programming of the nematic director was achieved by heating above the temperature for bond exchange to occur (70 °C) yet below the nematic-to-isotropic transition temperature (100 °C) such that order was maintained between mesogens. The observed thermal stability of each of the diarylethene isomers of over 72 h allowed for decoupling of photo-induced processes and polymer network effects, showing that both polymer relaxation and back-isomerization of the diarylethene contributed to LCE relaxation over a period of 12 hours after actuation unless bond exchange occurred.

A high-performance holographic recording medium was developed based on a unique combination of photoinitiated thiol–ene click chemistry and functional, linear polymers used as binders. Allyl reacti...

The reaction of thiols and anhydrides to form ring opened thioester/acids is shown to be highly reversible and it is accordingly employed in the fabrication of covalent adaptable networks (CANs) that possess tunable dynamic covalent chemistry. Maleic, succinic, and phthalic anhydride derivatives were used as bifunctional reactants in systems with varied stoichiometries, catalyst, and loadings. Dynamic characteristics such as temperature-dependent stress relaxation, direct reprocessing and recycling abilities of a range of thiol-anhydride elastomers, glasses, composites and photopolymers are discussed. Depending on the catalyst strength, 100 % of externally imposed stresses were relaxed in the order of minutes to 2 hours at mild temperatures (80-120 °C). Pristine properties of the original materials were recovered following up to five cycles of a hot-press reprocessing technique (1 h/100 °C).

Beyond their central role in storing and transmitting genetic information, nucleic acids are renowned for their high-specificity, high-affinity hybridization. In the past several decades, scientists have become increasingly interested in emulating this unique property of nucleic acids using synthetic mimics. Many creative strategies for the synthesis of xenonucleic acids (XNAs) have been developed, with the field ultimately striving for high-efficiency, scalable routes to achieving sequence-controlled XNA synthesis. Emerging strategies in both biology (e.g., directed evolution) and chemistry (e.g., dynamic covalent reactions) are leading to new breakthroughs in XNA synthesis that will make applications of nucleic acids, such as gene therapy, agricultural disease management, and electronics, more accessible.

Dynamic photopolymer networks that take advantage of the thermodynamically controlled reversibility of thiol–succinic anhydride adducts were synthesized from commercial substrates and investigated as a new class of covalent adaptable networks (CANs). Through systematic studies of the catalyst and stoichiometry effects on the exchange dynamics two distinctive exchange mechanisms were found, and then demonstrated to contribute to the overall dynamic characteristics. By varying the catalyst activity, i.e. basicity and/or nucleophilicity, control over the dynamic responsiveness through changes in the type of dynamic covalent chemistry mode (reversible addition vs. reversible exchange) was achieved in otherwise compositionally analogous materials. More specifically, the participation of the associative mechanism (thiol–thioester exchange) in the otherwise dissociative networks, and its relevance on materials properties was demonstrated by dielectric analysis (DEA) and dynamic mechanical analysis (DMA). The activation energies (Ea) for viscous flow obtained from DMA stress relaxation experiments and from dielectric modulus and loss crossover points were shown to match well between the two techniques. The Ea in stoichiometric systems was found to be 110–120 kJ mol−1, whereas 50% excess thiol systems were characterized by Ea ranging 95–105 kJ mol−1. The thermodynamic equilibrium conversion, estimated in the temperature controlled FTIR, for a stoichiometric 3-mercaptopropionate-succinic anhydride combination was determined at 92 ± 1% at ambient temperature, and decreased to 67 ± 1% at 120 °C within one hour of equilibration time (ΔH° = −46 ± 5 kJ mol−1). Such high potential for reversibility of the thioester anhydride linkages resembles maleimide-furan Diels–Alder networks but has many other attributes that make these CANs of unprecedented value in fundamental research on dynamic materials.

Photopolymers formed from the family of thiol-X “click” reactions notably form sulfur-containing thioether linkages. While sulfur-containing materials are conventionally expected to result in high ...

An athermal approach to mRNA enrichment from total RNA using a self-immolative thioester linked nucleic acids (TENA) is described. Oligo(thymine) (oT) TENA has a six-atom spacing between bases which allowed TENA to selectively base-pair with polyadenine RNA. As a result of the neutral backbone of TENA and the hydrophobicity of the octanethiol end group, oT TENA is water insoluble and efficiently pulled down 93±2 % of EGFP mRNA at a concentration of 10 ng μL-1 . Self-immolative degradation of TENA upon ambient temperature exposure to nucleophilic buffer components (Tris, DTT) allowed recovery of 55±27 ng of mRNA from 3.1 μg of total RNA, which was not statistically different from the amount recovered using Dynabeads® mRNA DIRECT Kit (89±24 ng). Gene expression as measured by RT-qPCR was comparable for both enrichment methods, suggesting that the mild conditions required for enrichment of mRNA using oT TENA are compatible with RT-qPCR and other downstream molecular biology applications.

At its basic conceptualization, photoclick chemistry embodies a collection of click reactions that are performed via the application of light. The emergence of this concept has had diverse impact over a broad range of chemical and biological research due to the spatiotemporal control, high selectivity and excellent product yields afforded by the combination of light and click chemistry. While the reactions designated as “photoclick” have many important features in common, each has its own particular combination of advantages and shortcomings. A more extensive realization of the potential of this chemistry requires a broader understanding of the physical and chemical characteristics of the specific reactions. This review discusses the features of the most frequently employed photoclick reactions reported in the literature: photomediated azide alkyne cycloadditions, other 1,3-dipolarcycloadditions, Diels Alder and inverse electron demand Diels Alder additions (IEDA), radical alternating addition chain transfer additions and nucleophilic additions (e.g. thiol-ene and thiol-Michael), among others. Applications of these reactions in a variety of chemical syntheses, materials chemistry and biological contexts are surveyed with particular attention paid to the respective strengths and limitations of each reaction and how that reaction benefits from its combination with light. Finally, challenges to broader employment of these reactions are discussed along with strategies and opportunities to mitigate such obstacles.

Polymers that possess dynamic covalent bonds activated at ambient conditions are ideal platforms for smart, responsive materials. Herein, a class of dynamic covalent polymerizations is developed based on the thiol-thioester exchange, that is, transthioesterification, reaction. Shifts in the equilibrium extent of the exchange reactions are deliberately utilized to drive the formation of oligomers and polymers. In particular, a series of AB and A

Classical materials readily switch phases (solid to fluid or fluid to gas) upon changes in pressure or heat; however, subsequent reversion of the stimulus returns the material to their original phase. Covalently cross-linked polymer networks, which are solids that do not flow when strained, do not change phase even upon changes in temperature and pressure. However, upon the addition of dynamic cross-links, they become stimuli responsive, capable of switching phase from solid to fluid, but quickly returning to the solid state once the stimulus is removed. Reported here is the first material capable of a bistable switching of phase. A permanent solid to fluid transition or vice versa is demonstrated at room temperature, with inherent, spatiotemporal control over this switch in either direction triggered by exposure to light., Polymers cross-linked with dynamic bonds can switch the phase from solid to fluid upon stimulus but return quickly to the solid state once the stimulus is removed. Here the authors report a light triggered permanent solid to fluid transition at room temperature with inherent spatiotemporal control in either direction

The exchange of thiolates and thiols has long been held as a nearly ideal reaction in dynamic covalent chemistry. The ability for the reaction to proceed smoothly in neutral aqueous media has propelled its widespread use in biochemistry, however, far fewer applications and studies have been directed towards its use in material science which primarily is performed in organic media. Herein, we present the exploration of this dynamic exchange in both small molecule and polymer settings with a wide sampling of thiols, thioesters, organic bases, and nucleophilic catalysts in various organic solvents. Effects of the character of the thiol and thioester, pKa or nucleophilicity of the catalyst, and heat on the reaction were investigated. The mechanism regarding the previously unexplored effectiveness of nucelophilic catalysts, such as quinuclidine or DABCO, to affect the thiol-thioester exchange was also explored. Finally, the use of the thiol-thioester exchange in a network polymer to reduce applied stresses or change shape of the material following polymerization was shown and the ability of basic and nucleophilic catalysts to promote these effects were benchmarked. The influence of polarity in these networks was also explored, with the rate of exchange shown to be easily tuned by the addition of diluents with varying polarities. Presented here is a so-called “user's guide” to the thiol-thioester exchange; we hope that this guide is instructive to practitioners in the field of material science which seek to utilize the thiol-thioester exchange in both linear and network polymers.

Two-stage holographic photopolymers capable of high refractive index modulation (Δn) on the order of 10–2 enable the fabrication of a myriad of optical elements. While there are commercial products available that meet these requirements, researchers often want the flexibility to customize both the form factor of the samples as well as the mechanical and chemical properties for their specific applications. We present a novel high refractive index acrylate writing monomer in a low refractive index urethane matrix as a model material for customization for optical applications. We discuss the achievable Δn of this custom monomer, 1,3-bis(phenylthio)-2-propyl acrylate (BPTPA) in the urethane matrix as a function of solubility, along with a comparison to a commercially available high refractive index monomer, 2,4,6- tribromophenyl acrylate. Formulations with BPTPA exhibit a peak-to-mean Δn ≈ 0.029 in transmission holograms without any obvious deficiencies in transparency, color, or scatter. This writing monomer and the synthetic processes present a promising platform for the fabrication of high-performance holographic photopolymers for a wide range of research applications.

The synthesis of thiolactone monomers that mimic natural nucleosides and engage in robust ring opening polymerizations (ROP) is herein described. As each repeat unit contains a thioester functional group, dynamic rearrangement of the polymer is feasible via thiol-thioester exchange, demonstrated here by depolymerization of the polymers and coalescing of two polymers of different molecular weight or chemical composition. This approach constitutes the first step toward a platform that enables for the routine synthesis of sequence controlled polymers via dynamic template directed synthesis.

High molecular weight polybutadienes and rhodium complexes were used to produce single chain organometallic nanoparticles. Irradiation of high cis-polybutadiene in the presence of a photosensitizer isomerised the double bonds to produce differing cis/trans ratios within the polymer. Notably, a higher cis percentage of carbon–carbon double bonds within the polymer structure led to faster binding of metal ions, as well as their faster removal by competing phosphine ligands. The experimental results were supported and rationalized by DFT computations.

Correction for ‘Mixed mechanisms of bond exchange in covalent adaptable networks: monitoring the contribution of reversible exchange and reversible addition in thiol–succinic anhydride dynamic networks’ by Maciej Podgórski et al., Polym. Chem., 2020, 11, 5365–5376, DOI: 10.1039/D0PY00091D.

Synthetic unilamellar liposomes, functionalized to enable novel characteristics and behavior, are of great utility to fields such as drug delivery and artificial cell membranes. However, the generation of these liposomes is frequently highly labor-intensive and time consuming whereas in situ liposome formation presents a potential solution to this problem. A novel method for in situ lipid formation is developed here through the covalent addition of a thiol-functionalized lysolipid to an acrylate-functionalized tail via the thiol-Michael addition reaction with potential for inclusion of additional functionality via the tail. Dilute, stoichiometric mixtures of a thiol lysolipid and an acrylate tail reacted in an aqueous media at ambient conditions for 48 hours reached nearly 90% conversion, forming the desired thioether-containing phospholipid product. These lipids assemble into a high density of liposomes with sizes ranging from 20 nm to several microns in diameter and include various structures ranging from spheres to tubular vesicles with structure and lamellarity dependent upon the catalyst concentration used. To demonstrate lipid functionalization, an acrylate tail possessing a terminal alkyne was coupled into the lipid structure. These functionalized liposomes enable photo-induced polymerization of the terminal alkyne upon irradiation.

Thiol lysolipids undergo thiol–thioester exchange with two phenyl thioester-functionalized tails to produce phospholipid structures that assemble into liposomes with differences in exchange rates, temperature sensitivity, permeability, and continued exchange behavior. This in situ formation reaction imparts dynamic characteristics into the membrane for downstream liposome functionalization and mimics native membrane remodeling.

Holographic photopolymers capable of high refractive index modulations (Δn) on the order of 10-2 are integral for the fabrication of functional holographic optical elements (HOEs) for use in a range of optical applications. A novel high refractive index liquid writing monomer suitable for two-stage photopolymer systems was designed and synthesized. This monomer exhibits facile synthetic procedure, low viscosity, high refractive index as well as excellent solubility in a low refractive index urethane matrix. The solubility limit, refractive index change and reaction kinetics/conversion were studied against a commercial reference high refractive index monomer, 2,4,6-tribromophenyl acrylate (TBPA). Superior performance in solubility to TBPA is shown with similar reaction kinetics and final conversion as confirmed by realtime Fourier transform infrared spectroscopy (FTIR) and real-time monitoring of diffraction grating growth. We demonstrate the ability to load substantial amounts of these writing monomers enabling a straightforward path to higher achievable Δn values (peak-to-mean Δn ~ 0.03) without sacrificing optical properties (transparency, color or scatter) as validated through recording ~100% efficiency volume transmission holograms in sub-15 μm thick films.

Holographic photopolymers capable of high refractive index modulation (Δn) on the order of 10-2 are integral for the fabrication of functional holographic optical elements that are useful in a myriad of optical applications. In particular, to address the deficiency of suitable high refractive index writing monomers for use in two-stage holographic formulations, here we report a novel high refractive index writing monomer, 1,3-bis(phenylthio)-2-propyl acrylate (BPTPA), simultaneously possessing enhanced solubility in a low refractive index (n = 1.47) urethane matrix. When examined in comparison to a widely used high refractive index monomer, 2,4,6-tribromophenyl acrylate, BPTPA exhibited superior solubility in a stage 1 urethane matrix of approximately 50% with a 20% higher refractive index increase per unit amount of the writing monomer for stage 2 polymerizations. Formulations with 60 wt % loading of BPTPA exhibit a peak-to-mean holographic Δn ≈ 0.029 without obvious deficiencies in transparency, color, or scatter. To the best of our knowledge, this value is the highest reported in the peer-reviewed literature for a transmission hologram. The capabilities and versatility of BPTPA-based formulations are demonstrated at varying length scales via demonstrative refractive index gradient structure examples including direct laser write, projection mask lithography of a 1″ diameter Fresnel lens, and ∼100% diffraction efficiency volume transmission holograms with a 1 μm fringe spacing in 11 μm thick samples.

The ability to selectively guide consecutive chemical processes towards a preferred pathway by using light of different frequencies is an appealing concept. Herein we describe the coupling of two photochemical reactions, one the photoisomerization and consequent activation of a sulfur-chelated latent olefin-metathesis catalyst at 350 nm, and the other the photocleavage of a silyl protecting group at 254 nm. Depending on the steric stress exerted by a photoremovable neighboring chemical substituent, we demonstrate the selective formation of either five- or six-membered-ring frameworks by light-triggered ring-closing metathesis. The orthogonality of these light-induced reactions allows the initiation of these processes independently and in interchangeable order, according to the wavelength of light used to promote them.

A comprehensive methodology to prepare nanometric size organometallic particles (ONPs) containing rhodium(I), iridium(I) and nickel(0) with ROMP-derived polycycloocta-1,5-diene (pCOD) by a controlled single chain collapse mechanism was developed. The polymeric complexes could be produced via direct exchange of the respective labile ligands of metal complexes by the 1,5-hexadiene elements in pCOD, or via in situ reduction of metal ions in the presence of the polymer. These well-defined π-bound polymeric complexes were characterized by UV-Vis spectroscopy, dynamic light scattering (DLS) and size exclusion chromatography (SEC) measurements and the resulting polymer sizes were found to be inversely proportional to the amount of metal added due to concomitant single chain collapse. Moreover, these procedures were readily extended to the synthesis of organobimetallic nanoparticles containing two metals; which could be added in commutative order and specific metal ratios. The embedded metal elements were found to be readily accessible for applications in catalysis, where the close proximity of the catalytic centers led to distinctive reactivity compared to the isolated complexes.

The original version of this Article contained errors in Fig. 3. In Fig. 3a, the word ‘fluid’ in grey was incorrectly given as ‘solid’ in green, below that, ‘solid’ in green was previously ‘fluid’ in grey. Also, the label on the arrow incorrectly read ‘TMG (1 mol%) HABI-Cl (3 mol%) 455 nm, 1 min’; the correct version reads ‘TMG (1 mol%) HABI-O-n-oct (4 mol%) 455 nm, 4 min’. In the accompanying legend, the word ‘photobase’ was originally incorrectly given as ‘photoacid’. Additionally, in Fig. 3b, the label on the central image was ‘As is: solid’, rather than the correct ‘As is: fluid’. This has been corrected in both the PDF and HTML versions of the Article.