Name: synthesis of terpolymers at mild temperatures using dynamic sulfur bonds in poly(s-divinylbenzene)
Uploaded: 2019-05-20T15:00:00.000+00:00
Duration: 9 min 16 s
Description: Watch this Scientific Journal Video about Synthesis of Terpolymers at Mild Temperatures Using Dynamic Sulfur Bonds in PolyS-Divinylbenzene at JoVE.com

Thanks are owed to The American Chemical Society Petroleum Research Fund (PRF # 58416-UNI7) for financial support. The authors would like to thank Indiana STEM Louis Stokes Alliance for Minority Participation for student support provided by the National Science Foundation under Grant No. HRD1618-408.

1. Synthesis of poly(S-divinylbenzene)
<ol>
	<li>To prepare poly(S-divinylbenzene), combine elemental sulfur (S8) and divinylbenzene (DVB) at various weight ratios (30:70, 40:60, 50:50, 60:40, 70:30, 80:20, and 90:10 of S8:DVB). Prepare the reaction according to prior methods described below3,25. 
	NOTE: All reactions here were conducted on a 1.00 g scale. A typical reaction contains 500 mg of S8 and 500 mg of DVB.
	<ol>
		<li>Place the reagents in a 1-dram vial equipped with a magnetic stir bar. Insert the vials in an oil bath at 185 &#176;C for 30 min.</li>
		<li>Remove the samples from the oil bath and immediately quench the reaction by placing the vials in liquid nitrogen. Break open the vials to remove the polymer. Liquid nitrogen not only quenches the reaction but also aids in complete removal of the polymer. 
		CAUTION: All samples are extremely hot upon removing from bath. Use caution when handling the samples. Use proper PPE when dealing with broken glass.</li>
	</ol>
	</li>
</ol>
2. Preparation of terpolymers
<ol>
	<li>Synthesize terpolymers by combining poly(S-DVB) and an additional monomer in a 1-dram vial equipped with a magnetic stir bar. 
	NOTE: All samples were prepared on a 600 mg scale. Monomers examined include 1,4-cyclohexanedimethanol divinyl ether (CDE), cyclohexyl vinyl ether (CVE), and allyl ether (AE).
	<ol>
		<li>Crush poly(S30-90%-DVB10-70%) with a mortar and pestle for higher surface area interaction with CDE. Alter the composition by varying the ratio of poly(S-DVB):CDE from 1:1 to 1:100 by weight. Additional monomers are only tested at a 1:1 ratio of poly(S50%-DVB50%):monomer.</li>
		<li>Place the samples in an oil bath at 90 &#176;C for 24 h and then cool to room temperature. Longer reaction times are required for some monomers.</li>
		<li>Some reactions will not result in complete monomer incorporation. For those reactions, dissolve the soluble polymer portions in dichloromethane (DCM) and precipitate in cold methanol. For samples with limited solubility, wash the solid polymer samples with cold methanol to remove any unreacted monomer.</li>
	</ol>
	</li>
	<li>Prepare terpolymers using maleimide 
	NOTE: Maleimide does not have a low boiling point. However, it does have just one reactive site towards thiyl radical modification.
	<ol>
		<li>Synthesize poly(S-DVB) prepolymer using slightly altered methods. Combine sulfur and DVB at a 30:70 S8:DVB ratio. Combine the reagents in a glass vial equipped with a magnetic stir bar on a 5.00 g scale.</li>
		<li>Place the vials in an oil bath at 185 &#176;C for 1 h. Immediately place the samples in liquid nitrogen upon removal from the oil bath.</li>
		<li>Combine the prepolymer with maleimide in a 1-dram glass vial with a 3:1 poly(S-DVB):maleimide ratio (w/w). Prepare all samples on a 200 mg scale and dissolve in 10 mg/&#956;L of dimethylformamide (DMF). Place the vials in an oil bath at 100 &#176;C for 24 h. 
		CAUTION: Inverse vulcanization reactions produce a small amount of gas. For reactions above a 1.00 g scale, use larger vials or drill a hole in the vial cap to prevent the build-up of pressure. 
		NOTE: Prepolymers that are more malleable cannot be crushed into a powder. However, these polymers soften very easily when heated providing miscibility with most monomers.</li>
	</ol>
	</li>
	<li>Monitor percent conversion for the addition of a variety of monomers (CDE, CVE, AE, and maleimide).
	<ol>
		<li>Prepare all samples using poly(S-DVB) as described in section 2.2.1-2.2.2. Synthesize poly(S-DVB-CDE), poly(S-DVB-CVE), and poly(S-DVB-AE) in a 1-dram glass vial with a 3:1 poly(S-DVB):monomer ratio by weight. A typical sample should have 150 mg of prepolymer and 50 mg monomer. No solvent is needed for most of these polymerizations. However, in order for maleimide and poly(S-DVB) to interact fully, 20 &#956;L of DMF must be added.</li>
		<li>Remove the samples at various time points (t= 0, 15, 30, 60, 180, 360, 720, and 1440 min). Dissolve the polymer in 600 &#956;L of chloroform-d and analyze them by 1H NMR.</li>
	</ol>
	</li>
</ol>
3. Control polymerizations
<ol>
	<li>Synthesize poly(S50%-DVB50%) as described in section 1.1. The sample can then be used in three control reactions. Combine the finely crushed polymer with additional DVB. Place only poly(S-DVB) in a separate vial. Heat all samples at 90 &#176;C for 24 h, then cool them to room temperature.</li>
	<li>Test elemental sulfur under a variety of conditions in order to confirm that sulfur from the polymer rather than S8 is required for polymerization. Conduct individual reactions by combining S8 with CDE, DVB, and AE, as well as using S8 alone. Combine S8, CDE, and poly(S50%-DVB50%) in another vial. Heat all samples at 90 &#176;C for 24 h, then cool to room temperature.</li>
</ol>
4. Polymer characterization
<ol>
	<li>Use thin layer chromatography (TLC) for initial detection of S8 in polymers. Spot polymer samples onto silica TLC plates with hexanes eluent. In hexanes, S8 has a Rf value of 0.7, and polymers do not move from the baseline, Rf &#8776;0.</li>
	<li>Analyze all polymers by 1H NMR in chloroform-d. Integrate the resulting 1H-NMR spectra to determine the extent of the reaction. Prepare all samples by dissolving the polymer of interest in chloroform-d. Perform simple filtration to remove undissolved particulates.</li>
	<li>Analyze the samples by gel permeation chromatography (GPC) using DCM eluent. Use a GPC with two mesopore columns in sequence and a refractive index detector for analysis.
	<ol>
		<li>Due to the relatively low solubility of most terpolymers and broad polydispersity, dissolve each polymer at a seemingly high concentration, 75 mg/mL in DCM. Remove particulates from the soluble portion using a 0.45 &#956;m hydrophobic filter.</li>
		<li>Determine the number average and weight average molecular weights (Mn and Mw respectively) based on a calibration curve of polystyrene standards. Use these values to obtain the polydispersity index (PDI).</li>
	</ol>
	</li>
	<li>Study the thermal properties of the polymer samples. Fill the aluminum pans with 30-50 mg of polymer providing enough sample to adequately discern the glass transition temperature (Tg) from the resulting thermograms. Scan the samples from -50 &#176;C to 150 &#176;C at a rate of 10 &#176;C/min, cool back to -50 &#176;C at 20 &#176;C/min and heat them again to 150 &#176;C at 10 &#176;C/min. Obtain all Tg values from the second scan.</li>
</ol>
5. Solubility studies
NOTE: Terpolymers demonstrated highest solubility in DCM. Solubility of the polymers can be altered by varying the composition.
<ol>
	<li>Measure approximately 150 mg of each polymer into a pre-weighed vial and dissolve in DCM to reach 75 mg/mL. Dissolve the samples for 8 h before removing the soluble portion. Wash the insoluble portion with DCM two times and dry the remaining insoluble sample in an oven for 10 min to remove remaining solvent.</li>
	<li>Reweigh the vial after letting the vial cool to room temperature. Calculate the percent solubility by determining the difference in starting and final weights.</li>
</ol>

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The authors have nothing to disclose.

The primary benefit of this method is the ability to form polysulfides at mild temperatures, 90 &#176;C versus &#62;159 &#176;C for traditional inverse vulcanization. The extended sulfur chains and sulfur loops in poly(S-DVB) are less stable than S-S bonds in S823,26. Lower temperatures can then be used to cause homolytic scission and thiyl radical formation24. For monomers with melting points well below the reaction temperature...

Conversion of organosulfur compounds to S8 during petroleum refinement has led to the amassing of large stockpiles of sulfur1. Elemental sulfur is primarily used for the production of sulfuric acid and phosphates for fertilizers2. The relative abundance provides a readily available and inexpensive reagent making elemental sulfur an ideal feedstock for materials development.
Inverse vulcanization is a relatively new polymerization technique that repurposes sulfur into functional materials3. The S8 ring converts to a diradical, linear chain upon heating above 159 &#176;C. The thiyl radicals then initiate polymerization with monomers to form polysulfides3. In addition to traditional radical polymerizations, inverse vulcanization has been utilized to initiate polymerization with benzoxazines4. The resulting polymers have been used for a wide range of applications including cathodes in Li-S batteries1,5,6,7, self-healing optical lenses8,9, mercury and oil sorbents5,10,11,12,13,14,15, thermal insulators15, to aid in the slow release of fertilizer16 as well as demonstrating some antimicrobial activity17. One group has provided a thorough systematic analysis of these polysulfides providing more information about the insulating character and mechanical properties with varied S content18. The specific details may aid in further applications development. The dynamic bonds present in these materials have also been utilized to recycle the polysulfides19,20. However, the high temperatures required by inverse vulcanization, typically 185 &#176;C, and lack of miscibility with S8, limit the monomers that can be used3.
Early efforts focused on the polymerization of aromatic hydrocarbons, extended hydrocarbons, and natural monomers with high boiling points5. These methods have been expanded by using poly(S-styrene) as a prepolymer improving miscibility between S8 and more polar monomers including acrylic, allylic, and functionalized styrenic monomers21. Another method utilizes nucleophilic amine activators to enhance reaction rates and lower reaction temperatures22. However, many monomers have boiling points well below 159 &#176;C and thus require an alternate method for polysulfide formation.
In the stable crown form, S-S bonds are the strongest, thus requiring high temperatures for cleavage23. In polysulfides, sulfur is present as linear chains or loops, allowing S-S bonds to be cleaved at much lower temperatures1,24. By using poly(S-DVB) (DVB, divinylbenzene)as a prepolymer, a second monomer with a lower boiling point such as 1,4-cyclohexanedimethanol divinylether (CDE, boiling point of 126 &#176;C), can be introduced24. This work demonstrates further improvement by lowering the reaction temperature to 90 &#176;C with a family of allyl and vinyl ether monomers. Reactions incorporating a second monomer remain solvent-free.

<table><tbody><tr><td>Sulfur, 99.5%, sublimed, ACROS Organics</td><td>Fisher Scientific</td><td>AC201250250SDS</td><td></td></tr><tr><td>divinylbenzene</td><td>Fisher Scientific</td><td>AA4280422</td><td></td></tr><tr><td>1,4-Cyclohexanedimethanol divinyl ether, mixture of isomers</td><td>Sigma Aldrich</td><td>406171</td><td></td></tr><tr><td>Cyclohexyl vinyl ether</td><td>Fisher Scientific</td><td>AC395420500</td><td></td></tr><tr><td>Allyl ether</td><td>Sigma Aldrich</td><td>259470</td><td></td></tr><tr><td>maleimide</td><td>Sigma Aldrich</td><td>129585</td><td></td></tr><tr><td>dichlormethane</td><td>Fisher Scientific</td><td>D37</td><td></td></tr><tr><td>N,N-dimethylformamide</td><td>Fisher Scientific</td><td>D119</td><td></td></tr><tr><td>Auto sampler Aluminum Sample Pans, 50&amp;micro;L, 0.1mm, Sealed</td><td>Perkin Elmer</td><td>B0143017</td><td></td></tr><tr><td>Auto sampler Aluminum Sample Covers</td><td>Perkin Elmer</td><td>B0143003</td><td></td></tr><tr><td>EMD Millipore 13mm Nonsterile Millex Syringe Filters - Hydrophobic PTFE Membrane, 0.45 um</td><td>Fisher Scientific</td><td>SLFHX13NL</td><td></td></tr></tbody></table>

synthesis of terpolymers at mild temperatures using dynamic sulfur bonds in poly(s-divinylbenzene)

Elemental sulfur (S8) is a byproduct of the petroleum industry with millions of tons produced annually. Such abundant production and limited applications lead to sulfur as a cost-efficient reagent for polymer synthesis. Inverse vulcanization combines elemental sulfur with a variety of monomers to form functional polysulfides without the need for solvents. Short reaction times and straight forward synthetic methods have led to rapid expansion of inverse vulcanization. However, high reaction temperatures (&#62;160 &#176;C) limit the types of monomers that can be used. Here, the dynamic sulfur bonds in poly(S-divinylbenzene) are used to initiate polymerization at much lower temperatures. The S-S bonds in the prepolymer are less stable than S-S bonds in S8, allowing radical formation at 90 &#176;C rather than 159 &#176;C. A variety of allyl and vinyl ethers have been incorporated to form terpolymers. The resulting materials were characterized by 1H NMR, gel permeation chromatography, and differential scanning calorimetry, as well as examining changes in solubility. This method expands on the solvent-free, thiyl radical chemistry utilized by inverse vulcanization to create polysulfides at mild temperatures. This development broadens the range of monomers that can be incorporated thus expanding the accessible material properties and possible applications.

Poly(S-DVB) was synthesized according to published protocols using high temperatures (185 &#176;C) to initiate S8 ring cleavage forming radicals3. These radicals then initiate polymerization with DVB. The molten sulfur and liquid DVB eliminate the need for solvents. Within 30 min, sulfur and DVB react completely for form poly(S-DVB). Upon removal from the vial, the polymer is a hard, brittle material at lower sulfur content (30-40%). Mid-range sulfur con...

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Synthesis of Terpolymers at Mild Temperatures Using Dynamic Sulfur Bonds in PolyS-Divinylbenzene

The goal of this protocol is to initiate polymerization using dynamic sulfur bonds in poly(S-divinylbenzene) at mild temperatures (90 &#176;C) without using solvents. Terpolymers are characterized by GPC, DSC and 1H NMR, and tested for changes in solubility.

Synthesis of Terpolymers at Mild Temperatures Using Dynamic Sulfur Bonds in Poly(S-Divinylbenzene)

Elemental sulfur (S8) is a byproduct of the petroleum industry with millions of tons produced annually. Such abundant production and limited applications ...

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7.6K Views.  Ball State University. The goal of this protocol is to initiate polymerization using dynamic sulfur bonds in poly(S-divinylbenzene) at mild temperatures (90 °C) without using solvents. Terpolymers are characterized by GPC, DSC and 1H NMR, and tested for changes in solubility.

Video: Synthesis of Terpolymers at Mild Temperatures Using Dynamic Sulfur Bonds in PolyS-Divinylbenzene

Synthesis of Ligand-free CdS Nanoparticles within a Sulfur Copolymer Matrix

Aliphatic ligands are typically used during the synthesis of nanoparticles to help mediate their growth in addition to operating as high-temperature solvents. These coordinating ligands help solubilize and stabilize the nanoparticles while in solution, and can influence the resulting size and reactivity of the nanoparticles during their formation. Despite the ubiquity of using ligands during synthesis, the presence of aliphatic ligands on the nanoparticle surface can result in a number of problems during the end use of the nanoparticles, necessitating further ligand stripping or ligand exchange procedures. We have developed a way to synthesize cadmium sulfide (CdS) nanoparticles using a unique sulfur copolymer. This sulfur copolymer is primarily composed of elemental sulfur, which is a cheap and abundant material. The sulfur copolymer has the advantages of operating both as a high temperature solvent and as a sulfur source, which can react with a cadmium precursor during nanoparticle synthesis, resulting in the generation of ligand free CdS. During the reaction, only some of the copolymer is consumed to produce CdS, while the rest remains in the polymeric state, thereby producing a nanocomposite material. Once the reaction is finished, the copolymer stabilizes the nanoparticles within a solid polymeric matrix. The copolymer can then be removed before the nanoparticles are used, which produces nanoparticles that do not have organic coordinating ligands. This nascent synthesis technique presents a method to produce metal-sulfide nanoparticles for a wide variety of applications where the presence of organic ligands is not desired.

Herein we present a method to synthesize ligand-free cadmium sulfide (CdS) nanoparticles based on a unique sulfur copolymer. The sulfur copolymer operates as a high temperature solvent and a sulfur source during the nanoparticle synthesis and stabilizes the nanoparticles after the reaction.

Aliphatic ligands are typically used during the synthesis of nanoparticles to help mediate their growth in addition to operating as high-temperature ...

Electroactive Polymer Nanoparticles Exhibiting Photothermal Properties

A method for the synthesis of electroactive polymers is demonstrated, starting with the synthesis of extended conjugation monomers using a three-step process that finishes with Negishi coupling. Negishi coupling is a cross-coupling process in which a chemical precursor is first lithiated, followed by transmetallation with ZnCl2. The resultant organozinc compound can be coupled to a dibrominated aromatic precursor to give the conjugated monomer. Polymer films can be prepared via electropolymerization of the monomer and characterized using cyclic voltammetry and ultraviolet-visible-near infrared (UV-Vis-NIR) spectroscopy. Nanoparticles (NPs) are prepared via emulsion polymerization of the monomer using a two-surfactant system to yield an aqueous dispersion of the polymer NPs. The NPs are characterized using dynamic light scattering, electron microscopy, and UV-Vis-NIR-spectroscopy. Cytocompatibility of NPs is investigated using the cell viability assay. Finally, the NP suspensions are irradiated with a NIR laser to determine their effectiveness as potential materials for photothermal therapy (PTT).

A protocol is presented for the synthesis and preparation of nanoparticles consisting of electroactive polymers.

A method for the synthesis of electroactive polymers is demonstrated, starting with the synthesis of extended conjugation monomers using a three-step ...

Engineering

The Preparation and Properties of Thermo-reversibly Cross-linked Rubber Via Diels-Alder Chemistry

A method for using Diels Alder thermo-reversible chemistry as cross-linking tool for rubber products is demonstrated. In this work, a commercial ethylene-propylene rubber, grafted with maleic anhydride, is thermo-reversibly cross-linked in two steps. The pending anhydride moieties are first modified with furfurylamine to graft furan groups to the rubber backbone. These pendant furan groups are then cross-linked with a bis-maleimide via a Diels-Alder coupling reaction. Both reactions can be performed under a broad range of experimental conditions and can easily be applied on a large scale. The material properties of the resulting Diels-Alder cross-linked rubbers are similar to a peroxide-cured ethylene/propylene/diene rubber (EPDM) reference. The cross-links break at elevated temperatures (&#62; 150 &#176;C) via the retro-Diels-Alder reaction and can be reformed by thermal annealing at lower temperatures (50-70 &#176;C). Reversibility of the system was proven with infrared spectroscopy, solubility tests and mechanical properties. Recyclability of the material was also shown in a practical way, i.e., by cutting a cross-linked sample into small parts and compression molding them into new samples displaying comparable mechanical properties, which is not possible for conventionally cross-linked rubbers.

A simple two-step approach involving rubber modification and cross-linking yields fully reworkable, elastic rubber products.

A method for using Diels Alder thermo-reversible chemistry as cross-linking tool for rubber products is demonstrated. In this work, a commercial ...

Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level

We demonstrate a method for the synthesis of cyclic polymers and a protocol for characterizing their diffusive motion in a melt state at the single molecule level. An electrostatic self-assembly and covalent fixation (ESA-CF) process is used for the synthesis of the cyclic poly(tetrahydrofuran) (poly(THF)). The diffusive motion of individual cyclic polymer chains in a melt state is visualized using single molecule fluorescence imaging by incorporating a fluorophore unit in the cyclic chains. The diffusive motion of the chains is quantitatively characterized by means of a combination of mean-squared displacement (MSD) analysis and a cumulative distribution function (CDF) analysis. The cyclic polymer exhibits multiple-mode diffusion which is distinct from its linear counterpart. The results demonstrate that the diffusional heterogeneity of polymers that is often hidden behind ensemble averaging can be revealed by the efficient synthesis of the cyclic polymers using the ESA-CF process and the quantitative analysis of the diffusive motion at the single molecule level using the MSD and CDF analyses.

A protocol for the synthesis and characterization of diffusive motion of cyclic polymers at the single molecule level is presented.

We demonstrate a method for the synthesis of cyclic polymers and a protocol for characterizing their diffusive motion in a melt state at the single ...

Self-assembling Morphologies Obtained from Helical Polycarbodiimide Copolymers and Their Triazole Derivatives

A facile method for the preparation of polycarbodiimide-based secondary structures (e.g., nano-rings, &#34;craters,&#34; fibers, looped fibers, fibrous networks, ribbons, worm-like aggregates, toroidal structures, and spherical particles) is described. These aggregates are morphologically influenced by extensive hydrophobic side chain-side chain interactions of the singular polycarbodiimide strands, as inferred by atomic force microscopy (AFM) and scanning electron microscopy (SEM) techniques. Polycarbodiimide-g-polystyrene copolymers (PS-PCDs) were prepared by a combination of synthetic methods, including coordination-insertion polymerization, copper(I)-catalyzed azide alkyne cycloaddition (CuAAC) &#34;click&#34; chemistry, and atom transfer radical polymerization (ATRP). PS-PCDs were found to form specific toroidal architectures at low concentrations in CHCl3. To determine the influence of a more polar solvent medium (i.e., THF and THF/EtOH) on polymer aggregation behavior, a number of representative PS-PCD composites have been tested to show discrete concentration-dependent spherical particles. These fundamental studies are of practical interest to the development of experimental procedures for desirable architectures by directed self-assembly in thin film. These architectures may be exploited as drug carriers, whereas other morphological findings represent certain interest in the area of novel functional materials.

Here, we present a protocol to prepare and visualize secondary structures (e.g., fibers, toroidal architectures, and nano-spheres) derived from helical polycarbodiimides. The morphology characterized by both atomic force microscopy (AFM) and scanning electron microscopy (SEM) was shown to depend on molecular structure, concentration, and the solvent of choice.

A facile method for the preparation of polycarbodiimide-based secondary structures (e.g., nano-rings, &#34;craters,&#34; fibers, looped fibers, fibrous ...

Scale-up Chemical Synthesis of Thermally-activated Delayed Fluorescence Emitters Based on the Dibenzothiophene-S,S-Dioxide Core

We report a procedure to linearly scale-up the synthesis of 2,8-bis(3,6-di-tert-butyl-9H-carbazol-9-yl)dibenzothiophene-S,S-dioxide (compound 4) and 2,8-bis(10H-phenothiazin-10-yl)dibenzothiophene-S,S-dioxide (compound 5) using Buchwald-Hartwig cross-coupling reaction conditions. In addition, we demonstrate a scaled-up synthesis of all non-commercially available starting materials that are required for the amination cross-coupling reaction. In the present article, we provide the detailed synthetic procedures for all of the described compounds, alongside their spectral characterization. This work shows the possibility to produce organic molecules for optoelectronic applications on a large scale, which facilitates their implementation into real world devices.

Scale-up synthesis of highly efficient thermally activated delayed fluorescence emitters is described in the presented article.

We report a procedure to linearly scale-up the synthesis of 2,8-bis(3,6-di-tert-butyl-9H-carbazol-9-yl)dibenzothiophene-S,S-dioxide (compound 4) and ...

Synthesis of a Thiol Building Block for the Crystallization of a Semiconducting Gyroidal Metal-sulfur Framework

We present a method for preparing thioester molecules as the masked form of the thiol linkers and their utilization for accessing a semiconducting and porous metal-dithiolene network in the highly ordered single crystalline state. Unlike the highly reactive free-standing thiols, which tend to decompose and complicate the crystallization of metal-thiolate open frameworks, the thioester reacts in situ to provide the thiol species, serving to mitigate the reaction between the mercaptan units and the metal centers, and to improve crystallization consequently. Specifically, the thioester was synthesized in a one-pot procedure: an aromatic bromide (hexabromotriphenylene) reacted with excess sodium thiomethoxide under vigorous conditions to first form the thioether intermediate product. The thioether was then demethylated by the excess thiomethoxide to provide the thiolate anion that was acylated to form the thioester product. The thioester was conveniently purified by standard column chromatography, and then used directly in the framework synthesis, wherein NaOH and ethylenediamine serve to revert in situ the thioester to the thiol linker for assembling the single-crystalline Pb(II)-dithiolene network. Compared with other methods for thiol synthesis (e.g., by cleaving alkyl thioether using sodium metal and liquid ammonia), the thioester synthesis here uses simple conditions and economical reagents. Moreover, the thioester product is stable and can be conveniently handled and stored. More importantly, in contrast to the generic difficulty in accessing crystalline metal-thiolate open frameworks, we demonstrate that using the thioester for in situ formation of the thiol linker greatly improves the crystallinity of the solid-state product. We intend to encourage broader research efforts on the technologically important metal-sulfur frameworks by disclosing the synthetic protocol for the thioester as well as the crystalline framework solid.

Here, we present a one-pot, transition-metal-free synthesis of thiols and thioesters from aromatic halides and sodium thiomethoxide, followed by the preparation of single crystals of a metal-dithiolene network using thiol species generated in situ from the more stable and tractable thioester.

We present a method for preparing thioester molecules as the masked form of the thiol linkers and their utilization for accessing a semiconducting and ...

Synthesis of Soft Polysiloxane-urea Elastomers for Intraocular Lens Application

This study discusses a synthesis route for soft polysiloxane-based urea (PSU) elastomers for their applications as accommodating intraocular lenses (a-IOLs). Aminopropyl-terminated polydimethylsiloxanes (PDMS) were previously prepared via the ring-chain equilibration of the cyclic siloxane octamethylcyclotetrasiloxane (D4) and 1,3-bis(3-aminopropyl)-tetramethyldisiloxane (APTMDS). Phenyl groups were introduced into the siloxane backbone via the copolymerization of D4 and 2,4,6,8-tetramethyl-2,4,6,8-tetraphenyl-cyclotetrasiloxane (D4Me,Ph). These polydimethyl-methyl-phenyl-siloxane-block copolymers were synthesized for increasing the refractive indices of polysiloxanes. For applications as an a-IOL, the refractive index of the polysiloxanes must be equivalent to that of a young human eye lens. The polysiloxane molecular weight is controlled by the ratio of the cyclic siloxane to the endblocker APTMDS. The transparency of the PSU elastomers is examined by the transmittance measurement of films between 200 and 750 nm, using a UV-Vis spectrophotometer. Transmittance values at 750 nm (upper end of the visible spectrum) are plotted against the PDMS molecular weight, and &#62; 90% of the transmittance is observed until a molecular weight of 18,000 g&#183;mol&#8722;1. Mechanical properties of the PSU elastomers are investigated using stress-strain tests on die-cut dog-bone-shaped specimens. For evaluating mechanical stability, mechanical hysteresis is measured by repeatedly stretching (10x) the specimens to 5% and 100% elongation. Hysteresis considerably decreases with the increase in the PDMS molecular weight. In vitro cytotoxicity of some selected PSU elastomers is evaluated using an MTS cell viability assay. The methods described herein permit the synthesis of a soft, transparent, and noncytotoxic PSU elastomer with a refractive index approximately equal to that of a young human eye lens.

This study describes synthetic routes for aminopropyl-terminated polydimethylsiloxanes and polydimethyl-methyl-phenyl-siloxane-block copolymers and for soft polysiloxane-based urea (PSU) elastomers. It presents the application of PSUs as accommodating an intraocular lens. An evaluation method for in vitro cytotoxicity is also described.

This study discusses a synthesis route for soft polysiloxane-based urea (PSU) elastomers for their applications as accommodating intraocular lenses ...

Efficient Synthesis of Polyfunctionalized Benzenes in Water via Persulfate-promoted Benzannulation of &#945;,&#946;-Unsaturated Compounds and Alkynes

Benzannulation reactions represent an effective protocol to transform acyclic building blocks into structurally varied benzene skeletons. Despite classical and recent approaches toward functionalized benzenes, in water metal-free methods remains a challenge and represents an opportunity to expand even more the set of tools used to synthesize polysubstituted benzene compounds. This protocol describes an operationally simple experimental setup to explore the benzannulation of &#945;,&#946;-unsaturated compounds and alkynes to afford unprecedented functionalized benzene rings in high yields. Ammonium persulfate is the reagent of choice and brings notable advantages as stability and easy handling. Moreover, the use of water as a solvent and the absence of metals impart more sustainability to the method. A modified workup procedure that avoids the use of drying agents also adds convenience to the protocol. The purification of the products is performed using only a plug of silica. The substrate scope is currently limited to terminal alkynes and &#945;,&#946;-unsaturated aliphatic compounds.

Efficient Synthesis of Polyfunctionalized Benzenes in Water via Persulfate-promoted Benzannulation of &#945;,&#946;-Unsaturated Compounds and Alkynes

A persulfate-promoted metal-free benzannulation of &#945;,&#946;-unsaturated compounds and alkynes in water toward the synthesis of unprecedented polyfunctionalized benzenes is reported.

Benzannulation reactions represent an effective protocol to transform acyclic building blocks into structurally varied benzene skeletons. Despite ...

Solution Blow Spinning of Polymeric Nano-Composite Fibers for Personal Protective Equipment

Light-weight, protective armor systems typically consist of high modulus (&#62;109 MPa) and high-strength polymeric fibers held in place with an elastic resin material (binder) to form a non-woven, unidirectional laminate. While significant efforts have focused on improving the mechanical properties of the high-strength fibers, little work has been undertaken to improve the properties of the binder materials. To improve the performance of these elastomeric polymer binders, a relatively new and simple fabrication process, known as solution blow spinning, was used. This technique is capable of producing sheets or webs of fibers with average diameters ranging from the nanoscale to the microscale. To achieve this, a solution blow spinning (SBS) apparatus has been designed and built in the laboratory to fabricate non-woven fiber mats from polymer elastomer solutions.
In this study, a commonly used binder material, a styrene-butadiene-styrene block-co-polymer dissolved in tetrahydrofuran, was used to produce nanocomposite fiber mats by adding metallic nanoparticles (NPs), such as iron oxide NPs, that were encapsulated with silicon oil and thus incorporated in the fibers formed via the SBS process. The protocol described in this work will discuss the effects of the various critical parameters involved in the SBS process, including the polymer molar mass, the selection of the thermodynamically appropriate solvent, the polymer concentration in solution, and the carrier gas pressure to assist others in performing similar experiments, as well as provide guidance to optimize the configuration of the experimental setup. The structural integrity and morphology of the resultant non-woven fiber mats were examined using scanning electron microscopy (SEM) and elemental X-ray analysis via energy-dispersive X-ray spectroscopy (EDS). The goal of this study is to evaluate the effects of the various experimental parameters and material selections to optimize the structure and morphology of the SBS fiber mats.

The primary goal of this study is to describe a protocol to prepare polymeric fiber mats with consistent morphology via solution blow spinning (SBS). We aim to use SBS to develop novel, tunable, flexible polymeric fiber nanocomposites for various applications, including protective materials, by incorporating nanoparticles in a polymer-elastomer matrix.

Light-weight, protective armor systems typically consist of high modulus (&#62;109 MPa) and high-strength polymeric fibers held in place with an elastic ...