Durable composites by vulcanization of oleyl-esterified lignin.

Productive utilization of lignocellulosic biomass is critical to the continued advancement of human civilization. Whereas the cellulose component can be efficiently upconverted to automotive fuel-grade ethanol, the lack of upconversion methods for the lignin component constitutes one of the grand challenges facing science. Lignin is an attractive feedstock for structural applications, in which its highly-crosslinked architecture can endow composite structures with high strengths. Prior work suggests that high-strength composites can be prepared by the reaction of olefin-modified lignin with sulfur. Those studies were limited to ≤5 wt% lignin, due to phase-separation of hydrophilic lignin from hydrophobic sulfur matrices. Herein we report a protocol to increase lignin hydrophobicity and thus its incorporation into sulfur-rich materials. This improvement is affected by esterifying lignin with oleic acid prior to its reaction with sulfur. This approach allowed preparation of esterified lignin-sulfur (ELS) composites comprising up to 20 wt% lignin. Two reaction temperatures were employed such that the reaction of ELS with sulfur at 180 °C would only produce S-C bonds at olefinic sites, whereas the reaction at 230 °C would produce C-S bonds at both olefin and aryl sites. Mechanistic analyses and microstructural characterization elucidated two ELS composites having compressive strength values (>20 MPa), exceeding the values observed with ordinary Portland cements. Consequently, this new method represents a way to improve lignin utilization to produce durable composites that represent sustainable alternatives to Portland cements.

High strength composites from low-value animal coproducts and industrial waste sulfur.

Herein we report high strength composites prepared by reaction of sulfur, plant oils (either canola oil or sunflower oil) and brown grease. Brown grease is a high-volume, low value animal fat rendering coproduct that represents one of the most underutilized products of agricultural animal processing. Chemically, brown grease is primarily comprised of triglycerides and fatty acids. The inverse vulcanization of the unsaturated units in triglycerides/fatty acids upon their reaction with sulfur yields CanBG x or SunBG x (x = wt% sulfur, varied from 85-90%). These composites were characterized by infrared spectroscopy, dynamic mechanical analysis (DMA), mechanical test stand analysis, elemental analysis, and powder X-ray diffraction. CanBG x and SunBG x composites exhibit impressive compressive strengths (28.7-35.9 MPa) when compared to other materials such as Portland cement, for which a compressive strength of ≥17 MPa is required for residential building. Stress-strain analysis revealed high flexural strengths of 6.5-8.5 MPa for CanBG x and SunBG x composites as well, again exceeding the range of ∼2-5 MPa for ordinary Portland cements. The thermal properties of the composites were assessed by thermogravimetric analysis, revealing decomposition temperatures ranging from 223-226 °C, and by differential scanning calorimetry. These composites represent a promising new application for low value animal coproducts having limited value to be used as organic crosslinkers in the atom-efficient inverse vulcanization process to yield high sulfur-content materials that have impressive mechanical properties.

Sterically crowded 1,4-diiodobenzene as a precursor to difunctional hypervalent iodine compounds.

A bulky 1,4-di-iodobenzene having four adjacent para-tBu-C6H4 group (Ar') substituents (1) was used to prepare the di-hypervalent iodine compound 1,4-[I(OAc)2]2-2,3,5,6-Ar'4-C6 (2). Despite the steric encumbrance of the iodine center by the flanking aryl substituents, compound 2 undergoes ready cyclization under mild conditions (excess CF3COOH at 55 °C, 30 min) to afford a dicyclic di-iodonium di-triflate salt 3. The single crystal structures of compounds 2 and 3 were examined and compared to the formerly characterized precursor 1. The para-tert-butyl groups on these compounds also render the compounds more soluble than multifunctional hypervalent iodine (HVI) compounds. HVI compounds having multiple iodine(III) centers are increasingly of interest for applications as recyclable reagents, materials precursors, and as Lewis acids.

High Performance of Anion Exchange Blend Membranes Based on Novel Phosphonium Cation Polymers for All-Vanadium Redox Flow Battery Applications.

The deployment of alkaline anion exchange membranes (AEMs) in flow battery applications has the advantage of a low cationic species crossover rate. However, the alkaline stability conjugated to the low conductivity of hydroxide ions of anion exchange membranes (AEMs) still represents a major drawback for the large deployment of such technology. In this study, three types of tetraarylpolyphosphonium (pTAP)-based copolymers (namely, CP1, CP2, and CP3) are synthesized and blended with chitosan and polyvinylidene fluoride (PVDF) for the fabrication of AEMs. Chitosan, a green biopolymer, was employed as a blend to enhance the water uptake of the base ionomer matrix. It is proposed that the abundancy of hydroxyl groups in chitosan improves considerably the ionic conductivity, water transport, and ion selectivity of the membrane, together with facilitating the dispersion of the chitosan in the pTAP copolymer matrix. The purpose of blending PVDF is instead to provide stable mechanical strength to the composite blend. The chemical, mechanical, and thermal stabilities of the three fabricated composite-blend membranes (i.e., CM1, CM2, and CM3) were characterized. All the membranes exhibited a high water retaining capacity of up to 36.26% (recorded for CM2) along with a hydroxyl ion conductivity of 17.39 mS cm-1. Due to the strong interactions between pTAP copolymers, chitosan, and PVDF polymers (confirmed also by Fourier transform infrared spectroscopy), the studied anion exchange membranes are able to retain up to 97% of the original OH conductivity after 1 M KOH treatment at room temperature for 100 h. The three membranes, namely, CM1, CM2, and CM3, have vanadium ion permeabilities measured at 20 °C of 1.775 × 10-8, 1.718 × 10-8, and 1.648 × 10-8 cm2/s, respectively, which are lower than that for the commercially available Nafion. The good stability and remarkable cell performance of the composite-blend membranes reported here make them definitely excellent candidates for the future generation of vanadium redox flow batteries.

Investigating the suitability of poly tetraarylphosphonium based anion exchange membranes for electrochemical applications.

Anion exchange membranes (AEMs) are becoming increasingly common in electrochemical energy conversion and storage systems around the world (EES). Proton-/cation-exchange membranes (which conduct positive charged ions such as H+ or Na+) have historically been used in many devices such as fuel cells, electrolysers, and redox flow batteries. High capital costs and the use of noble metal catalysts are two of the current major disadvantages of polymer electrolyte membrane (PEM)-based systems. AEMs may be able to overcome the limitations of conventional PEMs. As a result, polymers with anion exchange properties have recently attracted a lot of attention due to their significant benefits in terms of transitioning from a highly acidic to an alkaline environment, high kinetics for oxygen reduction and fuel oxidation in an alkaline environment, and lower cost due to the use of non-precious metals. The aim of this research was to learn more about the development of a new AEM based on poly tetraarylphosphonium ionomers (pTAP), which has high ionic conductivity, alkaline stability, thermal stability, and good mechanical properties, making it a more cost-effective and stable alternative to conventional and commercial AEMs. A simple solution casting method was used to build novel anion exchange composite membranes with controlled thicknesses using the synthesized pTAP with polysulfone (PS). To ensure their suitability for use as an electrolyte in alkaline electrochemical systems, the composite membranes were characterized using FTIR, XRD, water uptake, ionic conductivity, and alkaline stability. At 40 °C, the PS/pTAP 40/60 percent membrane had a maximum ionic conductivity of 4.2 mS/cm. The thermal and mechanical stability of the composite membranes were also examined, with no substantial weight loss observed up to 150 °C. These findings pave the way for these membranes to be used in a wide variety of electrochemical applications.

Recent advances in starch-based films toward food packaging applications: Physicochemical, mechanical, and functional properties.

Interest in starch-based films has increased precipitously in response to a growing demand for more sustainable and environmentally sourced food packaging materials. Starch is an optimal candidate for these applications given its ability to form thermoplastic materials and films with affordable and often sustainably sourced plasticizers like those produced as waste byproducts by biodiesel and agricultural industries. Starch is also globally ubiquitous, affordable, and environmentally benign. Although the process of producing starch films is relatively straightforward, numerous factors, including starch source, extraction method, film formulation, processing methods, and curing procedures, drastically impact the ultimate material properties. The significant strides made from 2015 to early 2020 toward elucidating how these variables can be leveraged to improve mechanical and barrier properties as well as the implementation of various additives or procedural modifications are cataloged in this review. Advances toward the development of functional films containing antioxidant, antibacterial, or spoilage indicating components to prevent or signal the degradation of food products are also discussed.

Highly Luminescent Heavier Main Group Analogues of Boron-Dipyrromethene.

The preparation and photophysical properties of two heavier main group element analogues of boron-dipyrromethene (BODIPY) chromophores are described. Specifically, we have prepared dipyrrin complexes of dichlorogallate (GADIPY) or phenylphosphenium (PHODIPY) units. Whereas cationic PHODIPY is labile, decomposing to a phosphine over time, GADIPY is readily prepared in good yield as a crystalline solid having moderate air- and water-stability. Crystallographically characterized GADIPY displays intense green photoluminescence (λem = 505 nm, Φem = 0.91 in toluene). These inaugural heavier main group element analogues of BODIPY offer a glimpse into the potential for elaboration to a panoply of chromophores with diverse photophysical properties.

Durable, acid-resistant copolymers from industrial by-product sulfur and microbially-produced tyrosine.

The search for alternative feedstocks to replace petrochemical polymers has centered on plant-derived monomer feedstocks. Alternatives to agricultural feedstock production should also be pursued, especially considering the ecological damage caused by modern agricultural practices. Herein, l-tyrosine produced on an industrial scale by E. coli was derivatized with olefins to give tetraallyltyrosine. Tetraallyltyrosine was subsequently copolymerized via its inverse vulcanization with industrial by-product elemental sulfur in two different comonomer ratios to afford highly-crosslinked network copolymers TTS x (x = wt% sulfur in monomer feed). TTS x copolymers were characterized by infrared spectroscopy, elemental analysis, thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis (DMA). DMA was employed to assess the viscoelastic properties of TTS x through the temperature dependence of the storage modulus, loss modulus and energy damping ability. Stress-strain analysis revealed that the flexural strength of TTS x copolymers (>6.8 MPa) is more than 3 MPa higher than flexural strengths for previously-tested inverse vulcanized biopolymer derivatives, and more than twice the flexural strength of some Portland cement compositions (which range from 3-5 MPa). Despite the high tyrosine content (50-70 wt%) in TTS x , the materials show no water-induced swelling or water uptake after being submerged for 24 h. More impressively, TTS x copolymers are highly resistant to oxidizing acid, with no deterioration of mechanical properties even after soaking in 0.5 M sulfuric acid for 24 h. The demonstration that these durable, chemically-resistant TTS x copolymers can be prepared from industrial by-product and microbially-produced monomers via a 100% atom-economical inverse vulcanization process portends their potential utility as sustainable surrogates for less ecofriendly materials.

Thermally-healable network solids of sulfur-crosslinked poly(4-allyloxystyrene).

Network polymers of sulfur and poly(4-allyloxystyrene), PAOS x (x = percent by mass sulfur, where x is varied from 10-99), were prepared by reaction between poly(4-allyloxystyrene) with thermal homolytic ring-opened S8 in a thiol-ene-type reaction. The extent to which sulfur content and crosslinking influence thermal/mechanical properties was assessed. Network materials having sulfur content below 50% were found to be thermosets, whereas those having >90% sulfur content are thermally healable and remeltable. DSC analysis revealed that low sulfur-content materials exhibited neither a T g nor a T m from -50 to 140 °C, whereas higher sulfur content materials featured T g or T m values that scale with the amount of sulfur. DSC data also revealed that sulfur-rich domains of PAOS90 are comprised of sulfur-crosslinked organic polymers and amorphous sulfur, whereas, sulfur-rich domains in PAOS99 are comprised largely of α-sulfur (orthorhombic sulfur). These conclusions are further corroborated by CS2-extraction and analysis of extractable/non-extractable fractions. Calculations based on TGA, FT-IR, H2S trapping experiments, CS2-extractable mass, and elemental combustion microanalysis data were used to assess the relative percentages of free and crosslinked sulfur and average number of S atoms per crosslink. Dynamic mechanical analyses indicate high storage moduli for PAOS90 and PAOS99 (on the order of 3 and 6 GPa at -37 °C, respectively), with a mechanical T g between -17 °C and 5 °C. A PAOS99 sample retains its full initial mechanical strength after at least 12 pulverization-thermal healing cycles, making it a candidate for facile repair and recyclability.

Convenient route to tetraarylphosphonium polyelectrolytes via metal-catalysed P-C coupling polymerisation of aryl dihalides and diphenylphosphine.

A P-C bond-forming reaction has been applied to the convenient preparation of tetraarylphosphonium polyelectrolytes (TPELs) from aryl dihalides and diphenylphosphine. A TPEL having a thermal decomposition temperature of 460 °C that is also stable to heating at 65 °C in 6 M NaOH(aq) for at least 24 h has been prepared by this method.

Comparison of 1,4-distyrylfluorene and 1,4-distyrylbenzene analogues: synthesis, structure, electrochemistry and photophysics.

A series of nine 1,4-distyrylfluorene derivatives (2) functionalized with substituents of variable electrondonating or -accepting capabilities was synthesised. The photophysical properties of the molecules were investigated, including UV/vis absorption, photoluminescence emission, and fluorescence quantum yields. Photophysical properties of chromophores 2 were found to exhibit significant solvatochromic effects, especially in the Stokes shift and photoluminescence maxima. The electrochemical properties of series 2 were also assessed by cyclic voltammetry and differential pulse voltammetry. Results of photophysical and electrochemical analyses were further supported by DFT calculations (B3LYP/6-31G*) and single crystal X-ray diffraction on select molecules. The contributions of intermolecular π-stacking and hydrogen bonding to crystal packing are discussed. A series of nine 1,4-distyrylphenylene derivatives (3) were also synthesised and similarly characterized for comparison to photophysical and solvatochromic effects observed in series 2. Properties of similarly-substituted molecules in series 2 and 3 were compared to one another in order to assess the influence of the 1,4-fluorenylene unit.

Naphthoxaphospholes as examples of fluorescent phospha-acenes.

Seven new fluorescent 2-R-naphtho[2,3-d]oxaphospholes (R-NOPs) (4a­g; R = tBu (a), Ad (b), C(6)H(5) (c), 4-MeC(6)H(4) (d), 4-ClC(6)H(4) (e), 4-BrC(6)H(4) (f ), 4-MeOC(6)H(4) (g)), have been synthesized by cyclocondensation reactions of benzimidoyl chlorides with 3-phosphino-2-naphthol (3). The compounds were characterized by multinuclear NMR, UV-vis, and fluorescence spectroscopy. Compounds 4a­d and 4g were characterized by cyclic voltammetry experiments. The solid state structures of compounds 4b and 4d were also determined by single-crystal X-ray diffraction experiments.

Photochemically-induced dioxygenase-type CO-release reactivity of group 12 metal flavonolate complexes.

Exposure of 3-hydroxyflavonolate complexes of the group 12 metals to UV light under aerobic conditions results in oxidative carbon-carbon bond cleavage and CO release. This reactivity is novel in that it occurs under mild reaction conditions and suggests that light-induced CO-release reactivity involving metal flavonolate species may be possible in biological systems.

Metal ion detection by luminescent 1,3-bis(dimethylaminomethyl) phenyl receptor-modified chromophores and cruciforms.

Chromophores ranging from simple small molecule π-conjugated systems comprised of phenylene ethynylene or fluorenylethynyl units to cross-conjugated Bunz-type cruciforms have been derivatized to include 1,3-bis(dimethylaminomethyl)phenyl moieties. The photophysical responsiveness of these diamino-substituted chromophores to metal ions has been examined. Both emission enhancement (turn-on) and ratiometric fluorescence detection of Cu(2+) and Zn(2+) ions have been achieved in THF.

Interchromophore orientation scaffolding by m-terphenyl oxacyclophanes.

Modular oxacyclophanes featuring m-terphenyl units scaffold inter-pi-system interaction in face-to-face stacked or orthogonal orientations, leading to distinct photophysical properties.

Bifunctional cross-conjugated luminescent phosphines and phosphine derivatives: phospha-cruciforms.

Cross-conjugated bifunctional species including a phosphine, phosphine oxide, phosphine sulfide, phosphonium salt, phosphorus ylide and a gold(I) phosphine complex have been prepared. The photophysical characteristics of the series of compounds have been determined experimentally and are discussed/compared with simpler analogues lacking cross-conjugated branches and rationalized on the basis of DFT calculations.

Poly(p-phenylenevinylene) Derivatives with Defined Conjugation Segments and Post-Polymerization Modification with Sterically Enshrouded Chromophores.

Two poly(p-phenylenevinylene) derivative alternating copolymers (P1-I and P2-I) have been prepared featuring iodo substituents and m-phenylene units to periodically disrupt conjugation. P1-I was derivatized with various chromophores to yield P1a-f. In P1a-f, the chromophores were positioned within a sterically protected pocket shielding them from interchain interactions so that intrachain interactions between polymer segments could be observed. Solution and film properties of polymers have been examined. Post-polymerization chromophore modification leads to new photophysical properties such as intramolecular charge transfer and fluorescent resonance energy transfer processes in some cases.

Visible chromophore phosphines as functional elements of luminescent metallopolymers.

A general modular route to fluorophore-linked diphosphines from (4-iodophenyl)P(O)Ph(2) is described. The preparation of chromophoric diphosphine (LHP1) proceeded readily using this route. LHP1 was employed to prepare luminescent metallopolymers of platinum (P1) and palladium (P2) exhibiting modest degrees of polymerization (13-14) and extents of polymerization ( approximately 97%). P1 and P2 appear to be the first metallopolymers polymerized via a visible-absorbing/emitting diphosphine. The photophysical properties of these novel materials are discussed.

Canopied trans-chelating bis(N-heterocyclic carbene) ligand: synthesis, structure and catalysis.

The terphspan scaffold was employed to support a bis(N-heterocyclic carbene) ligand () that provides a m-terphenyl canopy over one side of its metal complexes. Single-crystal X-ray diffraction studies on a silver complex of {[Ag()]AgBr(2)}(2) revealed an unusual tetranuclear silver core with a Ag-Ag bond distance of 3.0241(8) A with as a trans-chelating ligand (C-Ag-C = 171 degrees ). A preliminary X-ray structure of pseudo-square planar [PdCl(2)()] showed a similar binding mode of (C-Pd-C = 177 degrees ). High yields were obtained in Suzuki-Miyaura coupling reactions utilizing [PdCl(2)()] as the procatalyst and the results were compared with analogous complexes of trans-spanning diphosphine () and diphosphinite () complexes. The diphosphinite complex, [PdCl(2)()], decomposes to [mu-ClPd(PPh(2)OH)(PPh(2)O)](2) at room temperature.

Poly(p-phenylene ethynylene) Incorporating Sterically Enshrouding m-Terphenyl Oxacyclophane Canopies.

A sterically encumbered m-terphenyl oxacyclophane substituted with two aryl iodide substituents has been prepared as a versatile monomer for the preparation of π-conjugated polymers. The monomer has been used to prepare a poly(p-phenylene ethynylene) derivative (P1) incorporating oxacyclophane units as canopies that shield one side of the π-system from inter-chain interactions. The photophysical properties of P1 in dilute solution compare well to those of a poly(p-phenylene ethynylene) derivative (P2) that lacks the canopy. The presence of the steric canopy leads to a diminished inter-chain interaction in the solid state and enhances the kinetic response of P1 to vapors of nitro-organics such as TNT, presumably by increasing the permeability of P1 to these analytes over that of P2.