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

   https://doi.org/10.1039/c9ra06213k  

   Thiounn, Timmy ; Tennyson, Andrew G. ; Smith, Rhett C. ( October 2019 , RSC Advances)

   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 TTSx ( x = wt% sulfur in monomer feed). TTSx 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 TTSx through the temperature dependence of the storage modulus, loss modulus and energy damping ability. Stress–strain analysis revealed that the flexural strength of TTSx 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 TTSx , the materials show no water-induced swelling or water uptake after being submerged for 24 h. More impressively, TTSx copolymersmore »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 TTSx 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.« less
2. Copolymerization of an aryl halide and elemental sulfur as a route to high sulfur content materials

   https://doi.org/10.1039/c9py01706b  

   Karunarathna, Menisha S. ; Lauer, Moira K. ; Tennyson, Andrew G. ; Smith, Rhett C. ( March 2020 , Polymer Chemistry)

   High sulfur-content materials (HSMs) have been investigated for a plethora of applications owing to a combination of desirable properties and the low cost of waste sulfur as a starting monomer. Whereas extended sulfur catenates are unstable with respect to orthorhombic sulfur (S 8 rings) at STP, oligomeric/polymeric sulfur chains can be stabilized when they are confined in a supporting matrix. The vast majority of reported HSMs have been made by inverse vulcanization of sulfur and olefins. In the current case, a radical aryl halide–sulfur polymerization (RASP) route was employed to form an HSM ( XS81 ) by copolymerizing elemental sulfur with the xylenol derivative 2,4-dimethyl-3,5-dichlorophenol (DDP). XS81 is a composite of which 81 wt% is sulfur, wherein the sulfur is distributed between cross-linking chains averaging four sulfur atoms in length and trapped sulfur that is not covalently attached to the network. XS81 (flexural strength = 2.0 MPa) exhibits mechanical properties on par with other HSMs prepared by inverse vulcanization. Notably, XS81 retains mechanical integrity over many heat-recast cycles, making it a candidate for facile recyclability. This is the first report of an HSM comprising stabilized polymeric sulfur that has been successfully prepared from a small molecular comonomer by RASP. Preparationmore »of XS81 thus demonstrates a new route to access HSMs using small molecular aryl halides, a notable expansion beyond the olefins required for the well-studied inverse vulcanization route to HSMs from small molecular comonomers.« less
3. Robust, remeltable and remarkably simple to prepare biomass–sulfur composites

   https://doi.org/10.1039/d0ma00538j  

   Lauer, Moira K. ; Karunarathna, Menisha S. ; Tennyson, Andrew G. ; Smith, Rhett C. ( October 2020 , Materials Advances)

   Lignocellulosic biomass holds a tremendous opportunity for transformation into carbon-negative materials, yet the expense of separating biomass into its cellulose and lignin components remains a primary economic barrier to biomass utilization. Herein is reported a simple procedure to convert several biomass-derived materials into robust, recyclable composites through their reaction with elemental sulfur by inverse vulcanization, a process in which olefins are crosslinked by sulfur chains. In an effort to understand the chemistry and the parameters leading to the strength of these composites, sulfur was reacted with four biomass-derivative comonomers: (1) unmodified peanut shell powder, (2) allyl peanut shells, (3) ‘mock’ allyl peanut shells (a mixture containing independently-prepared allyl cellulose and allyl lignin), or (4) peanut shells that have been defatted by extraction of peanut oil. The reactions of these materials with sulfur produce the biomass–sulfur composites PSx , APSx , mAPSx and dfPSx , respectively, where x = wt% sulfur in the monomer feed. The influence of biomass : sulfur ratio was assessed for PSx and APSx . Thermal/mechanical properties of composites were evaluated for comparison to commercial materials. Remarkably, unmodified peanut shell flour can simply be heated with elemental sulfur to produce composites having flexural/compressive strengths exceeding those of Portland cement,more »an effect traced to the presence of olefin-bearing peanut oil in the peanut shells. When allylated peanut shells are used in this process, a composite having twice the compressive strength of Portland cement is attained.« less
4. Lignin-derivable alternatives to petroleum-derived non-isocyanate polyurethane thermosets with enhanced toughness

   https://doi.org/10.1039/d2ma00895e  

   Mhatre, Sampanna V. ; Mahajan, Jignesh S. ; Epps, Thomas H. ; Korley, LaShanda T. ( January 2023 , Materials Advances)

   The structural similarities between lignin-derivable bisguaiacols and petroleum-derived bisphenol A/F (BPA/BPF) suggest that bisguaiacols could be ideal biobased alternatives to BPA/BPF in non-isocyanate polyurethane (NIPU) thermosets. Herein, bisguaiacol/bisphenol-derived cyclic carbonates with variations in methoxy content and bridging-carbon substitution were cured with two triamines of different chain lengths, and the impact of these differences on the thermomechanical properties of NIPU networks was examined. The methoxy groups present in the lignin-derivable cyclic carbonates led to thermosets with significantly improved toughness (∼49–59 MJ m −3 ) and elongation at break ( ε b ∼195–278%) vs. the BPA/BPF-based benchmarks (toughness ∼ 26–35 MJ m −3 , ε b ∼ 86–166%). Furthermore, the addition of dimethyl substitution on the bridging carbon resulted in increased yield strength ( σ y ) – from ∼28 MPa for networks with unsubstituted bridging carbons to ∼45 MPa for the dimethyl-substituted materials. These enhancements to mechanical properties were achieved while retaining essential thermoset properties, such as application-relevant moduli and thermal stabilities. Finally, the triamine crosslinkers provided substantial tunability of thermomechanical properties and produced NIPUs that ranged from rigid materials with a high yield strength ( σ y ∼ 65–88 MPa) to flexible and tough networks. Overall, the structure-property relationships presentedmore »highlight a promising framework for the design of versatile, bio-derivable, NIPU thermosets.« less
5. Rapidly-cured isosorbide-based cross-linked polycarbonate elastomers

   https://doi.org/10.1039/c5py01659b  

   Kristufek, Tyler S. ; Kristufek, Samantha L. ; Link, Lauren A. ; Weems, Andrew C. ; Khan, Sarosh ; Lim, Soon-Mi ; Lonnecker, Alexander T. ; Raymond, Jeffery E. ; Maitland, Duncan J. ; Wooley, Karen L. ( January 2016 , Polymer Chemistry)

   The rapid synthesis of an optically-transparent, flexible elastomer was performed utilizing the naturally-derived source, isosorbide. A novel monomer based on isosorbide (isosorbide dialloc, IDA) was prepared by installing carbonate functionalities along with external olefins for use in thiol–ene click chemistry. Cross-linked networks were created using the commercially-available cross-linker, trimethylolpropane tris(3-mercaptopropionate) (TMPTMP) and resulted in IDA- co -TMPTMP, an optically-transparent elastomer. Systematically, IDA- co -TMPTMP networks were synthesized using a photoinitiator, a UV cure time of one minute and varied post cure times (0–24 h, 125 mm Hg) at 100 °C to observe effects on mechanical, thermal and surface alterations. The mechanical properties also had limited changes with post cure time, including a modulus at 25 °C of 1.9–2.8 MPa and an elongation of 220–344%. The thermal decomposition temperatures of the networks were consistent, ca. 320 °C, while the glass transition temperature remained below room temperature for all samples. A cell viability assay and fluorescence imaging with adherent cells are also reported in this study to show the potential of the material as a biomedical substrate. A degradation study for 60 days resulted in 8.3 ± 3.5% and 97.7 ± 0.3% mass remaining under accelerated (1 M NaOH, 60 °C) andmore »biological conditions (pH 7.4 PBS at 37 °C), respectively. This quickly-synthesized material has the potential to hydrolytically degrade into biologically-benign and environmentally-friendly by-products and may be utilized in renewable plastics and/or bioelastomer applications.« less