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1. Copolymerization of a Bisphenol a Derivative and Elemental Sulfur by the RASP Process

   https://doi.org/10.3390/suschem1020013  

   Thiounn, Timmy ; Lauer, Moira K. ; Karunarathna, Menisha S. ; Tennyson, Andrew G. ; Smith, Rhett C. ( September 2020 , Sustainable Chemistry)

   Fossil fuel refining produces over 70 Mt of excess sulfur annually from for which there is currently no practical use. Recently, methods to convert waste sulfur to recyclable and biodegradable polymers have been delineated. In this report, a commercial bisphenol A (BPA) derivative, 2,2′,5,5′-tetrabromo(bisphenol A) (Br4BPA), is explored as a potential organic monomer for copolymerization with elemental sulfur by RASP (radical-induced aryl halide-sulfur polymerization). Resultant copolymers, BASx (x = wt% sulfur in the monomer feed, screened for values of 80, 85, 90, and 95) were characterized by thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis. Analysis of early stage reaction products and depolymerization products support proposed S–Caryl bond formation and regiochemistry, while fractionation of BASx reveals a sulfur rank of 3–6. Copolymers having less organic cross-linker (5 or 10 wt%) in the monomer feed were thermoplastics, whereas thermosets were accomplished when 15 or 20 wt% of organic cross-linker was used. The flexural strengths of the thermally processable samples (>3.4 MPa and >4.7 for BAS95 and BAS90, respectively) were quite high compared to those of familiar building materials such as portland cement (3.7 MPa). Furthermore, copolymer BAS90 proved quite resistant to degradation by oxidizing organic acid, maintaining its full flexuralmore »strength after soaking in 0.5 M H2SO4 for 24 h. BAS90 could also be remelted and recast into shapes over many cycles without any loss of mechanical strength. This study on the effect of monomer ratio on properties of materials prepared by RASP of small molecular aryl halides confirms that highly cross-linked materials with varying physical and mechanical properties can be accessed by this protocol. This work is also an important step towards potentially upcycling BPA from plastic degradation and sulfur from fossil fuel refining.« 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. Sulfur-Containing Polymers Prepared from Fatty Acid-Derived Monomers: Application of Atom-Economical Thiol-ene/Thiol-yne Click Reactions and Inverse Vulcanization Strategies

   https://doi.org/10.3390/suschem1030015  

   Smith, Ashlyn D. ; Tennyson, Andrew G. ; Smith, Rhett C. ( December 2020 , Sustainable Chemistry)

   This paper is review with 119 references. Approaches to supplant currently used plastics with materials made from more sustainably-sourced monomers is one of the great contemporary challenges in sustainable chemistry. Fatty acids are attractive candidates as polymer precursors because they can be affordably produced on all inhabited continents, and they are also abundant as underutilized by-products of other industries. In surveying the array of synthetic approaches to convert fatty acids into polymers, those routes that produce organosulfur polymers stand out as being especially attractive from a sustainability standpoint. The first well-explored synthetic approach to fatty acid-derived organosulfur polymers employs the thiol-ene click reaction or the closely-related thiol-yne variation. This approach is high-yielding under mild conditions with up to 100% atom economy and high functional group tolerance. More recently, inverse vulcanization has been employed to access high sulfur-content polymers by the reaction of fatty acid-derived olefins with elemental sulfur. This approach is attractive not only because it is theoretically 100% atom economical but also because elemental sulfur is itself an underutilized by-product of fossil fuel refining. The thiol-ene, inverse vulcanization, and mechanistically-related thiol-yne and classic vulcanization are therefore discussed as promising routes to access polymers and composites from fatty acid-derived precursors.
5. Valorisation of waste to yield recyclable composites of elemental sulfur and lignin

   https://doi.org/10.1039/C9TA03222C  

   Karunarathna, Menisha S. ; Lauer, Moira K. ; Thiounn, Timmy ; Smith, Rhett C. ; Tennyson, Andrew G. ( January 2019 , Journal of Materials Chemistry A)

   Lignin is the second-most abundant biopolymer in nature and remains a severely underutilized waste product of agriculture and paper production. Sulfur is the most underutilized byproduct of petroleum and natural gas processing industries. On their own, both sulfur and lignin exhibit very poor mechanical properties. In the current work, a strategy for preparing more durable composites of sulfur and lignin, LSx , is described. Composites LSx were prepared by reaction of allyl lignin with elemental sulfur, whereby some of the sulfur forms polysulfide crosslinks with lignin to yield a three-dimensional network. Even relatively small quantities (<5 wt%) of the polysulfide-crosslinked lignin network provides up to a 3.4-fold increase in mechanical reinforcement over sulfur alone, as measured by the storage moduli and flexural strength determined from dynamic mechanical analysis (temperature dependence and stress–strain analysis). Notably, LSx composites could be repeatedly remelted and recast after pulverization without loss of mechanical strength. These initial studies suggest potential practical applications of lignin and sulfur waste streams in the ongoing quest towards more sustainable, recyclable structural materials.