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1. 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)

   null (Ed.)

   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. Preparation 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. 

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2. Sequential crosslinking for mechanical property development in high sulfur content composites

   https://doi.org/10.1002/pol.20200521  

   Thiounn, Timmy; Karunarathna, Menisha S.; Slann, Lauren M.; Lauer, Moira K.; Smith, Rhett C. (September 2020, Journal of Polymer Science)

   Abstract This report details how sequential crosslinking processes can be applied to develop properties in sulfur‐bisphenol A composites. Olefinic carbons were first crosslinked by inverse vulcanization (InV) at 180°C and then aryl carbon crosslinking was affected via radical‐induced aryl halide‐sulfur polymerization (RASP) at 220°C. To demonstrate that these two crosslinking mechanisms are orthogonal and can be used to affect stepwise property changes,O,O′‐diallyl‐2,2′,5,5′‐tetrabromobisphenol A was selected as a comonomer. After InV of the monomer with 90 wt% sulfur, a flexible plastic material having an elongation at break of 89% was obtained, whereas after heating this premade polymer to initiate RASP, the polymer develops a threefold increase in its tensile strength and has an elongation at break of only 29%. The sequential crosslinking strategy demonstrated herein thus provides an innovative approach to tuning the properties of high sulfur‐content materials. 

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3. 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)

   null (Ed.)

   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 flexural 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. 

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4. NMR spectroscopic characterization of polyhalodisulfides via sulfenyl chloride inverse vulcanization with sulfur monochloride

   https://doi.org/10.1016/j.polymer.2023.126539  

   Olikagu, Chisom; Kumirov, Vlad K; Njardarson, Jon T; Hahn, Megan J; Pyun, Jeffrey (January 2024, Polymer)

   The preparation of sulfur containing polymers from inexpensive, commodity sulfur base chemicals is an emerging field of polymer chemistry as a route to consume elemental sulfur generated from fossil fuel refining. Recently a new process, termed, sulfenyl chloride inverse vulcanization has been developed that exploits the high reactivity and miscibility of sulfur monochloride, (S2Cl2) with a broad range of allylic monomers to prepare soluble, high molar mass linear polymers, segmented block copolymers and crosslinked thermosets with greater synthetic precision than achieved using classical inverse vulcanization with elemental sulfur. However, the ring opening of episulfonium intermediates from this polymerization can proceed via Markovnikov, anti-Markovnikov, or alternative pathways resulting in complex regioisomeric microstructures, particularly when used with allylic ester monomers. Hence, to accelerate structural characterization of this new class of polyhalodisulfides prepared by the sulfenyl chloride inverse vulcanization process, we report on a detailed structural characterization to quantify the molar composition of regioisomeric units in these materials using NMR spectroscopy,focusing on sulfenyl chloride additions to allylic benzoate substrates. We report on a general methodologyusing one- and two-dimensional NMR spectroscopic techniques to enable direct integration of 2D NMRspectroscopic cross peaks to quantify the molar composition of regioisomeric units in 1,3-diallyl isophthalate(DAI) polymerized with S2Cl2, along with detailed studies on model compound reactions to detail the analytical methodology. 

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5. 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)

   null (Ed.)

   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, 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. 

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