An excess of elemental sulfur is generated annually from hydrodesulfurization in petroleum refining processes; however, it has a limited number of uses, of which one example is the production of sulfuric acid. Despite this excess, the development of synthetic and processing methods to convert elemental sulfur into useful chemical substances has not been investigated widely. Here we report a facile method (termed 'inverse vulcanization') to prepare chemically stable and processable polymeric materials through the direct copolymerization of elemental sulfur with vinylic monomers. This methodology enabled the modification of sulfur into processable copolymer forms with tunable thermomechanical properties, which leads to well-defined sulfur-rich micropatterned films created by imprint lithography. We also demonstrate that these copolymers exhibit comparable electrochemical properties to elemental sulfur and could serve as the active material in Li-S batteries, exhibiting high specific capacity (823 mA h g(-1) at 100 cycles) and enhanced capacity retention.

Polymers for IR imaging: The preparation of high refractive index polymers (n = 1.75 to 1.86) via the inverse vulcanization of elemental sulfur is reported. High quality imaging in the near (1.5 μm) and mid-IR (3-5 μm) regions using high refractive index polymeric lenses from these sulfur materials was demonstrated.

Sulfur-rich copolymers based on poly(sulfurrandom-1,3-diisopropenylbenzene) (poly(S-r-DIB)) were synthesized via inverse vulcanization to create cathode materials for lithium−sulfur battery applications. These materials exhibit enhanced capacity retention (1005 mAh/g at 100 cycles) and battery lifetimes over 500 cycles at a C/10 rate. These poly(Sr-DIB) copolymers represent a new class of polymeric electrode materials that exhibit one of the highest charge capacities reported, particularly after extended charge− discharge cycling in Li−S batteries.

Recent developments in the polymerizations of elemental sulfur (S 8 ) to prepare high sulfur content polymers are reviewed. While the homopolymerization of S 8 via ring-opening processes to prepare high molar mass polymeric sulfur has long been known, this form of polymeric sulfur is chemically unstable and depolymerizes back to S 8 . In the current report, we discuss the background into the production of sulfur via petroleum refining and the challenges associated with utilizing S 8 as a chemical reagent for materials synthesis. To circumvent these long standing challenges in working with sulfur, the use of S 8 as a reaction medium and comonomer in a process termed, inverse vulcanization, was developed to prepare chemically stable and processable sulfur copolymers. Furthermore, access to polymeric materials with a very high content of sulfur-sulfur (S-S) bonds enabled for the first time the creation of materials with useful (electro)chemical and optical properties which are reviewed for use in Li-S batteries, IR imaging technology and self-healing materials.

We report on dynamic covalent polymers derived from elemental sulfur that can be used as thermally healable optical polymers for mid-IR thermal imaging applications. By accessing dynamic S−S bonds in these sulfur copolymers, surface scratches and defects of free-standing films of poly(sulfur-random-1,3-diisopropenylbenzene) (poly(S-r-DIB) can be thermally healed, which enables damaged lenses and windows from these materials to be reprocessed to recover their IR imaging performance. Correlation of the mechanical properties of these sulfur copolymers with different curing methods provided insights to reprocess damaged samples of these materials. Mid-IR thermal imaging experiments with windows before and after healing of surface defects demonstrated successful application of these materials to create a new class of "scratch and heal" optical polymers. The use of dynamic covalent polymers as healable materials for IR applications offers a unique advantage over the current state of the art (e.g., germanium or chalcogenide glasses) due to both the dynamic character and useful optical properties of S−S bonds.T he development of stimuli-responsive polymers has been recently investigated as a means to healable materials. 1 While a number of functional groups have been utilized to create dynamic covalent polymers, these typically require that the dynamic functional groups are orthogonal to the polymer forming reaction. 2−5 However, disulfide and polysulfide bonds are a class of dynamic covalent functional groups that can be installed via the polymer forming reaction by direct (co)-polymerization with elemental sulfur (S 8 ) or di/polysulfides. 6−8 The early work by Tobolsky et al. on polyurethane copolymer networks demonstrated the stress-relaxation properties imparted via the inclusion of di-and tetrasulfide bonds. 9−11 More recently, Rowan et al. reported the preparation of polymeric disulfide networks via oxidative polymerizations of di-and tetrasulfide comonomers to create self-healing films and shape memory materials. 12 We recently reported on the synthesis of dynamic covalent polymers via the inverse vulcanization of S 8 and 1,3-diisopropenylbenzene (DIB), enabling the generation of the first dynamic covalent polymers with composed primarily of dynamic bonds. In this system, the dynamic behavior in high sulfur content copolymers was directly controlled by the comonomer feed ratios and copolymer composition, demonstrating that such properties were modulated by altering sulfur rank (number of S−S bonds) within these materials. 13 To date, numerous applications of dynamic covalent polymers have been explored, with an emphasis on the creation of stimuli-responsive macromolecules and self-healing materials. 5,14,15 In these materials, the primary function of the dynamic covalent bonds served to enable reversible bond scission, or reorganization within the macromolecular framework. However, there remains opportunities to create dynamic covalent polymeric materials that exhibit multiple functions in addition to those relat...