Dynamic Covalent Polymers via Inverse Vulcanization of Elemental Sulfur for Healable Infrared Optical Materials

Abstract

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...

Infrared Fingerprint Engineering: A Molecular‐Design Approach to Long‐Wave Infrared Transparency with Polymeric Materials

“…Surprisingly,w holly aliphatic organic polymers such as polyethylene or norbornene-olefinic co-polymers (Topas ) exhibit simplified fingerprint region spectra due to the presence of only cyclic aliphatic CÀCb onding of sp 3hybridized carbon atoms and have hence been used as thin LW IR-barrier coatings ( Figure 1a). [4][5][6][7][8] Thef irst generation CHIP for MWIR imaging was poly(sulfurrandom-(1,3-diisopropenylbenzene)poly(S-r-DIB)). [4][5][6][7][8] Thef irst generation CHIP for MWIR imaging was poly(sulfurrandom-(1,3-diisopropenylbenzene)poly(S-r-DIB)).…”

A sulfur–eugenol allyl ether copolymer: a material synthesized via inverse vulcanization from renewable resources and its application in Li–S batteries

“…Recently, it has been reported that self-healing of sulfur copolymer materials can be induced by thermal treatment above 90°C through S-S bond rearrangement. 10 Thus, this broad transition at approximately 125°C can be attributed to the enhanced dynamic bond character of S-S bonds. In particular, for sulfur copolymer with high sulfur content, this dynamic bond character appears to be more pronounced due to the large number of polysulfide bonds.…”

“…Consequently, this simple, economic and solvent-free synthesis protocol was successfully adopted to further comonomers such as diethynylbenzene (DEB) 5 , 1,4-diphenylbutadiyne 6 or benzoxazines. 7,8 The obtained sulfur copolymers found uses as cathode materials in lithium sulfur (Li-S) batteries 6,9 , self-healable optical lenses 10 , electrolyte in dye-sensitized solar cells 11 or as mercury absorber 12 . Li-S batteries are of great interest to meet the growing demand for high capacity energy storage systems owing to the low toxicity, low cost and vast abundance of the active material.…”

Sulfur and Its Role In Modern Materials Science

“…[20] These properties are attributed to their very high sulfur content. [24] Given their properties,m any opportunities exist for the use of these types of polymers in IR-optical applications. It has been further shown that, as aresult of the dynamic nature of these polymers,damage caused to the surface (e.g.scratches) can be remedied by heating, thus restoring the desirable transmission capabilities.…”