Reactive Compression Molding Post‐Inverse Vulcanization: A Method to Assemble, Recycle, and Repurpose Sulfur Polymers and Composites

Abstract

Inverse vulcanization provides dynamic and responsive materials made from elemental sulfur and unsaturated cross-linkers. These polymers have been used in av ariety of applicationss uch as energy storage, infrared optics, repairable materials, environmental remediation, and precision fertilizers. In spite of thesea dvances, there is an eed for methods to recycle and reprocess these polymers. In this study,p olymers prepared by inverse vulcanization are shown to undergo reactive compression molding. In this process, the reactive interfaces of sulfur polymers are brought into contact by mechanicalc ompression.U pon heating these molds at relatively low temperatures (% 100 8C), chemical bonding occurs at the polymer interfaces by SÀSm etathesis. This method of processing is distinct from previouss tudies on inverse vulcanization because the polymers examined in this study do not form al iquid phase when heated. Neither compression nor heatinga lone was sufficient to mold these polymers into new architectures, so this is an ew concept in the manipulation of sulfur polymers. Additionally,h igh-level ab initio calculations revealed that the weakest SÀSb ond in organic polysulfides decreases linearly in strength from as ulfur rank of 2t o4 ,b ut then remains constant at about 100kJmol À1 for highers ulfur rank. This is criticali nformation in engineering these polymers for SÀSm etathesis. Guidedb yt his insight, polymer repair,r ecycling, and repurposingi nto new composites was demonstrated.

Sequential crosslinking for mechanical property development in high sulfur content composites

“…The uniform distribution of sulfur, carbon, and bromine was confirmed for both materials by scanning electron microscopy (SEM) with element mapping by energy dispersive X‐ray analysis (EDX, Figure 2). In some HSMs, migration of sulfur to the surface of the thermally‐cured samples has been observed, [ 32 ] but this was not noted in EDX analysis of either I‐BPA 80 or R‐BPA 80 samples.…”

“…The polymeric sulfur chains also undergo S S bond metathesis (via radicals) above 90 C. This S S metathesis allows for innovative lower-temperature processing approaches for HSMs. [32][33][34][35] Polymeric sulfur domains can reform following their rearrangement by metathesis when the material is cooled back to room temperature, provided that the supporting network is intact , allowing materials to be reshaped or thermally healed. [6,22,26,[36][37][38][39][40] Two types of S S bonds are typically present in these materials: those in polymeric/oligomeric catenates that undergo metathesis at temperatures as low as 90 C and those in cyclic S 8 allotropes that generally require heating to above 159 C to undergo metathesis.…”

Robust, remeltable and remarkably simple to prepare biomass–sulfur composites

“…14,37 Pioneering insight into facile processing techniques relying on a clever S-S metathesis process have made HSMs even more attractive as candidates for commercial applications by opening up the possibility for their use in additive manufacturing and compression moulding. 38,39 Encouraged by advances in HSM processing and the high mechanical strength of APS 95 , we hypothesized that the properties of durable biomass-sulfur composites could be tuned by subtly changing the biomass : sulfur ratio or biomass composition in monomer feeds. We also hypothesized that unsaturated triglycerides that make up naturally occurring plant oils -present to varying extent in lignocellulosic waste streams -could contribute to crosslinking in biomass-sulfur composites derived from lessprocessed sources.…”

A role for terpenoid cyclization in the atom economical polymerization of terpenoids with sulfur to yield durable composites

“…[31][32][33][34] Many applications for resulting materials have been noted, 35,36 as highlighted in the aforementioned references. Significant advances in synthetic methodologies to allow lower-temperature/catalytic reactions [37][38][39][40] and facile processing 41,42 of high sulfur-content materials have recently made high sulfur content materials even more attractive candidates for commercialization.…”