Abstract
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.
Highlights
High sulfur-content materials (HSMs) are attractive alternatives to petrochemical polymers because they can be synthesized primarily from waste sulfur for which there are limited uses and HSMs have distinct physical and optical properties from those of typical polyolefins [1,2]
RASP proceeds by the Macallum mechanism whereby thermal reaction of aryl halides forms aryl rRaAdiScPalps r(oScceheedms eby2Ath),egMenaecraalllulymatmteecmhapneirsamturwesheorfeb≥y22th0e◦rCma[4l 8r]e.acItniotnheofparreyslenhcaelidoefsefxocremsss saurlyflurra, daircyallsra(Sdcihcaelms ea2nAd)h, gaelongeernallryaadtictaemls prearpaitdulryesreoafc≥t2w20it°hCe[l4e8m].eInntathl esuplrfeusre,nlceeadofinegxcteossSs–uClfauryrl, aryl radicals and halogen radicals rapidly react with elemental sulfur, leading to S–Caryl bond
RpuArScPhaaslesod pfrroomveAs leffafeActeisvaer.atTshteasbeilcizhienmg ipcoalsymwerriecususelfduwr withitohuint faunrtehtweroprkurmifiacdaetioexnc.luAslilvperloycbeyssSe–s wCaeryrlebcoanrdri-efdoromuitnugnrdeearctaimonbsi,einntacomnadnitnioernsanuanlloegsosuosthtoertwheissetsapbeilciizfiaetido.n of polymeric sulfur afforded in HSMs prepared by inverse vulcanization
Summary
High sulfur-content materials (HSMs) are attractive alternatives to petrochemical polymers because they can be synthesized primarily from waste sulfur for which there are limited uses and HSMs have distinct physical and optical properties from those of typical polyolefins [1,2]. Sulfur–sulfur bonds can form in a thermally reversible fashion, so HSMs can be thermally healable and recyclable thermoplastics, even when highly cross-linked, in which cases traditional organic polymers are thermosets [3–8]. The inverse vulcanization route, which requires an olefin comonomer for reaction with elemental sulfur (Scheme 1A), has been the primary approach to preparing such HSMs [9]. Inverse vulcanization was reported only a few years ago, its potential for facile production of versatile materials was quickly recognized. In a very short time, olefins derived.
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