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BACKGROUND: Cyclic aromatic disulfides (CAD) can be used as cross-linking agents or precursors for the synthesis of high temperature resistant polymers such as poly(phenylene disulfides) (PPD). Chemical synthesis of CAD relies on the use of corrosive agents, detrimental for the environment. This paper reports an environment friendly chemoenzymatic procedure to obtain PPD starting from simple aromatic dithiols. RESULTS:The enzymatic reaction was carried out in an aqueous mixture with acetonitrile as co-solvent, using 1,4-and 1,3-benzenedithiol as monomers and a fungal laccase (EC 1.10.3.2) as catalyst. The products obtained were identified as mainly cyclic aromatic disulfides. Thermal analysis suggested that the enzymatically-synthesized CAD display thermal stability and are amenable precursors of high molecular weight sulfur-containing polymers through solvent-free, melt ring opening polymerization (mROP). After mROP, polymeric molecules around 12.8 kDa were obtained and identified as PPD. The resultant PPD shows uniform size, resistance to temperatures up to 400 ∘ C and electrical insulating properties. CONCLUSION: Laccase-catalyzed synthesis of CAD represents a novel reaction, not previously described elsewhere for oxidoreductases. A 100% substrate conversion was achieved under mild reaction conditions and no over-oxidation of CAD was observed, representing an advantage over chemical synthesis. The CAD products precipitated completely from the reaction medium, thus simplifying the purification process.

The cover image, by Estefanía Sierra et al., is based on the Research Article Chemoenzymatic synthesis of poly(phenylene disulfides) with insulating properties and resistant to high temperatures, DOI: .