Dithiol Post‐Modification of a High‐Sulfur Composite: Structure–Property Relationships for Aromatic and Aliphatic Additives

ABSTRACT High sulfur composites are crosslinked networks in which oligo‐ and polysulfide catenates connect organic units and can be post‐modified via labile S–S bonds. Building on our demonstration that aryl dithiols raise the glass transition of GS 80 (made by heating 80 wt% sulfur and 20 wt% guaiacol), we establish structure–property rules by varying dithiol identity—butane‐1,4‐dithiol (BuDT), hexane‐1,6‐dithiol (HDT), benzene‐1,4‐dithiol (BDT), biphenyl‐4,4′‐dithiol (BPDT), and naphthalene‐1,5‐dithiol (NDT)—and GS 80 :dithiol mass ratio (10:1 to 2:1). Twenty five compositions were characterized by thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). Aromatic dithiols raise decomposition temperature ( T d ) and promote carbonization: at 2:1, T d = 326°C–333°C with 20–27 wt% char; at 10:1, T d = 300°C–313°C; char = 5–7 wt%. Aliphatic dithiols are weaker modifiers: HDT gives T d = 262°C–269°C with 7–15 wt% char, whereas BuDT yields T d = 250°C–268°C and ≈0–1 wt% char, consistent with S–C aryl formation above 220°C anchoring higher boiling HDT but not more volatile BuDT. Glass transition temperature ( T g ) is tunable over 73°C, from −48°C (HDT, 2:1) to +25°C (NDT, 2:1), with aliphatic dithiols acting as plasticizers and aromatic dithiols stiffening the network in near linear proportion to loading. These results deliver quantitative, mass‐ratio‐based compositions for targeting T d , char yield, and T g in post‐modified high‐sulfur composites.