Thermal curing of poly-4 was investigated to test if cross-linking would provide a material that is more chemically and thermally robust than the linear polymer (S93-S94). This route also would provide a safe method for the synthesis and curing of sulfur-dicyclopentadiene co-polymers that are prone to runaway reactions when produced through inverse vulcanization. Poly-4 (250 mg) was cured at 190 °C for 6 hours, which caused it to turn from brown to black (Fig. ). The thermal stability of cured poly-4 was studied using thermal gravimetric analysis (TGA) which shows a distinct change in initial mass loss at 235 °C compared to poly-4 which begins degrading at 180 °C. Solvent stability studies showed cured poly-4 was insoluble in THF and chloroform, whereas uncured poly-4 was soluble in both (Fig. ). An increase in thermal stability and decrease in solubility suggests crosslinking during thermal curing due to S-S bond scission and addition of thiyl radicals to the alkene in poly-4 (Fig. ).