Sulfur-Rich Photocurable Networks: High Refractive Index, Dynamic Bonds, Odour, Stability and Processing

Sulfur is attractive in photocurable materials because its high electronic polarisability can raise refractive index, while thiol-X reactions and sulfur-containing dynamic bonds offer routes to rapid curing, stress control and post-print transformation. Those advantages do not define one material class. A formulation may contain sulfur in thiols, thioethers, thiourethanes, disulfides, dithiolanes or inorganic/organic sulfur-rich domains, each with different viscosity, odour, cure kinetics, optical loss, oxidation sensitivity and network mobility. This review treats sulfur-rich photocurable networks as a state-and-chemistry problem rather than as a simple sulfur-content optimisation. It examines how refractive index, dispersion, transparency, network conversion and service stability must be measured on the same conditioned specimen; distinguishes permanent thiol-ene networks from exchange-capable sulfur chemistries; and defines qualification tests for odour, extractables, yellowing, humidity, heat and optical ageing. Direct vat-photopolymerisation evidence is still much thinner than the broader high-index and thiol-X literature, so the review explicitly separates demonstrated printing results from transferable chemical principles. ER-412.