Sulfur-rich polymers are highly useful materials with emerging high-value applications as sorbents for gold recovery, heavy metal remediation and novel anti-fungal agents. Despite this, there are limited methods for their synthesis. This presentation will discuss photopolymerization methods to make poly(trisulfides) with well-defined sulfur-rank and stereochemistry, narrow dispersity, and controlled molecular weights (Fig. 1). The reaction features photochemical cleavage of an S–S bond in a cyclic trisulfide to generate a diradical that can undergo ring-opening polymerization. To generate polymers with molecular weights exceeding 20,000 g/mol, spatial or temporal control of irradiation is required because the same wavelengths of light that initiate the reaction also cleave S–S bonds in the target polymer. Spatial control of photoinitiation was achieved using a photochemical flow reactor that physically separates the polymer products from the light source after synthesis. Temporal control was imparted with pulsed light-emitting diode (LED) irradiation with precisely controlled on and off times.