Density functional theory calculations were used to gain further insight into the mechanism of the reaction. First, simulated UV-Vis spectra of 2 closely matched experimentally obtained spectra, and revealed the relevant photochemical transitions of the monomer (Fig ). Additional computations of the polymerization mechanism corroborated the Raman spectra obtained for poly-2, which indicated the formation of linear trisulfides as the main component of the polymer backbone (Fig. and Fig. ). Upon photochemical excitation, intersystem crossing to the triplet manifold promotes S-S scission in monomer 2 to afford a diradical species with terminal monothiyl (RS•) and perthiyl (RSS•) radical centers. Propagation, in principle, could be initiated from either radical, but RS• is approximately 9 orders of magnitude more reactive than RSS•. The RS• species can attack either sulfur of monomer 2 with similar rate coefficients. Reaction at the central sulfur affords a trisulfide linkage and a new RS• radical; reaction at the terminal sulfurs affords a disulfide linkage and the less reactive RSS• radical (Stage 1, Fig. ). This latter species can propagate, but more slowly and more selectively (Stage 2, Fig. ). In fact, RSS• is only expected to attack the terminal sulfur of the monomer, forming trisulfide linkages and RSS• radicals. Attack of RSS• at the central sulfur of monomer 2 (forming a tetrasulfide linkage and a terminal RS• radical) is kinetically and thermodynamically disfavored. Thus, while formation of a single disulfide linkage has a high probability for each initiation event in Stage 1 of the propagation, the final polymer is predominantly a poly(trisulfide). Termination events were not investigated computationally but could involve recombination or oxidation of the radical intermediates.