Network Formation and Structure–Property Relationships in Photoinduced Inverse Vulcanization

Photoinduced inverse vulcanization offers a mild route for converting elemental sulfur into sulfur-rich polymers, but the relationship between photochemical conditions, network formation, and polymer properties remains insufficiently established. Herein, the sulfur–1,3-diisopropenylbenzene (DIB) system was used as a model to establish how photochemical parameters control sulfur-rich polymer network formation at room temperature. Irradiation at 435 nm promoted efficient vinyl-group consumption and gel formation. Time-dependent analysis showed that the S–DIB network developed mainly within the first 6 h, with the insoluble fraction increasing from ca. 25% to 82% and Tg increasing from −7.1 to 52.3 °C. Light intensity further regulated network structure, with moderate irradiation favoring higher effective crosslinking density, whereas stronger irradiation resulted in networks with reduced compactness and increased swelling. The reaction atmosphere also influenced network development and polymer composition. Compared with air, N2 promoted higher gel content, narrower molecular-weight distributions of the soluble fraction, and higher sulfur content, suggesting more favorable formation of sulfur-rich networks under an inert atmosphere. Comparison of DIB, soybean oil (SO), and 5-ethylidene-2-norbornene (ENB) further showed that alkene conversion alone does not determine gel formation. Instead, monomer architecture controls the balance among conversion, network buildup, chain mobility, and thermal behavior. This study establishes relationships between photochemical conditions, network structures, and polymer properties for understanding and controlling sulfur-rich polymer network formation in photoinduced inverse vulcanization.