Sulfur-Rich Polythiol Resin Based on Polyalkylene Sulfides: Peculiarities of Preparation and Properties of the Cross-Linked Materials

Preparation of polyalkylene sulfides bearing a latent thiol functionality via ring-opening copolymerization of propylene sulfide and dithiocarbonate-functionalized episulfide (O-isobutyl S-(thiiran-2-ylmethyl) carbonodithioate, ETiBX) was demonstrated. Potassium O-methyl xanthate in complex with 18-crown-6 ether PMX[18C6] was used as an activator of the polymerization process. In contrast to polymerization of propylene sulfide, the process associated with (co)polymerization of ETiBX was found to be complicated by the pronounced chain transfer reaction. It was shown that copolymerization of propylene sulfide with even as low as 1 mol % of ETiBX leads to a dramatic decrease in the Mn of the resulting polymer (from 117 to 17.8 kg/mol) accompanied by the distinct multimodality of the copolymers obtained. Consecutive aminolysis of thus obtained copolymers bearing xanthate groups provided SH-functionalized polyalkylene sulfides as a viscous resin, which allows one to perform multiple possible pathways for the subsequent modification of the synthesized polythiols. The obtained polythiols were tested as UV-curable one-component (solvent-free) compositions to prepare the first generation of cross-linked polyalkylene sulfides. Thus, the prepared transparent elastomers show a relatively high refractive index close to 1.6 and enhanced thermal properties in terms of glass transition and the onset of thermal degradation compared to high-molecular-weight polypropylene sulfide. The tested organogels show high swelling ratios in toluene, tetrahydrofuran, and chloroform. The highest swelling ratio was determined for the organogel cross-linked with triallyl isocyanurate and soaked in chloroform (614%).