Having learned that the polysulfide R-S-Sy-R links remain reactive after formation, we were intrigued to see if these could serve as sites for the crosslinking of multiple chains. Inspired by the precedence concerning base-mediated thiol-disulfide exchange, we attempted crosslinking of the copolymers in situ after ROTERP by addition of a tetrafunctional thiol (pentaerythritol tetrakis(3mercaptopropionate), ca. 25 wt% versus polymer) in air. We assumed that the anionic lithium chain ends could act as a base to catalyse the thiol-disulfide exchange reaction. Indeed, while the diluted ROTERP reaction mixture (Table run #13) at full PO consumption was freely flowing, it turned into a stable network or gel, which resided at the top of the reaction vial after inversion, upon addition of the crosslinker (Figure ). Interestingly, during crosslinking, we recognized the evolution of a gas, which could be identified as carbonyl sulfide (IR ṽ (COS) = 2060 cm -1 , ESI Figure S 59); a mechanistic hypothesis of the crosslinking process is shown in the supporting information (Scheme S6). The Raman spectrum of the crosslinked material clearly shows the presence of polysulfide R-Sx-R groups (ṽ = 350 -550 cm -1 ) but no SH functionalities (ṽ = 2500-2600 cm -1 ) (ESI Figure -67). We infer that this is due oxidative coupling of thiols to R-S-S-R disulfides as part of the crosslinking process in air.