Photodegradation of Polytrithiocarbonates Switched by the Built-In Xanthate Chain End Group

Poly(propylene trithiocarbonates) rank among the most sulfur-rich polymers accessible by the copolymerization of propylene sulfide with carbon disulfide, yet the chemistry of these materials has remained largely unexplored. This work shows that these polymers are inherently stimuli-sensitive and can be switched between rapid photodegradation and high photostability simply by choosing the right xanthate initiator. Choosing O-methyl xanthate as the starting initiating system, the obtained polymer undergoes near-quantitative (>96%) degradation into cyclic trithiocarbonate within minutes of irradiation, a behavior that makes it attractive for applications where light-triggered breakdown is needed, such as degradable coatings or photopatterning. Using the functional O-allyl xanthate, the polymer gains remarkable resistance to light, and the allylic C–H bonds act as built-in radical traps that shut down depolymerization. Beyond the light-triggered behavior, the mechanism that governs the copolymerization itself was clarified. Combining experiments and quantum-chemical calculations, the competing reaction pathways in the carbon disulfide–episulfide–xanthate system were mapped out. The addition of propylene sulfide to the terminal trithiocarbonate group emerged as the rate-limiting step, and the potassium–crown ether complex enforces a specific geometry in the key intermediate. This steric control channels the two enantiomers of propylene sulfide from a racemic mixture into distinct pathways, which is consistent with a highly regular polymer microstructure. The same mechanistic picture accounts for the formation of the cyclic trithiocarbonate side product and explains why thioether sequences are completely absent from the final polymer.