Thioacyl-Transfer Ring-Expansion Polymerization ofThiiranes Based on a Cyclic Dithiocarbamate Initiator

We report the novel thioacyl-transfer\nring-expansion polymerization\n(REP) of thiiranes, using 3H-benzothiazol-2-thione\n(BTT) as the cyclic dithiocarbamate initiator and tetrabutylammonium\nchloride (TBAC) as the catalyst. REP proceeded in a controlled manner\nto produce cyclic polysulfides with a narrow Mw/Mn of 1.1 and whose cyclic structures\nwere confirmed by MALDI-TOF mass spectrometry. Time-course studies\nrevealed unique sigmoidal profiles due to the stable five-membered\ncyclic structure of the BTT initiator. The GPC curves were analyzed\nby the Gaussian fitting method, which revealed that the cyclic polymers\nare accompanied by another fraction with nearly twice the molecular\nweight of the main product due to ring-crossover reactions between\ncyclic polysulfides during REP. The BTT-initiated cyclic polysulfides\nproduced in this manner act as macroinitiators for the REP of thiiranes,\nhighlighting the living characteristics of the BTT-initiated REP developed\nherein. Post-polymerization further enabled the preparation of cyclic\nblock copolymers with different combinations of thiiranes.