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

We report the novel thioacyl-transfer ring-expansion polymerization (REP) of thiiranes, using 3H-benzothiazol-2-thione (BTT) as the cyclic dithiocarbamate initiator and tetrabutylammonium chloride (TBAC) as the catalyst. REP proceeded in a controlled manner to produce cyclic polysulfides with a narrow M_w/M_n of 1.1 and whose cyclic structures were confirmed by MALDI-TOF mass spectrometry. Time-course studies revealed unique sigmoidal profiles due to the stable five-membered cyclic structure of the BTT initiator. The GPC curves were analyzed by the Gaussian fitting method, which revealed that the cyclic polymers are accompanied by another fraction with nearly twice the molecular weight of the main product due to ring-crossover reactions between cyclic polysulfides during REP. The BTT-initiated cyclic polysulfides produced in this manner act as macroinitiators for the REP of thiiranes, highlighting the living characteristics of the BTT-initiated REP developed herein. Post-polymerization further enabled the preparation of cyclic block copolymers with different combinations of thiiranes.