Facile Synthesis of Well‐Defined Branched Sulfur‐Containing Copolymers via a “One‐Pot” Copolymerization of Carbonyl Sulfide and Epoxide

: The discovery of topological polymers dramatically expands the applications of these synthetic polymers, as they possess many advantages which are inaccessible in the case of linear polymers. However, when it comes to the poly(monothiocarbonate)s, no topological polymers have been reported, though impressive progress has been made in the synthetic methodology of linear poly(monothiocarbonate)s. Herein, we describe a facile and efficient approach for synthesizing well-defined branched poly(monothiocarbonate)s in a "grafting through" manner by copolymerizing carbonyl sulfide (COS) with epichlorohydrin (ECH), where the side chain forms in situ in one pot. The length of side chains are tunable through performing the reaction at different temperatures before elevating reaction temperature to 25 °C. More importantly, enhancement in thermal properties of the branched copolymer was observed, as the Tg was increased by 22 °C compared to the linear analogs. Especially, when chiral ECH was utilized, semicrystalline branched poly(monothiocarbonate)s were accessible with a Tm of 112 °C, which is 40 °C higher than that of the corresponding linear poly(monothiocarbonate). The strategy for synthesizing branched polymers presented herein explores the methodology library for accessing topological polymers in an efficient and more concise way.