Monomer design strategy has become a powerful tool to access polymers with desired and diverse functionalities. This work described a novel monomer 2‐(benzyloxy)methyl)‐1,4‐oxathiepan‐7‐one (BTO) via installing a benzyl ether side chain to the structure of 1,4‐oxathiepan‐7‐one (OTO). The ring‐opening polymerization of BTO with Zn1 as the catalyst featured a living polymerization with turnover frequency (TOF) up to 2520 h−1. The oxidation and debenzylation of the resulting P(BTO) led to the formation of sulfone and hydroxyl groups in the materials. Additionally, BTO could be utilized to modulate the mechanical properties of P(L‐LA) via copolymerization. More importantly, P(BTO) could be degraded to recover the corresponding hydroxyl acid intermediate, which could be used to prepare the monomer again and complete the closed loop from monomer to polymer to monomer. More details are discussed in the article by Zhu et al. on page 2973—2980.image