<scp>Ring‐Opening</scp> Polymerization of a <scp>Benzyl‐Protected</scp> Cyclic Ester towards Functional Aliphatic Polyester^†

Abstract

Comprehensive Summary Monomer design strategy has become a powerful tool to access polymers with desired and diverse functionalities. Here, we designed 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 demonstrated the characteristics of living polymerization with turnover frequency (TOF) up to 2520 h −1 . With a [BTO] 0 /[ Zn1 ] 0 /[I] 0 feed ratio of 2000/2/1, polymer with high number‐average molecular weight ( M n = 536 kDa) and narrow dispersity ( Ð = 1.06) was obtained. The produced polymer with a glass transition temperature of ‐17°C behaved as an elastomer at room temperature. Consequently, the monomer BTO was copolymerized with L ‐LA to modulate the mechanical properties of P( L ‐LA). When the BTO content is 10%, the copolymer exhibits excellent strength (24 MPa) and elongation at break (270%), affording a crystalline, hard, and tough plastic material that combines the high ductility of P(BTO) and the high modulus of P( L ‐LA). In addition, the oxidation of P(BTO) to P(BTO)‐SO 2 led to an improvement of T g from ‐17°C to 38°C. Debenzylation of P(BTO)‐SO 2 afforded P(BTO)‐SO 2 ‐OH containing free hydroxyl groups. Ultimately, P(BTO) could be hydrolyzed under a base condition 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.