Interfacial chain-growth polymerization enables polypropylene-like and circular polythioglycolide

Much of research on developing chemically circular alternatives to nondegradable/recycle polyolefins has focused on polyethylene-like materials with cleavable bonds, but it is more challenging to create a circular alternative of matched high-performance properties to isotactic polypropylene (<i>i</i>PP) that accounts for 40% of polyolefins produced worldwide. Here, we introduce high-molecular-weight poly(thioglycolic acid) (PTGA) that exhibits not only closed-loop recyclability but also <i>i</i>PP-like thermal properties, even superior mechanical and barrier properties, and processability well suited for common processing techniques such as blow molding into bottles. To circumvent long-standing challenges of extensive transthioesterification side reactions in the ring-opening polymerization (ROP) of thioglycolide, which typically yielded only oligomers, we developed the interfacial chain-growth ROP occurring at the interface between the semicrystalline polymer surface and the monomer-organocatalyst solution phase, enabling the synthesis of high-molecular-weight PTGA. Overall, we show that PTGA is a scalable circular polymer that provides <i>i</i>PP-like properties and that the interfacial ROP method solves the challenges in typical solution-phase polymerization.