High-performance recyclable polymers enabled by stereo- and sequence-controlled polymerization

Monomer design strategy has become a powerful tool to access chemically recyclable polymers with desired and diverse properties. The presence of two or multiple stereogenic centres in one monomer offers a new dimension to fine-tune the polymer performance. However, it is still a formidable challenge in synthetic polymer chemistry to achieve precise stereocontrol and sequence control over the polymer microstructure. Here we report a stereo- and sequence-controlled polymerization of 5H-1,4-benzodioxepin-3(2H)-one-based monomers with two stereogenic centres (M) to furnish a series of isoenriched AB diblock polymers P(cis-M)-b-P(trans-M) and ABA triblock polymers P(trans-M)-b-P(cis-M)-b-P(trans-M). Notably, P(cis-M2)₉₀₀-b-P(trans-M2)₃₈ delivered impressive toughness and ductility, comparable to the commodity plastic isotactic polypropylene; the ABA triblock P(trans-M2)₂₆-b-P(cis-M2)₉₀₀-b-P(trans-M2)₂₆ appeared to be softer and resembled low-density polyethylene. These various materials could fully convert to the monomer M. The establishment of stereo- and sequence-controlled polymerization not only provides an effective and robust strategy to tailor polymer properties on the molecular level, but also delivers various chemically recyclable materials that can be converted back to monomers.