Monomer-controlled self-switchable polymerization: a metal-free strategy for synthesizing multiblock copolymers from epoxides, O-phthalaldehyde, and CO2

Advances in chemoselective ring-opening polymerization have enabled the preparation of copolymers with precisely controlled chain structures. However, the building blocks for sequence-controlled polymers are mostly limited to polyether, polycarbonate and polyester. Therefore, it is very desirable to incorporate new classes of polymer segments into chemoselective or self-switchable copolymerization systems, thus opening avenues to a wide variety of structurally and functionally diverse copolymers. Polyacetal is an important class of degradable polymer with high strength and thermal stability and is an interesting segment for use in block copolymers. However, the utilization of polyacetal in sequence-controlled self-switchable copolymerization is still under-explored. Herein, using a Lewis pair of triethylborane and tetrabutylammonium chloride, we succeeded in incorporating polyacetal into various block copolymers through a monomer-controlled self-switchable polymerization. Specifically, from comonomers of epoxides, o-phthalaldehyde and carbon dioxide, the self-switchable polymerization delivers diverse sequences composed of polyacetal, polyether and polycarbonate. At the same time, it facilitates the easy control of the sequence and content in the block copolymers, allowing the convenient preparation of ABC and ABAC block copolymers. In addition, the self-switchable strategy is amenable to various types of epoxides. Facilitated by the fine tuning of the polymer microstructure, the thermal properties of the polymers could be further adjusted.