A photo-thermal dual-regulated latent monomer strategy for sequence control of polymers

Sequence-control, widely found in biopolymers (e.g., DNA), remains a significant challenge in polymer synthesis. Here, the concept of the photo-thermal dual-regulated release of the methyl maleimide (MMI) monomer in RAFT copolymerizations is presented, aiming to enrich the current methodologies of polymer sequence control. Photo-sensitive dithienylfuran-protected methyl maleimide (DTFMMI) was used as a latent monomer in which the dithienyl groups were in the "ring-closed" form under ultraviolet irradiation. This rigid structure significantly reduced its activity towards the retro Diels-Alder (rDA) reaction and the monomer remained dormant at a high temperature. However, the dithienyl group transformed to its "ring-open" analogue with the irradiation of visible light and triggered the rDA reaction of DTFMMI, allowing the release of active MMI and its gradual incorporation into the growing polymer chains. As a result, the structural isomerization of DTFMMI and the onset release of MMI could be well controlled by light and temperature, collectively, to regulate the polymer sequence in a more facile and non-invasive way. This proof-of-concept study sheds light on the development of synthetic methods for the construction of more advanced sequence-controlled polymers.