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Efficient Synthesis of Asymmetric Miktoarm Star Polymers
- Levi, Adam E., Fu, Liangbing, Lequieu, Joshua, Horne, Jacob D., Blankenship, Jacob, Mukherjee, Sanjoy, Zhang, Tianqi, Fredrickson, Glenn H., Gutekunst, Will R., Bates, Christopher M.
- Macromolecules 2020 v.53 no.2 pp. 702-710
- catalysts, polymerization, polymers, statistics
- Asymmetric miktoarm star polymers produce unique material properties, yet existing synthetic strategies are beleaguered by complicated reaction schemes restricted in both the monomer scope and yield. Here, we introduce a new synthetic approach coined “μSTAR”, miktoarm synthesis by termination after ring-opening metathesis polymerization, that circumvents these traditional synthetic limitations by constructing the block–block junction in a scalable one-pot process involving (1) grafting-through polymerization of a macromonomer followed by (2) in situ enyne-mediated termination to install a single mikto-arm with exceptional efficiency. This modular μSTAR platform cleanly generates ABₙ and A(BA′)ₙ miktoarm star polymers with unprecedented versatility in the selection of A and B chemistries as demonstrated using many common polymer building blocks. The average number of B or BA′ arms (n) is easily controlled by the equivalents of Grubbs catalyst. While these materials are characterized by dispersity in n that arises from the statistics of polymerization, they self-assemble into mesophases that are identical to those predicted for precise miktoarm stars. In summary, the μSTAR technique provides a significant boost in design flexibility and synthetic simplicity while retaining the salient phase behavior of precise miktoarm star materials.