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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.