Miktoarm Stars via Grafting-Through Copolymerization: Self-Assembly and the Star-to-Bottlebrush Transition

• DOI: 10.1021/acs.macromol.8b02321
• Publication Date: 2019-02-12T19:39:14Z
• Authors: Adam E. Levi; Joshua Lequieu; Jacob D. Horne; Morgan W. Bates; Jing M. Ren; Kris T. Delaney; Glenn H. Fredrickson; Christopher M. Bates
• Keywords: 01 natural sciences; 0104 chemical sciences

The grafting-through copolymerization of two distinct macromonomers via ring-opening metathesis polymerization is typically used to form statistical or diblock bottlebrush polymers with large total backbone degrees of polymerization (NBB) relative to that of the side-chains (NSC). Here, we demonstrate that Grubbs-type chemistry in the opposite limit, namely NBB ≪ NSC, produces well-defined materials with excellent control over ensemble-averaged properties, including molar mass, dispersity, composition, and number of branch points. The dependence of self-assembly on these molecular design parameters was systematically probed using small-angle X-ray scattering and self-consistent field theoretic simulations. Our analysis supports the notion that two-component bottlebrush copolymers with small NBB behave like miktoarm star polymers. The star-to-bottlebrush transition is quantifiable for both statistical and diblock sequences by unique signatures in the experimental scaling of domain spacing and simulated dis...