Benefits of Catalyzed Radical Termination: High-Yield Synthesis of Polyacrylate Molecular Bottlebrushes without Gelation

• Published in: Macromolecules Vol. 51; no. 16; pp. 6218 - 6225
• Main Authors: Xie, Guojun, Martinez, Michael R, Daniel, William F. M, Keith, Andrew N, Ribelli, Thomas G, Fantin, Marco, Sheiko, Sergei S, Matyjaszewski, Krzysztof
• Format: Journal Article
• Language: English
• Published: American Chemical Society 28.08.2018
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/acs.macromol.8b00849

Catalyzed radical termination (CRT) in atom transfer radical polymerization (ATRP) of acrylates is usually considered as an unfavorable side reaction, as it accelerates termination and decreases chain-end functionality. CRT proceeds via a L/CuII–Pn organometallic intermediate and results in saturated chain-ends. Thus, CRT can help to suppress gelation in the synthesis of densely grafted poly­(n-butyl acrylate) molecular bottlebrushes using the “grafting-from” method by decreasing the fraction of chains terminated by conventional bimolecular radical combination. Molecular bottlebrushes by ATRP are typically prepared slowly in low yield and to limited monomer conversion to prevent radical combination, cross-linking, and gelation. Under conditions promoting CRT with highly active ATRP catalysts, a relatively high monomer conversion (>70%) was achieved without macroscopic gelation. CRT was favored using conditions that favored the formation of the L/CuII–Pn intermediate such as lower temperature and higher concentration of increasingly more active L/CuI catalysts. These conditions were beneficial for the fast and high-yield synthesis of polyacrylate molecular bottlebrushes, since they reduced the fraction of chains terminated by combination and prevented cross-linking of molecular bottlebrushes. High grafting density (>85%) and wormlike structures of molecular bottlebrushes were confirmed by side-chain cleavage and by molecular imaging via atomic force microscopy (AFM), respectively.