Synthesis of Star and Network Architectures from Reactive Molecular Bottlebrushes
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The development of smart materials using branched architectures requires robust synthetic methods. Several approaches have been investigated to access cross-linked structures or self-assembled organizations using bottlebrush copolymers. Reactive bottlebrush-linear block copolymers with different side chains and linear poly(glycidyl methacrylate) (PGM) end blocks were prepared by a grafting-from method using a combination of reversible addition-fragmentation chain transfer polymerization (RAFT) and atom transfer radical polymerization (ATRP). LiBr-catalyzed ring-opening of epoxides in the presence of ethylenediamine at room temperature was utilized for efficient cross-linking of PGM blocks leading to star-brush architectures. The developed method provided means to connect giant bottlebrush copolymer arms (Mn > 300 kg/mol) into a star architecture in an effective and tunable manner. As an alternative cross-linking way, olefin cross-metathesis has been utilized to connect giant bottlebrush molecules together. Appending olefinic functional groups to the end blocks through coupling to hydrolyzed PGM blocks was followed by subsequent olefin cross-metathesis cross-linking and led to the fast and efficient formation of star-brush copolymers with a complete conversion within a few hours irrespective of bottlebrush side chain dimensions.