Synthesis of star-brush polymer architectures from end-reactive molecular bottlebrushes

Reactive bottlebrush-linear block copolymers with poly(methyl methacrylate) side chains and linear poly(glycidyl methacrylate) (PGMA) end blocks were utilized for the fabrication of brush-star architectures. Well-defined bottlebrush copolymers with reactive end blocks were prepared by a grafting-from method, where a block copolymer backbone was synthesized by sequential reversible addition–fragmentation chain transfer (RAFT) polymerization of functionalized monomers, while side chains were installed by atom transfer radical polymerization (ATRP) of methyl methacrylate initiated from the bromide groups of the backbone. LiBr-catalyzed ring-opening of epoxides in the presence of ethylenediamine at room temperature was utilized for efficient cross-linking of PGMA blocks leading to star-brush architectures. Various structural parameters, such as side chain length and reactive end block length, were found to impact the efficacy of the cross-linking step. The developed method provided means to connect giant bottlebrush copolymer arms (M_n > 300 kg/mol) into a star architecture in an effective and tunable manner.