Synthesis of Bottlebrush Copolymers Using a Polypseudorotaxane Intermediate

A new paradigm for the synthesis of bottlebrush copolymers is introduced. A polyester containing a crown ether moiety in each repeat unit efficiently forms a pseudorotaxane in styrene solution with a viologen (N,N′-dialkyl-4,4′-bipyridinium salt) fitted at each end with initiators for nitroxide-mediated polymerization. Heating brings about polymerization of the styrene, producing a bottlebrush polymer in which narrow polydispersity polystyrene macromolecules are attached to the viologen threaded through the macrocyclic units of the polyester. This protocol allows control of the average spacing of the brushes (via stoichiometry) and their nature (by monomer selection) and length (by kinetic control), thus providing the ability to produce bottlebrush polymers of the same or similar architectures and brush lengths, but different arm compositions on the same backbone polymer. The concept can be broadened to other backbones, other host–guest systems, and other chain growth polymerization methodologies.