Bottlebrush Polymers Carrying Side Chains on Every Backbone Atom: Controlled Synthesis, Polymerization-Induced Emission, and Circularly Polarized Luminescence

Controlled synthesis of bottlebrush polymers with high grafting density and carrying polymeric side chains on every backbone atom remains a great challenge. In this work, a series of well-defined poly­(l-lactic acid) (PLLA) and poly­(d-lactic acid) (PDLA) bearing polymerizable phenyl isocyanide on chain ends were prepared. Polymerization of the terminal phenyl isocyanide of these macromonomers by an alkyne-palladium­(II) catalyst yielded bottlebrush polymers carrying PLLA or PDLA side chains on every backbone atom. The grafted side chains were directly packed together without separating from other atoms. The polymerizations were proceeded in a living/controlled manner, and the degree of polymerization could be up to 250. The chiral macromonomers induced an asymmetric polymerization and resulted in a poly­(phenyl isocyanide) backbone with a preferred one-handed helix and large optical activity. Remarkably, the densely grafted bottlebrush polymers exhibited intriguing photoluminescence, although the macromonomers and poly­(phenyl isocyanide) backbone were all nonluminescent. Moreover, the preferred one-handed helix of the backbone induced clear circularly polarized luminescence (CPL) with defined handedness and a tunable dissymmetric factor.