High molecular weight cyclic polysiloxanes from organocatalytic zwitterionic polymerization of constrained spirocyclosiloxanes†
Cyclic polymers are macromolecules which exhibit interesting topological structures and unique properties. Cyclic polysiloxane formation by organic zwitterionic polymerization of cyclic siloxanes offers the advantage of a simple process, no metal residue and adjustable catalyst activity, but is retarded by the low strain energy of cyclosiloxanes. Herein, we demonstrate the design and synthesis of highly strained spiral cyclosiloxane molecules, and realized the first high molecular weight cyclic polysiloxane formation by zwitterionic polymerization. The cyclic morphology of the resulting polymer was unambiguously identified by NMR, AFM and FESEM, with the mechanism proved by DFT calculations. This research opens a new way of generating cyclic polysiloxanes with unique structural features.