Catalyst-Free and Spontaneous Polymerization Enabled by the Imine-yne Click Reaction and Ethynyl Umpolung

Umpolung is a powerful strategy in organic synthesis, yet its application in polymerization reactions remains limited, especially for alkyne-based systems. Herein, we introduce the concept of umpolung into alkyne-based polymerization for the first time and successfully establish a spontaneous imine-yne polymerization of pyrroline and ester-activated diynes. This polymerization is enabled by the imine-yne click reaction and ethynyl umpolung without the need for any transition metal or organic base catalysts. Soluble, thermally stable, and regio- and stereoregular poly(pyrrolidine)s with high weight-average molecular weights (M_w, up to 25,500) were obtained in high yields (up to 85%). The resultant polymers exhibit high refractive indices (up to 1.6957 at 632.8 nm) because of the presence of aromatic units, vinyl groups, and heteroatoms. Additionally, these poly(pyrrolidine)s display tunable nonconventional luminescence and distinct excitation- and concentration-dependent emission properties, attributed to intramolecular and intermolecular through-space interactions involving ester groups and nitrogen atoms. This ethynyl umpolung-based spontaneous imine-yne polymerization not only expands the scope of activated alkyne polymerizations but also provides a versatile approach for preparing functional polymers with potential applications in the optical and photonic fields.