Ultrahigh-molecular-weight tadpole polymers with statistically symmetric head-to-tail geometry: the key topological...

Polymer topology profoundly influences material properties by regulating chain arrangement, conformational entropy, and interactions, yet understanding topological entanglement constraints like threading and knotting remains a fundamental challenge in polymer science, partly due to the scarcity of structurally precise, ultrahigh-molar-mass ring-containing polymers as model systems. Herein, we address this synthetic challenge with a dual-terminal intramolecular cyclization strategy to synthesize tadpole polymers, the key architectural intermediate bridging linear and monocyclic topologies. This approach leverages synergistic dual-end groups and viscoelastic effects to maintain chain-end functionality, enabling efficient synthesis of tadpole polymers with ultrahigh molar masses (0.4-1.0 MDa) and statistically symmetric head-to-tail geometry. Such precise structural control facilitates direct visualization of individual tadpoles via advanced microscopy techniques. Physical characterization shows their distinct properties: an average ∼10% reduction in intrinsic viscosity (signaling compact packing) while the fractal dimension (d _f ≈ 1.7) remains unchanged; in the melt, rheology exhibits an entanglement plateau extended by 1-2 orders of magnitude, indicative of long-lived, threading-stabilized transient networks. Additionally, we develop a versatile post-polymerization strategy to build functional tadpole polymer libraries. This work provides a valuable experimental platform for examining the linear-to-cyclic topological transition and establishes a robust platform for investigating constrained dynamics and engineering advanced soft materials in future work.